Transmission Electron Microscopy (TEM) is a reliable tool for chemical and structural studies of nanostructured systems. The shape, size and volumes of nanoparticles on surfaces play an important role in surface chemistry. As nanostructured surfaces become increasingly important for catalysis, protective coatings, optical properties, detection of specific molecules, and many other applications, different techniques of TEM can be used to characterize the properties of nanoparticles on surfaces to provide a path for predictability and control of these systems. This dissertation aims to provide fundamental understanding of the surface chemistry of Electroless Metallization onto Polymeric Surfaces (EMPS) through characterization with TEM. The research focuses on a single EMPS system: deposition of Ag onto the cross-linked epoxide "SU8", where Au nanoparticles act as nucleation sites for the growth of Ag nanoparticles on the polymer surface. TEM cross sections were analyzed to investigate the morphology of the Au nanoparticles and to determine the thicknesses of the Ag nanoparticles and of the Ag layers. A method for the direct measurement of the volume and thickness of nanomaterials has been developed in the project using High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM). The morphology of Au and Ag NPs has been studied to provide reliable statistics for 3-D characterization. Deposition rates have been obtained as a function of metallization conditions by measuring the composition and thickness of the metal for EMPS. In the present work a calibration method was used to quantify the sensitivity of the HAADF detector. For thin samples a linear relationship of the HAADF signal with the thickness of a material is found. Cross-sections of multilayered samples provided by Triquint Semiconductors, FL, were analyzed as calibration standards with known composition in a TECNAI F30 transmission electron microscope to study the dependence of the HAADF detector signal on sample thickness and temperature. Dynamical diffraction processes play an important role in electron scattering for larger sample thicknesses. The HAADF detector intensity is not linearly dependent on sample thicknesses for thick samples. This phenomenon involves several excitation processes including Thermal Diffuse Scattering (TDS) which depends on temperature-dependent absorption coefficients. Multislice simulations have been carried out by Python programming using the scattering parameters (2) available in the literature. These simulations were compared with experimental results. Wedge-shaped Focused Ion Beam (FIB) samples were prepared for quantitative HAADF-STEM intensity measurements for several samples and compared with these simulations. The discrepancies between the simulated and experimental results were explained and new sets of absorptive parameters were calculated which correctly account for the HAADF-STEM contrasts. A database of several pure elements is compiled to illustrate the absorption coefficients and fractions of scattered electrons per nanometer of the sample. In addition, the wedge-shaped FIB samples were used for studying the HAADF-STEM contrasts at an interface of a high- and a low-density material. The use of thick samples reveals an increased signal at the interfaces of high- and low-density materials. This effect can be explained by the transfer of scattered electrons from the high density material across the interface into the less-absorbing low-density material. A ballistic scattering model is proposed here for the HAADF-STEM contrasts at interfaces of thick materials using Python. The simulated HAADF-STEM signal is compared with experimental data to showcase the above phenomenon. A detailed understanding of the atomic number contrast in thick samples is developed based on the combination of experimental quantitative HAADF-STEM and simulated scattering. This approach is used to describe the observed features for Ag deposition on SU8 polymers.

No description available.

Santa Monica Bay and its vast beaches are important Los Angeles icons, while also providing significant ecosystem services to over millions of recreational visitors annually. Contaminated runoff from numerous watersheds surrounding the Bay, especially the 87% urbanized Ballona Creek Watershed, have historically resulted in poor water quality along areas of the Bay shoreline. Decades of monitoring for fecal indicator bacteria (FIB) along the Bay’s shoreline has been associated with NPDES wastewater discharge and stormwater programs. Many projects have been implemented throughout the watersheds (e.g. sewer improvements, biofiltration systems, low-flow diversions (LFDs)) to lessen flows of runoff from contaminating surf zone recreational waters. Despite decades of monitoring, there has been no long-term assessment of trends in shoreline FIB, especially in response to implementation of projects to improve water quality. The goal of this study was to assemble 30 years of monitoring data (1988-2017) for E. coli and enterococci to assess trends along the entire shoreline of Santa Monica Bay. Data were analyzed by calculating rolling 30-day geometric means, and comparing means by geographic subdivision, between wet and dry weather, and over time. Resulting trends for both E. coli and enterococci were: 1) concentrations peaked around 2005 when many stations shifted to sampling points where runoff mixed directly with surf zone water; 2) after 2005, concentrations fell to present levels, especially at beaches where LFDs were implemented; 3) concentrations were extremely variable during the 2016-17 wet season; 4) the north and central areas of the Bay, impacted by runoff from the Ballona Creek and Malibu Creek Watersheds, had greater concentrations relative to the south area; and 5) dry weather concentrations were steadily low, whereas wet weather displayed a higher degree of variability and may present a more significant challenge to meet water quality standards going forward. Implementation of LFDs and other best management practices to restrict polluted runoff from flowing into the surf zones of the Bay’s beaches most likely improved water quality throughout the Bay.

Grâce à ses propriétés d’antioxydant, d’anti-usure et éventuellement d’extrême pression le dithiophosphate de zinc (ZDDP) fait partie des additifs les plus utilisés dans les lubrifiants pour moteurs thermiques. De nos jours, dans un souci de respect de l’environnement, de nouveaux lubrifiants possédant de bonnes performances en lubrification (frottement faible et usure limitée) sont développés en prenant compte des limitations d’utilisations actuelles du ZDDP. L’idée étant de réduire dans ceux-ci les teneurs en phosphore et soufre (Normes euros VI), éléments essentiels du ZDDP qui endommagent les pots catalytiques. L’objectif de cette thèse est l’étude du comportement tribologique du phosphate de zinc di alkyl (ZP) en comparaison avec le ZDDP. La méthodologie expérimentale étudiée pour comprendre le mécanisme d’action de ces additifs, associe des essais de frottement à descaractérisations physico-chimiques des surfaces frottantes après essais.Cette comparaison a été effectuée en fonction de la température (25°C et 100°C), la vitesse de glissement (25, 50 et 100 mm/s) et la concentration en additif (200 et 600 ppm dephosphore). Les meilleures actions anti-usure sont obtenues avec le ZDDP pour une température de 100°C et une vitesse de glissement de 100 mm/s et le ZP pour une température de 25°C et une vitesse de glissement de 25 mm/s. Les analyses de surface XPS, AES, XANES et MET-EDX ont permis de mettre en évidence la présence d’un film protecteur constitué principalement de phosphate de zinc, ceci pour les deux additifs.Une synergie de comportement tribologique a été mise en évidence avec un lubrifiantconstitué de ZP (usure faible) et d’oléate d’urée (frottement faible). Des essais complémentaires sur un tribomètre dynamique ont permis d’étudier le niveau de frottement du tribofilm formé à partir du ZDDP. Le caractère visqueux du tribofilm de ZDDP a été mis en évidence. / Thanks to its antioxidant, anti-wear and extreme pressure properties, zinc dialkyldithiophosphate (ZDDP) is nowadays the most used anti-wear additives in engine oil. Due to environmental protection concerns, new lubricants with good tribological performances (low friction and low wear) are developed. This research aims to evaluate the current limitations of ZDDP and to find alternative environmentally friendly solutions. Thus, the target is to reduce the quantity of phosphorus and sulphur in lubricants, two essential elements of ZDDP molecule that damage catalytic. The objective of this thesis is to study tribological behavior of zinc phosphate di alkyl (ZP) in comparison to ZDDP. The experimental method performed is the coupling of friction test with surface physico-chemical characterisation of rubbing surface after tests.This comparison carried out according to the temperature (25°C and 100°C), the sliding speed (25, 50, 100 mm/s) and additives concentrations (200 and 600 ppm). The best anti-wear efficiency is obtained with the ZDDP additive at 100°C - 100 mm/s and with the ZP at 25°C - 25 mm/s. For both additives and under these conditions, tribofilms are mainly made of zinc phosphate.A tribological synergy are obtained with a lubricant contained ZP (low wear) and oleyl urea (low friction). Complementary tests were made on a original dynamic tribometer for a better understanding of ZDDP tribofilm friction behavior. The viscous character of ZDDP tribofilm was obtained.

L’étude des formations de fer rubané (BIF) permet de comprendre les conditions des océans de et de l’atmosphère terrestres au cours de l’Archéen et du début du Protérozoïque. L’objectif de cette thèse est de fournir une analyse minéralogique et géochimique détaillée de BIFs de deux localités distinctes, séparées par la frontière Archéen-Protérozoïque. Une attention particulière est portée à la minéralogie de leurs carbonates et oxydes de fer. Les BIFs de 2,7 Ga de la formation Manjeri, Zimbabwe et de 2,4 Ga du Groupe Itabira, Brésil, ont dans les deux cas été précipités par mélange de fluides hydrothermaux marins oxygénés. Ceci est démontré par la présence d’inclusions de nano-hématite dans les lames de chert (Itabira et Manjeri) et de dolomite (Itabira seulement), qui sont interprétées comme la phase minérale la plus ancienne dans les échantillons. En outre, la microscopie électronique à transmission à faisceau d’ions focalisé (FIB-TEM) révèle la présence de plaquettes de nano ferrihydrite dans les BIF dolomitiques (carbonate d’itabirite). La dolomite est interprétée comme étant une phase primaire précipitée à des températures plus élevées (~100°C) de fluides hydrothermaux riches en CO2. Des anomalies positives en Eu dans les deux formations indiquent une composante hydrothermale, susceptible d’être la source du fer réduit. Les changements de faciès dans les deux unités sont le résultat de transgression/régression; et des évènements hydrothermaux post dépôt masquent les conditions primaires. Les carbonates riches en fer dans les deux faciès ont différentes origines: diagénétiques (Itabira) et hydrothermales post dépôt (Manjeri). Toutefois, les carbonates riches en fer des deux formations ont des valeurs négatives de ∂13C, ce qui indique qu’au moins une partie du carbone dans les carbonates est d’origine organique.Des analyses en balance de Curie dans le carbonate d’itabirite révèlent que la maghémite est le produit de transformation de la ferrihydrite lorsque de la dolomite se décompose à ~790°C. La maghémite a une température de Curie comprise entre 320 et 350°C et est stable jusqu’à une température de 925°C. Les analyses en FIB-TEM sur le processus de martitisation ont révélé deux mécanismes possibles à partir de deux échantillons de martite provenant respectivement du Brésil et d’Inde. En fonction de la cause de la martitisation, que nous avons déterminé être soit la déformation soit l’hydrothermalisme, la martitisation se produit respectivement par l’intermédiaire de:1. La réorganisation de défauts ponctuels, pour former des jumeaux. Ces défauts sont causés par les vacances dans la structure spinelle de la maghémite, dues à la suppression des ions Fe3+ en excès au cours de l’oxydation de la magnétite. C’est dans ce jumelage que le mécanisme de martitisation se produit.2. La migration des joints de grains par l’hématite au détriment de la magnétite, qui est due à la présence de fluide le long des interfaces du cristal. La maghémite se forme en raison de l’excès de Fe3+ produit pendant la martitisation de la magnétite, qui se déplace vers la surface des cristaux de magnétite. / It is the study of banded iron formations (BIFs) that provides understanding into the conditions of the Earth’s oceans and atmosphere during the Archean and Early Proterozoic. The aim of this thesis is to provide a detailed mineralogical and geochemical understand of BIFs from two separate localities separated by the Archean Proterozoic boundary. Close attention is paid to their carbonate and iron oxide mineralogy.The BIFs of the 2.7 Ga Manjeri Formation, Zimbabwe and 2.4 Ga Itabira Group, Brazil were both precipitated from oxygenated mixed marine-hydrothermal fluids. This is demonstrated by the presence of nano-hematite inclusions in the chert (Itabira and Manjeri) and dolomite (Itabira only) laminae, which is interpreted as the oldest mineral phase within the samples. Additionally, focused ion beam transmission electron microscopy (FIB-TEM) reveals the presence of nano ferrihydrite platelets within the dolomitic BIFs (carbonate itabirite). The dolomite is interpreted to be a primary phase precipitated at higher temperatures (~100°C) from CO2-rich hydrothermal fluids. Positive Eu anomalies in both formations indicate a hydrothermal component, likely to be the source of the reduced iron. Facies changes in both units are the result of transgression/regression and post depositional hydrothermal events mask primary conditions. Iron-rich carbonates in both facies have different origins; diagenetic (Itabira) and post depositional hydrothermal (Manjeri). However, the iron-rich carbonates of both formations have negative ∂13C values, indicating that at least part of the carbon in the carbonates is of organic origin. Curie Balance analyses into the carbonate itabirite reveals that maghemite is the transformation product of the ferrihydrite when dolomite decomposes at ~790°C. The maghemite has a Curie temperature between 320 and 350°C and is stable up to temperatures of 925°C.FIB-TEM investigations into the martitisation process revealed two possible mechanisms from two martite samples, from Brazil and India. Depending of the cause of the martitisation, here found to be deformation and hydrothermalism, the martitisation occurs respectively via either: 1. Ordering of point defects caused by vacancies in the spinel structure of maghemite, due to the removal of excess Fe3+ ions during the oxidation of magnetite, to form twins. It is in this twinning that the martitisation mechanism occurs.2. Grain boundary migration by hematite at the expense of magnetite is due to the presence of fluid along the crystal interfaces, where maghemite forms due to excess Fe3+ produced during martitisation of the magnetite, moving towards the surface of the magnetite crystals.

Um dos métodos mais utilizados para proteção contra a corrosão de aços comuns consiste na proteção catódica com revestimentos metálicos eletroquimicamente mais ativos, que estes. Os revestimentos de zinco são os mais usados para este tipo de proteção. De forma a protegerem o substrato, estes revestimentos devem atuar como anodos de sacrifício, sofrendo corrosão e transformando o substrato de aço em catodo. Todavia, não é de interesse, que o revestimento de zinco apresente altas taxas de corrosão de forma que a proteção contra a corrosão conferida ao aço seja duradoura. Uma das formas mais empregadas para reduzir a velocidade de corrosão do revestimento de zinco é por meio de tratamentos da superfície, por exemplo, por tratamentos de conversão. Os tratamentos de conversão mais eficientes são os que utilizam e geram rejeitos, que contêm íons de cromo hexavalente. Todavia, estes íons são carcinogênicos e tóxicos e, dessa forma, os processos que os utilizam em alguma etapa do tratamento, vêm sofrendo crescentes restrições, já sendo proibidos em países com leis ambientais mais rígidas. Esta é a razão para o crescente interesse e grande investimento em pesquisa tratamentos, que possam resultar em revestimentos com potencialidade para substituir, de forma eficiente e efetiva o uso do cromo hexavalente. Este foi o objetivo do presente trabalho. Neste estudo, foi investigado o efeito de tratamentos, que resultam em camadas de conversão na presença de ácido oxálico e na proteção contra a corrosão da superfície do zinco. Camadas de conversão foram obtidas por imersão de amostras de zinco em soluções de ácido oxálico (ácido etanodióico) com diferentes concentrações. Todas as soluções de tratamento apresentaram elevada acidez e resultaram em ataque da superfície de zinco com formação de revestimento de conversão com diferentes características. Ensaios preliminares de névoa salina foram então realizados para investigar a proteção conferida pelo sistema revestimento de conversão-verniz contra a corrosão do substrato de zinco. Estes ensaios foram decisivos para a escolha da faixa de concentração do banho de conversão com maior potencial para formação de revestimentos de conversão protetores. Os resultados deste ensaio e os de espectroscopia de impedância eletroquímica mostraram que tratamentos em soluções com composição superiores a 10-1 M de ácido oxálico resultaram em camadas muito defeituosas, nas quais o ataque localizado do substrato metálico é favorecido, sendo obtidas impedâncias menores que a superfície do zinco sem qualquer tratamento. Os resultados de XPS mostraram, que os revestimentos de conversão formados em soluções de ácido oxálico na faixa de 10-3 M a 10-1 M são compostos de oxalato de zinco e produtos de corrosão do zinco, especificamente ZnO, Zn (OH)2, e ZnCO3. Já a concentração de 10-1 M de ácido oxálico foi a, que produziu os resultados mais promissores com a formação de um revestimento, que conferiu proteção mais duradoura à superfície do zinco entre os obtidos. As espessuras médias das camadas de conversão de oxalato de zinco formadas em soluções com 10-1 M e 1 M de ácido oxálico, estimadas por FIB, foram respectivamente 600 nm e 300 nm, o que mostra que a concentração de 1 M de ácido causou intenso ataque corrosivo da superfície, enquanto a camada formada em meio com 10-1 M permitiu a deposição de camada mais espessa e mais protetora contra a corrosão do substrato. Os resultados de XPS indicaram a degradação da camada de oxalato de zinco com o tempo de ensaio, porém o ataque desta ao longo do ensaio de corrosão, resulta na formação de simonkolleite, identificada por difração de raios X, para períodos mais longos do ensaio de corrosão, no caso do revestimento formado em solução com 10-1 M em comparação a 1M. A simonkolleite atua por efeito barreira bloqueando os defeitos/porosidade da camada. O crescente acúmulo destes produtos de corrosão com a continuidade do processo corrosivo e a aderência destes ao substrato metálico foi indicada para superfície tratada em solução com 10-1 M de ácido oxálico. Finalmente, foi proposto um modelo para interação entre o revestimento de conversão de oxalato de zinco e os produtos de corrosão em que a retenção dos produtos de corrosão na superfície faz com, que a camada na superfície se torne mais espessa e mais compacta com o tempo de exposição ao ensaio de corrosão. Estas observações explicam o aumento de impedância observado com o tempo de ensaio nesta condição. Os resultados obtidos permitiram concluir, que o revestimento de conversão de oxalato de zinco formado em solução com 10-1 M de ácido oxálico resulta em proteção efetiva do substrato metálico além de apresentar boa aderência com camada de verniz. Estes resultados indicam potencialidade deste tratamento como preparação de superfícies de zinco, que serão recobertas com revestimentos orgânicos (tintas, vernizes ou lacas). / One of the most used methods for protection of common steels is the cathodic protection by galvanic coupling with metallic coatings electrochemically more active than these. Zinc coatings are the most commonly used for this type of protection. In order to protect the metallic substrate, these coatings must act as sacrificial anodes, corroding themselves and converting the steel substrate into cathode. However, it is not appropriate that the zinc coating presents high corrosion rates, so that the corrosion protection conferred to the steel is long-lasting. One of the most commonly employed methods of reducing the corrosion rate of zinc coatings is by surface treatments, such as, conversion treatments. The most efficient conversion treatments to date are those that use hexavalent chromium ions or generate residues containing these ions. However, hexavalent chromium is carcinogenic and toxic and, therefore, the processes that involve their use at some stage of the treatment, are under increasing restrictions, and have already been prohibited in developed countries. This is the reason for the growing interest and great investment in research studies in search for treatments that may result in coatings with the potential to efficiently and effectively replace the use of hexavalent chromium. This was the objective of the present study. In this study, the effect of treatments in oxalic acid solutions that resulted in conversion layers on the corrosion protection of zinc surface has been investigated. Conversion layers were obtained by immersion of zinc samples in solutions of oxalic acid (ethanedioic acid) with different concentrations. All the treatment solutions presented high acidity and resulted in attack of zinc surface and formation of conversion coatings of different characteristics. A layer of varnish was applied and preliminary salt spray tests were then carried out to investigate the corrosion protection provided by the system conversion coating -varnish to the zinc substrate. These tests were decisive for the choice of the conversion bath composition range with greater potentialities for the formation of protective conversion coatings. The results of the salt spray test and of electrochemical impedance spectroscopy (EIS) showed that treatments in solutions with compositions greater than 10-1 M of oxalic acid resulted in very defective conversion layers in which the localized attack of the metallic substrate is favored, and lower impedances than the zinc surface without any treatment were obtained for surfaces treated in these solution. The XPS results showed that conversion coatings formed in oxalic acid solutions in the range of 10-3 M to 10-1 M are composed of zinc oxalate and zinc corrosion products, specifically ZnO, Zn (OH)2, and ZnCO3. The concentration related to the most promising results was 10-1 M and in this solution, the coating formed that promoted the longer lasting protection of the zinc surface among those obtained. The average thicknesses of the zinc oxalate conversion layers formed in solutions with 10-1 M and 1 M of oxalic acid, estimated by FIB, were respectively 600 nm and 300 nm. This result showed that in 1 M of oxalic acid an intense corrosive attack of the zinc surface occurred, while the layer formed in 10-1 M was thicker and more protective against substrate corrosion. The XPS results indicated degradation of the zinc oxalate layer formed in 10-1 M solution with time of exposure to the test solution, but for the protection of the coating lasted for longer periods, comparatively to that formed in 1M solution, once the attack of the first film resulted in formation of simonkolleite, which was identified by X-ray diffraction. Simonkolleite acts by barrier effect blocking defects / porosity in the conversion layer. The increasing accumulation of corrosion products with test time and their adhesion to the metallic substrate was indicated for surface treated in solution with 10-1 M of oxalic acid. Finally, a model has been proposed for the interaction between the zinc oxalate conversion coating and the corrosion products in which the retention of these products on the surface is promoted by the conversion coating and the surface layer becomes thicker and more compact with time of exposure. These observations explain the increased impedance observed with the test time associated to this coating. The obtained results allowed concluding that the conversion coating of zinc oxalate formed in solution with 10-1 M of oxalic acid results in effective protection of the metallic substrate besides promoting good adhesion with a layer of varnish. These results indicate the potential of this treatment as preparation of zinc surfaces that will be covered with organic coatings (paints, varnishes or lacquers).

Die vorliegende Dissertation befasst sich mit dem Wachstum und der Charakterisierung von Silizium- und Germanium-Nanodrähten. Diese Strukturen gelten als aussichtsreiche Komponenten für zukünftige Bauelemente. Für die Anwendung ist die genaue Kenntnis der Größe, der kristallographischen Orientierung und der Position der Nanodrähte erforderlich. Ziel dieser Arbeit war daher die Untersuchung von Si- und Ge-Nanodrähten im Hinblick auf ihre Größe, Orientierung und Position. Die Herstellung erfolgte durch Physikalische Gasphasenabscheidung (PVD) im Ultrahochvakuum nach dem Vapor-Liquid-Solid (VLS)-Verfahren, das auf dem Wachstum aus Lösungsmitteltröpfchen basiert. Die Größe der Nanodrähte konnte im Falle von Silizium auf Si(111) mit Gold als Lösungsmittel durch die Parameter des Experiments reproduzierbar bestimmt werden. Höhere Goldbedeckung und höhere Substrattemperaturen führten zu Tröpfchen mit größerem Duchmesser und somit zu dickeren Drähten. Längere Si-Verdampfungszeiten und höhere Si-Verdampfungsraten führten zu längeren Drähten. Dünnere Drähte wuchsen schneller als dickere. Als zweites Lösungsmittel wurde Indium untersucht, da es sich im Vergleich zu Gold nicht nachteilig auf die elektronischen Eigenschaften von Silizium auswirkt. Basierend auf den Ergebnissen zur Tröpfchenbildung konnten die besseren Wachstumsresultate mit Gold erklärt werden. Germanium-Nanodrähte, die aus Goldtröpfchen auf Ge(111) gezüchtet wurden, zeigten im Gegensatz zu den Si-Nanodrähten nicht die kristallographische [111]-Orientierung des Substrates, sondern eine -Orientierung, was durch Berechnungen von Keimbildungsenergien auf verschiedenen Kristallflächen erklärt werden konnte. Zur Anordnung von Metalltröpfchen und damit von Nanodrähten wurden Substrate mithilfe von fokussierten Ionenstrahlen (FIB) vorstrukturiert, um die Tröpfchenbildung an bestimmten Stellen zu begünstigen. Es gelang, aus angeordneten Goldtröpfchen epitaktisch gewachsene Si- und Ge-Nanodrähte zu züchten. / This dissertation deals with the growth and the characterization of silicon and germanium nanowhiskers, also called nanorods or nanowires. The investigation of these structures is of great interest as they represent promising building blocks for future electronic devices. With regard to a possible application, the knowledge of size, crystallographic orientation and position of the nanowhiskers is essential. The purpose of this work was, therefore, to investigate the growth of Si and Ge nanowhiskers with regard to their size, orientation and position. The nanowhiskers were grown via physical vapor deposition (PVD) in ultra-high vacuum using the vapor-liquid-solid (VLS) mechanism which is based on growth from solution droplets. The size of the nanowhiskers could be reproducibly determined by the experimental parameters in the case of Si nanowhiskers on Si(111) with gold as the solvent. A higher gold coverage as well as a higher substrate temperature led to larger droplet diameters and thus to thicker whiskers. A longer silicon evaporation time and a higher silicon rate led to longer whiskers. Thinner whiskers grew faster than thicker ones. A second material used as the solvent was indium as it is more suitable for electronic application compared to gold. Based on results of droplet formation of the two solvents on silicon, the better results of whisker growth using gold could be explained. Ge nanowhiskers grown from gold droplets on Ge(111) did not show the [111] orientation of the substrate as in the case of Si nanowhiskers on Si(111) but a orientation. By calculating nucleation energies on different crystal facets, the experimental findings could be explained. To position nanodroplets of the solvent material and thus to obtain a regular arrangement of nanowhiskers, substrates were pre-structured with nanopores by focused ion beams (FIB). Silicon and germanium nanowhiskers could be epitaxially grown from ordered arrays of gold droplets.

La zircone 3Y-TZP présente un grand intérêt pour les applications dentaires, en implantologie orale, elle semble être un matériau extrêmement prometteur: elle allie une biocompatibilité à un aspect esthétique satisfaisant et présente aussi des propriétés mécaniques très supérieures aux autres céramiques. Ces bonnes propriétés mécaniques sont intimement liées à la microstructure du matériau, elle-même directement liée aux procédés d’élaboration comme nous l’a rappelé l’alarmante série de ruptures de plus de 800 têtes de prothèses de hanche en zircone au début des années 2000, due au phénomène de vieillissement de ce matériau. Cependant, les études cliniques menées à ce jour ne font toujours pas état des interrelations existant entre la microstructure, les propriétés mécaniques et la sensibilité au vieillissement. Il était donc primordial de valider et d’appliquer les connaissances acquises dans le domaine des sciences des matériaux pour l’application de la zircone 3Y-TZP en implantologie oral. C’est l’objectif de notre première publication. Nous avons également développé, dans notre deuxième publication, un protocole d’évaluation permettant dans un premier temps, d’évaluer l’effet de l’état de surface et de la microstructure sur la résistance mécanique d’implants neufs, puis de suivre leurs cinétiques de vieillissement tout en analysant l’évolution de la microstructure et son influence sur la résistance mécanique au cours du vieillissement. Tout cela permettant in fine, de prédire la durabilité d’un type d’implant. Nous avons par la suite, développé un programme informatique permettant la détection et la quantification du vieillissement pour un volume donné. Cette détection de la zone vieillie ou transformée est basée sur des modifications microstructurales caractéristiques engendrées lors du vieillissement. Enfin, nous avons pu mettre en évidence l’occurrence du phénomène de vieillissement in vivo, par l’analyse d’explants issus d’une étude clinique et démontrer leur probable implication dans ces cas d’échec. Le logiciel informatique de traitement d’image développé a été également, appliqué aux explants dans le but de mettre en lumière et d’expliciter l’occurrence du phénomène de vieillissement in vivo, afin de sensibiliser les acteurs de ce marcher aux problématiques rencontrées et d’optimiser de ce dispositif médical, à la lumière des connaissances actuelles. / 3Y-TZP zirconia is gaining interest in oral implantology, it seems to be a promising material with good biocompatibility, esthetic appearance and also the highest mechanical properties for a ceramic. These mechanical properties are closely related to the microstructure of the material itself directly related to production processes as we recalled the alarming series of breaks of more than 800 heads of zirconia hip replacements in the early 2000, due to the aging phenomenon of the material. However, clinical studies to date are still not state of the interrelationships between microstructure, mechanical properties and sensitivity to aging. It was therefore important to validate and apply the knowledge gained in the field of materials science for the application of 3Y-TZP zirconia oral implantology. This is the goal of our first publication. We also have developed in our second publication, a protocol to assess the effect of the surface modification and microstructure on the mechanical strength of new implants and follow their kinetics of aging and also, the evolution of the microstructure and its influence on the mechanical strength during aging, to predict the durability of a type of implant. We have subsequently developed a computer program for the detection and quantification of the aging for a given volume. This detection of the aged or transformed area is based on microstructural modifications produced during aging. Finally, we have been able to demonstrate the occurrence of the phenomenon of aging in vivo, by analyzing explants from a clinical study and demonstrate their involvement in the case of dental implant failure. The image processing developed was also applied to the explants in order to highlight and explain the occurrence of in vivo aging phenomenon. The objective is to optimize this medical device, in the light of current knowledge.

Le carbure de silicium est pressenti comme un matériau prometteur dans plusieurs domaines de l’électroniquetels que la nano-électronique, l’électronique de puissance ou les capteurs travaillant en milieuxhostiles (hautes températures, milieux corrosifs, milieux biologiques) du fait de ses propriétés physicochimiquessupérieures à celles du silicium, notamment. Cependant, parmi les différentes méthodesd’élaboration par voie descendante ou ascendante permettant de fabriquer des nano-objets à 1D enSiC, aucune n’a pour l’instant permis d’obtenir du SiC d’excellente qualité cristalline.Le travail de cette thèse a porté sur la démonstration de l’élaboration de nanostructures 1D àbase de SiC, à savoir nanofils coeur-coquille Si-SiC, nanofils de SiC et nanotubes de SiC, par unprocédé original de carburation de nanofils de silicium, eux-mêmes élaborés par gravure plasma. Cettedémonstration a été possible grâce au contrôle de la pression de carburation, ce qui permet la maîtrisede l’exodiffusion des atomes de silicium à travers le carbure de silicium.À pression atmosphérique l’exodiffusion des atomes de silicium est restreinte ce qui permet d’élaborerdes nanofils coeur-coquille Si-SiC avec une coquille de SiC monocristalline et entièrement recouvrante.En se servant de la biocompatibilité du SiC et du bon contrôle électronique dans le silicium, ilest possible d’envisager l’utilisation de ces nanofils coeur-coquille Si-SiC pour des bio-nano-capteurs.En diminuant la pression au cours de la carburation, il est possible d’augmenter l’exodiffusion etainsi d’obtenir des nanotubes de SiC cubique de très bonne qualité cristalline avec des parois denses.Ces nanotubes de SiC sont largement modulables en termes de dimensions, et la faisabilité de leurouverture a été démontrée, permettant ainsi l’utilisation du fort rapport surface sur volume de telsnano-objets pour des capteurs électroniques notamment.Un premier pas a été franchi vers les applications des nanofils coeur-coquille Si-SiC et des nanotubesde SiC, puisque les mesures électriques réalisées sur des nano-transistors à effet de champ utilisant cesdeux types de nano-objets comme canal sont prometteurs. / Due to their superior physical and chemical properties —such as high breakdown field, high thermalconductivity and biocompatibility— compared to other semiconductors, silicon carbide is forseento be a promising materials for power electronics, bio-nano-sensors and nano-electronics in harsh environments.However, among the numerous top-down or bottom-up methods used to synthesise siliconcarbide 1D nano-objects, none has been able yet to produce SiC with a high cristalline quality.The aim of this project is to demonstrate the synthesis of silicon carbide- based 1D nanostructures—e.g. core-shell Si-SiC nanowires, SiC nanowires and SiC nanotubes— through an original processbased on the carburization of plasma-etched silicon nanowires. This demonstration is based on thecontrol of the pressure during the carburization process, which leads to the monitoring of the outdiffusionof silicon atoms through silicon carbide.Thus if the pressure is kept at the atmospheric pressure, the out-diffusion of silicon is limited andSi-SiC core-shell nanowires can be synthesized with a single-crystalline cubic SiC shell. Thanks to thebiocompatibility of the SiC shell and the good electronic transport into the Si core, bio-nano-sensorscan be considered.If the pressure is decreased during the carburization process, the outdiffusion of silicon atomsthrough SiC is enhanced, and leads to SiC nanotubes synthesis. SiC nanotubes sidewalls are dense,with an excellent crystalline quality. These original SiC nanotubes have a high surface to volume ratioand thus can be used for sensors or storage devices.The first step for direct applications has also been demonstrated since first results on electricalperformances of nano-field effect transistors, with these nano-objects as channel, are promising.

Um dos métodos mais utilizados para proteção contra a corrosão de aços comuns consiste na proteção catódica com revestimentos metálicos eletroquimicamente mais ativos, que estes. Os revestimentos de zinco são os mais usados para este tipo de proteção. De forma a protegerem o substrato, estes revestimentos devem atuar como anodos de sacrifício, sofrendo corrosão e transformando o substrato de aço em catodo. Todavia, não é de interesse, que o revestimento de zinco apresente altas taxas de corrosão de forma que a proteção contra a corrosão conferida ao aço seja duradoura. Uma das formas mais empregadas para reduzir a velocidade de corrosão do revestimento de zinco é por meio de tratamentos da superfície, por exemplo, por tratamentos de conversão. Os tratamentos de conversão mais eficientes são os que utilizam e geram rejeitos, que contêm íons de cromo hexavalente. Todavia, estes íons são carcinogênicos e tóxicos e, dessa forma, os processos que os utilizam em alguma etapa do tratamento, vêm sofrendo crescentes restrições, já sendo proibidos em países com leis ambientais mais rígidas. Esta é a razão para o crescente interesse e grande investimento em pesquisa tratamentos, que possam resultar em revestimentos com potencialidade para substituir, de forma eficiente e efetiva o uso do cromo hexavalente. Este foi o objetivo do presente trabalho. Neste estudo, foi investigado o efeito de tratamentos, que resultam em camadas de conversão na presença de ácido oxálico e na proteção contra a corrosão da superfície do zinco. Camadas de conversão foram obtidas por imersão de amostras de zinco em soluções de ácido oxálico (ácido etanodióico) com diferentes concentrações. Todas as soluções de tratamento apresentaram elevada acidez e resultaram em ataque da superfície de zinco com formação de revestimento de conversão com diferentes características. Ensaios preliminares de névoa salina foram então realizados para investigar a proteção conferida pelo sistema revestimento de conversão-verniz contra a corrosão do substrato de zinco. Estes ensaios foram decisivos para a escolha da faixa de concentração do banho de conversão com maior potencial para formação de revestimentos de conversão protetores. Os resultados deste ensaio e os de espectroscopia de impedância eletroquímica mostraram que tratamentos em soluções com composição superiores a 10-1 M de ácido oxálico resultaram em camadas muito defeituosas, nas quais o ataque localizado do substrato metálico é favorecido, sendo obtidas impedâncias menores que a superfície do zinco sem qualquer tratamento. Os resultados de XPS mostraram, que os revestimentos de conversão formados em soluções de ácido oxálico na faixa de 10-3 M a 10-1 M são compostos de oxalato de zinco e produtos de corrosão do zinco, especificamente ZnO, Zn (OH)2, e ZnCO3. Já a concentração de 10-1 M de ácido oxálico foi a, que produziu os resultados mais promissores com a formação de um revestimento, que conferiu proteção mais duradoura à superfície do zinco entre os obtidos. As espessuras médias das camadas de conversão de oxalato de zinco formadas em soluções com 10-1 M e 1 M de ácido oxálico, estimadas por FIB, foram respectivamente 600 nm e 300 nm, o que mostra que a concentração de 1 M de ácido causou intenso ataque corrosivo da superfície, enquanto a camada formada em meio com 10-1 M permitiu a deposição de camada mais espessa e mais protetora contra a corrosão do substrato. Os resultados de XPS indicaram a degradação da camada de oxalato de zinco com o tempo de ensaio, porém o ataque desta ao longo do ensaio de corrosão, resulta na formação de simonkolleite, identificada por difração de raios X, para períodos mais longos do ensaio de corrosão, no caso do revestimento formado em solução com 10-1 M em comparação a 1M. A simonkolleite atua por efeito barreira bloqueando os defeitos/porosidade da camada. O crescente acúmulo destes produtos de corrosão com a continuidade do processo corrosivo e a aderência destes ao substrato metálico foi indicada para superfície tratada em solução com 10-1 M de ácido oxálico. Finalmente, foi proposto um modelo para interação entre o revestimento de conversão de oxalato de zinco e os produtos de corrosão em que a retenção dos produtos de corrosão na superfície faz com, que a camada na superfície se torne mais espessa e mais compacta com o tempo de exposição ao ensaio de corrosão. Estas observações explicam o aumento de impedância observado com o tempo de ensaio nesta condição. Os resultados obtidos permitiram concluir, que o revestimento de conversão de oxalato de zinco formado em solução com 10-1 M de ácido oxálico resulta em proteção efetiva do substrato metálico além de apresentar boa aderência com camada de verniz. Estes resultados indicam potencialidade deste tratamento como preparação de superfícies de zinco, que serão recobertas com revestimentos orgânicos (tintas, vernizes ou lacas). / One of the most used methods for protection of common steels is the cathodic protection by galvanic coupling with metallic coatings electrochemically more active than these. Zinc coatings are the most commonly used for this type of protection. In order to protect the metallic substrate, these coatings must act as sacrificial anodes, corroding themselves and converting the steel substrate into cathode. However, it is not appropriate that the zinc coating presents high corrosion rates, so that the corrosion protection conferred to the steel is long-lasting. One of the most commonly employed methods of reducing the corrosion rate of zinc coatings is by surface treatments, such as, conversion treatments. The most efficient conversion treatments to date are those that use hexavalent chromium ions or generate residues containing these ions. However, hexavalent chromium is carcinogenic and toxic and, therefore, the processes that involve their use at some stage of the treatment, are under increasing restrictions, and have already been prohibited in developed countries. This is the reason for the growing interest and great investment in research studies in search for treatments that may result in coatings with the potential to efficiently and effectively replace the use of hexavalent chromium. This was the objective of the present study. In this study, the effect of treatments in oxalic acid solutions that resulted in conversion layers on the corrosion protection of zinc surface has been investigated. Conversion layers were obtained by immersion of zinc samples in solutions of oxalic acid (ethanedioic acid) with different concentrations. All the treatment solutions presented high acidity and resulted in attack of zinc surface and formation of conversion coatings of different characteristics. A layer of varnish was applied and preliminary salt spray tests were then carried out to investigate the corrosion protection provided by the system conversion coating -varnish to the zinc substrate. These tests were decisive for the choice of the conversion bath composition range with greater potentialities for the formation of protective conversion coatings. The results of the salt spray test and of electrochemical impedance spectroscopy (EIS) showed that treatments in solutions with compositions greater than 10-1 M of oxalic acid resulted in very defective conversion layers in which the localized attack of the metallic substrate is favored, and lower impedances than the zinc surface without any treatment were obtained for surfaces treated in these solution. The XPS results showed that conversion coatings formed in oxalic acid solutions in the range of 10-3 M to 10-1 M are composed of zinc oxalate and zinc corrosion products, specifically ZnO, Zn (OH)2, and ZnCO3. The concentration related to the most promising results was 10-1 M and in this solution, the coating formed that promoted the longer lasting protection of the zinc surface among those obtained. The average thicknesses of the zinc oxalate conversion layers formed in solutions with 10-1 M and 1 M of oxalic acid, estimated by FIB, were respectively 600 nm and 300 nm. This result showed that in 1 M of oxalic acid an intense corrosive attack of the zinc surface occurred, while the layer formed in 10-1 M was thicker and more protective against substrate corrosion. The XPS results indicated degradation of the zinc oxalate layer formed in 10-1 M solution with time of exposure to the test solution, but for the protection of the coating lasted for longer periods, comparatively to that formed in 1M solution, once the attack of the first film resulted in formation of simonkolleite, which was identified by X-ray diffraction. Simonkolleite acts by barrier effect blocking defects / porosity in the conversion layer. The increasing accumulation of corrosion products with test time and their adhesion to the metallic substrate was indicated for surface treated in solution with 10-1 M of oxalic acid. Finally, a model has been proposed for the interaction between the zinc oxalate conversion coating and the corrosion products in which the retention of these products on the surface is promoted by the conversion coating and the surface layer becomes thicker and more compact with time of exposure. These observations explain the increased impedance observed with the test time associated to this coating. The obtained results allowed concluding that the conversion coating of zinc oxalate formed in solution with 10-1 M of oxalic acid results in effective protection of the metallic substrate besides promoting good adhesion with a layer of varnish. These results indicate the potential of this treatment as preparation of zinc surfaces that will be covered with organic coatings (paints, varnishes or lacquers).