La thèse porte sur cette couche de nitrure ou d’oxynitrure de silicium. Le déroulé prévoit l’élaboration des deux types de dépôts par voie gazeuse (par Chemical Vapor Infiltration CVI), la caractérisation de ces dépôts (par tous les moyens scientifiques à disposition et jugés utiles), ainsi que des essais en conditions proches de l’application visée (haute température, présence de phases liquides) pour juger de l’efficacité de ces dépôts et notamment effectuer une comparaison entre le nitrure et l’oxynitrure. Une étude complète des paramètres modifiables lors de l’élaboration et de leur effet sur la chimie (et par conséquent l’influence sur le comportement du matériau en conditions d’utilisation) représente le cœur du travail considéré. / Ceramics are usually used at high temperature because of their refractory nature. However, they are too brittle to be submitted to high stresses, such as in the rotating parts of aircraft engines. One way to reduce the brittleness of ceramics is to design them as composites. The fiber/matrix architecture displays a damageable character thanks to a suitable interfacial layer, which is deposited on the fiber cloths before the infiltration with molten silicon. The aim of the thesis is to propose and evaluate a solution to protect the fiber reinforcement during the impregnation step with liquid silicon. This solution involves the deposition of a protective layer made of silicon nitride or oxynitride.

abstract: This work explores the application and optimization of laser patterning of dielectrics on textured crystalline silicon for improving the performance of industrial silicon solar cells. Current direct laser patterning processes introduce defects to the surface of the solar cell as a result of the film transparency and the intensity variation of the laser induced by the textured surface. As a means of overcoming these challenges, a co-deposited protective masking film was developed that is directly patterned with laser light at greatly depreciated light intensities that allows for selective chemical etching of the underlying dielectric films without incurring substantial defects to the surface of the device. Initial defects produced by the process are carefully evaluated with electron microscopy techniques and their mechanism for generation is identified and compensated. Further, an analysis of the opening fraction within the laser spot is evaluated –the area of removed film within the laser spot divided by the area of the laser spot– and residue produced by the laser process within the contact opening is studied. Once identified, this non-damaging laser process is a promising alternative to the standard screen print and fire process currently used by industry for metallization of silicon solar cells. Smaller contacts may be made with the laser process that are as of yet unattainable with screen printing, allowing for a decrease in shading losses. Additionally, the use of patterning allows for silver-free metallization and improved conductivity in the contacts, thereby decreasing parasitic losses in the device. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018

La photocatalyse est une technique émergente de traitement des déchets qui nécessite un faible apport d’énergie présentée sous forme lumineuse. L’emploi de catalyseurs supportés autorise une séparation efficace des produits de réaction, en dépit d’une réduction de leur surface spécifique. De par les avantages qu’offre la pulvérisation réactive (bonne tenue mécanique, synthèse sur substrats froids, contrôle aisé de la microstructure, …), la synthèse de revêtements de TiO2 par cette technique fait l’objet de recherches intensives.Après une description des mécanismes mis en jeu lors d’une réaction photocatalytique, les phénomènes physiques à la base de la synthèse de revêtements céramiques par pulvérisation réactive à haute pression sont détaillés. Afin de s’affranchir de la contamination du catalyseur par le sodium du verre, une barrière de diffusion de SiNx est intercalée. Les influences de la position du substrat par rapport au flux de vapeur métallique, de la température de recuit, de la pression totale et de l’épaisseur des films catalyseurs sur leurs propriétés physicochimiques et photocatalytiques sont étudiées, autorisant la formulation d’hypothèses quant aux liens qui les unissent. Enfin, des premiers travaux portant sur la synthèse d’un photocatalyseur TiO2-xNy cristallisé in situ à haute pression sont présentés. / AThe photocatalysis is a new way of organic pollutants treatments which needs a low energy supplied under light wave. The use of supported catalyst allows an efficient separation of the reaction products, in spite of their specific area reduction. Owing to the advantages that offers reactive sputtering (good mechanical adhesion, synthesis on cold substrates, easy control of the microstructure, …), the synthesis by this technique of the most promising semiconductor photocatalyst, namely the titanium dioxide, is the subject of intensive researchs. After a description of the mechanisms occurring during a photocatalytic reaction, the physical phenomena at the origin of the ceramic coating synthesis are detailed. In order to hinder the sodium contamination of the catalyst from the glass substrate, a SiNx diffusion barrier is intercalated. The influences of the substrate position relatively to the metallic flux, the annealing temperature, the total pressure and the TiO2 coating thickness on the physico-chemical and photocatalytic properties are investigated allowing the formulation of hypothetic relations combining them. Finally, first studies on in situ crystallized TiO2-xNy photocatalyst deposited at high pressure are presented.

Novel electrophoresis devices for protein and DNA separation and identification have been presented and studied. The new device utilizes a contact resistance change detection method to identify protein and DNA in situ. The devices were prepared with a microelectronic micromechanical system (MEMS) fabrication method. Three model proteins and six DNA fragments were separated by polyacrylamide gel microchannel electrophoresis and surface electrophoresis. The detection of the proteins or DNA fragments was accomplished using the contact resistance increase of the detection electrode due to adsorption of the separated biomolecules. Key factors for the success of these devices were the optimization of fabrication process and the enhancement of detection efficiency of the devices. Parameters, such as microchannel configuration, size of electrode, and affinity of protein or polyacrylamide gel to the microchannel sidewall and bottom surface were explored in detail. For DNA analysis, the affinity to the bottom surface of the channel was critical. The surface modification method was used to enhance the efficiency of the microchannel surface electrophoresis device. The adsorption of channel separated protein and DNA on the detection electrode was confirmed with the electron spectroscopy for chemical analysis (ESCA) method. The electrical current (I) from the protein microchannel electrophoresis was usually noisy and fluctuated at the early stage of the electrophoresis process. In order to remove the current perturbation, an amorphous silicon (a-Si:H) thin film transistor (TFT) was connected to the microchannel device. The self-aligned a-Si:H TFT was fabricated with a two-photomask process. The result shows that the attachment of the TFT successfully suppressed the current fluctuation of the microchannel electrophoresis process. In summary, protein and DNA samples were effectively separated and detected with the novel TFT-driven or surface microchannel electrophoresis device.

For more than 50 years total hip replacements have been a common and successful procedure to increase patient mobility and quality of life. The 10-year implant survival rate is 97.8%. However, for longer implantation times there are limitations linked to the negative biological response to wear and corrosion products from the currently used biomaterials. In this thesis silicon nitride (SiNx) coatings were evaluated for use in total hip replacements, on the articulating bearing surface and modular taper connections. Homogeneous, dense SiNx coatings were deposited using reactive high power impulse magnetron sputtering (HiPIMS) up to a thickness of 8 µm. The N/Si atomic ratios ranged from 0.3 to 1.1 and the coatings showed a low surface roughness. The wear rate of a SiNx coated cobalt chromium molybdenum alloy (CoCrMo) was similar to that of bulk Si3N4, and less than one 46th of uncoated CoCrMo, an alloy that is commonly used in joint replacements. Wear debris generated from SiNx coatings was round in shape, with a mean size of 40 nm, and ranged between 10 and 500 nm. Model particles, similar in size and shape as the wear debris, were soluble in simulated body fluid. The dissolution rate was higher than the expected rate of debris generation. Along with the size of the debris, which is not in the critical range for macrophage activation, this dissolution may limit negative biological reactions. The SiNx coatings also dissolved in simulated body fluid. The coating with the highest N/Si ratio exhibited the lowest dissolution rate, of 0.2 to 0.4 nm/day, while CoCrMo under the same condition dissolved at a rate of 0.7 to 1.2 nm/day. SiNx-coated CoCrMo exhibited a reduced release of Co, Cr and Mo ions into the solution by two orders of magnitude, compared to uncoated CoCrMo. Si3N4 evaluated under micro-displacement in a corrosive environment, replicating the modular taper, showed a lower corrosion current compared to common biomedical alloys. SiNx coatings may also act beneficially to reduce issues associated with this type of contact. SiNx coatings have shown several properties in a laboratory environment that are hypothesised to increase the longevity of joint replacements. The promising results encourage further evaluation closer to the clinical application of total hip replacements, in particular in the articulating bearing surface and in modular tapers.

Le développement de photocatalyseurs en couches minces supportées constitue un intérêt majeur autorisant une séparation efficace des produits de réaction, en dépit d’une réduction de leur surface spécifique par rapport à des nanopoudres du même matériau. La synthèse de revêtements de TiO2 par pulvérisation cathodique magnétron en condition réactive fait l’objet de recherches intensives. Cette technique permet de contrôler, à travers les paramètres d’élaboration, la structure et les propriétés physicochimiques et photocatalytiques des revêtements.Afin de s’affranchir de la contamination du catalyseur par le sodium du verre lors de traitements en température ou lors de recuits de couches déposées à l’ambiante, une barrière de diffusion en SiNx est intercalée et son épaisseur est fixée pour la suite de l’étude. Différentes couches de TiO2 ont été élaborées à haute pression dans un réacteur doté d’un système de contrôle en boucle fermée basé sur la spectroscopie d’émission optique. L’effet de la cristallisation in situ à différentes températures sur les différentes propriétés des revêtements TiO2 a été étudié et les propriétés de ces derniers ont été comparées à celles des échantillons synthétisés sur des substrats froids et recuits ex situ aux mêmes températures.Enfin, des premiers travaux portant sur l’influence de l’introduction de l’argent en différentes teneurs sur l’efficacité photocatalytique sous lumière visible des couches de TiO2 cristallisées in situ et ex situ sont présentés. / The development of supported photocatalysts thin films is of major interest allowing an efficient separation of the reaction products, in spite of their specific area reduction compared to nanometric scale powders. The synthesis of TiO2 coatings by reactive magnetron sputtering is the subject of intensive researches. This technique allows, trough the control of the deposition parameters, to manage the structure and the physicochemical and photocatalytic properties of the coatings. In order to hinder the sodium contamination of the catalyst from the glass substrate, either during in situ or ex situ heating of the coating, a SiNx diffusion barrier is intercalated with a fixed thickness. Different layers of TiO2 were prepared at high pressure in a reactor equipped with a closed-loop control system based on optical emission spectroscopy. The influence of the in situ crystallization at different temperatures on the properties of the TiO2 coatings was studied. These properties were compared with those of samples synthesized ex situ and at the same temperatures. Finally, first studies on the influence of silver enrichment at different contents on photocatalytic activity under visible light of TiO2 layers crystallized in situ and ex situ, are presented.