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4th National Symposium on Pulsed Laser Deposition of Thin Films and Nanostructured Materials, PLD 2007 (pdf)

Contents
Messages: i-vi
From Convener: 1
From Scientific Program Committee: 2
Technical Program: 3 - 16
Abstracts of Invited Tutorial Talks: 17 - 19
Abstracts of Invited Review Talks: 20 - 36
Abstracts of Invited Paper Talks: 37 - 66
Abstracts of Oral Presentations: 67 - 74
Abstracts of Theses Presentations: 75 - 80
Abstracts of Poster Presentations: 81 - 122
FROM THE CONVENER?
Dear Invitees, Participants, Colleagues and Friends,
It gives me immense pleasure to welcome you all at the DAE BRNS 4th National Symposium on Pulsed Laser Deposition of Thin Films and Nanostructured Materials, PLD 2007 for short. Since its inception in 2001 biennial PLD meets have provided a forum for intense professional interactions amongst scientists, students and suppliers of the Indian PLD community. Countless ideas have been discussed, collaborations have been planned and executed, suggestions have been mooted and contemplated and an enormous amount of scientific knowledge has been disseminated and absorbed through these meetings. At PLD meets researchers from national laboratories and universities come closer to share their respective strengths and do away with their respective lacunae. We are indeed indebted to DAE ?BRNS for their continued support to hold these meetings and hence to fulfill the purpose of these meetings.
Albeit in a small way, PLD 2007 is witnessing something special that for sure is a reason for all of us to feel upbeat. Not only that we have registered a quantitative increase in the number of abstracts submitted, we notice a qualitative improvement of the research being presented in the papers. Not only that we have delegates from all the important institutes of the country, for the first time, we have a sizable participation of highly acclaimed scientists from Germany and China. These are harbingers of an upward contribution that Indian scientists are vying to make and enhancing integration of our research with the global science. Individually our forward moving steps may still be small but collectively we can proceed at a gallop. This is the goal we will strive to achieve together.
As you can see from the planned proceedings of PLD 2007, the sequences of presentations are so elaborate that it will make your cup of time overflow. But I believe you will welcome this. By the time we wind up this meet, although we all will be extremely tired but will also be extremely happy to get soaked with new knowledge, new ideas and something significant to take home. I wish you all a very successful and enchanting participation in PLD 2007.
Lalit M. Kukreja
August 20, 2007 1
FROM THE SCIENTIFIC PROGRAM COMMITTEE?br> We take this opportunity to welcome you all to the PLD-2007 symposium. It is a great pleasure to share with you the feeling of overwhelming response of abstract submissions in this symposium. We have received about 85 abstract for PLD 2007 from most of the active groups from Indian Laboratories and some foreign participants from China and Germany. The number of total submitted abstracts in PLD 2007 is significantly higher than the total number of abstract received in previous PLD symposia e.g., in 28 in PLD-2005, 26 in PLD-2003 which and 19 in PLD-2001. The scientific standard of the contributed abstract has also improved significantly over the years. This year we received abstracts for thesis presentations also and included it in scientific program. The scientific programs will run all the three days and every day there will be different sessions of presentations such as invited tutorial talks (ITT), Invited review talks (IRT), Invited Paper talks (IPT), Oral presentations (OPT), thesis presentations (THP) and poster presentations (PSP).We have included a special session for corporate presentations on the last day of the symposium. In this session discussions about scientific products pertinent to the scope of the symposium will be carried out. An arrangement to display the product catalogues and handouts etc from the corporate sector have been made at the venue for all the three days.
We thank Prof. L. M. Kukreja, Symposium Convener for his constant guidance and suggestions for preparing this compendium of abstracts. We would also like to thank our colleague Mr. Amit K. Das of RRCAT, Indore for his help in designing the cover pages of the abstract book. Thanks are also due to Dr. B. N. Singh of RRCAT, Indore and Mr. R. Bankar of Pune University, Pune for their help during preparation of the abstract book.
We wish you all a very fruitful participation in PLD 2007 and happy back home.
Pankaj Misra Kiran P. Adhi
Secretary Convener
Scientific Program Committee
PLD-2007
2
October 2, 2007 (Tuesday)
20:00 hrs onwards: Welcome Dinner and Registration at Hotel Rangoli Park, Rajkot
Scientific Program
Venue: Resort Chouki Dhani, Rajkot
October 3, 2007 (Wednesday)
Time
8:30-
9:30
9:30-
10:30
10:30-11:00
11:00-13:00
13:00-14:00
14:00-15:00
15:00-15:30
15:30-16:30
16:30-17:30
17:30-18:30
19:00-21:00
Sessions
Break
Fast &
Registration
Inauguration of the symposium
High
Tea
IRT1
IRT2
IRT3
IRT4
Lunch
ITT1
OPT1
OPT2
Tea +
PSP1
IPT1
IPT2
THP1
THP2
Cultural
Program and
Dinner
October 4, 2007 (Thursday)
Time
8:30-
9:00
9:00 ?br> 11:00
11:00-
11:30
11:30- 13:00
13:00-14:00
14:00-15:00
15:00-15:30
15:30-16:30
16:30-17:30
17:30-18:30
19:00-
21:00
Sessions
Break
Fast &
Registration
IRT5
IRT6
IRT7
IRT8
TEA
IRT9
IRT10
IRT11
Lunch
ITT2
OPT3
OPT4
Tea +
PSP2
IPT3
IPT4
THP3
THP4
Dinner
October 5, 2007 (Friday)
Time
8:30-
9:00
9:00 ?br> 11:00
11:00-
11:30
11:30- 13:00
13:00-14:00
14:00-15:00
15:00-15:30
15:30-16:00
16:00-17:30
17:30-
19:00
19:00-21:00
Sessions
Break
fast
IRT12
IRT13
IRT14
IRT15
TEA
IRT16
IPT5
IPT6
Lunch
ITT3
OPT5
OPT6
TEA
THP5
IPT7
OPT7
OPT8
CPT1
CPT2
CPT3
CPT4
CPT5
Closing
and
Dinner
ITT: Invited Tutorial Talk; IRT: Invited Review Talk; IPT: Invited Paper Talk; OPT: Oral Presentation; THP: Theses Presentation; PSP: Poster Presentation
CPT: Corporate Presentation
Time durations: ITTs: 60 min; IRTs: 30 min; IPTs: 30 min; OPT: 15 min; THPs: 30 min; CPTs: 15 min
3
Invited Tutorial Talks (ITT)
S. No.
Code
No.
Title
Speaker
Address
Co-authors
1
ITT1
Optical Properties of Semiconductors at the fundamental absorption edge
Claus Klingshirn
Institut für Angewandte Physik Universität Karlsruhe Karlsruhe Germany
Claus.Klingshirn@ physik.uni-karlsruhe.de
J. Fallert, H. Zhou, and H. Kalt
2
ITT2
Field Emission From Nanomaterials - A Tutorial
D. S. Joag
Centre for Advanced Studies in Condensed Matter Physics and Material Science
Department of Physics
Pune University
Pune 411 007
dsj@physics.unipune.ernet.in
3
ITT3
Pulsed Laser Growth of Nanostructured Materials: Some Recent Experiments
L. M. Kukreja
Thin Film Laboratory, RRCAT, Indore ?452 013
kukreja@cat.ernet.in
Invited Review Talks (IRT)
S. No.
Code
No.
Title
Speaker
Address
Co-authors
4
IRT
1
Research on p-type ZnO
Z. Z. Ye
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, 310027, E-mail:
yezz@zju.edu.cn
Y. F. Lu, Y. J. Zeng, J. G. Lu, L. P. Zhu
5
IRT
2
Electrical, Optical And Magnetic Properties Of Oxide Based Nanostructures
M. S. Ramachandra
Rao
Department of Physics,
Indian Institute of Technology, Madras, Chennai
msrrao@iitm.ac.in
6
IRT
3
Temperature-dependent photoluminescence from ZnO/Zn0.85Mg0.15O quantum well grown on Si(111) substrates
L.P. Zhu
State Key Lab of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, People抯 Republic of China
zlp1@zjuem.zju.edu.cn
X.Q. Gu, H.P. He, F. Huang, M.X. Qiu, Z.Z. Ye, Y.Z. Zhang, B.H. Zhao
7
IRT
4
Electron doped manganites: Reality or illusion?
Pratap Raychaudhuri
Department of Condensed Matter Physics and Materials Science,TIFR,, Homi Bhabha Rd., Colaba, Mumbai-400005
4
pratap@tifr.res.in
8
IRT
5
Multiferroic behavior of modified BiFeO3 thin films grown by PLD: A Review
V. R. Palkar
Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400 076, India
palkar@ee.iitb.ac.in
9
IRT
6
Nanostructured Thin Films of Titania Prepared by Pulsed Laser Ablation: Process and Properties
P. Kuppusami
Physical Metallurgy Division
Indira Gandhi Centre for Atomic Research
Kalpkkam-603 102, Tamilnadu
pk@igcar.ernet.in
S. Murugesan and E. Mohandas
10
IRT
7
Combinatorial Pulsed Laser Abltation for Parallel Synthesis and High Throughput Characterization of Functional Inorganic materials
Utpal S. Joshi
Department of Physics, School of Sciences, Gujarat University, Ahmedabad?80009
usjoshi@gmail.com
11
IRT
8
Single Step Single Shot Lithography Techniques via Selective laser ablation
Alika Khare
Department of Physics
Indian Institute of Technology Guwahati, Guwahati 781039
alika@iitg.ernet.in
12
ITR
9
Pulsed laser deposition of amorphous oxides for transparent electronics
M.K. Jayaraj
Optoelectronic Devices Laboratory, Department of Physics, Cochin University of Science and Technology, Kochi 682 022
mkj@cusat.ac.in
K.J. Saji
13
IRT
10
Preparation of Luminescent Nanostructures by Pulsed Laser Ablation
V.P.Mahadevan Pillai
Department of Optoelectronics, University of Kerala, Kariavattom, Kerala, India
vpmpillai9@rediffmail.com
14
IRT
11
Studies on manganite based Thin films and Heterostructures grown by PLD
D. G. Kuberkar
Department of Physics,
Saurashtra University
Rajkot- 360 005 Gujarat
dgkcmr@rediffmail.com
15
IRT
12
Laser ablation of Zn/ZnO Core-Shell Nanoparticles: Effect of SDS Concentration
R. K. Soni
Laser Spectroscopy Laboratory, Physics Department
Indian Institute of Technology, Delhi, New Delhi-110016
ravisoni@physics.iitd.ac.in
First author: Geetika Bajaj
5
16
IRT
13
Characterization of pulsed laser deposited Fe3O4 thin films
on different substrates
D. M. Phase
UGC-DAE Consortium for Scientific Research, University Campus, Indore-452017, India.
dmphase@csr.ernet.in
17
IRT
14
Application of pulsed laser deposited thin films of ZnO as varistors and InN as field emitters
K. P. Adhi
Center for Advanced Studies in Material Science and Condensed Matter Physics.
DST unit on Nanoscience,
Department of Physics, University of Pune, Pune ?11 007, India
kpa@physics.unipune.ernet.in
18
IRT
15
Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition.
S. I. Patil
Department of Physics,
University of Pune, Pune 411 007
patil@physics.unipune.ernet.in
M. S. Sahasrabudhe, Deepak N. Bankar, A. G. Banpurkar and K. P. Adhi
19
IRT
16
Tailoring the electrical and magnetic properties of LaFe1-xNixO3 thin films by swift heavy ion irradiation
Ravi Kumar
Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi-110067
ranade@iuac.ernet.in
Invited Paper Talks: (IPT)
S. No.
Code
No.
Title
Speaker
Address
Co-authors
20
IPT1
Study of device characteristics on Pulsed Laser Deposited manganite-semiconductor heterostructures
S.N. Kale
Fergusson College
Pune 411 004, India
snkale@vsnl.com
J. Mona, H. Mamgain, R.R. Rawat, V. Ganesan, R.J. Choudhary, D.M. Phase
21
IPT2
Pulsed Laser Deposition of La1.5Dy0.5CaBa2Cu5Oz Superconducting Thin Films
S. Rayaprol
UGC-DAE CSR-Mumbai centre, R-5 Shed, BARC, Trombay, Mumbai
rayaprol@gmail.com
sudhindra@csr.ernet.in
K. R. Mavani, D. G. Kuberkar, N. A. Shah, J. John, R. Pinto
22
IPT3
Basic Photoluminescence Processes at different Temperatures in ZnO / (0001) Sapphire Thin Films Grown by Pulsed
P. Misra
Laser Program, Raja Ramanna Centre for Advanced Technology, Indore?452 013 (M.P.)
T. K. Sharma and L. M. Kukreja
6
Laser Deposition
pmisra@cat.ernet.in
23
IPT4
Synthesis and properties of pulsed laser deposited Fe doped MoO3-d thin films
R. J. Choudhary
UGC-DAE Consortium for Scientific Research, University Campus, Indore-452017, India.
ram@csr.ernet.in
Ram Prakash, D. M. Phase and Ravi Kumar
24
IPT5
UV Excimer lasers for smart materials and nanostructures
B. Fechner
Coherent GmbH, Hans-Böckler-Str. 12, D-37079 Göttingen, Germany
burkhard.fechner@coherent.com
R. Pätzel, R. Delmdahl
25
IPT6
Precise photonic engines for UV pulsed laser deposition
R. Delmdahl
Coherent GmbH, Hans-Böckler-Str. 12, D-37079 Göttingen, Germany
ralph.delmdahl@coherent.com
J. Sieber, B. Fechner
26
IPT7
Research and Development in Pulsed Laser Deposition:
A Scientometric Perspective
G. Surwase
Scientific Information Resource Division, Knowledge Management Group
Bhabha Atomic Research Centre, Mumbai-400 085 (India)
bskademani@yahoo.co.in; bsk@barc.gov.in
B.S. Kademani and Vijai Kumar
Oral presentations: (OPT)
S. No.
Code
No.
Title
Speaker
Address
Co-authors
27
OPT1
Large Room Temperature Magnetization of Pulsed Laser Deposited Cobalt Ferrite Thin Film
Subasa C. Sahoo
Department of physics,Indian Institute of Technology Bombay Powai, Mumbai ? 400076
ramani@iitb.ac.in
M. Bohra, N.Venkataramani, Shiva Prasad, D. S. Misra and R. Krishnan
28
OPT2
Photoluminescence of ZnO nanowires grown by thermal evaporation on pulsed laser deposited ZnO buffer layer
A. Mohanta
Department of Physics and Centre for Laser Technology,
Indian Institute of Technology Kanpur-208016
antary@iitk.ac.in
A. P. Singh, Vandna S., and R. K. Thareja
29
OPT3
Nanostructured Growth of AlN Thin Films by Pulsed Laser Deposition
Gaurav Shukla
Department of Physics
Indian Institute of Technology Guwahati, Guwahati 781039
alika@iitg.ernet.in
Alika Khare
30
OPT4
Resistivity of thin films of YBa2Cu3O7-δ and
L.S.Vaidhyanat-han
Materials Science Division, Indira Gandhi Centre for
D.K. Baisnab, M.P.
7
Multilayers of YBCO/Ga2O3
Atomic Research, Kalpakkaam
lsv@igcar.ernet.in
Janawadkar and Y. Hariharan
31
OPT5
Morphological and physical property changes in ZnO thin films grown by PLD due to Mg doping
Shubra Singh
Department of Physics and Materials Science Research Centre
IIT Madras, Chennai-36, India
shubra@physics.iitm.ac.in
M. S. Ramachandra Rao
32
OPT6
Characteristics of pulsed laser deposited Zn1-xNixO/ZnO bi-layer thin films
Subhash Thota
Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur-208016
jk@iitk.ac
Pankaj Misra, Lalit M Kukreja and Jitendra Kumar
33
OPT7
Structural and Optical Characterization of UV-transparent β-Ga2O3
V. Sridharan
Material Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102.
varadu@igcar.gov.in
L.S. Vaidhyanathan, V. Srihari, G. Raghavan, S. T. Sundari, M. Kamruddin, M. Premila, H.K. Sahu, B. K. Panigrahi, V.S. Sastry and C.S. Sundar
34
OPT8
The low temperature electrical transport in La0.7Ca0.3MnO3
P.R. Sagdeo
UGC-DAE Consortium for scientific research, University campus Khandwa road indore 452017, M.P. INDIA
sagdeo@csr.ernet.in
R.J. Choudhary and D.M. Phase
Thesis Presentations: (THP)
S. No.
Code
No.
Title
Speaker
Address
Co-authors
35
THP1
Oxygen Reduction Kinetics and Transport Properties of
(Ba,Sr)(Co,Fe)O3-delta Solid Oxide Fuel Cell Cathode Materials
Lei Wang
Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
lei.wang@fkf.mpg.de
Rotraut Merkle1, Frank S. Baumann1, Jürgen Fleig2, and Joachim Maier1
36
THP2
Study on p-type ZnO thin films and ZnO homojunction LED
Y. Lu
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, 310027, People抯 Republic of China
sailinglu27@gmail.com
Z. Z. Ye, Y. J. Zeng, L. P. Zhu
37
THP3
Magnetoresistive and
Jaysukh H
Department of Physics,
8
Transport Properties of Pulsed
Laser Deposited Manganite Thin Films and Heterostructure.
Markna
Saurashtra University, Rajkot-360 005 INDIA
jaysukh28@rediffmail.com
38
THP4
Pulsed Laser Deposited Thin Films of ZnO, GaN, AlN, ZnO/GaN
WBSC: Structural, Micro-structural, Optical & Electrical Characterization
Suhas Madhav Jejurikar
Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411 007, India.
suhas@physics.unipune.ernet.in
Dr. K. P. Adhi, Co-guide: Dr. A. V. Limaye
39
THP5
Synthesis and characterization of LaB6 thin films on tungsten, rhenium and silicon substrates and their investigations as Field Emitters
D. J. Late
Center for Advanced Studies in Material Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune - 411007, India
dsj@physics.unipune.ernet.in
Poster Presentations: (PSP)
PSP 1 (October 3, 2007)
S. No.
Code
No.
Title
Speaker
Address
Co-authors
40
PSP1.1
Effect of oxygen pressure on the photoluminescence of Gd2O3 :Eu 3+ films
grown by PLD
Geo Rajan
Department of Optoelectronics, University of Kerala, Kariavattom, Thiruvananthapuram-695 581, India
gopchandran@yahoo.com
Nissamudeen K. M, Sasi B and K.G.Gopchandran
41
PSP1.2
A comparative study of nanostructures Co thin films deposited on different substrates by pulsed laser deposition
A. Sharma
University Grant Commission- Department of Atomic Energy Consortium for Scientific Research, University Campus, Khandwa Road, Indore-452 017, India.
anupamsharma2003@yahoo.co.in
S. Tripathi, R. Brajpuriya, Ram Prakash, R. J. Chaudhari, D. M. Phase and T. Shripathi
42
PSP1.3
Raman Study of oriented thin films of PrMnO3 deposited on different
Aditi Dubey
UGC-DAE Consortium for Scientific Research, University Campus, Khandwa
V. G. Sathe
9
substrates
Road, Indore ?452 017
aditidubey@csr.ernet.in
43
PSP1.4
Application of pulsed laser deposited ZnO thin films as a solar blind detector
Alka V. Deshmukh
Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411 007, India.
alka_d@physics.unipune.ernet.in
S. M. Jejurikar, K. P. Adhi and S. I. Patil
44
PSP1.5
DC-Discharge Assisted Pulsed Laser Growth of Ultra-thin Silicon-Oxinitride Films
B. N. Singh
Thin Film Lab., Raja Ramanna Centre for Advanced Technology, Indore 452 013
bnsingh@cat.ernet.in
P. Misra, A. K. Das, R. Kumar, Binsu J Kailath, M. Mishra, D.M. Phase, A. DasGupta, N. DasGupta and L. M. Kukreja
45
PSP1.6
Unique nanostructures in pulsed laser ablated NiO thin films
B. Sasi
Department of Optoelectronics, University of Kerala, Thiruvananthapuram-695 581, India
thazhavasasi@sancharnet.in
K.M. Nissamudeen and K. G. Gopchnadran
46
PSP1.7
Influence of Ti2+ doping on the structural and optical properties of WO3 thin films prepared by pulsed laser ablation technique.
Lethy K.J
Department of Optoelectronics, University of Kerala, Kariavattom, Kerala, India
vpmpillai9@rediffmail.com
Beena
D, Bahna.A.H
V.P.Mahadevan Pillai
47
PSP1.8
Effect of Substrate on Pulsed Laser Deposition of InN Thin Film
Gaurav Shukla
Department of Physics
Indian Institute of Technology Guwahati, Guwahati 781039
alika@iitg.ernet.in
Alika Khare
48
PSP1.9
Synthesis and Optical Properties of Cr2O3 Films Prepared by Pulsed Laser Ablation
G. Balakrishnan
Physical Metallurgy Division, Indira Gandhi Centre for Atomic Research,
Kalpakkam-603 102, Tamil nadu
pk@igcar.ernet.in
P. Kuppusami, T.N. Sairam, E. Mohandas and D. Sastikumar
49
PSP1.10
Synthesis and Characterization of La0.7Ba0.3MnO3-SnO2 bilayer using
Pulsed Laser Deposition Technique
J. Mona
Fergusson College, Fergusson College Road, Pune 411004
snkale@vsnl.com
Ram Prakash, R. Rawat, R.J. Choudhary, D.M. Phase, S.N. Kale
10
50
PSP1.11
Semiconductor Nano-pattern formation through laser induced diffusion
U. Das
Dept of Physics, Tezpur University, Napaam, Tezpur ?784028, India
upam2005@gail.com
A.Choudhury
51
PSP1.12
Growth of n-Zinc Oxide on various substrates using pulsed laser deposition and its photo conducting properties
G. Naresh Kumar
Loyola institute of frontier energy (LIFE), Physics Department, Loyola college, Chennai 600 034, India
naresh_matsci@yahoo.co.in
V.Immanuel, Francis P. Xavier
52
PSP1.13
Characterisation of pulsed laser deposited PZT and PLZT thin films on oxide pervoskite electrodes
R.Reshmi
Optoelectronics Device Laboratory, Department Of Physics, Cochin University of Science and Technology, Kochi-682022, India
mkj@cusat.ac.in
M.K.Jayaraj, M.T.Sebastian
53
PSP1.14
Effect of Structural Disorder on Electronic Transport in La0.5Pr0.2R0.3MnO3 (R = Sr, Ba) Manganite Thin Films
P.S. Solanki
Department of Physics, Saurashtra University, Rajkot ?360 005
dgkcmr@rediffmail.com
R.R. Doshi, J.H. Markna, C.M. Thaker, N.A. Shah and D.G. Kuberkar
K.R. Mavani, D.S. Rana and S.K. Malik
P. Misra, B.N. Singh and L.M. Kukreja
54
PSP1.15
Improvement in field sensitivity of La-based manganite multilayered structure
P.S. Vachhani
Department of Physics, Saurashtra University, Rajkot ?360 005, India
dgkcmr@rediffmail.com
J.H. Markna, J.A. Bhalodia and D.G. Kuberkar
P. Misra, B.N. Singh and L.M. Kukreja
V. Ganesan and R. Rawat
55
PSP1.16
Synthesis and Characterization of PrCoO3 thin films grown by Pulsed Laser Deposition
Ram Prakash
UGC-DAE Consortium for Scientific Research, Indore (M.P.) 452017, India.
ramprakash@csr.ernet.in
R. J. Choudhary, D. M. Phase
56
PSP1.17
Effect of laser energy on the structural and optical properties of non-reactive pulsed laser ablated tantalum oxide thin films
Renju R Krishnan
Department of Optoelectronics, University of Kerala, Kariyavattom, Trivandrum-695581, Kerala, INDIA
vpmpillai9@rediffmail.com
V.P.M. Pillai
57
PSP1.18
Room temperature luminescence from low temperature grown ZnMgO/ZnO Quantum wells using pulsed laser deposition.
R.S. Ajimsha
Optoelectronics Devices Laboratory, Department of Physics,
Cochin University of Science and Technology, Cochin-22.
mkj@cusat.ac.in
M.K.Jayaraj
P Misra, L.M. Kukreja
58
PSP1.19
Novel feature of quantum transport through finite
Santanu K. Maiti
1Theoretical Condensed Matter Physics, Saha Institute
11
width mesoscopic ring
of Nuclear Physics,
1/AF, Bidhannagar, Kolkata-700 064, India
59
PSP1.20
Structural, Optical and Electrical Properties of Co and Ga codoped ZnO Thin Films Prepared by Pulsed Laser Deposition
M. Subramanian
Crystal Growth Centre, Anna University, Chennai ?600 025
subu_mjs@yahoo.co.in
G. Mohan Kumar, P. Misra. Amit K Das, B. N. Singh, S. Venkatraj, S. Vijayalakshmi, R. Jayavel and L.M. Kukreja
PSP2 (October 4, 2007)
60
PSP2.1
Structural, Optical and Electrical Properties of Zn1-(x+y)MnxGayO THIN FILMS Prepared by Pulsed Laser Deposition
M. Subramanian
Crystal Growth Centre, Anna University, Chennai ?600 025
subu_mjs@yahoo.co.in
P. Ilanchezhiyan, P. Misra. A. K Das, B. N. Singh, S. Venkatraj, S. Vijayalakshmi, R. Jayavel and L.M. Kukreja
61
PSP2.2
Effect of doping and substrate temperature on the structural and optical properties of reactive pulsed laser ablated Aluminium Oxide doped Tantalum Oxide thin films
Renju R Krishnan
Department of Optoelectronics, University of Kerala, Kariavattom, Trivandrum-695581, Kerala, INDIA.
vpmpillai9@rediffmail.com
V.P.M. Pillai
62
PSP2.3
Optimizing the doping concentration in a single experiment by using Combinatorial Laser Molecular Beam Epitaxy (CLMBE)
Utpal S. Joshi
Department of Physics, School of Sciences, Gujarat University, Ahmedabad ?380 009, India
usjoshi@gmail com
Kenji Itaka, Yuji Matsumoto, Masatomo Sumiya
and Hideomi Koinuma
63
PSP2.4
Superparamagnetism in epitaxial thin films of Fe, Cr, Co, Mn and V doped p-type NiO
U. V. Chhaya
Physics Department, St. Xavier抯 College, Ahmedabad-380 009, India
usjoshi@gmail com
P.S. Raval, P.A. Joshi, S. Trivedi, K. Itaka, Y.Matsumoto,
H. Koinuma and U.S. Joshi
64
PSP2.5
Structural and Optical properties of GdO doped ZnO Thin Films by Pulsed Laser Deposition Technique.
R.Vinodkumar
Department of Optoelectronics, University of Kerala, Thiruvananthapuram, Kerala,
India ?695581.
vpmpillai9@rediffmail.com
D.Beena, Geo Rajan, Jayasree R.S. and V.P.Mahadevan Pillai
65
PSP2.6
Structural, Morphological and Optical studies of Potassium Lithium Niobate thin films prepared under ambient conditions of substrate temperature
V. Jayasree
Department of Optoelectronics, University of Kerala, Kariavattom, Trivandrum, Kerala, 695 581 India
nayarvu@sancharnet.in
R Vinod Kumar, R Ratheesh, V. P Mahadevan Pillai & V. U Nayar
12
66
PSP2.7
Studies on effect of europium concentration on the photoemission of laser ablated Y2O3:Eu based nano-phosphors.
K.M. Nissamudeen
Department of Optoelectronics, University of Kerala, Kariavattom, Thiruvananthapuram
gopchandran@yahoo.com
R Krishnan, Geo Rajan and K.G. Gopchandran
67
PSP2.8
Studies on Si Doped ZnO Thin Films Grown by Sequential Pulsed Laser Deposition
A.K. Das
Thin Film Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013
amitdas@cat.ernet.in
B. N. Singh, P. Misra and L. M. Kukreja
68
PSP2.9
Textured CeO2 thin films on amorphous substrate by PLD at room temperature
T. K. Chaudhuri
Dr. K C Patel Research and Development Centre
Education Campus ?Changa, Changa (Petlad), Anand
Gujarat 388 421, INDIA
tkchaudhuri@gmail.com
R N Bhattacharya
69
PSP2.10
Synthesis of II-VI Oxide Semiconductor Nanocrystals by
Pulsed Laser Ablation in Liquid Media
S. C. Singh
Laser and Spectroscopy Laboratory,
Department of Physics,
University of Allahabad, Allahabad-211002
Spectra2@rediffmail.com
R.K. Swarnkar and R. Gopal
70
PSP2.11
Studies on CoZnO thin films grown by Pulsed Laser Deposition
Satyapal S.
Rathore
Dept. of Applied Physics, Birla Institute of Technology, Mesra ?835215
and
Thin Film Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013
satyapal03@gmail.com
A.K.Das, B.N. Singh, P.Misra, L.M.Kukreja
71
PSP2.12
Laser assisted growth of Eu3+ doped Ba0.7Sr0.3TiO3 thin film for optoelectronic and ferroelectric application
R.Reshmi
Optoelectronics Device Laboratory, Department Of Physics, Cochin University of Science and Technology, Kochi-682022, India
mkj@cusat.ac.in
M.K.Jayaraj, M.T.Sebastian
72
PSP2.13
Comparative studies of irradiation induced modifications in Fe3O4 thin films on MgO and Si substrates grown by pulsed laser ablation
Shailja Tiwari
UGC-DAE Consortium for Scientific Research, Indore-452 017, INDIA email:
shailja@csr.ernet.in
Ram Prakash, R. J. Choudhary and D. M. Phase
Ravi Kumar
73
PSP2.14
Synthesis and Characterization of SnO2 Thin Films by PLD for Sensor Applications
K. Prabakar
Materials Science Division,
Indira Gandhi Centre for AtomicResearch,
Kalpakkam ?603102,Tamil Nad
kpr@igcar.gov.in
R. Krishnan, B. Yasodhaadevi, Ashok S. Chauhan, S. Tripura Sundari, S. Dash and J. Jayapandian 13
74
PSP2.15
Structural and electrical characterization of pulsed laser deposited Ga doped ZnO thin films on Si(100)
S.D. Shinde
Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics,
University of Pune, Pune 411 007, India.
shashi@physics.unipune.ernet.in
S.M. Jejurikar and K.P. Adhi
75
PSP2.16
Thickness dependent multiferroic properties of Bi0.7Dy0.3FeO3 polycrystalline thin films grown by pulse laser deposition technique
Prashanthi K
Electrical Engineering, Indian Inof Technology Bombay, Mumba076, India
shanthi@ee.iitb.ac.in
S. P. Dattagupta, R. Pinto and V. R. Palkar
76
PSP2.17
Electroresistive and Magnetoresistive effects in electron doped manganite La0.7Ce0.3MnO3 thin films
Kavita Bajaj
Department of Condensed Matter Physics and Materials Sciences, TIFR, Homi Bhabha Rd., Colaba, Mumbai 400005, India.
and
Department of Physics, Mumbai University, Mumbai 400098, India.
bajajkp@rediffmail.com johnj@tifr.res.in
John Jesudasan, Vivas Bagwe, Pratap Raychaudhuri
77
PSP2.18
Size dependent study of CuFe2O4 nanoparticles
Archana Rai
Department of Physics, Indian Institute of Technology, Powai, Mumbai-400 076
archana3@iitb.ac.in
M. Banerjee
78
PSP2.
19
A theoretical approach to the effect of particle size on the luminescence intensity in nanocrystals
Anamika Awadhwal
Department of Post Graduate Studies and Research in Physics and Electronics
Rani Durgavati University, Jabalpur-482001
B.P. Chandra
79
PSP2.
20
Third Order Non-Linear Optical Properties of Eurhodin Dye Doped Ppolymer Film
Rekha R.K
Centre for Laser Technology, Department of Physics, Anna University, Chennai-600 025
rekhasri71@yahoo.com
A. Ramalingam , G. Vinitha
80
PSP2.21
Nonlinear characterization and optical limiting of organic dye doped polymer
G.Vinitha
Centre for Laser Technology, Department of Physics,Anna University, Chennai-25, India.
svini2005@yahoo.co.in
R.K REKHA., A. RAMALINGAM
81
PSP2.22
Studies on the Fluorescence emission from nano silver / silver oxide thin films for optical read write
A. Subrahmanyam
Department of Physics, Indian Institute of Technology Madras, Chennai-600036, India
N.Ravichandra Raju 14
memory applications
ravichandra@physics.iitm.ac.in
Corporate Talks: (CPT)
S. No.
Code
No.
Company
Speaker
Address
82
CPT1
Oerlikon leybold Vacuum
S. Inamdar
EL-22, J-Block, MIDC
Bhosari, Pune-411 026
Shrikant.inamdar@oerlikon.com
www.oerlikon.com
83
CPT2.
Laser Science
L. Kumar
Laser Science Services Pvt. Ltd.
A-454, MIDC, TTC Industrial Area,
Mahape, Navi Mumbai ?400 701
laser_science@vsnl.com
84
CPT3
Specialise Instruments Pvt. Ltd.
P. Deshpande
Specialise Instrument Marketing Co.
18th Fort-view, Scheme No. 6, Road No.1,
Sion (East), Mumbai 400 022, India
specmo@vsnl.in
85
CPT4
Excel Instruments
S. P. Pai
Excell Instruments
A/15 Guru Nanak Compound
Opp. Hindustan Lever, Chakala Road
Andheri (East) Mumbai 400 099
sppai@tifr.res.in
86
CPT5
Laser Spectra Services India Pvt. Ltd.
N.R.P.Kumar
Laser Spectra Services India Pvt. Ltd.,
80/10, I Floor, Raj Towers,
M. S. Ramiah Main Road,
Mathikere,
BANGALORE-560 054.
lss@bgl.vsnl.net.in
15
ITT1
Optical Properties of Semiconductors at the fundamental absorption edge
Claus Klingshirn, J. Fallert, H. Zhou, and H. Kalt
Institut für Angewandte Physik
Universität Karlsruhe
76128 Karlsruhe, Germany
email: Claus.Klingshirn@physik.uni-karlsruhe.de
In this tutorial talk we review the optical properties of direct gap semiconductors and semiconductor quantum structures close to the fundamental absorption edge, using essentially ZnO as model substance.
In a first part we start with the band structure, i.e. the one particle states, proceed to the electron-hole pair states i.e. the excitons and end this section with the mixed state of excitons and photons, the exciton polaritons.
The second part will be devoted to the properties of and processes in a dense exciton or generally electron-hole pair system reaching the electron-hole plasma at the highest densities.
Frequently, these processes allow stimulated emission and we spend the third part on this aspect.
16
ITT2
Field Emission From Nanomaterials - A Tutorial
DILIP S. JOAG
Centre for Advanced Studies in Condensed Matter Physics and Material Science
University of Pune : Department of Physics
dsj@physics.unipune.ernet.in
Field electron emission phenomenon is known for more than a century and is the best example of quantum mechanical tunneling process. Since the invention of the field emission microscope, it has been an important tool in the study of surface adsorption phenomena, work function measurements, diffusion kinetics etc. The specimen in the field emission microscope is required to be in the form of a sharp needle in order to create electric field of the order of 106 ?107 V/cm necessary for measurable emission current. Technologically, the phenomenon is important for its potential application as a high brightness electron source.
In the era of nanomaterials, there has been renewed interest and an upsurge in the study of field emission. This is due to the advantage of the size and shape of nanocrystallites of various materials. These nanometeric materials become eligible candidates for `low onset voltage?field emitters. Several such materials have been investigated worldover for their potential applications in field emission based devices such as flat panel displays.
This tutorial is aimed at giving the basic background required for the study of field emission from nanomaterials. Various case studies will be presented illustrating the suitability of these materials in the development of field emission cathodes and devices. Work from the author抯 laboratory on pulsed laser deposited nanometric films of ZnO and LaB6 will also be presented elucidating the scope of the studies.
17
ITT3
Pulsed Laser Growth of Nanostructured Materials: Some Recent Experiments
L. M. Kukreja
Thin Film Laboratory, Raja Ramanna Centre for Advanced Technology,
Indore ?452 013
Email: kukreja@cat.ernet.in
In this tutorial talk results of our two ongoing experiments will be discussed. One experiment is on the behavior of sub-monolayer gold nano-islands grown on (0001) Sapphire substrates by Pulsed Laser Deposition (PLD). The other experiment is about a variant of PLD to grow ultra-thin high k-dielectric layer of SiO2 and silicon oxy-nitride for MOS technology.
Nanometer size gold depositions on oxide substrates have recently come under scrutiny since the experimental observation of their large catalytic activity. Using high resolution Atomic Force Microscopy (AFM) we observed in normal ambient atmosphere the slow morphological dynamics of apparently sessile gold nano-islands grown on (0001) Sapphire substrates by Pulsed Laser Deposition (PLD) at room temperature with an equivalent average thickness of about 0.55 Å, i.e. one fourth of the monolayer. Within approximately one day, a transient wavy surface structure developed with rms roughness of about 0.6 nm and a two-fold symmetry. After about 6 days under ambient conditions this structure completely transformed into a de-wetted phase of spherical gold beads with average diameter of ~20 nm and a broad size distribution. Each bead was found to be surrounded by a concentric layer, which could be seen as corona in the AFM images. This concentric shell layer appears to be mainly the condensed moisture from atmosphere since by dehydration of the sample in vacuum using molecular sieves the corona layer completely vanished. While the shape and size distributions of the as-prepared Au nano-islands are attributed to the specific deposition technique of PLD with its large fraction of high energy particles arriving at the substrate, the de-wetting and bead formation under ambient conditions are probably mainly due to the condensation of atmospheric moisture modifying the surface interactions. These observations are expected to have significant implications for our understanding on the wetting characteristics of gold on oxide substrates in sub-monolayer regime.
In another experiment a novel technique for the growth of ultra-thin SiO2 at room temperature using a pulsed laser has been demonstrated. It is observed that, after an initial high growth rate, the oxide thickness reduces with time and the quality of the oxide improves. The results of our experiments show that this technique can be used to grow high quality ultra-thin SiO2 films with excellent control suitable for ULSI of MOSFETs. However there are certain unsettled issues. It is still not very clear that why does the thickness of the dielectric layer decrease with time of laser irradiation. One of the hypotheses is that while the laser irradiation facilitates the oxidation, it also etches the surface through photo-sputtering, thermal evaporation or both. This proposal of photo-sputtering is supported by the directional exfoliation observed at the surface of the lasers oxidized Si wafer. Recently we have also extended the scope of the laser induced oxidation process by incorporating a DC discharge assisted supply of atomic / reactive nitrogen during the growth process. This has enabled us to grow silicon oxy-nitride layers structurally integrated with the Si wafer. The oxy-nitride has shown superior dielectric characteristics. We could also succeed in getting effective dielectric thickness in the sub-nanometer regime using this methodology. The detailed results of these experiments will be discussed.
18
IRT1
Research on p-type ZnO
Z. Z. Ye*, Y. F. Lu, Y. J. Zeng, J. G. Lu, L. P. Zhu
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, 310027 People抯 Republic of China
*E-mail: yezz@zju.edu.cn
Research activitites on ZnO have increased over the past few years. It is known that lack of high quality p-type ZnO has been a bottle neck in developing ZnO optoelectronic devices since ZnO is naturally n type. In this study, we report on our research p-type ZnO. P-type ZnO is grown by different methods using different dopant sources. The specific doping mechanism is investigated at the same time.
For the first time, a nitrogen substituting ?hydrogen passivating method is used to increase the solubility of nitrogen in ZnO. Nitrogen atoms that are passivated by hydrogen are introduced into the crystal lattice. Then the N-H bonds are broken and the N dopants are activated. Using this nonequivalent way, p-type ZnO is realized by magnetron sputtering method.
P-type ZnO with high crystalline quality and good electrical property is also realized firstly by using donor-acceptor codoping method. Al-N and In-N codpoed p-type ZnO thin films are grown by magnetron sputtering. The codoped donors, such as Al, In, are found to increase the concentration of N in ZnO evidently. And the codoped ZnO based p-n homo-junctions show good rectifying property.
In addition to codping method, Li mono-acceptor is introduced into ZnO successfully and the best condition window for growth of Li doped p-type ZnO is investigated. It is found that there exist two acceptor levels for Li in ZnO. And to control the relative proportion of the two acceptor levels is of essential importance for realizing p-type transformation.
Besides donor-acceptor codoping, a Li-N dual acceptor codoping method is prompted to increase the hole concentration in ZnO. More importantly, the stability of the p-type conduction is improved largely. The energy level of Li-N dual acceptor and the codoping mechanism of Li-N dual acceptor are investigated.
The success in growth of P, Sb doped p-type ZnO confirmed the theoretical large-size-mismatched doping mechanism.
Furthermore, normally undoped p-type ZnO is obtained using plasma-assisted MOCVD. The oxygen concentration in ZnO is enhanced obviously by using radio frequency plasma, which is an important reason for p-type conduction.
Finally, room-temperature electroluminescence is observed in ZnO homojunction using nitrogen as the acceptor dopant, which is a great progress towards the application of ZnO based light emitting diods.
19
IRT2
ELECTRICAL, OPTICAL AND MAGNETIC PROPERTIES OF OXIDE BASED NANOSTRUCTURES
M.S.Ramachandra Rao
Department of Physics and Materials Science Research Centre
Nano Functional Materials Technology Centre (NFMTC)
Indian Institute of Technology (IIT) Madras, Chennai ?600036, INDIA.
msrrao@iitm.ac.in; www.physics.iitm.ac.in/~msrrao
The properties of nanoscale elecronics will be controlled by novel engineered nanomaterials. I will give a brief review of our research activity in different fields namely, multiferroics, magnetic oxides (CoFe2O4, Fe3O4 etc.) and transparent conducting oxides.
I will devote the rest of the time on ZnO Fe3O4. ZnO is a unique material that offers about a dozen different application possibilities. The physics of doping in ZnO is intriguing. We found that Ni doping in ZnO drastically reduces the electrical resistivity of ZnO which is due to the 3d orbital splitting contributing to the increase in conduction [1]. We observe that small amounts of transition metal ion doping has a marked influence on the morphology of ZnO leading to interesting changes in optical properties. We also observed changes in the non-linear characteristics upon UV irradiation in ZnO heterostructures grown by PLD. Light emission in ZnO is a defect driven phenomenon. ZnO nanostructures prepared in different gas environments lead to interesting photoluminescence and microstructural changes. We have succeeded in preparing ZnO encapsulated Fe3O4 nanoparticles (5-8 nm core diameter) which show promising trends suitable for device applications. PLD grown Fe3O4 films on glass show high degree of orientation and yield good MR. Nanostructured fabrication of ZnO has many futuristic technological applications (blue and white LEDs, UV emitters/detectors and gas sensors).
[1]. Shubra Singh, N. Rama and M.S. Ramachandra Rao. Appl.Phys.Lett. 88 (2006)
222111.
20
IRT3
Temperature-dependent photoluminescence from ZnO/Zn0.85Mg0.15O quantum well grown on Si(111) substrates
L. P. Zhu, X.Q. Gu, H.P. He, F. Huang, M.X. Qiu, Z.Z. Ye, Y.Z. Zhang, B.H. Zhao
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, 310027 People抯 Republic of China
Electronic address: zlp1@zjuem.zju.edu.cn
A set of ten-period ZnO/Zn0.85Mg0.15O multiple quantum wells with well thickness varying from 2.5 to 5 nm has been grown on Si_111_ substrates by pulsed laser deposition. A periodic structure with sharp interfaces was observed by cross-sectional transmission electron microscopy. The room-temperature photoluminescence resulting from the well regions exhibits a significant blue shift with respect to the ZnO single layer. The well layer thickness dependence of the emission energy from the well regions was investigated and compared with a simple theoretical model. The results suggest that the quantum confinement effects in the quantum wells can be observed up to room temperature
21
IRT4
Electron doped manganites: Reality or illusion?
Pratap Raychaudhuri
Department of Condensed Matter Physics and Materials Science,TIFR,, Homi Bhabha Rd., Colaba, Mumbai-400005
pratap@tifr.res.in
Electron doped manganites are a new addition in the family of doped rare-earth manganites showing colossal magneto-resistance. In these materials Mn is beleived to exist in a mixture of Mn3+ and Mn2+ valence states. However, despite decade long of research controversies regarding the valence state of Mn in these compounds still persist. In this talk I will review the recent progress in the field of electron doped manganites grown through pulsed laser deposition. I will highlight some of the distinct properties of these materials which might make them important from an application perspective.
22
IRT5
Multiferroic behavior of modified BiFeO3 thin films grown by PLD: A Review
V. R. Palkar
Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400 076, India
palkar@ee.iitb.ac.in
Multiferroics are materials that exhibit ferroelectric and magnetic ordering simultaneously in the same phase in certain range of temperature. Moreover, there is coupling between two order parameters. As a result spontaneous magnetization can be switched by applying an electric field and spontaneous electric polarization can be switched by a magnetic field. Hence multiferroics are likely to offer a whole range of novel applications. Apart from their application potential, multiferroics are rich in physics and in recent years the basic science aspects too have attracted a great deal of attention. The primary experimental efforts continue to be focused on attempts to find novel systems with ferromagnetic and ferroelectric properties at room temperature with significant coupling (ME) coefficient which is a primary requirement for bringing these materials in device applications. Moreover, there are very few systems to date that satisfy the requirements. It is therefore a subject of front line research all over the world. BiFeO3 is one of the known multiferroic system showing antiferromagnetic and ferroelectric properties at room temperature. There are continued efforts to enhance magnetic and ferroelectric properties of BiFeO3 system through different possible ways. Controlling film growth conditions so as to bring strain on the lattice during film growth has been tried apart from trying substitutions at Bi or Fe site. In my talk I will try to review the work done in this direction with more emphasis on the study carried out by us on thin films of BiFeO3 and related systems. The advantage of using PLD technique is discussed. The presence of magnetic and ferroelectric domains in same spatial area of few microns obtained by using multimode scanning probe microscopy will be shown.
23
IRT6
Nanostructured Thin Films of Titania Prepared by Pulsed Laser Ablation: Process and Properties
P. Kuppusami, S. Murugesan and E. Mohandas
Physical Metallurgy Division
Indira Gandhi Centre for Atomic Research, Kalpkkam-603 102, Tamilnadu
E mail : pk@igcar.ernet.in
Titania (TiO2) has generated a considerable interest due to their unique physical and chemical properties such as large band gap, high refractive index and dielectric constant. Thin films of titanium oxides are widely used in photovoltaic devices, photocatalysts or dielectric thin film capacitors and in filters. TiO2 has mainly three types of crystallographic structures: anatase (tetragonal), rutile (tetragonal) and brookite (orthorhombic). Anatase is metastable and is only synthesized at relatively low temperature. Brookite is formed only in extreme conditions. The anatase to rutile transformation is irreversible and, generally , occurs at temperatures higher than about 700oC. Interestingly, the anatase phase exhibits better photocatalytic activity compared with rutile or brookite phases. Pulsed laser deposition has been applied to synthesize TiO2 films because control of gas atmospheres for a good quality of films is relatively easier than in other deposition techniques. In this work, we present a simple fabrication procedure to synthesize nanostructured thin films of rutile and anatase phases of chromia doped and undoped titania.
The investigation studies the influence of laser energy, oxygen addition and substrate temperature on the film growth of both anatase and rutile thin films from a sintered rutile target of an undoped TiO2 and 2 mol% chromia doped TiO2 by pulsed laser ablation technique. X-ray diffraction analysis of the films indicated that the films are single phasic and nano crystalline. Titania films deposited in at a base pressure of 5x10-5 mbar and at 673 K are rutile with particle sizes in the range 5-10 nm, whereas the films formed at the oxygen partial pressure of 0.04-0.1 mbar are anatase with particle sizes in the range 10-24 nm. In contrast, chromia doped titania films show mixed phases of anatase and rutile at 673 K, while pure anatase films form at 873 K.
The influence of the microstructural state of the films on the optical and thermal properties is also discussed.
24
IRT7
Combinatorial Pulsed Laser Abltation for Parallel Synthesis and High Throughput Characterization of Functional Inorganic materials
Utpal S. Joshi
Department of Physics, School of Sciences, Gujarat University, Ahmedabad?80009
e-mail : usjoshi@gmail.com
Pulsed laser deposition (PLD) is one of the most powerful techniques for the epitaxail quality thin film growth for variety of functional materials. Conventional 憃ne by one?synthesis approach using the PLD has been a major rate limiting step in the systematic exploration of increasingly complex materials in nano regime for the demanding new technologies. Derived from the new concepts of 慶ombinatorial chemistry? recently introduced continuous composition spread technique based on the non-uniformity of the deposition rate typically observed in pulsed laser deposition (PLD) is applied to the parallel growth of large number of functional oxides and related materials for the growth of opto-electronic and variety of semiconductor nano-structures and their devices. In this talk, the concepts of inorganic combinatorial chemistry, particularly applied to the modern PLD technique and high throughput characterization tools, for rapid optimization of growth parameters, will be discussed. Results of some case studies of COMBI-PLD applied to (a) transparent and semiconducting oxides (TCO), (b) novel diluted magnetic semiconductor (DMS) nano-structured films and (c) organic field effect devices (OFET), will be presented.
We acknowledge the financial support from the DST, India, Kato Foundation, Japan, DAE-BRNS, India and UGC-IUAC, India.
25
IRT8
Single Step Single Shot Lithography Techniques via Selective laser ablation
Alika Khare
Department of Physics
Indian Institute of Technology Guwahati, Guwahati 781039
Email: alika@iitg.ernet.in
The scope of the pulsed laser ablation is tremendous in processing any material. One can engineer the materials with the desired properties and desired surface morphology. The selective laser ablation can be used as a powerful technique of single step single shot laser lithography. In the present talk, the focus is on following two schemes of single shot lithography technique for writing the complete periodic structures of dimensions of the order of wavelength and below using Selective laser ablation without using any mask .
1. Selective ablation of thin films via high power laser Interferometry: This technique is based on modifying the surface morphology to the order of tens of nanometer sizes via selective ablation of material by laser. This technique is very general and is applicable to any kind of materials. In this technique, thin films of metal, semiconductors, polymers or any other complex material is ablated selectively by illuminating it with interference pattern formed by high power laser. This results into the ablation of materials in the region of maximum intensity (bright fring) leaving the area of minimum intensity (dark fringe) unaffected. Width and periodicity of the ablated region depends on the laser intensity distribution with in the bright fringe and wavelength of laser respectively. By using the two interferometers in tandem, one can generate desired two-dimensional tiny arrays of the materials1. This technique is a single step with the advantage of having on line control on the configuration of the nano structures simply by modifying the interference pattern. With this technique one write more than 2000 spot/mm2 in a single shot without using any mask2.
2. Manipulation of atomic trajectories via dipole force: Manipulation of atomic trajectories in presence of near resonant optical field is coming up because of its potential application towards direct deposition of neutral atoms on to a substrate resulting feature size of sub -100nm. This atomic lithography technique offers the advantage of creating the two and three-dimensional complex structure without using any mask. An atom in an off resonance radiation field having gradient in intensity distribution experiences the dipole force. This dipole force can modify the trajectories of atoms and with the care full choice of the parameters; it can lead to the focusing of the atomic beam by an order of magnitude down to 103. Thus the dipole force acts as an atomic lens. If a two dimensional periodic arrays of slow moving atomic beam is subjected to such atomic lens it will compress the complete arrays of atomic beam in the transverse direction, to yield a pattern having periodicity and spot sizes much less than the wavelength of the laser. The periodic arrays of slow moving atomic beams can be generated via selective laser ablation technique4,5. These arrays of atomic beams are allowed to interact with the counter propagating TEMoo mode of off resonance laser. Because of the gradient in intensity of TEMoo mode, the dipole force is experienced by the atoms and result into the focusing of parallel arrays of beams, which can be deposited on to the suitable substrate4.
References:
1. Kamlesh Alti, A. S. Patra and Alika Khare (2007), J Optics research, 10, 19-25.
2. A S Patra and Alika Khare (2006), Optics and Laser Technology, 38, 37-45.
3. Kamlesh Alti, A S Patra and Alika Khare (2006), J Microlitho Microfab, Microsystems, 5, no. 2, 023005.
26
4. Kamlesh Alti and Alika Khare, (2006), Microelectronic Engineering, 83,1975-1980.
5. Kamlesh Alti and Alika Khare (2006), Laser and Particle beams, 4, 469-473.
IRT9
Pulsed laser deposition of amorphous oxides for transparent electronics
M.K. Jayaraj and K.J. Saji
Optoelectronic Devices Laboratory, Department of Physics,
Cochin University of Science and Technology, Kochi ?682 022, India
E-mail: mkj@cusat.ac.in
Transparent and electrically conductive materials are rapidly growing in technological applications in optoelectronic devices like solar cells, liquid crystal displays, energy efficient windows and 慽nvisible electronic circuits? Crystalline materials like tin doped indium oxide (ITO), aluminium doped zinc oxide (ZnO:Al) and antimony doped tin oxide (SnO2:Sb) are presently being used for such applications. Amorphous transparent conductors are much attractive because of uniformity of device characteristics and low processing temperature and can be grown on plastic substrates. The bottom of the conduction band in oxide semiconductors with cation electronic configuration (n-l)d10ns0 (with n ≥ 4) is primarily composed of spatially spread metal ns orbital (n is the principal quantum number). Isotropic shape of metal ns orbitals allows direct overlap among neighbouring orbitals and they are insensitive to the intrinsic structural randomness of amorphous materials. Hence degenerate band conduction and large mobility are possible in amorphous oxide semiconductors containing post transition metal cations. This contrasts to low mobility covalent bonded amorphous materials where carrier transport is controlled by hopping between localized tail states.
In this paper we describe the growth and characterization of transparent conducting zinc tin oxide thin films at room temperature and their use as channel layer in thin film transistors (TFTs). Zinc tin oxide films have the advantages of both ZnO (higher transparency and more stability in activated hydrogen environments than ITO and SnO2) and SnO2 (high stability in acidic, basic solutions and in oxidizing environments at higher temperatures). TFTs using transparent oxide semiconductors as the channel layer have several merits compared with conventional Si-TFTs such as the insensitivity of device performance to visible light illumination and efficient use of backlight in LCDs or emitted light in OLEDs etc. In addition, oxide TFTs have potential advantages over covalent semiconductor-based TFTs in terms of their high voltage, temperature, and radiation tolerances.
Zinc tin oxide thin films are deposited on glass substrates at room temperature (RT) by pulsed laser deposition (PLD) from a ceramic zinc tin oxide target with a KrF excimer laser (248 nm wavelength, 10 Hz repetition frequency). Laser ablation was carried out at a laser energy density of ~ 35 mJ cm-2 pulse-1. By varying oxygen pressure from 0 to 9 Pa during deposition, the carrier concentration can be controlled in the range 1012 cm-3 to 1019 cm-3.
Amorphous nature of the films was confirmed by glancing angle x-ray diffraction analysis. Optical and electrical properties of the films were studied for various Zn/Sn ratio in the film and also the dependence of oxygen partial pressure during the deposition. Thin film transistors were fabricated on silicon substrates using amorphous zinc tin oxide as channel layer. Typical n-channel enhancement mode operation is achieved in these devices with field effect mobility 0.015 cm2 V-1 s-1 and on-off ratio 105.
Acknowledgment
The authors thank Prof. H.Hosono and Prof. T.Kamiya of Tokyo Institute of Technology for discussions and extending the facilities. 27
IRT10
Preparation of Luminescent Nanostructures by Pulsed Laser Ablation
V.P. Mahadevan Pillai
Department of Optoelectronics, University of Kerala, Kariavattom, Trivandrum, Kerala 695 581
*E mail : vpmpillai9@rediffmail.com
Pulsed laser deposition technique is a simple and efficient method for the preparation of nanostructured films. In PLD, one can control size distribution and shape of nanocrystals by varying the parameters like target to substrate distance, laser fluence, background gas pressure, substrate temperature etc and thus it emerges as an effective tool for the growth of quantum structures with high chemical purity and controlled stochiometry. This paper is a review report on the preparation of nanostructures of technologically important materials like Si, SiC, WO3, ZnO, Ta2O5, In2O3, ITO, KLN and BaWO4 using PLD under various conditions in our laboratory. Effect of dopants, laser energy, deposition time, substrate temperature, post deposition annealing, nature of substrate, substrate to target distance and back ground gas pressure etc. on the structural and optical properties of these materials are investigated. XRD, SEM, EDX, AFM, TEM, XPS, UV-visible spectra, Photoluminescence spectra, FTIR spectra, Raman spectra, and open aperture Z scan technique are used for the characterization of the films. Silicon quantum dots of average size 1 nm were synthesized by off-axis pulsed laser deposition. TEM analysis reveals that the mean size of silicon nanoparticles has a direct dependence on the off-axis height of the substrate from the axis of the plume. The synthesized films exhibit PL peak in the UV-Visible region. The PL emission peak and intensity are dependent on the nature of the substrate used. The observed luminescence in Si films does not originate from localized states in gap but from extended states. The growth of SnO2 doped Si nanorings with minimum outer diameter of 20 nm and average thickness of 5nm have been achieved on sapphire substrate by pulsed laser deposition. The atomic force microscopy and Transmission electron microscopy displays several interesting self-assembling forms of polycrystalline as well as amorphous forms of silicon nanorings. Tungsten oxide thin films are prepared using reactive pulsed laser ablation technique and the structural, optical and morphological properties of deposited films are systematically studied by changing the ambient oxygen pressure (pO2). Structural dependence of Tungsten oxide films on ambient oxygen pressure is discussed using Grazing Incidence X-ray diffraction (GIXRD) and Micro-Raman spectra. The section analysis using Atomic Force Microscopy exposed the smooth surface features of the films. The blue shift in optical band gap with increase in ambient oxygen pressure is expounded in terms of electronic band structure of tungsten oxide. The influence of oxygen pressure on optical constants like extinction coefficient, band edge sharpness, refractive index and optical band gap are also investigated. The structural morphological and optical characterization of indium oxide films deposited on fused silica substrates (quartz ) at the ambient temperature and post annealed in the temperature range 473 ?73 K were investigated using XRD, SEM, AFM, UV-Visible spectra. The lattice constants, grain size, microstrain and dislocation density of the films are calculated and correlated with annealing temperature. Indium tin oxide (ITO) films deposited in a reactive oxygen atmosphere on glass substrate at different substrate temperatures (Ts) ranging from 300 K to 573 K are characterized using GIXRD, AFM and UV-visible spectroscopy to study the effect of substrate temperature on the structural and optical properties of films. The XRD patterns suggest that the films deposited at room temperature are amorphous in nature and the crystalline nature of the films increases with increase in substrate temperature. The thickness of the film decreases with increase in substrate temperature. The AFM data show that substrate temperature plays a dominant role on the surface morphology of the films. UV-Visible spectra show that all the deposited ITO films prepared by PLD exhibit a direct allowed transition. The XRD analysis of BaWO4 thin films were prepared on quartz substrate revealed that on annealing, the films show crystalline nature as well as attains a more stable homogeneous structure of monoclinic phase from a co-existed phase of tetragonal scheelite and monoclinic BaWO4 phase.This was well supported by the SEM, AFM and optical studies. Thin films of tantalum oxide are deposited on glass substrates as a 28
function of laser fluence (laser energy from 45 to 65 mJ in steps of 5 mJ) . Bandgap energy was found to decrease with the increase in laser energy. SEM and TEM (transmission electron microscopy) studies show the formation of tantalum oxide nanotubes of diameter less than 50 nm and length greater than 3000 nm in the energy range 50-55 mJ. KLN thin films are prepared using pulsed laser deposition technique for the first time with stoichiometric ceramic target in a non reactive atmosphere. The AFM images revealed a four fold symmetric grain growth. As on annealing the grain size is found to be decreasing. The surface roughness is also found to be decreasing due to annealing. SiC thin films (undoped and doped with SnO2 at 1 at.%, 5 at.% and 10 at.% concentrations) are prepared using pulsed laser deposition on quartz substrates kept at room temperature. SEM and TEM analysis show the formation SiC nanorods of length more than 1 micron and diameter ~20nm in the 10% SnO2 doped SiC films. Zinc oxide (ZnO) films were prepared by pulsed laser ablation, on an optically flat fused silica (quartz) substrate for different deposition timeviz.10, 15 and 20 minutes. The influence of annealing temperatures, ranging from 573 to 773 K, on the structural and optical properties of ZnO films deposited at different ablation time was investigated systematically using X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDX), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Raman spectra, UV-VIS Spectroscopy and Photoluminescence spectroscopy (PL). All these annealed films show a polycrystalline hexagonal wurtzite structure. Effect of CdO doping is also studied.
29
IRT11
Studies on manganite based Thin films and Heterostructures grown by PLD
D. G. Kuberkar
Department of Physics, Saurashtra University, Rajkot- 360 005
dgkcmr@rediffmail.com
The practical applicability of the manganite materials is a topic of great interest, such as manganite based thin films, multilayers and p-n junction devices. Owing to high sensitivity of the electronic and magnetic properties of doped manganites to external magnetic field, electric field or irradiation, these materials exhibit several interesting characteristics.
We have investigated the structural, microstructural and magnetotransport properties of Pr doped La0.5Ba0.3MnO3 (LBMO) manganite thin films with optimum Pr concentration of (La0.5Pr0.2)Ba0.3MnO3 (LPBMO) and studied the thickness dependent effects of swift Heavy Ion (SHI) irradiation on the electronic transport of these films. It is shown that, effect of irradiation on the transport properties increases with increasing film thickness. In addition, we have shown that, the (La0.5Pr0.2)Sr0.3MnO3 (LPSMO) manganite thin films exhibit the half metallicity in a broad range of temperature (up to 200K) , a behavior useful for spin injector devices.
we have also studied the effect of non-magnetic spin scattering in (La0.5Pr0.2)Sr0.3MnO3/Al2O3/(La0.5Pr0.2)Sr0.3MnO3 heterostructure, grown by the PLD technique. A large MR ~77 % is observed at TIM (~220K) in this heterostructure, possibility due to the magnetic field induced spin fluctuations in the scattering barrier of Al2O3, controlled by external applied field.
Recently we have investigated properties of manganite based La0.5Pr0.2Sr0.3MnO3 [5] / La0.5Pr0.2Ba0.3MnO3 [4] / STO multilayered structure grown by PLD technique. It is observed that a large Field Coefficient of Resistance (FCR) ~ 35% along with an appreciably large MR ~ 56% is exhibited by this heterostructure at RT.
30
IRT12
Laser ablation of Zn/ZnO Core-Shell Nanoparticles: Effect of SDS Concentration
Geetika Bajaj and R.K.Soni1
Laser Spectroscopy Laboratory, Physics Department
Indian Institute of Technology, Delhi, New Delhi-110016
1Email: ravisoni@physics.iitd.ac.in
Pulsed laser ablation in liquid (PLAL) has gained considerable popularity in recent years for the growth of metal and semiconductor nanoparticles 1-2. It involves ablating the target material in liquid media that confines the plasma plume formed when the high-energy laser beam interacts with the material. Laser induced reactive quenching can lead to the formation of the metal and metal oxide nanoparticles. The size control can be achieved by varying laser parameters and liquid media. The advantage of this method over the conventional chemical methods is that it is a single step process and nanoparticles produced are of high purity and defect free.
We have used Zn in the powder form to enhance the interaction with the laser in order to improve the nanoparticle yield. A suspension of 20 mg Zn (99.9%) dust in 15 ml of deionised water and aqueous solution of Sodium dodecyl sulfate (SDS) with concentrations 0.1 M, 0.05 M, 0.01 M and 0.0067 M was used as target material. The target, kept in a glass vessel, irradiated for 45 minutes with the second harmonic (532 nm) of a pulsed Nd: YAG laser operating at 10 Hz with a 5 ns pulse width and the beam was focused to maximize the laser interaction with the Zn powder particles for high nanoparticle yield. The maximum pulse energy used was 17mJ. The concentrations of SDS were chosen both above and below the CMC (0.008M) to investigate the effect of micelle formation on the fabrication of the nanoparticles. No visible change was observed in the solutions after the ablation.
Figure 1 shows the TEM image of Zn/ZnO sample prepared in aqueous solution with 0.1M SDS concentrations. Optical absorption spectra of the colloidal solution in deionised water and in SDS is shown in Fig. 2.. There are three distinct features in the spectra at around 242 nm, 270 nm and 350 nm which can be attributed to Zn nanoparticles, surface plasmon resonance (SPR) from Zn and ZnO excitonic absorption, respectively. These peaks exhibit marked variation in their relative strength with variation in SDS concentration. High SDS concentration corresponds to high relative amount of Zn nanoparticles existing as the core in the core/shell nanostructures, whereas low SDS concentration leads to large ZnO shell thickness. This can be understood as laser ablation of the target induces local zinc plasma above the target, which results in the formation of Zn clusters during extinguishment of the zinc plasma plume, and subsequent aqueous oxidation can lead to the formation of ZnO nanoparticles. However, SDS can depress such oxidation because of its surface capping on the particles and can lead to the formation of Zn/ZnO core/shell nanoparticles. Thus varying amounts of components Zn and ZnO can thus evolve with varying SDS concentration in solution.
200250300350400450500Wavelength (nm)Core-shell Zn/ZnOAbsorption (
arbitary units) deionised water 0.1M SDS 0.05 SDS 0.01M SDS 0.0067M SDS
Fig.1 TEM image of Zn/ZnO prepared in aqueous solution Fig. 2 Room temperature optical absorption spectra from Zn/ZnO core-shell nanostructures
1. T. Sasaki, Y. Shimizu and N. Koshizaki, J. Photochem and Photobio A: Chemistry 182, 335 (2006).
31
Haibo Zeng, Weiping Cai, Yue Li, Jinlian Hu, Peisheng Liu: J. Phys. Chem B 109, 18260 (2005).
IRT13
Characterization of pulsed laser deposited Fe3O4 thin films
on different substrates.
D.M.Phase
UGC-DAE Consortium for DAE facilities
Khandwa Road, University Campus, Indore-452 017
Magnetite (Fe3O4) is a well known half metallic ferromagnetic material and enjoys the ability to inject 100 % spin polarized electrons. The Curie temperature of Fe3O4 is 858K, which is very high as compared to other half metallic ferromagnetic materials. These properties make the Fe3O4 a potential candidate for spintronic devices. Magnetite has a cubic inverse spinel structure and it consists of Fe2+ and Fe3+ ions. At room temperature the electrons continuously hop between Fe2+ and Fe3+ ions at B sites leading to metallic nature of the system. At 120K hopping is frozen and consequently resistivity is increased by two orders of magnitude as the temperature is lowered. This transition is termed as Verwey transition. Though the precise origin of Verwey transition is still under review, works is progressing in the direction of further harnessing the important features of magnetite for superior technological relevancies. In this scenario it is essential to study the properties of Fe3O4 in thin film form since for any application thin films finally hold the key. There are several reports1-3 available on thin film growth of Fe3O4 by various techniques. From these studies it is evident that the electrical or magnetization property of Fe3O4 thin films immensely depend on the method of preparation, substrate used, nature of defects and the defect density. In this talk we present a review of our recent research work4-6 on the growth and characterization of Fe3O4 thin films on different substrates. Some of the issues, which will be addressed, are Raman scattering across Verwey transition, substrate independent oriented growth and modifications in structural and electrical properties due to swift heavy ion irradiation.
References:
[1] D. T. Margulies, F. T. Parker, M. L. Rudee, F. E. Spada, J. N. Chapman, P. R. Aitchison, and A. E. Berkowitz, Phys. Rev. Lett. 79, 5162 (1997).
[2] S. K. Arora, R. G. S. Sofin, and I. V. Shvets
Phys. Rev. B 72, 134404 (2005).
[3] S. B. Ogale, K. Ghosh, R. P. Sharma, R. L. Greene, R. Ramesh, and T. Venkatesan, Phys. Rev. B 57, 7823 (1998).
[4] D. M. Phase, S. Tiwari, Ram Prakash, Aditi Dubey, V. G. Sathe and R. J. Choudhary, J. Appl. Phys. 100, 123703 (2006).
[5] S. Tiwari, R. J. Choudhary, Ram Prakash, and D. M. Phase,
J. Phys. Cond. Mat. 19, 176002 (2007).
[6] S. Tiwari, Ram Prakash, R. J. Choudhary, and D. M. Phase,
J. Phys. D (Appl.Phys.). 40, 4943 (2007).
32
IRT14
Application of pulsed laser deposited thin films of ZnO as varistors and InN as field emitters
K. P. Adhi*
Center for Advanced Studies in Material Science and Condensed Matter Physics.
DST unit on Nanoscience,
Department of Physics, University of Pune,
Pune ?11 007, India
*Corresponding authors e-mail: kpa@physics.unipune.ernet.in
We discuss the application of pulsed laser deposited ZnO thin films as varistors and InN thin films as field emitters. Abstract of the work in this context is as given below;
Pulsed laser deposition technique was used to grow thin films of ZnO on Si (100) substrate held at different temperatures (Ts) ranging from 100 to 600 癈. All the as-deposited or the pristine (P) films show a preferential c-axis orientation. Current-voltage (I-V) characteristics of the P films show Ohmic behavior for all the samples. These films were subjected to annealing at 800 癈 in air ambient for 4 hours. Interestingly, these annealed films (A) show nonlinear variation of current with applied voltage, very similar to the one observed in doped ZnO varistors [1]. Attempt is made, using X-ray photoelectron spectroscopy (XPS), to comprehend the drastic difference in I-V characteristics of the P and A films. The O1s and the Zn2P3/2 spectra reveal the chemical environments in the P and A films. The spectra recorded for A films is significantly different from that of the P films. It is found that annealing results in the formation of Zn(OH)x barrier in the ZnO films. The nonlinear behavior, in case of the annealed films, is attributed to the tunneling of electrons through the aforesaid barrier during inter grain electron transport [2]. The nonlinearity in I-V characteristics of A films suggests the use of PLD-grown thin films subjected to annealing as thin-film varistors in electronic industry.
DC plasma assisted pulsed laser deposition technique was used to grow thin films of InN on c-cut Al2O3 substrates. X-ray diffraction (XRD) studies revealed the single phase, polycrystalline nature of the InN thin films with wurtzite structure. The root mean square (rms) surface roughness, as seen by atomic force microscopy (AFM), was estimated to be ~ 35 nm. The surface morphology showed hexagonal features having sharp edges and protrusions. Using the diode configuration, the field emission characteristics of InN/Al2O3 were investigated in ultra high vacuum (1×10−8 Torr). The turn-on field, required to draw an emission current density of 10μA/cm2, was observed to be ~3.5 V/μm. The maximum emission current density obtained was 230μA/cm2 when the applied electric field strength was ~ 4 V/μm. The Fowler朜ordheim (FN) plot obtained from the current杤oltage characteristic was found to be linear in accordance with the quantum mechanical tunneling phenomenon. The field enhancement factor β, estimated from the slope of the FN plot was 21,167 cm−1[3]. To the best of our knowledge this is the first report of field emission studies of InN/Al2O3 with such high values of β. The study indicates strongly that InN nanostructured thin films can be used successfully in integrated field emitting devices.
References-
1. S. M. Jejurikar, A. G. Banpurkar, A. V. Limaye, S. K. Date, S. I. Patil, and K. P. Adhi, P. Misra, L. M. Kukreja, Ravi Bathe
J. of Applied Physics 99, 014907 (2006)
2. Suhas. M. Jejurikar, S. S. Ashtaputre, S. K. Kulkarni, S. K. Date and K. P. Adhi
L. M. Kukreja
Communicated to J. of Applied Physics
3. K.P. Adhi, Sanjay Harchirkar, Suhas M. Jejurikar, P.M. Koinkar, M.A. More, D.S. Joag, L.M. Kukreja
33
Solid State Communications 142, 110?13 (2007)
IRT15
Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition.
S. I. Patil, M. S. Sahasrabudhe, Deepak N. Bankar, A. G. Banpurkar and K. P. Adhi
Department of Physics, University of Pune, Pune 411 007, India
Ravi Kumar
Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067, India
E-mail:patil@physics.unipune.ernet.in
In perovskite manganite of the form R1-xAxMnO3 the spin, lattice, charge and orbital degrees of freedom are coupled to one another. Since interaction energies are also of the same order of magnitude, their properties are extremely sensitive to small changes in the material parameters thereby leading to very rich phase diagram. To study the role of heavy ion irradiation on the thin films of manganites, highly c-axis oriented LSMO thin films were grown on LaAlO3 (100) (LAO) substrates by the pulsed laser deposition (PLD) technique. The well-characterized films were implanted and irradiated with different ions, with varying energies and dose values. Influence of irradiation on the structural, electrical, magnetic and magnetoresistance properties were studied.
A detailed investigation of the surface morphology of the pristine and swift heavy ion (SHI) irradiated La0.7Sr0.3MnO3 (LSMO) thin film using atomic force microscope (AFM) is presented. The films were annealed at 800 癈 for 12 hours in air (pristine films) and subsequently irradiated with SHI of oxygen and silver. The incident fluence was varied from 1 x 1012 to 1 x 1014 ions/cm2 and 1 x 1011 to 1 x 1012 ions/cm2 for oxygen and silver ions respectively. X-ray diffraction (XRD) studies reveal that the irradiated films are strained. From the AFM images, various details pertaining to the surface morphology show drastic modifications, which is dependent on the nature of ions and the incident fluence. However, the surface is found to remain self-affine. The difference in the modifications of surface morphology for both the ions will be discussed in detail.
The future work in this context on the strontium doped manganite system is ongoing and will also be discussed in detail.
34
IRT16
Tailoring the electrical and magnetic properties of
LaFe1-xNixO3 thin films by swift heavy ion irradiation
Ravi Kumar
Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi-110067
ranade@iuac.ernet.in
We have investigated the effect of 190MeV Ag ion irradiation on the structural, electrical and magnetic properties of the pulsed laser deposited thin films of LaFe0.5Ni0.5O3. It is observed that following the irradiation, the lattice of the composition relaxes with enhanced c-axis orientation. Consequently the resistivity of the composition, which shows semiconducting trend, decreases with irradiation possibly due to the enhanced hybridization between the transition metal 3d and oxygen 2p orbitals. The pristine sample shows the activated variable range hopping behavior through out the studied temperature range, though the irradiated samples deviate from this behavior at lower temperatures. The pristine as well as the irradiated films exhibit room temperature ferromagnetic behavior and the magnetization increases with the irradiation fluence, almost doubled as compared to that of the pristine value.
35
IPT1
Study of device characteristics on Pulsed Laser Deposited Manganite-semiconductor Heterostructures
S.N. Kale1, J. Mona1, Hitesh Mamgain2, R.R. Rawat3, V. Ganesan3, R.J. Choudhary3, D.M. Phase3
1 Fergusson College, Pune 411 004, India
2 Nanonics Imaging Limited, Jerusalem., Israel
3UGC-DAE Consortium for Scientific Research, Indore 452 017, India
Email for correspondence: snkale@vsnl.com
There have been numerous reports on study of manganite systems juxtaposed with either another manganite system or with a semiconductor to yield interesting p-n junctions which can have potential applications in the area of spintronics.1-4 In this context, we report on study of morphology, optical contrast and transport characteristics of two different manganite-semiconductor thin film systems, namely, La0.7Ba0.3MnO3 (LBMO) bilayered with SnO2 and La0.7Sr0.3MnO3 (LSMO) bilayered with SnO2 on Si (001) substrate, synthesized using Pulsed Laser Deposition system. X-ray Diffraction studies reveal that while LBMO exhibits oriented growth, LSMO grow in a polycrystalline manner on polycrystalline SnO2. Atomic Force Microscopy shows interesting pyramidal structures of both manganite systems of size ~ 2 μm x 1 μm x 200 nm. On the other hand, SnO2 grows in the form of close packed cylindrical clusters of ~ 200 nm radius. Near-Field Optical Microscopy (NSOM) study using 532 nm laser reveal that optical NSOM output intensity in manganites (both LBMO and LSMO) is four times less than SnO2 signal. Transport characterizations of LBMO:SnO2 system exhibits non-linear current-voltage characteristics at 300 K which becomes linear at 60 K. On the other hand, LSMO:SnO2 system show non-linear current-voltage characteristics at both at 300K and 60K. The results have been interpreted in terms of lattice matching and strain in both the systems. The work will essentially project the systems as a promising candidate in non-conventional device category.
References
[1] K. Lord, D. Hunter, T.M. Williams, A.K. Pradhan, Appl. Phys. Lett. 89 (2006) 052116.
[2] T. Li, M. Zhang, X. Song, B. Wang, H. Yan, J. Appl. Phys. 100 (2006) 063711.
[3] H. Tanaka, J. Zhang, T. Kawai, Phys. Rev. Lett. 88 (2002) 027204.
[4] J.R. Sun, C.M. Xiong, T.Y. Zhao, S.Y. Zhang, Y.F. Chen, B.G. Shen, Appl. Phys. Lett.
84 (2004) 1528.
36
IPT2
Pulsed Laser Deposition of LaDyCaBaCuO Superconducting Thin Films
1.5
0.525z
Sudhindra Rayaprol1, K. R. Mavani2, 3, D. G. Kuberkar2, N. A. Shah2, J. John4 and R. Pinto4, 5
1UGC-DAE CSR-Mumbai centre, R-5 Shed, BARC, Trombay, Mumbai
2Department of Physics, Saurashtra University, Rajkot
3Institute of Laser Engineering, Osaka University, Osaka Japan
4DCMP&MS, Tata Institute of Fundamental Research, Colaba, Mumbai
5Indian Institute of Technology ?Bombay, Powai, Mumbai
The La and Ca substituted, tetragonal superconductors have enhanced corrosion resistance compared to RE-123 type orthorhombic superconductors. These tetragonal superconductors have a stable oxygen stoichiometry and structure with lesser aging effect in the atmosphere compared to the orthorhombic RE-123 superconductors. This property of tetragonal superconductors, particularly La-Ca substituted systems, is desirable for possible thin film applications.
A single-phase target of polycrystalline La1.5Dy0.5CaBa2Cu5Oz (La-2125) was used for the deposition of thin films using Pulsed Laser Deposition technique. A KrF excimer laser (λ = 248 nm) with pulse repetition rate of 10 Hz, energy density of 0.9 J/cm2 on the target, the substrate-target distance of 4.5 cm distance was used to deposit the La-2125 thin films (~2000 Å) on single crystal LaAlO3 (001) substrates held at temperature of 820癈. The O partial pressure in the chamber was maintained at 500 mTorr during the deposition.
2
The XRD patterns showed that the thin films were pure phase (La-2125) and c-axis oriented on single crystal LaAlO3 (001) substrates. The resistance was measured as a function of temperature for determining the Tc of the thin films. The films showed the onset of superconducting transition at ~79 K and the Tc ~ 75 K, which is close to the Tc (~78 K) of single-phase bulk La-2125 compound.
Recent irradiation studies on the La-2125 thin films using Ag and O beams have shown that the columnar defects created by the ion beams of certain fluence (ions/cm2) have desirable effect on the critical current density, i.e., up to certain fluence Jc increases with increasing fluence. The typical Jc for pristine and irradiated thin film of La-2125 composition is of the order of 106 A/cm2. The irradiation results in two or three fold increase in the Jc value.
In this presentation, we will highlight the results of ERDA experiments and effect of ion-beam irradiation on the modification of superconducting properties of La-2125 thin films.
37
IPT3
Basic Photoluminescence Processes at different Temperatures in ZnO / (0001) Sapphire Thin Films Grown by Pulsed Laser Deposition
P. Misra*, T. K. Sharma and L. M. Kukreja
Laser Program, Raja Ramanna Centre for Advanced Technology, Indore?452 013
*Corresponding author email: pmisra@cat.ernet.in
Photoluminescence (PL) transitions associated with free (FX) and bound (BX) excitons and their corresponding phonon replicas in ZnO thin film have been studied in the range of 10 to 300K. As shown in Fig.1 the low temperature PL spectra were dominated by recombination of donor bound excitons and their phonon replicas (B/X & B//X) while with increasing temperature, free exciton PL and the associated LO phonon replicas (F/X & F//X) increased in intensity at the expense of their bound counterparts. The BX peak with line width of ~6 meV at 10K exhibited thermal activation energy of ~ 17 meV, consistent with the exciton-defect binding energy. The FX and BX peak positions were found to converge with increasing temperature, which was attributed to the transformation of BX into the shallower donor bound exciton complexes at consecutive lower energy states with increasing
Figure 2. Temperature dependence of
energy positions of FX, BX, F/
X, B/
X, F//
X
and B//
X peaks.
Figure 1. Photoluminescence spectra of ZnO
thin film taken at different temperatures in
the range of 10-300K
temperature. The energy separation between FX peak and its corresponding 1-LO phonon replica showed stronger dependence on temperature that of 2-LO phonon replica as shown in Figure 2. However their bound counterparts did not exhibit this behavior. The observed temperature dependence of the energy separation between the free exciton and its?LO phonon replicas are explained by considering the contribution of kinetic energy of free excitons
38
IPT4
Synthesis and properties of pulsed laser deposited Fe doped MoO3-d thin films
R. J. Choudhary1, Ram Prakash1, D. M. Phase1 and Ravi Kumar2
1UGC-DAE Consortium for Scientific Research, University Campus, Indore-452017, India.
2Inter University Accelerator Center, N. Delhi-110067, India.
Email:ram@csr.ernet.in
Over the last few years there has been insurgence in the research field of spintronics, wherein the spin controlled electrical, optical and magnetic properties are desired. It is commonly believed that if the two degrees of freedom of a carrier, namely charge and spin, can be coupled together so that there is a coalition of electrical and magnetic properties, the emerging device would possess unparallel opportunities of applications. One way to realize this arrangement is to dope some magnetic impurity in a semiconducting material and hope that it harnesses the ferromagnetic property alongwith the semiconducting property. The new system of magnetic impurity doped semiconductor system has been branded as diluted magnetic semiconductors. Molybdenum oxide (MoO3) is a wide band gap (2.85 eV) n-type semiconductor having orthorhombic unit cell with the space group of Pnma. For the last several years, molybdenum oxide has attracted attentions because of their potential applications in electrochromism, photochromism, gas sensing devices, optically switchable coatings, catalysis etc. The demonstration of such a wide range applications is due to the non-stoicheometric nature of molybdenum oxide and to the occurrence of several different allotropes and phases of molybdenum oxide (such as MoO3, MoO2, β-MoO3, Mo4O11, etc.). The dependence of electrical property on oxygen concentration is such that MoO3 is optically transparent and electrically insulating in nature while MoO2 is metallic. This provides a window to optimize oxygen concentration between these two members of molybdenum oxide in a way to achieve transparent conducting semiconductor with desired band gap. Besides the above-mentioned attracting physical and optical applications, if another degree of dimensionality in terms of magnetic property could be induced in the system by doping some magnetic impurity, the resulting device will grant a boost to the existing MoO3 based technology. Though the room temperature ferromagnetism in transition metal elements doped in other oxides system has been realized, there have been controversies regarding the cause of origin of ferromagnetism in the system. We report the growth of molybdenum oxide and iron doped (2 and 5 at. %) molybdenum oxide thin films on c-plane of sapphire substrate using pulsed laser deposition in oxygen ambient. The structure was characterized using x-ray diffraction, x-ray photoelectron spectroscopy (XPS). The electrical resistivity and magnetization behavior were investigated using four point probe resistivity and vibration sample magnetometer respectively. XRD results show that the films are oriented in (100) direction and have monoclinic structure based on MoO2 phase. We do not observe any impurity phase of iron oxide in iron doped films in their XRD patterns. The resistivity data show a minima at 101 K for undoped which is shifted to 57 K for 5% Fe doping. The Fe doped samples show ferromagnetic behavior at room temperature. X ray photo spectroscopy data reveal that Fe is in +2 valence state, excluding the possibility of formation of Fe clusters.
39
IPT5
UV excimer lasers for smart materials and nanostructures
B. Fechner, R. Pätzel, R. Delmdahl
Coherent GmbH, Hans-Böckler-Str. 12, D-37079 Göttingen, Germany
E-mail: burkhard.fechner@coherent.com
Abstract
From medicine through consumer electronics, device manufacturers face market pressure to increase miniaturization while increasing device functionality and hence complexity. As a result, many industries are turning to laser micromachining as a manufacturing solution to meet these needs. Excimer lasers have already proven particularly well-suited to these micromachining applications. Ongoing progress in material research and processing industry is fueled to a large extent by the technique of pulsed laser deposition (PLD). With this powerful and versatile approach, multi-component target materials can be ablated and deposited onto a substrate to form stoichiometric layers which exhibit the desired properties. Monitoring of growth parameters such as thickness and surface roughness is frequently in-situ monitored via electron diffraction or other diagnostic tools.
Both quality and longevity of the microstructures acting e.g. as sensors, actuators, bioreactors or information transmitters strongly depend on the degree of accuracy achieved in the manufacturing process.
1. Introduction
Pulsed Laser Deposition (PLD) as a physical vapour deposition technique for coating development and material screening opens up nearly unlimited pathways to functional coatings by means of rapid protocoating. Prerequisites for a successful rapid protocoating are well-conceived ablation systems and lasers enabling efficient, development of thin film coatings for medical device manufacturing, mechanical engineering, microsystems technology or optics on a short timescale. In the PLD technique a high pulse energy laser beam, preferably the rectangular profile of a short wavelength excimer laser at 248 or 193 nm, is demagnified on the target material which is to be deposited. Due to the short wavelength of the pulsed excimer light (20ns) and the resulting small penetration depth, the absorption takes place selectively in a limited volume near the surface leading to fast heating and explosive evaporation1. This non杢hermal equilibration mechanism is the basis for depositing multi-component substrate materials controlling stoichiometry and crystal properties during thin film growth.
The high energy photons of the excimer laser allow virtually all target materials to be deposited such as oxides, nitrides, and carbides for isolators, metals, complex ceramics, and polymers for semiconductors. The flexibility in view of the employed materials which can be varied during the deposition process allowing straightforward tayloring of multicoatings has rendered PLD an established and productive technology for coating and material development2.
2. Pulsed Laser Deposition
40
2.1 Ablation source
Uniform pulse energy, at both low repetition rates and in burst operation, is among the most critical laser output parameters for PLD. A constant, uniform pulse energy produces consistent
Fig.1 Pulse energy and energy stability of COMPexPro as a
function of operation voltage at 248 nm and 10Hz.
deposition parameters, resulting in homogeneous films and a repeatable process. High laser pulse energy provides several benefits for PLD. First, it enhances the deposition rate of target materials. Depending on laser pulse energy several microns per minute are achievable. Next, it enables a larger area on the target to be ablated at a given fluence. This area enlargement increases the deposition rate and reduces the plume angle, resulting in higher deposition efficiency. Finally, higher photon energies as provided by excimer lasers at wavelengths of 193 nm and 157 nm provide an even larger process window, allowing consistent, successful material ablation well above the ablation threshold also for transparent polymers and hard target samples3. Even compact excimer lasers provide high pulse energies between 200mJ and 500mJ with excellent pulse-to-pulse stability of typically 0.5%, 1 sigma.
2.2 Vacuum system
In order to generate smart material layers most effectively next to the ablation light source which is preferably a short wavelength excimer laser a sophisticated vacuum system is the key to success. Its essential components are the vacuum chamber containing heated substrate holder, target holder and UV optical elements for demagnifying the laser beam to the required on-target energy density of typically 1-5 J/cm2. Both a constant deposition rate and homo-geneous thin film properties over a large thin film area are provided by the exceptional pulse-to-pulse stability and beam homogeneity of advanced high-pulse energy lasers.
Fig.2 Target holder in an advanced PLD vacuum system,
consisting of six rotatable targets.
Fully automated vacuum systems with up to 6 inch diameter substrates enable efficient and reproducible thin film development for scientific as well as industrial research facilities. Rotatable revolvers, as shown in figure 2, allow to variably deposit up to 6 different target materials. The individual targets generally consist of small pellets offering high flexibility and reducing target costs to a minimum.
2.3 Coating capabilities of Pulsed Laser Deposition
Of particular interest both in mechanical and optical engineering are coatings combining hydrophobic functionality with a high degree of trans-parency in a thin layer as provided by poly-tetrafluoroethylene (PTFE). This material cannot be deposited other than with pulsed laser deposition and demonstrates the fle-xibility of PLD. Thin PTFE layers of a thickness of above 100 nm significantly increase the contact angle on a given substrate to 110?as is shown in figure 3 for glass substrate and at the same time provide a transmission of >98 % as useful for e.g. self-cleaning surfaces.
41
In medical device technology PLD deposited coatings lend the required biocompatibility to novel implants. As in the case of stents many devices cannot be made from biocompatible materials such as titanium directly but need to be chosen in view of their mechanical properties supporting high tensile stress during expansion in the blood vessel. The appropriate layer ma-terial deposited with PLD exhibits high adherence also on the usually four times expanded stent mate-rial which is the prerequisite for its biocom-patibility.
In figure 4, a biocompatible metal oxide target has been used for pulsed laser deposition with excellent thin film homogeneity and strength. Deposition time for a 150 nm film on a 20 mm long stent is in the range of minutes.
Fig.4 Expanded stent coated with a thin metal oxide layer (left). The enlarged view (right) gives evidence for the high thin film quality (Axyntec GmbH).
3. Microfluidics
Highly miniaturized devices in biomedicine include relatively simple products, such as micro-arrays used in the pharmaceutical industry for high throughput drug discovery, and more complex microfluidic devices. These lab-on-chip devices are widely used in genomics and proteomics, and will soon enable the miniaturization and automation of analytical testing. Typically resembling microscope slides, lab-on-chip devices are fabricated in optically transparent materials, such as pyrex glass and PMMA, to enable analysis using some type of modified microscope setup. Unfortunately, it is difficult to create microscopic channels, grooves, holes and bridges in these materials by traditional methods, particularly in the case of glass. But excimer micromachining can create these features with the desired resolution and without any
Fig.3 Water droplet on a glass surface before (left picture) and after (right picture) coating with a PTFE thin film (Axyntec GmbH).
42
microcracking or other problems (see figure). The 248 nm output wavelength is commonly used for polymers and the 193 nm wavelength is mostly used for glass and quartz machining.
In addition, many lab-on-chip systems require electrical contacts, to enable processes such as electrophoresis. The excimer can also be used to fabricate these electrodes in the back-side of the lab-on-chip. Each electrode is produced by ablating a small through hole at the required location. These often have a circular cross-section with typical diameters of a few tens of microns or less. Other shapes can be created with an appropriate photomask, which also allows all the electrodes to be drilled in a single step. After laser-drilling, the holes are completely filled with metal in a vapor deposition or pulsed laser deposition process, forming both a liquid-tight seal and a through electrode (see fig. 5).
Fig.5 Microfluidic structure and sensors
(Bartels Mikrotechnik, GmbH)
4. Direct Patterning of Circuits
There is growing demand for low unit cost, miniaturized electrical circuits for applications such disposable medical sensors and radio frequency identifiers (RFID).In this application, the output beam from a 308 nm (XeCl) excimer is reshaped in a beam homogenizer and passed through a photomask (typically chrome on quartz) containing the pattern for one or even several circuits. The mask is re-imaged at the work surface which consists of a plastic film or web on which a thin layer of metal has been vapor-deposited. Most of the UV radiation passes through the film and is strongly absorbed at the plastic-metal interface. This vaporizes a thin layer of the plastic, completely removing the overlying metal film (see figure 6). Providing the metal layer thickness is 150 nanometers or less, a single laser pulse performs a complete lift with clean edges and no breaks even on lines as narrow as 10 microns.
43
The optimum thickness is actually around 500 angstroms which is more than sufficient for most flex circuit applications, which typically do not carry high current. At this thickness, a circuit with area up to 400 mm2 can be processed at a pulse energy of 1 J.
Excimer lasers designed for this application typically operate at pulse repetition rates of several hundred Hz. At 300 Hz for example, this 搒ingle pulse?laser process can generate 18,000 circuits/minute. The pro-cess can be set up as reel-to-reel with continuous feed because the short pulse of the laser eliminates the possibility of blur even at feedrates of tens of meters/second. Alternatively some manufacturers have implemented a roll-to-roll process in which optics sweep across the web which undergoes stepped motion. Laser direct patterning can be used with several different flexible plastic substrates (PET, polyimide, PEN, and PMMA) and a full range of conductors including copper, gold, silver, platinum, aluminum, and even titanium. Manufacturers cite several process advantages, compared to traditional lithography using wet photochemistry. The most important is process simplicity; a single dry process replaces about seven separate steps. It also eliminates the cost and disposal of the chemical reagents. In addition, the metal debris can be trapped by a vacuum system, allowing recycling of this valuable material. Fig.6 Laser Direct Patterning process (LPKF AG)
5. Conclusion
Intelligent thin film development and rapid prototyping for various fields of applications is largely facilitated by means of short excimer laser wavelengths. Combined with compact, automated vacuum systems for fast and convenient substrate handling stoichiometric multi-layer thin-films with good homogeneity and taylored physical characteristics are efficiently generated. Stable, high pulse energy output characteristics provide controlled and reproducible target ablation for nanotechnology which can often be upscaled in output rate by reel to reel approaches.
6. References
[1] Delmdahl, R F.; Oldershausen, G.:
Quantitative solid sample analysis by ArF excimer laser ablation, Journal of Molecular Structure, Vol. 744, p. 255-258 (2005).
[2] Ashfold, M. N. R.; Claeyssens, F.; Fuge, G. M.; Henley, S. J.:
Pulsed laser ablation and deposition of thin films, Chemical Society Review, Vol. 33, p. 23-31 (2003).
[3] Pedarnig, J. D.; Peruzzi, M.; Vrejoiu, I.; Matei, D. G.; Dinescu, M.; Bäuerle, D.: Pulsed-laser deposition of inclined ZnO, of GaPO4 and of novel composite thin films, Applied Physics A, Vol. 81, p. 339-343 (2005).
44
IPT6
Precise photonic engines for UV pulsed laser deposition
R. Delmdahl, J. Sieber, B. Fechner
Coherent GmbH, Hans-Böckler-Str. 12, D-37079 Göttingen, Germany
E-mail: ralph.delmdahl@coherent.com
Abstract
High pulse energy excimer lasers with pulse energies between 300 and 1200 mJ/pulse and photon energies between 5eV and 7.9 eV lend maximum flexibility to the technique of pulsed laser deposition. On account of the high energy densities accessible with the latest generation of excimer lasers, the entire material spectrum including high band-gap metal oxides such as ZnO is amenable to precise and controlled ablation with subsequent stoichiometric transfer to the substrat. Because the transferred material needs time to smoothly deposit and position itself optimally on the substrate, the repetition rate of the ablation laser is typically on the order of only 10 Hz. These requirements are best met by pulsed lasers with short wavelengths (248 nm is the most common), high pulse energies (100 to 1000 mJ) and homogeneous spatial energy distribution. Thin film quality is very sensitive to shot-to-shot energy density fluctuations, and because deposition time in a lab takes up to one hour, both spatial (beam profile) and temporal (shot-to-shot) energy stability are essential in order to obtain reproducible results.
1. Introduction
Pulsed excimer lasers are the strongest and most efficient laser sources in the ultraviolet spectral region. Record short wavelengths from 351 nm down to 157 nm as well as record high 1200 mJ pulse energy as available for the 248 nm excimer lasers are commercially provided for numerous laser material ablation approachesi. Virtually no material is able to withstand the high photon energies ranging from 3.5 to 7.9 eV emitted by excimer lasers. As a result of the irradiation of material with high energy excimer laser photons at sufficient fluence immediate bond breaking due to electronic excitation is induced. In combination with short-term laser material interaction of only 10 to 30 ns excimer pulse duration, material ablation proceeds via fast vaporization and consecutive ejection of material with only negligible dissipation of heat transfer to the surrounding zone. The effect is an inherently precise and clean ablation quality.
The latest excimer laser versions LPXPro and COMPexPro as described in this paper were specifically redesigned to provide the beam and energy stability required for achieving the homogeneous layer growth essential in todays抯 most advanced thin film applications.
2. Advances in excimer laser tube design
Excimer lasers used for precise material ablation must meet high standards in regards to performance and output characteristics. For reproducible results of high-quality the excimer laser must keep his performance stable over a long period in order to increase productivity even at very high pulse energies. In the following paragraphs recent technical advances in excimer lasers for pulsed laser deposition and resulting output energy characteristics and beam parameters are discussed.
2.1 Smooth Ceramic Preionization
Based on proven metal-ceramic technology NovaTube? the preionization concept of both the new LPXPro series and the new COMPexPro series has been optimized in order to obtain highest pulse
45
energies in combination with homogeneous discharge conditions. The newly employed patented smooth ceramic preionization design uniquely combines the efficiency of a discharge driven preionization source, surch as spark preionization designs with the smoothness and homogeneous volume preionization as provided by e.g. the corona preionization which is far less efficient and thus only viable for low pulse energy excimer lasers.
2.2 Optimized Gas Flow and Gas Purification System
In order to extend the hands-off operation time of both the LPXPro series and the COMPexPro series, the gas flow architecture and the internal electrostatic gas purification systems have been redesigned. Laser gas contaminants are efficiently filtered out by careful optimization of the gas flow via capable electrostatic filter elements. With the sophisticated gas purification system inside the LPXPro and COMPexPro laser gas performance remains to a large extent unaffected during long-term operation even at multi-hundred millijoules of laser pulse energy (see Fig. 1).
Figure 1: Dynamic gas behavior of LPXPro with smooth ceramic preionization and optimized gas purification. 40 million pulses (>60 hours) non-stop operation are achieved with a single gas fill at a wavelength of 193 nm.
3. Specific advantages of excimer lasers in PLD
In view of optical properties excimer laser have pivotal advantages over Nd:YAG lasers in PLD applications. These advantages are based on superior ablation characteristics and much better energy stability that are available at comparable costs and similar maintenance expenses. Major drawbacks of the Nd:YAG lasers for PLD include, inherently inappropriate gaussian beam profile instead of a flat-top profile as well as temperature-induced polarization and thermal lensing effect create donut-shaped beam profile and lateral distortions, respectively (see Fig. 2, left and right).
46
Fig. 2: Typical Nd:YAG laser beam profiles with rod polarization effects (left) and thermal lensing effect (right)
47 3.1 Wavelength and beam parameter considerations the following section, the three key laser-related characteristics that are of particular relevance for 3.1.1 Laser-material interaction ) High-energy photons are directly absorbed by molecular bonds with lno bulk heating
Moreover, poor short-term and long-term pulse-to-pulse stability of typically 10 to 15%, rms are provided by Nd:YAG lasers due to the necessary frequency conversion the efficiency of which is severely degrading toward shorter output wavelengths such as 266 nm.
Another limiting factor of Nd:YAG lasers in PLD experiments is the fixed repetition rate of 10 or 20 Hz which is not alterable but represents a fixed parameter.
Table I gives an overview of excimer laser versus Nd:YAG with regard to photon energies, performance parameters, and maintenance. The overview clearly shows that excimer technology excels in photon energy, variability of use, long-term and short-term pulse stability, and ablation homogeneity. Parameter Excimer Laser Photon Energy Flash-lamp pumped Nd:YAG Laser
Wavelength
351nm,
308nm,
248nm
193nm
157nm
1.17eV
2.33eV
3.53eV
4.02eV
4.66eV
5.00eV 6.42eV 7.90eV 248nm: 100 to 1200mJ 193nm: 50 to 600mJ 157nm: 15 to 50mJ variable, 1 to 200Hz 0.5 to 1%, rms 0 %, rms Flat-top profile 1064nm
532nm
355nm
266nm
Output Energy
355nm: 60 to 200mJ 266nm: 40 to 90mJ 213nm: 5 to 15mJ fixed, 10Hz (20Hz) 8 to 12%, rms 10 to 15%, rms 揹istorted Gaussian?br> Repetition Rate
Shot-to-Shot Stability
Long Term Drift, 4hrs
Ablation Geometry
Pulse Width, FWHM 15 to 20ns 5 to 8ns
Consumables Premix bottle, optics set Flash-lamps, crystals
In
PLD experimenters are described in detail.
a
When a laser interacts with a solid surface, the laser energy is transformed into heat. The temp
48
Fig. 4: Nd:YAG ablation profile erature
f the solid material increases, leading to melting and evaporation of the solid material. Because the
stoichiometry and a smoother thin film without unwanted
) High photon energy results in better depth control and more controlled ablation conditions
.
or excimer lasers at 193 nm and 248 nm, the ablation depth is in the 100 nm range. For 157 nm,
ue to shallow energy density gradients.
Fig. 3: Excimer laser ablation track in a PLD target.
) Shot-to-shot stability
solutely essential in PLD, because it determines the reproducibility of the
in film material properties. Generally, excimer lasers exhibit a much better pulse-to-pulse stability
o
temperature in the vapor plume can rise to high values (10,000K and higher), a plasma is formed. Besides atoms, electrons and ions, the material plume also consists of particulates, with dimensions ranging from nm to μm. The smallest particles (~nm size) are probably formed in the expanding vapor plume, by condensation of vapor atoms. The larger particles (~μm size) are probably created by direct ejection from the solid target. Moreover, at very high laser irradiance (above 1010 W/cm2), explosive boiling of the target material beneath the surface layer, as well as mass ejection of large particulates, may occur. Higher photon energies, or equally shorter wavelengths, yield faster plume heating and smaller particle sizes. The result is a preserved
particulates.
b
The shorter the wavelength, the smaller the penetration depth of the laser radiation into the material
F
penetration depths are on the order of 50 nm. This limited penetration results in very controlled layer-by-layer ablation with virtually no volume heating, thus eliminating the ejection of particulates. Additionally, the laser energy is deposited in a very restricted volume, and the quick and even material evaporation leads to clean ablation zones. These are visible in figure 3, which shows a typical target ablation track cross section obtained with a 248 nm excimer laser. On the contrary, due to their rippled beam profile structure and longer wavelength, Nd:YAG laser beam ablation profiles (see Fig. 4) induce melting and uncontrolled material splashing d
Higher photon energies or equivalent shorter wavelengths yield clean ablation zones.
c
Shot-to-shot stability is ab
th
than frequency-converted Nd:YAG lasers (ref. Table I). As a matter of fact, COMPexPro lasers featuring ceramic preionization technology provide superior pulse-to-pulse stability of less than 1% rms at typical PLD conditions, i.e., at pulse energies of several hundred millijoules and repetition rates of typically 1 to 50 Hz. Note that even at 100 Hz operation, the energy stability is still 1% rms (see Fig. 5). This stable, high energy performance of the COMPexPro excimer series even at elevated repetition rates up to 100Hz is unprecedented. An integrated burst generator also enables bursts of pulses with precise energy, from the first to the last pulse of each burst.
2502602702802903003103203303403500500100015002000250Pulse NumberPulse Energy /
mJCOMPexProburstover25 secondsat 100 Hz, energystabilizedAverageEnergy= 298.91mJ, StdDev.= 2.99mJ, Std.Dev.= 1%
Fig. 5: Burst over 2500 pulses obtained with COMPexPro 110 at 248nm at a repetition rate of 100Hz.
3.1.2 Energy density and spot size
A lack in pulse energy on first sight migh be compensated by tighter focusing. However, this leads to limitations in ablation and hence film quality.
In fact, in PLD the excimer beam is not simply focused, as is shown in figure 6. Instead, the beam profile is preferably imaged onto the target surface in order to achieve clean ablation conditions from a flat-top, on-target energy distribution. Typically, the on-target image has a 1 to 5 mm2 area. This demagnification is easily obtained with the COMPexPro 100 series and 200 series, which also provide a wide range of homogeneous on-target energy densities of 0.5J/cm2 to 15J/cm2, both at 248 nm and 193 nm wavelengths.
49
Fig. 6: Excimer laser beam imaging versus focusing in Pulsed Laser Deposition. When the on-target laser spot size is decreas1/u+1/v=1/f Demagnification= v/u L
O
Image
u v
Focus
ed, the following problems occur: (1) the inhomogeneous
n-target energy density distribution in the focal plane induces uncontrolled sub-surface boiling and
The smaller and
maller spot sizes lead to an increasingly spherical plume geometry and a smaller fraction of material
aches the substrate, which is typically located at a 3 to 5 cm distance from the target.
Fig.7: Plume shapes obtained with small spot size (left) and larger spot size (right).
?br> zers or
ty is essential to achieve stoichiometric material transfer
om target to substrate. Only a homogeneous flat-top energy distribution of the excimer laser beam
aged down to a homogeneous area of ca. 2mm2 onto the target can avoid uncontrolled sub-surface
oiling, splashing and material cracking, which otherwise results from energy density fluctuations
and the short axis has a gaussian like shape. The highly homogeneous spatial
distribution of the COMPexPro beam profile obtained from a single shot exposure 70cm behind the
laser exit at 400m is shown in
o
liquid m
3.1.3 Beam homogeneity Due to direct imaging of the laser output beam on the target without the aid of homogenidiffractive optical elements spatial homogenei
aterial splashing; (2) large particulate ejection also occurs; (3) the deposition rate becomes smaller and smaller as the spot size decreases, creating deposition times of an hour or longer; and (4) as the spot size decreases, the plasma plume becomes less directed (see fig. 9).
s
re
Laser
Beam
fr
imb
across the ablation area. Excimer lasers have typically a rectangular beam profile, whereas the long axis has a top head
J pulse energy
50
Fi
gure 8, The short axis cross-section g a near- n distribu e long ax t-top
di e to the efficient and oth ceram ionization e in COM o and
LP homogeneity tained at lse energy ion.
showin
gaussia
tion, th
is the fla
stribution. Du
smo
ic pre
schem
PexPr
XPro lasers this high
is main
high pu
operat
Figure 8: Homogeneous beam profile of the COMPexPro excimer laser, with typical dimensions of 24 mm (FWHM, long axis) by 12 mm (FWHM, short axis). The short axis has a gaussian like distribution, whereas the long axis is flat top.
Table 2 summarizes the main specifications of the COMPexPro and LPXPro excimer lasers for wavelengths of 193 nm and 248nm. COMPexPro LPXPro Wavelength 193 nm 248 nm 193 nm 248 nm Maximum pulse energy 400 mJ 700 mJ 650 mJ 1200 mJ Average power 12 W 30 W 50 W 90 W Maximum repetition rate 100 Hz 100Hz 200 Hz 200 Hz
Energy stability (typical, sigma) < 2 % < 1 % < 2 % < 1 %
Beam size (FWHM, v x h, typ.) 24 x 10 mm² 24 x 12 mm² 10 x 24 mm² 12 x 24 mm²
Divergence (FWHM, v x h, typ.) 3 x 1 mrad² 3 x 1 mrad² 3 x 1 mrad² 3 x 1 mrad²
Beam pointing stability (1 sigma) < 200 μrad < 50 μrad < 50 μrad
< 200 μrad
Pulse Length (typical, FWHM) 13 ns 20 ns 13 ns 20ns
?4. Thin Film Applications With proper focusing conditions the fluence of the excimer laser beam is sufficiently intense to vaporize any hard and transparent target material lending maximum flexibility in terms of the material spectrum which is to be ablated. On account of the unique lateral resolution of 2 μm achievable with short-wavelength excimer laser based ablation systems as well as of the high depth resolution
aching down to 0.1 μm, excimer lasers are extensively used in high-precision marking, surface
treatment, micro patterning and microm but a few. Due to the unique spectral
properties of excimer lasers, composites and allo enly ablated without fractionation of the
ed in
reating thin films by means of the pulsed laser deposition technique (PLD). In this particularly
perpendicularly to the target surface in a highly
irected so-called plasma plume consisting of excited and ionized species. The plume particulates
re
achining to name ys can be ev
different constituents. Excimer lasers are hence the first-choice ablation sources to be employ
c
straightforward method a pulsed excimer laser beam focused on the target leads to rapid evaporation of the target material. The vaporized material recoils
d
51
evolve at high-speed toward the substrate which is typically located at some centimeters distance
here they deposit and grow forming a thin film.
pulse repetition rate of the excimer laser need to be controlled during the process of thin film creation.
The targets used in PLD are small compared with the large size required for other sputtering
techniques. Multi-layered films of different materials are easily produced by sequential ablation of
assorted targets on a rotating disk. By adapting the number of pulses, accurate control of film
thickness down to atomic monolayer is possible. With the short wavelength excimer laser light the
stoichiometry of the target like the crystal structure of the target can be retained. A recent overview
over latest PLD developments is given in reference4.
?5. Conclusion
The advanced high-pulse energy excimer laser series LPXPro and COMPexPro have been described
in this paper. Based on proven technologies applied for industrial and lithography excimer laser
sources, stable and cost-efficient, high-pulse energy lasers fitted to thin film production demands have
been realized. The COMPexPro and LPXPro lasers deliver pulse energies up to 1200 mJ with high
stability and beam homogeneity over many 10 million pulses hands-off operation at the preferred
ser wavelengths of 193 and 248 nm.
1 R. Delmdahl: LaserFocusWorld Supplement (2002) pp. 3.
2 T. Kuntze, M. Panzn al Symposium on Laser
Precision Mic
3 G. Spiecker, R. Delmd
M. N. R. Ashfold, F. Claeyssens, G. M. Fuge, S. J. Henley: Chem. Soc. Rev., 33 (2003) pp. 23.
w
The PLD method is straightforward and only a few parameters including pressure, energy density and
la
?References
, July 2002, Optoelectronics World
er, U. Klotzbach, E. Beyer: Proc. 4th Internation
rofabrication, Munich (2003) pp. 543.
ahl: Laser Magazin 6, (2002) pp. 10.
4
52
IPT7 Research and Development in Pulsed Laser Deposition: A Scientometric Perspective
Ganesh Surwase, B.S. Kademani and Vijai Kumar
Scientific Information Resource Division, Knowledge Management Group
Bhabha Atomic Research Centre, Mumbai-400 085 (India) E-mail: bskademani@yahoo.co.in; bsk@barc.gov.in This paper attempts to highlight quantitatively the growth and development of world literature in the field of Pulsed Laser Deposition in terms of publication output as per Science Citation Index (1982-2006). During 1982-2006 a total of 8534 papers were published by the scientists in the field 慞ulsed
aser Deposition? The average number of publications published per year was 341.36. The highest
red
ublications and 196 (2.30 %) single authored publications. Chinese Academy of Sciences (Peoples-
-Technol-Bomaby,
umbai) with 38 publications, M.S. Hegde (Indian-Inst-Sci, Bangalore) with 31 publications, S.B.
L
number of papers 1074 were published in 2005. There were 84 countries involved in the research in this field. USA is the top producing country with 2014 publications (19.35%) followed by Japan with 1553 publications (14.92%), Peoples-R-China with 1106 publications (10.63%), Germany with 763 publications (7.33%) South Korea with 694 publications (6.67%) and France with 615 publications (5.91%). India ranked 9th among other countries with 291 publications during 1985-2006. Authorship and collaboration trend was towards multi-authored papers. There were 8338 (97.70%) multi-autho
p
R-China) topped the list with 304 publications followed by Nanjing University (Peoples-R-China) with 244 publications, Tokyo Institute of Technology (Japan) with 233 publications and CNRS (France) with 217 publications. The most productive Indian institutions were: Tata Institute of Fundamental Research, Mumbai with 52 publications and Indian Institute of Science, Bangalore with 49 publications. The most prolific Indian authors were: R. Pinto (Indian-Inst
M
Ogale (Univ Poona, Poona) with 29 publications, L.M. Kukreja (Raja Ramanna Ctr-Adv-Technol, Indore) with 21 publications, P. Misra (Raja Ramanna Ctr-Adv-Technol, Indore) with 16 publications, R.K. Thareja (Indian-Inst-Technol-Kanpur) with 15 publications. The most preferred journals by the scientists were: Applied Physics Letters with 962 publications, Journal of Applied Physics with 714 publications, Applied Surface Science with 614 publications and Thin Solid Films with 541 publications. The high frequency keywords were: Pulsed Laser Deposition (3661), Thin Films (2611), Laser Ablation (1137), Films (571) and Silicon (562).
Introduction
m
ells of several sizes and shapes.
ulsed Laser Deposition as a film growth technique has gained importance and attracted wide spread
ed by the scientists, institutions and
Invention of laser in 1960 has opened up new areas of research and found various applications in many scientific fields. Pulsed Laser Deposition (PLD) is one of the several techniques of the deposition of the thin film on the substrates besides other techniques like Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapour Deposition (MOCVD) and Sputtering1-2. The Pulsed Laser Deposition has several advantages over other deposition techniques. There are several applications of the thin films developed because of its helpful technique in developing quantum dots and quantu
w
P
interests after it has been used successfully to grow high-temperature Tc superconducting films3 in 1987. During the last decade, Pulsed Laser Deposition has been used to fabricate crystalline thin films with epitaxy quality. Ceramic oxide, nitride films, metallic multilayers, and various super-lattices grown by Pulsed Laser Deposition have been demonstrated. It has been reported in the literature that Pulsed Laser Deposition is being used to synthesise nanotubes4, nanopowders5 and quantum dots6. Evaluation is a key component of any research and development activity. One well known productivity indicator is the number of publications produc
53
countries. Studies like this will provide some insight into the complex dynamics of research
acti ntists, policy makers and science administrators to provide adequate
cilities and proper guidance in which direction the research has to be conducted.
esearch publications are clearly one of the quantitative measures for the basic research activity in a
8-21.
Objectives
vity and enable the scie
fa
R
country. It must be added, however, that what excites the common man, as well as the scientific community, are the peaks of scientific and technological achievement, not just the statistics on publications. There are also other kinds of research and technology development-mission oriented, industry-oriented, country-specific, etc., and progress in these cannot be obviously measured by counting only the number of publications7. Many scientometric studies have appeared in the literature to focus on the performance of science in various domains
The main objective of the study is to present the growth of world literature in Pulsed Laser Deposition
and make the quantitative assessment of the research in terms of year-wise research output,
geographical distribution of research output, nature of collaboration, characteristics of highly
productive institutions, the characteristics of references cited in the publications and publications with
more number of references in the field, the channels of communications used by the scientists, and the
high frequency keywords appeared in the Key-Words-Plus and Author-Keywords field in the SCI.
Materials and Methods
Data was collected from the Science Citation Index-On Disc (CD-ROM) (1982-2006) published by a
division of the Thomson Corporation (formerly Institute of Scientific Information, Philadelphia).
Science Citation Index is one of the very comprehensive databases covering all aspects of science.
The study period (1982-2006) is selected as the database is available in machine readable form since
1982. The search string 慞ULSED LASER DEPOSIT* OR PULSE LASER DEPOSIT*?in the
態ASIC INDEX?field of SCI was used for the years 1982-2006 to download the records on the
subject 慞ulsed Laser Deposition? A total of 8534 records were downloaded and analysed by using
the spreadsheet application as per the objectives of the study.
Results a
igure that growth of the literature was
ery low ed Laser
epositio
nd Discussion
Growth of Publications in Pulsed Laser Deposition During 1982-2006 a total of 8534 publications were published in Pulsed Laser Deposition by various countries. The average number of publications produced per year were 341.36. The highest number of publications 1074 were produced in 2005. Figure? gives year-wise growth and collaboration rate in ulsed Laser Deposition. It can be clearly visualized from the f
Pv
during 1982-1990 and it peaked during 1991-2006. It indicates that research in Pulsn received a major impetus during this period.
D
54
19821984198619881990199219941996199820002002200420060100200300400500600Number of PuYear010002000300040005000Cumulative Number o
700800900100011001200blications Number of Publications6000700080009000f Publications Cumulative Number of Publications
Figure-1: Year-wise publication productivity growth in PLD research
An exponential growth in number of publications was observed during 1982-2006. The highest
growth rate (1154.55%) was found during 1987-1991 with 138 publications followed by (552.17%)
with 900 publications during 1992-1996, (208.44%) with 2776 publications during 1997-2001 and
(69.63%) with 4709 publications during 2002-2006. Table-1 gives the growth rate of publications in
Pulsed Laser Deposition research in different five year blocks.
Table-1: Growth rate of publications in different five-year blocks in PLD research
Five Year Number of Growth Rate
Blocks Publications (1982-2006) 1982-1986 11 - 1987-1991 138 1154.55
1992-1996 900 552.17
1997-2001 2776 208.44
2002-2006 4709 69.63
Geographical Distribution or Research Output
There were as many as 84 countries carrying out research in the field of Pulsed Laser Deposition and
roduced 10409 authorships. Figure-2 provides a list of countries whose research output is more than
50 publications. USA is the g co 20 ions (19.35%), followed by
Japan with 1553 publications Peop with 1106 publications (10.63%) Germany
with 763 publications (7.33%), F ce with 615 ications ( ). Italy with 336 publications
(3.49%), England with 297 publications (2.85%), India with 291 publications (2.80%) and Spain with
253 publications (2.43%).
p
top producin(14.92%),
untry withles-R-China
14 publicat
ran
l
pub
5.91%
55
USA JAPAN PEOPLES-R-CHINA GERMANY SOUTH-KOREA FRANCE ITALY ENGLAND INDIA SPAIN SINGAPORE TAIWAN ROMANIA CANADA RUSSIA SWEDEN NETHERLANDS 02004006008001000120014001051151421551721741752532912973636156947631106Number of publicCountries
160018002000220015532014ations
Figure-2: Country-wise distribution of number of publications (≥100) in PLD research
(during the years 1982-2006 as per SCI database)
ab Pulsed Laser Deposition research. Out of 8534
Countries Publications Percentage
nternational Collaboration
I
T
le-2 gives the country-wise collaboration trend in
publications 1587 publications had international collaboration. Bilateral collaboration was found with 1335 (84.12%) publications and 205 (12.92%) publications had collaboration with three countries. Table-2: Country-wise collaboration trend in PLD research Collaborating Number of
2 1335 84.12
3 205 12.92
4 38 2.39
5 8 0.50
6
00
ship and Collaboration Pattern
researc
uth
hip and collaboration t
ult
thored publications. Only 196 (2.30
bl
tions (1622) accounted for 19.01 percent, follow
authored
9) wi
7.80
ercent, three author
ith
.82 percent and seven aut
percen
t. 1 0.06
Total 1587 100.
Author
Authorship and collaboration trend in Pulsed Laser Deposition h is given in Figure-3.
A ors rend was towards multi-authored papers. As there were 8338 (97.70%)
m i-au %) were single-authored publications. Four authored
pu ica ed by five publications (151 th
1 p ed publications (1268) with 14.86 percent, six authored publications (1179)
w 13 hored publications (785) with 9.20
56
2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A171820 A22 A31 A001125254715198126817133299102785Number of Authors
1
A
1516
A A A A
0
200
400
600
800
1000
1200
1400
16
1800
311853719
196
16221179Num
ber of Publ
ications
F re p and collaboration trend in PLD resea
rg
In l, t organizations involved in the research in Pulsed Laser Deposition. Table-3
shows the organizations that have contributed 50 or more publications during 1982-2006. Chinese
Academ -R-China) topped the list with 304 publications followed by Nanjing
U ers titut apan) wi 33
p cat tifiq S) (France) with 217
p cat
T tutions as per number of publicat 0) in PLD research
l. No. Institute Country
Publication
s
igu
-3: Authorshi
rch
O
anisation-wise Distribution of Publications
al
here were 2035
y of Science (Peoples
niv
ity (Peoples-R-China) with 244 publications, Tokyo Insions and Centre National De La Recerche Scien
e of Technology (J
th 2
ubli
ue (CNR
ubli
ions.
able-3: Distribution of insti
ions (≥5
S
1 CHINESE ACAD SCI PEOPLES-R-CHINA 304
2 NANJING UNIV PEOPLES-R-CHINA 244
3 TOKYO INST TECHNOL JAPAN 233 4 CENTRE NATIONAL DE LA RECERCHE SCIENTIFIQUE (CNRS) FRANCE 217 5 OSAKA UNIV JAPAN 196 6 UNIV TOKYO JAPAN 161 7 OAK RIDGE NATL LAB USA 158 8 CONSEJO SUPER INVEST CIENTIFICAS SPAIN 152 9 CONSIGLIO NAZIONALE DELLE RICERCHE (CNR) ITALY 148 10 UNIV MARYLAND USA 145
11 NATL UNIV SINGAPORE SINGAPORE 138
12 LOS ALAMOS NA 135
TL LAB USA
13 UNITED STATES NAVY USA 129
14 UNIV FLORIDA USA 124
15 INT SUPERCONDUCT TECHNOL CTR JAPAN 8
11
N CAR
TATE UN116
HO
ONG POL
PEOPLES-R-C
UN
RIS
FRANCE
TO
UNIV
YO
UNIV
SOUTH-KOREA
MA
ANCK IN
UCT PHYS GERMANY
PEN
ATE UNIV
US
16 OLINA S IV USA
17 NG K YTECH UNIV HINA 114
18 IV PA 109
19 HOKU JAPAN 103
20 NSEI 101
21 X PL ST MICROSTR 97
22 N ST A 97
57
23
SEOUL N 91
ATL UNIV
SOUTH-KOREA
UNITED STATES AIR FORCE
NATL INST ADV IND SCI &
HNOL JAPAN
NAT
ST LAERS
ADIAT PHYS ROMANIA
NAG
A UNIV
NAT
SING HU
TAIWAN
UNI
IPZIG
GERMANY
NAT
ST MAT S
JAPAN
ROY
INST TE
SWEDEN
UNI
MBRIDGE
UNI
LIF BERKEL
USA
ACA
CI CZECH
FUD
UNIV
PEOPLES-R-CHINA
JAP
KYO
UNIV
JAPAN
KYU
UNIV
JAPAN
ELE
& TELECOMMUN
INST S
RUS
N ACAD SCI
INS
STKORPER & W
FFORSCH DRESDEN GER
NAG
A INST TECH
JAPAN
UNI
ENTE
NET
POH
UNIV SCI & TEC
SOU
INR
ERGIE & MAT
CANADA
QUE
UNIV BELFAST
NORTH
INS
TO NAZIONALE PER
A FISICA DELLA MATERIA
(INF
TAT
ST FUNDAMEN
S INDIA
UNI
USTON
USA
UNI
MA TOR V
ITALY
PUK
G NATL U
Most Prolific Indian Authors
There were 67 ndian ed 291 publications with 1423
authorships. Th c Indian (Indian-Inst-Technol-Bomab Mumbai)
with 38 lica .S. Hegde (In ns, S.B. O le (Natl-
Chem-L Poo blicatio Ramanna Ctr-Adv-Technol, I ore) with
21 publi ons, Raja Rama ions, R . Thareja
(Indian-Inst-Tec pur) with 1 es the list of authors ho have
contributed 5 or ications.
-4: Mo in PLD reseach
(as
Sl. No. Num
Publications
3 authors in I
publications who have publish
e most prolifi
authors were: R. Pinto
y,
pub
tions, M
dian-Inst-Sci, Bangalore) with 31 publicatio
ga
ab,
na) with 29 pu
ns, L.M. Kukreja (Raja
nd
cati
P. Misra (
nna Ctr-Adv-Technol, Indore) with 16 publicat
.K
hnol-Kan
5 publications. Table-4 provid
w
more publ
Table
st prolific Indian authors
per SCI database 1982-2006)
Author
Affialiation
ber of
1
Pinto-R
INDIAN-INST-TECHNOL-BOMABY, MUMBAI
38 24 USA 87
25 TEC 85
26 L IN PLASMA & R 81
27 OY JAPAN 80
28 L T A UNIV 80
29 V LE 80
30 L IN CI 79
31 AL CHNOL 79
32 V CA ENGLAND 77
33 V CA EY 76
34 D S REPUBL CZECH-REPUBLIC 75
35 AN 74
36 AN SCI & TECHNOL CORP JAPAN 74
37 TO 74
38 SHU 73
39 CTR RES OUTH-KOREA 72
40 SIA RUSSIA 71
41 T FE ERKSTO MANY 68
42 OY NOL 66
43 V TW HERLANDS 61
44 ANG HNOL TH-KOREA 56
45 S EN 55
46 ENS -IRELAND 54
47
TITU L
M) ITALY 53
48 A IN TAL RE 52
49 V HO 51
50 V RO ERGATA 51
51 YON NIV SOUTH-KOREA 50
2 Hegde-MS INDIAN-INST-SCI, BANGALORE 31
3 Ogale-SB NATL-CHEM-LAB, POONA 29
4 Kukreja-LM RAJA RAMANNA CTR-ADV-TECHNOL, INDORE 21
5 Misra-P RAJA RAMANNA CTR-ADV-TECHNOL, INDORE 16
6 Thareja-RK INDIAN-INST-TECHNOL-KANPUR 15 7 Joseph-M INDIRA-GANDHI-CTR-ATOM-RES, KALPAKKAM 12 8 Kanetkar-SM UNIV POONA, POONA 12 9 Manoravi-P INDIRA-GANDHI-CTR-ATOM-RES, KALPAKKAM 12 10 Apte-PR TATA-INST-FUNDAMENTAL-RES, MUMBAI 11 11 Chaudhari-SM UNIV POONA, POONA 11
12 John-J TATA-INST-FUNDAMENTAL-RES, MUMBAI 10
13 Krupanidhi-SB INDIAN-INST-SCI, BANGALORE 10
14 Kumar-R CTR-NUCL-SCI, DIV MAT SCI, NEW-DELHI 10
58
15 Pai-SP TATA-INST-FUNDAMENTAL-RES, MUMBAI 10
16 Vispute-RD UNIV POONA, POONA 10
17 Hussain-OM SRI-VENKATESWARA-UNIV, TIRUPATI 9
18 Patil-SI UNIV POONA, POONA 9
19 Satyalakshmi-KM INDIAN-INST-SCI, BANGALORE 9
20 Adhi-KP UNIV POONA, POONA 8
21 Malik-SK TATA-INST-FUNDAMENTAL-RES, MUMBAI 8
22 Prasad-V INDIAN-INST-SCI, BANGALORE 8
23 Subramanyam-SV INDIAN-INST-SCI, BANGALORE 8
24 Godbole-VP UNIV POONA, POONA 7
25 Karunagaran-B BHARATHIAR-UNIV, COIMBATORE 7
26 Lekshmi-IC INDIAN-INST-SCI, BANGALORE 7
27 Mangalaraj-D BHARATHIAR-UNIV, COIMBATORE 7
28 Narayandass-SK BHARATHIAR-UNIV, COIMBATORE 7
29 Ramachandra Rao-MS INDIAN-INST-TECHNOL-MADRAS, CHENNAI 7
30 Ramamoorthy-K ALAGAPPA UNIVERSITY, KARAIKUDI 7
31 Sankaranarayanan-K ALAGAPPA UNIVERSITY, KARAIKUDI 7
32 Sharon-M BIRLA COLLEGE, KALYAN 7
33 Bhattacharya-P RAJA RAMANNA CTR-ADV-TECHNOL, INDORE 6
34 Budhani-RC INDIAN-INST-TECHNOL-KANPUR, KANPUR 6
35 Gupta-LC TATA-INST-FUNDAMENTAL-RES, MUMBAI 6
36
Gupta-V UNIV DELHI, DELHI 6
37 Koinkar-VN UNIV POONA, OONA 6
P-U 38 Kumar-RTR BHARATHIAR NIV, COIMBATORE 6
39 Ramana-CV SRI-VENKATESWARA-UNIV, TIRUPATI 6
40 Raychaudhuri-P TATA-INST-FUNDAMENTAL-RES, MUMBAI 6
41 Vasanthacharya-NY INDIAN-INST-SCI, BANGALORE 6
42 Venimadhav-A INDIAN-INST-SCI, BANGALORE 6 43 Venkatesan-T UNIV POONA, POONA 6 44 Vitta-S INDIAN-INST-TECHNOL-BOMABY, MUMBAI 6 45 Choudhary-RJ UNIV POONA, POONA 5 46 Date-SK UNIV POONA, POONA 5 47 Ganguli-T RAJA RAMANNA CTR-ADV-TECHNOL, INDORE 5 48 Gayen-A INDIAN-INST-SCI, BANGALORE 5 49 James-AR SOLID-STATE-PHYS-LAB, DELHI 5
50 Jayachandran-M CENT-ELECTROCHEM-RES-INST, KARAIKKUDI 5
51 K 5
shirsagar-ST NATL-CHEM-LAB, PUNE undaliya-DC TATA-INST-FUNDAMENTAL-RES, MUMBAI 52 K 5
53 Manoharan-SS INDIAN-INST-SCI, BANGALORE 5
54 h-C SOLID-STATE-PHYS-LAB, DELHI 5
Prakas
Pur
re-SC TATA-INST-FUNDAMENTAL
San
raja-C ALAGAPPA UNIV
ibu
n of Indian Contribution in Pulsed Laser De
bu
of Indian contribution in the f
we
91 publications published during
ly o
cati
were published during 198
ears 2003 and 2005 respectively. The average num
55 anda -RES, MUMBAI 5
56 jeevi ERSITY, KARAIKUDI 5
Year-wise Distr tio position
Year-wise distri tion ield of Pulsed Laser Deposition is given in
Figure-4. There re 2 1985-2006. There was on ne publication in
1985. No publi ons 6-1987. The highest number of publications (41)
were published in the y ber of publications per year
was 13.22.
59
1986199019921994199619982000200420060510152045 Number of PublicationsNur ofsYea050100150250300Cumulativember otionss
40 Cumulative Number of Publication
253035 Publication200f Publica
mbe Nu
1988
2002
r
ndian
ions
Figure-4: Year-wise distribution of I publicat in PLD research
Sl. No. Institute Publications
Distribution of Indian Institutions in Pulsed Laser Deposition
There were 73 research institutes and universities involved in research in pulsed laser deposition. The leading institutes were Tata Institute of Fundamental Research, Mumbai with 52 publications, Indian Institute of Science, Bangalore with 49 publications, University of Poona, Poona with 38 publications, Indian Institute of Technology, Kanpur with 28 publications, Raja Ramanna Centre for Advanced Technology, Indore with 24 publications and Indira Gandhi Centre for Atomic Research, Kalpakkam with 18 publications. Table-5 provides a list of prominent Indian research institutes which had published five or more publications. Table-5: Distribution of Indian Research Institutes in PLD research
1 52
TATA INST FUNDAMENTAL RES, MUMBAI
2 INDIAN INST SCI, BANGALORE 49
3 UNIV POO NA 38
NA, POO
5 RAJA RAMANNA CTR ADV TECHNOL, INDORE 24
6 INDIRA GANDHI CTR ATOM RES, KALPAKKAM 18
7 CTR NUCL SCI, NEW DELHI
13
8 INDIAN INST TECHNOL BOMBAY
13
9 INDIAN INST TECHNOL MADRAS
10
10 IUC DAE FACIL, INDORE 10
11 NATL CHEM LAB, POONA 10
12 SRI VENKATESWARA UNIV, TIRUPATI 10
13 UNIV DELHI, DELHI
10
14 BHABHA ATOM RES CTR, MUMBAI 9
15 SOLID STATE PHYS LAB, NEW DELHI 9
16 ALAGAPPA UNIV, KARAIKKUDI 8
17 BHARATHIAR UNIV, COIMBATORE 7
18 COCHIN UNIV SCI & TECHNOL, COCHIN 7
19 SAURASHTRA UNIV, RAJKOT
7
20 UNIV HYDERABAD, HYDERABAD
7
21 NATL PHYS LAB, NEW DELHI
6
22 CENT ELECTROCHEM RES INST, KARAIKKUDI
5
23 INDIAN ASSOC CULTIVAT SCI, KOLKATA 5
4 INDIAN INST TECHNOL KANPUR 28
60
Prefe mmunication by Scientists
Scien communications channels. Table-6
ic at 97.25 percent of the literature was published in journal by eviews 1.34
ce ercent.
ublications in various channe ti
Document Type Publications Percentage
rence of Channels of
Co
tists communicated their publications through variety of ts th
dep
articles followed
r
per
nt, notes 0.46 percent and letters 0.42 p
Table-6: Distribution of p
ls of communica
on Articles 8299 97.25
Reviews 114 1.34
Notes 39 0.46
Letters 36 0.42
Meeting-Abstracts 27 0.32
Corrections 11 0.13
Editorial-Materials 4 0.05
News-Items 4 0.05
Total 8534 100
Preference of Journals for Communication by Scientists
The distribution of publications were spread over 315 journals. The leading journals preferred by the
scientists were Applied Physics Letters with 962 publications followed by Journal of Applied Physics
with 714 publications, Applied Surface Science with 614 publications, Thin Solid Films with 541
publications, Physica C with 432 publications, Applied Physics- A with 320 publications and Japanese
Journal of Applied Physics-I with 269 publications. Table-7 provides journal-wise scattering of
publications. More than 92 percent of the publications were published in the journals with impact
factors ranging from 0.01 to 32.18. This indicates that the publication behaviour of scientists who
prefe the
publ per
-5.
Sl s
rred to publish their publications in high impact-factor journals. About 22.43 percent of ications were published in the journals having no impact-factor. The distribution of journals as
impact factors range is given in the Figure
Table-7: Journals publishing articles (≥50) in PLD research . No. Journal Country IF-2005 Publication1 APPLIED PHYSICS LETTERS USA 4.127 962 2 JOURNAL OF APPLIED PHYSICS USA 2.498 714 3 APPLIED SURFACE SCIENCE NETHERLANDS 1.263 614
4 THIN SOLID FILMS SWITZERLAND 1.569 541
5 PHY 432
SICA -C NETHERLANDS 0.948 LIED PHYSICS -A USA 1.990 6 APP 320
7 JAPANESE JOURNAL OF APPLIED PHYSICS -I JAPAN - 269
8 PHYSICA 85 196
L REVIEW- B
USA
3.1RYSTAL
NETHEANDS 1.6
CTIVITY
USA
ONDUCTOR
ENG
ATED FERROELE
ENG
H
USA
L OF VACU
- A
USA
E & COAT
SW
D
SW
D
SO
A
SW
D
SE JOURNAL OF
YS
JAP
L OF MAGNE
GN
NE
DS 9 JOURNAL OF C GROWTH RL 81 193
10 IEEE TRANSACTIONS ON APPLIED SUPERCONDU 1.071 177
11 SUPERC SCIENCE & TECHNOLOGY LAND 1.896 177
12 INTEGR CTRICS LAND 0.345 161
13 JOURNAL OF MATERIALS RESEARC 2.104 155
14 JOURNA UM SCIENCE & TECHNOLOGY 1.399 137
15 SURFAC INGS TECHNOLOGY ITZERLAN 1.646 135
16 MATERIALS SCIENCE AND ENGINEERING- B ITZERLAN - 127
17 JOURNAL OF THE KOREAN PHYSICAL SOCIETY UTH KORE 0.828 122
18 DIAMOND AND RELATED MATERIALS ITZERLAN 1.988 113
19 JAPANE APPLIED PH ICS - II AN - 112
20 JOURNA TISM AND MA ETIC MATERIALS THERLAN 0.985 104
61
21 FERROELECTRICS
EN
TATE C
EN
L OF PHY
EN
IALS LETT
L OF PHYSICS-CO
M
EN
S RES
NE
DS
US
US
SWI
D GLAND 0.459 96
22 SOLID S OMMUNICATIONS GLAND 1.489 94
23 JOURNA SICS- D GLAND 1.957 90
24 MATER ERS NETHERLANDS 1.299 67
25 JOURNA NDENSED ATTER GLAND 2.145 64
26 NUCLEAR INSTRUMENTS & METHODS IN PHYSIC EARCH
- B THERLAN - 56
27 IEEE TRANSACTIONS ON MAGNETICS A 1.014 53
28 JOURNAL OF THE ELECTROCHEMICAL SOCIETY A 2.190 53
29 MATERIALS SCIENCE FORUM TZERLAN 0.399 52
0.00-0.0001.01-1.501.51-2.002.51-3.003.01-3.504.01-4.504.51-5.005.01-10.0010.01-20.0020.01-30.9302505007501000Number of publImFactor r
2000
125015001750cations
0.00-0.51
0.5-1.0
0
2.01
-2.5
0
3.51-
4.0
0
pact-
ange
Figure-5: Impact-factor range and distribution of journals publishing articles in PLD research
ountry-wise Distribution of Journals
sed Laser Deposition research were spread over 20
ountries. Table-8 gives country-wise distribution of journals and publications. USA has published
country
Number of
journals Percentage Number of
publications Percentage
C
The Journals (315) publishing articles in Pul
c
3300 (38.67%) publications in 102 (31.29%) journals, publications followed by England with 1257 (14.73%) publications in 83 (25.46%) journals, Netherlands with 1854 (21.72%) publications in 46 (14.11%) journals, Switzerland with 1176 (13.78%) publications in 22 (6.75%) journals and Germany with 129 (1.51%) publications in 21 (6.44%). Table-8: Country-wise distribution of journals publishing articles in PLD research Journal publishing
USA 102 31.29 3300 38.67 ENGLAND 14.73
83 25.46 1257 46 14.11 1854 NETHERLANDS 21.72
SWITZERLAND 22 6.75 1176 13.78
GERMANY 6.4
21
4 129 1.51
FRANCE
10 3.0 0.75
7 64
10
PEOPLES R CHINA 2.7 0.60
9
6 51
4
3 6
4
3 131
SINGAPORE
3 0.92 76 0.89
JAPAN 3.07 427 5.00
RUSSIA 1.2 0.07
SOUTH KOREA 1.2 1.54
62
AUSTRIA
2 0.6 0.05
1 4
INDIA
2 0.6 0.11
1 9
POLAND
2 0.61 13 0.15
CANADA 0.3 0.01
1
1 1
1
ITALY
1 0.3 4 0.05
1
1
1
1
1 1
TAIWAN 0.3 0.09
1
1 8
Total
utio
ations in Pulsed
sh w
he most predominant langua
8468
publications, follow
0.42%) publica
(0.1
ch 184 0.430%) publ
0.07%) publ
(0.0
ations.
age-
ution of publications
Per
99
0.42
0.11
0.07
CZECHREPUBLIC 0.31 17 0.20
MEXICO 0.3 6 0.07
ROMANIA 0.3 0.01
326 100 8534 100
Language-wise Distribution of Publications
Table-9 depicts the language-wise distrib n of public Laser Deposition. Engli as
t ge with (99.23%) ed by Chinese with 36
( tions, Japanese with 14 6%), Fren ications, Russian with 9
( ications and Spanish with 1 1%) public
Table-9: Langu wise distrib
Language Publications centage
English 8468 .23
Chinese 36
Japanese 14 0.16
French 9
Russian 6
Spanish 1 0.01
Total 8534 100
Distribution of Keywords Keywords are one of the best scientometric indicators to understand and grasp instantaneously the thought content of the papers and to find out the growth of the subject field. By analyzing the keywords appeared either in the title or assigned by the indexer or the author himself help in knowing in which direction the knowledge grows. The high frequency keywords will enable us to understand what are all the aspects that have been studied. In the current study the keywords appeared in the Key-Words-Plus field and Author Keywords in SCI were analysed for the purpose. The high frequency keywords were: Table-10 lists the keywords appeared 100 or more times in the Key Word Plus field and Author Keywords in SCI. Table-10: Keywords with ≥ 100 frequencies appeared in Key-Word-Plus field and Author-Keywords in SCI in PLD research
Keyword Frequency
PULSED LASER DEPOSITION 3661
THIN FILMS 2611 OXIDES 373 LASER ABLATION 1137
FILMS 571 SILICON 562 ZINC OXIDE 367 OPTICAL PROPERTIES 361
DEPOSITION 478
CHEMICAL VAPOR DEPOSITION 436
TEMPERATURE 391
LAYERS 303
EPITAXIAL GROWTH 367
63
ELECTRICAL PROPERTIES 286 RUCTURE 277 LAR BEAM EPITAXY 271 LUMINESCENCE 139 MAGNETIC PROPERTIES 138 CRYSTALS 135 MICROST
MOLECU
BUFFER LAYERS 263 SAPPHIRE 252 ORESISTANCE 243 TRANSITION 134 CERAMICS 133 FATIGUE MAGNET
SURFACE 225 219 ORS INTERFACE 132 PEROVSKITES 130 133
EPITAXY
CAPACIT 215
X RAY DIFFRACTION 210 DIELECTRIC PROPERTIES 200 MINESCENCE 195 D LIKE CARBON FERROELECTRIC THIN FILMS 123 AMORPHOUS CARBON 122 MEMORIES 122 SINGLE CRYSTALS 126
PHOTOLU
DIAMON 186
EVAPORATION 183 MPERATURE GIANT MAGNETORESISTANCE 119
SUPERCONDUCTIVITY 122
ROOM TE 179
SUBSTRATE 179 CURRENT DENSITY 172 MULTILAYERS 116 SEMICON
EMISSION 116
CRITICAL
FABRICATION 171 BEHAVIOR 170 TRUCTURES 170 S 162 GRAPHITE 114 RESISTIVITY 111 OXYGEN 107 FERROELECTRIC PROPE
DUCTORS 116
HETEROS
COATING
SPECTROSCOPY 158 156 PLASMA 106 COATED CONDUCTORS 105
RTIES 106
MGO
SRTIO3 154
DEPENDENCE 153 DEVICES 153 O7 DELTA 150 PHASE 104 STRAIN 104 LASER DE
ORIENTATION 105
YBA2CU3
ELECTRODES 149 TTICES 146 GAN 102 TRANSPORT 101 POSITION 103
SUPERLA
SUPERCONDUCTORS 143 142 MANGANITES 100 SYSTEM
Conclusi
on comes ne
which ma
growth of publications was observed which indicates the sustained impetus received for the research
g 19
more tha
tremendo oration trend is towards multipublicatio
Institute 3 publications and CNRS (France) with 217 publications.
Indian in d
were pub
of scienti uted journals. Citation analysis of these
rs ma
Referenc
2. thin films, John-Wily, (1994).
USA is the major producer of scientific output with 2014 publications to its credit in this field. Japan xt with 1553 publications. The growth of the literature was very low during 1982-1990 y be attributed for not receiving boost for research in this field. Since 1991, an exponential
durin91-2006. Four countries (USA, Japan, Peoples-R-China and Germany) have contributed n fifty percent of the total publications indicates that these countries have received us official support for the research in this field. Collab
authored papers. Chinese Academy of Sciences (Peoples-R-China) topped the list with 304 ns followed by Nanjing University (Peoples-R-China) with 244 publications, Tokyo of Technology (Japan) with 23
India ranked 9th among other countries with 291 publications during 1985-2006. The most productive stitutions were: Tata Institute of Fundamental Research, Mumbai with 52 publications an
Indian Institute of Science, Bangalore with 49 publications. More than 92 percent of the publications lished in the journals with impact factors which is suggestive of the publications behaviour sts who preferred to publish their papers in highly rep
papey give interesting insights into the dynamics of this field. es:
1. D.J. GARDINER, P.R. GRAVES, Practical pulsed laser deposition, Springer-Verlag, (1989). D.B. CHRISEY, G.K. HUBLER, Pulsed laser deposition of 64
3. D. DIJKKAMP, T. VENKATESAN, X.D. WU, S.A. SHAHEEN, N. JISRAWI, Y.H. MINLEE,
W.L. McLEAL, M. CROFT, Preparation of Y-Ba-Cu oxide superconductor thin films
u
4. Y. ZHANG, H. GU, S. LI tubes synthesized by laser ablation
in a nitrogen atmosphere, A (1998). 3827-3829.
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2007, 1-21.
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spectrometry research in nuclear science and technology. In: ISMAS symposium cum
workshop on mass spectrometry, March 25-30, 2007, 1-16.
sing pulsed laser from high Tc bulk material, Applied physics letters, 51 () (1998) 619-621. JIMA, Single-wall carbon nanopplied physics letters, 73 (26)
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(25) (1999) 3788-3790. T.J. GOODWIN, V.J. LEPPERT, S.H. RISBUD, I.M. KENNEDY, H.WH. LEE, Synthesof gallium nitride quantum dots through reactive laser ablation, Applied physics letters, 70(23) (1997) 3122-3124.
R. CHIDAMBARAM, Measures of progress in science and technology, Current Science, 8(6) (2005) 856-860.
STREWISKI, C. OPPENHEIM, A bibliomntometrics, 2 (3) (1980) 227-237.
9. R.K. VERMA, Y.K. SHARMA, H.S.D. KHATRI, Trends in nuclear research and its publications: An analysis based on five years coverage in the Indian Science Abstracts, Annals of Library Science and Documentation, 29 (2) (1982) 64-69. 10. D.H. HALL, The interface between geoscience and industry: A case study of the interaction between research and discovery and mining of areas for nuclear fuels, Scientometrics, 11 (3-4) (1987) 199-216. 11. P. TROFIMENKO, Scientometric analysis of the development of nuclear physics during the last 50 years, Scientometrics, 11 (3-4) (1987) 231-250. 12. H. J. CZERWON, Scientometric indicators for a specialty in theoretical high energy physics: Monte Carlo methods in lattice field theory, Scientometrics, 18 (1-2) (1990) 5-20. 13. P. MAVGUIN, Using a contracts database for evaluating the dynamics of a technological pr
(1991) 207-228. D.H. HALL, The Science-industry interface: Correlation time serispectra, and growth models in the nuclear fields industry, Scientome280. B.S. KADEMANI, VIJAI KUMAR, ANIL SAGAR, ANILdimensions of nuclear science and technology research in India: A study(1970-2002) database, Malaysian Journal of Library and Informati23-48. B.S. KADEMANI, VIJAI KUMAR, ANIL SAGAR, ANIL KUGANESH SURWASE, scientometric dimensions of thorium resBulletin of Information Technology, 11 (2) (2006) 87-104. B.S. KADEMANI, GANESH SURWASE, ANIL SAGAR, VIJliterature on Bose-Einstein Condensation. Malaysian Journal ofScience, 11 (2) (2006) 87-104. B.S. KADEMANI, VIJAI KUMAR, ANIL SAGAR, ANILthorium: A study based on Science Citation Index, Scientometrics, B.S. KADEMANI, ANIL KUMAR, VIJAI KUMAR, Analyscience and technology. In: DAE-BRNS symposium on role of nuclear technology, January 4-6, 2007, 135-148.
1
20. ANIL KUMAR, B.S. KADEMANI, VIJAI KUMAR, GANESH SURWASE, LALIT in Ind
65
OPT1
Large Room Temperature Magnetization of Pulsed Laser Deposited Cobalt Ferrite Thin Film
Subasa C. Sahoo1, M. Bo ra1 and R. Krishnan3
1Department of physics,In i, Mumbai ?400076,
2Department of Metallurgical Engineering and Material Science, Indian Institute of Technology
Bombay Powai, Mumbai ?400076,3Groupe d'étude de la matière condensée, CNRS / Universite de
*
Puls
vari
ferr
(Fil
hou
sho
fou
thin
wer
und
pro
hra1, N.Venkataramani2#, Shiva Prasad1*, D. S. Mis
dian Institute of Technology Bombay Powa
Versailles-St-Quentin, 45, avenue des Etats-Unis, 78035 Versailles Cedex, France Current Address: Director, Indo-French Centre for Promotion of Advanced Research, 5B, India Habitat Centre, New Delhi-110003 # Corresponding Author; ramani@iitb.ac.in ed laser deposition technique is a very convenient and successful method for the growth of a ety of thin films. We have deposited cobalt ferrite thin films using this technique from cobalt ite target. In this work, two films, one deposited at insitu substrate temperature (TS) of 750 ºC m-1) and another deposited at ambient temperature and exsitu annealed at 750 ºC in air for two rs (Film-2) were studied. Single phase cobalt ferrite was observed by XRD in both the films. Fig.1 ws MH loops of both the films and that of the target used. The 4πMS value of the Film-1 was nd to be 3490G which is less than that value of 5360G of the target, which is generally expected in films. But in the Film-2 the 4πMS value was found to be 5820G. Coercivity and MR/MS ratio e found to be 1.76kOe, 0.33 and 0.86kOe, 0.37 for Film-1 and Film-2 respectively. It was erstood that insitu heating and external annealing affect the microstructure and hence the magnetic perties. -6-4-202468TargetFilm-2-2000-1500-1000-5000500100015002000-2500-2000-1500-1000-50005001000150020002500 4πM ( G )H ( Oe ) 4πM ( KG )Film-1
H ( T )
Fig. y of the films and the
-8 -6 -4 -2 0 2 4 6 8
-8
1 MH loops of both the films and of target used. Inserted fig. shows coercivit
target.
66
OPT2
Photoluminescence of ZnO nanowires grown by thermal evaporation on pulsed laser
deposited Zn
A. Mohanta, A. P. Singh, andna S., and R. K. Thareja
Department of Physics an Centre for Laser Technology,
Ind 08016
ZnO is a semi-conduct both microelectronics and
optoelectronics. Due to i mperature) and direct wide
band gap (3.37 eV), it has been a promising cand e for efficient ultraviolet emitters as high excitonic
binding energy gives assurance of excitonic recombination at room temperature1. The synthesis of 1D
nanostructures such as nanowires, nanorods etc. has become a great interest due to the size effect and
properties is rarely reported. In this article, we demonstrate a simple approach to synthesize
nanowires on Si substrate coated with pulsed laser deposited ZnO thin films. Photoluminescence study is
also undertaken. A thin buffer layer of ZnO film eposited on silicon substrates by PLD system. The
target was a ZnO pellet (99.99%) which is sintered at 1000oC for five hours. The silicon substrate was kept
at 4 cm distance parallel to the target surface at 515 . The third harmonics of Nd: YAG laser beam (DCR-
4G, Spectra Physics, ν = 10 Hz, FWHM = 5 ns) w focused through a lens onto a rotating target at a 45o
angle of incidence. The deposition chamber was in ially evacuated down to a pressure of 6.8 x 10-7 mbar,
and then oxygen gas was introduced into the chamber to maintain oxygen pressure of 1.2 x 10-2 mbar. After
film deposition, nanostructures of ZnO were fabricated by using a simple thermal evaporation process. A
mixture of ZnO powders and carbon with molar ratio 1:1 were used as source materials. The source
materials were kept at 950o C for 30 minutes and the ZnO coated Si substrate was kept at 19.8 cm from the
source position. The whole system was held at a b ressure of 3 x 10-2 Torr under the constant flow of
argon with a flow rate of 40 sccm. Figure-1 show e SEM images of ZnO nanowires deposited on ZnO
coated Si substrates. It is obvious that the wires are nding to form closed loop and one such loop is shown
in figure-1 (b). The diameters of the wires distrib e in the range of 101 ?125 nm and have an average
value of 113 nm. Figure-2 shows photoluminescence profile of the nanowires at room temperature. The
UV emission band at 380 nm is due to a near-ban -edge (NBE) transition which is the recombination of
free excitons through exciton-exciton collision pro ess, 4 as shown in figure-2(a). Figure ?2(b) shows a
deep-level emission band which falls in the visible region. There are many suggested sources of deep-level
emission.5In this case; they are expected to be due to oxygen related defects such as oxygen vacancies.
However, the actual nature of this deep level em ion is still under debate. The temperature dependent
photoluminescence and exciton dynamics at variou mperatures will be presented at the conference.
References:
1 B. D. Yao, Y. F. Chan, and N. Wang, Appl. Phys. Lett., 81 (2002) 757
2 C. C. Chang, C. S. Chang, Solid State Commun. 135 (2005) 765.
3 X. Kong, X. Sun, X. Li and Y. Li, Materials chem try and Physics 82 (2003) 997
4Y. c. Kong, D. P. Yu,, B. Zhang, W. Fang, S. Q. F , Appl. Phys. Lett. 78 (2001) 407.
5 W. Lee, M. Jeong and J. Myoung, Nanotechnology, 15 (2004) 1441.
O buffer layer
V
d
ian Institute of Technology Kanpur-2
ing material which has many different applications ints high excitonic binding energy (~ 60 meV, at room te
idat
quantum confinement effect. Several techniques have been employed to fabricate 1D nanostructure. Thermal evaporation is a simple way for formation of ZnO nanostructures. The desired growth of nanostructures on Si substrate is more preferable for nanodevices due to conducting nature of Si. Although growth of nanostructures on Si substrates has been reported, 2, .3 it has required the use of metal catalyst, for example a thin gold (Au) layer has to be deposited on the Si substrate before the growth of nanostructures. This use of catalyst may introduce impurity to the samples and hence become a cause of poor device performances. Recently, a thin buffer layer of ZnO film is used instead of Au catalyst for nanowires or nanorods growth.4 However, the extensive study of this catalyst-free growth of nanostructures and their optical
was d
oC
as
it
ase p
s th te
ut
d
c
iss
s te
is
eng
67
OPT3
Nanostructured Growth of AlN Thin Films by Pulsed Laser Deposition
Indian Institute of Te ti, Guwahati 781039
*Corresponding author email: alika@iitg.ernet.in
vestigation because of its wide band gap (6.1 eV). The thin films of single crystalline AlN with well
Gaurav Shukla and Alika Khare*
Department of Physics
chnology Guwaha
Growth of high quality epitaxial wurtzite AlN on different substrates is a subject of intensive
in
defined microstructures are required for electrical insulation, electronics and optical applications. We report in this paper, studies on the crystalline growth of AlN via reactive pulsed laser deposition as a function of background pressure of nitrogen gas and target substrate distance. At low N2 pressure the columnar growth of single crystalline AlN <002> is observed probably for the first time. The dependence of Photoluminescence spectra of AlN on to the nanostructure formation shall also be discussed.
68
Resistivity of thin films of YBa Multilayers of YBCO/Ga2O3
L.S.Vaidh riharan
Material kkaam
OPT4
2Cu3O7-δ and
yanathan, D.K. Baisnab, M.P. Janawadkar and Y. Ha
s Science Division, Indira Gandhi Centre for Atomic Research, Kalpa
lsv@igcar.ernet.in igh Tc superconductors rmal state. The detailed
nderstanding of the excitations which give rise to normal state resistivity might be important for
room temperature with different cooling rates but with a 45 min stay at 550 C and at 500 C. Although different
a
we observe a linear resistivity with temperature which is not affected by changing the current from 50 μA to 200
the observations of Daniel Hsu et.al1 who reported an abrupt increase
of normal state resistivity at 220 K with increasing Ia.
YBCO/Ga2O3 multilayers were deposited by PLD on MgO (100) and several other substrates. YBCO thickness
was kept at 90 nm and Ga2O3 layer thickness was maintained at 3.5 nm. Each multilayer had 10 layers of YBCO
and Ga2O3. Fig.2. shows the normalized resistance as a function of temperature for these multilayers. Above Tc,
unlike YBCO, R is not linear with temperature and shows a behaviour reminiscent of resistance saturation.
Analysis of these results will be presented.
Hu
exhibit extraordinary transport properties in the no
superconductivity of these materials. For samples with Tc of 90 K, the T-dependence of resistivity (ρ) is linear. For samples with reduced oxygen content, T-linear dependence is generally seen at higher temperature, although deviation from T-linear dependence was measured by several authors. Thin films of YBCO (500 nm) were deposited by Pulsed Laser Deposition (PLD) system on MgO (100) substrates with KrF (248nm) excimer laser. During deposition, the substrate temperature was maintained at 800 C in flowing oxygen atmosphere of 50 Pa. Films were deposited in the constant energy mode with an energy of 200 mJ. The films were subsequently annealed in oxygen at a pressure of 9.5 x 104 Pa and were cooled down to contact methodologies were studied such as post-deposition of Ag films on YBCO contact pads followed by indium solder, use of silver paste etc, here we present results obtained by directly soldering indium contacts on YBCO films. Fig.1. shows the normalized resistance versus temperature for various values of applied current I in the range 50 μA to 200 mA. The important observation here is that for the entire range of applied currents, mA. This is in complete contradiction to
050100150200250300-0.2T(K) 0501001502002503000.0
0.00.20.40.60.81.0YBCO thin filmnormailzedresistance 50 μA 1 mA 50 mA 100 mA 150 mA 190 mA 200 mA
Fig.1.0.4Finor
Fig.1. Temperature dependence of normalized resis- Fig.2. Normalized resistance vs temperature
tance for YBCO thin film for various applied currents for YBCO-Ga2O3 multilayers. Upper curve
om 50 μA to 200 mA. The curves actually shows resistance saturation at high
perimpose on each other but have been scaled temperatures.
ong the resistance axis for clarity.
1. Daniel Hsu et.al., Appl.Phys. Lett. 90, 162504 007)
0.8
1.2
g.2.
malized
resistance
T(K)
YBCO/Ga2O3 Multilayer
80 120 160 200 240 280
0.88
0.92
0.96
1.00
norm. resistance
T(K)
fr
sual
(2
69
OPT5
Morphological and physical property changes in ZnO thin films grown by PLD due to
Department of Physi search Centre
IIT Madras, Chennai-36, India
* Corresponding author: shubra@physics.iitm.ac.in
Mg doping
*Shubra Singh and M. S. Ramachandra Rao
cs and Materials Science Re
Visible photoluminescence (PL) from ZnO has been found to be tunable through doping. Mg-doped and undoped ZnO thin films were deposited on quartz substrates by PLD method at a temperature of 500癈. The blue-related PL appeared to be caused by energetic shifts of the valence band and/or the conduction band of ZnO. Optical properties (like IR spectra and PL) and structural properties (XRD) exhibit that Mg ion replaces Zn ions in the wurtzite structure of ZnO. The thermodynamic solubility of MgO in ZnO has been reported to be less than 4 mol% according to the phase diagram of the ZnO-MgO binary system. The MgxZn1-xO samples can thus be considered as metastable phases. Pulsed laser deposition is actually a suitable method for growth of such metastable phases because of the high peak energy of the laser light.
Fig.1. Atomic Force Microscopy AFM pictures reveal the average grain size of is 15nm and that of doped films image of 5 mol % Mg doped ZnO. about 300nm. The average roughness of undoped films is 50 nm. This shows that the surface of ZnMgO films is not as
smooth as the surface of ZnO film.
70
71
OPT6
Characteristics of pulsed laser deposited Zn1-xNixO/ZnO bi-layer thin films
Subhash Thota, Pankaj Misra*, Lalit M Kukreja* and Jitendra Kumar
Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur-208016, India
*Thin Films Laboratory, Raja Ramanna Centre for Advanced Technology, Indore-452013, India
*Email: jk@iitk.ac.
Zn1-xNixO (0.01≤x≤0.163) /ZnO bi-layer thin films were deposited over [0001] oriented Al2O3
substrates using a Q-switched Nd:YAG (wavelength 355 nm, pulse duration 6 ns, repetition rate 10
Hz) at a fluence of ~ 2 J cm-2 under oxygen partial pressure of 10-4 mbar. For this, a buffer layer of
pure ZnO (~50 nm thickness) and Zn1-xNixO film were deposited in succession at a substrate
temperature of 700oC and 400oC, respectively. Their x-ray diffraction patterns reveal the presence of
wurtzite-type hexagonal structure with preferential growth of (0001) film plane and decrease of cparameter
with increase in the nickel content 憍? A series of characteristic optical absorption bands
(Fig. 1) in the UV-visible regions have been identified with d-d transitions from 3T1(F) to 3A2(F),
3T1(P), and 3T2(F) of the Ni2+ (2d8) ions, occupying zinc sites (i.e. centre of oxygen tetrahedron).
This is supported by the observed gradual red shift of optical band gap absorption edge with increase
in 憍?(typical values being ~ 3.27 and 3.05eV for 憍?= 0.01 and 0.163, respectively). The films
ters
Oe fi e
Fig. 1 Fig. 2
-1000 -800 -
-60
-40
-20
0
20
exhibit hysteresis loops at room temperature with val8.45 emu/cm3, respectively for 2-16.3 at% nickel saand magneto-resistance data under -80 to 80 kdominance of hopping conduction with evidence of 4x10145x10146x10147x10148x101450607080692 nm650 nm538 nmZnO-Ni 5%e (%) Zn0.99Ni0.01O Zn0.98Ni0.02O Zn0.96Ni0.04O Zn0.95Ni0.05O Zn0.837Ni0.163O
(αhν)2 cm-2 eV2
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
0
1x1014
2x1014
3x1014
200 300 400 500 600 700 800
-10
0
10
20
30
40
441 nm
Wavelength (nm)
Transmittanc
Photon energy (eV)
ues of Hc and Mr in the range 99-153 Oe, 3.22-mple (Fig. 2). The dc and ac transport parameeld in the temperature range 5-300 K suggest thferromagnetic ordering at room temperature. 40603) Zn0.98Ni0.02 O Zn0.96Ni0.04 O Zn0.90Ni0.10 O Zn0.837Ni0.163 O
600-400-20002004006008001000H (Oe)H (Oe)
-2000 -1500 -1000 -500 0 500 1000 1500 2000
-400
-200
0
200
400
M (emu/cm3)
M (emu/cm
Structural and Optical Characterization of UV-transparent β-Ga2O3
V. Sridharan, L.S. Vaidhyanathan, V. Srihari, G. Raghavan, S. T. Sundari, M. Kamruddin, M. Premila, H.K. Sahu, B. K. Panigrahi, V.S. Sastry and C.S. Sundar
Material Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102.
e-mail: varadu@igcar.gov.in
Introduction: Recently, there is a renewed interest in β-Ga2O3 due to its possible application as transparent conducting coating. It has a wide band gap of 4.8 eV and can be converted to a n-type semiconductor by heat treating in inert atmosphere. It is a versatile gas sensor as it can be used for sensing both oxygen above 800 oC and reducing gases below 700 oC. Due to its wide band gap, is has a potential applications in the field of photolithography. However, for realization of the envisaged applications, thin films of Ga2O3 in β-phase should be stabilized against other competing metastable (α, γ and ε) phases. In this paper, we report thin film deposition of polycrystalline β-Ga2O3 using pulsed laser deposition and post deposition annealing. Structural, surface, compositional and optical characterizations of the films are also reported in the paper.
Experimental details: Thin films of β-Ga2O3 on quartz and silicon substrates have been prepared by pulsed laser deposition method using KrF laser (284 nm excitation) with laser energy of 400 mJ and under oxygen partial pressure of 0.015 mbar. Surface morphology was characterized using atomic force microscopy, structural characterization through glancing incidence X-ray diffraction (GIXRD) and compositional analysis through Rutherford back scattering technique. Optical characterization was carried out using UV-Vis spectrometer and a variable angle rotating polarizer spectroscopic ellipsometer.
Results and discussions: The room temperature GIXRD pattern of the as grown film on silicon and quartz along with that of γ-phase of bulk nanocrystalline Ga2O3 are shown in Fig. 1. It is seen that for
Fig. 1. GIXRD patterns of bulk γ-Ga2O3,
thin films grown on silicon and quartz
Fig. 2. AFM surface image of the film grown on
quartz over an area of 3000X3000 nm.
OPT7
Fig. 3. (αhν)2 Vs hν plot for the film
the same growth conditions, films deposited on quartz substrates contain lower fraction of γ-phase. From the line broadening analysis of the XRD profile, the average grain size was determined to be less than 15 nm. The films grown on quartz are transparent and colourless. A comparison between the relative intensity of the reflection of as deposited films and bulk polycrystalline sample indicates a strong texturing in the as deposited films. AFM studies also indicated that the surface morphology (Fig. 2) of the films is textured with ridge like features, having a rms surface roughness of ~ 8nm. Figure 3 shows the (αhν)2 Vs (hν) plot based on UV-Vis spectroscopic studies. By extrapolation the linear portion of the curve at higher energies to α=0, the band gap (Eg) is determined to be 4.7 eV. From pseudo-dielectric spectra of the films obtained through ellipsomety, the thickness of the film was determined to be 705 nm and the refractive index was fond to increase monotonically from 1.905 to 2.1 in the energy range 1.2 to 4.3 eV and close to the reported value for the bulk. From the ellipsomety studies, the Eg was determined to be 4.8 eV, in agreement with the value estimated from UV-Vis studies.
8 1
grown on quartz substrate. Estimated
band gap Eg is ~4.7 eV.
GIXRD studies on 600 oC annealed (12 hr) films indicated the absence of γ-phase. This is in agreement with reported γ→β transformation above 500 oC. Detailed structural, compositional and optical properties of the annealed films will be presented.
OPT8
Characterisation of pulsed laser deposited PZT and PLZT thin films on oxide pervoskite electrodes
R.Reshmi1,A.S.Asha1, M.K.Jayaraj1 ,M.T.Sebastian2
1Optoelectronics Device Laboratory, Department Of Physics
Cochin University of Science and Technology
Kochi-682022, India
2Regional Research Laboratory, Thiruvananthapuram 695019, India,
Email: mkj@cusat.ac.in
Ferroelectric thin films have attracted attention for their application in various microelectronic devices such as nonvolatile ferroelectric random access memory and ferroelectric field effect transistors. Pervoskite Pb(ZrxTi(1-x))O3 or PZT thin films are the most extensively studied due to its small coercive field, large polarisation and high curie temperature. The functional response of ferroelectric thin film strongly depends on the electrode material. La0.5Sr0.5Co1-xNixO3 (LSCNO) is a conducting ceramic which has good potential for use as electrode in hetrostructures for all oxide ferroelectric devices.
In this work we report the growth of PZT and PLZT thin films on the pervoskite LSCNO layer by pulsed laser ablation. The top and bottom LSCNO were deposited by RF magnetron sputtering. The electrodes crystallise in pervoskite structure. The structural and electrical properties of PZT and PLZT thin films deposited on Pt as well as oxide LSCNO are investigated. The polarisation of the hetrostructure gave a coercive field of 56kV/cm and remnant polarisation of 3 C/cm2 and saturation polarisation of 6 C/cm2.
8 2
THP1
Oxygen Reduction Kinetics and Transport Properties of
(Ba,Sr)(Co,Fe)O3-delta Solid Oxide Fuel Cell Cathode Materials
Lei Wang1, Rotraut Merkle1, Frank S. Baumann1, Jürgen Fleig2, and Joachim Maier1
1 Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
2 Institute of Chemical Technologies and Analytics, Vienna University of Technology, A-1060 Vienna, Austria
Email: lei.wang@fkf.mpg.de
The oxygen reduction at the surface of cathode materials is crucial for the performance of solid oxide fuel cells (SOFC), but a detailed understanding of the mechanism is not available yet. (BaxSr1-x)(Co1-yFey)O3-δ shows strongly improved oxygen reduction rates compared to previously applied perovskite cathode materials. In this work, surface rate constants as well as bulk transport properties are studied.
(BaxSr1-x)(Co1-yFey)O3-δ with 0≤x≤0.5, 0.2≤y≤1 was synthesized by the Pechini method. Oxygen stoichoimetry was obtained from thermo-gravimetric analysis, confirming that Ba0.5Sr0.5Co0.8Fe0.2O3-δ has an exceptionally low oxygen content which is generally smaller than 2.5.
Dense thin films were grown by pulsed laser deposition (PLD) and patterned into circular microelectrodes by photolithography. The surface resistances Rs, which dominate the overall electrode resistance, were measured by impedance spectroscopy on individual microelectrodes at different T, pO2 and applied electrical bias. PLD technique greatly helps to study the oxygen reduction kinetics since only measurements on dense thin films allow to record absolute Rs values without interference from morphology effects. These Rs values were found to be much lower than those for (La,Sr)(Co,Fe)O3-δ.
The variation of the surface reaction rates with A-site and B-site composition was studied and correlations with bulk materials properties such as oxygen nonstoichiometry, ionic mobility or oxidation enthalpy were examined. Plausible reaction mechanisms as well as possible reasons for the high absolute surface reaction rates will be discussed.
8 3
THP2
Study on p-type ZnO thin films and ZnO homojunction LED
Y. F. Lu*, Z. Z. Ye, Y. J. Zeng, L. P. Zhu
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, 310027
People抯 Republic of China
*E-mail: sailinglu27@gmail.com
Fabrication of p-type ZnO promises to be important in realizing ZnO short-wave optoelectronic devices such as light emitting diodes and laser diodes. Among all the available group V and group I p-type dopants, nitrogen substituting oxygen seems to be promising, which has been well confirmed by the reports on ZnO homojunction light-emitting diodes. In this study, we report our research on N-doped p-type ZnO by MOCVD. First, the effects of growth parameters such as substrate temperature, radio frequency power, flux of DEZn, on the optical and electrical properties of N-doped ZnO thin films are discussed. Then the ultraviolet photoconductivity in N-doped p-type ZnO thin film is investigated. Surface adsorption of C and O is believed to be a major contribution to the UV conductivity. Plasma-free growth of N-doped p-type ZnO is also reported, which is easier to operate and more preponderant in growth of p-type ZnMgO and quantum-well LEDs. At last, room-temperature electroluminescence from ZnO:N / ZnO homojunction diode is observed.
Besides nitrogen, group I dopants, such as Li, Na, have also been introduced to realize p-type ZnO. The doping mechanism in Li-N-H codoped p-type ZnO is investigated experimentally and theoretically.
In order to develop ZnO based optoelectronic devices, an ohmic contact to p-type ZnO is another important issue. Ni /Au ohmic contacts on N-doped p-type ZnO are investigated as a function of annealing temperature. And the transport mechanism in the contacts is investigated from the temperature-dependent contact resistance.
8 4
THP3
Magnetoresistive and Transport Properties of Pulsed Laser Deposited Manganite Thin Films and Heterostructure.
Jaysukh H Markna
Department of Physics, Saurashtra University, Rajkot-360 005 INDIA
Email Id: jaysukh28@rediffmail.com
In this talk a brief review of our work on thin films and hetero-structures of Manganites suitable for spintronic applications will be presented. We have used Pulsed Laser Deposition (PLD) to synthesize high quality Mangenite structures and studied their structural, electrical and magnetic characteristics. We observed enhanced Magneto-resistance (MR) in Mangenite hetero-structures LPSMO/Al2O3/LPSMO containing a thin sandwiched layer of insulting Al2O3 barrier between the two ferromagnetic La0.5Pr0.2Sr0.3MnO3 (LPSMO) layers. Effect of Swift Heavy Ion (SHI) irradiation on the transport and magnetic properties of these structures has been studied, which will also be presented and discussed.
8 5
THP4
Pulsed Laser Deposited Thin Films of ZnO, GaN, AlN, ZnO/GaN
WBSC: Structural, Micro-structural, Optical & Electrical Characterization
Suhas Madhav Jejurikar Guide: Dr. K. P. Adhi, Co-guide: Dr. A. V. Limaye
Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411 007, India.
Corresponding author: suhas@physics.unipune.ernet.in
Wide band gap semiconductors (WBSC) such as II - oxide compounds (ZnO) and III - nitride compounds (AlN, GaN and their alloys) are viewed as promising systems for a wide variety of applications in optoelectronic devices like light emitting diodes (LED), Laser diodes (LDs) operating in UV and blue region for digital data read - write applications, wave guides, UV detectors, displays etc. ZnO has applications for electrical devices like varistors, piezo-electric crystals, surface acoustic wave (SAW) devices, field emitters etc. also due to its radiation hardness the devices realized through ZnO have potential applications in space technology.
The technique of pulsed laser deposition (PLD) was employed for the growth of the above-mentioned materials on different substrates. Bulk targets of ZnO, AlN and GaN were used for the ablation and deposition. AlN bulk target was procured from Kurt J. Leskar, USA, while the targets of ZnO and GaN were synthesized in laboratory by the solid-state route. The deposited films were characterized structurally, micro-structurally, optically and electrically using different techniques like X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, Raman spectroscopy, current - voltage (I-V) measurements (four point probe measurement and field emission studies) and Hall measurement. The thickness of the deposited films was estimated using the Tally step setup. The work on ZnO thin films was carried out to study the influence of substrate temperature on the properties of ZnO thin films and the role of thermal annealing on the deposited films. During deposition the substrate temperature was varied from 100 oC to 600 oC keeping all the other deposition parameters same. Two sets of samples were prepared. One set was annealed in air at 800 oC for four hours. Expected Ohmic behavior is recorded in case of all the as deposited ZnO thin films. While in the case of annealed ZnO thin films, non-linear I-V behavior was observed which is interesting. The non-linear behavior, in terms of the plateau region in I-V characteristics, symmetry / asymmetry in the plateau, etc is dictated by the substrate temperature maintained during deposition. An attempt is made to correlate the structural as well as the morphological properties with the electrical observations. To comprehend the non-linearity in I-V characteristics observed in case of annealed ZnO thin films the local chemical analysis at the microscopic level was performed using XPS (Mk-II-VG scientific spectrometer) technique. Thin films, deposited at 400 C and annealed at 800 C in air, have been used for this study. The stoichiometry of ZnO was studied by recording O 1s and Zn 2P peaks, as they are very strong. Presence of bound H - OH and the interstitial Zn is observed after annealing the samples. This suggests that ZnOH is formed at the grain boundaries, which probably acts like a barrier between two ZnO crystallites / grains. The tunneling of electrons through such barriers could probably explain the non-linearity in I-V measurement for the annealed ZnO thin films.
oo3/2Europium (Eu) doping in ZnO for low doping concentrations (1% and 3 %) was studied from the point of view of optical emission. Thin films of Eu: ZnO were deposited on c ?AlO substrate and characterized for structural, optical and electrical variations. The influence of oxygen deficiency on the structural, optical and electrical properties was investigated and discussed using 3 % Eu: ZnO thin films grown on c-AlO substrate under different oxygen ambient pressure conditions range between 50 mTorr to 5 x 10 Torr. 232-5
3The synthesis, characterization and possible application as a field emitter of GaN was also studied. No suitable substrates are available for obtaining the highly oriented / epitaxial growth of this material, ZnO due to its structural as well as lattice match could prove to be suitable low cost substrate for GaN. Hence the bilayer growth of GaN / ZnO / c-Al2O was undertaken and under optimized deposition
3
8 6
conditions, highly c-axis oriented bilayers of GaN and ZnO were obtained. Oriented growth of wurtzite GaN along the c-axis was also obtained on c-Al2O3 and Si (100) / SiOx substrates. The growth of GaN thin films is on Si (100) / SiOx, a highly lattice mismatched, and thermally incompatible substrate did not show formation or development of cracks. The surface morphology of these films was investigated using atomic force microscopy which showed a smooth surface with the presence of randomly distributed needle like structures of nanometer dimensions clustered together. Such films show excellent field emission characteristics like low turn on voltage (field), high field enhancement factor and high stability in electron emission over extended time periods of two and half hours.
A systematic study of the role of substrate temperature (Ts) and the effect of ambient nitrogen pressure on the structural and optical properties of pulsed laser deposited AlN thin films on c-axis Al2O3 substrate was also carried out. It is found that along with the band-gap of the pulsed laser deposited AlN thin films, the crystallographic orientation turns from (1000) to (0002) depending on the substrate temperature (Ts) and the ambient nitrogen pressure. Attempts have been made to explain the observations in terms of the temperature and pressure dependent growth modes
8 7
THP5
Synthesis and characterization of LaB6 thin films on tungsten, rhenium and silicon substrates and their investigations as Field Emitters
Dattatray J. Late*
Center for Advanced Studies in Material Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune - 411007, India
Lanthanum hexaboride films were grown on tungsten and rhenium tips and foils and also on silicon substrates by Pulsed Laser Deposition and arc plasma methods. The X-ray diffraction spectra of the LaB6 films shows crystalline nature. The field emission studies of pointed and foil specimens were performed in conventional and planar diode configurations respectively, under ultra high vacuum condition. An estimated current density of ~1.2 x104A / cm2 was drawn at the electric field of 3 x 103 V/μm and 6 x 103 V/μm from the LaB6 coated tips of tungsten and rhenium, respectively. The Fowler-Nordheim plots were found to be linear showing metallic behavior of the emitters. The field enhancement factors were calculated from the slopes of the Fowler-Nordheim plots, indicating that the field emission is from LaB6 nanoscale protrusions present on emitter surfaces. The emitters were operated for long time current stability (3h) studies. The post field emission surface morphology of the emitters showed no significant erosion of LaB6 films during three hours continuous operation. The observed behavior indicates that it is linked with the growth of LaB6 films on W and Re. The enhancement in the field emission was observed in the PLD LaB6 film on Zr and gold coated Si substrates, and this has been explained with the increase in the field enhancement factor.
8 8
PSP1.1
Effect of oxygen pressure on the photoluminescence of Gd2O3 :Eu 3+ films
grown by PLD
Geo Rajan, Nissamudeen K. M, Sasi B and K.G.Gopchandran
Department of Optoelectronics, University of Kerala
Kariavattom, Thiruvananthapuram-695 581, India
gopchandran@yahoo.com
Luminescent films play an important role in high resolution devices such as cathode ray tubes (CRT抯), electroluminescent devices (ELED抯), plasma display panels (PDP抯) and field emission displays (FED抯). Displays with thin film phosphors have higher contrast and resolution, superior thermal conductivity as well as high degree of uniformity and better adhesion. Due to the higher stability of oxide based phosphors, Gd2O3:Eu3+ thin films are one of the most promising red phosphor systems. Due to a 5D0-7F2 transition with europium, Gd2O3:Eu3+ shows red luminescence at 612nm. In this work, pulsed laser deposition has been used for the growth of Gd2O3:Eu3+ films. In thin film phosphors brightness may be associated with several factors such as interaction between film and substrate, film processing conditions and compositions of the films. The effect of oxygen partial pressure on structural and optical properties is discussed with X-ray diffraction (XRD), scanning electron microscopy (SEM) UV visible and photoluminescence (PL) spectroscopic techniques.
8 9
PSP1.2
A comparative study of nanostructures Co thin films deposited on different substrates by pulsed laser deposition
A. Sharma*, S. Tripathi, R. Brajpuriya, Ram Prakash, R. J. Chaudhari, D. M. Phase and T. Shripathi
University Grant Commission- Department of Atomic Energy Consortium for Scientific Research, University Campus, Khandwa Road, Indore-452 017, India.
anupamsharma2003@yahoo.co.in
Nanostructure materials have attracted intense research interest over the recent years, as they provide the critical building blocks for the booming nanoscience and nanotechnology. Their novel properties can be tailored through extra degrees of freedom, such as structure and constituent materials etc. In this regard, recent progress on magnetism and magnetic materials has made magnetic nanostructures a particularly interesting class of materials for both scientific and technological explorations. For example, studies on interlayer coupling, giant and transmission magnetoresistance, exchange bias, half-metallic ferromagnets (FM), forms a future generation of electronic devices (spintronics) that use the spin of the electron in addition to its charge for manipulating information.
In this respect, Co and Co based alloys has been the subject of a lot of studies in the last decade; they have been investigated as a thin films [1-2], as a part of multilayers system [3-4], as a nanowires [5-6] and as a stripes, or dots [7-8]. The magnetic properties of these materials depend greatly on the methods and condition of preparation. Similarly, in recent years, the study of Co thin films and their interfaces with semiconductor surfaces has received considerable attention due to their potential applications, e.g. formation of Co-Silicide is extensively used as a conductive material in many microelectronic devices [9] and Co/GaAs system as potential candidate in spintronics, giant magneto resistance and many optoelectronic devices because of high spin polarization of the carriers at Fermi level [10-11].
One of the probable barriers for practical applications, however, is thermal stability. For the case of Co, this problem should be carefully consider due to its larger dependence of magnetic crystalline anisotropy (Ku1) constant on temperature. The large change in Ku1 value with temperature makes the easy axis of the crystal parallel to the basal plane, which leads to a change in the magnetization direction of the Co magnetic particle.
Therefore, in the present work, we have deposited Co (400Å) film on three different substrate viz. Si, GaAs and float Glass at room temperature and at 400癈 substrate temperature by pulse laser deposition technique using KrF excimer laser with 2J/Cm2 energy density. The investigation of structural, magnetic and transport properties were carried out using X-ray diffraction (XRD) Magneto optical Kerr effect (MOKE) and four probe resistivity measurements, respectively. Structural studies shows three different structures in three different cases. The crystallinity increases in case of film deposited at 400癈 as compared to room temperature. The corresponding changes in anisotropy, coercivity and resistivity in all the cases will be discussed in terms of structural changes at the interface.
Reference
1. A. Sharma et al, J of Nano Sci Nano Technol, 7 (2007) 2041.
2. A. Sharma et al Mat Sci Engg. B 130 (2006) 120.
3. G. Ausanio et al JMMM, 230 (2001) 1740.
4. M. Labrune et al Eur Phys J B 31 (2003) 195.
5. Y. Henry et al. Eur Phys J B 20 (2001) 35.
6. S M Cherif et al Phys Rev B 59 (1999) 9482.
7. M. Natali et al. J, Vac Sci Technol B 19 (2001) 2779.
8. J. Raabe et al. J. Appl. Phys 88 (2000) 4437.
9. Jyh-Shen Tsay et al, Appl. Phys Lett 74 (1999) 1311.
10. S. S. P. Parkin, Phy. Rev. Lett. 71 (1993) 1641.
11. K. Ueda, et al, Appl. Phys. Lett. 79 (2001) 988.
9 0
PSP1.3
Raman Study of oriented thin films of PrMnO3 deposited on different substrates
Aditi Dubey* and V. G. Sathe
UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore ?452 017
E-mail: aditidubey@csr.ernet.in
In this study we describe our Room temperature Raman spectroscopy results on c-axis oriented thin films of PrMnO3 compound deposited on SrTiO3 (001) and LaAlO3 (001) substrate of about ~200 nm thickness by Pulsed Laser deposition technique. PrMnO3 bulk compound has peroveskite structure with orthorhombic Pnma space group. At low temperature this compound undergoes from paramagnetic to Antiferromagnetic phase at 99 K. PrMnO3 compound was prepared by using standard solid-state reaction method with intermediate grinding and sintering at very high temperatures. The films were grown in 300 mTorr oxygen pressure and substrate temperature was kept about ~6500 C.
The X-ray diffraction confirms that the films are highly orientated along the c-axis and of very good crystalline quality. The calculated out of plane lattice parameter are shown in table 1. The lattice parameter of bulk compound in respect to the pseudo cubic unit cell is ~3.85 Ǻ. Therefore the film deposited on LaAlO3 substrate (3.79 Ǻ) experiences the in-plane compressive strain and out of plane elongation while the film grown on SrTiO3 substrate (3.90 Ǻ) experience the in-plane tensile strain and out of plane compression.
Figure 2 gives the room temperature Raman spectrum of both the films. The effect of strain of opposite nature on PrMnO3 films is also reflected in the Raman mode position. It is seen that for higher out of plane lattice parameter film (on LaAlO3), the Raman peak positions are relatively at lower positions than compared to film that has lower out of plane lattice parameter (on SrTiO3). To conclude, the variation of phonon frequency with substrate induced strain of opposite nature in-plane tensile on SrTiO3 substrate and in-plane compressive on LaAlO3 substrate) were correlated with appearance of the Raman mode positions.
Table 1: Room temperature out of plane lattice parameter and Raman peak positions and corresponding line widths of PrMnO3 thin films deposited on SrTiO3 (001) and LaAlO3 (001) substrates
Sample
2 θ
(Deg)
Out of plane Lattice parameter c (Ǻ)
ω1
(cm-1)
ω2
(cm-1)
ω3
(cm-1)
PMO (STO)
47.49
3.82
313.90
492.28
612.58
PMO (LAO)
46.15
3.93
312.15
490.73
609.96
Figure 1: Room temperature (300 K) Raman spectra of PrMnO3 films of thickness 200 nm deposited on SrTiO3 and LaAlO
10020030040050060070080090010001100Intensity (
a.u.)Raman Shift (cm-1) PMO (STO) PMO (LAO)
9 1
PSP1.4
Application of pulsed laser deposited ZnO thin films as a solar blind detector
Alka V. Deshmukh, S. M. Jejurikar, K. P. Adhi and S. I. Patil
Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411 007, India.
Corresponding author: alka_d@physics.unipune.ernet.in
Highly c-axis oriented thin films of ZnO were grown by pulsed laser deposition (PLD) technique on different substrates. For this study we have used Si (100), SiO2/Si (100), c-Al2O3 and GaAs. The films were grown under identical deposition conditions. Deposited samples were characterised structurally using x-ray diffraction technique. Electrical properties of the samples were measured, by making indium contacts on the surface of the samples. Hall measurement was done to measure the carrier concentration of the above prepared samples. For this Van der Pauw geometry was used. Photo response of all the samples was recorded. For this purpose KrF excimer laser having wavelength 248 nm was used. ZnO deposited on Si (100) and SiO2/Si (100) shows very interesting results, towards the direct application of these samples as a solar blind window.
9 2
PSP1.5
DC-Discharge Assisted Pulsed Laser Growth of Ultra-thin
Silicon Oxynitride Films
B. N. Singh*, P. Misra, A. K. Das, R. Kumar#, Binsu J Kailath+, M. Mishra#, D.M. Phase!, A. DasGupta+, N. DasGupta+ and L. M. Kukreja
Thin Film Lab., Raja Ramanna Centre for Advanced Technology, Indore 452 013
+Department of Electrical Engineering, IIT Madras, Chennai 600036
!UGC-DAE Consortium for Scientific Research, Indore 452 017
# Department of Electronics, D D Upadhyay University, Gorakhpur, 273 016
*Corresponding author, email address: bnsingh@cat.ernet.in
We have evolved a novel DC discharge assisted laser induced oxynitridation scheme of silicon to grow ultra-thin films for gate dielectric applications. A 3rd harmonic of Q-switched Nd:YAG laser (355 nm, 6 ns and 10Hz) at a fluence of ~ 60 mJ/cm2 was used to heat the Si substrates mounted in a growth chamber. Schematic of the growth setup is shown in figure1. The growth chamber was initially evacuated to a base pressure of ~ 5x10-6 mbar and then filled with mixture of Oxygen and Nitrogen ambient in different ratios but at constant total pressure of ~2 mbar. The DC discharge was created in this gaseous ambient by applying ~800V (DC) between a circular metal ring kept at ground potential at a distance of ~ 2 cm from the substrate as shown in figure1. The X-ray Photo-electron Spectrum, shown in figure 2 confirmed the presence of N in the grown over layer and hence the formation of Silicon oxynitride.
020040060080010001200140002004006008001000*NCounts/SecEnergy (eV)
LASER+800V DC Discharge Si wafer TMPN2+O2
SiOxNy
Figure 1 Figure 2 Figure 3
The Capacitance-Voltage measurements as shown in figure 3 on the MOS structures (shown in the inset) containing Silicon oxynitride as gate dielectric revealed an effective dielectric thickness (EDT) in sub-nanometer range. The Current-Voltage studies (figure not shown here) on these devices also revealed low leakage current with high break-down voltage. Further investigations on these structures are underway. Thus laser and DC discharge assisted oxynitridation of Si provides a simple and effective methodology of producing ultra-thin Silicon based gate dielectrics.
93
PSP1.6
Unique nanostructures in pulsed laser ablated NiO thin films
B.Sasi, K.M. Nissamudeen and K. G. Gopchnadran
Department of Optoelectronics, University of Kerala, Thiruvananthapuram-695 581, India
E-mail: thazhavasasi@sancharnet.in
Nanostructured oxides prepared in the form of rods, fibers, ribbons, channels and other shapes display unique properties that make them suitable for many new applications such as transparent conductors, sensors, lasers, smart windows, luminescent materials and solid electrolytes. Depending on the properties and fabrication route, the crystal boundaries are associated with various degrees of structural and compositional disorder. A very simple but successful way is a slightly controlled oxidation of the surface. In this study preparation of nanostructured nickel oxide and lithium doped nickel oxide thin films were done using pulsed laser deposition technique. Growth of thin films from atoms deposited from the gas phase is intrinsically a nonequilibrium phenomenon governed by a competition between kinetics and thermo dynamics. Direct and indirect oxidation mechanisms involved in the formation of a variety nanostructures like mesoporous, Stranski-krastanov nanoislands, nanochannels, nanochick and self-assembly of nanocrystals in nickel oxide thin films are discussed.
94
PSP1.7
Influence of Ti2+ doping on the structural and optical properties of WO3 thin films prepared by pulsed laser ablation technique.
Lethy.K.J, Beena. D, Bahna.A.H & V.P.Mahadevan Pillai
Department of Optoelectronics, University of Kerala, Kariavattom, Kerala, India
Corresponding author: vpmpillai9@rediffmail.com
Inorganic nanostructures of metal oxides are of interest as they are the backbone of many smart and functional materials which finds applications in photonics, nano-electronics, information storage, catalysis and biosensors. Tungsten trioxide is a wide band gap n-type metal oxide semiconductor. Intrinsic as well as doped WO3 thin films are crucial in the fields of electrochromic and gas sensing applications [1, 2]. The essential theme of the present investigation is the structural and optical properties of pure and Ti2+ doped WO3 thin films deposited on heated (600 0C) quartz substrates in an ambient oxygen pressure of 0.12 mbar. The deposition is carried out using a Q- switched Nd: YAG laser (Quanta朢ay INDI ?Series, Spectra Physics) with a maximum energy of 200 mJ at frequency doubled 532 nm radiation having pulse width 7 ns and repetition frequency 10 Hz. The deposition of the films are done on quartz substrates kept at an on-axis distance of 45 mm from the target in reactive oxygen atmosphere of 0.12 mbar pressure and at a substrate temperature of 873 K. The targets used are pure WO3 and TiO2 doped (1, 3, 5 & 10 wt %) WO3 pellets. The incorporation of the titanium into the polycrystalline WO3 matrix was confirmed from X-ray diffraction (XRD) and Energy dispersive X-ray (EDX) measurements. Crystallographic investigation based on X-ray diffraction studies shows an orthorhombic WO3 crystalline phase existing in these films. No structural phase transformation could be observed with different doping levels. Crystalline grain size deduced from XRD pattern, decreases from 40 nm to 20 nm depending on the TiO2 doping concentration. Surface morphology analysis at the nano scale domain has been investigated by Scanning electron microscopy and Atomic force Microscopy (AFM) techniques. Crack free surface morphology has been obtained for all the films except the one with 1 wt % TiO2 doping. To get a deeper insight into the structure and phase existing in these, they were subjected to micro-Raman and FTIR measurements. Optical transmittance spectra recorded using JASCO V550 double beam spectrophotometer reveal that, transmittance in the visible range decreased from 80% for the undoped WO3 films to 40 % for the 10 wt% TiO2 doped films. A large red shift (around 50 nm) in absorption edge and hence narrowing of band gap energy was observed for the TiO2 doped WO3 films. Additionally, noticeable correlation of the optical constants like refractive index, thickness, extinction coefficient etc of the WO3 films with respect to different doping level is explored in detail. In conclusion the analysis imply that TiO2 doping can be applied to tailor make the structural, optical and morphological properties of WO3 thin films.
Reference:
1. Granqvist C.G., Handbook of Electro chromic Materials, Elsevier, Amsterdam, 1995
2. Wang S.H., Chou. T.C and Liu. C.C., Sensors and .Actuators, B, Chem. , 2003, 94, 343p
3. Swanepoel. R., J.Phys.E:Sci.Instrum . 1983, 16, 1214p.
95
PSP1.8
Effect of Substrate on Pulsed Laser Deposition of InN Thin Film
Gaurav Shukla and Alika Khare*
Department of Physics
Indian Institute of Technology Guwahati, Guwahati 781039
*Corresponding author email: alika@iitg.ernet.in
Indium nitride is emerging as a potential semiconducting material for various applications, viz: high efficiency solar cell, high quality electronics components and sensors. The deposition of thin films of InN for the device applications is challenging due to its low dissociation temperature and the large lattice mismatch with commonly used substrate. The low dissociation energy restricts the use of high substrate temperature and hence the short diffusion length of the growth precursor resulting into poor quality of the thin film. This problem can be overcome by pulsed laser deposition as PLD gives the high kinetic energy to the atom/ions and molecules impinging on to the substrate for deposition. In this paper, we report the deposition of polycrystalline InN thin films via PLD using indium metal as the target in the environment of N2. The dependence of crystal structure and the surface morphology on to the substrate and the background nitrogen pressure shall also be discussed in the paper.
96
PSP1.9
Synthesis and Optical Properties of Cr2O3 Films Prepared by Pulsed Laser Ablation
G. Balakrishnan1, P. Kuppusami, T.N. Sairam2, E. Mohandas and D. Sastikumar1
Physical Metallurgy Division, Indira Gandhi Centre for Atomic Research,
Kalpakkam-603 102, Tamil nadu
1National Institute of Technology, Tiruchirapalli- , Tamilnadu
2Materials Science Division, Indira Gandhi Centre for Atomic Research,
Kalpakkam-603 102, Tamil nadu
Chromium oxide (Cr2O3) is material having high hardness, chemical inertness, mechanical strength and stability. Among the various chromium oxides (CrO2, CrO3, Cr2O3), Cr2O3 is the most stable under ambient conditions. Cr2O3 thin films are widely used as protective coatings against wear, corrosion and oxidation. It also finds applications as electrochromic coatings, IR transmitting coatings, selective black absorber and optically selective surface of solar collectors.
In the present work, thin films of chromium oxide prepared from a sintered target of Cr3C2 by pulsed laser ablation is investigated. Silicon (100) oriented and glass substrates were mounted on the substrate holder in the chamber using silver paste and chamber was evacuated by a turbo-molecular pump backed with a rotary pump. The KrF excimer laser (λ=248 nm ) was used to deposit chromia films with varying repetition rates, laser energy, substrate temperature and background gas. The thickness of the prepared films were measured by the Dektak profilometer (DEKTAK 6M-stylus profiler by Veeco, USA).The structure of the deposited films were studied using XRD-INEL XRG ?3000 Diffractometer. For the optical studies, films were analyzed using the UV-VIS-NIR (model No:310/PC, Shimadzu) spectrophotometer in the range of 190-3000nm . The optical band gap energy has been calculated from (αhυ)1/2 vs hυ plot.
XRD patterns of the Cr2O3 films show peaks which coincide with Cr2O3 structure in agreement with JCPDS. However the films formed at 700oC have several reflections with higher particle size than those formed at 600oC. Absorption characteristics of Cr2O3 clearly show that the absorption increases with the decreasing wavelength in the range 300-800 nm. The films deposited in base pressure and Ar atmosphere show larger band gap (4.6 eV) and the band gap energy decreases steeply for the films prepared under methane atmosphere (2.5 eV). When the substrate temperature is increased from 600癈 to 700癈, the band gap energy decreases further to a value of 2.3 eV due to better crystallinity of the films. The variation in the microstructure and band gap energy as a function of the background gas is presented in detail.
97
PSP1.10
Synthesis and Characterization of La0.7Ba0.3MnO3-SnO2 bilayer using
Pulsed Laser Deposition Technique
J. Mona1, Ram Prakash2, R. Rawat2, R.J. Choudhary2, D.M. Phase2, S.N. Kale1
1. Fergusson College, Fergusson College Road, Pune 411004
2. UGC-DAE CSR, Khandwa Road, Indore 452 017
e-mail id: snkale@vsnl.com
Manganite based p-n junction bilayers were deposited using pulsed laser deposition technique as this technique stands to be unique to grow stoichiometric and oriented films. These manganite based bilayers are interesting to study as they are expected to show rectifying properties over a wide temperature range and even work at high temperatures [1-3]. In this context we have deposited p-type manganite La0.7Ba0.3MnO3 and n-type SnO2 on Si (001) substrates. The La0.7Ba0.3MnO3 and SnO2 bulk samples were synthesized through chemical routes that were used as target material in the deposition chamber. Thin films were deposited in pulsed laser deposition chamber using KrF eximer laser (λ=248 nm tp ~20 ns). Deposition of these bilayers was performed in two steps. In first step a thin layer (~950 nm) of SnO2 was deposited on Si (001) substrate at 580 癈 in the oxygen partial pressure of 1.3x10-4 Torr, the deposited samples were cooled to room temperature at same oxygen pressure. In the second step a part of this film was masked and then La0.7Ba0.3MnO3 film (~950 nm) was deposited at 500 癈 in the oxygen partial pressure of 400 mTorr, the deposited samples were cooled to room temperature in 500 Torr oxygen ambient. In both of the cases laser energy density and pulse frequency was 2 J/cm2 and 10 Hz, respectively. The bilayers were further examined for the structural and transport properties. The films were characterized by various techniques such as x-ray diffractometry (XRD), atomic force microscopy and four probe resistivity measurements. Crystal structure was determined using XRD. The XRD pattern of La0.7Ba0.3MnO3 shows oriented growth, SnO2 exhibits polycrystalline growth on Si (001) substrate. Atomic force microscopy reveals that the surface of the La0.7Ba0.3MnO3-SnO2 films is smooth. Good rectifying characteristics were observed at room temperature, which projects promising applications of these bilayers as diode-like device. Possible scenario of the surface morphology of the bilayers and the transport properties will be discussed. These results indicate that this p-n junction may be developed into functional, strongly correlated electronic devices at room temperature.
Relevant References:
1. Hidekazu Tanaka, Jun Zhang and Tomoji Kawai, Phys. Rev. Lett., 88 (2002) 027204-1.
2. Ashutosh Tiwari, C. Jin, D. Kumar and J. Narayan, Appl. Phys. Lett., 83 (2003) 1773.
3. J. R. Sun, C. M. Xiong and B. G. Shen, P. Y. Wang and Y. X. Weng, Appl. Phys. Lett., 84 (2004) 2611.
98
PSP1.11
Semiconductor Nano-pattern formation through laser induced diffusion
U. Das , D. Mohanta , A.Choudhury
Dept of Physics, Tezpur University, Napaam, Tezpur ?784028, India
upam2005@gail.com
Due to strong particle-particle interaction, polymeric/inorganic nano-composites generally have primary affrications even agglomerations of inorganic nanoparticles. The particle agglomeration appears during self assembly of nanostructures and the interaction forces between the molecules and the nanoparticles play an important role in controlling the structures and consequently, the properties of the nanoparticles. When ZnS nanoparticles are embedded in an insulating matrix, it will show long term stability but diffusion of atom in the polymer is present. This material transport is driven by the free surface energy of the nanoparticles and associated with lattice defects and grain boundaries. These diffusion processes result in changes of the size and shape distribution of the embedded particles. The diffusion process is accelerated through laser irradiation. Controlled laser irradiation diffuses the atoms in a particular direction which will form some elongated nano-patterns. Better stability and these nano-patterns, make them a useful candidate for optoelectronics and photonics application.
99
PSP1.12
Growth of n-Zinc Oxide on various substrates using pulsed laser deposition and its photo conducting properties
G. Naresh Kumar, V.Immanuel, Francis P. Xavier
Loyola institute of frontier energy (LIFE), Physics Department, Loyola college, Chennai 600 034, India
email:naresh_matsci@yahoo.co.in
Pulsed laser deposition (PLD) has been shown to be a very successful method for preparing epitaxial layers as well as amorphous films. The advantages with PLD method are stoichiometric transfer of the target material, fine control of film thickness down to atomic monolayer and simplicity of operation 1. In the present study Nd:YAG (λ = 532 nm) laser (with power density of 1 x 10-8 W/cm2) has been used as an excitation source to ablate ZnO. Photo conductivity and temperature dependent conductivity of ZnO thin films deposited on sapphire, p-silicon and glass substrates by pulsed laser deposition (PLD) technique have been investigated. The X-ray diffraction (XRD) results indicate that the epitaxial growth has been achieved for sapphire substrate and poly crystalline growth has been achieved for silicon and glass substrates .The photoconductivity studies exhibit maximum photo response for epitaxially grown ZnO on sapphire substrate This might be due to the capture of nonequilibrium holes at surface oxygen states to produce an equivalent number of excess electrons in the conduction band 2. From the temperature dependent conductivity studies the activation energy of the ZnO on sapphire was found to be 1.1 meV. This can be attributed either to the promotion of carriers to the conduction band, or the thermal field emission of these carriers through grain boundary barrier 2. It is believed that the defects in the zinc oxide lattice behave as localized hopping centers, as well as carrier suppliers, that give rise to the observed conductivity.
References
1. W. M. K. P. Wijekoon and M. Y. M. Appl. Phys. Lett. 67, 1698 (1995).
2. S. A. Studenikin, Nickolay Golego, and Michael Cocivera J. Appl. Phys 87,
2413, (2000)
100
PSP1.13
The low temperature electrical transport in La0.7Ca0.3MnO3
P.R. Sagdeo, R.J. Choudhary and D.M. Phase
UGC-DAE Consortium for scientific research, University campus Khandwa road indore 452017, M.P.
Email: sagdeo@csr.ernet.in
The electrical transport in manganites is one of the challenging problems to our present understanding of 揺lectrons in matter? The phenomenon of colossal magnetoresistance (CMR), spin polarized transport, scattering of electrons from grain boundaries, low temperature resistivity minima, grain boundary magnetoresistance etc, are still not well understood through a common framework. Extensive theoretical and experimental efforts have been made right from 1951, but the electrical transport in manganites still remains unresolved.
The fellomagnetic metallic manganites are known to show the minimum in the resistivity at low temperature (~40K). But there is a debate regarding the origin of this resistivity minimum. The observed minima have been attributed to quantum interference effects, including weak-localizations and electron-electron interaction effects, and Kondo scattering, whereas the other possibility of inter grain antiferromagnetic coupling has also been predicated in the literature.
As in the literature there are various controversies regarding the origin of such resistivity minimum, i.e. whether is it due to the antiferromagnetic coupling between the grains, in polycrystalline samples, or due to the some scattering mechanisms, in the present studies we have carried out the comparative study on the pulsed laser deposited polycrystalline and oriented thin sample.
The polycrystalline and highly oriented thin films of La0.7Ca0.3MnO3 has been simultenously deposited using pulsed laser deposition technique on silicon [111] and LaAlO3 (001) substrates respectively. The electrical transport measurements on these samples have been carried out starting from room temperature down to 4K. The polycrystalline thin film and oriented sample show the insulator to metal like transition around 250K, with further decrease in the polycrystalline sample of La0.7Ca0.3MnO3 shows the resistivity minimum around 35K, where as the oriented thin film sample dose not show any resistivity minimum. The observation of resistivity minimum for polycrystalline thin film sample has been explained on the basis of disorder produced by grain boundary network.
101
PSP1.14
Effect of Structural Disorder on Electronic Transport in La0.5Pr0.2R0.3MnO3 (R = Sr, Ba) Manganite Thin Films
P.S. Solanki, R.R. Doshi, J.H. Markna, C.M. Thaker and D.G. Kuberkar
Department of Physics, Saurashtra University, Rajkot ?360 005
K.R. Mavani, D.S. Rana and S.K. Malik
DCMP & MS, TIFR, Mumbai ?400 005
P. Misra, B.N. Singh and L.M. Kukreja
Thin Film Laboratory, RRCAT, Indore ?452 013
Epitaxial thin films of La0.5Pr0.2Sr0.3MnO3 (LPSMO) and La0.5Pr0.2Ba0.3MnO3 (LPBMO) manganites on LAO substrates were synthesized using Pulsed Laser Deposition (PLD) technique with desired thickness of 150nm. To understand the effect of A-site cationic size disorder (σ2) on the electronic transport properties of La0.5Pr0.2R0.3MnO3 (R = Sr+2, Ba+2) thin films, the d.c. resistivity studies were carried out with and without applied fields. It is observed that the LPSMO films exhibit half metallic behavior in a broad range of temperature below the insulator ?metal transition (TIM) while the LPBMO films exhibit low temperature resistivity minima. These results have been discussed in the light of the cationic size disorder at A-site in both the films. Also, the effect of size disorder on the temperature coefficient of resistance (TCR), a parameter useful for temperature sensing application, has been understood in the present work.
102
PSP1.15
Improvement in field sensitivity of La-based manganite multilayered structure
P.S. Vachhani, J.H. Markna, J.A. Bhalodia and D.G. Kuberkar
Department of Physics, Saurashtra University, Rajkot ?360 005, India
P. Misra, B.N. Singh and L.M. Kukreja
Thin Film Lab, Centre for Advances Technology, Indore- 452 013, India
V. Ganesan and R. Rawat
UGC-DAE CSR, Indore centre, Indore ?452 017
We report the results on the field sensitivity studies on the manganite based La0.5Pr0.2Sr0.3MnO3 [5] / La0.5Pr0.2Ba0.3MnO3 [4] / STO multilayered structure grown by Pulsed Laser Deposition (PLD) technique. It is observed that a large Field Coefficient of Resistance (FCR) ~ 35% alongwith an appreciably large MR ~ 56% is exhibited by this heterostructure at RT. It is proposed that, the improved field sensitivity of the LPSMO/LPBMO/STO multilayer can be attributed to the spin dependent percolative transport at large number of interfaces in the heterostructure. The results on the microstructural, transport and magnetotransport properties of the multilayer studied will be discussed in detail.
103
PSP1.16
Synthesis and Characterization of PrCoO3 thin films grown by Pulsed Laser Deposition
Ram Prakash*, R. J. Choudhary, D. M. Phase
UGC-DAE Consortium for Scientific Research, Indore (M.P.) 452017, India.
*Email: ramprakash@csr.ernet.in
Cobaltates ACoO3, where A is the rare earth element, form an interesting class of compounds in the perovskite family having miscellaneous interesting properties. These compounds show magnetic and electric transitions. It is believed that such transitions occur due to the thermally driven spin state transition of Co3+ ions. The spin transition temperature and mechanism (from low spin to directly high spin or via intermediate spin states) for different A elements are different and the difference is mainly attributed to the different ionic radii of A elements. This leads to different pressure on CoO6 octahedra of the series members. The ground state of PrCoO3 (PCO) is nonmagnetic insulator. The crystal structure of PCO is a slightly distorted perovskite with orthorhombic structure (space group, Pbnm) at room temperature. To understand the effect of substrate induced strain on these properties in PCO, we have deposited thin films of PrCoO3 on (111) Si, (001) LaAlO3 (LAO) and (001) SrTiO3 (STO) substrates by pulsed laser deposition technique. The bulk target was prepared by sintering the powder, which was prepared by combustion method, at 1200 癈 for 12 hours. The KrF (wavelength =248 nm) excimer laser was used as source. The deposition was done at O2 partial pressure 100-400 mTorr. The substrate temperature was kept at 680 癈. These films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XRD) techniques. XRD results revel that all films are single phase and films on silicon substrates are polycrystalline while films deposited on STO, LAO are highly oriented along c-axis. The SEM images show highly smooth surface and films having very less particulates on the surface of the film. The XPS measurements used to get the chemical state of ions present in the films. XPS results clearly indicate that our films are free from impurity and chemical state are as expected for PrCoO3. The effect of deposition conditions on their physical properties is reported in this paper.
104
PSP1.17
Effect of laser energy on the structural and optical properties of non-reactive pulsed laser ablated tantalum oxide thin films
Renju R Krishnan, K. M. Nissamudeen, K. G. Gopchandran and V. P. Mahadevan Pillai*
Department of Optoelectronics, University of Kerala, Kariyavattom, Trivandrum-695581, Kerala, INDIA
*corresponding author: vpmpillai9@rediffmail.com
Thin films of Tantalum Oxide (Ta2O5) were deposited on glass substrates by non-reactive pulsed laser ablation technique using a 532 nm radiation from Spectra Physik Quanta Ray INDI Pulsed Nd:YAG laser having a pulse width of 9 ns and repetition frequency 10 Hz. Pressed pellets of Ta2O5 were used as the target. The chamber was evacuated to a base pressure of 5 x 10-6 mbar. The films were deposited by keeping target to substrate distance (On-axis) of 6.5 cm for a deposition time of 15 minutes. The effect of laser energy on the structure and morphology of the deposited films were investigated by varying the laser energy from 45 mJ to 65 mJ , in steps of 5 mJ. XRD studies show an amorphous nature for the as-deposited films irrespective of the laser energy. Stretching vibration mode of Ta-O-Ta was identified from the FTIR spectra of the films. The weak bands observed in the region 1000-1800 cm-1 in the spectra of films deposited at 60 mJ and 65 mJ is due to the absorbed impurities by the films. This suggests the possibility of using these films for gas sensing applications. The SEM micrographs showed a granular structure for the film deposited at a laser fluence of 45 mJ which changed to tubular form for the films deposited at 50 and 55 mJ.. The structural change was gradual and is described with SEM micrographs, the transition found effecting at about 50 mJ. At 60 mJ, the tubular form completely disappeared and the morphology again showed a granular form different from that obtained for 45 mJ. This structural change reveals the strong dependence of laser fluence on the morphology of Ta2O5 thin films.
105
PSP1.18
Room temperature luminescence from low temperature grown ZnMgO/ZnO Quantum wells using pulsed laser deposition.
R.S. Ajimsha, M.K.Jayaraj*
Optoelectronics Devices Laboratory, Department of Physics,
Cochin University of Science and Technology, Cochin-22.
P Misra, L.M. Kukreja
Thin Film Lab, Raja Ramanna Centre for Advanced Technology, Indore - 13
*Email: mkj@cusat.ac.in
ZnO based materials are excellent candidates for optoelectronics applications in the visible and ultra violet (UV) regions. A large exciton binding energy (59 meV) permits excitonic recombination even at room temperature (RT). In fact RT lasing in ZnO epilayers on sapphire (0001) has been experimentally demonstrated. The quantum well approach is necessary towards the goal of current injection laser. When lattice matched substrate ScAlMgO4 (SCAM) was used instead of sapphire, a significant improvement in the structural and optical properties was obtained, which was evident from their efficient photoluminescence. The scarce availability and expensive nature of SCAM substrates necessitated to improve the method of growing ZnMgO/ZnO quantum wells on sapphire. The literatures on the room temperature photoluminescence from ZnMgO/ZnO MQW on sapphire substrate are limited.
In this paper we report the growth of ZnMgO/ZnO MQWs of well layer thickness of 2 nm on sapphire (0001) substrate by PLD at a substrate temperature 400oC. The depositions were carried out with a high purity oxygen pressure of 10-4 mbar and laser energy density of 2 J/cm2. The target to substrate distance was 60 mm and the substrate temperature was kept at ~400oC. The typical growth rate (measured through separate experiments) at these optimized conditions was found to be 0.18 nm /s for ZnO and 0.14 nm/s for ZnMgO targets. These growth rates were used to determine the thickness of well and barrier layer respectively. Initially, a buffer layer of ZnO (thickness 50 nm) was deposited on sapphire substrate to minimize the lattice mismatch between sapphire and barrier layer of MQW. Then, ten periods of ZnMgO/ZnO layers were grown with a ZnMgO barrier layer thickness of 8 nm and a ZnO well layer thickness 2 nm on this ZnO template. Efficient room temperature photoluminescence was observed from these MQW抯, which was found to be blue shifted as compared to the RT near band edge PL from ZnO thin film as shown in the figure above. A detailed investigation on the temperature dependence of PL line width and spectral peak position of ZnMgO/ZnO MQW and ZnO thin film was made in a broad temperature range from 77 K to 300 K. The observations have been explained using the existing theoretical models.
106
PSP1.19
Novel feature of quantum transport through finite width mesoscopic ring
Santanu K. Maiti
1Theoretical Condensed Matter Physics, Saha Institute of Nuclear Physics,
1/AF, Bidhannagar, Kolkata-700 064, India
2Department of Physics, Narasinha Dutt College, 129, Belilious Road, Howrah-711 101,India
The advancements in nanoscience and technologies prompting a growing number of researchers across multiple disciplines to attempt to devise innovative ways for decreasing the size and increasing the performance of microelectronic circuits. One possible route is based on the idea of using molecules and molecular structures as functional devices. In 1974 Avriam et al.1 first studied theoretically the electron transport characteristics in molecular bridge systems. Later several numerous experiments2,3,4 have been carried out on electron transport through molecules placed between two non-superconducting electrodes with few nanometer separation. From experimental developments, theory can give a better insight in understanding the new mechanism of conductance but yet the complete knowledge of the conduction mechanism in this scale is not well understood even today.
In this article we explore the effect of edge disorder on quantum transport through a finite width mesoscopic ring attached with two semi-infinite metallic electrodes by the use of Green's function technique. Parametric calculations are given based on the tight-binding formulation5,6,7,8 to describe the transport properties through such bridge system. A novel transport phenomenon is observed which gives the enhancement of the current amplitude with the increase of the edge disorder strength in the strong disorder regime, while, the amplitude decreases in the weak disorder regime. This feature is completely opposite to that of the bulk disordered ring. In this context we also study the effects of the radius and the width of the ring on such transport and see that the transport properties are significantly influenced by them.
1. A. Aviram and M. Ratner, Chem. Phys. Lett. 29, 277 (1974).
2. J. Chen, M. A. Reed, A. M. Rawlett and J. M. Tour, Science 286, 1550 (1999).
3. M. A. Reed, C. Zhou, C. J. Muller, T. P. Burgin and J. M. Tour, Science 278, 252 (1997).
4. T. Dadosh, Y. Gordin, R. Krahne, I. Khivrich, D. Mahalu, V. Frydman, J. Sperling, A. Yacoby and I. Bar-Joseph, Nature 436, 677 (2005).
5. S. K. Maiti, Phys. Lett. A 362, 225 (2007).
6. S. K. Maiti, Solid State Commun. 142, 398 (2007).
7. S. K. Maiti, Physica B 394, 33 (2007).
8. S. K. Maiti, Phys. Lett. A 366, 114 (2007).
107
PSP1.20
Structural, Optical and Electrical Properties of Co and Ga codoped ZnO Thin Films Prepared by Pulsed Laser Deposition
M. Subramaniana*, G. Mohan Kumarb, P. Mishrac. Swati Pandyac, A. Dasd, B. N. Singhd, S. Venkatraja, S. Vijayalakshmia, V. Ganesanc, R. Jayavela,b and L.M. Kukrejad
aCrystal Growth Centre, Anna University, Chennai ?600 025
bCentre for Nanoscience and Technology, Anna University, Chennai ?600 025
cUGC-DAE CSR, Uniersity Campus, Khandwa Road, Indore-652 017
dThin Film Laboratory, RRCAT, Indore-652 013
ZnO, Zn0.95Co0.05O and Zn0.95Co0.05Ga0.03O films have been prepared by Pulsed laser deposition on sapphire substrates. The structural properties were characterized by HRXRD and Raman spectroscopy and the results reveal that the films are having wurtzite structure. But when we introduce Ga, full width half maximum for (002) peak was increases and this may be due to increase the disorder in the film. Surface analysis performed by scanning electron microscopy (SEM). From the UV-VIS spectroscopy were studied and the optical band gap increases for Mn and Ga codoped films compared with undoped ZnO and the results were discussed indetail. The electrical properties were studied and the results will discuss in detail. The magnetic properties were studied by VSM and discussed in detail.
108
PSP2.1
Structural, Optical and Electrical Properties of Zn1-(x+y)MnxGayO Thin Films Prepared by Pulsed Laser Deposition
M. Subramaniana*, P. IlanchezhiyanbP. Mishrac. Swati Pandyac, Amit Dasd, B. N. Singhd, S. Venkatraja, S. Vijayalakshmia, V. Ganesanc, R. Jayavela,b and L.M. Kukrejad
aCrystal Growth Centre, Anna University, Chennai ?600 025
bCentre for Nanoscience and Technology, Anna University, Chennai ?600 025
cUGC-DAE CSR, Uniersity Campus, Khandwa Road, Indore-652 017
dThin Film Laboratory, RRCAT, Indore-652 013
ZnO, Zn0.95Mn0.05O and Zn0.95Mn0.05Ga0.03O films have been prepared by Pulsed laser deposition on sapphire substrates. The structural properties were characterized by HRXRD and Raman spectroscopy and the results reveal that the films are having wurtzite structure. But when we introduce Ga, the crystalline quality found to be deteriorated. The surface analysis performed by scanning electron microscopy (SEM). From the UV-VIS spectroscopy were studied and the results will discuss in detail. The optical band gap increases for Mn and Ga codoped films compared with undoped ZnO. The electrical properties were studied and the results will discuss in detail. The magnetic properties were studied by VSM and discussed in detail.
109
PSP2.2
Effect of doping and substrate temperature on the structural and optical properties of reactive pulsed laser ablated Aluminium Oxide doped Tantalum Oxide thin films
Renju R Krishnan, K. M. Nissamudeen, K. G. Gopchandran and V. P. Mahadevan Pillai*
Department of Optoelectronics, University of Kerala, Kariavattom, Trivandrum-695581, Kerala, INDIA *corresponding author: vpmpillai9@rediffmail.com
Tantalum oxide (Ta2O5), a potential candidate in microelectronics industry, has received considerable attention because of its high dielectric constant, high refractive index, chemical and thermal stability and promise of being compatible with microelectronic processing. Thus far, Ta2O5 films have found applications in various fields such as gate insulators in metal oxide semiconductor (MOS) devices, optical coatings and antireflection coatings. Thin films of Ta2O5 doped with 5 wt. % Al2O3 (Aluminium oxide) are deposited on quartz substrates by reactive pulsed laser deposition (PLD) technique using a Q-switched Nd: YAG laser (Quanta-Ray INDI series, Spectra Physics) with frequency doubled 532 nm radiation of energy 200 mJ (pulse width 7 ns and pulse repetition frequency-10 Hz). The chamber is evacuated down to base pressure of 5 x 10-6 mbar prior to deposition. The films are deposited at different substrate temperature, viz, 300 , 673 , 773 , 873 and 973 K at an oxygen pressure of 0.002 mbar for duration of 15 minutes, keeping the target to substrate distance at 6.5 cm. The effect of Al2O3 doping and substrate temperature on the deposited films are systematically studied using Grazing Incidence X-ray Diffraction (GIXRD), Micro-Raman spectroscopy, Fourier Transfrom Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM) and UV-VIS spectrophotometry techniques.
110
PSP2.3
Optimizing the doping concentration in a single experiment by using Combinatorial Laser Molecular Beam Epitaxy (CLMBE)
Utpal S. Joshi1, Kenji Itaka2, Yuji Matsumoto3, Masatomo Sumiya4
and Hideomi Koinuma2,5
1. Department of Physics, School of Sciences, Gujarat University, Ahmedabad ? 380 009, India
2. Institute of Solid State Physics, The University of Tokyo, Kashiwa, Kashiwanoha, Chiba 277-8581, Japan
3. Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
4. Department of Electrical Engineering, Shizuoka University, 3-5-1, Hamamatsu, Japan
5. CREST, Japan Science & Technology Corporation (JST), 4-1-8, Honcho, Kawaguchi, 332-0012, Japan
p-type wide band gap oxide semiconductors are of fundamental importance for optoelectronics and photonics. There are well known n-type transparent & conducting oxide semiconductors (TCO), such as ZnO, TiO2, SnO2 etc. NiO, when doped with monovalent Li is a promising p-type semiconductor with an optical band gap of 3.7 eV. In order to obtain high conductivity with better optical transparency, optimum substitution of Li in NiO is required. It is time and energy consuming to achieve an optimized Li content in the NiO films by using the conventional pulsed laser ablation technique. Here we report on the combinatorial laser MBE technique of parallel thin film fabrication for rapid optimization of dopant concentration. Details of thin film fabrication by CLMBE will be presented. The films were characterized by grazing angle XRD, AFM, optical spectroscopy, secondary ion mass spectroscopy (SIMS) and room temperature conductivity measurements. Atomically smooth surface with RMS roughness comparable to the NiO unit cell was obtained. High optical transparency beyond 75% in the visible region was achieved. Room temperature conductivity of the order of 1.41 mho cm-1 was obtained in the 50 nm thick films grown on single crystalline MgO(100) substrates. Detailed SIMS analysis for the optimized Li concentration will be discussed.
This was carried out at Tokyo Institute of Technology under the BOYSCAST fellowship award to USJ by DST India.
111
PSP2.4
Superparamagnetism in epitaxial thin films of Fe, Cr, Co, Mn and V doped p-type NiO
U. V. Chhaya1, P.S. Raval2, P.A. Joshi2, S. Trivedi2, K. Itaka3, Y.Matsumoto4,
H. Koinuma3,5 and U.S. Joshi2,*
1. Physics Department, St. Xavier抯 College, Ahmedabad-380 009, India
2. Department of Physics, School of Sciences, Gujarat University, Ahmedabad ? 380 009, India
3. Institute of Solid State Physics, The University of Tokyo, Kashiwa, Kashiwanoha, Chiba 277-8581, Japan
4. Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
5. CREST, Japan Science & Technology Corporation (JST), 4-1-8, Honcho, Kawaguchi, 332-0012, Japan
e-mail : usjoshi@gmail com
Discovery of room temperature ferromagnetism in Co doped TiO2, prompted a growing interest to explore new diluted magnetic semiconductors. Recent theoretical calculations showed half metallic behavior in the vacancy induced NiO, which is considered to be an inherent property of almost all the known DMS compounds including transition metal doped III-V semiconductors. To explore a possible magnetic ordering in p-type wide band gap oxides, we have investigated the effect of transition metal substitution in NiO. Thin films of TM0.1Ni0.9Oy (TM = Co, Cr, Fe, Mn and V) were fabricated by pulsed laser deposition on MgO(100) substrate using KrF excimer laser (248 nm). XRD confirmed an epitaxial growth with a systematic shift in the NiO(200) peak corresponding to various transition metal ions. RMS roughness of the films, determined from the AFM was about 0.31 nm, which is less than the NiO unit cell. Magneto-optical Kerr effect exhibited negative magnetic rotation with a dip for all the 3d ions and a systematic shift in the dip with the photon energy, is attributed to d electron transitions in the dip levels of 3d ions. SQIUD measurements showed a superparamagnetic behavior down to 5 K in fe and Cr doped NiO films. Possible spin interaction of Ni and TM ions will be discussed.
We thank DST, India and Kato Foundation, Japan for financial support.
112
PSP2.5
Structural and Optical properties of GdO doped ZnO Thin Films by Pulsed Laser Deposition Technique
R.Vinodkumar , D.Beena, Geo Rajan, Jayasree R.S. and V.P.Mahadevan Pillai*.
Department of Optoelectronics, University of Kerala, Thiruvananthapuram, Kerala,
India ?695581.
e-mail- vpmpillai9@rediffmail.com
Recent developments in the fabrication of devices like nano-scale lasers, electrochemically gated quantum doted transistor and the highly efficient exciton UV lasing action under optical pumping from the ZnO nanoclusters and thin films, indicate that ZnO is a promising material for applications in modern nano-electronics and nanophotonics. Zinc oxide is an n-type semiconductor with a wide band gap of 3 37 eV[1-2]. Wei Lin et.al. have studied the structural, electrical and optical properties of GdO doped ZnO thin films prepared by RF magnetron sputtering[3]. To the best of our knowledge this is the first report PLD prepared GdO doped ZnO films. Undoped ZnO and GdO doped ZnO thin films were deposited on an optically flat fused silica (quartz) substrate using pulsed laser deposition technique. The depositions were carried out inside a vacuum chamber using a Q-switched Nd: YAG laser (Quanta-Ray INDI-series, Spectra Physics) with frequency doubled 532 nm radiation with pulse width 7 ns and repetition rate 10 Hz. The deposition was carried out under room temperature and a base pressure of 6 x 10-6 .mbar. The distance between the substrate and target was 6 cm and the laser energy for the deposition was 160 mJ. The experiment was repeated at different duration and at different annealing temperatures. The crystal structure and surface morphology of the films were investigated using X-ray diffraction and AFM measurements. Optical absorption spectra were recorded using a UV-VIS double beam spectrophotometer (JASCO V 550) in the spectral range of 200 ?900 nm. Photoluminescence spectra of the samples were recorded by Horiba Jobin Yvon Flourolog III modular spectroflourometer. The optical constants are calculated from the transmission spectra using the swanepoel抯 envelope method. In addition to the UV peaking there is a deep level emission in the blue and green region. The influence of GdO doping, ablation time and annealing temperature on the structural and optical properties of the ZnO thin films are investigated.
References
1. S . Lanzerstorfer et al, Appl. Phys . Lett. 72, 809, 1998
2.Bixia Lin and Zhuxi Fu , Yunbo Jia, Appl. Phys. Lett., 79, 2001 3.M.J.H.Henseler,W.C.T.Lee,P.Miller,S.M.Durbin,R.J.Reeves.J.Crystal Growth
287,48,2006.
113
PSP2.6
Structural, Morphological and Optical studies of Potassium Lithium Niobate thin films prepared under ambient conditions of substrate temperature.
V. Jayasree, R Vinod Kumar, R Ratheesha, V. P Mahadevan Pillai & V. U Nayar*
Department of Optoelectronics, University of Kerala, Kariavattom, Trivandrum, Kerala, 695 581 India
a Centre for materials for electronic Technology, Athani P. O Thrissure 680771, India.
* nayarvu@sancharnet.in
Filled tungsten- bronze ferroelectrics which have a general chemical formula (A1)(A2)2C2(B1)(B2)4O15 have attracted much attention as materials for the fabrication of optoelectronic devices, especially for nonlinear optical applications because they have a large optical damage threshold originating from their crystal structure. K3Li2Nb5O15 (KLN) is a typical compound of completely filled tungsten- bronze ferroelectrics having tetragonal structure and is one of the most promising material for various optical applications because of its large electro optic, nonlinear optic and piezoelectric properties. Pulsed Laser Deposition is a suitable technique for depositing such complex materials .In the present investigation, thin films of the ferroelectric potassium lithium niobate are prepared by pulsed laser deposition technique on glass substrate under reactive atmosphere with different substrate temperatures and their morphological and optical properties are studied. The irradiations are performed using a Q- switched Nd: YAG laser with frequency doubled 532 nm radiation of energy 70 mJ, having pulse width 7 ns and repetition frequency 10 Hz (Quanta ? Ray INDI ?series, Spectra Physics). The laser impinged on the target at 450 with respect to the normal in a dynamic flow of oxygen. The vacuum chamber was evacuated down to a base pressure of 4.8x10-6 mbar using a diffusion pump and two rotary pumps. The depositions of the films were done on a glass substrate kept at a distance of 70 mm from the target at various background pressures. The target was prepared from the stoichiometric compositions of K2CO3 (99.99%), Li2CO3 (99.99%) and Nb2O5 (99.99%). These materials were mixed well using an agate mortar for an hour using distilled water as solvent. The resultant mixture is dried in an oven at 100 ºC. The mixture is then transferred to an alumina crucible and calcined at 1100 ºC for 2 hours. The powder is then pressed into the pellet of size 7 mm thickness and 11 mm diameter and the pellets are heated to 1000 ºC for 2 hours to get well sintered target for PLD operation. During ablation the target was rotated with constant speed to avoid pitting of target at any given spot and to obtain uniform thin films. The films were prepared in a reactive atmosphere for an ablation time of 20 minutes. This paper reports the effect of the substrate temperature on the structural, morphological and optical properties of laser ablated potassium lithium niobate thin films. The crystalline nature and orientations of these films are characterized by gracing incidence X-ray diffraction (GIXRD) (Siemens D5000 diffractometer) measurements employing Cu Kα radiation with a wavelength of 0.15405 nm. The surface morphology of the deposited films has been investigated using the AFM images recorded by a Digital Instrument Nanoscope E atomic force microscope. AFM tip of Si3N4 having a force constant of 0.58 N/m in contact mode operation has been employed for the measurements. The optical transmission and reflectance spectra of the films are recorded using a JASCO V 550 UV-VIS double beam spectrophotometer in the wavelength range of 190-900 nm. It has been found that the substrate temperature has a strong influence on the structure morphology and optical characteristics of KLN thin films.
1. R. Delmdahl: LaserFocusWorld, July 2002, Optoelectronics World Supplement (2002) pp. 3.
2.T. Kuntze, M. Panzner, U. Klotzbach, E. Beyer: Proc. 4th International Symposium on Laser Precision Microfabrication, Munich (2003) pp. 543.
3.G. Spiecker, R. Delmdahl: Laser Magazin 6, (2002) pp. 10.
4.M. N. R. Ashfold, F. Claeyssens, G. M. Fuge, S. J. Henley: Chem. Soc. Rev., 33 (2003) pp. 23.
114
PSP2.7
Studies on effect of europium concentration on the photoemission of laser ablated Y2O3:Eu based nano-phosphors.
K.M. Nissamudeen, Renju R Krishnan, Geo Rajan and K.G. Gopchandran
Department of Optoelectronics, University of Kerala, Kariavattom, Thiruvananthapuram
gopchandran@yahoo.com
Phosphors are essential materials in display applications. Oxide-based phosphors are likely to emerge as the potential choice for the FED red phosphor. Among those oxide-based phosphors, there has been significant research interest in the development of Y2O3:Eu thin films as one of the most promising oxide based red phosphor systems. Yttrium oxide mixed with europium exhibit strong UV and cathode-ray-excited luminescence that are useful in lamp and display applications. Dielectric Y2O3 film has recently attracted much attention for its potential application as an electric insulation layer in electroluminescent devices and high-density dynamic random access memory gate dielectrics because of its high band gap (5.8 eV) and large dielectric constant (14 to18). Another important application of Y2O3 has been in luminescent displays as a host material for rare-earth ions, specifically europium, in order to get emission of red light. In the present study thin films were deposited under a vacuum of 10-6 mbar on fused amorphous quartz substrates using a Q- switched Nd: YAG laser, 532 nm, pulse width 9 n sec, and repetition frequency of 10 Hz, with sintered Y2O3 pellets having different europium concentration as target material. Attempts were made to understand the effect of europium concentration and annealing process on the photoemission properties of the films.
A europium concentration of 8 wt% and an annealing temperature of 1173 K were found to be optimum conditions for maximum photoemission. The dependence of structure and morphology of the films on the photoemission intensity are described with XRD patterns and images obtained from AFM and SEM studies.
115
PSP2.8
Studies on Si Doped ZnO Thin Films Grown by Sequential Pulsed Laser Deposition
A. K. Das*, B. N. Singh, P. Misra and L. M. Kukreja
Thin Film Laboratory, Raja Ramanna Centre for Advanced Technology, Indore 452 013
*Corresponding author email: amitdas@cat.ernet.in
We have grown ZnO films doped with different concentrations of Si on sapphire substrates using sequential Pulsed Laser Deposition. These films show excellent optical and electrical characteristics suitable for transparent conducting electrodes applications. 3rd harmonic of a Q-switched Nd:YAG laser (355 nm, 10 Hz & 6 ns) at a fluence of ~ 1 J/cm2 was used for the ablation of the Si and ZnO targets consecutively, with variable ratio of their respective times of ablation to vary the Si concentration in these films. The depositions were carried out at 600ºC substrate temperature and 1x10-4 Torr of oxygen ambient pressure. All the films were found to be highly transparent (~80%) in the visible spectral region as shown in figure 1. This figure also shows that the band-gap of ZnO increased slightly with increasing Si concentration. The x-ray diffraction studies on these films revealed hexagonal wurtzite structure with high c-axis orientation. Figure 2 shows the variation of the electrical resistivity of the ZnO films with different Si concentrations. As can be seen the resistivity of the films initially decreased drastically and then increased modestly with increasing the Si concentration. This could be because Si, being in group IV, might act as a donor, an acceptor or go to the interstitial sites. However, it appears that the predominant role of Si, particularly at low concentrations is to act as a donor, which in turn is expected to enhance the conduction electron density, thereby decreasing the resistivity.
Figure 1 Figure 2
116
PSP2.9
Textured CeO2 thin films on amorphous substrate by PLD at room temperature
T K Chaudhuri
Dr. K C Patel Research and Development Centre
Education Campus ?Changa, Changa (Petlad), Anand, Gujarat 388 421, INDIA
tkchaudhuri@gmail.com
and
R N Bhattacharya
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden,
Colorado 80401, USA
Textured CeO2 thin films are of special interest because of their use as templates for growing textured silicon and yttrium barium copper oxide (YBCO) films. Further low temperature deposition of textured CeO2 films on amorphous substrates may open up the possibility of fabricating textured Si films on glass and plastics. Textured (200) CeO2 films have been grown at room temperature on amorphous quartz glass either by PLD based high energy ion beam-assisted deposition (IBAD) or by two-beam IBAD. However, IBAD-like conditions may be attained if suitable laser pulse energy, substrate-target distance and gas pressure is selected. The generation of high speed particles in the plume during PLD is likely to assist in texturing of film. This paper reports the use of such a condition to deposit of textured CeO2 films on glass by PLD at room temperature. CeO2 films were deposited at RT (~20 oC) in a standard PLD chamber (Neocera) with an excimer KrF laser (Lambda Physik, Compex 201, λ=248 nm) operated at 3 to 10 Hz and fluence of 2 to 4 J/cm2. Gas used was either 0.4 Pa of O2 or forming gas (4% H2 and 96% Ar). The target was aligned parallel to the surface of the substrate separated by 2.5 cm. The thickness of films was around 0.2 μm. The films were characterized by X-ray diffractometer (XGEN-4000, Scintag Inc., USA) and atomic force microscopy (Autoprobe cp, Park Scientific Instruments, USA).
Sample Gas Repetition
Rate (Hz)
Fluence
(J/cm2)
Film A oxygen 3 2
Film B oxygen 10 2
Film C forming 3 2
Film D forming 10 2
Film E forming 10 4
Fig.1 . X-ray diffraction plot of CeO2 films on glass
prepared at different conditions as above.
The XRD plots of typical CeO2 films prepared at different PLD conditions are shown in Fig. 1 A to B. The figure reveals that in general the CeO2 films are polycrystalline in nature. Films A and B deposited in O2 (2 Jcm-2 fluence) have weak broad XRD lines of (111) and (311) and very weak (220) implying poor crystallinity. Further, increasing the rate of deposition from 3 Hz (film a) to 10 Hz (Film B) did not have any effect on the crystallinity or orientation of films. Film prepared in forming gas (Film C) with repetition rate of 3 Hz and fluence of 2 Jcm-2 exhibits only weak XRD lines of (200) and (220), which is different than that observed in films A and B. However, XRD plots of A, B and C films show that there is a tendency for CeO2 films to grow along (110) direction if deposited with the experimental conditions of the present investigation. XRD plot of film (Film d) deposited with higher repetition rate of 10 Hz shows a very strong (220) line along with a very weak (111) line. Pole figure in (111) direction did not show any distinct poles but a ring which means that in-plane orientation is absent in these films. This implies that these films are preferentially (out-of-plane) orientated along the (110) direction. The rate of deposition has a pronounced effect on the crystallinity of CeO2 films prepared in forming gas. By increasing the rate of deposition from 3 Hz to 10 Hz the poor polycrystalline films (Film C) were changed to highly oriented polycrystalline films (Film D) due to increased flux of laser ablated material reaching the substrate. The AFM studies show that CeO2 films are fairly smooth with Root-Mean-Square roughness of about 2 nm. The above results indicate that the preferred direction of growth for CeO2 film on glass at room temperature is (110) if deposited by PLD using the conditions mentioned above. This implies that (100) growth may be effected by tilting the substrate by 45o with respect to the normal of the surface of the target.
117
PSP2.10
Synthesis of II-VI Oxide Semiconductor Nanocrystals by Pulsed Laser Ablation in Liquid Media
S.C. Singh, R.K. Swarnkar and R. Gopal
Laser and Spectroscopy Laboratory, Department of Physics,
University of Allahabad, Allahabad-211002
Spectra2@rediffmail.com
Pulsed laser ablation in liquid media with different ablation parameters is used for the synthesis of nanocrystals of II-VI semiconductor oxides. Various ablation parameters are wavelength, energy, focusing condition, temperature and pressure of ablation media, nature and concentration of surfactant used, and dipole moment of liquid media. Possible mechanism of the synthesis of these nanocrystals will be discussed. UV-visible absorption, XRD, SEM, TEM, FTIR, Raman, and Photoluminescence spectroscopy will be used for characterization of produced nanocrystals. Oxides and sulphides nanocrystals of Zinc and Cadmium will be main theme of the presentation. A comparative study between different (ZnO, CdO, ZnS, CdS) nanocrystals produced by laser ablation will be investigated.
118
PSP2.11
Studies on CoZnO thin films grown by Pulsed Laser Deposition
Satyapal S. Rathore*, A.K.Das, B.N. Singh, P.Misra and L.M.Kukreja
*Dept. of Applied Physics, Birla Institute of Technology, Mesra 835 215 Thin Film Lab., Raja Ramanna Centre for Advanced Technology Indore 452 013
* satyapal03@gmail.com
Currently there is world wide interest in developing Diluted Magnetic Semiconductors based on wide bandgap Oxide materials ZnO, TiO2 and ZrO2 etc for futuristic spintronic and spin-photonic devices based entirely on oxide materials. Among these materials ZnO is of prime interest due to its rugged wurtzite crystal structure, ability of controlled bi-polar carrier doping and large solubility of magnetic impurities. Recent theoretical and experimental reports indicated that the ZnO doped with transition metal elements (eg, Mn, Co, Ni and Fe etc) may undergo ferromagnetic transitions even at room temperatures. In the present work, we have deposited Co doped ZnO films by Pulsed Laser Deposition and studied their optical and structural properties. 3rd harmonic of a Q-switched Nd:YAG laser (355 nm, 10 Hz & 6 ns) at a fluence of ~ 1 J/cm2 was used for the ablation of Co doped ZnO pellets. The pellets containing 3, 5 and 7 mole % of Co were prepared by the standard cold ceramic processing techniques and then sintered at 1000ºC for 2 Hrs. Prior to the deposition, the chamber was evacuated to a base vacuum of 1x10-6 mbar and depositions were carried out at an oxygen partial pressure of 1x10-4 mbar and at a substrate temperature of 600oC. The Transmission spectra of these films taken using UV-Visible spectrophotometer in the wavelength range 800 nm to 250 nm is shown in the figure 1 below. The conspicuous mid-gap absorption bands at ~659 nm, 616 nm and 568 nm can clearly be seen in the transmission spectra of all the compositions. These mid gap absorption bands are due to the Co2+ interatomic d-d transition associated with the crystal-field splitting in ZnO host. And are represented as the transitions from 4A2(F) to 2E(G), 4T1(P) and 2A1(G) respectively. These transitions implies that Co2+ have substituted the tetrahedrally coordinated Zn sites in ZnO lattice. The Bandgap was calculated from the transmission spectra using Tauc plot. The bandgap of the films was found to red shifted with increasing Co concentration. The high resolution X-ray diffraction pattern of these films as shown in figure 2 also confirmed hexagonal wurtzite structure of CoZnO with a high c axis orientation and without any impurity segregation. Further works in this direction are underway.
300400500600700800020406080100Co~3%Co~5%Co2+ interatomic d-d transition(c)(b)(a)% TransmittanceWavelength (
nm)Co~7%(a) λ~ 568nm [ 4A2(F) --- 2A1(G)](b) λ~616nm [ 4A2(F) --- 4T1(P)](c) λ~659nm [ 4A2(F) --- 2E(G)]152025303540Intensity (
arb. unit)ω (degrees) (0004) ZnO(0006) Al2O3(0002) ZnO Figure 1 Figure 2
119
PSP2.12
Laser assisted growth of Eu3+ doped Ba0.7Sr0.3TiO3 thin film for optoelectronic and ferroelectric application
R.Reshmi1,, M.K.Jayaraj1 ,M.T.Sebastian2
1Optoelectronics Device Laboratory, Department Of Physics
Cochin University of Science and Technology
Kochi-682022, India
2Regional Research Laboratory, Thiruvananthapuram 695019, India,
Email: mkj@cusat.ac.in
Luminescent rare earth doped materials are extensively being studied because of their technological application in photonic devices and next generation flat panel displays. Rare earth ions exhibit a characteristic intra 4f shell luminescence which is almost insensitive to host material and temperature. This feature can be used to tune the emission spectrum for specific application by the appropriate doping of rare earth ions in host material. Pervoskite structure materials are attractive as host materials for rare earth doping because of their application in integrated light emitting devices, field emission devices (FED抯) all solid ?compact laser devices operating in the blue-green region and positive temperature coefficient (PTC) resistors. ABO3 type of pervoskite compounds such as BaTiO3, SrTiO3 and solid solution of them viz BaxSr(1-x)TiO3 (BST) have drawn a good deal of attention due to their attractive ferroelectric and electro optic properties.
In this work we report the Pulsed Laser deposition of Europium doped barium strontium titanate (BST:Eu) thin films. The structural, optical properties and electrical properties of the PLD grown BST film have been investigated. The photoluminescence spectrum showed the transitions of Eu3+ at 615nm (5D0 - 7F2) and 699 nm (5D0 - 7F3) on excitation with 405nm. The PL intensity of the BST:Eu films was found to increase with substrate temperature. The BST:Eu films can be used for both ferroelectric as well as for optoelectronic application.
120
PSP2.13
Comparative studies of irradiation induced modifications in Fe3O4 thin films on MgO and Si substrates grown by pulsed laser ablation
Shailja Tiwari*, Ram Prakash, R. J. Choudhary and D. M. Phase
UGC-DAE Consortium for Scientific Research, Indore-452 017, INDIA
Ravi Kumar
Inter University Accelerator Centre, New Delhi-110067, INDIA
*Corresponding author email: shailja@csr.ernet.in
Magnetite (Fe3O4) is an important half metallic ferromagnetic material and has prospects in spintronic devices. Some of its interesting properties are its high Curie temperature (850 K), low electrical resistivity at room temperature, charge ordering at Verwey transition (Tv =120K) with a concomitant structural transition from cubic high temperature to a monoclinic low temperature phase. We have deposited magnetite thin films using pulsed laser deposition technique on single crystal MgO (100) and Si (111) substrates. We have irradiated these films with 200 MeV Au ions and have studied the effect of irradiation on structural properties of these films. The fluence value of irradiation has been varied in the range of 5 x 1010 ions/cm2 to 1 x 1012 ions/cm2. Before irradiation, X-ray diffraction study of pristine samples shows the spinel cubic structure of the films with preferential (111) orientation on Si (111) and (100) orientation on MgO (100) substrate. Raman spectroscopy suggests the single-phase growth of Fe3O4 films on both the substrates. After irradiation, XRD and Raman spectroscopy suggest that Fe3O4 film on Si substrate is more irradiation resistant than on MgO substrate. Possible reason for this behavior could be related to the lattice mismatch of Fe3O4 with Si and MgO substrate. Because of the fact that the lattice parameter of Fe3O4 is almost half of the MgO substrate, the film is epitaxial with the presence of strain and anti phase boundaries. After irradiation, these defects are annealed and modify the structure of Fe3O4. Whereas in the case of Si substrate, due to higher lattice mismatch, the substrate control over the film growth is weak and the growth orientation is determined by the thermodynamically stable state having minimum internal energy. Therefore, such a film is rather free from substrate induced strain and other related defects and, hence possibly more stable.
121
PSP2.14
Synthesis and Characterization of SnO2 Thin Films by PLD for Sensor Applications
K. Prabakar, R. Krishnan, B. Yasodhaadevi*, Ashok S. Chauhan*, S. Tripura Sundari, S. Dash and J. Jayapandian
Materials Science Division,
Indira Gandhi Centre for Atomic Research,
Kalpakkam ?603102,Tamil Nadu.
* Amity Institute of Nanotechnology
Amity University, Uttar Pradesh
Tin Oxide (SnO2) is a transparent n-type semiconductor with high chemical and mechanical stability with a stable tetragonal phase. Tin oxide films have attracted great scientific interest because of its wide applications ranging from manufacturing of flat panel displays, transparent conductive electrodes in thin film solar cells, gas sensors to several opto-electronic devices. In the present work, amorphous and polycrystalline SnO2 thin films were deposited on silicon and quartz substrates using Pulse Laser Deposition (PLD) technique at different temperatures. Depositions were also carried out for various oxygen partial pressures ranging from 0.003 Pa to 30 Pa. Structure, morphology and optical properties of these thin films were investigated using XRD, AFM, optical absorption and spectroscopic ellipsometry. The films deposited under high vacuum conditions at room temperature were found to be amorphous. Polycrystalline films could be obtained either by post deposition annealing of these films in air at 700 癈 or by depositing these films under increased partial pressure of oxygen at 350 癈. The refractive indices of these films were calculated from ellipsometric parameters measured in the range 350-800 nm. The band gap of the as-deposited amorphous films and e polycrystalline films was calculated to be 3.17 eV and 3.67 eV respectively. This corroborates well with the optical absorption measurements made using UV-Visible spectroscopy. The widening of the band gap can be attributed to the reduction in oxygen vacancies that are responsible for n-type semi-conducting behavior. In addition, change in surface electronic properties brought about by embedding metal and/or oxide nanoparticles in SnO2 matrix by PLD for possible applications in realm of sensors will be presented.
122
123
PSP2.15
Structural and electrical characterization of pulsed laser deposited Ga doped
ZnO thin films on Si(100)
S.D. Shinde, S.M. Jejurikar and K.P. Adhi
Center for Advanced Studies in Materials Science and Condensed Matter Physics,
Department of Physics,
University of Pune, Pune 411 007, India.
Corresponding author: shashi@physics.unipune.ernet.in
Highly c-axis oriented thin films of Ga doped ZnO were grown on SiOx/Si(100)
substrate using pulsed laser deposition technique. Thin films with different Ga concentrations
viz. 0, 3 and 5 % were prepared under identical deposition conditions. Variation of Ga in ZnO
thin films is observed to affect its structural properties evident from X-ray diffraction
technique. Surface morphology investigations using AFM technique also support X-ray
analysis as far as crystallite size is concerned. Electrical measurements using four-point probe
technique shows significant decrease in resistance with increase in Ga concentration in ZnO.
124
PSP2.16
Thickness dependent multiferroic properties of Bi0.7Dy0.3FeO3 polycrystalline
thin films grown by pulse laser deposition technique
Prashanthi K., S. P. Dattagupta, R. Pinto and V. R. Palkar
Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400 076, India
e-mail: palkar@ee.iitb.ac.in
In recent years there is growing interest in developing multiferroic systems that are simultaneously exhibiting
magnetic and ferroelectric ordering at room temperature. It is mainly due to their potential for device
applications and fascinating physics. Moreover, most of the known multiferroic systems are typically
antiferromagnetic with transition temperatures below room temperature. Earlier we have shown that
Bi0.6La0.1Dy0.3FeO3 thin films grown on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition technique are
multiferroic at room temperature1. In recent study we observed that the removal of La from Bi0.6La0.1Dy0.3FeO3
phase helps to enhance magnetic properties to a large extent while keeping ferroelectric properties and leakage
current undisturbed. It confirms non-requirement of La in case of Dy modified BiFeO3 for stabilization of
perovskite phase or to reduce leakage current. Study of thickness dependence on multiferroic properties of
Bi0.7Dy0.3FeO3 films has indicated some interesting behavior. Magnetic anisotropy developed non-linearly with
the thickness could be correlated to internal stress developed in random order during growth process (Fig. 1).
The lattice cell parameter c also changes randomly with the thickness of the film. However, the trend is similar
to that of stress. The saturation polarization (Ps) values scale with c parameter (Fig. 2). This information could
be meaningfully utilized while designing device patterns using such advanced but complex system.
Figure 1 Figure 2
1 V. R. Palkar, R. Anisha, R. Pinto & S. Bhattacharya, to appear in Journal of M
(2007)
015030045013.1613.2013.2413.28 Film Thickness (nm) c
parameter (
Å)100200300400 Stress (M Pa)(a)-10-50510-1300-65006501300 // to field ⊥ to field100 nm-10-50510-1200-60006001200 // to field ⊥ to field500 nm-10-50510-1200-60006001200 220 nm // to field ⊥ to fieldMagnetic field (KOe)M (emu/cc)aterials Research .
22, 2068 (KV/cm)
-70 -35 0 35 70
-30
-15
0
15
30
100 nm
220 nm
500 nm
Electric field
Polarization (μC/cm2)
(b)
125
PSP2.17
Electroresistive and Magnetoresistive effects in electron doped manganite
La0.7Ce0.3MnO3 thin films
Kavita Bajaja, b, John Jesudasana, Vivas Bagwea, Pratap Raychaudhuria
aDepartment of Condensed Matter Physics and Materials Sciences,
Tata Institute of Fundamental Research, Homi Bhabha Rd.,
Colaba, Mumbai 400005, India.
bDepartment of Physics, Mumbai University, Mumbai 400098, India.
The influence of electric current and magnetic field separately and in conjugation on the
transport behavior of patterned La0.7Ce0.3 MnO3 thin films on (001) LaAlO3 substrate is
studied. Measurements were carried out in the regime of low current densities, for dc currents.
In absence of magnetic field significant reduction in peak resistance (Rp) was found with
increasing bias current. This effect is also present when a magnetic field is applied though the
magnitude of the electroresistance (ER=[R(I=0.05μA)-R(I=50μA)]/R(I=50μA)) decreases.
The metal-insulator transition temperature (Tp) increases both with increasing current and
with magnetic field. The current-voltage characteristics at various temperatures above and
below Tp show nonlinearity for small currents due to electroresistance and large currents due
to Joule heating. The behavior of resistance with current is similar at various temperatures
decreasing initially with increasing current and then nearly leveling off. We observe an
interesting correlation between effect of electric current and magnetic field: The
magnetoresistance (MR = [RH=0-RH=1T]/RH=0) decreases with increasing bias current, while ER
decreases with increasing magnetic field. Both ER and MR show a maximum near Tp. This
interesting correlation between these two effects suggests that both these effects arise from
the same origin.
126
PSP2.18
Size dependent study of CuFe2O4 nanoparticles
Archana Rai* and M. Banerjee
*Department of Physics, Indian Institute of Technology, Powai,
Mmbai-400 076
School of Physics, Vigyan Bhawan, Takshashila Campus, DAVV,
Khandwa Road, Indore: 452017, India
E-mail: archana3@iitb.ac.in ,
The properties of nanostructured magnetic materials are extraordinarily different from those
of conventional magnetic systems. Exchange coupling, super-paramagnetism and tunneling
magnetoresistance, all describe some of the unique characteristics that could be obtained from
nanomagnetic and bulk materials produced from nanomaterials. Nanocryrstalline ferrites
have emerged as a new class of technologically important magnetic materials1, 2.Cu1-
xNixFe2O4 nanoparticles were prepared by co-precipitation and digestion method. The average
particles size as determined by XRD was found to be from 3 nm to 11nm. AFM confirms the
formation of spherical shape spinel nanoparticles. Mössbauer spectroscopic investigation has
been carried out to study the distribution of cations among A and B sites. Mössbauer spectra
for x= 0.25, 0.5, 0.75 and 1.0 shows superparamagnetic behavior at room temperature.
Mössbauer studies of our samples were also performed at low temperature i.e. at 25 K.
Absorption spectra shows clear transformation from super-paramagnetic behavior to
ferrimagnetic while going from room temperature to low temperature. Iron is present as Fe3+
in both tetrahedral as well as octahedral sites.
Keywords: Ferrites, Mössbauer spectroscopy, Super-paramagnetism
References
1. M.Kishimoto, Y.Sakurai and T. Ajima, J. Appl. Phys, 76, 7506 (1994).
2. R.D. McMichael, R.D. Shull, L.J Swastzendruberand L.H.Benett, J. Magn.
Magn. Mater. 111, 29 (1992).
Fig.1 AFM image of CuFe2O4 nanoparticles of size 7.2 nm
127
PSP2.19
A theoretical approach to the effect of particle size on the luminescence intensity
in nanocrystals
Anamika Awadhwal, B.P. Chandra*
Department of Post Graduate Studies and Research in Physics and Electronics
Rani Durgavati University, Jabalpur-482001
*Ex Vice-Chancellor Pt. Ravishankar Shukla University, Raipur-492010
The recombination of electron and hole occurs when electron is within the capture distance
from the recombination center. In ultrafine particles, all the excited electrons may be within
the capturing range and recombination will depend on the Coulomb force between them,
which increases as the particle size is reduced. This consideration suggest high luminescence
intensity for smaller particles.In the present paper the luminescence intensity in nanocrystals
and the relation between the intensity and particle size have been discussed.
PSP2.20 Centre for Laser Technologyfor application in photonicpossible approaches, is utilizing third orparticular the ability action of optical field. This pror non-lidoped polymer filmconsiderable creative freThe optical absorption 800nm using PerkinEimThird Order Non-Linear Optical PropertFilm Rekha R.K*, A. Ra, Department of* rekhasri71@There is a continuing interest in the developmen switches, optical liof these materials to chaoperty is usually near refractive index. We report the th using Z-Scan technique withedom for optical and mproperties of the dye in er spectrophotometer & shies of Eurhodin Dye Dopemalingam , G. Vinitha Physics, Anna Universityyahoo.com t of optical material, which womiter, 3D optical data storage etder non-linear optical properties of nge the value of the refractive idescribed in terms ird orde polymechanical design. methanol were investigated in thown in Fig
d Ppolymer
, Chennai-600 025
uld be suitable
c., One of the
such materials, in
ndex under the
of third order susceptibility
r non-linear response of neutral red dye
er (PMMA) host, because they have
e range 300?br> 1. Methanol was chosen as
additive because it combines good solubility and enhancement of host laser- damage
resistance. The absorption peak wavelength (λa), molar extinction coefficient (ε), Bandwidth
(Δν) 1/2, Oscillator strength (f) were calculated and shown in Table 1.
The dye doped polymer film was prepared by bulk polymerization method, by pouring the
viscous PMMA + Dye mixture with initiator mixture on to a glass slide placed inside a glass
enclosure kept at temperature of 400Cin temperature controlled water bath. The Z-Scan
experiment was performed using second harmonic Nd:Yag laser which was focused by 3.5cm
focal length lens. The laser beam waist ω0 at the focus is measured to be 18.7μm & Rayleigh
range ZR =_2.1mm.The peak intensity Io of the incident laser beam was 3.7KMW/cm2. The
Rayleigh length was found to be satisfying the basic criterion of the Z-Scan experiment, ZR >
L.
Table1: Optical absorption and Non Linear parameters of Dye doped polymer film
The transmitted energy through the sample was measured by using a photo detector fed to the digital
power meter. Both open and closed aperture studies were carried out to find out the absorptive (β)and
refractive non- linearity (n2) in the film. For an Open aperture Z-Scan a lens to collect the entire laser
beam transmitted through the sample replaced the aperture. A Pre-focal transmittance maximum (Peak)
followed by post focal transmittance minimum (Valley) obtained from the closed aperture Z-Scan data,
shown in Fig 3 indicates that the sign of refraction non-linearity is negative i.e self-defocusing. The
self-defocusing effect is due to the local variation of refractive index with temperature. The enhanced
transmission near the focus in the open aperture shown in Fig 2 is indicative of saturation absorption at
high intensity. Pure non-linear refraction of the film is shown in Fig 4 (division of open/closed)
Optical absorption parameters Non Linear parameters ?Dye doped polymer film
λa (nm) ε X
104
Lmol-1
Cm-1
(Δν)1/2
cm
-1
fX10-
24
Lmol-1
cm-2
ΔTp-v n2 X10-7
cm2/W
βX10-3
cm/W
χR
(3) X10-6
(e.s.u)
χI
(3) X10-7
(e.s.u)
lχ(3)l X10-6
(e.s.u)
553 .07 4700 .0133 1.5192 -1.16 -1.572 5.233 -2.97 5.23
128
UV-VI S absor pt i on spect r a
of Neut r al Red
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
350 400 450 500 550 600 650 700 750
wa v e l e n g t h ( nm)
Open aperture Z -Scan curve for
dye doped polymer film
0.94
0.99
1.04
1.09
1.14
1.19
-15 -10 -5 0 5 10 15
Z (mm)
Normalized transmittance
Closed Z- scan curve- dye
doped polymer film
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
-15 -10 -5 0 5 10 15
Z(mm)
Normalized transmittance
00.20.4-15-10-505Z (mm) Fig 2 e Fig 14 (3)
Fig
The study shows that neutral red film sorption and negative
non-linearity. The dye doped polymer film
susceptibility lχ l can be a promising candidate for optical limiter and photonic
application.
References:
1. M.S. Bahae, A.A Said, T H Wei, D J Hagan and E W Van Stryland, IEEE J.
Quantum Electronics 26, 760 (1990) 2. A.Costela, I.Garcia-Marino,
J.M. Figuera, F.Amat Guerri, J. Barroso, R.Sastre, Opt.Commun. 130
3. J. Wang, M. S. Bahae, A.A Said, D J Hagan and E W Van Stryland, J. Opt.
Soc. Am. B Vol.11, No.6 (1994)
Fig 3 xhibited saturation ab with reasonably high third order
PURE NON LINEAR REFRACTION CURVE OF DYE
DOPED POLYMER FILM
0.6
0.8
1
1.2
1.4
1.6
1.8
10 15
Normalized transmittance
129
130
QE.26 (4) (1990)
760-769
PSP2.21
Nonlinear characterization and optical limiting of organic dye doped polymer
G.VINITHA1, R.K REKHA., A.RAMALINGAM,
Centre for Laser Technology, Department of Physics,Anna University, Chennai-25, India.
1svini2005@yahoo.co.in
There has been a large need for nonlinear optical materials that can be used with low intensity lasers for
applications such as phase conjugation, image processing, and optical switching. Large nonlinear optical susceptibility
resulting from the nonlinear response of organic molecules has attracted much attention.
The dye doped polymer films of dye concentrations 0.4 mM were synthesized by thermal bulk free radical
polymerization method 1. Films of thickness 0.6 mm were prepared and were considered for further studies.
The Z-scan experiments2 were performed in liquid and solid media using a 532 nm diode pumped Nd:Yag laser
beam Fig 1 gives closed, open and ratio of normalized Z-scan of Pararosanilin in 1- Butanol and thin polymer film at
concentration 0.4 mM at incident intensity 4.38 KW/cm2. The peak followed by a valley-normalized transmittance
obtained from the closed aperture Z-scan data, indicates that the sign of the refraction nonlinearity is negative i.e. selfdefocusing.
The nonlinear absorption coefficient β can be estimated from the open aperture Z-scan data.
Closed
0
0.5
1
1.5
2
2.5
-12.5 -7.5 -2.5 2.5 7.5 12.5
z(mm)
Normalized Transmittance
Solvent
Film
Open
0.98
1
1.02
1.04
1.06
1.08
1.1
1.12
-13 -7.5 -2.5 2.5 7.5 12.
5
z(mm)
Normalized Transmittance
Solvent
Film
Closed/Open
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
-12.5 -7.5 -2.5 2.5 7.5 12.5
z(mm)
Normalized Transmittance
Solvent
Film
Figure 1. Closed, open and ratio of normalized Z-scan of Pararosanilin in 1- Butanol and thin polymer film
Pararosanilin dye ΔTp-v n2 x 10 -8 (cm2/W) Δn x10 ? β x 10-4 cm/W χ (3) x 10−6 esu
In 1- Butanol 1.326 -6.8 -2.96 -7.7 3.384
Polymer film 1.371 -7.11 -3.09 -7.93 3.53
Table 1. Nonlinear parameters of the dye
Characteristic curves for the optical limiting behaviors of the sample at focus and beyond focus are as shown in
fig.2. From the figure, we can observe that at the valley positions, the optical limiter works at very low powers as the
self-defocusing effect induced by photochromism is also enhanced by the thermal effect which is closely related to the
absorptive properties of the samples used. Thus we, conclude that the best position of a sample when used for optical
limiting based on self-defocusing is at the valley of the Zscan curve of the medium.
0
1
2
3
4
5
0 20 40
Input intensity(mW)
At focus
Bey focus
Figure 2. Optical limiting behaviors of the sample at focus and beyond focus.
Conclusion
The nonlinear optical response of thermo-optic origin exhibited by Pararosanilin dye at low continous wave
laser powers was studied and optical limiter action based on nonlinear refraction is demonstrated in liquid and solid
media .The nonlinear refractive index was determined using the Z scan technique. The origin of the nonlinearity appears
to be predominantly thermo-optic. The variation in the output intensity was studied for different sample positions.
Acknowledgement
The authors wish to thank the DAE-BRNS for their financial support.
References
1. A.Costela, I.Garcia-marino, J.M.Figuera, F.Amat Guerri, J.Barroso, R.Sastre, Opt. Commun. 130 (1996) 44-50
2. Mansoor Sheik-Bahae, Ali.A.Said, Tai-Huei Wei, David J.Hagan, E.W.Van Stryland, IEEE J. Quant.Electron.
131
PDP2.22
Studies on the Fluorescence emission from nano silver / silver oxide thin films for
optical read write memory applications
A.Subrahmanyam and N.Ravichandra Raju
Department of Physics, Indian Institute of Technology Madras, Chennai-600036, India
Email:ravichandra@physics.iitm.ac.in
The fluorescence emission from silver nano clusters is having a potential for read / write nonvolatile
ultra high density optical memories. In the present work, nano silver films are prepared by two
techniques: DC magnetron sputtering at room temperature (300 K) with pure metallic silver as target
and Pulsed laser deposition at 470 and 570 K with pure silver oxide as the target. Films of different
thicknesses (5 nm to 60 nm) are grown and the fluorescence property is compared. The as grown films
in both the techniques are polycrystalline. Emission spectrum was recorded using fluoro-meter. When
these DC Magnetron films are oxidized at 520 K for 30 minutes and are irradiated with blue light ( =
485 nm), a fluorescence emission is observed in the red region ( ~ 650 nm).The PLD grown films also
show multiple fluorescence peaks at 565 nm, 587 nm and 660 nm. These films are analyzed by XRD
and AFM. It is observed that the fluorescence emission from the silver clusters (of size 35 nm)
depends on the growth parameters in sputtering (like substrate temperature or deposition rate) and on
the oxidation temperature. The plasma in both the techniques is analyzed using the emission lines.
The fluorescence emission is attributed to the surface plasmon resonance.

Del Mar Photonics - Newsletter Fall 2010 - Newsletter Winter 2010

 


PLD-2005: Invited Review Talks -RT1 (pdf)
PULSED LASER DEPOSITION - A REVIEW
Richard Pinto
Department of Electrical Engineering
Indian Institute of Technology Bombay
Powai, Mumbai 400076
Email: rpinto@ee.iitb.ac.in
Abstract
Although pulsed laser deposition (PLD) had its origin in the early 1980's,it came into prominence in 1987 with
the first realization of thin films of high Tc superconductor YBa2Cu3O3-x (YBCO) using this growth technique. In
the absence of a convenient technique for the growth of high quality films of multicomponent oxide materials, PLD
has advanced phenomenally during the last 18 years - first with the realization of thin films of high Tc superconductors,
and subsequently of colossal magnetoresistance (CMR) and ferroelectric materials. Further, the ability
to realize high quality films from small targets (unlike the requirement of big targets in sputtering) has made the
PLD technique extremely attractive for research laboratories. However, two disadvantages viz, particulate formation
and the difficulty in realizing films on large area substrates, have made PLD virtually limited to research
laboratories.
In this talk I shall discuss the physics and the kinetics of thin film growth by PLD and its progress since it was
first used for YBCO film growth in 1987. From growth kinetics considerations, PLD is perhaps the most complex of
the techniques, and yet, as experience has shown, it is the most convenient and versatile among the techniques for
the realization of multicomponent oxide thin films. This talk will review the impact of the PLD technique in the
light of our own work (carried out at TIFR since 1991) in the realization of high quality films of high Tc
superconductors, CMR materials, ferroelectrics and multiferroics. I shall also highlight the contributions of PLD in
the realization of some of our finest results such as highest Jc YBCO films, first synthesis of unstable LuBa2Cu3O7-
x thin films, synthesis of ferroelectric PbTiO3 films on <100> Si, and the recent work on multiferroic BiFeO3 films
and Bi0.6Dy0.3La0.1FeO3 films which show coexistence of ferroelectric and magnetic ordering.
8
PLD-2005: Invited Review Talks -RT2
Pulsed Laser Deposition for MOS Gate Dielectric Films
Nandita DasGupta*, RavneetSingh, Roy Paily, Amitava DasGupta, Pankaj Misra
and Lalit M. Kukreja
* Department of Electrical Engg., IIT Madras, Chennai 600 036
*Email: nand@ee.iitm.ernet.in
Abstract
Downscaling of device dimensions is essential for the development of new generation Ultra Large Scale
Integrated Circuits (ULSI) based on Complementary Metal Oxide Semiconductor Field Effect Transistors
(CMOSFET). Silicon dioxide(SiO2) has been used for more than 35 years as the primary gate-dielectric material in
MOSFETs because of its excellent properties. However, current technology requires that the thickness of the gate
dielectric be reduced to only a few monolayers of SiO2. Further thinning of SiO2 poses a serious challenge because
of large gate leakage current1,2. In order to overcome the large gate leakage current mainly due to direct tunneling,
introduction of new gate dielectric materials with high dielectric constant (high-k) is being seriously investigated 3-6.
Using high-k dielectric, the physical thickness of the dielectric layer can be kept large, thereby reducing the gate
leakage current, while maintaining the same value of capacitance. There are many materials systems under
consideration which have potential to replace SiO2 as the gate dielectric material. Of the various high-k dielectric
materials, TiO2, Ta2O5, ZrO2, and HfO2 have generated a lot of interest due to their high dielectric constant and
adequate barrier height. Various deposition techniques have been employed to deposit these materials.
We have recently reported for the first time, the use of Pulsed Laser Deposition (PLD) technique for the
deposition of TiO2 as gate dielectric in Metal-TiO2-SiO2-Si (MTOS) capacitors with TiO2-SiO2 stacked gate
dielectric7, 8. One interesting observation in our work is that by optimizing the conditions during PLD, one can
actually achieve an increase in capacitance of the MTOS capacitor by introducing the additional TiO2 layer over
SiO2. The reduction in the Effective Dielectric Thickness (EDT), defined as oxA/Cmax, where ox is the dielectric
constant of SiO2, A is the device area and Cmax is the accumulation capacitance is due to an intermixing of the TiO2
layer with the underlying SiO2.
Previous reports indicate that it has been rarely possible to obtain an EDT < 2 nm using TiO2 thin films 3.
We have however, been able to combine the reduction in the EDT with a reduction in the gate leakage current by
controlling the intermixing of the TiO2 and SiO2 layers during PLD. To achieve this, we have used a dualtemperature
deposition process, where a buffer layer of TiO2 has been deposited at low temperature followed by
deposition of TiO2 at higher temperature and annealing resulting in an EDT < 2 nm as well as low leakage 9. As
shown in Fig.1, the leakage current densities (J) of the MTOS devices are at least five orders of magnitude smaller
than that in the simulated MOS devices with comparable EDT. It can also be seen that while for the simulated MOS
devices, the leakage current changes by five orders of magnitude as the gate oxide thickness reduces from 2.5 to 1.5
nm, for the MTOS devices, the leakage current changes only by one order of magnitude for a similar reduction in
EDT from 2.4nm to 1.6 nm. This is because, the leakage current is determined by the physical thickness and the
9
physical thickness of the gate dielectric for these MTOS devices is comparable, even though their EDT values are
different.
Even though the results of MTOS devices have been encouraging, for preserving the interface quality, a
very thin layer of SiO2 has to be grown on silicon prior to PLD of TiO2. Conventional thermal oxidation has been
used for growing this thin SiO2 layer. It would, however, be extremely useful if both PLD of TiO2 and the growth of
SiO2 can be carried out using the same process. To this end, we have developed a novel technique of Laser Induced
Oxidation (LIO) to grow ultrthin SiO2 (<4nm) using only a pulsed laser source and maintaining the substrate at
room temperature 10. Pulsed laser source generates energy pulses of nano-seconds time duration. These short time
pulses have been used to heat the silicon wafer surface in O2 ambient to grow SiO2 in a very controlled manner. As
shown in fig.2, the leakage current density was found to be low and the breakdown field strength high (> 10 MV/cm
for LIO3), signifying the excellent quality of the Laser-induced oxide.
References
1) S. -H. Lo, D. A. Buchanan, Y. Taur, and W. Wang, IEEE ED Lett. 18 (1997) 209.
2) D.A.Buchanan and S.H.Lo, Microelectronic Engineering 36 (1997) 13.
3) Masaru Kadoshima, Masahiko Hiratani, Yasuhiro Shimamoto, Hiroshi Miki, Shinichiro Kimura,
Toshihide Nabatame, Thin Solid Films, 424 (2003) 224.
4) Jing-Chi Yu, B.C. Lai, J.Y. Lee, IEEE ED Lett. 21 (2000) 537.
5) W. K. Chim, T. H. Ng, B. H. Koh, W. K. Choi, J. X. Zheng, C. H. Tung, A.Y. Du, J. Appl. Phys. 93
(2003) 4788.
6) Q. Fang, J.-Y. Zhang, Z. M. Wang , J. X. Wu, B. J. O扴ullivan, P. K. Hurley, T. L. Leedham, H. Davies,
M. A. Audier, C. Jimenez, J.-P. Senateur, Ion W. Boyed, Thin Solid Films, 428 (2003) 263.
7) Roy Paily, Amitava Das Gupta, Nandita Das Gupta, Pijush Bhattacharya, Pankaj Mishra, Tapas
Ganguli,Lalit M. Kukreja, A.K. Balamurugan, S.Rajgopalan, A.K.Tyagi, Applied Surface Science 187
(2002) 297.
8) Roy Paily, Amitava DasGupta, Nandita DasGupta, Pankaj Misra and Lalit M.Kukreja, Thin Solid Films,
Vol. 462-463C pp. 57-62, 2004.
9) Ravneet Singh, Roy Paily, Amitava DasGupta, Nandita DasGupta, Pankaj Misra and Lalit M. Kukreja,
Semiconductor Sc. & Technol., Vol.20, No.1, Jan.2005
10) Ravneet Singh, Roy Paily, Amitava DasGupta, Nandita DasGupta, Pankaj Misra and Lalit M. Kukreja,
Electronics Letters, Vol. 40, No.25, pp.1606-08, Dec. 9, 2004
10
Fig.1: Comparison of J-V characteristics of MTOS devices with those of simulated MOS devices with comparable
EDT
0.0 0.5 1.0 1.5 2.0 2.5 3.0
1E -6
1E -4
0.01
1
100
EDT = 15A0,S im ulated for S iO2
EDT = 20A0,S im ulated for S iO2
EDT = 25A0,S im ulated for S iO2
MT OS B1 (E DT =1.7 nm )
MT OS B2 (E DT =1.6 nm )
MT OS B3 (E DT =2.4 nm )
Leakage Current Density (A/cm2)
|G ate Vo ltag e| (V)
-0 -2 -4 -6 -8
10-8
10-6
10-4
10-2
100
MOS, tox=3.9 nm
LIO3, 90s,tox=3.9 nm
LIO2, 60s,tox=5.5 nm
LIO1, 30s, tox=5.1 nm
Gate Voltage (V)
Leakage Current density (A/cm2)
Fig. 2. J-V characteristics of LIO1, LIO2, LIO3 and MOS capacitors.
11
PLD-2005: Invited Review Talks -RT3
Some studies on oxide and nitride thin films grown by pulsed laser deposition
K. P. Adhi
Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of
Pune, Pune - 411 007, India
Email: kpa@physics.unipune.ernet.in
Abstract
Pulsed laser deposition (PLD) has emerged as a relatively simple and highly versatile technique for the
growth of thin films of variety of materials1. Deposition of epitaxial, stoichiometric thin films of simple materials2 or
multi-element complex compounds on suitable substrates3, multilayers4, nano-particles5 and nano-structures etc. are
some of the achievements which reflect the versatility of this technique. We present a review of our recent research
work on the growth, characterization and analysis of oxide and nitride thin films. The presentation is focused on the
following oxide materials; a) Fe3O4 b) La0.7Ca0.3MnO3 and c) bi-layers of Fe3O4 / La0.7Ca0.3MnO3. Some of the
issues which will be addressed are growth of highly oriented thin films of the above mentioned materials,
modifications in their structural and electrical properties due to external processing like swift heavy ion irradiation,
ionimplantation etc . In case of nitrides, the growth of highly oriented AlN thin films on sapphire, its
characterization along with brief mention of InN and GaN thin films will be discussed. Generation of nanoparticles
of Fe3O4 / FeO by PLD will also be discussed.
References:
1. 揚ulsed Laser Deposition of Thin Films?edited by D. B. Chrisey and G. K. Hubler, A Wiley ?br> interscience publication, New York (1994)
2. S. M. Jejurikar, A. G. Banpurkar, A. V. Limaye, S. K. Date, S.I. Patil, K. P. Adhi, P. Misra, L. M.
Kukreja, Ravi Bathe, communicated to J. Appl. Phys.
3. Ravi Bathe, K. P. Adhi, S. I. Patil, G. Marest, B. Hannoyer, S. B. Ogale, Appl. Phys. Lett. 76, 2104
(2000)
4. S. N. Sadakale, R. J. Choudhary, M. S. Sahasrabudhe, A. G. Banpurkar, K. P. Adhi, S. I. Patil, S. K.
Date, J. Mag. Mag. Mater. 286, 450 (2005)
5. S. R. Shinde, A. G. Banpurkar, K. P. Adhi, A. V. Limaye, S. B. Ogale, S. K. Date, G. Marest,
Mod. Phys. Lett. B 10, 1517 (1996)
12
PLD-2005: Invited Review Talks -RT4
Micro- nano patterning in a single step via selective laser ablation
Alika Khare
Department of Physics
Indian Institute of Technology Guwahati, Guwahati 781039
Email: alika@iitg.ernet.in
Abstract:
Optoelectronics devices viz; grating couplers, micro mirrors, tiny arrays of lasers and photonic band gap materials
require ordered arrays of dimensions ranging from nanometers to tens of microns. These tiny arrays of materials can
be produced by modifying the surface morphology of thin films by illuminating it with interference pattern formed
by interference of multiple beams from a pulsed high power laser. The interference patterns are periodic, so the
materials of the thin film exposed to the maximum intensity (bright fringe) gets ablated leaving the area of minimum
intensity (dark fringe) unaffected. Width and periodicity of the ablated region depends on the intensity distribution
with in the bright fringe and wavelength of laser respectively. For writing the grating like structure, a simple two
beam Michelson interferometer can be used. For patterning in the format of arrays of dots of the material in square
or rectangular geometry, two Michelson interferometers in tandem can be used. For hexagonal geometry,
interference pattern from the eight beams coming out of system of three interferometers in tandem can be used. This
is a direct lithographic technique without requiring any mask. The whole writing can be performed in a single step.
The technique of selective laser ablation via high power interferometer can be applied to the thin film of any
material. The material ablated from the region of bright fringe results into the formation of arrays of cold atomic
beam having relatively low divergence. The application of these atomic beams for nano lithography via dipole force
shall also be presented in the talk.
13
PLD-2005: Invited Review Talks -RT5
Electron doped rare-earth manganites: A current scenario
Pratap Raychaudhuri
Department of Condensed Matter Physics and Materials Science,Tata Institute of Fundamental Research,
Homi Bhabha Rd., Colaba, Mumbai-400005.
Email: pratap@tifr.res.in
Abstract
Electron doped rare-earth manganites of the form (R1-xAxMnO3, where R=rare-earth, A=tetravalent cation) fall the
class of compounds which have so far been synthesized in single phase only through the pulsed laser deposition
technique. The most well known member of this series La1-xCexMnO3 was first synthesized in TIFR in 1999 and
showed the magnetic and transport properties to be very similar to its hole-doped counterpart [1]. Subsequently,
studies using a variety of techniques such X-ray absorption spectroscopy[2], Tunneling conductance in artificial
tunnel junctions with La0.7Ce0.3MnO3[3] established this material to be a minority spin carrier ferromagnet where the
manganese is in a mixture of Mn3+ and Mn2+ valence states. These findings led to an active search for other electron
doped manganites among many groups in recent years and several new candidates have been reported. This also led
to the synthesis electron doped cobaltates [4] using Pulsed Laser deposition using the same principle as that used for
the manganites.
In this talk I will present an overview of the current status on the investigations on electron doped manganites and
related systems.
References:
1. P. Raychaudhuri, S. Mukherjee, A. K. Nigam, J. John, U. D. Vaisnav, R. Pinto, and P. Mandal, J. Appl. Phys. 86,
5718 (1999).
2. C. Mitra, Z. Hu, P. Raychaudhuri, S. Wirth, S. I. Csiszar, H. H. Hsieh, H.-J. Lin, C. T. Chen, and L. H. Tjeng,
Phys. Rev. B 67, 092404 (2003).
3. C. Mitra, P. Raychaudhuri, K. Dörr, K.-H. Müller, L. Schultz, P. M. Oppeneer, and S. Wirth, Phys. Rev. Lett. 90,
017202 (2003).
4. D. Fuchs, P. Schweiss, P. Adelmann, T. Schwarz, and R. Schneider, Phys. Rev. B 72, 014466 (2005).
14
PLD-2005: Invited Review Talks -RT6
Exploring Novel Magneto-resistive and Transport Properties in Pulsed Laser Deposited
Manganite Thin Films
D. G. Kuberkar
Department of Physics, Saurashtra University
Rajkot 360 005
Email: dgk@icenet.net
Abstract
For the past one decade, a significant upsurge in research on ABO3 type manganites is mainly attributed to
the application potential of colossal magnetoresistance (CMR) property exhibited by these compounds. Though the
realization of applications of these oxides still remains an open question, the compounds continue to attract the
scientific community due to the rich physics evolving as a result of spin, charge and orbital degrees of freedom.
During this talk , the results of our recent studies, both on tailoring these materials to obtain enhanced magnetoresistance
(MR) for applications point of view and on some exotic transport properties at low temperatures, will be
presented.
The fabrication of manganite thin films is essential because films could find applications and also help in
studying the clean physics in the absence of dominant grain boundary effects. Pulsed Laser Deposition (PLD) is an
efficient tool to fabricate the high quality epitaxial thin films of manganite oxides and to grow multilayer structures,
which could be evaluated for possible applications. We show that, by controlling the growth parameters, phaseseparation
may be induced to obtain unusually high MR in A-site disordered (La,Pr)0.7A0.3MnO3 (A=Sr, Ba)
manganites. Swift Heavy Ion (SHI) irradiation is another technique employed to induce the controlled defects in the
thin films. Our detailed investigations on the SHI irradiation induced modifications in the structural and transport
properties of thin films of varying thicknesses reveal that, SHI effect on transport and MR properties gets more
pronounced with increasing thickness of the films. In addition to MR properties, we also observed some low
temperature transport anomalies arising due to structural disorder in Ba-based compounds. Present talk will
highlight some interesting findings of our recent investigations on CMR manganites in the context of all the abovementioned
aspects.
15
PLD-2005: Invited Review Talks -RT8
Photonic and Spin-photonic Semiconductor Nanostructures Grown by Pulsed
Laser Deposition
Lalit. M. Kukreja
Thin Film Laboratory
Centre for Advanced Technology, Indore ?452 013, INDIA
Email: kukreja@cat.ernet.in
Abstract
This paper reviews our recent research on structural and optical properties of quantum dots of Si, quantum wells and
dots of ZnO and thin films of Mn and Co doped ZnO grown by Pulsed Laser Deposition (PLD). A particulate free
multilayer structure of Al2O3 capped Si quantum dots of different mean sizes grown by an off-axis deposition
scheme showed variable band-gap in photoabsorption spectra in line with the putative quantum confinement effects.
Room temperature photoluminescence from Si quantum dots grown for different times showed features without any
apparent size dependent spectral shift which, albeit has earlier been explained by others originating from the defect
levels at the interface of Si and SiO2 shells surrounding the nanoparticles but still have certain mysteries attached.
On the contrary ZnO quantum dots, also capped with Al2O3 in multilayer structure, showed size dependent band-gap
shifting in photoabsorption spectra in the range from about 3.3 to 4.5 eV when the mean dot radii varied from about
4 to 2 nm. High quality ZnO/MgZnO quantum wells grown by an in-house developed methodology of buffer
assisted growth showed a monotonic blue shift of the band-gap from about 3.35 to 3.75 eV both in photoabsorption
and photoluminescence when the well thickness decreased from about 5 to 1 nm. These quantum structures are
expected to play vital role for the development of future photonic devices.
An equally exciting area of spint-photonics is currently on the horizon. Diluted magnetic semiconductors (DMS) of
Mn and Co doped ZnO are being studied extensively to explore if those could be potentially useful for spinoptoelectronic
devices. We have synthesized bulk and thin films of these materials with different dopand
concentrations. The PLD grown films of a few hundred nm thickness are found to have high crystalline quality and a
homogenous wurtzite phase with monotonic increase in the band-gap of the resulting alloy with increasing
concentration of Mn and Co in their corresponding films. We have also observed broad mid gap absorption in the
photoabsorption spectra of both Mn and Co doped ZnO films. Low temperature photoluminescence of MnZnO alloy
films with different concentrations of Mn, showed efficient band edge emission with additional features, which
might originate from the clusters of MnO or MnO2 due to the crystal field transitions of Mn2+ ions. Further
investigations on the optical and magnetic characteristics of these spin-photonic semiconductor films are under way.
16
PLD-2005: Invited Review Talks -RT9
The Evolution of PLD: From High Tc Superconductors to Spintronics
M.S. Ramachandra Rao
Department of Physics and Materials Science Research Centre
Indian Institute of Technology (IIT) Madras, Chennai ?600 036
Email: msrrao@iitm.ac.in
Abstract
Pulsed laser deposition (PLD) has proved to be one of the most versatile techniques to realize high quality thin films
of not only oxide materials but also a variety of solid state materials. With a modest beginning as a not-so-popular
technique in the sixties [1], it has come to stay, with the advent of high Tc superconductivity [2], as the most
profoundly used deposition technique in the past two decades. Applications of the technique include the fabrication
of high current density superconducting films, high quality ultrathin gate-dielectric layers, biocompatibility for
medical applications, hardware resistant coatings, diamond coatings, production of carbon nanotubes, epitaxial
transparent conducting oxide (TCO) films, hydrogen and other gas sensors, films with nanostructured and selfassembled
arrays, magnetic multilayers and heterostructures and GMR/CMR based magnetic tunnel junctions
(MTJs) and diluted magnetic semiconductors (DMS) for spintronic applications. PLD by virtue of its simplicity
scores over other techniques in terms of, i). stoichiometric production of films of multicomponent systems, ii).
relatively high deposition rate (~ 100 Å/min @ moderate laser fulences), iii). use of laser as an external energy
source to avoid contamination and iv). facilitation of multilayer film deposition without breaking vacuum. It is the
fastest evaporation (occurring in time scales of few nanoseconds) technique in which the laser produced plasma
(plume) expands rapidly away from the target surface with particle velocities typically in the range 106 cms-1 and
kinetic energies of the emanating species ~ 80 eV as compared to 2-10 eV in the case of filament-based-thermalevaporation.
The fundamental aspect of plume generation during the laser-target interaction process is still a matter
of intense research.
In this review talk, I will give a brief glimpse of the technique, highlighting salient results pertaining to two research
areas, HTSC and manganites, in which PLD was extensively used. I will also highlight the recent trends in PLD to
realize nanostructured and self assembled arrays of some oxide systems. I will then talk about the emerging field of
spintronics, in the context of oxide electronic materials, which is an emerging field for future spin electronic and
quantum computational devices [3,4].
References:
[1]. H.M. Smith and A.F. Turner. Appl.Opt. 4 (1965) 147.
[2]. D. Dijkamp et al. Appl. Phys. Lett. 81 (1987) 619.
[3]. H. Ohno et al. Appl. Phys. Lett. 69 (1996) 363.
[4]. D.D. Awschalom and J.M. Kikkawa. Physics Today, 52 (1999) 33.
17
PLD-2005: Invited Review Talks -RT10
Pulsed laser Deposition of Oxides on polymer substrates for Optoelectronic Applications
M.K.Jayaraj*, R.Manoj, R.S.Ajimsha., R.Reshmi
Optoelectronics Device laboratory, Department of Physics,
Cochin University of Science and Technology, Cochin ?682 022.
*Email: mkj@cusat.ac.in
Abstract
Wide band gap oxide films are important component in Optoelectronic devices. Thin films deposited on organic
substrates can be used in plastic liquid crystal displays, Transparent electromagnetic shielding material, flexible
electro optical devices, solar cells, thin film electro luminescent devices etc. Due to the poor thermal endurance of
organic substrates films should be deposited at low substrate temperature. Wide variety of methods, such as
sputtering, chemical deposition, and sol gel method are commonly used to deposited oxide films. A high
temperature post deposition heat treatment is required to produce crystalline film which is not possible with these
organic substrates. In this paper we review the work that we have carried out on ZnO and ZnGa2O4 thin films grown
by pulsed laser deposition. Highly oriented ZnO films and polycrystalline ZnGa2O4 films were grown by PLD on
various substrates like quartz, silicon and organic polymer substrates (kapton HPP-ST polyamide). By controlling
the deposition parameters like substrate to target distance, oxygen partial pressure and laser fluence crystalline films
were grown on organic substrates at a substrates temperature of 250C. The films were characterized by studying the
optical, electrical and structural properties. The Photoluminescent emission and excitation of the PLD grown oxide
films on organic substrates were also discussed.
18
PLD-2005: Invited Review Talks -RT11
Synthesis of Epitaxial AlN thin films by pulsed laser deposition
Ravi Bathe
International Advanced Research Center for Powder Metallurgy and New Materials, Balapur PO, Hyderabad 500
-005, India
Email: ravi@arci.res.in
Abstract
AlN has a large potential to become important in a wide range of applications. Its wide (6.2 eV), direct, band gap
combined with well matched structural and thermal properties to SiC makes it an ideal candidate for future
MESFET and MISFET SiC-transistors as well as high temperature and high power electronics applications. Due to a
small lattice mismatch to SiC (~ 1%), epitaxally grown AlN thin films seem to be promising candidates for
dielectric applications and ion-implantation anneal cap. We have investigated the epitaxy, interfaces, surfaces and
defects in epitaxial AlN thin films grown on SiC by pulsed laser deposition. The crystalline structure and surface
morphology of the epitaxially grown AlN thin films on SiC (0001) substrates have been studied using x-ray
diffraction ( and scans) and atomic force microscopy, respectively. The defect density and analysis have
been studied by using Rutherford backscattering spectrometry, ion channeling technique and transmission electron
microscopy. The films were grown at various substrate temperatures ranging from 500 to 1100 0C. X-ray diffraction
measurements show highly oriented AlN films above growth temperature of 750 0C, and single crystalline nature
above 800 0C. The films grown in the temperature range of 950 0C to 1000 0C have been found to be highly strained,
where as the films grown above 1000 0C were found to be relaxed after crack propagation along the crystallographic
axes. We found that during initial stages, growth of a 20 nm thick AlN low-temperature buffer layer is critical for
obtaining crack free, smooth, high-quality epitaxial films. By controlling the initial stages of growth in a two-step
deposition process, it is shown that high quality epitaxial layers on SiC can be obtained with low intrinsic stresses,
good surface morphology, and higher electrical break-dawn strength. The significance of these results towards
development of high temperature-high-power electronics is also discussed.
19
PLD-2005: Invited Talks 朓T1
Nanocrystalline Films of Gadolinia Doped Ceria Prepared
by Pulsed Laser Ablation
P. Kuppusami
Physical Metallurgy Section
Indira Gandhi Centre for Atomic Research
Kalpkkam-603 102, Tamilnadu
Email : pk@igcar.ernet.in
Abstract
Nanocrystalline oxides are displaying electrical properties which appear to be unique and may
lead to applications that are not attainable by conventional microcrystalline oxides. As a result, it is very
important to understand the relationship between microstructure and electrical properties as well as to be
able to control the microstructure in the nanocrystalline range. New phenomena observed in nanocrystalline
oxides are related to the increasing grain boundary volume and in the change of stoichiometry, which may
lead to enhance the reaction kinetics and electrical conductivity.
Synthesis of nanocrystalline materials has been carried out most frequently by assembling pregenerated
small clusters by means of consolidation and sintering. A variety of cluster generation methods
such as sol-gel technique, laser ablation, sputter deposition and precursor spin coating technique have been
reported. In comparison with methods such as consolidation and sintering of clusters, the latter techniques
are the low temperature methods, which have significant advantage. Pulsed laser ablation is a unique
technique where the deposition is not only carried out at low substrate temperatures, but also the
stoichiometry of the target is retained in the ablated films. The technique is also capable of depositing
metastable materials that are difficult to synthesize in bulk form by other deposition methods. These
features enable to control the grain size and to obtain stable microstructure and make it possible to study
microstructure-property relationships.
In the present work, microstructure of thin films of gadolinia doped ceria (GDC) prepared by
pulsed laser ablation is investigated. The growth characteristics of the films as a function of substrate
temperature, oxygen partial pressure and laser energy are investigated using the techniques of x-ray
diffraction and electron microscopy. The influence of growth induced defects on the ionic conductivity of
the doped ceria will be highlighted.
20
PLD-2005: Invited Talks 朓T2
Pulsed Laser Ablation grown Relaxor based bilayers, multilayers and heterostructures for
multiferroic applications
R. Ranjith* and S. B. Krupanidhi
Materials Research Centre, Indian Institute of Science, Bangalore-560 012
*Email: ranjith@mrc.iisc.ernet.in
Abstract
Ferroelectric heterostructure like super lattices and multilayers have shown superior properties and have been the interest
of study in the recent years1. The interfaces present and the size of the individual layers present play a crucial role in
these heterostructure. In this work multilayer of PMN-PT with varying composition of PT across the film was fabricated
using pulsed laser ablation technique. Samples with varying individual layer thickness were fabricated to study the size
dependent behavior of these multi-layer thin films. Multilayer films with individual layer thickness of 10,20,30,50,70
and 100nm were fabricated. Polarization studies were carried out on these films with a multilayer structure. A field
driven antiferroelectric to ferroelectric transition was observed in the films of individual layer thickness greater than
50nm. The dominance of the interaction between the adjacent layers via the interfacial coupling dominates at low fields
to stabilize the antiferroelectric coupling and the dominance of the external field coupling with the individual layers
stabilizes the ferroelectric behavior of these films. Figure 1. shows the field driven ferroelectric polarization. Films with
low individual layer thickness exhibited ferroelectric behavior and on increase of individual layer thickness they
exhibited an anti-ferroelectric behavior and on further increase of thickness they showed a weak anti-ferroelectric
followed by a weak ferroelectric behavior on further increase of thickness. This phenomenon is attributed to the longrange
coupling observed in these materials2, which gives an averaged property, and on increase of thickness they behave
as individual materials put together. Figure 2. shows the size induced antiferroelectric polarization behavior.
Artificially grown superlattice structures have been an interest of study due to their striking properties both in
technological point of view and fundamental physics aspects. In this work superlattices based on Pb(Mg1/3Nb2/3)O3
(PMN) ?PbTiO3 (PT) were deposited through pulsed laser ablation deposition with different periodicities
(10,20,30,40,50,60 and 70nm) for a constant total thickness of the film. The presence of superlattice reflections in the Xray
diffraction pattern clearly shows the superlattice behavior of the films. Polarization hysteresis and the Capacitance ?br> Voltage characteristics of these films shows a clear size dependent Ferro and Antiferro characteristics. Presence of long
range coupling in superlattices with lower periodicities (<10nm) exhibited a clear ferroelectric behavior similar to a solid
solution of PMN and PT3. Superlattices with higher periodicities (20-50nm) exhibited antiferroelectric behavior, which
could be understood from the energy arguments. On further increase of periodicities they again exhibited ferroelectric
behavior. On increase of temperature beyond the Curie point of PMN the interaction is changed to a Ferroelectric ?br> Paraelectric interlayer interaction and loses its antiferroelectric behavior. The Capacitance 朧oltage characteristics and
its temperature is given in figure 3.
21
-10 -5 0 5 10
2.0
2.1
2.2
2.3
10kHz
d=40nm
Capacitance (nF)
Voltage (Volts)
27oC
120oC
Figure 3. CV characteristics of a PTPMN
superlattice
Figure 2. Size driven Antiferroelectric characteristics.
Major References
1. G.Rijnders and Dave.H.A.Blank, Nature, 433, 369 (2003).
2. H.M.Christen,E.D.Specht, D.P.Norton, M,F,Chisholm and L.A.Boatner, Appl.Phys.Lett., 72,2535,(1998).
3. Jian Shen and Yu-qiang Ma, Phys. Rev.B, 61(21), 14279, (2000).
Figure 1. Field driven Antiferroelectric to Ferroelectric transition.
22
PLD-2005: Invited Talks 朓T3
Optical Quantum Confinement Effects in ZnO/MgZnO Multiple Quantum Wells Grown
by Pulsed Laser Deposition
P. Misra*, T. K. Sharma, S. Porwal and L. M. Kukreja
Thin Film Laboratory, Centre for Advanced Technology, Indore 452 013
*Email: pmisra@cat.ernet.in
Abstract
Current worldwide interest in ZnO as a semiconductor to evolve futuristic optoelectronic, spintronic and other
devices has spurred rigorous research on its quantum structures [1]. We have grown ZnO Multiple Quantum Well
(MQW) structures on (0001) Sapphire substrates by Pulsed Laser Deposition using a third harmonic of Q-switched
Nd: YAG laser. A 10 layer MQW structure was grown with 8 nm thick ternary alloy Mg0.16Zn0.84O layer with a band
gap of ~ 4.1 eV as a barrier and the active layer of ZnO had variable thickness in the range of 5 ?1 nm . Prior to the
growth of MQWs a 50 nm thick ZnO buffer layer was grown at 750癈, which provided a highly crystalline, smooth
and oxygen terminated template for subsequent growth of nanostructures at a lower temperature [2] of 600癈. This
low temperature growth ensured chemically sharp interfaces while the high crystalline quality was facilitated by the
high temperature grown buffer layer. Room temperature absorption spectra of MQW structures showed two
prominent peaks due to excitonic transitions with in the well and barrier layers. The ZnO absorption edge shifted
monotonically towards blue with decreasing well layer thickness up to 1 nm due to putative size dependent quantum
confinement effects. Photoluminescence (PL) measurements carried out on all the quantum wells at 10K and room
temperature using a He-Cd laser to further strengthen our observation. Room temperature PL in the UV spectral
range was observed for the MQW samples up to 2 nm of well thickness bellow which the PL signals was too weak
to be detected by our PL setup. It is worth mentioning here that the minimum thickness of ZnO QW grown on
sapphire by us which showed quantum confinement effect is 1 nm, which is better than reported by Ohtomo et al
which was 1.7 nm. Ohtomo et al also could not observe room temperature PL observed by us. All the samples
showed strong PL at 10K due to excitonic recombination in ZnO QW. PL spectra of these samples showed a clear
blue shift in the ZnO band edge from ~ 3.4 to ~ 3.7 eV with decreasing well layer thickness. The FWHM of PL
peak was found to increase monotonically with decreasing well layer thickness probably due to fluctuation in the
well layer thickness which is more pronounced at lower thickness of QW. The band gaps obtained from the
experimental PL data at 10K were compared with the theoretically calculated values by using one dimensional
square well potential approximation and a band offset ratio, Ec: Ev of 9:1. Both were found to be in good
agreement. Further experiments are underway to investigate the interface quality and to measure the accurate
thickness of the quantum wells and to include size dependent variation of the excitonic binding energy in theoretical
calculations.
References:
1. A. Tsukazaki, A. Ohtomo, T. Onuma, M. Ohtani, T. Makino, M. Sumiya, K. Ohtani, S. F. Chichibu, S. Fuke,
Y. Segawa, H. Ohno, H. Koinuma, M. Kawasaki, Nature Materials, 4, 42-46, (2005)
2. P. Misra and L.M. Kukreja, Thin Solid Films, 485, Issues 1-2, 42-46 (2005)
3. A. Ohtomo, M. Kawasaki, I. Ohkubo, H. Koinuma, T. Yasuda, Y. Segawa, Appl. Phys. Lett. 75, 980 (1999)
23
PLD-2005: Invited Talks 朓T4
High-pulse energy excimer lasers for precise material ablation
Burkhard Fechner and Ralph Delmdahl
Coherent Lambda Physik GmbH, Hans-Boeckler-Str. 12, D-37079 Goettingen, Germany
Email: bfechner@lambdaphysik.com
Abstract
Pulsed excimer lasers are the strongest and most efficient laser sources in the ultraviolet spectral
region. Record short wavelengths from 351 nm down to 157 nm as well as record high 1200 mJ
pulse energy as available for the 248 nm excimer lasers are commercially provided for numerous
laser material ablation approaches. Virtually no material is able to withstand the high photon
energies ranging from 3.5 to 7.9 eV emitted by excimer lasers. As a result of the irradiation of
material with high energy excimer laser photons at sufficient fluence immediate bond breaking
due to electronic excitation is induced. In combination with short-term laser material interaction
of only 10 to 30 ns excimer pulse duration, material ablation proceeds via fast vaporization and
consecutive ejection of material with only negligible dissipation of heat transfer to the
surrounding zone. The effect is an inherently precise and clean ablation quality. Latest
developments in excimer laser technology with particular respect to pulsed laser deposition as
well as applications will be discussed.
24
PLD-2005: Invited Talks 朓T5
Pulsed laser ablation at the liquid solid interface
D. M. Phase
UGC-DAE Consortium for Scientific Research, Khandwa Road, University Campus, Indore-452 017.
Email: dmphase@csr.ernet.in
Abstract
Pulsed laser ablation (PLA) is a well-known method to produce thin films by ablating material from a solid
target of known composition1. PLA usually occurs in vacuum or in a background of inert gas or reactive gas. Very
recently, PLA at the liquid/solid interface, a new variation of PLA has been reported by Simakin et al2. Earlier the
concept of pulsed laser induced liquid solid interfacial reaction was used to prepare surface alloys and compounds,
which are in the metastable states3. Now this novel LP-PLA technique which is also based on same concept has been
used to produce a variety of materials, including diamond like carbon films, nanocrystals of carbon nitride and nano
meter size particles of Ti, Ag, Au, Si and TiC. This technique shows a great potential as route to novel nanocrystalline
materials. However this technique is still in its infancy with much of the parameter space yet to be
investigated. In this talk a basic concept of pulsed laser reaction at liquid/solid interface will be described along with
some examples of synthesis of metastable compounds. This will be followed by a detailed description of LP-PLA
technique with examples of synthesis of nano-structures and nano-particles.
References:
1. R.K.Singh and J.Narayan, Phys.Rev.B 41 (13) (1990) 8843
2. A.V.Simakin, G.A.Shafeev, E.N.Loubnin, Appl. Surf. Sci. 154 (2000) 405.
3. P.P.Patil, D.M.Phase, S.V.Ghaisas, S.K.Kulkarni, S.M.Kanetkar and S.B.Ogale,
Phys.Rev.Lett 58(3) (1987) 238.
25
PLD-2005: Invited Talks 朓T6
Pulsed laser deposition of ZnO and Silicon thin films
V. Narayanan and R. K. Thareja
Department of Physics and Centre for laser Technology, Indian Institute of Technology ?Kanpur
Email: vnara@iitk.ac.in
Abstract
The thin films of zinc oxide (ZnO) and silicon (Si) were deposited employing reactive and nonreactive
pulsed laser deposition technique under various ambient gas conditions of oxygen and helium respectively. The thin
films were characterized by atomic force microscopy (AFM). The deposited films were studied using
photoluminescence (PL). The work on second harmonic generation (SHG) and third harmonic generation (THG) in
ZnO thin films will be discussed. ZnO targets were ablated in ambient oxygen and vacuum using 355 nm third
harmonic of Nd:YAG laser with the pulse width of 5 ns and repetition rate of 10 Hz. Laser was focused onto the
rotating cylindrical target and plume is emitted normal to the surface and a thin film deposited on the quartz
substrate which was kept at 4 cm from the target. The role of zinc and oxygen species on the reactive pulsed laser
deposited ZnO films in the ambient oxygen and vacuum was investigated by studying the spatial and temporal
evolution of ZnO plasma using optical emission spectroscopy and imaging techniques. Spatially resolved emission
spectra showed the abundance of Zn I at 100 mTorr and Zn II at 900 mTorr ambient oxygen respectively. The
temporally resolved 2D-images of the expanding ZnO plume were recorded in the ambient gas environment using
intensified-CCD (ICCD) and the distance ?time (R-t) plot from the recorded images followed shock model of the
form R(t) = atn (n = 0.36 at 100 mTorr and n = 0.4 at 900 mTorr of oxygen), where a is a constant. ZnO thin films
were deposited at ambient oxygen pressure of 100 and 900 mTorr and an attempt is made to correlate the
spectroscopic observations with that of film properties. The films were deposited at room temperature. Surface
morphology of the films were carried out using AFM and showed dependence on oxygen pressure. To investigate
the non-linear properties of ZnO thin films, harmonic generation (SHG and THG) were performed in the deposited
films. The second harmonic co-efficient (ceff
(2)) and third harmonic co-efficient (c(3)) were 3.2 pm/V and 0.9 x 10-
12 esu respectively for the films deposited at 100 mTorr oxygen. The third harmonic generated at varying input
intensity of fundamental wavelength showed cubic dependence on intensity. A third harmonic (355 nm, pulse width
5 ns FWHM) at pulsed repetition rate of 10 Hz of a Q-switched Nd:YAG laser was used for creating silicon plasma
both in vacuum and ambient helium gas. For the thin film deposition of silicon, silicon and quartz substrates were
kept close to the target and the helium gas was used for condensation of the nanoclusters in the gas phase. The
particle size distribution in the deposited films was analyzed using AFM. The mean cluster size ranging from1.8 nm
to 4.4 nm is observed that depended on the laser intensity. To investigate PL properties of the nc-Si films, the films
were optically pumped by third harmonic (355 nm) of the Nd:YAG (1064nm) laser. The PL spectra of the silicon
thin films showed three distinct emission bands at 2.7, 2.2, and 1.69 eV.
26
PLD-2005: Invited Talks 朓T7
Pulsed laser deposited, highly c-axis oriented GaN thin films for field emitter applications
S. M. Jejurikar*, A. V. Limaye and K. P. Adhi
Advanced Laser Material Processing Laboratory, Centre for advanced studies in Materials Science and Solid State
Physics, Department of Physics, University of Pune, Pune -411 007, India
P. M. Koinkar, M. A. More, and D. S. Joag
Field ion microscopy and Field emission spectroscopy Laboratory, Centre for advanced studies in Materials Science
and Solid State Physics, Department of Physics, University of Pune, Pune -411 007, India
L. M. Kukreja
Thin Film Laboratory, Center for Advanced Technology, Indore ?452 013, India
*Email: suhas@physics.unipune.ernet.in
Abstract
Realizing GaN in highly oriented / epitaxial thin film form is currently a subject of active research interest.
This interest stems from the fact that GaN is potentially an important material for applications like UV-visible light
emitting device (LED), laser diodes, detecting devices, high temperature / high power electronics etc1-3. Further, the
lattice mismatch between GaN/ZnO and GaN/AlN is ~ 2 % and ~ 4 % respectively, suggesting that the thin films of
GaN could be ideal buffer layers for the epitaxial / highly oriented growth of AlN wide band gap semiconductor
films, for which no suitable low cost substrates are presently available. Here, we explore the possibility of using
GaN thin films for applications based on cold emission. We also discuss the field enhancement factor, stability of
emission etc. However in such applications, it is imperative to grow good quality thin films of GaN especially on
substrates of the most used electronic material i.e. Silicon (Si) albeit it is totally lattice mismatched. GaN thin films
were grow on Si/SiOx substrates by PLD. Excimer-laser (KrF gas; wavelength = 248 nm, pulse duration tp = 20
nsec, repetition rate = 10Hz) was used for the ablation of the GaN target which was synthesized in-house using
99.999% purity GaN powder (Aldrich Sigma). The laser fluence on the target surface was kept at 1.5 J/cm2. Base
vacuum in the chamber was of the order of 1 x 10 -6 Torr. High purity (99.999%) nitrogen was introduced into the
deposition chamber and the pressure was maintained at 5 x10-5 Torr throughout the deposition. The depositions
were carried out at substrate temperature of 800 癈 for duration of 1200 sec.
Inspite of large lattice mismatch (16 %), high thermal mismatch4-6 (~ 54%) and the large difference in the
crystal structure, highly c-axis oriented growth of GaN has been successfully obtained on Si / SiOx substrate. This is
clearly evident from the presence of (0002) plane of GaN in the XRD pattern. The FWHM of the (0002) peak is
estimated to be ~1.0o suggesting a highly strained film which is obvious. The surface morphology, as seen by AFM,
however does not show any cracks in the films, which is encouraging. The rms surface roughness of the films is ~
3.5 Å.
The field emission current-voltage (I-V) characteristics were recorded at a base pressure of 10-6 Torr. Field
emission current of ~ 30 nA was obtained at an applied voltage of 2.8 kV. Linear relationship in the corresponding
27
Fowler-Nordheim (F-N) plot of log (I/V2) versus 104/V confirms that the current is due to field emission7. The field
enhancement factor can be calculated using formula
= [ 2.97 × 103 × 3/2] / m
where is the work function of GaN (4.995 eV) and m is the slop of F-N plot. The factor in our case is estimated
to be 28,931 cm-1. High factor is desirable for devices using cold emission.
Acknowledgement: The authors KPA, AVL, LMK and SMJ would like to thank DAE- BRNS for the financial
support extended for carrying out this work under the project sanction No. (2002/34/21/BRNS).
References:
1. A. Castaldini, A. Cavallini, and L. Polenta, Appl. Phys. Lett. 87, 122105 (2005)
2. M. A. Reshchikov and H. Morkoc, Appl. Phys. Lett. 97, 061301 (2005)
3. S.Ito, J. Ohta, H. Fujioka, M. Oshima, Appl. Surf. Sci. 197 -198, 384 (2002)
4. Srinivasan Raghavan, Xiaojun Weng, Elizabeth Dickey, and Joan M. Redwing, Appl. Phys. Lett. 87, 142101
(2005)
5. A. Krost, A. Dadgar, G. Strassburger, and R. Clos, Phys. Status Solidi A 200, 26 (2003)
6. L. Macht,a_ P. R. Hageman, S. Haffouz, and P. K. Larsen, Appl. Phys. Lett. 87, 131904 (2005)
7. V. N. Tondare, C. Balasubramanian, S. V. Shende, D. S. Joag, V. P. Godbole,, S. V. Bhoraskar, M. Bhadbhade,,
Appl. Phys. Lett. 80, 4813 (2002)
28
PLD-2005: Invited Talks 朓T8
Growth and characterization of excimer laser-ablated bismuth vanadate
(Bi2VO5.5) thin films
Neelam Kumari* , K.B.R. Varma, S.B. Krupanidhi
Materials Research Centre, Indian Institute of Science, Bangalore-560 012
*Email : neelam@mrc.iisc.ernet.in
Abstract
Ferroelectric thin films have become increasingly important as future materials for electronic devices. Ferroelectric
random access memory (FeRAM) has been developed as an ultimate memory with both nonvolatility and a highspeed
read /write operation cycle, which have been quite difficult to attain in conventional fast static (SRAM) or
electrical erasable programmable read only memories (EEPROM)1. Bismuth based layered ferroelectric compounds
are being considered as potential candidates for memory devices due to their better fatigue characteristics2. Bismuth
vanadate Bi2VO5.5 (BVO) is a vanadium analogue of an n=1 member of Aurivillius family, [Bi2O2]2+[An-
1BnO3n+1]2- of oxides3.Bismuth vanadate, Bi2VO5.5 (BVO) is one of the most promising ferroelectric materials
owing to its low relative dielectric constant and requirement for low deposition temperature to grow an epitaxial thin
film4. Pulsed laser ablation technique has been employed to deposit the polycrystalline thin films of layered -
structure ferroelectric Bi2VO5.5 (BVO) on Pt coated Si substrates. The effect of oxygen pressure on the growth of
BVO thin films has been studied by depositing the thin films at different pressures. The substrate temperature was
optimized to be 6500C to obtain crystalline films. Figure 1.shows the x-ray diffraction pattern of BVO thin films at
different oxygen pressures. The strong and sharp Bragg peaks indicate that the pulsed laser ablation-grown films
were highly textured and possessed high degree of crystallinity. Scanning electron microscopy (SEM) was employed
to study the microstructure and the cross-sectional SEM images revealed a densely packed grains across the film and
the same was used to estimate the thickness of the film. Figure 2a and2b shows the surface and cross-sectional SEM
micrograph respectively and the thickness of the film estimated was around 600 30nm. The electrical properties
were studied in Metal-Insulator-Metal configuration. Ferroelectricity of the films was verified by examining the
polarization with the applied electric field and was also confirmed from the capacitance voltage characteristics (CV).
Figure 3a and 3b shows the polarization hysteresis and the capacitance-voltage characteristics of the film
deposited at 6500C. The film exhibited well-defined hysteresis loops, and the values of saturation (Ps) and remnant
(Pr) polarization were 7.89 C/cm2 and 3.09 C/cm2, respectively. Figure 4 shows the dielectric constant and loss
as a function of frequency at room temperature. The room temperature dielectric constant and dissipation factor
were 88 and 0.7, respectively, at a frequency of 100kHz. The charge transport in terms of oxygen ion vacancy
migration and dielectric relaxation phenomena are the most important characteristics for any oxide thin film device,
for practical as well as scientific reasons. These phenomena will be discussed.
29
PLD-2005: Invited Talks 朓T9
Pyramidal Nanostructures of ZnO
S. Angappane,* Neena Susan John and G. U. Kulkarni
Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O.,
Bangalore - 560 064, INDIA.
*Email: angappan@jncasr.ac.in
Abstract
Nanostructures of Zinc oxide have received considerable attention.1,2 Pulsed laser deposition (PLD) is a versatile
technique which has been used to obtain nanowires and nanorod arrays of ZnO.3 We have sought to prepare ZnO
nanostructures on silicon substrates using PLD under different deposition conditions and find their hardness and gas
sensing characteristics. We report here an unusual growth of ZnO in the form of well-defined pyramidal
nanostructures grown on a thin film of the same material.
A frequency tripled pulsed Nd:YAG laser (Quanta-Ray GCR-170, Spectra-Physics, USA) with a pulse
width of ~ 5 ns and repetition rate of 10 Hz was used for the ablation of ZnO target. A convex lens of 50 cm focal
length was used to focus the laser beam on to the target, through a quartz window fastened to the deposition
chamber, held at 10-6 Torr. The substrate, Si(100) was placed directly opposite to the target at ~ 5 cm, fastened to a
molybdenum boat whose temperature could be varied up to 1500 ºC. Prior to mounting, the silicon substrate was
cleaned using the piranha solution (1:2 H2O2:H2SO4) (Caution: this mixture reacts violently with organic matter) and
etched in HF (1:10 HF:H2O). The energy of the laser was optimized at 200 mJ per pulse to enable the desired
growth of the nanostructures. The deposition was made at different substrate temperatures (600 ºC and 900 ºC) and
for different deposition times (15, 30 and 45 minutes) under a pressure of 10 mTorr of oxygen.
Figure 1: AFM images of ZnO deposited for
45 minutes on a Si(100) surface held at
600ºC: (a) height image (b) friction image.
(c) Profile analysis of the image in (a), (d)
SEM image of the nanostructures collected
with the substrate oriented at ~ 5º to the
beam.
30
Atomic force microscope (AFM) and scanning electron microscope (SEM) images of the ZnO
nanostructures obtained after 45 minutes of deposition on the Si(100) surface held at 600 ºC, are shown in Figure 1.
The topography and friction images shown in Figures 1 a and b respectively reveal complimentary details of the
nanostructures. While the presence of micron-sized structures is apparent from the topography image (Fig. 1a), their
pyramidal morphology is revealed by the friction image in Figure 1b. The facets and the associated fine structures
with sharp edges are clearly seen in the friction image. The line-profiles of two of the nanostructures in Figure 1c
provide a base width of ~ 2 mm and a height of ~ 1 mm. The SEM image shown in Figure 1d, contains several such
pyramidal structures. Imaging in larger areas has shown that the pyramidal structures vary in a narrow size range of
1.5 to 2 mm. AFM images show a few small features after 15 minutes of deposition and a longer deposition for 30
minutes clearly produces larger and more number of structures of pyramidal morphology. Though pyramid-like
surface roughness has been reported,4 the pyramids observed in this work are unique in that they exhibit well
defined ordered growth of pyramidal nanostructures. By employing a higher substrate temperature of 900 ºC, we
could obtain a higher density of ZnO structures in the form of hexagonal islands.
The pyramidal morphology of ZnO nanostructures can be explained based on the growth habit of ZnO, as
illustrated in Figure 2. The growth rates of different faces of ZnO bear the following relation:
V > V > V V > V . <0 0 0 1> < 0 1 1 1> 0 1 1 0 <0 1 1 1> < 0 0 0 1> > < >
5 It may be noted that a crystal face whose growth is relatively fast would
eventually disappear giving space to a face that grows at a slower rate. Thus, the {0 1 1 1 } and {01 1 1 } faces having
higher growth rates have almost disappeared resulting in a four faced pyramid structure (see Fig. 2). Such a structure
perhaps belongs to an intermediate state in the growth of hexagonal nanorods reported by others.3 X-ray diffraction
from the sample containing pyramidal nanostructures showed a prominent peak corresponding to the (002) plane,
thereby implying a highly oriented nature of the nanostructures. As can be seen from Figure 1, the edges along the
Figure 2: (a) AFM image of a single pyramid (b) Growth habit of ZnO.
31
base of the pyramids are oriented along the axes of Si. The oriented pyramids of ZnO could be due to matching of
domains of 5 unit cells of ZnO (a, b = 3.25 Å) with 3 unit cells of Si (a = 5.43 Å).
The force-distance response following nanoindentation on a ZnO pyramid is shown in Figure 3 along with
that from the film surface. The projected area of the indent was calculated from the AFM images. The projected area
of the indent on the pyramid (770 nm2) is much less than that on the plane surface (4330 nm2). The hardness value
comes out to be 70 ?10 GPa for the pyramid, in contrast to 6 ?0.5 GPa for ZnO film.6 The increased hardness for
ZnO nanorods could be due to the increased surface energy relative to bulk.
Using conducting AFM measurements,7 the gas sensing properties of the pyramidal structures were
studied while controlling the flow of oxygen. In an oxygen atmosphere, the current decreases for positive bias
voltages, due to depletion of electrons from the conduction band due to adsorbed oxygen ions. By holding the AFM
tip engaged while leaking oxygen into the environmental hood, upto 70% variation in the resistance was obtained
from a pyramid.
References
1. Z.L. Wang, Materials Today 7, 26 (2004).
2. C. N. R. Rao, F. L. Deepak, G. Gundiah and A. Govindaraj, Progr. Solid State Chem. 31, 5 (2003).
3. Y. Sun, G. M. Fuge and M. N. R. Ashfold, Chem. Phys. Lett. 396, 21 (2004) and references therein.
4. E. Vasco, C. Zaldo and L. Vázquez, J. Phys.: Condens. Matter 13, L663(2001).
5. W. 朖. Li, E. 朩. Shi, W. 朲. Zhong and Z. 朩. Yin, J. Crystal Growth 203, 186 (1999).
6. V. A. Coleman, J. E. Bradby, C. Jagadish, P. Munroe, Y. W. Heo, S. J. Pearton, D. P. Norton, M. Inoue
and M. Yano, Appl. Phys. Lett. 86, 203105 (2005).
7. N. S. John and G. U. Kulkarni, J. Nanosci. Nanotech. 5, 587 (2005).
Figure 3: Nanoindentation on
(a) ZnO pyramid and (b)
surface of the ZnO film on
Si(100). Inset of (a) shows the
phase image of the indented
region. The corresponding
force-distance curves are shown
in (c) and (d). Hysteresis in F-D
response is an indication of
deformation.
32
PLD-2005: Invited Talks 朓T10
Synthesis of novel lithiated transition metal oxide thin films for microbattery application
O.M.Hussain
Thin Film Laboratory, Department of Physics, Sri Venkateswara University, Tirupati-517 50,
Email: hussainom48@yahoo.co.in
Abstract
Introduction: Advances in microelectronic industry, in particular, the development of microelectromechanical
systems (MEMS) technology, have reduced the current and power requirements to
extremely low levels. This has prompted the development of all solid state thin film microbatteries as
light weight, noise free and compact power sources. The realization of such thin film batteries originate
from the identification of new thin film cathode materials with high energy density, high specific
capacity and structural stability towards lithium insertion. The most recent candidates are a family of
lithiated transition metal oxides (TMO) 1,2. These compounds exhibit high potentials (>4V) with lithium
anode, structurally stable in fully lithiated state and can show very good reversibility. The synthesis of
these compounds in thin film form is of great interest as a result of their possible use as a binder free
positive electrode in all solid state microbatteries to power microelectronics. In the fabrication of TMO
films, the formation of open structure is found to be more crucial. The low temperature synthesis
provides smaller grain size and high surface area that greatly improves the cell performance. Recently
the pulsed laser deposition technique has been widely recognized as a very promising, versatile and
efficient method in the growth of high quality films from a variety of materials even containing volatile
components with complex stoichiometry 3. For this reason, it is a well suited for the growth of
transition metal oxide thin films compared to other conventional evaporation techniques where lithium
loss occurs due to volatilization. Hence in the present investigation, thin films of lithiated transition metal
oxides such as LiCoO2 and LiMnO2 were prepared by pulsed laser deposition technique. The structure
and surface morphology of these films were studied as a function of deposition parameters. The
electrochemical behavior of these films were studied by investigating the charge ?discharge profiles for
their effective utilization as cathode materials in microbattery applications.
Experimental: Thin films of LiCoO2 and LiMnO2 were prepared by pulsed laser deposition technique on
silicon substrates. The targets were prepared from high purity powders pressed at 5 tons/cm2 to make
pellets of 3 mm thickness and 13 mm diameter and sintered at 800 o C for 10 hrs. The target was rotated
at 10 rotations per minute to avoid depletion of material at the same spot. A KrF excimer laser with a
wavelength of 248 nm was used to ablate the target with an energy density of 300 mJ with a pulse
repetition rate of 10 Hz. The distance between the target and the substrate was typically 4.0 cm. The
films were deposited at various substrate temperatures (100 ?600 o C) and oxygen partial pressures (50 ?br> 200 mTorr).The structure of the films was studied by a Seifert X-ray diffractometer with a nickel filtered
CuK radiation (
= 1.5406 Å). The surface morphology of the films was studied by atomic force
microscopy (Digital instruments, 3100 series). The electrochemical measurements were carried out using
galvanostatic mode of a Mac-pile system in the potential range 2.0 ?4.2 V.
Results and discussion: Pulsed laser deposited films were found to pin hole free and well adherent to the
substrate surface. The influence of oxygen partial pressure ( pO2) and substrate temperature (Ts) on the
structure and surface morphology of the films was studied. The electrochemical properties of these films
were studied.
LiCoO2 thin films: The X- ray diffraction patterns of LiCoO2 thin films grown on silicon substrates
maintained at a substrate temperature of 300 oC in an oxygen partial pressure of 100 mTorr from a target
without Li2O additive displayed the presence of two additional small peaks at 2 = 45 and 59 o along
with the peaks at 2 = 18.95 and 38.48 o which can be attributed to the presence of cobalt oxide
impurities (Co3O4 Phase) due to lithium deficiency 4.
33
the LiCoO2 + 10% of Li2O target. The films exhibited only two peaks at 2 = 18.95 and 38.48 o which
are indexed as the (003) and (006) reflections (Fig.1) respectively, of hexagonal LiCoO2. The other
reflections such as (101), (012) and (104) which were usually observed for LiCoO2 powder samples were
not observed in XRD pattern. This indicates that the film has a preferred c-axis (00l) orientation
perpendicular to the substrate surface. In fact, this is the advantage of pulsed laser deposition for the
growth of oriented films at low temperatures when compared to other physical deposition methods like
electron beam evaporation. The AFM data demonstrated that the films deposited at 300 o C are
homogeneous and uniform with regard to the surface topography and thickness over an area of 1 cm2.
The surface topography reveals that the film is composed of roughly spherical grains of varying sizes and
the estimated average grain size was found to be 80 nm with a root mean square surface roughness of
about 6 nm. The individual grains are clearly visible and are seem to be in good contact with each other.
The films exhibit characteristic open and porous structure with small grains when deposited at low
substrate temperature (300 o C) and are highly useful as cathode materials.
The electrochemical properties of LiCoO2 films were tested by fabricating an electrochemical cell
with 1 M LiClO4 in propylene carbonate as an electrolyte and Lithium as an anode. The electrochemical
measurements were carried out at a rate of C/100 in the potential range 2.0 - 4.2 V. Typical chargedischarge
curves of Li//LiCoO2 cell is shown in Fig.2. The electrochemical process is seems to be a
classical intercalation mechanism for lithium ions into LixCoO2 matrix. In the high voltage region, the
cell delivers a specific capacity of 195 mC/cm2. m.
LiMn2O4 films: Thin films of LiMn2O4 were prepared by pulsed laser deposition technique onto well
cleaned silicon wafers maintain at 300 o C in an oxygen partial pressure of 100 mTorr from a target of
LiMn2O4 in which the Li/Mn ratio was 1.1. The X-ray diffraction pattern displays peaks at 2 = 16.1,
35.9 and 47.2 o which are attributed to the (111), (311) and (400) Braggs lines of regular spinel
Fig. 1 XRD pattern of LiCoO2 thin film deposited at Ts = 300 o C in pO2 = 100 mTorr
Fig. 2 Charge Discharge profile of Li / LiCoO2 cell Fig. 3 Charge Discharge curves of a Li / LiMn2 O4Microbattery
34
structure 5. The surface morphological data of these films demonstrated that the film consists of uniform
spherical grain with an average grain size of 50 nm. The films were used as cathode materials and tested
in lithium microbatteries with 1 M LiC1O4 in propylene carbonate as an electrolyte. The charge and
discharge curves of Li//LiMn2O4 were tested in the potential region 3.0 ?4.2 V at a rate of C/100 (Fig.3).
An initial voltage of about 3.4 V vs. Li/Li+ was observed for the LiMn2O4 thin film cathode cells. The
cell voltage profiles displayed several plateaus and the voltage of each plateau is a function of structural
arrangement. In the high voltage, region the cell delivers a specific capacity of 120 mC/cm2 m.
Conclusions: Lithiated transition metal oxides such as LiCoO2 and LiMn2O4 thin films were deposited
by pulsed laser deposition technique. The films deposited in an oxygen partial pressure of 100 mTorr and
at a substrate temperature of 300 o C were found to be nearly stoichiometric with good crystalline
structure. The surface morphology of these films exhibited uniformly distributed roughly spherical
grains. The electrochemical properties of these were tested by fabricating electrochemical cells with the
grown films as cathode materials and Lithium as an anode. The cells with LiCoO2 thin films as cathode
delivered a specific capacity of 190 mC/cm2 m where as the cells with LiMn2O4 thin films delivered
only 120 mC/cm2 m. The results suggest that the pulsed lased deposition is an excellent method for the
growth of lithiated transition metal oxide thin films with a promising application in the fabrication of all
solid state thin film microbatteries.
References:
1. J.B.Bates, N.J.Dudney, B.Neudecker, A.Ueda, C.D.Evans, Solid State Ionics, 135(2000)33
2. C.Julien, H.E.Parriatovski, O.M.Hussain and C.V.Ramana, Ionics, 7(2001)165
3. J.C.Miller and R.F.Haglmel , Laser Ablation and Deposition, Academic Press, New York,1998
4. K.A.Striebel, C.Z.Deng, S.J.Wen and E.J.Cairns, J.Electrochem.Soc., 143(1996)1821
5. D.Singh, W.S.Kim, V.Cracium, H.Hofmann, R.K.Singh, Applied Surface Science,
197(2002)516.
35
PLD-2005: Invited Talks 朓T11
Preparation of Pure and Al-; Ga-; In-Doped ZnO Thin Films by Pulsed Laser Deposition
and Radio Frequency Sputtering and Their Characterization ?An Overview
V. N. Mani
Centre for Materials for Electronics Technology (C-MET),
Cherlapalli, Hyderabad 500 051
Email: vnm_crystal272001@yahoo.com
Abstract
The results highlighted in this talk pertain to the pure and Al-, Ga- and In-doped ZnO thin films growth by pulsed
laser deposition (PLD), radio frequency (RF) sputtering and their structural, optical, electrical and surface
characterization. The focused research methodology, which was adopted during the study, is as follows: Initially a
batch of pure and Al-, Ga-, In-doped ZnO samples have been prepared and their properties were studied. After
ascertaining the property improvement with respect to the varied and modified experimental conditions and
parameters, further optimized deposition cycles have been carried out. A series of pure and Al-, Ga-, In-doped ZnO
thin films on glass and silicon substrates have been grown by the PLD and pure ZnO thin films were also deposited
by RF sputtering. Gallium of 5N+ purity, aluminum and indium of 4N purity were used for depositing of doped ZnO
films. The effect of various experimental conditions and parameters such as laser and r.f. power, substrate
temperature, deposition time, partial pressure of gases on the structural, optical, electrical properties of the ZnO thin
films have been studied. X-Ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis-NIR spectroscopy,
hall measurement system were used to characterize the ZnO films. To conclude, growth parameters and heat
treatment influence the structural homogeneity and surface properties of the ZnO thin films. The results on the
crystalline quality and surface morphology of the pure and doped ZnO films vis-à-vis deposition conditions and
parameters are interpreted.
36
PLD-2005: Posters ?P 1
Bandwidth control effects in electron doped manganite La 0.7-x Y x Ce 0.3 MnO3
K. P. Bajaj#, P. Raychaudhuri*, John J*and V. Bagwe*
# Dept.of physics,Mumbai University,Mumbai-400089.
#Email: bajajkp@rediffmail.com
*Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi
Bhabha Rd., Colaba, Mumbai 400005.
Abstract
We report on the effect of average A site cation radius on the structural, magnetic & electrical
properties of electron doped manganite La0.7Ce0.3MnO3 thin films. A site cation radius rA is varied
systematically by replacing La+3 ions by smaller Y+3 ions in the parent compound. The carrier doping,
i.e. the fraction of tetravalent Ce atoms at the A-site was kept at 30%. A series of La0.7-xYxCe0.3MnO3
(x=0,0.05,0.1,0.15,0.25) thin films were prepared under identical conditions by using pulsed laser
deposition technique. Metal insulator transition temperature (Tp) & Ferromagnetic Curie temperature
(Tc) are found to be decreasing significantly with increasing yttrium concentration i.e decreasing rA .
Amplitude of resistivity increases by one order of magnitude, while Spontaneous magnetization
decreases with decreasing rA . Magnetoresistance as measured under field of 1Tesla is significant near
Tc. Structural analysis reveals the films are having single phase & c-axis lattice parameter decreasing
linearly from 7.7895 Ao to 7.7406 Ao as rA decreases from 1.294 nm for parent compound to 1.25 nm
for the highest doped sample. The decrease in rA (lattice distortion) results in decrease in Mn-O-Mn
bond angle which in turn reduces the matrix element of electron hopping between Mn+2 and Mn+3 and
reduces the carrier bandwidth of eg band. Thus we have studied the evolution of magnetotransport
properties of electron doped manganite by controlling Bandwidth.
37
PLD-2005: Posters ?P 2
Electrochemical Properties of
Pulsed Laser Deposited TiO2 ?Doped LiCoO2 Thin Films
M. C. Rao and O.M.Hussain*
Thin Film Laboratory, Department of Physics, Sri Venkateswara University,
TIRUPATI ?517 502, India.
*Email: hussainom48@yahoo.co.in
Abstract
LiCoO2, one among the transition metal oxides has received significant attention in the fabrication of
rechargeable lithium ion batteries because of its high theoretical specific capacity, energy density and high cycling
stability. The deposition of LiCoO2 in thin film form is of great interest because of their possible use as positive
electrode in all solid state microbatteries to power microelectronics. Hence in the present investigation Ti-doped
LiCoO2 thin films were grown by pulsed laser deposition technique. The influence of deposition parameters on the
growth and electrochemical properties of Ti-doped LiCoO2 thin films were studied. Li//LiTiyCo1-yO2 cells were
tested in the potential range 2.6-4.2 V. Specific capacity as high as 225 mC/cm2mm was measured. These results
suggest that the Ti-doped LiCoO2 PLD films find potential applications as binder free electrode in the fabrication of
all solid state microbatteries.
38
LD-2005: Posters ?P 3
39
40
41
PLD-2005: Posters ?P 4
Structural and electrical behavior of Mg doped ZnO thin films grown by pulsed laser ablation
Dhananjay and Nagaraju J.
Department Of Instrumentation, Indian Institute Of Science, Bangalore 560012, India
Palash Roy Choudhury and S.B.Krupanidhi
Email: dhaya@isu.iisc.ernet.in
Materials Research Center, Indian Institute Of Science, Bangalore, 560012, India
Abstract
Mg doped ZnO thin films were grown on various substrates like (100) oriented Si and corning glass by pulsed laser
deposition (PLD) technique. Highly c-axis oriented films were grown at a substrate temperature of 5000C and
100mTorr oxygen ambient. The films were highly resistive and possess a compact nodular surface morphology with
a columnar structure in cross-section. Both dc and ac transport properties of the films were carried out in order to
reveal the conduction mechanism in these films. The current-voltage characteristics of these films indicated an
ohmic behavior in the low voltage region, while higher voltages induced bulk space charge. Dielectric response of
these films deposited by PLD has been studied as a function of frequency over a wide range of temperature. The
films exhibited frequency dispersion in both real and imaginary part of the dielectric constant and could be attributed
to the space charge effect. It has been observed that the incorporation of Mg into the ZnO lattice enhances the
dielectric constant. The average transmittance of the films was higher than 90% in the wavelength range 400-
900nm. The band gap was enhanced to 3.7eV with 20%Mg doping into the ZnO lattice making the band gap
engineering feasible.
42
20 30 40 50 60 70
(c)
(b)
(a)
Intensity (arb.units)
2q
(a) 3000C
(b) 4000C
(c) 5000C
43
0.1 1
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
Current Density (Acm-2)
Voltage (V)
200 300 400 500 600 700 800 900
50
60
70
80
90
100
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
(ahn)2(cm-2ev2)
Energy (hn)
Transmittance (T)
Wavelength (nm)
100 1000 10000 100000
5
10
15
20
25
30
35
Dielectric Constant (e)
Frequency (Hz)
223 K
233 K
243 K
273 K
293 K
303 K
323 K
100 1000 10000 100000
0
5
10
15
Imaginary part of
dielectric constant (e")
Frequency (Hz)
223 K
233 K
243 K
273 K
293 K
303 K
323 K
References:
1. K.Matsubara, H.Tampo, H.Shibata, A.Yamada, P.Fons, K.Iwata, and S.Niki, Appl.Phys.Lett. 85 (2004)
1374
2. S.Choopun, R.D.Vispute, W.Yang, R.P.Sharma, and T.Venkatesan, Appl.Phys.Lett. 80 (2002) 1529
3. T.Minemoto, T.Negami, S.Nishiwaki, H.Takakura, and Y.Hamakawa, Thin Solid Films 372 (2000) 173
44
PLD-2005: Posters ?P 5
Bright Luminescence from Gadolinium
doped Silicon nanoparticles prepared by off axis Pulsed Laser Deposition
J.R.Rani*, and V.P.Mahadevan Pillai
Department of Optoelectronics, University of Kerala, Thiruvananthapuram,Kerala, India - 695581
*Email: ranijnair @rediffmail.com
Abstract
Silicon , which is the backbone of microelectronic industry is not widely used for optoelectronic
industry because of its indirect band gap . But silicon nanostructures having a quantum confinement effect have
provided a breakthrough to optoelectronic applications because the quantum confinement effect enhances the
electron-hole radiative recombination rate1 .Rare earth doping of silicon based compounds has been the subject of
intensive research because of its potential to combine sharp , temperature stable rare earth luminescence with the
convenience of electrical excitation . The approach of introducing Gd ions in to Silicon networks is a very promising
alternative for using Silicon in Optoelectronic industry . The distinctive energy level diagram of Gd3+ ions is
motivating the perspectives of a new compound for photonic applications . As a Light-emitting devices made of
silicon-based materials can be integrated into the existing microelectronic and optoelectronic technologies in a
highly economic way; therefore enormous efforts have been devoted to the development of silicon-based structures
that promise efficient light emission in the past decade2. From the point of view of optoelectronic applications ,
such devices should offer tunable light emission with utilizable efficiency in the whole visible light range or at even
shorter wavelengths.
In this paper we report the pulsed laser deposition of Gadolinium doped Si nanoparticles at room
temperature . The deposition was carried out by keeping the substrate in the off axis configuration . Gadolinium
doped Si pellets were used as the target material and fused quartz as the substrate. A Q - switched frequency
doubled Nd: YAG laser ( fluence of 4x 10-6 J/m2 at 532 nm, 9 ns pulse width, 10Hz repetition frequency ) was used
to ablate the target . The Gadolinium concentration used as 1at%.The Target was rotated with constant speed to
ensure uniform ablation .The substrates were kept at target to substrate distance 5mm and 3cm off axis with respect
to laser plume
Deposition chamber was initially evacuated to a base pressure of 5x10-6mbar and deposition was done at
room temperature. Optical absorption spectra were recorded using a UV-VIS-NIR spectrophotometer (Hitachi U
3410) in the spectral range of 200 ?800 nm. The band gaps were determined from the plot ( h )m verses h and
by extrapolating the linear position near the onset of absorption to the energy axis 3-4 . Photoluminescence spectra of
erbium doped Silicon nanoparticles specimens have been measured and analyzed to extract spectral contributions
due to quantum confinement effects . The PL measurements were recorded by JobinYvon Spectro flurometer
(Flurolog III) . PL emission wavelength varies between 375 and 550nm depending upon the excitation wavelength .
PL results shows that luminescence does not originate from localized states in gap but from extended states.
The nano structure of films was examined by a HITACHI H ?600 TEM operated at 75 KV.. The
transmission electron microscope image clearly shows that Si quantum dots are well organized in the silicon matrix
and the average grains size is around 1.5 nm.
[1] Takagi H, Ogawa H, Yamazaki Y, Ishizaki A and Nakagiri T 1990 Appl. Phys. Lett. 56 2379
[3] Baru V G, Chernushich A P, Lauzanov V A, Stepanov G V,Zakharov L Yu, O扗onnell K P, Bradley I V and
Melnik N N 1996 Appl. Phys. Lett. 69 4143
[4]A.Goswami, Thin film Fundamentals, New Age International (p) Limited (1996)
[5] Pankove J I, Optical processes in semiconductors, New Jersey, USA, 1971, p. 34
45
PLD-2005: Posters ?P 6
Characterization of Pulsed Laser Deposited Tungsten Trioxide (WO3) Thin films
K.J. Lethy*, J.R.Rani, D.Beena, R.Vinodkumar, K.G. Gopchandran &V.P.Mahadevan Pillai
Department of Optoelectronics,University of Kerala, Thiruvananthapuram,Kerala, India -695 581
*Email: lethykj@yahoo.co.in
Abstract
Tungsten trioxide (WO3) thin films are of great technological interest as transparent conducting
electrodes and hold a central role in the emerging field of optical switching devices1, 2. WO3 is an n-type transition
metal oxide semiconductor which is a representative of a group of materials known as chromogenics. It displays
both electrochromism -change of colour with an applied electric field, and photochromism 杢he change in colour
under illumination. Moreover WO3 is a widely used gas detector to detect toxic gases like CO, H2S, and NOx in
domestic, commercial and industrial applications3.
Thin films of tungsten oxide were deposited on fused quartz (silica) substrates using pulsed laser deposition
technique. A Q-switched Nd: YAG laser (Quanta-Ray INDI ?series, Spectra Physics) with a wavelength of 532 nm,
pulse width 8 ns, repetition rate of 10 Hz, and maximum output energy 250 mJ was used to ablate the WO3 target.
Commercial WO3 powder of 99.995% purity was used to make pressed target (11 mm in diameter and 4 mm
thickness). The target was rotated uniformly during deposition to avoid depletion of material at any given spot and
to obtain uniform thin films. The deposition chamber was evacuated to a base pressure of 4x10 -6 mbar using a
diffusion pump and a rotary pump. Thin films were grown in a non-reactive atmosphere at room temperature. Thin
films were deposited by both on-axis (substrate to target distance 7.5 cm) and off-axis (substrate to target distance 3
cm) laser deposition method. The deposition time was 15 minutes and the energy of the laser beam was maintained
at 93 mJ during deposition. The as deposited films (both on-axis and off-axis ) were metallic in appearance. It has
been reported by J.G Zhuang et.al that WO3-y films have a metallic aspect for y>0.5 and are conductors 4. Films
were annealed at two different temperatures 623K & 773K for 3 hours in air.
X-ray diffraction (XRD) measurements were carried out to study the crystalline properties of the prepared (asdeposited
and annealed at 623K &773K) WO3 films. The XRD pattern was recorded using CuK - radiation of
wavelength (1.54056 Ao). Study of x-ray diffraction pattern of films reveals that as-deposited films are amorphous
while the films heat-treated at 773K for 3 hours in air crystallize to WO3. The average grain size of the crystallites
were estimated to be about 30 nm by using Scherrer抯 formula 5. Effect of post -annealing on crystallization and
grain size was also studied.
Optical transmittance (T) and reflectance (R ) were measured by spectrophotometry in the wavelength range
200-800 nm. The quartz substrates used are transparent in this range. Measurements were carried out using UVVIS-
NIR Spectrophotometer (Hitachi U 3410). The transmittance of the as - deposited films were nearly 50%.
From the absorbance spectra band gap energy of the as deposited films were estimated to be about 3.8eV and it
shows a blue shift in band gap energy compared with the band gap energy of bulk sample which is about 3.25 eV.
The impact of heat-treatment on percentage transmittance and band gap energy were also examined.
46
Only a few reports were available on the photoluminescence properties of tungsten trioxide thin films6, 7.
Photoluminescence spectra of the films were recorded using Jobin Yvon Fluorolog-III (450 W Xe arclamp,
excitation at 260 nm) Spectroflurometer. These laser ablated films exhibit strong PL emission at 404 nm.
Variation of photoluminescence emission with annealing was also studied. The surface morphology and the
crystalline grain size of the grown films were investigated using Transmission Electron Microscopy (HITACHI H-
600 TEM) operating at 75 kV.
References
[1] Hiroharu Hawasaki, Jun Namba, Keitarou Iwatsuji , Appl.Surf.Sci. 197 -198 (2002) 547-551
[2] Robert G.Palgrave, Ivan P Parkin, J.Mater.Chem. 2004, 14, 2864-2867
[3 ]W.Gopel, K.D Schierbaum , Sens. Actuators B 26-27 (1995) 1
[4] J.G Zhuang, D.K benson, C.E Tracy, S.K Deb, A.W Czanderna, C.Bechinger, J.Electrochem.Soc. 144 (6) (1997)
2022
[5] B.D Cullity, Elements of X-ray Diffraction (Addison-Wesley, Reading, MA,1959)
[6] Kwangyeol Lee, Won Seok Seo, and Joon T. Park, J.AM.CHEM.SOC.2003, 125,3408-3409
[7] Feng. M , Pan A.L, Zhang H.R, Li . Z .A, Appl.Phys.Lett. 86 (14) 2005
47
PLD-2005: Posters ?P 7
AC conduction studies of pulsed laser ablated multiferroic BiFeO3 thin film
Somenath Bose?and S.B.Krupanidhi
Materials Research Centre, Indian Institute of Science, Bangalore-560 012
*Email: bose@mrc.iisc.ernet.in
Abstract
Magnetoelectric materials, in which both magnetic and electric ordering exists, has generated increasing interest in
recent times due to their application potential in different devices, e.g. sensors, memories, actuators etc [1]. Bismuth
ferrite (BFO) is a magnetoelectric multiferroic material in which both ferroelectricity and anti-ferromagnetism exists
at room temperature. In the present work BiFeO3 (BFO) thin films were deposited from sintered target of BiFeO3 by
pulsed laser deposition technique. BFO films were deposited at 675癈 at 50mTorr oxygen pressure. Laser pulse
frequency was 5 Hz and fluence 4 J/cm2 (approx.) during deposition. Polycrystalline nature of as-deposited films
was verified by x-ray diffraction pattern in a scintag xrd-instrument. BFO films obtained show a preferential
orientation along (110) direction with low intensity (012) and (024) peaks. Gold dots were deposited on top of asdeposited
films by thermal evaporation for electrical characterization. Ferroelectric hysteresis (fig.1) measured in a
RT-66A loop tracer confirms the ferroelectric nature of BFO films. A maximum polarization of 4.2 μC/cm2 was
obtained at a field of 81.7 kV/cm, which is comparable to other studies on polycrystalline BFO films [2]. Saturated
hysteresis loop could not be obtained due to leaky nature of the sample. Magnetic hysteresis was measured in a
lakeshore vibrating sample magnetometer and shows the ferromagnetic nature (fig.2) of the sample. Saturation
magnetization attained (1.75 emu/cm3) is very small as compared to magnetic ferrite thin films. This unexpected
ferromagnetic nature in thin film form is explained by the canting of spins of Fe atoms. DC and AC transport studies
were performed on BFO thin films to find out the exact nature of electrical conduction and dielectric relaxation
mechanism respectively. Leakage current density increases very fast with increase in temperature. AC impedance
analysis shows that the material response is non-Debye type with distribution of relaxation times. Only one
semicircle (fig.3) was obtained in the complex impedance plane plot (Z'-Z"). This is believed to arise from the grain;
grain boundary or electrode response was not observed in the frequency (100Hz-100kHz) window of the
experiment. AC conductivity of the material increases with frequency (fig.4) at low temperatures and obeys
Jonscher抯 power law [3] relationship. A frequency independent plateau in ac conductivity was observed at high
temperatures, which shifts towards high frequency side with increase in temperature. At temperatures higher than
200ºC ac conductivity becomes almost frequency independent, this was due to dc conduction, which is frequency
independent. AC conductivity shows Arrhenius type behavior with temperature (fig.5) with two distinct activation
energies, which can be attributed to two different conduction mechanisms. At low temperatures activation energy
varies between (0.07 to 0.13eV) for different frequencies and is expected to arise from hopping conduction between
defect states. At high temperatures the activation energy increases to 0.9 to 1.1eV, which is very common in
ferroelectric oxide thin films [4] and arises due to oxygen vacancy conduction. A further confirmation of the oxygen
vacancy transport was obtained from DC studies, where the dc conductivity v/s reciprocal temperature plot also
gives activation energy in the same range (0.85-1.15eV).
?Contact author email id: bose@mrc.iisc.ernet.in
48
-160 -120 -80 -40 0 40 80 120 160
-5
-4
-3
-2
-1
0
1
2
3
4
5
Fig1. Ferroelectric hysteresis loop of BFO thin film at room temperature.
Polarization
mC/cm2
Electric field
kV/cm
6 v
8 v
10 v
-1000 -500 0 500 1000
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
Fig2. Ferromagnetic hysteresis loop of BFO thin film at room temperature.
Magnetization (emu/cm3)
Applied magnetic field (G)
0 20000 40000 60000 80000
0
20000
40000
60000
80000
Fig.3. Complex impedance plane plots at different temperatures.
Z" (W)
Z' (W)
(205oC)
(215oC)
(225oC)
49
100 1000 10000 100000
1E-7
1E-6
1E-5
1E-4
1E-3
Fig.4. AC conductivity with frequency at different temperatures.
AC conductivity (ohm-1m-1)
Frequency (Hz)
40
100
130
150
175
195
215
235
255
Major References:
1. J. Wang, J. B. Neaton, H. Zheng, V. Nagarajan, S. B. Ogale, B. Liu, D. Viehland, V. Vaithylyanathan, D.
G. Schlom, U. V. Waghmare, N. A. Spal-din, K. M. Rabe, M. Wuttig, and R. Ramesh, Science 299,1719
(2003).
2. V. R. Palkar, J. John, and R. Pinto, Appl. Phys. Lett. 80, 1628 (2002).
3. A. K. Jonscher, Dielectric Relaxation in Solids (Chelsea Dielectrics, London, 1983).
4. S. Saha and S. B. Krupanidhi, J. Appl. Phys. 87,849 (2000).
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2
1E-6
1E-5
1E-4
1E-3
Fig.5. Arrhenius type behaviour of ac conductivity.
AC conductivity (ohm-1m-1)
1000/T (K-1)
ac conductivity(1khz)
ac conductivity (10khz)
ac conductivity (100 khz)
50
PLD-2005: Posters ?P 8
Pulsed Laser Deposition of Magnetite thin films
Murtaza Bohra1, Naresh Kumar1, D. S. Misra1, N.Venkataramani2 and Shiva Prasad1
1Physics Department, 2 Department of Metallurgical Engineering and Material Science2,
Indian Institute of Technology Bombay Powai, Mumbai 400076,
Abstract
INTRODUCTION
Pulsed laser deposition (PLD) has been shown to be very successful method for growth of materials in thin film
from both as epitaxial layers and as amorphous films. Few of the characteristics feature of PLD are, stoichiometric
transfer, and growth from an energetic beam, reactive deposition, and simplicity of operation.1 Recently Fe3O4 films
have received a lot of attention due to combination of several interesting properties. They are half metallic as per
band-structure calculations2. They also have high Curie temperature (Tc) of 858K and a weak magneto-crystalline
anisotropy. Hence they are being looked as future spintronic materials.
We have deposited Fe3O4 thin film by PLD from Fe3O4 and a-Fe2O3 targets. In this brief report, we will
discuss the magnetic, electrical, and crystalline properties of Fe3O4 film deposited by PLD from a-Fe2O3 target on to
fused quartz substrate.
EXPERIMENTAL DETAILS
The Fe3O4 thin films were grown on fused quartz substrates by PLD using Q switched Nd:YAG laser (
=355 nm,
pulsed width 5 ns and 10 Hz repetition rate) from a-Fe2O3 target. The typical fluence of the focused laser beam on
the target was 2.5 J/cm2. The substrates were kept at a distance 3.5 cm from the target and heated in situ to 350癈
during deposition. The chamber was evacuated to a base vacuum of 5.4 ´ 10-6 mbar and during the deposition
vacuum of 1 ´ 10-5 mbar was maintained. The as deposited film was also annealed in wet H2 atmosphere at 450癈
for 15 min. The crystal structures of the films were studied by x-ray diffraction (XRD). The MS was measured at RT
using a vibrating sample magnetometer (VSM). Resistivity (r) of the films was measured by four-probe method in
range of 50 K to RT and the magneto -resistance (MR) at RT in a field of 2.4T.
RESULTS AND DISSCUSTION
15 30 45 60 75 90
(220)
(444)
(440)
(333)
(400)
(222) (311)
(111)
Intensity (a.u.)
2q(Degree)
Figure1. XRD patterns for Fe3O4 film.
51
Figure 1 shows the X-ray diffraction pattern of the Fe3O4 film. The lattice constant a = 0.8392 nm is close .to the
JCPDS (card no.19-0629) value of cubic Fe3O4 bulk powder.
g -Fe2O3 has a similar crystal structure to that of Fe3O4 with a lower magnetization value. Hence the film has
been characterized using x-ray photoelectron spectroscopy (XPS). It is well established that the satellite peaks in the
XPS spectroscopy can help to identify the chemical states of iron in its oxides.3 One remarkable difference between
the g-Fe2O3 and the Fe3O4 is that the former has satellites in the Fe 2p core level spectra while the latter does not
have this satellite feature. Figure 2 shows the Fe 2p core-level spectroscopy of the film, obtained with normal
emission using Mg-K a radiation, which agrees well with the reported Fe3O4 spectra.3 The broad Fe-2p peaks are
attributed to the coexistence of Fe3+ and Fe2+ states, and at the same time, no satellites could be identified around the
binding energy of 719 eV. This excludes the possible presence of g-Fe2O3 in our film.
705 710 715 720 725 730
Fe Fe+3 +3 Fe+2 Fe+2
Fe 2pFe 2p 3/2 1/2
Intensity (a.u.)
B.E (eV)
Figure2. Fe 2p core-level XPS spectra for Fe3O4 film.
The value of saturation magnetization (4 Ms) of the Fe3O4 film is 5370 G, which is 91% of the bulk value of
5900G and the coercive field is about 320 Oe. The lower magnetization value for the film is in keeping with several
reported observations in the case of thin film materials.
The room temperature resistivity (r) values for Fe3O4 film was found to be ~90 mWcm. In Fig.3, the four-probe
resistance was recorded as a function of temperature. The Arrhenius plot (ln r vs 1/T in the inset) shows a linear
relation, suggesting a thermally activated hopping transport mechanism. An activation energy of Ea ~ 76 meV was
estimated by fitting the curve using r = r
0 exp (Ea/kBT). Also noteworthy is the absence of Verwey transition in
these films, which has also been observed in polycrystalline Fe3O4 films4. It was suggested that in a system with
high resistivity and small grain size, the linear hopping chain lengths are shortened5 and thus preventing the
occurrence of Verwey transititon.
The magnetoresistance, MR = 1− (RH/R0) for a resistance RH in a magnetic field H and the maximum value R0 for
the Fe3O4 film measured by applying the magnetic field of 2.4 T.
52
0 50 100 150 200 250 300
0.0
500.0k
1.0M
1.5M
2.0M
0.004 0.008 0.012
3
6
9
12
15
ln( r)
1/T(K)
R(W)
T(K)
Figure3. Resistance (R) vs temperature (T) curve. (Inset) lnr plotted as a function of 1/T.
The MR was measured in transverse geometry, with the current perpendicular to the magnetic field. A negative MR
of 2.1 % was observed for the films at room temperature in a magnetic field of 2.2 T. The negative MR in such thin
films has been described to occur though a spin dependent tunneling in the network of contiguous grains5.
Conclusion: We have deposited Fe3O4 thin films with magnetization value close to the bulk, from Fe2O3 target,
on quartz substrates using PLD. XPS data correlates the presence of single phase Fe3O4 inferred from the XRD
observation. A room-temperature MR of ~2.1 % was also observed.
References
1. W. M. K. P. Wijekoon and M. Y. M. Appl. Phys. Lett. 67, 1698 (1995).
2. Yanase and K. Siratori, J. Phys. Soc. Jpn. 53, 312 (1984).
3. Ruby, B. Humbert, and J. Fusy, Surf. Interface Anal. 29, 377 (2000).
4. Hui Liu, E.Y.Jing and X.X.Zhang Appl. Phys. Lett. 83, 3531 (2005).
5. W. Eerenstein, and S. Celotto, Phys. Rev. B 66, 20110(R) (2002).
53
PLD-2005: Posters ?P 9
Physical properties of doped ZnO thin films grown by Pulsed Laser Deposition
Shubra Singh, N Rama, M.S.Ramachandra Rao
Department of Physics and Material Science Research Centre,
Indian Institute of Technology (IIT) Madras, Chennai - 600 036.
Abstract
Pulsed laser Deposition (PLD) has been found to be a very viable technique for the deposition of diluted magnetic
semiconductor (DMS) thin films due to its versatility, simplicity, and control of stoichiometry. Recent trends in this
area have emphasized its unique properties and have made it a prime thin film growth tool for growing highly
crystalline compound semiconductor epitaxial layers. The purpose of this paper is to evaluate the physical properties
of rare-earth (RE) and transition metal (TM) ion doped ZnO thin films grown by PLD. The recent spur of activity
that promoted ZnO as a promising DMS (diluted magnetic semiconductor) host, compared to Mn-doped GaAs, with
metal ion doping [1] has prompted us to undertake the work reported in this abstract. ZnO can be grown into largescale,
high-quality single crystalline thin-films and ZnO is a potential host for rare-earth (RE) ion doping [2].
In a search for new methods for growing diluted magnetic semiconductors (DMS), we have made an attempt to
make Zn1-xDyxO and its structural and magnetic properties were studied. Role of ZnO as DMS host has also been
explored by doping it with a transition metal ion like Ni and the electrical, optical as well as magnetic properties
were studied. The bulk as well as thin film resistivity was found to decrease remarkably with small concentrations
(0.0 <x<0.3 mol%) of Ni which definitely makes, if magnetism is found, it a transparent ferromagnet that can offer
interesting magneto-optic applications.
Key words: PLD, ZnO, Thin films
[1]. J. M. D. Coey et al. Appl. Phys. Lett. 84, 1332 (2004).
[2] W.M. Jadwisienczak et al. Journal of Electronic Materials, 31,776-784,s (2002).
54
PLD-2005: Posters ?P 10
Deposition of silicon nitride films by DC discharge aided pulsed laser deposition
Ram Prakash* and D.M.Phase
UGC-DAE Consortium for Scientific Research, Khandwa Road, University Campus, Indore-452 017.
*Email : ramprakash@csr.ernet.in
Abstract
Silicon nitride is one of the most interesting thin film materials in the semiconductor device technology.
The outstanding advantages of thin films in the silicon-nitrogen system are the tailorable electronic and optical
properties, which are highly dependent on the chemical composition. There are some reports on the fabrication of
silicon nitride films by Pulsed Laser Ablation (PLA) technique in ammonia gas. Preparation of the silicon nitride
film from a Si target and nitrogen gas thought to be difficult since nitrogen gas is stable. In this paper we report a
synthesis of silicon nitride films by DC discharge aided reactive pulsed laser deposition (PLD). The PLD was
performed in a custom made high vacuum chamber. This PLD chamber is modified and two planer circular (7cm
dia.) electrodes were fitted above and below the target assembly. DC supply of 500V was connected to generate the
discharge. The ablation energy source was a KrF excimer laser of l = 248 nm. The beam was focused down to a size
of ~ 2 x 1 mm2, onto the surface of a target. A high purity single crystal silicon wafer was used for the target and
substrate. The distance between target and substrate was 40 mm. The target was rotated at 5 rev/min.. Silicon nitride
films were synthesized at room temperature by means of laser ablation of a silicon target with and without DC
discharge in pure nitrogen gas. Deposited films were characterized by using Scanning electron microscopy with
EDX analysis, Atomic force microscopy and x-ray photoelectron spectroscopy. The film deposited with and without
DC discharge show drastically different behavior. It is found that DC discharge aided films show higher and
uniform nitrogen content than that of film deposited without DC discharge. Our results indicate that presence of the
DC discharge during the deposition lead to enhance nitridation of the ablated silicon.
55
PLD-2005: Posters ?P 11
PLD grown nanostructured n-Carbon/p-Si thin film interfaces
K. Mohan Kant1,2,*, K.Sethupathi2, and M.S. Ramachandra Rao 1,2
1Materials Science Research Centre, Indian Institute of Technology Madras, Chennai.
2Department of Physics, Indian Institute of Technology Madras, Chennai.
*Email: mohankant@physics.iitm.ac.in
Abstract
Nanostructured carbon thin films are of great interest due to their potential device applications. Carbon films
interfaced with (n or p type) Si substrates which show non linear I-V characteristics have potential application in
field-emission devices (FEDs) [1]. We have studied the effect of growth parameters on the physical properties of
PLD grown carbon films using a graphite target at different Ar-partial pressures. Atomic force microscopy (AFM)
studies showed that the grain size is about 80-90 nm. Substructures were seen in the thin films grown for higher
deposition time (~ 30 min) corresponding to a thickness of 300 nm. With decrease in deposition time, grain size was
found to decrease correspondingly. All the films showed semiconducting behaviour. The conduction mechanism
was found to be 3D Variable Range Hopping (VRH) mechanism. Carbon films were found to be n-type (n-C). We
have deposited n-C films on p-Si substrates to study the current-voltage (I-V) characteristics. It is interesting to note
that the n-C/p-Si heterostructures showed non- linear current-voltage characteristics indicating the diode-like nature
of the interface. Electroresistance (ER) measured on these junctions yielded 96% ER which is a very significant
result. We are in the process of growing carbon films using metal catalyst to enhance the nanostructured growth
suitable for field emission in conjunction with a top phosphor layer. All the above results will be presented and
discussed in detailed.
56
200 250 300 350 400 450 500
lex = 322 nm
lem = 390 nm Ca3MgSi2O8:Ce0.02
Wavelength (nm)
Intensity (a.u)
PLD-2005: Posters ?P 12
Pulsed laser deposited Ca3MgSi2O8:Ce phosphor thin films for near UV LED converted
blue light emission
P.Thiyagarajan1,2, M.Kottiasamy2, M.S.Ramachandra Rao1,2,*
1Department of Physics, Indian Institute of Technology Madras, Chennai - 600 036.
2Material Science Research Centre, IIT-M, Chennai - 600 036.
*Email: msrrao@iitm.ac.in
Abstract
Thin film of Ca3MgSi2O8:Ce phosphor have been deposited by Pulsed Laser deposition (PLD) thin film
growh technique using Si as a substrate. Ce doping in Ca3MgSi2O8 produces a violet-blue emission on excitation by
UV and near UV regions1. To optimize the photoluminescent (PL) emission intensity, the concentration of the Ce
dopant was varied from 1 mol% to 5 mol%. Ce doped Ca3MgSi2O8 phosphor was prepared by carbothermal
reduction method using the chemical ingredients viz., CaCO3, MgCO3.4Mg(OH)2.5H2O, SiO2 and CeO2 in a
reducing atmosphere at an elevated temperature (1200º C). The powder was then pressed and sintered into a target
for PLD growth. Thin films were grown on Si substrate at low substrate temperature ~ 700º C in an oxygen partial
pressure of 0.32 mbar. The fluence of the laser power was kept at 2.2 Jcm-2 during the deposition. X- ray diffraction
(XRD) studies confirmed the phase formation. SEM pictures were taken.
Thin film photo-luminescent (PL) emission and
excitation spectra of the Ce doped Ca3MgSi2O8 are
shown in the Figure. Details of thin film growth and
PL spectra will be presented and discussed.
Reference
[1]. Huang Lihui, Zhang Xiao, Liu Xingren,
J.All.Com. 305 (2000) 14-16
Fig. PL emission and excitation spectra of PLD grown
Ca3MgSi2O8:Ce0.02 phosphor thin film
57
PLD-2005: Posters ?P 13
Effect of laser fluence on structure and properties of pulsed Nd/YAG laser
deposited iron oxide thin films.
Shailja Tiwari, Ram Prakash, Atul Tiwari, U.P.Deshpande, T.Shripathi, D.M.Phase*
UGC-DAE Consortium for Scientific Research, Khandwa Road, University Campus, Indore-452 017.
email : dmphase@csr.ernet.in
and
Pankaj Misra and L.M.Kukreja
Thin Film Lab, Centre for Advanced Technology, Indore-452 013
Abstract
Magnetite (Fe3O4) is perhaps one of the most studied iron compound of the past 50 years because of its rather
unique and interesting set of transport and magnetic properties. It has a cubic inverse spinel structure with
tetrahedral sites occupied by Fe3+ ion and octahedral sites shared by Fe 2+ and Fe3+ ions. The moments of the Fe3+
ion on octahedral sites are opposite to each other and the net moment arises only from the Fe2+ ion. The arrangement
being termed as Ferrimagnetic. The presence of Fe2+ and Fe3+ ion on octahedral sites leads to a Fairly low electrical
resistivity in this compound at room temperature. Due to carrier hopping between the Fe2+and Fe3+ion, it undergoes
the Verway transition at 120K, below which it becomes a nonmagnetic insulator.
Pulsed laser deposition has been extensively used in obtaining thin films of magnetites from Fe3O4 or a-Fe2O3
target. The previous research has concentrated on the dependence of the structural and magnetic properties with
oxygen flow rate and the substrate temperature. With increasing oxygen flow rate, the following sequence of phases
has been reported: Fe, Fe3O4, and Fe2O3. In addition, granular composite films of Fe/ Fe3O4, Fe/Fe1-xO and Fe3O4/
Fe2O3 have been reported between the single-phase regions. The purpose of our present investigation is to consider
the effect of laser fluence on the structural, compositional and magnetic behavior of Fe3O4 films. Magnetite thin
films were prepared by pulsed laser ablation from a-Fe2O3 target on single crystal Strontium titanate (STO)
substrate in a custom made high vacuum chamber. The ablation energy source was an Nd-YAG laser of l = 355 nm.
Laser fluence was varied from 1 J/cm2 to 3 J/cm2. The films were grown at a temperature of 600oC in vacuum (~10-6
torr). Deposited films were characterized using x-ray diffraction, scanning electron microscopy, x-ray photoelectron
spectroscopy and magneto optical Kerr effect (MOKE) technique. From obtained results an attempt have been made
to correlate the effect of laser fluence on structure and properties of deposited thin films.
58
PLD-2005: Posters ?P 14
Studies on La0.5Pr0.2Sr0.3MnO3 Epitaxial Thin Films: An Application Point of View
J. H. Markna1, R. N. Parmar1, C. M. Thaker1, P. S. Vachhani, J. A. Bhalodia1, P. Misra2, L. M. Kukreja2
, D.
G. Kuberkar1
1 Department of Physics, Saurashtra University, Rajkot-360 005, India
2 Thin Film Lab., Centre for Advances Technology, Indore- 452 013, India
Abstract
La1-XAXMnO3 ; A=Ca+2, Sr+2, Ba+2 etc. manganite having ABO3 type perovskite structure has recently
attracted much interest due to their potential application using the large magnetoresistance effect exhibited by them
[1]. In this communication we report the results of the studies on magnetotransport properties of La0.5Pr0.2Sr0.3MnO3
(LPSMO) epitaxial thin films. Samples of LPSMO thin films with thickness 50 nm and 100 nm were grown by
Pluses Laser Deposition (PLD) technique using the third harmonic (355 nm) of a Q-switched Nd: YAG laser having
energy density of about 2.17 J/cm2 at 10 Hz repetition rate. The films were deposited on chemically cleaned single
crystal SrTiO3 (l00) substrates. The structural studies using XRD revealed the epitaxial, single phase nature of
LPSMO films having (h 0 l) orientation on STO substrate.
The magnetotransport measurement performed on the 50 nm and 100 nm LPSMO thin films at various
temperatures under 0 to 9 Tesla applied magnetic field show that, both the films exhibits large magnetoresistance
(MR % ~ 55 %) near the insulator to metal transition temperature (TP) which can be primarily attributed to the large
size disorder at A-site in LPSMO system. At low temperature, the films exhibit negligible MR, probably due to no
grain boundary effect (Fig.1). To explore the half metallic nature of the films, unconventional one magnon scattering
law (T) = 0 + BTn was fitted on to ?T data, in which 0 is residual resistivity and B is electron ?magnon
scattering coefficient( not shown). The half metallicity is useful in understanding the spin valve mechanism in the
manganites, which is originate from low field magnetoresistance and spin polarized current [2].
Field coefficient of resistance (FCR) defined as FCR = 1/R×dR/dT % Tesla -1 is an important parameter
from application point of view. In the present studies, it is observed that in the 50 nm LPSMO thin film, FCR value
is 13 % in the 0.5 Tesla magnetic filed which is useful in the bolometric sensors. [3, 4]
59
0 2 4 6 8 10
0
10
20
30
40
50
0
10
20
30
40
50
MR %
H ( T )
50 nm
5 K
100 K
200 K
300 K
250 K
MR %
( La0.5Pr0.2 )Sr0.3MnO3
Thin film on STO
100 nm
200 K
300 K
100 K
250 K
5 K
Figure 1 MR vs H(T) isotherms plots of LPSMO thin films(50 nm and 100 nm)
0 2 4 6 8 10
-12
-8
-4
0 (La0.5Pr0.2)Sr0.3MnO3
Thin film on STO
FCR ( % T -1)
H (T)
50 nm - 250 K
100 nm - 250 K
Figure 2 FCR vs H (T) plots of LPSM thin films (50 nm and 100 nm)
References:
1. Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides, ed. by C. N.
R. Rao, B. Reveau. (World Scientific Publishing Co. Pvt. Ltd. 1998).
2. T. Akimoto, Y. Moritomo, A. Nakamura and N. Kurukawa Phys. Rev. Lett. 85, 39149 (2000)
3. M. Rajeswari, A. Goyal, A. K. Raychaudhuri, M. C. Robson, G. C. Xiong, C. Kwon, R. Ramesh, R. L.
Greene, T. Venkatesan, and S. Lakeou, Appl. Phys.Lett. 69 851(1996)
4. Ravi Bathe, K. P. Adhi , S. I. Patil, G. Marest, B. Honneyer, and S. B. Ogle, Appl.Phys.Lett. 76
2104 (2000)
60
PLD-2005: Posters ?P 15
Pulsed Laser Deposited Iso-Epitaxial WO3 thin films for Gas Sensing Applications
A.S.Swapnasmithaa, O.M.Hussaina* and R.Pintob
aThin Film Laboratory, Department of Physics, Sri Venkateswara University, Tirupati-517 502
bCondensed Matter Physics and Materials Science, Tata Institute of Fundamental Research,
MUMBAI ?400 005, India
*Email: hussainom48@yahoo.co.in
Abstract
The sensing of explosive, toxic and other pollutant gases has been the subject of research for more than two decades
for monitoring the environmental pollution. Recently, transition metal oxide thin films are being used as gas sensors
because of their suitable surface structure and good electrical properties. Tungsten oxide (WO3) thin films with
many interesting physical and chemical properties have been widely considered as good candidates for their use as
environmental gas sensors for detecting pollutant gases like NOx, NH3, COx etc. Among these pollutant gases the
nitrogen oxide NOx (NO & NO2) released from combustion facilities and automobiles have been one of the main
causes of acid rain and photochemical smog. Also this can cause diseases of respiratory system of human beings.
Hence the detection of nitrogen oxides are highly demanded to reduce the noxious effects on environment and
human beings. In the case of environmental monitoring, the threshold limit value (TLV) for NO2 is 3 ppm.
Accordingly, an NO2 sensor is required to have a high sensitivity than can correspond to such low TVLs. Thin films
of WO3 are considered to be one of the best candidates among NOx sensing materials1 due to its high sensitivity and
good selectivity to low concentrations. Several thin film deposition techniques have been employed to prepare WO3
thin films for their effective utilization in gas sensor applications. However the sensitivity, stability and repeatability
towards a particular gas are mainly dependent on the surface structure and electrical properties of WO3 thin films
which inturn depend on the deposition technique and the process parameters. Recently, pulsed laser deposition
technique has been widely recognized as a very promising, versatile and efficient method for the deposition of metal
oxide thin films because of its reproducibility, controllability of stoichiometry and crystal structure. Another chief
advantage is that pulsed laser deposited thin films crystallize at relatively lower deposition temperatures than the
other physical vapor deposited films due to the high kinetic energy (>1eV) of the ionized species in the laser
produced plasma2 . Hence in the present investigation WO3 thin films were prepared by reactive pulsed laser
deposition technique. The influence of process parameters like oxygen partial pressure and substrate temperature on
WO3 thin films were studied. The NO2 gas sensing properties of WO3 thin films coated on SrTiO3 substrates were
also examined.
A KrF excimer laser (Luminics PM 882) with a wave length of 248 nm and a pulse duration of 30 ns
delivered an energy of 300 mJ per pulse was used for ablation. The energy density of laser beam was 3 J/cm2. The
pulse repetition rate was set at 10 Hz. The distance between the target and the substrate was 4 cm. A sintered WO3
target at 1073 K for 20 h was used for laser ablation The target was rotated at the rate of 10 rotations/min to avoid
depletion of the material at the same spot during the deposition. The chamber was evacuated to a base pressure of
61
2x10-6 Torr before the film deposition. During the deposition pure oxygen was introduced into the chamber and the
desired pressure was maintained with a flow controller. The substrates were maintained in the temperature range 473
?873 K and the oxygen partial pressure was maintained in range 100 ?200 mTorr. The thickness of the laser
ablated WO3 thin films was about 0.3 m. The substrates used were (100) SrTiO3 single crystal substrates.
Single crystal (100) SrTiO3 substrate was chos
en as an ideal substrate because it is a good elelctrical insulator having high thermal and structural stability at higher
temperatures. Also it is having close lattice matching with WO3 thin films. The reported 2 positions for the (100)
peak of SrTiO3 and the (002) peak of WO3 in bulk are 22.782 0 and 23.118 0 respectively3. SrTiO3 possesses a cubic
perovskite structure and its lattice constant is 3.905 Å. The laser ablated WO3 thin films deposited on SrTiO3
substrates are found to be well adherent to the substrate surface. A minimum oxygen partial pressure of 100 mTorr
was maintained to grow transparent and stoichiometric WO3 thin films. The WO3 thin films deposited in the
temperature range 473-873 K in an oxygen partial of 100 mTorr exhibited three peaks in the 2 range 23-25 0 with
(002), (200) and (020) orientations. However all the films exhibited (002) predominant orientation with monoclinic
structure in consistant with the other reports4. The X-ray diffraction spectra of WO3 films deposited at 873 K and at
various oxygen partial pressures on (100) SrTiO3 is shown in figure1. It is observed from the X-ray diffraction
spectra that the (002) peak of the WO3 films overlaps with the (100) substrate peak because of very similar
interplanar spacings5. The 2 positions for the (100) peak of SrTiO3 and the (002) peak of WO3 are observed to be
at 22.78 0 and 23.10 0 respectively. A very low intensity of the (020) film peak is also observed in the films, whereas
Fig. 1: The XRD spectra of W03 thin films
deposited at 873K and at various oxygen
partial pressures on (100) SrTi03
Fig. 2: Surface morphology of the W03 thin film
deposited at a substrate temperature of 873K
with an oxygen partial pressure of 150 mTorr.
62
the (200) peak is not seen in the films. The intensity of the (020) peak decreased with the increase of oxygen partial
pressure and was almost diminished at an oxygen partial pressure of 150 mTorr. The diminishing of the (020) peak
implies the improved epitaxy. These observations reveal the (00l) plane epitaxy between WO3 films and (h00)
SrTiO3, which suggests that the film planes are crystallographically aligned with the substrate planes. These results
are comparable with the epitaxial WO3 films grown by Garg et al.3 using dc magnetron sputtering. The surface
morphology of the films deposited at 873 K in an oxygen partial pressure of 150 mTorr is shown in figure 2. Isoepitaxial
columnar growth has been observed in the topography of these films. These results indicate that the
epitaxial WO3 thin films grown on SrTiO3 substrates are attractive for NOx gas sensing applications. These isoepitaxial
WO3 films for NO2 gas testing were prepared by evaporating two gold contacts in gap configuration6. The
contacts were found to be ohmic for a wide range of voltages. The sample under test was placed on to a heated
sample holder in a stainless steel cell and exposed to different gas concentrations. A constant flow rate of 100 sccm
was maintained with a Tylan mass flow rate controller. The gas to be tested coming from a certified bottles was
diluted with dry air to obtain the desired composition. The temperature of the sample was continuously monitored
with a thermocouple. The gas sensitivity of WO3 thin films for 100 ppm NO2 at various temperatures was measured.
The gas sensitivity defined as DR/Rair where DR is the resistance change of the films upon exposure of NO2 and Rair
is the resistance in air. The sensitivity of WO3 thin films increases with the increasing temperature of the sensor. The
maximum sensitivity of WO3 films deposited at 873 K in an oxygen partial pressure of 150 mTorr for 100 ppm NO2
was about 150 at an operating temperature of 673 K. The response time to reach 90% of the maximum value of the
signal was about 2 minutes.
Pulsed laser deposited WO3 thin films were found to be highly influence by the substrate temperature and
oxygen partial pressure. We have observed that control of the deposition parameters promotes the films
stioichiometry, surface morphology and the crystal structure. WO3 thin films deposited on single crystal SrTiO3
substrates at a temperature of 873 K and in an oxygen partial pressure of 150 mTorr were found to have (001) plane
epitaxy between WO3 thin films and SrTiO3 substrate. The AFM data demonstrated the iso-epitaxial columnar
growth in the films.The sensing properties of these films for NO2 gases were studied to see the applicability of these
films for environmental monitoring. The iso-epitaxial WO3 thin films were found to be more sensitive to NO2 gas
with a sensitivity of about 150 at an operating temperature of 673 K.
1. T.Inoue, K.Ohtsuka, Y.Yoshida, Y.Matsuura and Y.Kajiyama,Sensors and Actuators B 24-25 (1995) 388
2. D.B.Chrisey, G.K.Hubler, Pulsed Laser Deposition of Thin Films (Wiley, Newyork) 1994
3. A.Garg, J.A.Leake, and Z.H.Barber, J.Phys.D.Appl.Phys. 33 (2000) 1048.
4. P.Tagtstrom and U.Jansson, Thin Solid Films 352 (1999) 107.
5. O.M.Hussain, A.S.Swapnasmitha, J.John and R.Pinto, Appl.Phys.A (2004),
DOI:10.1007/s00339-004-3041-z
6.O.M.Hussain and K.S.Rao, Materials Chemistry and Physics 80 (2003) 638
63
PLD-2005: Posters ?P 16
PLD GROWN PALLADIUM COATED WO3 THIN FILMS
FOR HYDROGEN SENSORS
M. Krishna Kumar1 M. S Ramachandra Rao2 and S. Ramaprabhu1
1Alternative Energy Technology, Department of Physics,
2Material Science Research Center and Department of Physics
Indian Institute of Technology Madras, Chennai - 600 036, India.
mkkumar@physics.iitm.ac.in , msrrao@iitm.ac.in and ramp@iitm.ac.in
Abstract
Hydrogen is essential in many fields of research and industry, and with the development of fuel cell technology the
application prospects of hydrogen are increased. Hydrogen concentrations in air exceeding 4% are easily flammable
and are highly explosive, hence detection and monitoring of hydrogen gas has received a great deal of importance.
Therefore, a sensor that can detect H2 gas at ambient conditions is a necessity. This paper presents the fabrication of
hydrogen sensors based on the changes in electrical and optical properties of Pd coated WO3 thin films grown using
pulsed laser deposition (PLD) technique. Pd is well known for its catalytic nature towards breaking of molecular
hydrogen into atomic hydrogen [1, 2]. WO3, a well known gasochromic material, when engineered in thin film form
with island like growth of Pd will be a good hydrogen sensing material. Pd thin films with different thickness have
been deposited on WO3 coated quartz substrates by PLD and the effect of film thickness on the performance of
sensor has been studied. Optimization of the thin film growth condition has been carried out by systematic variation
of growth parameters like substrate temperature, laser power density and ambient Ar gas pressure. The morphology
and composition of the films have been analyzed by XRD, SEM, AFM and EDAX. In-situ electrical resistance using
linear four-probe technique and in-situ optical properties have been measured and their dependence on different
concentrations and flow rates of hydrogen gas have been studied and discussed.
References
[1].T. Xu, M. P. Zach, Z. L. Xiao, D. Rosenmann, U. Welp, W. K. Kwok, and G. W.
Crabtree J. Appl. Phys. 86, 203104 (2005)
[2]. A. Chtanov and M. Gal, Sens. Actuators, B. 79 (2001) 196?99.
64
PLD-2005: Posters ?P 17
EPITAXIAL GROWTH OF ZINC OXIDE ON GALLIUM NITRIDE TEMPLATE BY PULSED LASER
DEPOSTION
T. Premkumar, P. Manoravi*, M. Joseph* and K. Baskar
Crystal Growth Centre, Anna University, Chennai 600 025, India
* Radiochemistry Laboratory, IGCAR, Kalpakkam 603102, India
email:prem_cgc@yahoo.co.in
Abstract
Lattice-matched epitaxy and good luminescence properties of ZnO/GaN heterostructures are promising for
optical devices. The near perfect lattice alignment of the ZnO epilayers on GaN as compared to those grown
directly on sapphire exhibits excellent properties for commercial applications [1]. ZnO epitaxial layer have been
grown heteroepitaxially on GaN templates using Pulsed Laser Deposition (PLD) system using Nd:YAG (l=532nm)
laser as a excitation source to ablate ZnO. The power density of the laser was 1x108 W/cm2. The base pressure of the
deposition chamber during the growth was maintained at 8´10-6 torr.
The surface morphology of the grown epilayers were studied using Scanning Electron Microscopy (SEM).
To study the optical properties the ZnO layers Photoluminescence (PL) and Time Resolved Photoluminescence
(TRPL) have been employed. The results of surface morphology of the layers, the full-width at half maximum of
photoluminescence spectrum and lifetime of the minority carriers were discussed.
References:
1. R.D. Vispute, M.He, and Y. X. Li 揌eteroepitaxy of ZnO on GaN and its implications for fabrication of
hybrid optoelectronic devices?Applied Physics Letter, Vol.73, No. 3, (1998), pp.348-350.
65
PLD-2005: Posters ?P 18
Pulsed laser deposited Y3Al5O12:Ce phosphor thin films for blue light converted white light
emitting diodes
M.Kottiasamy1, P.Thiyagarajan1,2 M.S.Ramachandra Rao1,2
1Material Science Research Centre, Indian Institute of Technology ?Madras, Chennai-600 036.
2Department of Physics, Indian Institute of Technology Madras, Chennai-600 036.
Abstract
Y3Al5O12:Ce phosphor thin films were deposited on quartz substrate by pulsed laser deposition (PLD)
technique. The as-deposited film showed an yellow colour emission with an emission maximum at 550 nm at the
blue LED excitation wavelength (465 nm). For the PLD deposition, the required target was prepared from phosphor
powder which was obtained by sol-gel method using stoichiometric starting chemicals viz., yttrium nitrate,
aluminium nitrate and cerium nitrate and citric acid. This method ensures the homogeneous distribution of Ce and
low temperature formation of the YAG. The as formed phosphor was then pressed and sintered at 1200o C for 24
hours to obtain a dense target for PLD growth. Thin films were grown on quartz substrates at low substrate
temperature ~ 700º C in an oxygen partial pressure of 0.32 mbar. The flounce of the laser power was kept at 2.2
Jcm-2 during the deposition. X- ray diffraction (XRD) studies confirmed the phase formation. SEM pictures were
taken to analyze the surface morphology of the films. Fig.1 shows a luminescent emission of the as deposited
YAG:Ce thin film phosphor along with a blue LED emission which results in white light. It is expected that further
annealing enhances the crystallinity and PL emission properties of the thin film. Details of thin film growth and PL
spectra will be presented and discussed.
300 400 500 600 700 800
PL Intensity (a.u)
Wavelength (nm)
YAG:Ce Thin film
deposited by PLD
YAG:Ce Thin film
Fig.1.White light emission from YAG:Ce thin film at the excitation of blue LED
66
PLD-2005: Posters ?P 19
Pulsed Laser Deposition of ZnO:Al thin films at room temperature
Manoj R and M.K. Jayaraj*
Optoelectronics Devices Laboratory, Department of Physics, Cochin University of Science & Technology, Kochi-22,
India
*Email: mkj@cusat.ac.in
Abstract
The excellent optoelectronic properties of zinc oxide have attracted considerable interest over the past few
years. The growth of crystalline ZnO at room temperature would be highly interesting from the point of device
development. It has been reported that ZnO can also be made p type by codoping third group elements (Ga, Al etc)
and with nitrogen. The development of room temperature thin film growth techniques would be very useful to the
optoelectronics industry.
In this paper we report the deposition of highly oriented ZnO:Al thin films by PLD at room temperature.
The ZnO films were deposited using Nd:YAG laser with pulse width 6-7 ns and repetition frequency of 10 Hz. The
second harmonics (l = 532nm) as well as the third harmonics (l = 355nm) were used for depositing the films. Better
film morphology and growth rates were obtained when the deposition was carried out using the third harmonics. The
substrate to target distance was kept at 6 cm. Oxygen gas was fed into the chamber during the deposition through a
mass flow controller (0.003 m bar to 0.008 m bar). The structural, optical and electrical properties of the thin films
were studied. The crystal structure of the ZnO:Al thin film was analysed using X-ray diffraction(XRD) technique.
The films were deposited at room temperature on glass, fused quartz and plastic substrates. All the films were
crystalline and showed good transmittance >85% in the visible range.
67
PLD-2005: Posters ?P 20
Transparent p-AgCoO2/n-ZnO p-n junction fabricated by Pulsed Laser Deposition
R.S.Ajimsha, K.A.Vanaja, M.K.Jayaraj*
Optoelectronics Devices Laboratory, Department of Physics,
Cochin University of Science and Technology, Cochin-22.
*Email: mkj@cusat.ac.in
P Misra and L.M.Kukreja
Thin Film Lab, Centre for Advanced Technology, Indore 452 013.
Abstract
Wide bandgap oxide semiconductors are now being extensively studied for their potential applications for
transparent electronics and opto-electronics. Transparent electronic and optoelectronic devices may be realized if
sufficiently high conductivity through electrons and holes doping could be achieved in such semiconductors1. The
wide bandgap oxides of p-block heavy metallic cations with ns0 electronic configuration (ZnO, In2O3 etc) show high
conductivity and their mixed oxides can be changed to an n-type by an appropriate doping with donor elements. In
practice it is difficult to obtain p-type Transparent Conducting Oxide (TCOs) because of the lower carrier mobility
and densities associated with narrow valance bands. The materials that are currently being investigated for the
application of p-type TCOs are ABO2 delafossites where A is the monovalent cation and B is the trivalent anion.
p-type delafossite thin films are all so far based on copper delafossites 2. Several strategies have been adopted to
explore the possibilities in the delafossite materials and have been implemented in thin film form. These include
varying the trivalent B cation and appropriate dopants and producing new films based on silver rather than copper.
In the present study we report the fabrication of p-n heterojunction using n-ZnO and p-AgCoO2. p-AgCoO2 thin
films were deposited by pulsed laser deposition of sintered target of AgCoO2 using third harmonic of a Q-switched
Nd: YAG laser with a fluence of 1 J/cm2 at 355nm, 7ns pulse width and10Hz repetition frequency. The bulk powder
of AgCoO2 was synthesized by hydrothermal reaction of AgNO3, Co3O4 and KOH in a Parr bomb at 2500C. The p-n
heterojunction diodes were grown with a structure of p-AgCoO2/n-ZnO/n-ITO/glass. Glass substrates coated with a
200nm thick sputtered ITO film had a transparency > 85% in the visible region. The ZnO was deposited over the
ITO coated glass by PLD under the conditions mentioned above. The ITO layer forms an ohmic contact with ZnO.
The AgCoO2 layer of thickness 200nm had a transmission of about 60% in the visible region. The current-voltage
(I-V) characteristics of the junction yielded an ideality factor which was much greater than 2. The I-V characteristics
showed that the turn on voltage was 0.75V. The low turn on voltage may be due to the large number of defects and
interfacial states. Rectification was observed with a ratio of forward to reverse current of 7 at 1.5V. Further work to
improve the quality of the diodes is underway.
References
1. G.Thomas, Nature, 389,907(1997)
2. N.Duan, A.W.Sleight, M.K.Jayaraj, J.Tate, Appl.Phys.Lett, 77,1325 (2000)
68
PLD-2005: Posters ?P 21
Structural, morphological and electrical characterization of InN thin films grown by pulsed
laser deposition
S. S. Harchirkar*, A.G.Banpurkar and K. P. Adhi
Advanced Laser Material Processing Laboratory, Centre for advanced studies in Materials Science and Solid State
Physics, Department of Physics, University of Pune, Pune India-411 007
P. M. Koinkar, M. A. More, and D.S.Joag
Field ion microscopy and Field emission spectroscopy Laboratory, Centre for advanced studies in Materials
Science and Solid State Physics, Department of Physics, University of Pune, Pune India-411 007
L. M. Kukreja
Thin Film Laboratory, Center for Advanced Technology, Indore ?452 013
* Corresponding authors e-mail address: hsanjay@physics.unipune.ernet.in
Abstract
Indium nitride (InN), so far, is least studied among the III- nitride semiconductors. Recent studies on wurtzite
InN have firmly established it to be a narrow band gap (0.6 to 0.7 eV) material1,2. This not only enhances the range of
emission spectra from deep UV to near Infrared region of III-nitrides, but with emission around 1.55 m, also becomes a
potential candidate for the telecommunication industry 3. InN has also been demonstrated as a useful material for cost
effective solar cells, optical coatings, sensor for chemical and biological applications etc.4-5. We have attempted to study
thin films of wurtzite InN grown by pulsed laser deposition (PLD) technique on (0001) sapphire from the point of view
of cold emission. Excimer-laser (KrF gas; wavelength = 248 nm, pulse duration tp = 20 nsec, repetition rate = 5Hz)
was used for the ablation of the commercial Indium (In) target (Kurt J. Lesker ? USA, purity 99.99%). The laser fluence
on the target surface was kept at about 0.5 J/cm2. High purity (99.999%) nitrogen was introduced into the chamber and
the pressure was maintained at 25mTorr through out the deposition. Discharge in the nitrogen ambient was initiated and
maintained by application of 900 V dc across the target holder and a grid placed in between the substrate and target. The
substrate temperature was maintained at 500 癈. After the deposition, samples were cooled to room temperature slowly
under the same conditions of pressure and discharge.
The thickness of the films, as estimated from Tallystep measurements was ~ 4000Å. The presence of
(1011) and (0002) planes in X-ray diffraction (XRD) pattern indicates the polycrystalline growth of wurtzite InN.
No peaks corresponding to Indium were observed within the detection limit. The surface morphology, RMS
roughness and the crystallite sizes were recorded by AFM in the contact mode (Jeol- JSPM 5200). The AFM results
show that the InN films are granular in nature and the rms surface roughness is approximately 35 Å
69
The cold electron emission from the thin films was studied by the technique of Field Emission Microscopy
(FEM). In this technique, the film is mounted on an insulating stand and placed in front of a ZnS screen at a distance
of ~ 2 mm. The chamber is evacuated to low pressures of the order of 10-9 Torr using a sputter ion pump in
conjunction with liquid nitrogen trap. High voltage of the order of few kV is applied between the film and the screen
in order to study the emission from the films. The field emission current杤oltage characteristics were analyzed by
using the Fowler朜ordheim (FN) equation;
( ) ( )






= ´ - ´ f y
y E
exp 6.83 10
t
E
J 1.54 10
2
3
7
2
2
-6 f
f
where J is current density, E is applied field, is work function of InN respectively. The turn on field 6 defined as
the field required to obtain current density of 10 A/cm2 is around 3.4V/ m. The FN plot of log(J/E2) vs 10/V4 has
a linear relation within the measurement range, which confirms that the current results from field emission.
Acknowledgement: The authors, KPA, AVL and LMK thank DAE - BRNS for the financial support to carryout
this work.
References
1. J. Wu, W. Walukiewicz, K. M. Yu, J. W. Ager III, E. E. Haller, H. Lu, W. J. Schaff, Y. Saito, and Y. Nanishi,
Appl. Phys. Lett. 80, 3967 (2002)
2. K. Sugita, H. Takatsuka, A. Hashimoto, and A. Yamamoto, Phys. Status Solidi B 240, 421 (2003).
3. B. Arnaudov, T. Paskova, P. P. Paskov, B. Magnusson, E. Valcheva, B. Monemar, H. Lu, W. J. Schaff, H.
Amoano, and I. Akasaki, Phys. Rev. B 69, 115216 (2004)
4. Hai Lu, William J. Schaff, and Lester F. Eastman, J. Appl. Phys. 96, 3577 (2004)
5. Z. G. Qian, W. Z. Shen, H. Ogawa, and Q. X. Guo, J. Appl. Phys. 92, 3683 (2002)
6. Y. B. Tang, H. T. Cong,a! Z. G. Zhao, and H. M. Cheng, Appl. Phys. Lett. 86, 153104 (2005)
70
PLD-2005: Posters ?P 22
Study of irradiation induced changes in the morphology and transport properties of
La0.7Sr0.3MnO3 thin films
M. S. Sahasrabudhe*, K. P. Adhi, and S. I. Patil
Advanced Laser Material Processing Laboratory, Centre for Advanced Studies in Materials Science and Solid State
Physics, Department of Physics, University of Pune, Pune - 411 007, India
Ravi Kumar
Nuclear Science Centre, Aruna Asaf Ali Marg, New Delhi - 110 067, India
* Corresponding authors e-mail address: mandar@physics.unipune.ernet.in
Abstract
The doped perovskite manganites, with the chemical formula R1-xAxMnO3, where R and A are rare杄arth
(La, Nd, Pr, etc.) and alkaline earth (Ca, Sr, Ba etc.) ions respectively, have been the focus of immense study in the
recent past1-3. With a high Curie temperature Tc of ~ 370 K, La0.7Sr0.3MnO3 (LSMO) appears to be an attractive
material for magnetic field sensing and magnetic storage applications at or above room temperature4. Controlling /
tailoring transport properties of this material is hence of importance. While the oxygen content of the film influences
the transport properties drastically, the interfacial strain has little effect as the thickness of the film increases beyond
~ 1000 Å5. In the present study, swift ion irradiation of LSMO thin films by 200 MeV Ag ions has been used to
create defects and hence, related strain over the entire thickness, which lead to the modifications of structural,
electrical and magneto resistance properties.
Highly c-axis oriented magneto resistive films of La0.7Sr0.3MnO3 (LSMO) were deposited on LaAlO3 (LAO
(100)) substrate by pulsed laser deposition (PLD) technique. During deposition the energy density of the incident
radiation on the surface of target was maintained at 2 J/ cm2 and the substrate temperature was 700 癈. Oxygen was
then introduced into the chamber and maintained at a pressure of 400 mTorr during deposition. After deposition, the
samples were slowly cooled at the rate of 5 癈/min. to room temperature in oxygen ambient maintained at
atmospheric pressure. The films thus deposited were characterized and then subjected to post deposition annealing
in air at 800OC. The structural quality in terms of orientation and phase formation was studied using x-ray
diffraction. The films were also characterized by four probe resistivity measurement technique from 400 K down to
125 K. The morphology of the films was studied using Atomic Force Microscopy (AFM). The effect of swift heavy
ion (SHI) irradiation on structural and electrical properties of these annealed films has been investigated. 200 MeV
silver ions at different dose values ranging from 1´1011 to 1´1012 ions/cm2 were used for the irradiation.
Post deposition annealed films show metallic behavior over a wide studied temperature range, which is
expected for LSMO films. Irradiated films show the metal-insulator transition. The peak transition temperature 慣p?br> of the irradiated films vary systematically, shifting towards room temperature with increasing dose values. The
71
structural properties also change with the irradiation dose value. The changes in the morphology of these films were
studied using AFM. The rms roughness of the film changes with the dose value. These variations were analyzed on
the basis of swift ion irradiation induced defects and related strain rather than change in oxygen content of the films.
Acknowledgement: One of the authors MSS would like to thank NSC-Delhi for providing the fellowship under the
UFUP program.
* A detailed paper on irradiation study has been communicated to NIMB.
References:
1. K. Chahara, T. Ohno, M. Kasai and Y. Kosono, Appl. Phys. Lett. 63, 1990 (1993).
2. R. Von Helmolt, J. Weckerg, B. Holzapfel, L. Schultz, and K. Samwer, Phys. Rev. Lett. 71, 2331 (1993).
3. S. Jin, T. H. Tiefel, M. McCromark, R. A. Fastnatch, R. Ramesh, and L. H. Chen, Science 264, 413 (1994).
4. T. Venkatesan, M. Rajeswari,Z. W. Dong, S. B. Ogale and R. Ramesh, Philos. Trans. R. Soc. London, Ser.
A 356, 1661 (1998)
5. ² Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides² Edt. By C.
N. R. Rao and B. Raveau, World Scientific Publication 1998, pg 155 -187
72
PLD-2005: Posters ?P 23
Influence of oxygen variation on the chemical properties of La0.7Ca0.3MnO3 thin films
M. S. Sahasrabudhe, S. K. Date, S. I. Patil and K. P. Adhi
Advanced Laser Material Processing Laboratory, Centre for Advanced Studies in Materials Science and Solid State
Physics, Department of Physics, University of Pune, Pune - 411 007, India
Ravi Bathe
International Advanced Research Center for Powder Metallurgy and New Materials, (ARCI)
Hyderabad -500 005, India.
S. Kharrazi, R. C. Purandare and S. K. Kulkarni
Surface Physics Laboratory, Centre for Advanced Studies in Materials Science and Solid State Physics,Department
of Physics, University of Pune, Pune - 411 007, India
* Corresponding authors e-mail address: mandar@physics.unipune.ernet.in
Abstract
The manganites of the form La1-XAXMnO3 (A = Ca, Sr, Ba etc., a divalent element) show variety of
interesting properties1-3 amongst which Colossal Magneto Resistance (CMR) is perhaps the most appealing one for
the applications such as memory devices, magnetic field sensors etc. The MnO6 octahedra or Mn ?O ?Mn network
plays an important role in defining the properties in these materials. It has been shown previously that in bulk
materials the oxygen stoichiometry plays a crucial role and with increase in oxygen deficiency the peak resistivity
temperature decreases where as CMR and the resistivity increases 4, 5. The present work is focused on the changes in
oxygen content of the La0.7Ca0.3MnO3 thin films and its influence on the local chemical environment in these films.
X-ray Photoelectron Spectroscopy has been used for this purpose.
Thin films of La0.7Ca0.3MnO3 were deposited on single crystal LaAlO3 (001) substrates by pulsed laser
deposition under different oxygen pressure conditions. The LCMO target was prepared by the standard solid-state
reaction route, taking high purity (99.99 %) component oxides in their stoichiometric ratios. The single phase
LCMO target, as conformed by XRD, was mounted in the chamber such that the polar angle between the incident
radiation and the normal to the surface of the target was 45o. The energy density at the target surface was adjusted to
2 J/cm2. The substrate temperature was maintained at 650?C throughout the deposition for all the depositions. Films
with varying content of oxygen were deposited by changing the oxygen ambient pressure in the chamber viz. 50
mTorr, 100 mTorr, 200 mTorr, 300 mTorr and 400 mTorr. After the deposition, the films were slowly (<5 癈/min)
cooled to room temperature at the same oxygen pressure at which they were deposited. The XPS spectra were
recorded using the Mk II VG scientific spectrophotometer. Al K radiation at 1486.6 eV was used for the study. A
hemispherical analyzer having resolution of ~1 eV at pass-energy of 50 eV was used to detect the emitted
73
photoelectrons. Cleaning of the surface of the films was done by Ar+ ion sputtering where in the ion energy was 4
keV and the duration of etching was 30 sec.
The XPS data was collected near La3d5/2, Ca2p, O1s and Mn2p3/2 levels. Studying these spectra illustrates
the changes in Mn+3/Mn+4 ratio caused due to oxygen variation. La3d5/2 peak after deconvolution shows two
components; one of lanthanum on the lower binding energy side and a satellite peak on the higher binding energy
side. Ca2p peak shows two components one of 2p1/2 and other of 2p3/2. As the oxygen pressure during deposition
increases the oxygen peak shifts towards higher binding energy side. The de-convoluted peaks of O1s and Mn2p3/2
levels further help in understanding the changes in MnO6 octahedra caused by oxygen content variation. The
conversion of Mn+4 to Mn+3 is a result of reduction in oxygen content of the films has also been established in our
case.
Acknowledgement: One of the authors MSS would like to thank NSC-Delhi for providing the fellowship under the
UFUP program.
References
1. R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, and K. Samwer, Phys. Rev. Lett. 71, 2331 (1993)
2. S. Jin, T. H. Tiefel, M. McCromack, R. A. Fastnacht, R. Ramesh, L. H. Chen, Science 264, 413 (1994)
3. H. L. Ju, C. Kwon, Q. Li, R. L. Greene, and T. Venkatesan, Appl. Phys. Lett. 65, 2108 (1994)
4. G. C. Xiong, Q. Li, H. L. Ju, R. L. Greene, and T. Venkatesan, Appl. Phys. Lett. 66, 1689 (1995)
5. H. L. Ju, J. Gopalakrishnan, J. L. Peng, Q. Li, G. C. Xiong, T. Venkatesan, and R. L. Greene, Phys. Rev. B
51, 6143 (1995)
74
PLD-2005: Posters ?P 24
Optical and Electrical Characteristics of Lithium Doped Zinc Oxide Thin Films Grown
By Pulsed Laser Deposition
N. Bodas*, B. N. Singh#, Ravi Kumar,V. K. Dixit, P. Misra and L. M. Kukreja
Thin Film Lab., Center for Advanced Technology, Indore 452 013
*Department of Applied Physics, SGSITS, Indore 452003
#Presenting and corresponding author, Email: bnsingh@cat.ernet.in
Abstract
In recent years, the current interest is to use wide-band gap semiconducting materials for optoelectronic devices
applications like blue light emitting diodes, UV laser etc. The Zinc Oxide (ZnO) is a strong and potential candidate
for such applications due to its higher band-gap of 3.37eV, high excitonic binding energy of 60 meV at room
temperature and having property of a high radiation resistance. Naturally occurring ZnO is predominantly n-type
and therefore p-type doping in ZnO is difficult to achieve. For this it is imperative to first suppress the n-type
conductivity of ZnO, which is of great importance for various applications. In present report, we discuss structural,
optical and electrical characteristics of highly transparent and crystalline lithium doped ZnO (Li:ZnO) thin films on
(0001) Sapphire substrates using Pulsed Laser Deposition. The deposition was carried out by using third harmonic
(355nm) of Q-Switched Nd-YAG laser, a pulse width of 6ns and 10Hz repetition rate and in an oxygen partial
pressure of ~ 1x10-4 Torr. The substrate temperature was kept at 600ºC and 300 nm thick films were grown at a laser
fluence of ~ 2J/cm2.
The X-ray Diffraction measurement and transmittance spectra of undoped and Li:ZnO thin films with different Li
concentration are indicating high crystalline and optical quality of all the films. The behavior of resistivity for ZnO
thin films with Li doping concentrations was studied. Resistivity of undoped ZnO film which was ~2 x10-2 -cm
increased up to ~2 -cm with ~1% of Li doping concentration and then started decreasing with further increase in Li
doping. This behavior in resistivity has been attributed to highly mobile Li atoms, as majority of them occupy
substitutional positions, thereby acting as acceptors up to concentration of ~1% and beyond this concentration, they
occupy interstitial sites, thereby acting as donors. Temperature dependent conductivity ( ) measurements were
performed for all the samples in the temperature range of 40-353K to deduce the activation energy of Li doped ZnO
using ln vs. 1000/T plot. The calculated activation energy was ~15.4 meV for the un-doped film, 49.7 meV for the
1% Li:ZnO film and ~10.5 eV for the 2% Li:ZnO film. For the undoped film, the carrier concentration was
estimated ~ 1x1019/cm3 at room temperature which dropped to 3x1018/cm3 in the case of 0.5% Li doped ZnO thin
films. A decrease in the free carrier concentration can be attributed to the fact that Li takes substitutional positions
and acts as an acceptor. The variation of carrier concentration with temperature is fairly constant for undoped and
0.5% Li doped ZnO thin films indicating that these films are degenerate throughout the temperature range of
measurement. We have observed significant reduction in the conductivity of ZnO thin film with Li doping, which
might be put to use in different piezo-electric and opto-electronic devices seeking resistive ZnO. Further studies are
underway to explore and understand electrical and photo-luminescence characteristics of Li doped ZnO thin films.
75
PLD-2005: Posters ?P 25
Structural and Optical Characterization Of CoxZn1-XO Thin Films grown by
Pulsed Laser Deposition.
Jabivul J. Sk*, Pankaj Misra, P. K. Sen* and L.M. Kukreja
Thin Film Laboratory, Centre for Advanced Technology, Indore-452 013
*Department of Applied Physics, SGSITS, Indore- 452 003
*Email: jabivul@hotmail.com
Recently there has been great interest in diluted magnetic semiconductors for their possible technological
applications in optoelectronic, magneto opto-electronic and microwave devices. Such applications using III-V
semoconductor materials have been demonstrated only at low temperatures because of their low Curie temperature
(Tc~110k) [1]. ZnO, a II-VI oxide semiconductor with a direct wideband gap of ~ 3.3 eV at room temperature with
the possibility of independent control on spin and charge carriers, is a suitable host material for such applications. In
particular, Zinc oxide based thin films doped with transition metal elements like Mn, Co etc. have strengthened the
hope of obtaining ferromagnetism at above room temperature [2]. We have studied structural and optical properties
of CoxZn1-xO alloy films grown by Pulsed Laser Deposition. The single wurtzite phase CoxZn1-xO targets with Co
concentrations ranging from 1 to 20 mole % were prepared by mixing CoO (99.997%) and ZnO (99.999%) powders
using standard ceramic processing. Thin films were grown at a temperature of 600癈 on (0001) sapphire substrates
using third harmonic of a Q-switched Nd: YAG laser (355 nm, 10 Hz, and 6 ns) at a fluence of ~ 2 J/cm2. The films
were characterized using X-ray diffraction studies and optical transmission spectroscopy.
The High Resolution XRD of the grown thin films revealed the highly crystalline and c-axis oriented growth without
changing wurtzite structure. There were no impurity peaks corresponding to CoO related phase segregation, which
indicated the homogeneous distribution of Co in the PLD grown films. The c-axis length and FWHM of (002) ZnO
peak increased monotonically with increasing Co composition up to ~ 7%. The optical transmittance spectra
measured at room temperature in the spectral range of 200 - 900 nm revealed highly transparent ~ 80% Co-ZnO thin
films with a conspicuous mid gap absorption at ~659, 617 and 568 nm respectively due to intra-band Co+2
transitions. In order to determine the band gap (Eg) of the films, the absorption coefficient, 2 was plotted with
respect to photon energy and linear portion of 2 was extrapolated to = 0. The band gap of Co doped ZnO blue
shifted monotonically with increasing Co concentration. The similar trend of occurrence of mid-gap absorption due
to Co doping was also reported by Tiwari et al. [3]. Further studies in this direction are underway.
References
1. H. Ohno, J. Magn. Magn. Matter. 200, 110 (1999)
2. K. Ueda, H. Tabata and T. Kawai, Appl. Phys. Lett. , 79, 988 (2001)
3. S. Ramachandran, A. Tiwari and J. Narayan, App. Phy. Lett. 84, 5255 (2004)
76
PLD-2005: Posters ?P 26
Growth of Nanostructured Al doped ZnO Thin Films by PLD
K.C. Dubey, Atul Srivastava, Anchal Srivastava+, R.K. Shukla, P. Misra* and L. M. Kukreja*
Department of Physics, Lucknow University, Lucknow-226 007, India
*Thin Film Lab., Centre for Advanced Technology, Indore 452 013
+ Presenting and corresponding author Email: vpsri@rediffmail.com
Abstract
Zinc Oxide, which is a transparent oxide semiconductor with naturally occuring n-type conductivity is emerging as
an alternative potential material to Indium tin oxide.This work reports the structural, electrical and optical
properties of ZnO and Aluminium doped ZnO (AZO) films deposited on glass substrates at a substrate temperature
of 4000C by PLD using third harmonic Q-switched Nd:YAG laser (355 nm, 10Hz, 6 ns). The oxygen partial
pressure was kept at ~ 10-3 Torr. The AZO film have Al doping of 2, 3 and 5 atomic percent in ZnO.The -2 XRD
patterns of these films show that the prominent peak occurs at 2q ~ 340 and corresponds to (002) diffraction line
indicating the presence of hexagonal wurtzite ZnO phase with strong c-axis orientation in all the cases. As the Al
doping increased from 0% to 5% a) the nano grain size in the film decreases from ~ 38 nm to ~ 25 nm as determined
by full width at half maxima of (002) ZnO peak using Debye-Scherer method, and b) the inter planar spacing of
(002) planes of ZnO increases as determined by the XRD peak shift to lower values of q. Such an effect is probably
due to the strain produced by the Al doping. Electrical characteristics of these films were studied at room
temperature by I-V and Hall measurements using Vander Paw four point probe method. The resistivity decreased
from ~3x10-2
W-cm for undoped ZnO to ~6x10-4
W-cm for 2% Al doping. However with further increase in Al
doping, the resistivity started increasing. The carrier concentration first increased from a value of ~7x1018
cm-3
(mobility ~24 cm2/V-sec) for undoped ZnO to the highest carrier concentration of ~8x1020
cm-3 (mobility ~13
cm2/V-sec) at 2% Al doping and then decreased. The electrical conductivity of the AZO film reported here
compares favorably well with those reported earlier by others [1,2]. The transmission spectra of these films show an
average transmission of ~ 80 % in the visible spectral region. A blue shift in the absorption edge of ZnO with
increasing Al concentration in the films is noteworthy as it leads to increase in the width of the transmission
window. The bandgap of ZnO and AZO films has been calculated by using 2 vs plot. It varies from 3.27eV to
3.67 eV as the Al doping increases from 0% to 5% and the variation is attributed to Burstein-Moss shift. Thus Al
doping is doubly beneficial as it increases the average transparency of ZnO film as well as the width of the
transmission window.
Acknowledgements AS and RKS thank the UGC New Delhi for financial assistance.
References
1. J. Mass, P. Bhattacharya and R.S. Katiyar; Mat. Sc. & Eng. B103 (2003) 9-15;
2. F. Shan, G.X. Liu, W.J. Lee, G.H. Lee, I.S. Kim, B.C.Shin, Y.C. Kim; J. of Crystal
Growth 277 (2005) 284-292
77
PLD-2005: Posters ?P 27
Structural and Optical Characteristics of Zn1-xMnxO Thin Films Grown by
Pulsed Laser Deposition
U. K. Pandey*, Pankaj Misra & L. M. Kukreja
Thin Film Lab, Centre for Advanced Technology, Indore-452013
*Department of Applied Physics, SGSITS, Indore- 452003
Abstract
Recently there has been worldwide interest in wide bandgap diluted magnetic semiconductors (DMS) which exploit
both the spin and charge of the carriers for the development of transparent spintronic and magneto-optical devices
such as spin valve transistors, spin light emitting diodes, and non-volatile storage and logic devices. ZnO with a
direct wideband gap of ~ 3.3 eV at room temperature, rugged wurtzite structure and controlled n-type doping is
being explored as a host material for such applications [1]. We have deposited Zn1-xMnxO thin films with x in the
range of 0.01 to 0.3 by Pulsed Laser Deposition technique and studied their optical and structural characteristics.
Predetermined amount of ZnO (99.999%) and MnO (99.997%) powders were mixed, calcined at 8000C for 4 Hrs,
pelletised and sintered at 1100 0C for 2 Hrs for making ceramic targets. Thin films were grown on sapphire (0001)
substrates at 600 0C, in 1 ´ 10-4 Torr of oxygen pressure using third harmonic of a Q-switched Nd:YAG (Quantel
YQ980) laser pulses (335 nm, 10 Hz, 6 ns) at a fluence of about 2 J/cm2. The distance between the substrate and
target was ~ 5.5 cm.
The High Resolution XRD of these films showed only (0002) and (0004) peaks of wurtzite Zn1-xMnxO without any
peaks corresponding to MnO related phase segregation indicating homogeneous distribution of Mn in the films. The
c-axis length of ZnO lattice was found to expand monotonically with the increase of Mn content up to x=0.30. The
optical transmittance spectra of these films measured at room temperature in the spectral range of 200 - 800 nm
revealed high transparency ~ 80% in the visible spectral region for all the films. The band gap (Eg), of the films was
found to increase monotonically with increasing Mn concentration in the film. A significant mid gap absorption,
which increased with increasing Mn concentration in the films, was also observed. This dominant mid-gap
absorption was assigned as 6A1-4T2, d-d transitions due to high spin d5 electron configuration of Mn+2 ions in the
crystal field of ZnO. The Energy dispersive analysis of the films confirmed that the Mn content in the film was
approximately the same as that in the targets. The photoluminescence measurements of Zn1-xMnxO thin films with
different Mn compositions at 10K revealed a strong luminescence at 368 nm (~3.369 eV) corresponding to
Zn1-xMnxO band gap which shifted slightly towards blue with increasing Mn concentration in ZnO from 3 - 20% .
We also observed an efficient transition at ~ 3.320 eV in Zn1-xMnxO thin films which was not present in pure ZnO.
This transition has been attributed in literature to the nano clustering of MnO or MnO2, which are anti-ferromagnetic
at 10K [2] or due to an efficient donor-acceptor pair transition as reported by Zang et al in ZnO nanorods [3]. The
nano segregations of MnO or MnO2 are generally difficult to be resolved by High resolution X-ray diffraction but
may contribute significantly in luminescence measurements. Further studies are underway to understand the
observed results.
References
1. T. Fukumura, Zhengwu Jin, A Ohtono, H Koinuma and M. Kawasaki, Appl. Phys. Lett., 75, 21,(1999)
2. Mariyana Diaconu et. al., Thin Solid Films, 486, 117(2005)
3. B.P. Zang et al., Appl.Phys.Lett., 83,1635, (2003)
78
PLD-2005: Posters ?P 28
Nanostructure Formation of Si and SiO2 from Laser Ablation of Amorphous Silicon
J Anto Pradeep, Kamlesh Alti, Siddananda Sarma, Pratima Agarwal and Alika Khare*
Department of Physic
Indian Institute of Technology Guwahati, Guwahti 781039
* Corresponding author email: alika@iitg.ernet.in
Abstract
Pulsed laser induced nano structures of Si and SiO2 formed under vacuum as well as in air are reported in the
present paper. High power Q switched Nd: YAG laser was focused on to the amorphous silicon wafer in the vacuum
(10-5 Torr). The ablated material was deposited on to the microscopic glass slide for the deposition of thin film of
nano crystallites of silicon. XRD and AFM studies confirm the formation of particle sizes down to 20nm. The
particle size shows the dependence on to the laser power as well as on to the exposure time. The amorphous Si
wafers were also exposed to the high power laser directly (unfocused ) and show the drastic modification in the
surface morphology. The XRD spectrum confirms the formation of nano crystallites of SiO2 on to the amorphous
target. The detail studies of the dependence of the nano crystallite size of Si as well as SIO2 will be presented in the
paper. These studies may find application in designing the waveguide for the optical integrated devices.

Del Mar Photonics - Newsletter Fall 2010 - Newsletter Winter 2010

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