Photovoltaic technologies use light from the sun to create electricity, using a wide range of materials and mechanisms. The generation of clean, renewable energy using this technology must become price competitive with conventional power generation if it is to succeed on a large scale. The field of photovoltaics can be split into many sub-groups, however the overall aim of each is to reduce the cost per watt of the produced electricity. One such solar cell which has potential to reduce the cost significantly is the dye sensitised solar cell (DSC), which utilises cheap materials and processing methods. The reduction in cost of the generated electricity is largely dependent on two parameters. Firstly, the efficiency that the solar cell can convert light into electricity and secondly, the cost to deposit the solar cell. This thesis aims to address both factors, specifically looking at altering the transparent conducting oxide (TCO) and substrate in the solar cell. One method to improve the overall conversion efficiency of the device is to implement the DSC as the top cell in a tandem structure, with a bottom infra-red absorbing solar cell. The top solar cell in such a structure must not needlessly absorb photons which the bottom solar cell can utilise, which can be the case in solar cells utilising standard transparent contacts such as fluorine-doped tin oxide. In this work, transparent conducting oxides with high mobility such as titanium-doped indium oxide (ITiO) have been used to successfully increase the amount of photons through a DSC, available for a bottom infra-red sensitive solar cell such as Cu(In,Ga)Se2 (CIGS). Although electrically and optically of very high quality, the production of DSCs on this material is difficult due to the heat and chemical instability of the film, as well as the poor adhesion of TiO2 on the ITiO surface. Deposition of a interfacial SnO2 layer and a post-deposition annealing treatment in vacuum aided the deposition process, and transparent DSCs of 7.4% have been fabricated. The deposition of a high quality TCO utilising cheap materials is another method to improve the cost/watt ratio. Aluminium-doped zinc oxide (AZO) is a TCO which offers very high optical and electronic quality, whilst avoiding the high cost of indium based TCOs. The chemical and thermal instability of AZO films though present a problem due to the processing steps used in DSC fabrication. Such films etch very easily in slightly acidic environments, and are susceptible to a loss of conductivity upon annealing in air, so some steps have to be taken to fabricate intact devices. In this work, thick layers of SnO2 have been used to reduce the amount of etching on the surface of the film, whilst careful control of the deposition parameters can produce AZO films of high stability. High efficiency devices close to 9% have been fabricated using these stacked layers. Finally, transferring solar cells from rigid to flexible substrates offers cost advantages, since the price of the glass substrate is a significant part of the final cost of the cell. Also, the savings associated with roll to roll deposition of solar cells is large since the production doesn't rely on a batch process, using heavy glass substrates, but a fast, continuous process. This work has explored using the high temperature stable polymer, polyimide, commonly used in CIGS and CdTe solar cells. AZO thin films have been deposited on 7.5um thick polyimide foils, and DSCs of efficiency over 4% have been fabricated on the substrates, using standard processing methods.

Cerâmicas elétricas de Ba2In2O5 foram preparadas pelo método convencional de mistura de óxidos, e pela mistura e cristalização dos nitratos metálicos, para verificar o efeito do tamanho inicial das partículas na transição de fase ordemdesordem e na condutividade elétrica. Foram feitas substituições utilizando os cátions Gd3+ e Er3+, para verificar o efeito destes cátions na condutividade elétrica do indato de bário. Foi também preparado o óxido de índio pela técnica de complexação de cátions, e as nanopartículas obtidas foram caracterizadas por diversas técnicas. As principais técnicas de caracterização utilizadas foram: análise térmica, espectroscopia de absorção na região do infravermelho com transformada de Fourier, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X convencional e utilizando radiação síncrotron, espalhamento de raios X a baixos ângulos, espectroscopia de energia dispersiva, espectroscopia Raman e medida da condutividade elétrica por espectroscopia de impedância. Os principais resultados mostraram que os tratamentos térmicos de calcinação e sinterização exercem forte influência na obtenção da fase Ba2In2O5. Fases espúrias são facilmente formadas no Ba2In2O5 também decorrentes da interação deste com a umidade. Um menor tamanho inicial de partículas favorece a redução na temperatura de transição de fase de segunda ordem. A introdução do Er, em teores relativamente baixos, produziu aumento na condutividade elétrica e simultânea redução na temperatura de transição de fase. Altos teores de Er e Gd dão origem a múltiplas fases. Na decomposição térmica do citrato de índio é formado um composto intermediário. A calcinação do citrato de índio produziu um material particulado com tamanho nanométrico, mesmo para temperaturas de até 900 ºC. / The Ba2In2O5 conducting ceramic was prepared by the conventional powder mixing technique and by the crystallization of a mixture of metallic nitrates. The main purpose of this work was to verify the particle size effect on the electrical conductivity and phase transition temperature of sintered ceramics. Gd3+ and Er3+ were used to study the effect of dopant cations in the electrical conductivity behavior of Ba2In2O5. Finally, indium oxide was prepared by the cation complexation technique, and the obtained nanoparticles were characterized by several techniques. The main characterization techniques used in this work were: thermal analyses, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, energy dispersive X-ray analysis, conventional X-ray diffraction and non-conventional X-ray diffraction using síncroton radiation, small angle X-ray diffraction, Raman spectroscopy and electrical conductivity by impedance spectroscopy. The main results show that special care should be taken in order to obtain single phase Ba2In2O5 powders, especially with thermal treatments of calcination and sintering of powders and compacts. The temperature for the second order phase transition decreased with reduction of the initial particle size. An increase of the electrical conductivity along with decrease in the temperature for phase transition was observed for small amounts of Er. Large contents of both Gd and Er give rise to more complexes phases. An intermediate compound was formed during the thermal decomposition of indium citrate. Calcination of this precursor up to 900 ºC gave rise to nanosized particles.

Cerâmicas elétricas de Ba2In2O5 foram preparadas pelo método convencional de mistura de óxidos, e pela mistura e cristalização dos nitratos metálicos, para verificar o efeito do tamanho inicial das partículas na transição de fase ordemdesordem e na condutividade elétrica. Foram feitas substituições utilizando os cátions Gd3+ e Er3+, para verificar o efeito destes cátions na condutividade elétrica do indato de bário. Foi também preparado o óxido de índio pela técnica de complexação de cátions, e as nanopartículas obtidas foram caracterizadas por diversas técnicas. As principais técnicas de caracterização utilizadas foram: análise térmica, espectroscopia de absorção na região do infravermelho com transformada de Fourier, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios X convencional e utilizando radiação síncrotron, espalhamento de raios X a baixos ângulos, espectroscopia de energia dispersiva, espectroscopia Raman e medida da condutividade elétrica por espectroscopia de impedância. Os principais resultados mostraram que os tratamentos térmicos de calcinação e sinterização exercem forte influência na obtenção da fase Ba2In2O5. Fases espúrias são facilmente formadas no Ba2In2O5 também decorrentes da interação deste com a umidade. Um menor tamanho inicial de partículas favorece a redução na temperatura de transição de fase de segunda ordem. A introdução do Er, em teores relativamente baixos, produziu aumento na condutividade elétrica e simultânea redução na temperatura de transição de fase. Altos teores de Er e Gd dão origem a múltiplas fases. Na decomposição térmica do citrato de índio é formado um composto intermediário. A calcinação do citrato de índio produziu um material particulado com tamanho nanométrico, mesmo para temperaturas de até 900 ºC. / The Ba2In2O5 conducting ceramic was prepared by the conventional powder mixing technique and by the crystallization of a mixture of metallic nitrates. The main purpose of this work was to verify the particle size effect on the electrical conductivity and phase transition temperature of sintered ceramics. Gd3+ and Er3+ were used to study the effect of dopant cations in the electrical conductivity behavior of Ba2In2O5. Finally, indium oxide was prepared by the cation complexation technique, and the obtained nanoparticles were characterized by several techniques. The main characterization techniques used in this work were: thermal analyses, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, energy dispersive X-ray analysis, conventional X-ray diffraction and non-conventional X-ray diffraction using síncroton radiation, small angle X-ray diffraction, Raman spectroscopy and electrical conductivity by impedance spectroscopy. The main results show that special care should be taken in order to obtain single phase Ba2In2O5 powders, especially with thermal treatments of calcination and sintering of powders and compacts. The temperature for the second order phase transition decreased with reduction of the initial particle size. An increase of the electrical conductivity along with decrease in the temperature for phase transition was observed for small amounts of Er. Large contents of both Gd and Er give rise to more complexes phases. An intermediate compound was formed during the thermal decomposition of indium citrate. Calcination of this precursor up to 900 ºC gave rise to nanosized particles.

Planar two-dimensional (2-D) nanostructured indium oxide (InOx) and one-dimensional (1-D) tin oxide (SnO2) semiconductor metal-oxide layers have been utilised for gas sensing applications. Novel layered Surface Acoustic Wave (SAW) based sensors were developed consisting of InOx/SiOxNy/36°YXLiTaO3, InOx/SiNx/SiO2/36°YXLiTaO3 and InOx/SiNx/36°YXLiTaO3 The 1 µm intermediate layers of silicon oxynitride (SiOxNy), silicon nitride (SiNx) and SiO2/SiNx matrix were deposited on lithium tantalate (36°YXLiTaO3) substrates by r.f. magnetron sputtering, electron-beam evaporation and plasma enhanced chemical vapour deposition (PECVD) techniques, respectively. As a gas sensitive layer, a 100 nm thin layer of InOx was deposited on the intermediate layers by r.f. magnetron sputtering. The targeted gases were ozone (O3) and hydrogen (H2). An intermediate layer has multiple functions: protective role for the interdigital transducers' electrodes as well as an isolating effect from InOx sensing layer, thereby improving the sensor performance. The developed SAW sensors' exhibited high response magnitudes with repeatable, reversible and stable responses towards O3 and H2. They are capable of sensing concentrations as low as 20 parts-per-billion for O3 and 600 parts-per-million for H2. Additionally a conductometric type novel sensing structure of SnO2/36°YX LiTaO3 was also developed by depositing a thin layer of SnO2 nanorods by PECVD. The gas sensing performance exhibited repeatable, reversible, stable responses towards NO2 and CO. The surface morphology, crystalline structure and preferred orientation of the deposited layers were investigated by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). A polycrystalline, oxygen deficient non-stoichiometric InOx with grain sizes of 20-40 nm was revealed. The 1-D nanostructures were characterised by Transmission Electron Microscopy (TEM) showing nanorods with needle-like shape , diameters of 10-20 nm a t the top and 30-40 nm at the base as well as a preferential growth orientation of [ ] on the LiTaO3 substrate. The developed sensors are promising for O3, H2 and CO sensing.

The work presented in this thesis focuses on the investigation and improvement of the window stack of layers for thin film CdTe solar cells fabricated in the Center for Renewable Energy Systems Technology (CREST) laboratories. In particular the aim was to change the standard structure including TCO, high resistive transparent (HRT)layer and CdS which is limited by the low transparency of the CdS layer, to a better performing one. The first result chapter of the thesis describes the study of ZnO HRT layers. ZnO thin films were deposited by radio frequency (RF) magnetron sputtering with different structural, optical and electrical properties which were characterized by X-ray diffraction, electron microscopy, spectrophotometry, Hall Effect method and 4-point probe. ZnO films were then incorporated in CdTe solar cells with the structure: FTO/ZnO/CdS/CdTe/Au back contact and the performance of these devices were compared with the film properties to single out trends and identify optimal film characteristics. By varying the deposition pressure of ZnO films, it was possible to increase their transparency and significantly increase their resistivity. While better transparency positively affected the solar cell current density output and efficiency, the resistivity of ZnO films did not show any clear impact on device efficiency. By increasing the deposition temperature the ZnO film grain size was increased. Increased FF was observed in devices incorporating ZnO layers with bigger grains, although this gain was partially counterbalanced by the Voc degradation, leading to a limited efficiency improvement. Finally the addition of oxygen had the main effect of increasing the resistivity of ZnO films, similarly to what happened with the increase of the sputtering pressure. In this case however, an improvement of FF, Jsc and efficiency was observed, especially at an O2/Ar ratio of 1%. By simulating the solar cells behavior with SCAPS-1D, it was found that these performance change can be explained by the variation of interface properties, precisely the amount of interface defects, rather than by bulk properties. The study presented in the second result chapter focuses on magnesium-doped zinc oxide (MZO) and the variation of its energy band structure. MZO was initially used as the HRT layer within a solar cell structure: FTO/MZO/CdS/CdTe/Au back contact. Sputtering MZO films with a target containing MgO 11 weight% and ZnO 89 weight% allowed for and increased band gap from 3.3 eV of intrinsic ZnO to 3.65 eV for MZO deposited at room temperature. Increasing the superstrate deposition temperature allowed for a further band gap increase up to 3.95 eV at 400 °C due mainly to an conduction band minimum upward shift. It was highlighted the importance to create a positive conduction band offset with the MZO layer conduction band slightly above the CdS conduction band, with an optimum found in this case to be 0.3 eV (efficiency 10.6 %). By creating a positive conduction band offset all the performance parameters (Voc, FF, Jsc, efficiency) significantly increased. One of the reasons for this improvement was found to be a diminished interface recombination due to a more ideal MZO/CdS band alignment. In the second part of this investigation the MZO was used as a replacement for the CdS in a simplified structure: FTO/MZO/CdTe/Au back contact. The concepts used to optimise the performance of these devices also involved tuning the conduction band alignment between MZO/CdTe and efficiencies of 12.5 % were achieved with a at conduction band offset. The efficiency increase was achieved mainly thanks to a better transparency of the MZO layer and a higher Jsc output, compared to devices using a CdS buffer layer. The MZO buffers have been tested in combination with different TCOs. Results are presented in the third result chapter and showed that AZO is a good alternative to FTO working effectively in combination with MZO. AZO/MZO efficiency thin film CdTe solar cells (12.6%, compared to 12.5% with FTO). It was found that increasing the IR transparency of the TCOs leads to a potentially higher Jsc. Achieving a better transparency was obtained by using TCOs with high mobility and lower carrier concentration (AZO and ITiO) and also by using a boro-aluminosilicate glass with low iron content. ITiO yielded the best opto-electrical properties among all the TCO materials. Devices incorporating ITiO however, showed lower performance then those using FTO and AZO. ITO/MZO windows also yielded poor performance. In addition, the ITO films deposited had a high carrier concentration leading to a high NIR absorption by plasma resonance and resulted not ideal for application in thin film CdTe PV.

L’acylation de Friedel-Crafts est parmi les réactions les plus fondamentales et les plus utiles pour former des cétones aromatiques. Bien que la mise en oeuvre de ces réactions soit habituellement pénalisante en termes de sous produits formés, de rendement atomique et de quantité de catalyseur utilisée, cette voie est encore largement utilisée dans l’industrie de la chimie fine. Ces dernières années, la prise de conscience de l’impact des activités industrielles sur l’environnement a mené les chimistes à travailler sur de nouvelles voies, moins dangereuses et plus respectueuses de l’environnement.Nous avons considéré ici l’acylation d’un dérivé du benzofurane par un chlorure d’acyle, correspondant à une étape intermédiaire pour la fabrication d’un principe actif pharmaceutique. Dans cette étude, la première proposition a consisté à remplacer les catalyseurs classiques (FeCl3 ou AlCl3) par des catalyseurs solides réutilisables. Dans ce travail, plusieurs catalyseurs (zéolites, résines échangeuses d’ions...) ont d’abord été testés dans des conditions « conventionnelles » , c’est-à-dire en utilisant un solvant organique, afin de déterminer le plus performant, en termes de réactivité, de durée de vie et de réutilisabilité. Une zéolite Y s’est avéré la plus adaptée. Cependant, l’utilisation d’un solvant organique (ici le 1,2-dichlorobenzène) reste discutable et l’utilisation du CO2 supercritique comme solvant a donc été envisagée. Pour cela, nous avons imaginé et dimensionné un réacteur tubulaire à lit fixe de catalyseur fonctionnant sous pression et en continu. Les résultats présentés montrent la faisabilité d’un tel procédé et pose les jalons pour arriver à une ou des solutions pour une meilleure mise en oeuvre industrielle des réactions de Friedel-Crafts. / Friedel-Crafts acylation is among the most fundamental and useful reactions to yield aromatic ketones, but it is one of the less acceptable in terms of unwanted polluting by-products or atom economy because of overconsumption of catalyst which is used in stoichiometric quantities in the conventional process. This route is nevertheless still widely used in the fine chemicals industry. In recent years, awareness of the impact of industrial activities on the environment has lead chemists to work on new chemical routes, less dangerous and more environmentally friendly. We considered here the acylation of a benzofurane derivative by an acid chloride, as an intermediary step for a pharmaceutical product. In this study, one of the first alternative was to replace conventional catalysts (FeCl3 or AlCl3), by reusable solid catalysts. In this work, different catalysts (zeolites, ion-exchange resins...) were first tested in "conventional" conditions, i.e., using an organic solvent (1,2-dichlorobenzene in our case), to determine the best one, in terms of reactivity, lifetime and reusability. The zeolite Y was found the most appropriate. However, the use of an organic solvent still remains questionable and the use of supercritical carbon dioxide as the solvent was also considered. Its inherent properties include non-flammability, mild critical conditions, tuneable solubility near to the critical point and very low environmental impact. The reaction was operated using a specifically designed continuous high pressure fixed bed and results concerning yield and selectivity are presented. These results demonstrate the feasibility of such an approach, which would ultimately yield to better industrial operation of Friedel-Crafts reactions.

<p>Predmet istraživanja ove doktorske disertacije&nbsp;su prahovi litijum-indijum oksida dopirani&nbsp;različitim jonima retkih zemalja (Eu³⁺; Sm³⁺;&nbsp;Er³⁺; Yb³⁺), sintetisani reakcijom u &nbsp;čvrstoj fazi.&nbsp;Litijum-indijum oksid ima raznovrsne&nbsp;potencijalne primene u viduscintilatora, &nbsp;matrice&nbsp;fosfora za jone retkih zemalja, za&nbsp; čuvanje i&nbsp;konverziju energije i u fotokatalizi. U&nbsp;<br />istraživanju je ustanovljena optimalna metoda&nbsp;sinteze fazno&nbsp; čistih prahova novih fosfora&nbsp;<br />LiInO₂:RE^3+&nbsp;i izvr&scaron;ena njihova detaljna&nbsp;karakterizacija primenom difrakcije X-zraka,&nbsp;<br />skenirajuće elektronske mikroskopije,&nbsp;termogravimetrije i diferencijalno termijske&nbsp;analize, Ramanske spektroskopije i difuzno-refleksione spektroskopije. &nbsp;Fotoluminescentna&nbsp;spektroskopija je primenjena u cilju ispitivanja&nbsp;osobina presudnih za &nbsp;primenu ovih materijala.&nbsp;Emisioni spektri i vrednosti vremena života&nbsp;pokazuju efikasne potencijalne fosfore, dok&nbsp;ispitivanja emisije uzorka LiInO₂:Er^3+&nbsp;na&nbsp;različitim temperaturama ukazuju na to da je u&nbsp;pitanju veoma dobar temperaturni senzor u&nbsp;<br />oblasti temperatura (10-300) K.</p> / <p>The subject of this dissertation are powders of&nbsp;lithium-indium oxide doped with different rare&nbsp;earth ions (Eu³⁺; Sm³⁺; Er³⁺; Yb³⁺), synthesized&nbsp;by solid-state reaction. Lithium-indium oxide&nbsp;has a variety of potential applications in the&nbsp;form of scintillators, phosphor matrixes for rare-earth ions, storage and energy conversion&nbsp;devices and photocatalysts. In this study the&nbsp;optimal method of synthesis of pure-phased&nbsp;powders of new phosphors LiInO₂:RE^3+&nbsp;was&nbsp;determined. Also, their detailed characterization&nbsp;<br />using the X-ray diffraction, scanning electron&nbsp;microscopy, thermogravimetry and &nbsp;differential&nbsp;thermal analysis, Raman spectroscopy and&nbsp;diffuse-reflection spectroscopy &nbsp;was performed.&nbsp;Photoluminescence spectroscopy was applied to&nbsp;investigate the properties crucial for the&nbsp;application of these materials. Emission spectra&nbsp;and lifetime values, showed these materials are&nbsp;potential efficient phosphors. Examining the&nbsp;emission of LiInO₂:Er^3+&nbsp;sample at different&nbsp;temperatures indicated that this is a very good&nbsp;temperature sensor in the temperature range (10-300) K.</p>

<p>As  thefundamentallimits  of  two-dimensional(2D)geometric  scaling  of  commercial transistors  are  being reached,  there  is  tremendous  demand  for  new  materials  and  process innovations  that  can  keep  delivering  performance  improvements  for  future  generations  of computing chips. One major avenue being explored istheincorporation ofan increasing degree of three-dimensionality   by   vertically   stacking   logic   and   memory   layerswith   high-density interconnections.In  this  dissertation,  high-performanceultra-thin  amorphousindium  oxide transistors  are  demonstrated as  an  excellent  candidate  for these  back-end-of-line  (BEOL)  and monolithic 3D (M3D) integration applications.</p> <p>A  major  pain-point  in the  development  of  BEOL  and  M3D  systems is  the  strict  thermal budget imposed –once the bottom layer of devices is fabricated, they can generally withstand no more  than  400 °C.  It  is  exceedingly  difficult  to  directly  deposit  single-crystal  material  at  these temperatures, and polycrystalline materials will have grain boundary instability issues. Amorphous materials  generally  have  low  carrier  mobilities,  which  would  seemingly  remove  them  from contention as well. Indium oxideand itsclass of related metal oxides are exceptions. Indium oxideis  a  wide  bandgap  semiconductor  with  high  electron  mobility  up  to  about  100  cm²/V∙s  in amorphous form. Ithas a strong preference for native degenerate n-type doping which has hindered prior  devices  fabricated  with it.  In  this  dissertation,  extremely  thin  layers  on  the  order  of  1  nm thick are used for which quantum confinement effects widen the bandgap further, reliably enabling gate-controllable  carrier  densitiesand  demonstration  of  excellent  transistor  performance  with  a low thermal budget of just 225 °C.</p> <p>Detailed characterization is performed down to 40 nm channel lengths revealing excellent transistor characteristics  includingenhancement-mode operation withon currents greater than 2 A/μm, low  subthreshold  swing,and  high  on/off  ratios  due  to  the  wide  bandgap.  Subsequent chaptersdemonstrate the fundamental lower limits of off current around 6 ×10^-20A/μmby a novel measurement  technique,  good  gate  bias  stress  stability  behaviorwith  small  parameter  drift  at silicon  complementary  metal  oxide  semiconductor  (CMOS)  logic  voltages,  and  high-frequency operationin the GHz regime enabling easy operation at CMOS clock frequencies.</p>

Recently, there has been a growing interest in semiconductor and semiconducting oxide nanowires for applications in electronics, energy conversion, energy storage and optoelectronic devices such as field effect transistors, solar cells, Li- ion batteries, gas sensors, light emitting diodes, field emission displays etc. Semiconductor and semiconducting oxide nanowires have been synthesized widely by different vapor transport methods. However, conditions like high growth temperature, low vacuum, carrier gases for the growth of nanowires, limit the applicability of the processes for the growth of nanowires on a large scale for different applications. In this thesis work, studies have been made on the growth of semiconductor and semiconducting oxide nanowires at a relatively lower substrate temperature (< 500 °C), in a high vacuum (1× 10-5 mbar), without employing any carrier gas, by electron beam and resistive thermal evaporation processes. The morphology, microstructure, and composition of the nanowires have been investigated using analytical techniques such as SEM, EDX, XRD, XPS, and TEM. The optical properties of the films such as reflectance, transmittance in the UV-visible and near IR region were studied using a spectrophotometer. Germanium nanowires were grown at a relatively lower substrate temperature of 380-450 °C on Si substrates by electron beam evaporation (EBE) process using a Au-assisted Vapor-Liquid-Solid mechanism. High purity Ge was evaporated in a high vacuum of 1× 10-5 mbar, and gold catalyst coated substrates maintained at a temperature of 380-450 °C resulted in the growth of germanium nanowires via Au-catalyzed VLS growth. The influence of deposition parameters such as the growth temperature, Ge evaporation rate, growth duration, and gold catalyst layer thickness has been investigated. The structural, morphological and compositional studies have shown that the grown nanowires were single-crystalline in nature and free from impurities. The growth mechanism of Germanium nanowires by EBE has been discussed. Studies were also made on Silicon nanowire growth with Indium and Bismuth as catalysts by electron beam evaporation. For the first time, silicon nanowires were grown with alternative catalysts by the e-beam evaporation method. The use of alternative catalysts such as Indium and Bismuth results in the decrease of nanowire growth temperature compared to Au catalyzed Si nanowire growth. The doping of the silicon nanowires is possible with an alternative catalyst. The second part of the thesis concerns the growth of oxide semiconductors such as SnO2, Sn doped Indium oxide (ITO) nanowires by the electron beam evaporation method. For the first time, SnO2 nanowires were grown with a Au-assisted VLS mechanism by the electron beam evaporation method at a low substrate temperature of 450 °C. SEM, XRD, XPS, TEM, EDS studies on the grown nanowires showed that they were single crystalline in nature and free of impurities. The influence of deposition parameters such as the growth temperature, oxygen partial pressure, evaporation rate of Sn, and the growth duration has been investigated. Studies were also done on the application of SnO2 nanowire films for UV light detection. ITO nanowires were grown via a self-catalytic VLS growth mechanism by electron beam evaporation without the use of any catalyst at a low substrate temperature of 250-400 °C. The influence of deposition parameters such as the growth temperature, oxygen partial pressure, evaporation rate of ITO, and growth duration has been investigated. Preliminary studies have been done on the application of ITO nanowire films for transparent conducting coatings as well as for antireflection coatings. The final part of the work is on the Au-assisted and self catalytic growth of SnO2 and In2O3 nanowires on Si substrates by resistive thermal evaporation. For the first time, SnO2 nanowires were grown with a Au-assisted VLS mechanism by the resistive thermal evaporation method at a low substrate temperature of 450 °C. SEM, XRD, XPS, TEM, and EDS studies on the grown nanowires showed that they were single crystalline in nature and free of impurities. Studies were also made on the application of SnO2 nanowire films for methanol sensing. The self-catalytic growth of SnO2 and In2O3 nanowires were deposited in high vacuum (5×10-5 mbar) by thermal evaporation using a modified evaporation source and a substrate arrangement. With this arrangement, branched SnO2 and In2O3 nanowires were grown on a Si substrate. The influence of deposition parameters such as the applied current to the evaporation boat, and oxygen partial pressure has been investigated. The growth mechanism behind the formation of the branched nanowires as well as nanowires has been explained on the basis of a self-catalytic vapor-liquid-solid growth mechanism. The highlight of this thesis work is employing e-beam evaporation and resistive thermal evaporation methods for nanowire growth at low substrate temperatures of ~ 300-500 °C. The grown nanowires were tested for applications such as gas sensing, transparent conducting coatings, UV light detection and antireflection coating etc. The thesis is divided into nine chapters and each of its content is briefly described below. Chapter 1 In this chapter, a brief introduction is given on nanomaterials and their applications. This chapter also gives an overview of the different techniques and different growth mechanisms used for nanowires growth. A brief overview of the applications of semiconductors and semiconductor oxide nanowires synthesized is also presented. Chapter 2 Different experimental techniques employed for the growth of Si, Ge, SnO2, In2O3, ITO nanowires have been described in detail in this chapter. Further, the details of the different techniques employed for the characterization of the grown nanowires were also presented. Chapter 3 In this chapter, studies on the growth of Germanium nanowires by electron beam evaporation (EBE) are given. The influence of deposition parameters such as growth temperature, evaporation rate of germanium, growth duration, and catalyst layer thickness was investigated. The morphology, structure, and composition of the nanowires were investigated by XRD, SEM, and TEM. The VLS growth mechanism has been discussed for the formation of the germanium nanowires by EBE using Au as a catalyst. Chapter 4 This chapter discusses the growth of Si nanowires with Indium and Bismuth as an alternate to Au-catalyst by electron beam evaporation. The influence of deposition parameters such as growth temperature, Si evaporation rate, growth duration, and catalyst layer thickness has been investigated. The grown nanowires were characterized using XRD, SEM, TEM and HRTEM. The Silicon nanowires growth mechanism has been discussed. Chapter 5 This chapter discusses the Au-catalyzed VLS growth of SnO2 nanowires by the electron beam evaporation method as well as Antimony doped SnO2 nanowires by co-evaporation method at a low substrate temperature of 450 °C. The grown nanowires were characterized using XRD, SEM, TEM, STEM, Elemental mapping, HRTEM, and XPS. The effect of deposition parameters such as oxygen partial pressure, growth temperature, catalyst layer thickness, evaporation rate of Sn, and the growth duration of nanowires were investigated. The SnO2 nanowires growth mechanism has been explained. Preliminary studies were made on the possible use of pure SnO2 and doped SnO2 nanowire films for UV light detection. SnO2 nanowire growth on different substrates such as stainless steel foil (SS), carbon nanosheets films, and graphene oxide films were studied. SnO2 nanowire growth on different substrates, especially SS foil will be useful for Li-ion battery applications. Chapter 6 This chapter discusses the self catalyzed VLS growth of Sn doped Indium oxide (ITO) nanowires by the electron beam evaporation method at a low temperature of 250-400 °C. The grown nanowires were characterized using XRD, SEM, TEM, STEM, HRTEM, and XPS. The effect of deposition parameters such as oxygen partial pressure, growth temperature, evaporation rate of ITO, and the growth duration of the nanowires were investigated. Preliminary studies were also made on the possible use of self-catalyzed ITO nanowire films for transparent conducting oxides and antireflection coatings. ITO nanowire growth on different and large area substrates such as stainless steel foil (SS), and Glass was done successfully. ITO nanowire growth on different substrates, especially large area glass substrates will be useful for optoelectronic devices. Chapter 7 In this chapter, studies on the growth of SnO2 nanowires by a cost-effective resistive thermal evaporation method at a relatively lower substrate temperature of 450 °C are presented. The grown nanowires were characterized using XRD, SEM, TEM, HRTEM, and XPS. Preliminary studies were done on the possible use of SnO2 nanowire films for methanol sensing. Chapter 8 This chapter discusses the self-catalytic growth of SnO2 and In2O3 nanowires by resistive thermal evaporation. The nanowires of SnO2 and In2O3 were grown at low temperatures by resistive thermal evaporation using a modified source and substrate arrangement. In this arrangement, branched SnO2 nanowires, and In2O3 nanowires growth was observed. The grown nanowires were characterized using XRD, SEM, TEM, HRTEM, and XPS. The possible growth mechanism for branched nanowires growth has been explained. Chapter 9 The significant results obtained in the present thesis work have been summarized in this chapter.

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