SYNOPSIS OF DEVELOPMENT OF GRAPHENE AND SILICON NANOWIRES FOR PHOTOVOLTAIC AND FIELD ELECTRON EMISSION APPLICATIONS

Transcription

1 SYNOPSIS OF DEVELOPMENT OF GRAPHENE AND SILICON NANOWIRES FOR PHOTOVOLTAIC AND FIELD ELECTRON EMISSION APPLICATIONS A Thesis to be submitted by SANJAY KUMAR BEHURA (Roll Number: 09SSEPH06) For the Award of Degree of DOCTOR OF PHILSOPHY SCHOOL OF SOLAR ENERGY PANDIT DEENDAYAL PETROLEUM UNIVERSITY GANDHINAGAR AUGUST 30,

2 1 INTRODUCTION Materials in their lower dimensions are extremely interesting not only for fundamental study of novel physical phenomenon, but also their unique electrical, optical, mechanical and chemical properties, which make them attractive from a technological standpoint. This thesis examines the development of low-dimensional carbon and silicon materials such as: Graphene (2-D) [1] and Silicon Nanowire (1-D) [2] using chemical vapor deposition (CVD) techniques for photovoltaic and electron-field emission applications. Graphene is an exceptionally thin zero gap semiconductor, consists of a single-layer of carbon atoms arranged in a honeycomb lattice with confined charge carriers within a 2-D plane. These charge carriers behave like mass-less Dirac particles and possess extremely high carrier mobilities. In addition to this remarkable 2-Dness, it is also peculiar that the behaviour of the electrons in graphene is governed by the Dirac equation rather than the well known Schrodinger s equation, leading to the discovery of several new physics phenomena. Such unusual properties of graphene have stirred up great excitements since it was first isolated in the lab about nine years ago. Silicon nanowire (SiNW), which is a quasi-one-dimensional structure, has attracted much research interest in the past decade due to its exceptional electrical and physical properties. The unique optical and electrical properties of graphene and SiNW make these materials useful for photovoltaic and electron-field emission applications. In this present work, a systematic study has been done to fabricate large-area and high quality graphene films primarily using CVD. Apart from that a novel technique was developed for synthesizing catalyst-free synthesis of SiNWs. The first part of research work mainly focuses on the fabrication of high-quality, large-area graphene samples (Area=1.5x1.5 cm 2 ) directly on SiO 2 /Si substrates primarily using CVD. The significant part of this research work is the synthesis of vertically oriented graphene by a vertical mass flow reactor through hot-filament CVD. The proposed growth mechanisms for both horizontally and vertically oriented graphene films are in good agreement with the spectroscopic characterizations. Additionally, other techniques such as micromechanical exfoliation of highly ordered pyrolytic graphite with chemical oxidation and reduction have been tried to synthesize bi-layer to few-layer graphene (FLG) samples on 2

3 various substrates such as glass, Cu foil, ITO-coated glass, SiO 2 /Si, Cu/SiO 2 /Si etc. In order to study the behavior of graphene in simple electronic devices, two basic solid state devices such as graphene-on-semiconductor junctions and electron-field emitter have been fabricated and studied both theoretically and experimentally. Graphene-on-silicon (p-type) device is fabricated and photovoltaic behavior is studied while testing the device under dark and light conditions. Field-emission from horizontallyoriented graphene sheets is a challenge due to less number of emission sites. Here, we have synthesized free-standing vertically-oriented FLG films directly on dielectric substrates by hot-filament chemical vapor deposition (HFCVD) without any catalyst or special substrate treatment. The fabricated FLGs are with a large smooth surface topography, oriented nearly vertical to the substrate and found to grow according to the Stranski-Krastanov growth mechanism. The feasibility of large area preparation and the low turn-on field of 22 V/µm in addition to the large field enhancement factor of 6520 and a field emission current density of 25 µa/cm 2 at an applied electric field of 44 V/µm suggest that the vertically-oriented FLGs could be used as a potential edge emitter. The second part of the research work focuses on developing a new technique for the growth of SiNWs which was grown by a simple oxidation and reduction process of silicon wafers using a high temperature furnace. The plausible growth mechanism is also suggested. The process involves H 2, in an inert atmosphere, reacts with thermally grown SiO 2 on silicon at 1100 o C enhancing the direct growth of nanowires on silicon wafers. High-resolution transmission electron microscopy studies show the crystalline silicon of diameter 30 nm as core with thin amorphous oxide shell of thickness as low as 2 nm. This structure of NW is confirmed by the selected area electron diffraction pattern. The grown SiNW possess a high aspect ratio of approximately 167; room temperature phonon confinement effect is also observed in the nanowires. This research of synthesizing crystalline SiNWs in a simple and economical way opens up vast opportunities for basic studies and nano-scale device applications. 3

4 2 MOTIVATION AND OBJECTIVES The first system under investigation in the present work is graphene. In order to reach the ambitious goal of using graphene in photovoltaic and electron-field emission applications, one needs reliable methods for the large-scale production of high quality graphene films. Conventionally, graphene is prepared on transition metal catalyst surfaces and then transferred to substrates suitable for characterizations and applications. This transfer process adds the complexity of the processing and also reduces the intrinsic properties of graphene. Therefore, it becomes essential to develop direct growth techniques of graphene on insulting substrates including SiO 2 /Si wafers, glasses or plastic foils. The second system under investigation in this present work is SiNW. Significant progress has been made for catalyst assisted growth of SiNWs and their applications, but only a few papers have been reported on the catalyst-free growth of SiNWs. So far, many methods have been developed to grow SiNWs, but a universal growth technique fulfilling all the requirements for potential applications has not yet emerged. CVD allows controlled and selective growth of nanowires (NWs) through prepatterning the metal catalysts on the substrate. However, it requires costly metals such as gold, indium, or platinum as catalysts. Supercritical-fluid based method produces thin quality NWs with high yield, but it is difficult to achieve controlled and epitaxial growth. MBE can produce single crystalline NWs on predefined positions on the substrate, but its low growth rate of a few nanometers per minute results in NWs of limited aspect ratios. Laser ablation technique is very simple, but difficult to achieve epitaxial growth. SiO evaporation technique is simple too, but it is difficult to control the diameters and lengths of grown NWs. Moreover, SiO powder is harmful to health. Neverthless, the limitations associated with the those growth methods have stimulated increasing interest in developing catalyst free synthesis of SiNWs without using any metal catalyst and SiO powders. In this research work, a simple, single step and cost-effective technique have been developed to sythesize SiNWs for large scale applications. Using this technque, SiNWs can be synthesized on Si substrate without any additional nano-sized metal catalyst seed layer by simply oxidizing and reducing Si wafers through oxide-assisted growth. Comparing with the previously reported catalyst assisted methods, this process presents many advantages, including (i) elimination of metal catalyst contamination; (ii) 4

5 avoiding the use of toxic precursor gases such as SiH 4 or SiCl 4 ; and (iii) no need to transfer the NWs for device manufacturing because NWs are directly grown on Si wafers. 3 SUMMARY OF RESEARCH WORK Thesis chapter 1 and 8 will be Introduction and Conclusion, respectively which are clearly stated in the proposed content of thesis. 3.1 Chapter 2: Theoretical Studies on Photovoltaic Response of Grapheneon-Semiconductors In chapter 2, analytical study has been done to understand the interface physics of intimate contact of graphene on both direct and indirect semiconductors. Graphene, due to its high transparency and electrical conductivity is a suitable candidate for photovoltaic applications. In photovoltaic science, graphene has demonstrated promising applications in dye-sensitized solar cells and organic solar cells. A very limited amount of experimental work has been done to explore graphene in semiconductor devices and in particular, as Schottky junction solar cells due to the lacking of proper understanding of the interface physics of graphene and semiconductors. In this work, we discuss analytically the photovoltaic effects upon intimate contact of graphene with different semiconductors such as silicon (Si) and gallium arsenide (GaAs). The open-circuit voltage (V OC ) is calculated based on the theory developed by S. K. Behura et al. [3] for high level injection (HLI) and by Dubey and Paranjape [4] for low level injection (LLI). HLI in a semiconductor refers to the concentration of charge carriers which is larger than the doping density i.e., n, p >> N d. The effects of semiconductor doping density and surface recombination velocity on the V OC of both systems are investigated [Figure 1]. The standard metal/semiconductor Schottky model [5] is considered for the calculation of the short-circuit current density. The V OC developed across the SJSC under high level injection formulated by Behura et al. [3] and low level injection formulated by Dubey and Paranjape [4], is given by (1) and (2), respectively. = - + [log { ]... (1) 5

6 and = (2) Where = is the surface potential, is the donor density and is the dielectric permittivity of the semiconductor. Figure 1. Open-circuit voltage vs. doping density for (a) graphene/n Si and (b) graphene/n GaAs under LLI and HLI at fixed SRV=100 cm/s. Open-circuit voltage vs. surface recombination velocity for (c) graphene/n Si and (d) graphene/n GaAs under LLI and HLI at N d = cm -3. 6

7 3.2 Chapter 3: Fabricating Graphene by Physical Exfoliation of Graphite and Its Properties as Transparent and Current Spreading Electrode In chapter 3, fabrication of graphene has been tried using micromechanical exfoliation of highly oriented pyrolytic graphite and TCAD 2D computational study was carried out to use graphene as transparent and current spreading electrode in silicon and InGaN solar cells. Physical exfoliation of highly-oriented pyrolytic graphite (HOPG) [1] is the first technique discovered by A. K. Geim and K. S. Novoselov in 2004 [Noble Prize in Physics, 2010] for the fabrication of high quality graphene films. This present thesis aims to develop high quality and large-area graphene films for the photovoltaic and electron-field emission applications. Herein, high quality graphene film has been fabricated using mechanical exfoliation of HOPG (Figure 2) and its properties are used as transparent and current spreading electrode (TCSE) in silicon (Si) P-N and InGaN P-I-N junction solar cells. The transferred graphene films on glass substrates were characterized using field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Raman spectroscopy, UV-vis spectroscopy (UV-Vis) and Fourier transform infrared spectroscopy (FTIR). A very high intensity ratio of 2D to G-band ( 1.67) and narrow 2D-band full-width at half maximum ( 40 cm -1 ) correspond to the bi-layer graphene (BLG) formation. Using Technology Computer Aided Design (TCAD) 2D simulation software and the characterized properties of exfoliated BLG, I have taken an attempt to study the effect of BLG as TCSE in Si wafer based and InGaN thin film based solar cells. In case of Si P-N junction solar cell, the Ag grids were replaced by BLG and it shows an increase in efficiency of % compared to % for Si solar cell with Ag grids. In another experiment, the conventional ITO has been replaced by BLG for InGaN P-I-N junction solar cell. The BLG/p-GaN/n-InGaN/n-GaN/GaN/Al 2 O 3 device exhibits an efficiency of % compared to the conventional ITO-based TCSE, which shows an efficiency of % with the system configuration of ITO/p-GaN/n-InGaN/n-GaN/GaN/Al 2 O 3. 7

8 Figure 2. (a) FESEM and (b) AFM images with step height (inset) of graphene film on glass. 3.3 Chapter 4: Fabricating Graphene by Chemical Exfoliation of Graphite and Fabrication of rgo/p-si Hetero-junction Solar Cell In this research work (Chapter 4), experimental and theoretical investigations on the heterojunctions of chemically derived graphene [6] with Si have been carried out. The stability study of graphene oxide (GO) and reduced GO (rgo) in aqueous medium were performed by visual observation and surface charge measurement. The detailed characterizations by FT-IR, UV-Vis and Raman exhibited the formation of rgo with a high optical band gap of 3.6 ev (Figure 3). The rgo was spin-coated on the p-si substrate for fabrication of a heterojunction device, with the structure of rgo/p-si. In the fabricated device, incident light was transmitted through the thin rgo film to reach the junction interface, generating photoexciton and thereby a photo-conversion efficiency of 0.02 % was achieved experimentally and its (rgo/p-si heterojunction device) theoretical simulation using SCAPS 1D tool showed the efficiency of 1.32 %. Such large deviations in efficiency between experiment and theory have been discussed in details. 8

9 Figure 3. Raman spectra of graphite, GO and rgo taken at Raman excitation wavelength of 514 nm. Inset indicates the reduction of D- and G-band intensity, which confirms the formation of rgo. 3.4 Chapter 5: Fabricating Graphene by Chemical Vapor Deposition on Copper Metal Catalyst Substrates and Its Field Electron Emission Study In chapter 5, a systematic study of the catalytic CVD growth of graphene on polycrystalline copper (Cu) foil [7] in a low pressure CVD conditions has been presented, aiming to achieve the highest quality with large-scale fabrications, which generally requires comprehensive understanding and effective controlling of the growth process (Figure 4). Herein, FLG films with large-domain sizes were grown on Cu metal catalyst substrates using a vertical massflow HFCVD reactor, with the intention of commercialization, by optimizing the CVD system and three of the process parameters namely: (i) gas flow compositions, (ii) substrate annealing time and (iii) growth deposition time. The optimized detailed growth process that has been tailored for the synthesis of graphene are as follows: the chamber was first evacuated to 0.1 mtorr, and then the Cu substrate was heated to 1000 C with a flow of 9

10 hydrogen at 10 sccm and held for 20 minutes for the annealing and subsequently grain growth of the Cu film. After that, the temperature was kept at 1000 C with a gas composition of CH 4 :H 2 =1:50 sccm flowing into the reaction chamber, and maintaining a pressure of mtorr for the growth of graphene films. After 10 minutes of growth, the chamber was cooled at 25 o C/min under the flow of hydrogen at 10 sccm. These assynthesized flat graphene films on Cu have shown the room temperature field electron emission characteristics under vacuum, hence appears to be potential candidate for vacuum electronic device applications. Figure 4. Mechanism for Catalytic CVD growth of graphene films on polycrystalline Cu foil with the schematic of electron field emission from horizontally oriented graphene films. The detailed scanning electron microscopy (SEM) and Raman spectroscopy analysis (Figure 5) indicate that all the above mentioned processed parameters affect growth of FLG film on Cu substrate. The presence of well resolved broad two intense peaks, G and 2D-band at cm -1 and cm -1, for synthesized sample at optimized conditions (H 2 /CH 4 ratio of 50:1 at graphene deposition time of 10 min and substrate annealed time for 20 min) revealed the formation of FLG films with large domain size. The G-band originates from the Stokes Raman scattering with one phonon (E 2g ) emission and its intensity increases almost linearly with the increasing number of layers. The 2D-band is due to the Stokes-Stokes double resonant Raman scattering with two phonon emissions. The broadening and the blueshift of the 2D-band are the signature of increasing number of graphene layers. The D-band at 10

11 cm -1 corresponds to the defects in the synthesized film, because the D-band originates from the backscattering of phonon by disorder sites (such as edges and defects). Figure 5. (a) SEM micrograph of annealed Cu surface, (b) digital image of the graphene film on annealed Cu surface, (c) SEM micrograph of graphene film on annealed Cu surface and (d) Raman spectrum of graphene film on Cu surface. 3.5 Chapter 6: Fabricating Graphene by Chemical Vapor Deposition Directly on Dielectric Substrates and Its Diode Characteristics and Field Electron Emission Study In chapter 6, an attempt has been made to synthesize graphene directly on dielectric substrates using thermal and hot filament chemical vapor deposition. Both horizontally and vertically oriented graphene films were fabricated and their diode and filed electron emission characteristics have been shown. Field-emission from flat graphene sheets is a challenge due to less number of emission sites. Here, we have synthesized free-standing vertically-oriented FLG films [8] directly on dielectric substrates by HFCVD without any catalyst or special substrate treatment. The fabricated FLGs with a large smooth surface topography, standing roughly vertical to the substrate and found to grow according to the Stranski-Krastanov 11

12 growth mechanism (Figure 6). The ease of large area preparation and the low turn-on field of 22 V/ m in addition to the large field enhancement factor of 6520 for electron field emission suggest that the vertically-oriented FLGs could be used as a potential edge emitter. Figure 6. Free-standing FLG film on a SiO 2 /Si substrate (a) FESEM micrograph, (b) AFM topography images with (c) Field emission mechanism, (d) Room temperature J-E characteristics and (d) Corresponding F-N plot with a ca. field enhancement factor of Chapter 7: Fabricating Silicon Nanowires by Chemical Vapor Deposition and Its Quantum Confinement Study In chapter 7, a new process has been developed to grow SiNWs [2] and their growth mechanisms were explored and discussed. This is a novel technique to grow SiNWs just by switching the gas compositions used for graphene synthesis process using thermal chemical vapor deposition. In this process, SiNWs were synthesized by simply oxidizing and then reducing Si wafers in a high temperature furnace. The process involves H 2, in an inert atmosphere, reacts with thermally grown SiO 2 on Si at 1100 o C enhancing the growth of 12

13 SiNWs directly on Si wafers. High-resolution transmission electron microscopy studies show that the NWs consist of a crystalline core of approximately 25 nm in diameter and an amorphous oxide shell of approximately 2 nm in thickness, which was also supported by selected area electron diffraction patterns (Inset of Figure 7 (e)). The synthesized NWs exhibit a high aspect ratio of approximately 167 and the room temperature phonon confinement effect has also been studied. This simple and economical process to synthesize crystalline SiNWs opens up a new way for large scale applications. Figure 7. FESEM micrograph images of SiNWs (a) at low magnification, (b) at high magnification, (c) A schematic of growth mechanism, (d) HR-TEM image with Si as core and amorphous SiO 2 as shell at low magnification and (e) at high magnification with the SAED pattern of the NWs (inset). 13

14 4 CONCLUSIONS Few-layer to bi-layer graphene films have been successfully synthesized using various techniques such as: micromechanical exfoliation, chemical vapor deposition and chemical oxidation-reduction methods on various substrates such as: glass, ITO-coated glass, Cu foil, Cu/SiO 2 /Si and SiO 2 /Si and characterized using FESEM, AFM, FT-IR, Raman etc. Free-standing vertically-oriented FLG films were grown directly on dielectric substrates by HFCVD without any catalyst or special substrate treatment. The ease of large area preparation and the low turn-on field of 22 V/µm in addition to the large field enhancement factor of 6520 for electron field emission suggest that the verticallyoriented FLGs could be used as a potential edge emitter. Analytical and computational study has been carried out using the characterized properties of graphene to study the possible applications in solar cells. In case of Si P-N junction solar cell, the Ag grids were replaced by BLG and it shows an increase in efficiency of % compared to % for Si solar cell with Ag grids. In another experiment, the conventional ITO has been replaced by BLG for InGaN P-I-N junction solar cell. The BLG/p-GaN/n-InGaN/n-GaN/GaN/Al 2 O 3 device exhibits an efficiency of % compared to the conventional ITO-based TCSE, which shows an efficiency of % with the system configuration of ITO/p-GaN/n-InGaN/n-GaN/GaN/Al 2 O 3. Chemically-derived graphene-on-p/si heterojunction have been fabricated and characterized which showed a photo-conversion efficiency of 0.02 %. The corresponding theoretical simulation of rgo/p-si heterojunction device using solar cell capacitance simulation 1D software showed the efficiency of 1.32 %. Such large deviations in efficiency between experiment and theory have been discussed in details. A new process has been developed to grow silicon SiNWs and their growth mechanisms were explored and discussed. The synthesized NWs exhibit a high aspect ratio of approximately 167 and room temperature phonon confinement effect. This simple and economical process to synthesize crystalline SiNWs opens up a new way for large scale applications. 14

15 All the above experimental and theoretical research work can be summarized using the following Figure 8. Figure 8. Systematic summary of the thesis work. 15

16 5 REFERENCES [1] A. K. Geim, K. S. Novoselov, The rise of graphene, Nat. Mater. 6, (2007). [2] Y. Cui, Z. Zhong, D. Wang, W. U. Wang, C. M. Lieber, High performance silicon nanowires field effect transistors, Nano Lett. 3, (2003). [3] S. K. Behura, P. Mahala, A. Ray, A model on the effect of injection levels over the open-circuit voltage of schottky barrier solar cells, J. Electron Devices 10, (2011). [4] P. K. Dubey, V. V. Paranjape, Open-circuit Voltage of a Schottky-barrier Solar cell, J. Appl. Phys. 48, (1977). [5] S. M. Sze, Semiconductor Devices: Physics and Technology, 2nd ed. (Wiley, India, 2002). [6] G. Eda, Y. Y. Lin, S. Miller, C. W. Chen, W. F. Su, M. Chhowalla, Transparent and conducting electrodes for organic electronics from reduced GO, Appl. Phys. Lett.; 92, (2008). [7] P. R. Kidambi, C. Ducati, B. Dlubak, D. Gardiner, R. S. Weatherup, M-B. Martin, P. Seneor, H. Coles, S. Hofmann, The parameter space of graphene chemical vapour deposition on polycrystalline Cu, J. Phys. Chem. C, 116, (2012). [8] Y. Zhang, J. Du, S. Tang, P. Liu, S. Deng, J. Chen, and N. Xu, Optimize the field emission character of a vertical few-layer graphene sheet by manipulating the morphology Nanotechnology 23, (2012). 16

17 6 PROPOSED CONTENT OF THESIS Based on my research results, I have planned to organize my thesis in the following chapters. Chapter 1: Introduction and Motivations. Chapter 2: Understanding Graphene and Theoretical Study on Photovoltaic Response of Graphene-on-Semiconductors. Chapter 3: Fabricating Graphene by Physical Exfoliation of Graphite and Theoretical Study on Using Graphene as Transparent and Current Spreading Electrode. Chapter 4: Fabricating Graphene by Chemical Exfoliation of Graphite and Combined Experimental and Theoretical Study on rgo/p-si Heterojunction Solar Cell. Chapter 5: Fabricating Graphene by Chemical Vapor Deposition on Copper Metal Catalyst Substrates and its Field Electron Emission Study. Chapter 6: Fabricating Graphene by Chemical Vapor Deposition Directly on Dielectric Substrates and its Diode Characteristic and Field Electron Emission Study. Chapter 7: Fabricating Silicon Nanowires by Chemical Vapor Deposition and Its Quantum Confinement Study. Chapter 8: Conclusions and Outlook. 17

18 7 PUBLICATIONS 7.1 Publications in SCI Journals [1] S. K. Behura, P. Mahala, A. Ray, I. Mukhopadhyay, O. Jani, Theoretical simulation of photovoltaic response of Graphene-on-semiconductors, Applied Physics A: Materials Science and Processing, Vol. 111, p (2013). [2] S. K. Behura, A. Hirose, Q. Yang, I. Mukhopadhyay, O. Jani, Vertically-oriented fewlayer graphene as an electron field-emitter, Physica Status Solidi (A): Applications and Material Sciences, Vol. 210, p (2013). [Findings Highlighted in Nature India, doi: /nindia , May 31, 2013] [3] S. K. Behura, P. Mahala, S. Nayak, Q. Yang, I. Mukhopadhyay, O. Jani, Fabrication of bi-layer graphene and theoretical simulation for its possible application in thin film solar cell, Journal of Nanoscience and Nanotechnology, doi: /jnn (2013). [Findings Highlighted in EQ International, p , May 2013] [4] S. K. Behura, Q. Yang, A. Hirose, O. Jani, I. Mukhopadhyay, Catalyst-free synthesis of silicon nanowires by oxidation and reduction process, Journal of Materials Science (2013) [Accepted]. [5] S. K. Behura, A. Hirose, Q. Yang, O. Jani, I. Mukhopadhyay, Diode Characteristics of few-layer graphene/p-silicon fabricated directly by chemical vapor deposition, Physica E: Low Dimensional Systems and Nanostructures (2013) [Under Review]. [6] S. K. Behura*, S. Nayak, I. Mukhopadhyay, O. Jani, Junction characteristics of chemically-derived graphene/p-si hetero-junction solar cell, Carbon (2013) [Under Review]. [7] S. K. Behura*, S. Nayak, Q. Yang, A. Hirose, O. Jani, I. Mukhopadhyay, A Systematic Study of CVD Graphene Growth on Polycrystalline Copper Foil, RSC Advances (2013) [Under Review]. 18

19 7.2 Publications in Referred Conference Proceedings [8] S. K. Behura, O. Jani, I. Mukhopadhyay, Exfoliated bi-layer graphene as an alternative to transparent and conductive film, Proceedings of International Congress on Renewable Energy (ICORE-2012), p , PDPU, India, December 6-7 (2012). [9] S. K. Behura*, I. Mukhopadhyay, O. Jani, Q. Yang, A. Hirose, Synthesis of Graphene on Copper by Hot Filament Chemical Vapor Deposition, Proceedings of 24 th Canadian Congress of Applied Mechanics, University of Saskatchewan, Canada, June 2-6 (2013). [10] S. K. Behura, M. V. Rao, Q. Yang, A. Hirose, O. Jani, I. Mukhopadhyay, Fabrication of multiple-layer graphene films on Cu/SiO2/Si substrate by hot-filament chemical vapor deposition, AIP Conference Proceedings, Vol. 1538, p (2013). 7.3 Conferences/ Workshops/ Schools/ Visit Abroad Sr. From To Place Purpose 9 Jun. 24, 2013 Jun. 27, 2013 SSGI, India Participation at IWMMS Dec. 6, 2012 Dec. 7, 2012 PDPU, India Oral Presentation at ICORE Nov. 1, 2012 Nov. 3, 2012 BARC, India Oral Presentation at CCM Oct. 1, 2011 June 30, 2012 University of Saskatchewan, Canada Study and Research under Canada Commonwealth Scholarship Programme ( ) 5 April 19, 2012 April 19, 2012 Saskatoon, Canada Seminar on FTIR Technologies 4 July 4, 2011 July 10, 2011 IIT Guwahati, India 3 Jan. 28, 2011 Jan. 30, 2011 MSU Baroda, India 2 Dec Dec. 17, 2010 IIT Mumbai, India Participation and Oral Presentation at India-UK Summer School on Efficient Fossil Energy Technology Poster Presentation at ISSMD Participation at India-UK Winter School on Nano-Scale Materials & Devices 1 Oct. 27, 2010 Oct. 29, 2010 Delhi, India Participation at DIREC