Le présent travail de thèse a pour but le développement du procédé de traitement de surface d’anodisation micro-arc (MAO), appliqué au titane et alliage de titane. L’objectif est de déterminer l’influence des paramètres tels que la nature du substrat (éléments d’alliage), la chimie de la solution électrolytique et les paramètres électriques, sur le comportement électrochimique in-situ des couches en formation, ainsi que sur les caractéristiques microstructurales et chimiques des revêtements. Des méthodes de caractérisations notamment morphologiques (imagerie MEB et MET), chimiques (EDS, DRX, diffraction des électrons, EELS) et électrochimiques ex-situ (potentiel libre, courbes de polarisation, SIE) sont utilisées afin d’étudier les revêtements formés. L’étude systématique réalisée par voltampérométrie et chronopotentiométrie a permis de différencier trois stades ou régimes d’anodisation (I/ classique, II/ micro-arc, et III/ d’arcs), caractérisés par une réponse électrochimique particulière de l’interface métal/électrolyte, et qui impacte les propriétés de revêtement finalement obtenues. Des modèles phénoménologiques sont proposés aux différents stades d’anodisation et en lien avec les paramètres du traitement MAO. Le titane commercialement pur de Grade 2 et l’alliage de titane Ti-6Al-4V (ou TA6V) ont été étudiés comparativement ; l’influence des éléments d’alliage (aluminium et vanadium) a été discutée sur la conduite du procédé. L’élaboration d’une solution électrolytique a été étudiée dans le but d’obtenir un revêtement épais, compact et composé majoritairement de titanate d’aluminium. L’incorporation dans les revêtements des éléments provenant de l’électrolyte a été discutée en lien avec la réponse électrochimique ; cette étude conduit à une proposition de mécanisme de croissance de couche où interviennent les éléments du substrat et les éléments d’alliage aux différents stades d’anodisation. L’étude des régimes pulsés unipolaires et bipolaires a permis de discuter l’effet des temps de pause et des pulsations cathodiques sur la réponse électrochimique du matériau et sur les propriétés des revêtements. L’étude du ratio des charges anodiques / cathodiques a montré qu’il s’agissait d’un paramètre essentiel pour garantir la croissance d’un revêtement à la fois épais, homogène et compact / This thesis manuscript relates to the study of process set up of an electrochemical surface treatment, called micro-arc oxidation (MAO), and applied to titanium and its alloys. The aim is to determine the influence of parameters such as nature of the substrate (alloying elements), chemistry of the electrolytic solution and electrical parameters, on the process. In-situ electrochemical behaviour of forming oxide layers is studied, as well as microstructural and chemical characteristics of formed coatings. Many methods mostly to characterize morphology (SEM, TEM imagery), chemistry (EDS, XRD, electron diffraction, EELS) and ex- situ electrochemical behaviour (OCP, polarizing, EIS) are used. Systematic study realised by voltamperometry and chronopotentiometry allowed to differentiate three anodizing stages (I/ conventional, II/ micro-arc, III/ of arcs), characterized by a particular electrochemical response of the metal/electrolyte interface, and which impacts obtained coating properties. Phenomenological models are proposed for each stage of anodizing and linked to MAO process parameters. Grade 2 commercially pure titanium and alloy Ti-6Al-4V (or TA6V) are comparatively studied; the influence of alloying elements (aluminium and vanadium) was discussed in relation with running of the process. Development of an electrolytic solution was carried out to obtain a thick and compact coating, mostly composed of aluminium titanate. Incorporation into the coating of elements from the electrolyte was discussed, and linked to in-situ electrochemical response; this study leaded to a proposed coating growth mechanism which involves elements from the substrate and from the electrolyte. Study of unipolar and bipolar pulsed regimes allowed discussing the effect of pause time and cathodic pulses on electrochemical response of the material and on coating properties. Study of the anodic / cathodic charge ratio showed it was an essential parameter to ensure growth of a thick, homogeneous and compact coating

The crystal growth of nanoporous materials is different from most other classes of material in that their framework architectures contain periodic arrangement of pores or voids in which there is no direct bonding between adjacent units of the framework. This poses a variety of questions as to how such parts of framework develop during the crystallization process, atomistically and energetically. Here we use the nanoporous metal-organic framework, ZIF-8 as a prototypical material to obtain a basic understanding of the growth of a nanoporous material. The crystals of ZIF-8 produced in the N,N-dimethylformamide solvent [ZIF-8(DMF)] and methanol-co-N,N-dimethylformamide solvent [ZIF-8(MeOH)] are both rhombic dodecahedron in shape with a much smaller crystal size in the latter. In the study of the kinetics of ZIF-8(DMF) crystallization, we get a good agreement in the values of activation energies using both Avrami-Erofe’ev-Hancock-Sharp and Gualtieri’s models, i.e. about 120 kJ mol-1 for nucleation, and 95 kJ mol-1 for crystal growth process. The study of kinetics of ZIF-8 surface growth, by in situ AFM, with ZIF-8(DMF) as seed crystal that are grown in the methanolic growth solution we see faster rate in the <100> directions than the <110> directions, with the most probable activation energy of about 80 kJ mol-1 in both directions. This is the first example of in situ AFM being used to obtain activation energy for a surface growth in MOF. We also reveal here that growth process of ZIF-8 occurs through the nucleation and spreading of successive metastable unenclosed sub-steps to eventually form stable terrace steps of the enclosed framework structure in which this process is reliant on the presence of nonframework species to connect the framework species that have voids between them. The experiments also enable identification of some of the fundamental units in the growth process and the stable crystal surface plane. Further, the spreading of terraces at high supersaturation condition (early state) is fairly isotropic as is seen through the formation of almost-rounded terraces on the surface of ZIF-8. The growth direction becomes clear as the supersaturation condition nears to equilibrium (later stage) by the formation of rhombohedral terraces with pointy ends growing along the <100>, and <110> directions and straight edges growing perpendicular to the <111> direction. Formation of this rhombohedral morphology is explained by a coarse grain approach similar to that used in the Kossel model by making assumptions that the sodalite cage is the growth unit and attachment of one sodalite cage in each growth direction is the rate determining step for the formation of a new row of sodalite cages in each direction. Finally, based on the profiles of growth spirals formed from screw dislocations on the ZIF-8 surface obtained from the ex situ AFM images and ICE theory, plausible screw dislocations with Burgers’ vector of 1/2 <111> and <100>, but not <110>, are deduced. Some of the findings in this work will be applicable to numerous nanoporous materials, and the work in general will support efforts to synthesize and design new framework materials and to control the crystal properties of these materials.

The reactivity of oxide surfaces and metal-oxide interfaces play an important role in many technological applications such as corrosion, heterogeneous catalysis, and microelectronics. The focus of this research was (1) understanding the effects of water vapor exposure of ultrathin aluminum oxide films under non-ultrahigh vacuum conditions (>10-9 Torr) and (2) characterization of Pt growth modes on ultrathin Ta silicate and silicon dioxide films and the effects of growth modes on adhesion of a Cu overlayer. These studies were conducted with X-ray photoelectron spectroscopy (XPS). Ni3Al(110) was oxidized (10-6 Torr O2, 800K) followed by annealing (1100K). The data indicate that the annealed oxide film is composed of NiO, Al2O3 and an intermediate phase denoted here as "AlOx". Upon exposure of the oxide film at ambient temperature to increasing water vapor pressure (10-6 - 5 Torr), a shift in both the O(1s) and Al(2p)oxide peak maxima to lower binding energies is observed. In contrast, exposure of Al2O3/Al(polycrystalline) to water vapor under the same conditions results in a high binding energy shoulder in the O(1s) spectra which indicates hydroxylation. Spectral decomposition provides further insight into the difference in reactivity between the two oxide films. The corresponding trends of the O(1s)/Ni0(2p3/2) and Al(2p)/Ni0(2p3/2) spectral intensity ratios suggest conformal changes of the oxide film on Ni3Al(110). The growth behavior of sputter deposited Pt at ~300K on Ta silicate and SiO2 ultrathin films formed on Si(100) was investigated. The XPS data show that Pt deposition results in uniform growth or "wetting" on Ta silicate and 2-D cluster growth on SiO2. Electroless Cu deposition on ~11 monolayers (ML) Pt/Ta silicate film results in an adherent Cu film which passed the Scotch tape test. In contrast, electroless Cu deposition on ~11ML Pt/SiO2 results in a non-adherent Cu film due to weak Pt/SiO2 interaction.

Cette thèse présente la synthèse de graphène par CVD catalytique sur feuille de cuivre, wafers de silicium revêtus de nickel et sur mousse de nickel. Les dépôts ont été réalisé à partir de méthane et d'éthylène. Pour l'ensemble de ces substrats, les études faites ont permis de mieux appréhender les mécanismes de croissance et de déterminer les paramètres opératoires optimaux. Des tests applicatifs ont été effectué pour utiliser le graphène synthétisé comme électrode d'OLED et de batterie Li-ion. / This study concerns graphene synthesis by catalytic CVD (Chemical Vapor Deposition) on copper foils, silicon wafers coated with nickel and nickel foam. Deposits have been synthesized from methane and ethylene. For the whole substrates studied, the results obtained have allowed to better understand the mechanisms of nucleation/growth of graphene and to determine the optimal operating parameters. Some applicative tests have been performed in the fields of OLED and Li-ion battery.

The present work covers investigation of the growth mechanism and growth kinetics of the ZnO nanowires and nanoneedles fabricated by using high-pressure pulsed laser deposition. The growth model based on the combination of four different flows of the interfacial particles is introduced. A variation of the free energy is given as a major reason of the change of the growth mechanism which appears by using different doped seed layers, growth temperature and the doping of the deposited material. A fabrication of the ultrathin nanowires with a diameter of d < 10 nm at CMOS compatible growth temperature of T = 400°C is demonstrated. The diameter of these nanowires is comparable with the Bohr radius. The growth of the Al and Ga doped and undoped ZnO nanoneedles with a sharp tip was shown. The doping of the nanowires and nanoneedles can be promising for their applications. By using a patterned sapphire substrate, an unidirectional growth of the nanowires and nanoneedles was achieved. These nanostructures are tilted by 58°ZnO with respect to the surface normal.:Bibliographic Record Contents 1 Introduction I Basics and Methods 2 Basic properties and growth concept 2.1 ZnO nanowires and nanoneedles 2.1.1 Applications 2.2 Nanowire and nanoneedle fabrication 2.2.1 Growth mechanisms which require a catalyst 2.2.2 Catalyst-free epitaxial growth mechanism 2.3 Free energy and the growth mechanism 2.4 NW growth techniques 2.5 Aligned tilted growth 3 Growth and characterization 3.1 Preparation of the seed layers by CVD 3.2 Preparation of the seed layers by low pressure PLD 3.3 HP PLD for the NW and NN growth 3.4 Characterization techniques 3.4.1 X-ray Diffraction 3.4.2 Atomic Force Microscopy 3.4.3 Scanning electron microscopy 3.4.4 Energy Dispersive X-ray Spectroscopy 3.4.5 Spectroscopic Ellipsometry 3.4.6 Cathodoluminescence 3.4.7 Angle-varied X-ray photoelectron spectroscopy 3.4.8 Etching of the seed layers 4 Seed layer characterization 4.1 Doping concentration 4.2 Surface morphology 4.3 Crystalline quality 4.4 Surface polarity 4.5 Summary of the Chapter II NW growth: results 5 NW growth characteristics 5.1 Material free energy and the deposited material parameters 5.2 Growth kinetics 5.3 Summary of the Chapter 6 NW growth on doped seed layers 6.1 Al doped seed layers 6.2 NW growth on Ga doped seed layers 6.3 Optical characteristics of the ZnO NWs 6.4 Summary of the Chapter 7 Growth of ZnO(Al) and ZnO(Ga) NWs 7.1 Al-doped ZnO NWs grown on ZnO(Al) seed layers 7.2 Ga-doped ZnO NWs grown on ZnO(Ga) seed layers 7.3 Summary of the Chapter 8 Growth of tilted ZnO NWs and NNs 8.1 Patterning of the substrates . 8.2 Growth of tilted NNs 8.3 Growth of tilted NWs 8.4 Optical properties of the tilted nanostructures 8.5 Summary of the Chapter 9 Summary and outloock 9.1 Summary 9.2 Outlook Acknowledgements Curriculum Vitae List of own Articles List of own Conference Talks and Posters References

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The product of interaction between Al and TiO2 at elevated temperature has a wide range of applications in refractory, structural and electronics industries (refractory tiles, tank armor, fuel cells, and microelectronic devices). This research attempts to understand the extent of interaction between Al and TiO2 when the reactant surfaces are in contact at elevated temperature and normal atmospheric pressure. The interfacial region between the reactant compounds is examined using analytical techniques; and the formation of TiAl as the interfacial compound is described. The thermodynamics of the Al – Ti – O system is explained as it relates to the particular conditions for the Al – TiO2 reaction research. Thermodynamic principles have been used to demonstrate that the formation of TiAl is favored instead of other TixAly compounds for the set of conditions outlined in this thesis. A study of the mechanism of interactions in the interfacial region can help towards being able to determine the reaction kinetics that lead to the control of microstructure and thus an improvement in the material performance. An appropriate model that describes the formation of TiAl at the interface is described in this study. The formation of TiAl at the interface is a result of the reduction reaction between TiO2 and Al. The O released during the reduction of TiO2 has been investigated and demonstrated to partly remain dissolved in TiAl at the interfacial region. Some O reacts with Al as well to form crystalline Al2O3 in the interfacial layer. / Ph. D.

Les fontes de fer sont des matériaux largement utilisés dans de nombreux domaines allant de l’industrie automobile au secteur de l’énergie en passant par la fabrication des tuyaux d’adduction d’eau. Du fait de la teneur en carbone élevée de ces alliages, du graphite et/ou des carbures de fer précipitent pendant la solidification. Les propriétés finales des pièces dépendent alors de la nature de la matrice, de la présence ou non de carbures et surtout de la forme du graphite. Celui-ci peut cristalliser sous la forme de lamelles, de sphères ou de particules de formes intermédiaires. Les éléments présents à l’état de traces dans le bain de fonte liquide influencent de manière considérable la croissance du graphite et conditionnent sa forme finale. Leur moyen d’action ainsi que le mécanisme de croissance du graphite sphéroïdal sont encore un sujet de débat et cette thèse a pour objectif de contribuer à la compréhension des phénomènes mis en jeu. Les échantillons utilisés ont été élaborés selon le procédé de coulée par centrifugation, son influence sur les mécanismes étudiés est d’ailleurs au cœur de ce projet. Les différents essais et analyses réalisés prouvent que la structure des nodules observés dans les échantillons centrifugés est la même que dans le cas des pièces moulées en sable. De plus, les éléments traces montrent une action similaire lors de la solidification et pendant la croissance en phase solide durant le traitement thermique destiné à éliminer les carbures. Ces résultats suggèrent que le mécanisme de croissance du graphite sphéroïdal est le même lors de la croissance à partir du liquide ou en phase solide par décomposition des carbures. Une proposition est d’ailleurs faite pour expliquer le développement des nodules par une germination continue du graphite sur les plans de base conjuguée à une croissance selon les directions prismatiques. Un modèle mathématique associé à ce mécanisme est présenté et son application au procédé de centrifugation donne des résultats en accord avec les observations expérimentales. / Cast irons are widely used in the foundry industries for applications mainly in the automotive, energy and pipes industries. Because of the high carbon content, graphite and/or iron carbides appear during solidification. The properties of the casting depend on the nature of the matrix, the presence or not of carbides and the shape of the graphite. It can crystallise under the form of lamellae, spheroids or particles with an intermediate shape. Trace elements present in the melt strongly influence graphite growth and shape. Their action and the growth mechanism of the spheroidal graphite are still under debate and the aim of this project is to contribute to the understanding of these phenomena. The samples have been cooled by the centrifugal casting process whose influence on the studied mechanisms is the focus of this project. The different analyses that have been carried out show that the structure of the nodules is the same in centrifugated and sand mold castings. Moreover, the trace elements exhibit a similar action during solidification and solid state growth during heat-treatment for carbide dissolution. These results suggest that the growth mechanism of spheroidal graphite is the same during growth from the liquid and by solid state decomposition of carbides. A schematic is proposed to explain the growth of the nodules by a continuous nucleation on the basal surface of the graphite coupled to a growth along the prismatic directions. A mathematical model associated to this mechanism is presented and its application to the centrifugal casting process gives results in good agreement with experimental observations.

Die Synthese von Kohlenstoffnanoröhren mit maßgeschneiderten Morphologien stellt bis heute eine große Herausforderung dar. In der vorliegenden Arbeit liegt der Fokus zunächst auf gerade gewachsene MWCNTs, welche insbesondere mit N-Dotierung erhalten werden können. Im Allgemeinen führt eine Dotierung mit Stickstoff zu Defekten im Kohlenstoff-Gitter und verursacht dadurch eine gekrümmte MWCNT-Morphologie. Dennoch konnten in dieser Arbeit gerade gewachsene, nadelförmige MWCNTs insbesondere unter Verwendung der N-haltigen Präkursoren Acetonitril sowie Pyrazin (30 Ma.-% in Toluol) bei einer Temperatur von 750 °C erfolgreich synthetisiert werden. Dafür eignete sich besonders eine CVD-Methode, bei welcher der Fe-Katalysatorpräkursor Ferrocen in einem separaten Ofen sublimiert wurde. Es stellte sich heraus, dass sich in einer stickstoffhaltigen Gasphase bevorzugt einkristalline Fe3C-Katalysatorpartikel bilden. Im Fall einer homogenen Katalysatormorphologie, d.h. ohne Krümmungen, scheiden sich Kohlenstoffwände an einer bestimmten Facette des Katalysatorpartikels ab. Nicht nur die Zusammensetzung und Beschaffenheit des Katalysatorpartikels bestimmen die MWCNT-Morphologie, die Konzentration an Stickstoff sowie dessen Bindungszustand sind ebenso von großer Bedeutung. Für eine gerade MWCNT-Morphologie sollte daher das Vorkommen pyridinischer sowie pyrrolischer N-Bindungen möglichst gering gehalten werden, da diese Defekte im Kohlenstoff-Gitter verursachen. Die Art der Stickstoffbindung beeinflusst nicht nur die MWCNT-Morphologie, sondern ebenso die Oberflächenpolarität von MWCNTs. Grundsätzlich wird angenommen, dass Stickstoff die Polarität an der MWCNT-Oberfläche erhöht. Jedoch weisen in dieser Arbeit selbst MWCNTs mit bis zu 2,5 at.-% Stickstoff hydrophobe Oberflächen auf, im Vergleich zu hydrophilen MWCNTs, welche bis zu 3,7 at.-% Stickstoff enthalten. XPS-Messungen ergaben dabei nur einen signifikanten Unterschied bezüglich des Anteils an molekularen Stickstoff innerhalb beider MWCNT-Typen. Mit Hilfe von DFT-Berechnungen konnte anschließend nachgewiesen werden, dass zwischen den CNT-Wänden interkalierter molekularer Stickstoff, im Vergleich zu pyridinisch und graphitisch gebundenen Stickstoff, den größten Einfluss auf die π-Elektronendichte der Röhrenoberflächen besitzt. Die Anwesenheit des Stickstoffs verursacht dabei eine signifikante Verschiebung der π-Elektronendichte in Richtung der Stickstoffmoleküle hin. Ist die Konzentration an molekularen Stickstoff zudem so hoch, dass sich die Stickstoffmoleküle ebenso zwischen den äußeren CNT-Wänden anreichern, so können diese die Oberflächenpolarität der äußersten CNT-Wand begünstigen. Pyridinische und graphitische N-Bindungen verursachen nur eine geringfügige Verschiebung der π-Elektronendichte der CNT-Wände. Da sie sich zudem bevorzugt in den inneren CNT-Wänden befinden, beeinflussen sie die Polarität der äußersten MWCNT-Oberfläche nur unzureichend. Aufgrund der vielfältigen Anwendungsmöglichkeiten von MWCNTs in Abhängigkeit von ihrer Morphologie und Oberflächeneigenschaften, wurde zusätzlich das toxische Potential verschiedener MWCNT-Typen untersucht. Die toxikologischen Untersuchungen ergaben dabei, dass insbesondere lange und hydrophobe MWCNTs, ähnlich wie Amosit Asbest, ein hohes toxisches Potential aufweisen. / The synthesis of carbon nanotubes with tailor-made morphologies is still a challenge. First of all, this thesis is focused on the synthesis of straight MWCNTs, especially obtained with N doping. In principle, N doping causes defects in the carbon lattice, leading to a curved MWCNT morphology. Nevertheless, straight and needle-like MWCNTs were successfully synthesized especially when using N-containing precursors like acetonitrile and pyrazine (30 wt.-% in toluene) at 750 °C. Therefore, a CVD method, allowing a separate sublimation of the Fe catalyst precursor ferrocene, was suitable for the synthesis of such straight MWCNTs. It could be emphasized that single crystalline Fe3C catalyst particles were formed in the presence of nitrogen before the beginning of the MWCNT synthesis. In case of a homogeneous catalyst morphology (without curvatures), the tube walls will grow on a specific facet. Not only the composition and constitution of the catalyst particle have a strong influence on the MWCNT morphology, but also the concentration of nitrogen and it’s kind of incorporation in the carbon lattice. Meaning, the presence of pyridinic or pyrrolic nitrogen should be minimized to decrease the defects in the carbon lattice. Furthermore, the kind of nitrogen bond has also a strong influence on the surface polarity of the MWCNTs. As a dopant, nitrogen should generally increase the polarity of the MWCNT surfaces. In contrast, even MWCNTs containing up to 2.5 at.-% N in this work exhibit hydrophobic surfaces, whereas surfaces of MWCNTs containing up to 3.7 at.-% N are very hydrophilic. The only significant difference between both MWCNT types is the amount of molecular nitrogen intercalated between the tube walls, confirmed by XPS measurements. Using DFT calculations it could be highlighted that molecular nitrogen has the strongest influence on the π-electron density of the tube walls, compared to pyridinic and graphitic nitrogen. The presence of nitrogen causes a significant shift of the π-electron density from the tube walls towards the nitrogen molecules. In case of a high concentration of molecular nitrogen, the nitrogen molecules can be intercalated more between the outer tube walls, so they are able to enhance the polarity of the outermost tube wall. The pyridinic and graphitic nitrogen are preferentially incorporated between the inner tube walls and thus cause only a slight π-electron density shift. So their influence on the polarity of the outermost tube wall is not sufficient enough. Due to the various application possibilities of MWCNTs depending on their morphology and surface properties, the toxic potential of different MWCNT types was additionally investigated in this work. The toxicological investigations revealed that especially long MWCNTs with hydrophobic surfaces, similar to amosite asbestos, exhibit a high toxic potential.

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