Les exigences de plus en plus élevés concernant la qualité et propriétés de couches minces ont soutenu le développement de nouveaux procédés de pulvérisation. Ainsi, la décharge magnétron conventionnelle en courant continu, une des sources d’atomes la plus utilisée pour le dépôt de couches minces, a été améliorée par le couplage avec une décharge additionnelle de radio fréquence pour obtenir le nouveau procédé RF-IPVD (Radio Frequency-Ionized Physical Vapour Deposition). Ce procédé permet de générer un degré d’ionisation supérieur à celui dans la décharge magnétron classique, nécessaire pour contrôler les propriétés des couches minces. Un procédé alternatif pour augmenter d’avantage l’ionisation consiste à appliquer des impulsions haute puissance sur la cathode HPPMS (High Power Pulsed Magnetron Sputtering), pour des durés courtes de l’ordre de ųs ou dizaines de ųs. L’étude menée porte sur les phénomènes de pulvérisation et de transport des espèces du métal dans ces trois versions de la décharge magnétron par les moyens de spectroscopie laser à l’aide des diodes laser accordables. Le développement récent de ces diodes nous a permis de sonder les niveaux fondamentaux du Titane et de l’Aluminium, et de caractériser la dépendance spatiale de la densité et température ainsi que la fonction de distribution en vitesse de ces atomes. L’effet des paramètres clés, comme l’intensité du courant et la pression du gaz, est étudie et décrit pour la décharge magnétron conventionnelle. La distribution spatiale et angulaire de la fonction de distribution en vitesses a été mesurée dans la région devant la cible magnétron, afin de caractériser les flux du métal et leur comportement dans le volume de la décharge. L’étude sur les atomes du métal dans le procédé RF-IPVD est concentrée sur l’effet de la décharge additionnelle sur le dépeuplement du niveau fondamental. Une efficacité plus grande des processus d’ionisation est trouvée à plus haute pression et plus haute puissance RF injecté. On a montré aussi que les atomes affectés par les processus d’ionisation sont ceux thermalisées, tandis que la distribution de atomes rapides n’est quasiment pas affectés par la décharge additionnelle.Le diagnostic de la décharge pulsée a nécessité le développement d’une nouvelle procédure expérimentale, capable de suivre l’évolution de la densité et de la température des espèces neutres avec une résolution de l’ordre de la ųs. Cette procédure nous a servi pour décrire l’évolution spatio-temporel des atomes du métal (Ti et Al) et les atomes métastables d’Ar. Ces études offrent une vue globale sur le transport de atomes pulvérisés pendant la post décharge, ainsi qu’une description du fonctionnement de la décharge pulsé via la création des métastables d’Argon. / The higher requirements on the thin films quality have supported the development of new sputtering techniques. Thus, the conventional DC magnetron discharge, one of the most widely used source of atoms for thin film deposition, has been improved by the addition of an auxiliary radio frequency discharge - new technique called RF-IPVD (Radio Frequency -Ionized Physical Vapor Deposition). This technique highly increases the ionization degree compared to conventional magnetron discharge, which is necessary for a better control of the thin films properties. An alternative method to increase the ionization is based on the use of high power pulses on the cathode, HPPMS (High Power Pulsed Magnetron Sputtering), for short periods of time ranging from ųs to tens of ųs.The present study focuses on the sputtering phenomena and the transport of metal sputtered species in these three versions of the magnetron discharge, by means of laser spectroscopy using tunable laser diodes. The recent developments of these diodes have allowed to probe the fundamental levels of titanium and aluminum, and to characterize the spatial dependency of the density and temperature as well as the velocity distribution functions of these atoms. The effect of key discharge parameters, such as current intensity and gas pressure, is studied and described for the conventional magnetron discharge. The spatial and angular velocity distribution functions were measured in front of the magnetron target, in order to characterize the metal fluxes and their behavior in the discharge volume.The study on the metal atoms in the RF-IPVD process is focused on the effect of the additional discharge on the depopulation of the ground state level. Higher ionization efficiency is found at relatively high pressure and it increases with the injected RF power. It was also showed that the thermalized atoms are the ones involved in the ionization process, while the distribution of fast atoms is almost unaffected by the additional discharge.The diagnostics of the HPPMS discharge required the development of a novel experimental procedure, able to monitor the density and temperature of neutral species with a time resolution of ųs. This procedure was used to describe the spatiotemporal evolution of metal atoms (Ti and Al) and Ar metastable atoms. These studies provide an overview on the transport of sputtered atoms during the afterglow, and a description of the pulsed discharge operation, via the creation of metastable argon atoms.

Revestimentos finos de carboneto de nióbio (NbC) puro e dopados com níquel (Ni) foram obtidos mediante a técnica de deposição reativa por magnetron sputtering, utilizando metano (CH4) como fonte de carbono (C). O filme de NbC usado como referência foi depositado aplicando uma potência de 2500 W ao alvo de Nb e, os revestimentos de NbxNiyCz foram depositados diminuindo a potência aplicada ao alvo de Nb e aumentando a potência aplicada ao alvo de Nb-Ni, dando origem à seis revestimentos com teores de Ni crescentes. As caracterizações microestrutural e estrutural dos revestimentos de NbC e NbxCyNiz foram realizadas por meio das técnicas de difração de raios-X (DRX), Espectroscopia Fotoeletrônica de Raios X (XPS), Espectroscopia Raman, Microscopia Eletrônica de Transmissão (MET) e Microscopia Eletrônica de Varredura (MEV). As propriedades mecânicas dos revestimentos foram estudas mediante a técnica de nanoindentação instrumentada, com o intuito de avaliar a dureza (H) e o módulo de elasticidade (E). A adesão dos revestimentos ao substrato foi avaliada usando ensaios Rockwell C e esclerometria linear instrumentada. A estabilidade térmica dos revestimentos foi realizada em forno com atmosfera controlada em temperaturas de 600 °C e 800 °C por 2h. Finalmente, a resistência à oxidação dos revestimentos foi estudada por meio de ensaios de Termogravimetria (TGA - \"Thermogravimetric Analysis\") de aquecimento contínuo e isotérmicos. Os resultados de adesão obtidos mostraram boa aderência (modo de falha HF1) dos filmes de NbC e NbxNiyCz ao substrato de aço AISI M2, nas condições como recém depositado e revenido a 600 °C, indicando que a deposição do gradiente de intercamadas de Cr, CrC e do gradiente CrC / NbC foi efetiva evitando falhas adesivas. A adição de Ni na estrutura dos revestimentos de NbC promoveu a formação de estruturas nanocompósitas, composta de nanocristalitos de NbC e NiCx. Adicionalmente, a introdução de níquel causou um aumento na dureza nos revestimentos como recém depositados, aumentando de 17 para 25 GPa para teores de Ni de 0 para 13 at. %, respectivamente, e, na resistência à oxidação sobre o revestimento puro de NbC, de 380 °C para 480 °C nos revestimentos com níquel. Finalmente, as análises de estabilidade térmica permitiram observar que os precipitados de NiCx se decompõem durante os tratamentos de recozimento a 600 e 800 °C, o que promoveu um aumento nos valores de dureza e módulo de Young para todos os revestimentos, atribuído ao aumento da cristalinidade dos revestimentos. / Niobium carbide (NbC) coatings doped with Nickel (Ni) were deposited by reactive DC - magnetron sputtering using methane (CH4) as carbon (C) source. Reference NbC coating was deposited with a total power of 2500 W and NbxNiyCz coatings were deposited by decreasing the power applied to the Nb target and increasing the power applied to the Nb-Ni target, giving rise to coatings with increasing Ni content. Structural and microstructural characterizations of NbC and NbxNiyCz coatings were performed using X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, Transmission Electron Microscopy (MET) and Scanning Electron Microscopy (MEV). Mechanical properties of the coatings were studied using the instrumented nanoindentation technique, in order to evaluate the Hardness (H) and Elastic modulus (E). The adhesion between coatings and substrate was evaluated using Rockwell C test and instrumented linear scratch tests. The tests for studying the thermal stability of the coatings were carried out in a controlled atmosphere chamber furnace at temperatures of 600 °C and 800 °C for 2h. Finally, the oxidation resistance of the coatings was studied by means of Thermogravimetric Analysis (TGA) tests of continuous and isothermal heating. The NbC and NbxNiyCz films in the as-deposited condition and annealed at 600 °C, showed good adhesion (failure mode HF1) to the AISI M2 steel substrate, indicating that the adhesion interlayer of the Cr, CrC and a gradient CrC/NbC layer was effective in avoiding adhesive failures. The increasing of Ni content in the structure of NbC coatings promoted the formation of nanocomposite structures, composed of a mixture of NbC and NiCx nanocrystallites. Additionally, the introduction of nickel allows increasing the hardness for the coatings in the as-deposited condition, from 17 to 25 GPa for Ni contents from 0 to 13 at. %, respectively, and, improving the oxidation resistance over the pure NbC coating, from 380 °C to 480 °C for the Ni-rich coatings. Finally, the thermal stability analyses showed that the NiCx precipitate decompose during the annealing treatments at 600 °C and 800 °C, which promoted an increase in the hardness and Young\'s modulus values for all coatings. These behaviors were attributed to the increase of crystallinity of the coatings.

A possibilidade produzir hidrogênio (H2) a partir da quebra da molécula da água, usando a radiação solar, foi descoberta ha mais de 40 anos e nas ultimas décadas tem recebido grande atenção científica. A síntese de semicondutores nanoestruturados representam um avanço no uso como fotocatalisadores para a produção de H2 a partir da quebra da molécula da água, devido a alta área superficial. Dos semicondutores nanoestruturados desenvolvidos, o TiO2 apresenta grande interesse por se tratar de um material abundante, barato e altamente estável quimicamente. Por outro lado, o TiO2 apresenta uma atividade fotocatalítica limitada devido ao seu alto band gap (~3,2 eV), relativamente alto, e a rápida recombinação do par elétron-buraco gerado pela radiação UV. Neste sentido, a adição de nanopartículas (NPs) de Au ao TiO2 aparece como uma solução viável para aumentar a eficiência do semicondutor na reação de water splitting (WS). Os mecanismos envolvidos no aumento de eficiência na produção de H2 devido as inserção de NPs de Au ainda não estão totalmente entendidos. Atualmente existem dois modelos que descrevem o fenômeno: i) o Au atua como um "reservatório" para os fotoelétrons promovidos pelo processo de transferência de carga do semicondutor quando excitados com radiação UV, fazendo com que as reações de fotocatalíticas de geração de H2 ocorram na superfície das NPs de Au e ii) as NPs de Au apresentam ressonância de plasmon de superfície “injetando” elétrons na banda de condução (BC) do TiO2, assim aumentando a quantidade de elétrons disponíveis para formação do H2, fazendo com que a reação de produção de H2 ocorra na superfície do semicondutor. Neste trabalho são apresentados resultados inéditos da produção e caracterização nanotubos de TiO2 (NTs de TiO2) modificados com Au e utilizados como fotocatalisadores para a produção de H2 a partir do processo de WS. A discussão está centrada na modificação das propriedades do TiO2 através da adição de NPs de Au na estrutura e na superfície, através de dois métodos: i) implantação iônica e ii) sputtering. Os resultados relacionam a atividade fotocatalítica na produção de H2. dos fotocatalisadores em função da posição das NPs de Au. / The possibility to produce hydrogen (H2) from the water splitting using solar radiation, was discovered for more than 40 years and in recent decades has received great scientific attention. The synthesis of nanostructured semiconductor represent an advancement in use as photocatalysts for the production of H2 from the splitting of the water, due to high surface area. Developed nanostructured semiconductors, TiO2 has a great interest in the case of a material abundant, inexpensive and high chemical stability. On the other hand, has a low efficiency TiO2photocatalyst for the H2 production due to its high band gap (~ 3.2 eV) and the rapid recombinant electron-hole pair generated by UV radiation. In this sense, the addition of Au nanoparticles (NPs) to TiO2 appears as a viable solution to increase the efficiency of reaction in the semiconductor water splitting (WS). The mechanisms involved in increased efficiency in H2 because the insertion of Au NPs are not yet fully understood. Currently, there are two models that describe the phenomenon: i) the Au acts as a "reservoir" for the photoemission process promoted by the charge transfer of the semiconductor when excited with UV radiation, causing the reactions of photocatalytic H2generation occur in NPs Au surface and ii) Au NPs surface plasmon resonance "pumping" electrons in the TiO2conduction band (CB), thus increasing the amount of electrons available for the formation of H2, making the reaction H2 production occurs in the semiconductor surface. This work presents the results of the production and characterization of TiO2 nanotubes (TiO2TNs) Au-modified and used as photocatalysts for the H2 production by WS. The discussion is focused on modifying the properties of NTs by the addition of Au NPs in the TiO2 structure or surface by means of two methods: i) ion implantation and ii) sputtering, and comparing its photocatalytic activity influences the position of the NPs in the Au H2 production.

Porté par les préoccupations actuelles en matière de sécurité et de qualité environnementale ainsi que par les efforts de recherche entrepris dans ce domaine, le marché mondial des capteurs de gaz est en pleine expansion. Dans le contexte de la commercialisation d'un capteur de gaz, une phase d'amélioration de ses performances, et notamment de sa sensibilité et de sa stabilité, est naturellement nécessaire. Cependant, il s'avère également pertinent d'envisager d'en diminuer le coût de fabrication. Pour cela, il convient de développer une technologie utilisant d'une part des matériaux bas coût et d'autre part permettant de réduire la consommation électrique du dispositif. Dans cette optique, ce travail de thèse a porté sur la réalisation et la caractérisation d'un capteur de gaz oxyde semi-conducteur entièrement basé sur le tungstène et le trioxyde de tungstène pour la détection d'hydrogène sulfuré en milieu industriel. Le principal onjectif était de fabriquer un capteur faible coût en utilisant des techniques d'élaboration simples et des matériaux peu onéreux. Pour cela, notre travail a consisté, dans un premier temps, à développer un élément chauffant en tungstène pouvant fonctionner jusqu'à 500°C. Les procédés mis au point pour la conception de l'élément chauffant ont été utilisés dans l'élaboration des électrodes permettant de mesurer la résistance électrique du film de trioxyde de tungstène. Ensuite, nous avons travaillé sur l'optimisation du procédé de pulvérisation cathodique radio fréquence pour l'élaboration de l'élément sensible en trioxyde de tungstène. Des essais sous gaz ont montré des résultats prometteurs pour la détection d'hydrogène, de dioxyde d'azote et d'ammoniac. / Driven by current safety and environmental quality concerns and research efforts in this area, the global market for gas sensors is expanding rapidly. In the context of the marketing of a gas sensor, a phase of improvement in its performance, and in particular its sensitivity and stability, is naturally necessary. However, it is also relevant to consider reducing the cost of manufacturing. To achieve this, it is necessary to develop a technology that uses low-cost materials and reduces the device's power consumption. In this perspective, this thesis work focused on the realization and characterization of a semiconductor oxide gas sensor entirely based on tungsten and tungsten trioxide for the detection of hydrogen sulfide in an industrial environment. The main objective was to manufacturate a low-cost sensor using simple processing techniques and low-cost materials. To achieve this, our work initially consisted in developing a tungsten heating element that can operate up to 500°C. The processes developed for the conception of the heating element were used in the development of the electrodes for measuring the electrical resistance of the tungsten trioxide film. Then, we worked on the optimization of the radio frequency sputtering process for the development of the tungsten trioxide sensing element. Gas measurements have shown promising results for the detection of hydrogen sulfide, nitrogen dioxide and ammonia.

Previous work done at Cal Poly has shown that thin-film nickel-titanium (NiTi) can be easily sputtered onto silicon wafers and annealed to create a crystallized shape memory alloy (SMA) film. Initial work on creating devices yielded cantilevers that were highly warped due to thin-film stress created during the sputtering process. The objective of this work was to create a thin-film NiTi SMA device that could be better characterized. A membrane was selected due to the simplicity of fabrication and testing which would also oppose the thin-film stress due to the increase in attachment points to the substrate. Silicon wafers were etched through the majority of the thickness (~75%) creating square etch pits of varying sizes varying from 1294 µm to 4394 µm. The wafers were then sputtered with an approximate NiTi film of 5 µm followed by a thin chromium film. The chromium film would act as a diffusion barrier and prevent oxygen from diffusing into the NiTi and reacting with the titanium and forming titanium dioxide. These wafers were then annealed in a custom built vacuum annealing chamber at 550 °C for 1 hour with a pressure around 77 kPa. The chromium was then etched away followed by the remaining silicon. This left a thin membrane of shape memory NiTi which was packaged in order for characterization. The devices were glued to an aluminum substrate using polydimethylsiloxane (PDMS) and sealed with a small Tygon tube leading to the sealed chamber. This packaged device was then able to be pressurized using a nitrogen tank and the resulting NiTi membrane deflection was measured using a profilometer. Due to the differences in elastic moduli of the room temperature phase (martensite) and the high temperature phase (austenite) a difference of deflection was expected. The austenite finish (Af) temperature of bulk NiTi films was found to be around 60 °C so the devices were tested at both room temperature and at 60 °C. After testing seven separate devices of varying sizes, a regression model was used to analyze the final data. It was found that pressure, membrane size and theoretical versus actual deflection all affected the maximum deflection, but temperature did not. Higher pressures and larger membranes led to higher deflections as membrane deflection models from fundamental principles indicated. Some devices showed inferior performance when compared to the model due to incomplete silicon etching which caused lower deflection due to the much higher modulus of the remaining silicon. Thickness could also limit the amount of deflection measured with a thicker film leading to less deflection, but this is likely not the case due to the high uniformity of the sputtering system. Other devices showed superior performance over the model most likely due to either local delamination or lateral silicon etching. Both these would create a membrane that was larger than expected leading to a higher deflection. Unforutnaly, differential scanning calorimetry (DSC) analysis showed no shape memory behavior on a test wafer which was anneald at 550 ˚C for 1 hour. A design of experiments was conducted in order to find a heat treatment that would anneal the NiTi film and ensure that shape memory behavior could be obtained. An annealing at 650 °C for 1 hour showed a sharper and clearer Af phase transformation at around the target temperature of 60 °C. Annealing a full wafer at this temperature and time also showed that no delamination would occur which has also been linked to nonideal behavior of the NiTi membranes which has also been linked to meaningful behavior of the NiTi membranes.

Avec le développement de nouvelles sources d’énergie, les technologies dédiées à son stockage ont un rôle capital. Le zirconate de Plomb (PZ de structure Pérovskite) présente un grand intérêt pour les futures capacités rapides permettant le stockage de forte densité d’énergie. Cette propriété est associée à la transition de phase ferroélectrique – anti ferroélectrique induite par le champ électrique et qui s’accompagne d’une grande capacité de stockage. Le PZ a été déposé par pulvérisation cathodique RF sur différents types de substrats et notamment le SrTiO3, les cibles sont obtenues par mélange des poudres et pressage à froid. L’étude s’est focalisée sur les effets d’interfaces entre le film et l’électrode inférieure (LaNiO3 dans notre cas), l’orientation préférentielle des films et la réalisation de films épitaxiés de PZ. La structure, la micro structure des films ainsi que leurs épaisseurs ont un impact sur les contraintes existantes dans le film et nous avons évalué ces effets sur la capacité de stockage du PZ dans la phase anti ferroélectrique. L’optimisation des propriétés des interfaces et de l’ingénierie des contraintes permettent d’améliorer la densité d’énergie stockée dans un film anti ferroélectrique. C’est une voie sérieuse pour les supers condensateurs à base de matériaux fonctionnels de type PZ. / With the development of new energy resources, the advanced energy storage technologies are also becoming more and more important. Perovskite lead zirconate PbZrO3 is of great interest for future high-energy and fast-speed storage capacitors, due to the field-forced phase transition into the ferroelectric state accompanied by large charge storage. The material is deposited on SrTiO3 by RF magnetron sputtering from cold pressed target made in laboratory. The study focuses on the effect of interface between films and electrodes, preferred orientations, epitaxial strain and measuring conditions on the energy storage properties of PbZrO3-based antiferroelectric films. The improvement of interface properties and strain engineering enhance the energy storage density of antiferroelectric film, which may open a route to advance studies on PbZrO3-based antiferroelectric functional devices.

Les systèmes électrochromes, dont les propriétés optiques changent sous l’effet d’une excitation électrique, suscitent un intérêt croissant dû au fait qu’ils permettent un contrôle des propriétés optiques dans le domaine du visible et du proche infrarouge. Le but, initié dans des travaux précédents, vise à optimiser la synthèse, par pulvérisation cathodique magnétron, de films minces d’une épaisseur de 300 nm pouvant être intégrés dans un futur dispositif électrochrome « tout céramique » à conduction de sodium. Dans ce travail de thèse, deux matériaux constituant ce dispositif ont été étudiés. Le premier concerné est l’oxyde de tungstène, connu pour servir de couche électrochrome dans les dispositifs. Les couches synthétisées possèdent des propriétés de conduction mixte, une structure amorphe et une morphologie poreuse permettant l’intercalation de cations de sodium Na+ en son sein. Une dégradation du film de WO3 due à une réactivité rédhibitoire vis-à-vis de l’eau a été observée. Pour éliminer cela, deux solutions ont été testées : un cyclage en milieu non aqueux ou le recouvrement du film par un électrolyte solide de type NaSICon. La stoechiométrie en oxygène des films, a permis de régler la conductivité électronique, l’absorption dans le visible et la capacité des films à échanger des ions Na+. Le second matériau étudié est un oxyde de tungstène pré-inséré en sodium NaxWOy. L’influence des conditions de synthèse et celle de la teneur en sodium sur les différentes propriétés des films a été étudiée. Ces propriétés ont ensuite été comparées à celles obtenues pour les films de WO3 et pour des bronzes de tungstène NaxWO3 reportées dans la littérature. / Electrochromic systems, whose optical properties change under the effect of an electrical excitation, see an increasing interest because they allow a control of optical properties in the visible and near infrared. The aim, initiated in previous works, is to optimize the synthesis of 300 nm thin films by magnetron sputtering to be integrated into a future electrochromic "all ceramic" device based on sodium conduction. In this PhD, two materials forming the system have been studied. The first material is the tungsten oxide, known to serve as the electrochromic layer in devices. The synthesized layers possess mixed conducting properties, an amorphous structure and a porous morphology allowing the intercalation of sodium cations. A degradation of the WO3 film due to redhibitory reactivity towards water was observed. To eliminate this reactivity, two solutions were tested: a non-aqueous cycling or covering of the initial film by depositing a solid electrolyte of the type NaSICon. The oxygen stoichiometry of the films, allowed to tune the electronic conductivity, the absorption in the visible and the ability of the film to exchange Na+ cations. The second studied material is a pre-inserted NaxWOy sodium tungsten oxide. The influence of the synthesis conditions and of the sodium content on the various properties of the films was investigated. These properties were then compared with those obtained for the WO3 films and those of NaxWO3 tungsten bronzes reported in the literature.

Zinc Oxide falls under the classification of transparent conductive oxides. They typical optical transmittance of Zinc Oxide is 90% in the visible wavelength region. Though stoichiometric ZnO is an insulator, due to the presence of internal defects such as Zn interstitials and Oxygen vacancies, it exists as a n-type conductor. The other important property of ZnO which could be used by the optical field is its widebandgap. ZnO has a wide bandgap of 3.2eV -3.3eV. The additional advantage of being a direct bandgap semiconductor has increased the probability of using ZnO for short wavelength applications. These practical applications are directly related to the fabrication of homostructural p-n junctions. ZnO can be readily doped n-type. Doping ZnO P-type is very difficult due to its native defects and the self-compensation that occurs during doping. But when P-type doping is obtained in ZnO it could be used in various optical applications such as light emitting diodes and laser diodes. This provided the motivation for this research. Theoretical studies have proposed nitrogen as a suitable material to achieve p-type ZnO. Literature provides a set of conditions that could be used to improve the doping in ZnO films. In this research, a set of these conditions were used to implement p-type doping in ZnO films. A sputtering system with a setup to support two Torus - 5M guns was used to deposit the ZnO films. A codoping technique using an aluminium doped zinc oxide target was the first method. Though an improvement in the nitrogen incorporation was found in this method in the beginning, a further increase in the nitrogen pressure did not show further improvement. A co-sputtering technique of a 99.999% pure ZnO target and a 99.99% pure Zn metal target was the second method. The ZnO target was rf sputtered while the Zn target was dc sputtered using the two guns provided in the deposition chamber. The extra Zinc obtained from sputtering the metallic Zn target was used to improve the incorporation of nitrogen. The films were later deposited in an oxygen ambient where the excess oxygen was used to suppress the oxygen vacancies that act as hole killers during the doping process. Four point probe measurement and Keithley 900 series Hall equipment were used for the electrical characterization of the films. An ORIEL monochromator was used to optically characterize the films. Hitachi S-800 T EDAX analysis system was used to measure the atomic weight % of nitrogen incorporated in the ZnO:N films. Deposition at an oxygen partial pressure of 0.3mT and 0.8mT of nitrogen produced p-type ZnO films. These films showed a carrier absorption in the short wavelength region. The carrier concentration and the mobility obtained for these films were 4.0 x1016 cm-3 and 0.12 cm2 /V-s respectively.

La thermoélectricité est un phénomène physique permettant la conversion directe de l’énergie thermique en énergie électrique, ou inversement. Cependant l’augmentation du rendement des modules thermoélectriques passe par un défi de taille : optimiser les propriétés électroniques du matériau pour obtenir un coefficient Seebeck élevé et une résistivité électrique faible, tout en minimisant la conductivité thermique. Une des voies d'optimisation consiste à réduire la dimensionnalité des matériaux afin de diminuer la contribution des phonons dans le transport thermique. Les matériaux siliciures sont prometteurs en raison de leur faible toxicité et coût. Parmi eux, le disiliciure de chrome, CrSi2, possède des propriétés de transport électronique intéressantes, mais ses performances sont limitées par une conductivité thermique trop élevée. L’objectif de cette thèse est d’étudier les propriétés thermoélectriques de ce composé sous différentes formes, monocristal, couche mince et nanofil. Dans ce but, le disiliciure de chrome a été élaboré sous formes de monocristal par la méthode Bridgman, de couche mince par pulvérisation cathodique, et de nanofil par dépôt chimique en phase vapeur. Ces différentes techniques d'élaboration ont été associées à des techniques de caractérisation spécifiques à chacune de ces formes afin d'étudier la relation entre les propriétés physiques et la microstructure du matériau. En couplant des modèles théoriques aux mesures thermoélectriques, les mécanismes de transport électronique et thermique ont été mis en évidence. L’étude de dynamique du réseau a été complétée par la première mesure de diffusion inélastique des neutrons sur monocristal et sur poudre nanométrique de CrSi2. Dans le cas des couches minces, l'effet de l'état de cristallinité et de l'épaisseur a été étudié. Enfin, dans le cas des nanofils, un microdispositif de mesure des propriétés thermoélectriques sur nanofil isolé a été conçu. L’ensemble des résultats présentés ouvre des perspectives intéressantes pour aborder l’amélioration des propriétés thermoélectriques de CrSi2. / Thermoelectricity is a physical effect related to the direct conversion between thermal and electrical energy. To improve the thermoelectric efficiency, the electronic properties of the materials must be optimized to get a large Seebeck coefficient and a low electrical resistivity while lowering the thermal conductivity. One of the optimization ways is to reduce the dimensionality of the materials to decrease the phonon contribution to the thermal conductivity. Silicides are promising materials because of their low toxicity and cost. Among them, chromium disilicide, CrSi2, shows interesting electronic transport properties, but a too high thermal conductivity, limiting its performance. The objective of this thesis is to study the thermoelectric properties of this compound with various forms, single crystal, thin film and nanowire.For this purpose, the chromium disilicide was elaborated in the forms of single crystal by the Bridgman method, thin film by sputtering, and nanowires by chemical vapor deposition. These elaboration routes have been associated with characterization techniques specific to each form in order to study the relationship between the physical properties and the microstructure of the material. By coupling theoretical models with thermoelectric measurements, the mechanisms of electronic and thermal transports have been determined. The vibrational study was completed by the first inelastic neutron scattering measurement on CrSi2 single crystal and nano-powder. In the case of thin films, the effect of the crystallinity state and the thickness has been studied. Finally, in the case of nanowires, a micro-device has been designed to measure the properties of a single nanowire. The presented results open interesting perspectives to improve the thermoelectric properties of CrSi2.

<p>The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al₂O₃, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult.</p><p>In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr₂O₃ nucleation layer. Moreover, it was found that an additional requirement for the formation of the <em>α</em> phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of <em>α</em> alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline <em>α</em>-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10^-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low.</p><p>In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the <em>α</em> phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth.</p> / Report code: LiU-TEK-LIC-2007:1.