Flow boiling heat transfer allows for the dissipation of large amounts of heat. In this work, the effect of heat flux and pressure on flow boiling of liquid refrigerant R-134a is studied in a vertical thin channel. The experimental setup mimics a refrigeration cycle and specifically looks at the effect of pressure and wall heat flux on the departure size and bubble generation rate. The experimental setup consists of a closed loop which includes a vertical narrow rectangular channel and two synchronized high speed cameras for optical measurements at either sides of the channel. The setup is built to employ an accurate measurement technique to define wall temperatures of the representative flow boiling process. Instead of using thermocouples on the surface channel, the thermochromic liquid crystallography (TLC) technique is used to determine non-invasively the heater surface temperature at high temporal and spatial resolution. The TLC interval range is 30-50°C. The TLC is attached to a Fecralloy heating section. The high speed Prosilica cameras simultaneously capture, colored TLC images as well as bubble nucleation and departure at very high frame rates. Experiments on subcooled flow boiling heat transfer have been conducted with refrigerant R-134a under a mass flux range of 484.838 kg/m2 s to 1212.1 kg/m2 s. With the low mass flux, the wall heat flux ranged from 167.2 to 672.1 kW/m2 , the inlet subcooling ranged from 0.35°C to 16.55 °C, the system pressure ranged from 621 kPa to 1034 kPa. At high mass flux, the wall heat flux ranged from 329.8 kW/m2 to 744 kW/m2 , the iv inlet subcooling from 0.16°C to 17.21 °C, and the system pressure from 621 kPa to 1034 kPa. A parametric study was done by maintaining various input parameters constant. From the high speed images, bubble parameters such as size and frequency are calculated. Temperature contours are utilized to determine the surface wall temperature at specific points. Sequential wall temperatures are traced over a short period of time to understand the cooling effects. The bubble propagation and coalescence are also visualized. Results show that bubble size and frequency increased with heat flux at any particular pressure. At higher pressure, the trend would be for the bubble size to decrease; however, the inlet subcooling and heat flux also affect bubble size. The bubble frequency is also seen to be affected by the inlet subcooling and the heat flux. Even though the inlet subcooling is maintained approximately constant, any slight decrease in subcooling increased bubble growth rate. Another trend that is observed is that at higher the heat flux, the bubble generation frequency is faster; however no specific trend is observed for wall superheat. With an increase in heat flux, the wall superheats are expected to increase; however, the localized nature of the nucleation activity sites is seen to affect the results. The variables are non-dimensionalized to note trends in parameters. In summary, the data analysis demonstrates that both heat flux and pressure significantly influence the bubble generation rate, size, propagation and coalescence.

<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>

<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>

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

Ce travail s'inscrit dans le cadre d'une thèse Cifre, en partenariat avec la société VIESSMANN Faulquemont SAS, dont l'objectif est d'aboutir à une couche absorbante de nouvelle génération qui vise à réguler de manière passive et réversible la température d'un capteur solaire. Cette couche absorbante est à base de dioxyde de vanadium (VO2), un matériau thermochrome qui présente une transition de phases de type semi-conducteur/métal en fonction de la température. Dans un premier temps, l'élaboration de films de VO2 à 500°C sera présentée puis nous montrerons un procédé inédit et original permettant d'obtenir une phase pure VO2 à partir d'un dépôt effectué à température ambiante. L'étude en température des propriétés optiques et électriques de ces deux types de revêtements sera discutée ainsi que les effets sur la transition de phases de paramètres tels que, la taille de grains ou encore les contraintes internes. Enfin, nous étudierons les propriétés physiques du système biphasé du type VO2+V4O9 qui sous forme de couche absorbante se trouve, in fine, être très avantageux pour la régulation thermique d'un panneau solaire / This work is incorporated within the framework of a Cifre thesis with the partnership of the VIESSMANN Faulquemont SAS society to end in a new generation of absorbent layer in order to regulate the temperature of a solar cell in a passive and reversible way. This absorbent layer is based on vanadium dioxide (VO2), this thermochromic material exhibits a phase semiconductor to metal transition depending on its temperature. In a first step, the synthesis of VO2 films at 500 °C will be exposed and then we will present a new process to obtain a pure VO2 phase with a film deposited at room temperature. The study in temperature of the optical and electrical properties of these two kinds of coatings will be discussed, same as the effects on the phase transition of parameters such as the grain size or the internal stresses. Eventually, we will study the physical properties of a VO2+V4O9 two-phase system as an absorbent layer which is, in fine, very beneficial for the thermal regulation of a solar panel

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.

No description available.

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

Les oxydes fortement corrélés sont largement étudiés pour l'hôte d'applications uniques, telles que la supraconductivité à haute température, la magnéto-résistance colossale, les commandes exotiques magnétiques, chargées et orbitales et les transitions isolant-métal. Les oxydes métalliques de transition qui forment la majorité des systèmes d'oxydes corrélés et des oxydes de vanadium, en particulier VO2 et V2O5, sont les deux systèmes les plus préférés parmi les chercheurs pour plusieurs applications. Dans cette thèse, la croissance et la caractérisation de VO2 et V2O5 sont discutées avec un accent particulier sur la propriété optique, en particulier les propriétés thermochromiques. Traditionnellement, le comportement SMT et l'infrarouge reflètent la zone de focalisation pour la recherche VO2 et c'est seulement jusqu'à récemment que la VO2 est traitée comme un système beaucoup plus complexe et a été étudiée comme un métamatériel naturellement désordonné très réactif près de la température de transition de phase où le matériau présente des matériaux semi-conducteurs et métalliques Coexistence de phase. Étant donné que chaque phase de VO2 a des propriétés optiques et électriques distinctes, elle contrôle l'étendue des transitions de phase par une modulation de température précise, permet d'exploiter le matériau pour de nouvelles propriétés, comme la modulation d'émissivité dans la région NIR et pour la création de motifs IR réversibles et réinscriptibles. Le V2O5 est traditionnellement considéré comme un matériau TCR élevé et considéré comme un matériau de choix pour une application allant de la catalyse, des capteurs de gaz aux batteries au lithium. Dans cette étude, nous nous concentrons sur les propriétés optiques du matériau, en particulier la nature thermochromique de la gamme visible des revêtements V2O5 synthétisés par recuit oxydatif des revêtements VOx développés par MOCVD. L'impact du dopage et de la production sélective de vacance d'oxygène sur la propriété thermochromique est discuté. / Strongly correlated oxides are studied widely for the host of unique applications, such as hightemperature superconductivity, colossal magneto resistance, exotic magnetic, charge and orbital ordering, and insulator-to-metal transitions. Transitional metal oxides which form the majority of the correlated oxide systems and oxides of Vanadium, especially VO2 and V2O5 are the two most favourite systems among researchers for several applications. In this thesis, the growth and characterization of VO2 and V2O5 are discussed along with a special focus on the optical property, especially thermochromic properties. Traditionally SMT behaviour and Infrared reflectively was the focus area for VO2 research, and its only until recently that VO2 is being treated as a much more complex system and investigated as highly responsive naturally disordered metamaterial near the phase transition temperature where the material exhibits semiconducting and metallic phase co-existence. Since each phase of VO2 has a distinct optical and electrical properties, controlling the extent of phase transitions by accurate temperature modulation, enables exploitation of the material for new properties like emissivity modulation in the NIR region and for creating IR visible reversible and rewritable patterns. V2O5 is traditionally seen as a high TCR material and regarded as material of choice for application ranging from catalysis, gas sensors to lithium batteries. In this study, however we focus on the optical properties of the material, especially the visible range thermochromic nature of V2O5 coatings synthesised by oxidative annealing of MOCVD grown VOx coatings. The impact of doping and selective oxygen vacancy generation on the thermochromic property are discussed.

This thesis deals with principles of thermochromism and its possible applications in heat distribution testing. Theoretical part describes mechanisms which allow the thermochromic properties of the substances. Particular attention is paid to cholesteric liquid crystals. Ability to measure the heat for this type of liquid crystals was varified. Also long service life in high humidity environment, enviroment with intense UV radiation, cyclic changes in temperature or immersion in water was tested. A possibility of their practical use in diagnosis was verified as well. Specifically mapping of heat distribution on an assembled PCB. Conclusion contains comparison and evaluation of this method in terms of accuracy, user comfort and economic advantages compared to conventional infrared sensors.