Conselho Nacional de Desenvolvimento Científico e Tecnológico / In the last decades, several applications of niobium nitride thin films has been proposed or effectively implemented. In the cubic δ − NbN phase, the bulk material presents a Tc for the superconducting transition near 17 K, what is far larger than those found in other normal (BCS) superconductors and useful in, for example, Josephson tunnel junctions. More recently, other phases have been also focus of interest, like the hexagonal δ-NbN phase. The hardness and resistance to chemical corrosion make this material well fitted for mechanically improved surface. Thin film preparation or deposition of niobium nitrides by physical methods (PVD) is not a trivial task. Stoichiometry, crystal structure and morphology of the resulting films are strongly affected by the deposition conditions, and even a qualitative model for the growth mechanisms of niobioum nitride is still lacking. In this work we have studied the effect of some parameters on the structural and morphologic properties of NbN thin films. The samples have been produced by reactive magnetron sputtering for different nitrogen partial pressures, substrate temperatures, bias voltages and deposition times. The crystallographic structure, preferred orientations, grain sizes and surface roughness were stablished by XR diffraction and, for some samples, atomic force microscopy. The results have shown that without bias voltage cubic NbN thin films are obtained, with or without substrate heating, when the partial pressure of N2 in the reactive atmosphere is between 13 and 25 %. Films produced with 17 % N2 are preferentially oriented in the <200> direction and this texture is enhanced by substrate heating. The analysis of the results in two samples with different thickness clearly indicates that for cubib NbN, the growth is remarkable different in the <111> and <200> directions. A possible mechanism to explain this difference is presented. The main effect of the voltage bias was to induce a hexagonal δ - NbN structure even for voltages as low as -10 V. These films present larger densities values than those found in the films with cubic phase, being the highest density achieved with -70V bias. All samples deposited with bias present a compressive stress and small grain size. The connections between stress, grain size and density are presented and discussed. In summary, we have identified a group of key parameters that makes possible the deposition of NbN thin films by reactive magnetron sputtering, either for superconductivity or tribological applications. / Nas últimas décadas, têm sido propostas e implementadas muitas aplicações para filmes finos de nitreto de nióbio. Na fase cúbica δ − NbN, o material na sua forma bulk apresenta Tc de transição supercondutora próxima a 17 K, o qual é de longe muito maior do que os valores encontrados para outros supercondutores normais (BCS). E, proveitoso, por exemplo, para junções túnel Josephson. Mais recentemente, outras fases também têm sido foco de interesse, como a hexagonal δ0 − NbN. A dureza e resistência à corrosão química fazem deste material bem equipado para melhoramento mecânico de superfícies. A preparação de filmes finos de nitretos de nióbio por PVD não é uma tarefa trivial. Estequiometria, estrutura cristalina e morfologia dos filmes resultantes são fortemente afetadas pelas condições de deposição. E, mesmo um modelo qualitativo para os mecanismos de crescimento do nitreto de nióbio ainda está faltando. Neste trabalho estudamos o efeito de alguns parâmetros sobre as propriedades estruturais e morfológicas de filmes finos de NbN. As amostras foram produzidas por magnetron sputtering reativo com diferentes pressões parciais de nitrogênio, temperaturas do substrato, voltagem bias e tempos de deposição. Os resultados mostraram que sem bias aplicado são obtidos filmes finos de NbN na fase cúbica, com ou sem aquecimento do substrato, quando a pressão parcial de N2 na atmosfera reativa está entre 13 e 25%. Filmes produzidos com 17% de N2 estão preferencialmente orientados na direção (200) e sua textura é aumentada por aquecimento do substrato. A análise dos resultados em duas amostras com diferentes espessuras indicou claramente que, para NbN cúbico, o crescimento é notavelmente diferente nas direções (111) e (200). Um possível mecanismo capaz de explicar esta diferença é proposto neste trabalho. O efeito significativo da aplicação do bias foi induzir a estrutura hexagonal δ − NbN mesmo para voltagens pequenas como -10 V. Estes filmes apresentam valores de densidade maiores do que para os filmes com fase cúbica, sendo a maior densidade alcançada para -70 V de bias. Todas amostras depositadas com aplicação de bias apresentaram estresse compressivo e tamanho de grãos pequeno. As conexões entre estresse, tamanho de grão e densidade são apresentados e discutidos. Em resumo, identificamos um grupo de parâmetros chave que tornam possível a deposição de filmes finos de NbN por magnetron sputtering reativo, seja para supercondutividade seja para aplicações tribológicas.

Au laboratoire, une famille de tyrosine kinases propres aux bactéries et ne présentant aucune ressemblance structurale avec les protéine-kinases d’origine eucaryote a été identifiée. Ces enzymes, appelées BY-kinases, sont notamment impliquées dans la biosynthèse des polysaccharides extracellulaires, mais leurs rôles précis ainsi que leurs mécanismes catalytiques sont encore peu compris.Dans la première partie de ce travail, nous avons caractérisé le rôle physiologique de la phosphorylation sur la tyrosine de la protéine Ugd, une UDP-glucose déshydrogénase, par les BY-kinases Wzc et Etk d’E. coli. Nous avons démontré que la phosphorylation d’Ugd sur un site commun à Wzc et Etk augmente son activité. Nous avons également établi que la phosphorylation d’Ugd par Wzc participe à la régulation de la quantité d’acide colanique produit, tandis que la phosphorylation d’Ugd par Etk influence la résistance de la bactérie à la polymyxine.Nous avons également effectué une analyse structure-fonction du domaine cytoplasmique de deux BY-kinases, CapA1/CapB2 de S. aureus et Wzc d’E. coli. Nous avons montré que ces deux protéines s’associent en octamère, grâce au motif EX2RX2R et qu’elle s’autophosphoryle selon un mécanisme intermoléculaire. Nous avons, de plus, identifié le mécanisme d’activation de ces protéines et révélé l’importance d’un domaine particulier dans l’autophosphorylation de Wzc et la biosynthèse de l’acide colanique.La caractérisation structurale et fonctionnelle des BY-kinases représente une approche prometteuse et originale en vue de l’élaboration de molécules inhibant spécifiquement leur activité et pouvant affecter le pouvoir virulent des bactéries pathogènes. / A new class of bacterial enzymes, named BY-kinases, has been shown to catalyze protein-tyrosine phosphorylation. These enzymes share no structural and functional similarities with their eukaryotic counterparts. Evidence of their involvement in extracellular polysaccharide biosynthesis has been provided, but their accurate functions and their catalytic mechanism remain largely unknown.First, we characterized the physiological role of tyrosine phosphorylation of Ugd, a UDP-glucose dehydrogenase, by the BY-kinases Wzc and Etk of E. coli. We demonstrated that Ugd phosphorylation by Wzc or Etk occurs on the same site and increases its activity. We also established that Wzc-mediated phosphorylation of Ugd participates in the regulation of colanic acid production whereas Ugd phosphorylation by Etk influences resistance to polymyxin.In addition, we performed a structure-function analysis of the cytoplasmic domain of two BY-kinases, namely CapA1/CapB2 from S. aureus and Wzc from E. coli. We showed that these two proteins associate in a ring-shaped octamer in which the motif EX2RX2R plays a crucial role. In addition, we showed that BY-kinases autophosphorylate using an intermolecular mechanism. We also identified the activation mechanism of BY-kinases and we revealed the role of a particular domain, found specifically in BY-kinases from proteobacteria, in Wzc autophosphorylation and colanic acid biosynthesis.Structural and functional characterization of BY-kinases represents an original and promising approach in order to develop new molecules inhibiting specifically these enzymes and to affect the virulence of bacterial pathogens.