<p>The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in VO2 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-VO2 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of VO2 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of VO2 thin films. A reversible thermal tunability of the optical/dielectric constants of VO2 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in VO2 host matrix.</p>

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Impedance Spectroscopy has been performed at the metal-semiconductor transition of vanadium dioxide thin films. The samples have been deposited by reactive magnetron sputtering onto heated glass substrates. The crystallographic properties and morphology of the samples have been established by X-ray diffraction. By the spectra measured between 30 and 100 celsius degrees, the volume fractions of the monoclinic and tetragonal phases were quantified. The real and imaginary parts of the electrical impedance have been measured in VO2 thin films as function of the frequency (100 kHz to 1GHz) and temperature (30ºC to 90ºC). For fixed frequencies larger than 100 MHz, the hysteresis presented by the real part of the impedance when the critical temperature is surpassed became inverted. Below the semiconductor/metal transition, the Argand plots can be well reproduced assuming a Debye-like system with one relaxation time. After the beginning of the transition this approach fails, and at least two relaxation times are needed. We attribute one of them to the intrinsic processes taken place in the material, and the other to extrinsic properties like grain boundaries. / Foi realizada uma análise, por espectroscopia de impedância, das propriedades de filmes finos de dióxido de vanádio. As amostras foram depositadas por magnetron sputtering sobre substratos de vidro aquecidos em atmosfera reativa de argônio e oxigênio. Características cristalográficas e morfológicas dos filmes foram estabelecidas por difração de RX. Através de medidas de espectros de difração em temperaturas compreendidas entre 30 e 100 graus Celsius, foram quantificadas as frações volumétricas das fases monoclínica e tetragonal. As partes real e imaginária da impedância elétrica foram medidas em filmes policristalinos de VO2 tanto em função da frequência (100 KHz a 1 GHz) quanto da temperatura (30 ºC a 90ºC). Para frequências fixas maiores que 100 MHz, o ciclo de histerese apresentado pela parte real da impedância é suprimido e invertido quando a temperatura da amostra ultrapassa a temperatura crítica. Abaixo da transição semicondutor/metal, os diagramas de Argand podem ser bem reproduzidos assumindo-se um sistema, tipo Debye, com um único tempo de relaxação. Após o início da transição, este aproximação falha e são necessários pelo menos 2 tempos de relaxação. Um destes tempos de relaxação foi atribuído a processos intrínsecos que ocorrem no material e o outro a propriedades extrínsecas, como fronteiras de grãos.

Philosophiae Doctor - PhD / The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in VO2 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-VO2 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of VO2 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of VO2 thin films. A reversible thermal tunability of the optical/dielectric constants of VO2 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in VO2 host matrix. / South Africa

No description available.

Metapovrchy sú nanoštruktúrované povrchy vytvorené za účelom špecifického ovládania propagácie svetla. Predstavujú revolúciu v oblastiach ultratenkých optických prvkov a nanofotonických obvodov. Zakomponovaním laditeľných dielektrických materiálov do metapovrchov sa otvára možnosť aktívne ovládať ich optické vlastnosti aj po tom, čo boli vyrobené. Oxid vanadičitý (VO2) takéto ladenie umožňuje vďaka svojej fázovej premene už pri teplote okolo 67°C a preto sa radí k najsľubnejším z laditeľných dielektrických materiálov. Nakoľko je možné postupnú fázovú premenu vo VO2 vybudiť opticky a lúč svetla je možné fokusovať do stopy s veľkosťou pár stoviek nanometrov, laditeľné metapovrchy obsahujúce VO2 by mohli byť ladené postupne a dokonca s nanometrovým rozlíšením. V tejto práci skúmame fázu a amplitúdu svetla po prechode VO2 nanoštruktúrami usporiadanými do metapovrchu navrhnutého pre viditeľnú zložku elektromagnetického žiarenia. Výskum fáze a amplitúdy je založený na numerických simuláciách VO2 nanoštruktúr (stavebných kameňov metapovrchov), ktoré sú následne overené experimentálnymi výsledkami. VO2 nanoštruktúry vykazujú taktiež Mieho dielektrické rezonancie, ktoré sú v závere tejto práce využité v postupne laditeľnom metapovrchu fungujúcom vo viditeľnej oblasti. Okrem termálneho ladenia je možné vyrobený metapovrch ovládať taktiež opticky, čo dokazuje možnosť postupného ladenia na nanometrových rozmeroch.

Magister Philosophiae - MPhil / The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in V02 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-V02 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of V02 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of V02 thin films. A reversible thermal tunability of the optical/dielectric constants of V02 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in V02 host matrix.

<p> Surface probes are producing a huge variety of spatially resolved images of materials during phase transitions. These images have complex pattern formation present across a variety of length scales. Here, I apply image cluster scaling analysis and machine learning to several such images. First, I apply cluster analysis techniques to charge stripe orientations in Bi2−zPbzSr2−yLayCuO6+x. Our experimental collaborators observe stripes with period 4a0 in Bi2−zPbzSr2−yLayCuO6+x. [1] The local orientation of these stripes forms complex patterns from which we extract relationships involving cluster sizes. We compare these experimental exponents to those computed at a phase transition in the following models: 2D percolation and the 2D and 3D clean and random field Ising models. We find that only the 3D clean and random field Ising models are consistent with the data. Combined with the stability of these exponents across the superconducting region, we conclude that the system is in the random field Ising model universality class. We apply these same cluster techniques to period-4 antiferromagnet order in NdNiO3. [2] Our experimental collaborators observed the intensity for 2 of 8 possible directions for period-4 antiferromagnetic order in NdNiO3 and find complex pattern formation that remains after a temperature cycle past the hysteresis loop. We threshold this experimental data and extract cluster exponents for this system. We then compare these models to the 4-state clean and random field clock models. This exponent comparison shows that the 4-state random field clock model is a match for the experimental data. We then train a convolutional neural network to distinguish the 4-state clean and random field clock models. The fit neural net is capable of labeling our entire testing dataset of 16000 images with 100% accuracy. This gives us a 95% confidence interval of (0.9998, 1) by the rule of three. [3] We then split the field of view into 52 sliding windows of the original experimental data which we feed into the trained model. The model classifies every input window as a 2D random field clock model which gives us a 95% confidence interval of (0.94, 1). The observed hysteresis in the experimental data, the cluster analysis and the machine learning prediction clearly show the observed patterns are in the random field 4-state clock model universality class. </p>

Thermochromic vanadium dioxide based materials undergo a metal-to-semiconductor transition. This ability can reduce the energy consumption in buildings with windows or glass facades, especially for passive cooling in warmer climates. In dependence on the temperature, the transmittance of the material for infrared light changes reversibly, regulating the amount of the solar heat transmitted into buildings. Although thermochromic vanadium dioxide based coatings have been extensively studied at laboratory scale, there are still fundamental challenges for industrial manufacturing. The present work aims to explore the prospects of the deposition of a tungsten-doped vanadium dioxide based coating onto ultra-thin glass in an upscaled roll-to-roll process. An existing laboratory scale layer stack design enabled the achievement of high performance using unipolar pulsed and high power impulse magnetron sputtering. For this purpose, a new oxygen control system was developed. Furthermore, the optical and structural properties of the deposited coatings were characterized, as well as the doping content, and further the potential for energy savings. A newly designed optical model allowed calculation of the dispersion relation of the layers and their electrical properties.:1 Introduction 1 2 Topic of the thesis 4 3 State of the art 6 3.1 Thermochromism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 Vanadium dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.1 Crystalline Structure . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.2 Phase transition – Band structure . . . . . . . . . . . . . . . . . . 12 3.2.3 Literature review of thermochromic VO2 coatings . . . . . . . . . 13 3.2.4 Limitations of VO2 in smart window applications . . . . . . . . . 14 3.2.5 Using multifunctional layers . . . . . . . . . . . . . . . . . . . . . 15 3.2.6 Reducing the transition temperature . . . . . . . . . . . . . . . . 15 3.3 Magnetron sputtering of thermochromic coatings . . . . . . . . . . . . . 17 3.3.1 Sputtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.3.2 Magnetron sputtering . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.3.3 Reactive magnetron sputtering . . . . . . . . . . . . . . . . . . . 22 3.3.4 Sputtering using multi-component targets . . . . . . . . . . . . . 24 3.3.5 Pulsed magnetron sputtering . . . . . . . . . . . . . . . . . . . . . 26 3.3.6 High-power impulse magnetron sputtering . . . . . . . . . . . . . 27 3.4 Layer growth and ion assistance . . . . . . . . . . . . . . . . . . . . . . . 30 3.5 Thin film optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 3.5.1 Interaction of light with surfaces . . . . . . . . . . . . . . . . . . . 34 3.5.2 Models for thin film optics . . . . . . . . . . . . . . . . . . . . . . 36 4 Methodology 39 4.1 Deposition process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.1.1 Roll-to-roll process . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.1.2 FOSA labX 330 Glass . . . . . . . . . . . . . . . . . . . . . . . . 39 4.1.3 Rotatable magnetrons . . . . . . . . . . . . . . . . . . . . . . . . 41 4.1.4 Materials used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.1.5 Oxygen flow controls . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.1.6 Challenges of the roll-to-roll deposition process on UTG . . . . . 46 4.2 Deposition of ZrO2 multifunctional layer . . . . . . . . . . . . . . . . . . 47 4.3 Deposition of ZrO2/V1-xWxO2/ZrO2 with HiPIMS . . . . . . . . . . . . . 48 4.3.1 The investigation of the effect of oxygen partial pressure . . . . . 48 4.3.2 Deposition of thermochromic layers with optical emission spec- troscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.4 Deposition of ZrO2/V1-xWxO2/ZrO2 with unipolar pulsed magnetron sputtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.5 Coating characterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 4.5.1 UV-Vis-NIR spectrophotometry . . . . . . . . . . . . . . . . . . . 51 4.5.2 Determination of the film properties with optical modelling . . . . 52 4.5.3 Scanning electron microscopy . . . . . . . . . . . . . . . . . . . . 55 4.6 Determination of the film thickness . . . . . . . . . . . . . . . . . . . . . 55 4.6.1 Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 4.6.2 X-ray diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.6.3 Atomic force microscopy . . . . . . . . . . . . . . . . . . . . . . . 58 4.6.4 Rutherford backscattering . . . . . . . . . . . . . . . . . . . . . . 59 5 Results and discussion 61 5.1 Bottom and top ZrO2 layers for thermochromic V1-xWxO2 coating . . . . 61 5.2 Process design for the deposition of thermochromic V1-xWxO2 coating with HiPIMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5.2.1 The effect of oxygen partial pressure . . . . . . . . . . . . . . . . 70 5.2.2 Deposition of the layer system with optical emission spectroscopy 72 5.2.3 Determination of the W content in the thermochromic films . . . 80 5.2.4 Resistivity measurements and structure assumption . . . . . . . . 86 5.2.5 Dependence of the doping concentration in the target on the film thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.2.6 Influence of the deposition temperature on the thermochromic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.2.7 Influence of the film thickness on the thermochromic properties . 90 5.3 Thermochromic V1-xWxO2 coating deposited with uPMS . . . . . . . . . 93 5.4 Comparison of HiPIMS (two-layer vs three-layer systems) and uPMS for V1-xWxO2 coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 6 Summary and outlook 101 6.1 Research goal and achievements . . . . . . . . . . . . . . . . . . . . . . . 101 6.2 Layer deposition and results overview . . . . . . . . . . . . . . . . . . . . 102 6.3 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 7 Appendix 105 8 Abbreviations 108 9 Formula symbols 109 Literature 118

La fotónica de silicio es actualmente la tecnología mejor posicionada para reemplazar las conexiones electrónicas tanto dentro de los mismos chips, como entre ellos mismos, con el fin de mejorar su rendimiento. Las principales ventajas de la tecnología fotónica de silicio residen en su bajo coste y en su compatibilidad con las actuales técnicas de fabricación desarrolladas por la industria microelectrónica. Dicha compatibilidad permitiría fabricar tanto chips ópticos como chips híbridos que incluyan componentes ópticos y electrónicos. Los moduladores y los conmutadores optoelectrónicos resultan dispositivos fundamentales en aplicaciones de telecomunicaciones. Las principales funciones de los conmutadores y moduladores optoelectrónicos son el enrutamiento y la transmisión de datos de alta velocidad. Esta tesis aborda el diseño y la optimización de la parte eléctrica y óptica (en menor medida) con el fin de optimizar el rendimiento de tales dispositivos desde el punto de vista optoelectrónico. Además, también se tratará la introducción de nuevos materiales compatibles con el silicio y sus procesos de fabricación, como el dióxido de vanadio o el titanato de bario con el fin de demostrar sus propiedades y aplicarlas a los dispositivos optoelectrónicos con el fin de mejorar su rendimiento. / Silicon photonics is nowadays the most promising technology to replace electrical inter- and intra-connections of the chips, increasing the performance in this way. The main advantages of silicon photonics technology lie on its low cost and its compatibility with the fabrications processes of microelectronics industry developed during years which allows the mass production of silicon photonics chips as well hybrid electronic and photonic devices in the same chip. Optoelectronics switches and modulators are key building blocks in photonic devices for tele/datacom applications. Such switches and modulators are devices which provides routing functionalities and the transmission of high speed data respectively. The work of this thesis delves with the design and optimization of silicon based switches and modulators spotlighting the electrical elements. Additionally, the work of this theses deals with the introduction of new silicon-compatible materials as vanadium dioxide and barium titanate, with the aim of demonstrating its functionalities and develop high-performance optoelectronic devices. / La fotònica de silici és actualment la tecnologia millor posicionada per a reemplaçar les connexions electròniques tant dins del propis xips, com entre ells mateixos, amb la finalitat de millorar el seu rendiment. Els principals avantatges de la tecnologia fotònica de silici resideixen en el seu baix cost i en la seua compatibilitat amb les actuals tècniques de fabricació desenvolupades per la indústria microelectrònica. Aquesta compatibilitat permetria fabricar tant xips òptics com a xips híbrids que incloguen components òptics i electrònics. Els moduladors i els commutadors optoelectrònics resulten dispositius fonamentals en aplicacions de telecomunicacions. Les principals funcions dels commutadors i moduladors optoelectrònics són l'encaminament i la transmissió de dades d'alta velocitat. Aquesta tesi aborda el disseny i l'optimització de la part elèctrica i òptica (en menor mesura) amb la finalitat d'optimitzar el rendiment de tals dispositius des del punt de vista optoelectrònic. A més, també es tractarà la introducció de nous materials compatibles amb el silici i els seus processos de fabricació, com el diòxid de vanadi o el titanato de bari amb la finalitat de demostrar les seues propietats i aplicar-les als dispositius optoelectrònics amb la finalitat de millorar el seu rendiment. / Rosa Escutia, Á. (2018). High-efficient electrodes for novel optoelectronic devices in silicon photonics [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/110364

Vanadium oxides are being used as the thermal sensing layer because of their applications in infrared detectors. They have high temperature coefficient of resistance, favorable electrical resistance and compatibility with the MEMS technology. Of all oxides of vanadium, only vanadium dioxide (VO2)has been highly investigated as it shows first order transition (semiconducting to metal transition-SMT)at 68 oC. First order transition is understood as the sharp change in the electrical resistance. The change in resistivity in this case is of the order of 105 over a temperature change of 0.1 oC at 68 oC in a single crystal. Doping vanadium oxides with elements like Mo and W reduce the transition temperature. This is very important for room temperature electrical and optical detection. Though most of the research groups subscribe to PLD, cost-effective methods with large area deposition are major focus of this research. Hence for synthesizing VO2 in bulk and thin films, Solution Combustion Synthesis (SCS), Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) Chemical vapour deposition (CVD)and microwave are explored. Synthesis of doped VO2 films in CVD has not been done extensively to yield optical quality thin films. Chapter I surveys the use of phase transition in oxides system for a variety of practical applications. In particular, Vanadium dioxide (VO2) is chosen as it is found to be very useful for infrared and metamaterials based applications. VO2 is known for its first-order semiconducting to metallic transition (SMT). This chapter attempts to explain the influence of processing, doping, annealing, etc on the SMT characteristics. Important aspects such as the idea of hysteresis in VO2 and similarity to martensitic transformation are discussed. The scope and objectives of the thesis are discussed here. Chapter II explains in detail the materials and methods used to synthesize VO2 both in bulk and in thin lm form and methods used to study their characteristics. Brief description on the principle and the working of the home-built experimental set up needed for this study is elicited. In chapter III, attempts were made to understand the phase stability of VO2 and the evolution of crystal structures during the phase transition. VO2 crystallizes in P21/c space group at room temperatures with lattice parameters a=5.752 Ab=4.526 Ac=5.382 Aα=90 β=122.60 γ=90 . Precise control of synthesis parameters is required in stabilizing pure phase in bulk as well as thin lm form. This study focuses on the novel large scale two step synthesis of VO2 using Solution Combustion Synthesis. This involves synthesis of product utilizing redox reaction between metal nitrate and suitable fuel. Generally the products are nanocrystalline in nature due to self-propagation of the exothermic combustion reaction. First step involved the synthesis of V2O5 by combustion reaction between Vanadyl nitrate and urea. In the second step, the as-synthesized V2O5 has been reduced by a novel reduction technique to form monophasic VO2. The presence of competing phases like M1, M2, M3 and R are investigated by XRD, Raman spectroscopy, DSC, Optical and high temperature X-ray diffraction. Chapter IV deals with the reduction in phase transition temperature by doping the SCS synthesized VO2 with W and Mo. Effect of doping on the transition temperature was studied using differential scanning calorimetry (DSC) in both W and Mo. Electrical characteristics of Mo doped VO2 and Optical characteristics of the W-doped VO2 were also studied using four probe resistivity measurements and UV-VIS Spectroscopy respectively. W addition was found to be more effective in reducing the phase transition temperature. To understand further more on the W addition, X-ray photo-electron spectroscopy measurements were performed. W-addition alters the V4+-V4+ bonding and with W addition it is observed that V was present in V3+state. W was present in W6+ state. The addition of W to VO2 introduces more electrons to the systems and disturbs the V4+-V4+ thus reducing the phase transition temperature of VO2. Chapter V describes the large scale, large area deposition of thin films of VO2 by a cost effective method. A novel technique to deposit vanadium dioxide thin films namely, UNSPACM is developed. This simple two-step process involves synthesis of a V2O5 lm on an LaAlO3(LAO) substrate followed by a controlled reduction to form single phase VO2. The formation of M1 phase (P21/c) is confirmed by Raman spectroscopic studies. A thermally activated metal{insulator transition (MIT) was observed at 61 oC, where the resistivity changes by four orders of magnitude. The infrared spectra also show a dramatic change in reflectance from 13% to over 90% in the wavelength range of 7-15 m. This indicates the suitability of the films for optical switching applications at infrared frequencies. A trilayer metamaterial absorber, composed of a metal structure/dielectric spacer/vanadium dioxide (VO2) ground plane, is shown to switch reversibly between reflective and absorptive states as a function of temperature. The VO2 lm, which changes its conductivity by four orders of magnitude across an insulator{metal transition, enables the switching by forming a resonant absorptive structure at high temperatures while being inactive at low temperatures. The fabricated metamaterial shows a modulation of the reflectivity levels of 58% at a frequency of 22.5 THz and 57% at a frequency of 34.5 THz. Chapter VI explains the W doped VO2 thin films synthesized by UN-SPACM. Morphology of the thin films was found to be consisting of globular and porous nanoparticles having size 20 nm. Transition temperature decreased with the addition of W. 1.8 at. %W doping in VO2 transition temperature has reduced upto 25 oC. It is noted that W-doping in the pro-cess of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration. The presence of W, as was seen in Chapter IV, altered V4+-V4+ bonds and introduced V3+. W was found to be in W6+ state suggesting W addition increased the carrier concentration. Hall Effect measurements suggested the increased carrier con-centration. The roughness of the synthesized films were very high for them to be of de-vice quality, despite encouraging results obtained by electrical measurements. Hence in order to further improve the smoothness and thereby the optical quality of thin films, Chemical Vapour Deposition (CVD) is employed. Chapter VII outlines the effect of processing parameters and post pro-cessing annealing on the semiconductor-metallic transition of VO2. Here in this chapter, the influence of substrate temperature on the SMT properties of VO2 is explored. At different substrate temperatures, the percentage of phase fraction of V in V3+, 4+ and V5+ differed. Besides, the morphology also varied with substrate temperatures. Similarly it is observed that with annealing the VO2 film deposited on glass substrates, SMT properties enhanced which was attributed to filling out of oxygen vacancies. Si based substrates and non-Si based substrates were used for depositing VO2 thin films by CVD. Their temperature coefficient of resistance and SMT properties were studied in order to understand their potential in bolometer and thermal to optical valve based applications. Chapter VIII involves the study of VO2 thin films for thermal to optical valves. ITO coated glass substrates were used for the purpose. Thin films were deposited by both UNSPACM and CVD. It was observed that the reflectivity pro les of the films synthesized by the above said methods were very different. Hence in the process of understanding the huge difference in the reflectivity pro les, classical harmonic oscillator, Lorentzian model was employed to t the experimental data at room temperature whereas Drude-Lorentzian model was used to t the data at higher temperature (at 100 oC- after transition). With this fitting plasma frequencies of the CVD films were calculated. It was observed that defect chemistry of films synthesized by these methods were different. In order to further improve the smoothness of the films, microwave method was proposed in Chapter IX. The preliminary results showed the presence of uniform spheres and 3 D hierarchical structures of VO2 consisting of nanorods. This was extended to deposit VO2 thin films on ITO. DSC and Infrared reflectance pro le of VO2 nanopowder suggested the phase transition. Chapter X summarizes the work done for the thesis and provides insights to the applications and to the future work. The work reported in this thesis has been carried out by the candidate as part of the Ph.D.program. She hopes that this would constitute a worth-while contribution towards development of VO2 thin film technology and its challenges for reliable infrared device applications.