Dissertations / Theses on the topic 'Annealing of metals'

Thesis (M.S. in materials science and engineering)--Washington State University, August 2009.
Title from PDF title page (viewed on Aug. 7, 2009). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 44-46).

The present research program is a renewed attempt at explaining the transformation mechanisms. The experimental investigations has focused on a model analysis of transformations which occur in single crystals, with stable orientations, i.e. Goss{110}<001> and brass{110}<112>, the deformation is carried out by channel-die compression to simulate the rolling process of thin sheets. Next, the samples were annealed at temperatures of primary recrystallization. The analysis of crystallographic transformations was conducted on metals from a wide spectrum of stacking fault energy: low - Cu-2%Al, average- Cu and Ni to high Al and Al-1%Mn. At work were analyzed the mechanisms controlling the initial stages of recrystallization. Detailed analysis of disorientation across the recrystallization front clearly showed that the initial grain orientations were not accidental. The axes of disorientation in the relationship across the front of recrystallization were near normal in {111} planes, but only sporadically covered with the <111> direction. The distribution of the recrystallization angle rotation in relation to the preferences presented through the formation of two maxima values near 30 ° and 45-55 °.

The forward modeling method (FMM) for analysis of near-field High Energy X-ray Diffraction Microscopy (nfHEDM) has emerged as a powerful tool for materials characterization, with the ability to non-destructively measure microstructures deep within the bulk of materials. A synchrotron based technique, nfHEDM images X-ray diffraction from polycrystals with high resolution cameras. The diffraction signal is used to reconstruct the ensemble of grains in the form of 2D maps with high orientation and spatial resolution, and can be extended to volumetric measurements through sequential measurement. The hallmark of this technique is the ability to monitor the same ensemble of grains as they evolve in response to an external stimuli. This thesis will investigate the response of microstructure to annealing. The three thermally activated phenomena of recovery, recrystallization, and grain growth will be observed with two high purity metal wire samples. The first measurement, performed on aluminum, demonstrates the replacement of a deformed microstructure with well ordered grains in the recovery and recrystallization processes. A grain growth measurement performed on a fully recrystallized nickel sample demonstrates sensitivity to the evolution of a population of low energy grain boundaries, common to many fcc metals.

The effect of initial microstructures of an 0.05 wt.% C low carbon steel, acicular ferrite (AF), Bainite (B), polygonal ferrite (PF), fine polygonal ferrite (FPF), and a microstructure produced by direct strip casting (DSC) (termed SC), on the deformation and recrystallization behaviour of cold rolled low carbon (LC) steel, was investigated. The initially prepared samples with the initial microstructures were cold rolled to 50, 70 and 90% reductions, then annealed isothermally in the temperature range 580 ??? 680 oC. The microstructures and textures produced by deformation and annealing were studied by optical microscopy, XRD, TEM, SEM and EBSD. The initial microstructures were characterized mainly by optical microscopy and EBSD. Using EBSD, the ferrite grain size of the AF, B and SC samples was considerably larger than that found by optical microscopy with a large fraction of low angle grain boundaries (LAGBs) observed within prior austenite grains. All samples exhibited a very weak texture close to random. After cold rolling, the microstructures of AF and SC contained shear bands with PF and FPF generating deformation bands. For AF and SC, the pearlite phase was more extensively elongated in rolling direction compared with PF and FPF. After 90% cold rolling reduction, PF, FPF and SC consist mainly of the texture component and AF and B . It was found that FPF recrystallized most rapidly followed by B, PF and AF with SC recrystallizing orders of magnitude more slowly due to the solution drag caused by its uniformly distributed higher Mn content. Very strong (???-fibre) texture was generated in cold rolled PF followed by FPF, with AF, SC and B generating very weak textures. The texture evolution during annealing 90% reduction PF was examined in further detail. The behaviour of nucleation and grain growth provides strong evidence of orientated nucleation as the dominant factor for CRA texture development in this material.

Approved for public release; distribution is unlimited.
Iron-based amorphous metals have incredible strength and hardness, and with the addition of alloying constituents, can also be formulated to have exceptional corrosion resistance. Compositions of several iron-based amorphous metals have been published, including several with very good corrosion resistance. The benefits of chromium, molybdenum, and tungsten on corrosion resistance has been previously studied and documented, however little is known about other alloying constituents and their effect upon devitrification and corrosion resistance. The compositions explored in this thesis research are the SAM40 base alloy and variations including systematic additions of nickel, yttrium, and titanium. Nickel is added to improve both mechanical properties and corrosion resistance. Yttrium is added to lower the critical cooling rate, thereby making the metallic glass easier to create and more stable once formed, thus improving the corrosion resistance. Adding titanium will enable the formation of an extremely stable protective titanium oxide film on the alloy's surface, which could enhance the corrosion resistance. Through xray diffraction and corrosion analysis, the effects of these alloy additions on the devitrification and corrosion resistance of this new class of amorphous metals have be quantified.

La sécurité des installations nucléaires est constamment un souci majeur lors de leur exploitation, mais aussi lors de la conception de nouveaux réacteurs. Leurs durées de vie est limitée à cause des changements de comportement mécanique de leurs composants métalliques (principalement la cuve du réacteur mais aussi ses composants internes), qui sont accélérés ou induits par l’irradiation de neutrons. Une prédiction quantitative précise de ces changements, en fonction de la composition des matériaux et des conditions d'irradiation, est par conséquent un objectif de première importance pour la science des matériaux nucléaires. La modélisation est, de nos jours, considérée comme un complément vital aux approches expérimentales, avec l'objectif d’apporter une meilleure compréhension des processus physiques et chimiques qui se produisent dans les matériaux métalliques sous irradiation de neutrons.

La modélisation des effets de l'irradiation de neutrons dans les aciers est par nature un problème multi-échelle. Le point de départ est la simulation des cascades de collisions atomiques initiées par les neutrons à hautes énergies qui pénètrent dans le matériau, créant ainsi des défauts ponctuels mobiles. Différents modèles physiques, considérant des échelles de temps et de longueur croissantes, doivent être développés afin de convenablement tenir en compte de tous les différents processus qui provoquent des changements de comportement macroscopique, à cause de la présence de ces défauts ponctuels mobiles. En outre, des liens entre les différents modèles doivent être créés, parce que les prédictions de chacun d'entre eux doivent servir de paramètres d'entrée pour les modèles qui travaillent aux échelles supérieures. Dans cette thèse, un tel lien est créé entre le niveau atomique et les modèles à gros-grains, en développant un nouvel algorithme Monte-Carlo cinétique atomistique (MCCA), où le matériau est décrit comme une collection d'atomes occupant des sites cristallographiques réguliers. Le processus simulé est dès lors naturellement décomposé en séries d'évènements élémentaires activés thermiquement, correspondant à la migration des défauts ponctuels (lacunes ou interstitiels) vers des positions de proches voisins, qui sont en permanence en compétition en fonction de leurs fréquences d'occurrences respectives. Ces dernières sont calculées en fonction des énergies de migrations, qui sont elles-mêmes calculées avec peu d'approximations par une méthode qui prend en compte tous les effets de la relaxation statique et des interactions chimiques à longue portée. Le nouvel algorithme MCCA est par conséquent un modèle physique, entièrement basé sur un potentiel inter-atomique approprié qui est utilisé de la manière la plus complète possible, sans définir de paramètres empiriques qui devraient être, par exemple, fittés depuis des données expérimentales. Finalement, l'algorithme est accéléré de plusieurs ordres de grandeur en utilisant des réseaux de neurones artificiels (RNA), entraînés à prédire les énergies de migrations des défauts ponctuels en fonction de leur environnement atomique local.

Le nouvel algorithme MCCA est utilisé avec succès pour simuler des expériences de recuits (pour lesquels une seule lacune doit être introduite dans la boîte), afin de valider le modèle grâce à une comparaison directe de ses prédictions avec des résultats expérimentaux trouvés dans la littérature. Une comparaison très satisfaisante est accomplie pour deux alliages modèles importants pour la science des matériaux nucléaires. Dans les deux cas, l'évolution avec le temps de recuit du rayon moyen des précipités formés, ainsi que de leur densité, est en très bonne adéquation avec les mesures expérimentales trouvées dans la littérature, contrairement à ce que d'autres auteurs avaient jusqu’à présent réussi. Ensuite, l'algorithme est généralisé avec succès afin de permettre l'introduction d'un grand nombre de lacunes, ce qui est un des deux ingrédients nécessaires pour la simulation des effets de l'irradiation de neutrons dans les métaux. Cet accomplissement permet la simulation de processus longs et complexes, par exemple le calcul de coefficients de diffusions et temps de vies d'amats de cuivre-lacunes, qui sont des paramètres d'entrée nécessaires pour des modèles de simulation à gros-grains. Finalement, des preuves convaincantes sont apportées que l'algorithme MCCA peut être, dans un futur proche, généralisé d'avantage et permettre la prise en compte des interstitiels, ouvrant ainsi la voie vers la simulation de cycles complets d'irradiation.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Philosophiae Doctor - PhD
Titanium oxynitride has attracted research interest for the fact that it is a bioactive non-toxic material. It is suitable for surface coating of biomaterials and in other applications such as anti-reflective coatings, while oxygen-rich titanium oxynitride has been applied in thin film resistors and photocatalysis. Two common types of titanium oxynitrides are TiOₓNᵧ. and TiO₂-ₓNᵧ. In this work, titanium mixed metals oxynitrides (Ti-TiO₂, Mg-TiO₂ and Mg-Sn-TiO₂) were synthesized for the first time using ball milling (BM) and annealing processes. Their structural, morphological, surface, optical, and gas sensing properties were studied in detail. Structural analyses showed that upon milling a pure TiO₂ phase, tetragonal to orthorhombic phase transformation occurred. However, when milling TiO₂ mixed with Mg, Sn and Ti no evidence of the transformation was observed. Furthermore, scanning electron microscopy, transmission electron microscopy and atomic force microscopy showed that the milling process promotes particle refinement. The gas sensing analyses also demonstrated that the sensing response of the TiO₂, Mg-TiO₂ and Mg-Sn-TiO₂ materials improved upon milling. Moreover, the Mg-TiO₂ showed improved sensing compared to pure TiO₂ due to incorporation of Mg, which might have resulted in a decrease of charge carrier concentration. The Mg-TiO₂ sensing materials showed fast response-recovery time of ~32 s and ~48 s, respectively, as well as high selectivity to NH₃ gas compared to other gases (H₂, and CH₄). In addition, the improved response observed for the milled samples is due to increased surface area and pore diameter, providing more active sites for the target gas and allowing more gas adsorption with an increase in point defects related to oxygen vacancies (Vo), which are the most favorable adsorption sites for oxygen species and thus can enhance the possibility of interaction with gas molecules. A combination of photoluminescence, x-ray photoelectron spectroscopy, vibrating sample magnetometer and sensing analyses demonstrated that a direct relation exists between the magnetization, sensing and the relative occupancy of the Vo present on the surface of TiO₂ nanoparticles. Therefore, based on these finding we conclude that the milling process promotes particle refinement, resulting in an increased BET surface and partial breaking of Ti–O bonds on the TiO₂ surface layer, which results in the formation of oxygen vacancies in the TiO₂ lattice, therefore anticipating improved sensing response.
National Research Foundation

With an aim to investigate methods to realise low thermal-budget fabrication of aluminium doped zinc oxide (AZO) and indium gallium zinc oxide (IGZO) thin films, a dual step fabrication process was studied in this research. Initially, an experimental programme was undertaken to deposit AZO and IGZO films by radio frequency (RF) magnetron sputtering with no external substrate heating and at a wide range of deposition parameters including oxygen to argon ratio, RF power, and sputtering pressure. Thereafter, the samples were subjected to post-depositing annealing in air at ambient temperature utilising the advantages of excimer laser annealing (ELA) with a pulsed krypton fluoride (KrF) excimer laser at different laser fluences and number of pulses. The electrical, structural, compositional, and optical properties of the fabricated samples were systematically investigated as a function of the fabrication (deposition and annealing) conditions. A range of thin film characterisation techniques was used including 4-point probe (4PP), Van der Pauw (VDP), Hall Effect, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Atomic-force microscopy (AFM), Energy-dispersive X-ray spectroscopy (EDX), and optical transmittance and reflectance spectroscopy. Sputter-deposition of AZO and IGZO at room temperature revealed that the electrical properties of the deposited films are profoundly controlled by the deposition conditions applied. Low sputtering pressure of 2 mTorr is desired to obtain the best quality materials. However, high RF power of 180 W (4 W/cm2) is required to produce AZO with enhanced crystallinity, high electron density, and thus low resistivity. While, moderate RF power of 50 W (1.1 W/cm2) is applied to produce amorphous IGZO films with moderate-to-high resistivity suitable for thin film transistors (TFTs). The oxygen to argon ratio is found to have the most significant impact on defining the electrical properties for both AZO and IGZO. The resistivity of IGZO films was dependant on their metallic composition which in turn is controlled by the deposition conditions. TFTs were fabricated on silicon substrates with 40 nm thick IGZO as the active layer deposited at room temperature and different growth conditions. TFT performance was largely affected by the active layer deposition conditions. TFTs with the optimised IGZO, deposited at 50 W and 2 mTorr of 2% oxygen to argon ratio, exhibited a field effect mobility of 0.67 cm2/Vs, an on/off current ratio of 5x105, a turn on voltage of -0.15 V, and a subthreshold swing S of 0.28 V/decade. Upon ELA, AZO showed a resistivity reduction which is shown to result from increasing both the free electron density and mobility. When the optimised as-deposited AZO, 180 nm thick deposited at 180 W and 2 mTorr of 0.2% oxygen to argon ratio, annealed with 5 pulses at 125 mJ/cm2, a 50% resistivity reduction to 5x10-4 Ω.cm was obtained. It was demonstrated that average grain size increase, oxygen related defects decrease, and aluminium activation in doped ZnO are the origin of the AZO resistivity reduction upon ELA. Rapid thermal annealing (RTA) was also examined on AZO; RTA in nitrogen at 300°C for 20s increased the AZO gain size and doping efficiency leading to similar resistivity reduction to that achieved by the optimised ELA. Both ELA and RTA enhanced the AZO visible transmission to > 85 %, while the near infrared transmission was degraded due to higher electron density after annealing. The electro-optical properties of the optimised AZO samples obtained by ELA and RTA, which are very close to those of standard tin doped indium oxide (ITO), demonstrate the viability of AZO as an attractive transparent conducting material for various electronic applications. The potential use of AZO for photovoltaics (PVs) as well as the AZO stability against damp heat exposure were also examined. PVs with optimised ELA and RTA treated AZO samples showed comparable power conversion efficiency (PCE) to that of PVs with high-quality commercial ITO. The damp heat stability of AZO samples was strongly dependant on the fabrication conditions. In regard to IGZO, ELA increased the free electron density and mobility leading to better conductivity, while the amorphous structure is maintained. ELA with single pulse at a low energy density of 30 mJ/cm2 resulted in an improved performance for IGZO TFTs on silicon substrates achieving a field effect mobility of 3.33 cm2/Vs, an on/off current ratio of 3x107, a turn on voltage of +0.35 V, and a subthreshold swing S of 0.27 V/decade. Moreover, ELA was successfully applied to IGZO TFTs on polymer flexible PEN leading to TFTs with enhanced performance. Hence, a combination of RF magnetron sputtering at room temperature and ELA, which are both efficiently applicable to thin films mass production, has been demonstrated to provide a low thermal budget fabrication route for functional materials including AZO, as the most promising substitute to ITO in a wide range of applications, and IGZO as the most attractive material for TFT applications. This combination is an alternative thin film fabrication route to using elevated substrate temperature or post-deposition thermal annealing typically applied in the dominant literature reports, to obtain thin films with suitable characteristics.

Los materiales conocidos como vidrios metálicos han sido sujeto de estudio e todo el mundo desde los años 50, por el cual se ha conseguido un progreso importante en el entendimiento del comportamiento de estos materiales. Como el nombre sugiere, son aleaciones metálicas amorfas en las que no existe el orden a largo alcance. La ausencia de este tipo de orden les dota de propiedades físicas, químicas y mecánicas que son únicas comparadas con las de otros materiales metálicos convencionales.
Sin embargo, los primeros sistemas amorfos fueron obtenidos por técnicas de solidificación rápida, y requerían velocidades de enfriamiento criticas de hasta 106 K s−1. Por consiguiente, se obtenían cintas finas con un espesor limitado hasta unas decenas de micrómetro. Unos treinta a cuarenta años más tarde, una gama de aleaciones multicomponentes, las cuales requiren velocidades de enfríamiento más lentas, fueron desarrolladas, lo cual significó el nacimiento de los vidrios metálicos macizos. Entre estas aleaciones multicomponentes, las que son a base de Zr han sido protagonistas por su capacidad extraordinaria de formar vidrios. Por el mismo, se hicieron como aleaciones modelo para el estudio de propiedades fúndamentales y comportamientos característicos.
Su límite de fluencia excepcionalmente alto, cerca del límite teórico, les proporciona a los vidrios metálicos macizos un potencial para ser utilizados en aplicaciones estructurales. Desafortunadamente, la deformación plástica a temperatura ambiente occure de una manera muy localizada en bandas de cizalladura. En vez de endurecimiento mécanico, los vidrios metálicos sufren un ablandamiento al deformarlos lo cual impide una deformación plástica estable. Así que, a pesar de su límite de fluencia alto, la ruptura occurirá después de una deformación macroscópica limitada. Este mecanismo de deformación inhomogénea a temperatura ambiente limita la fiabilidad de los vídrios metálicos macizos en aplicaciones estructurales. Lógicamente, la mejora de la plasticidad de estos materiales ha sido ampliamente estudiada durante la última década.
El concepto más explorado para evitar la ruptura catastrófica ha sido probablemente el desarollo de una microestructura heterogenea con una segunda fase. Ésta segunda fase puede tener dimensiones tanto a escala micrómetra como la escala nanométrica y puede ser tanto una fase cristalina como una fase amorfa. Varias rutas han sido probadas para obtener ésta segunda fase en la matriz amorfa: añadir directamente una fase reforzante al material fundido, diseñar una composición adecuada que resulta en un material compuesto al solidificarla o precipitar la segunda fase durante un tratamiento térmico después de colar.
Por tratamientos térmicos por debajo de la temperatura de transición vidria, cambios del orden topológico y químico a corto alcance han sido observado en la literatura. El primer efecto suele deteriorar la plasticidad por relajación de la estructura amorfa. La influencia del cambio de orden químico a corto alcanze se ha estudiado en muy poco detalle. Aparte de los tratamientos térmicos, los tratamientos mecánicos pueden inducir cambios estructurales y microestructurales. El estudio del efecto de estos dos tratamientos forma la parte parte de esta tesis.
Los cambios en el orden topólogico y químico de corto alcance de vídrios metálicos a base de Zr, inducidos por tratamientos térmicos y mecánicos, han sido caracterizados por técnicas de calorimetría, difracción de rayos-X y por microscópia electrónica. Luego, la influencia de estos mismos en el comportamiento mecánico de los vídrios se ha estudiado por tests de compresión y de nanoindentación.
Sin embargo, en la primera parte de ésta tesis, se demuestra que al aplicar la técnica de nanoindentación, se debería tomar en cuenta la existencia de un "size-effect", correlacionado directamente con los cambios estructurales que occuren durante la deformación. Este "size-effect" implica que la dureza y el módulo elástico bajan al aumentar la profundidad de la indentación, similar a lo que se observa normalmente para materiales cristalinos. Durante la deformación, aumenta el volumen libre del vídrio metálico. Este crecimiento del volumen libre influirá en la respuesta del material a la nanoindentación. En particular, se observa un ablandamiento dinámico cuando se aplican cargas elevadas al material. Además, concentraciones más altas de volumen libre en el estado inicial después del colado, ocasionan un ablandamiento mayor y por consecuencia, aumentan el "size-effect".
Después, se hizo un estudio sistemático de los cambios de corto y medio alcance, inducido por tratamientos térmicos, en particular por tratamientos a baja temperatura. Aplicando varias técnicas de caracterización, como por ejemplo la calorimetría, difracción de rayos X y microscopía electrónica, cambios importantes de orden quimico han sido observados. Ya durante tratamientos cortos a baja temperatura, se formaban clústers de Cu en una matriz con un contenido de Cu reducido. Más adelante, el estudio se enfocó en la influencia de los cambios microestructurales en las propiedades mecánicas. Aunque los cambios observados eran moderados, su influencia en el comportamiento mecánico, y en particular en la plasticidad en compresión, es enorme cuando los cambios topológicos son todavía moderados (como es el caso durante el tratamiento térmico a baja temperatura). La plasticidad aumenta significativamente, lo que va en contra a la fragilización que suele ocurrir durante los tratamientos térmicos. Durante tratamientos a temperaturas más elevadas, los cambios topológicos empiezan a dominar (disminución del volumen libre) y forman un contrapeso para el efecto positivo de los cambios del orden químico a corto alcance. Posteriormente, se investigó en más detalle la influencia de los cambios de orden químico en la cristalización. Los clústeres de Cu que se forman durante el calentamiento se puede interpretar como fases embrionarias en el proceso de cristalización.
Durante los tratamientos térmicos, se dan tanto cambios de orden topológico como de orden químico, pero tienen un efecto contradictorio en la plasticidad por lo cual puede ser difícil controlarlos. Sin embargo, los cambios beneficiosos de orden químico se pueden obtener por tratamientos mecánicos de deformación severa, por ejemplo por torsión a alta presión (TAP). La deformación no causa una reducción del volumen libre sino la aumenta incluso más. Además, TAP produce una muestra maciza bastante homogenea siempre y cuando el número de revueltas sea menor, lo que es lo contrario de lo que se sabe para materiales cristalinos. Estos materiales suelen requerir más vueltas para evitar una microestructura heterogenea.
Metallic glasses have been the subject of widespread research since the 1950's with significant progress in the understanding in their behavior. As the name suggests, they are amorphous metallic alloys, i.e. with the absence of long-range order. The absence of this long-range order offers them unique physical, chemical and mechanical properties compared to conventional metallic materials.
However, the early amorphous systems were obtained typically by rapid quenching techniques, with critical cooling rates up to 106 K s−1, resulting typically in ribbons or thin foils with a thickness limited to a few tens of micrometer. About thirty to forty years later, a large range of multicomponent alloys was developed which required significant lower critical cooling rates leading to the birth of so-called bulk metallic glass (BMG). Among these multicomponent systems, Zr-based alloys have been key players with outstanding glass forming ability, which has made them to model alloys for the study of fundamental properties and characteristic behaviors.
The exceptionally high yield strength, close to the theoretical limit, and yield strain of these amorphous metallic systems in bulk offer them potential for structural applications. However, plastic deformation at room temperature occurs in a highly localized manner by the formation of a few shear bands. Instead of work hardening, metallic glasses soften upon deformation, which prevents stable plastic elongation. Although BMGs possess a high fracture strength, once yielding has set in, early failure after a small percentage of macroscopic deformation appears. This inhomogeneous deformation mechanism at ambient temperature still limits the reliability of BMGs for structural applications. Logically, the enhancement of ductility of this type of materials has been the subject of many research works in the last decade.
Probably the most explored concept to avoid catastrophic failure has been the development of a heterogeneous microstructure, with a second phase on different length scales, both crystalline and amorphous. Various routes have been tried out to obtain this second phase in the amorphous matrix: physically adding a reinforcing phase to the melt, by direct precipitation from the melt of a properly designed composition or by (partial) nano-crystallization of the glass after casting.
Upon annealing below the glass transition, changes in both topological and chemical short range order have been reported. The former is believed to deteriorate plasticity due to structural relaxation of the amorphous structure.
The effect of changes of the chemical short range order on plasticity has hardly been studied into detail. Besides annealing, deformation has been reported to induce structural and microstructural changes. These (micro-)structural changes, induced by annealing and deformation, form the main topic of the work presented in this thesis.
Topological and chemical changes in the short range order of Zr-based bulk metallic glasses upon annealing and deformation treatments have been characterized by calorimetry, X-ray diffraction and electron microscopy. The influence of these changes on the mechanical behavior of these glasses was investigated through compression tests and nanoindentation tests.
However, in a first part of this thesis, it is shown that one should be aware when applying this technique of the existence of a so-called size-effect, directly linked with the structural changes upon deformation.
A decrease of hardness and elastic modulus on the maximum penetration depth was found, similar as what is typically observed for crystalline materials. Upon deformation, free volume typically increases. Due to this increase, free volume will influence the response of the material during nanoindentation testing. In particular, a dynamic softening is observed when being plastically deformed at higher loads. Larger free volume concentrations in the as-cast state result in enhanced mechanical softening and, concomitantly, more pronounced indentation size effects.
Afterwards, a systematic study on changes on the short and medium range order upon annealing was performed, in particular at low temperatures. By means of various characterization techniques, like by calorimetry, X-ray diffraction and electron microscopy, important changes in chemical ordering were found, with the formation of Cu-clusters in a more Cu-depleted matrix, already upon low temperature annealing for a short time. In a next step, the study focussed on the influence of this altered microstructures on the mechanical properties. Although the (compositional) changes observed were moderate, their influence on the mechanical behavior, and in particular plasticity under compression, is great, when the topological changes are still moderate (low temperature annealing). Plasticity is enhanced greatly, in large contrast to the generally assumed embrittlement upon annealing. A too large increase in topological short range order (free volume decrease) counterbalances the effect induced by the chemical short range order upon high temperature annealing. Finally, the influence of these changes of chemical short-range order on the crystallization behaviour was studied in more detail. The formation of the Cu-rich clusters upon annealing can thus be understood as a very embryonic phase towards crystallization.
Upon annealing, topological (densification) and chemical ordering occur simultaneously, but these processes have a contradictory effect on plasticity and it might be difficult to control them. Therefore, it is interesting that the beneficial changes in chemical ordering can be achieved also upon high-deformation treatments, e.g. by high-pressure torsion (HPT). Deformation does not lead to the adverse reduction of free volume but even produces some more. HPT itself is able to produce a rather homogeneous bulky sample, in particular for a low amount of revolution - contrary to what is observed in crystalline materials, where more revolutions are necessary to overcome the undesired inhomogeneous microstructure.

Magnetic nanoparticle assemblies were obtained using thermal annealing of thin Co films (initial effective film thickness 1,5-1,8 nm), condensed by thermal evaporation on Si3N4/Si substrates. After condensation samples were annealed (T = 1020 K) in vacuum (residual gas pressure P = 10 – 7 Pa).

Metal-semiconductor contacts have been widely studied in the past 60 years. These structures are of importance in the microelectronics industry. As the scaling down of silicon-based complementary metal-oxide-semiconductor (CMOS) devices becomes more and more challenging, new material and device structures to relax this physical limitation in device scaling are now required. Germanium (Ge) has been proposed as a potential alternative to silicon. In this thesis a systematic study of the thermally induced reaction of transition metals with the n-Ge substrate is outlined. Investigations in the change of the electrical properties of the metal germanide structures is studied in a wide range of temperatures. Current-voltage (I-V), capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and high-resolution Laplace-DLTS (L-DLTS) techniques have been used for the electrical characterization of the fabricated Schottky contacts. Results obtained indicate the variation of the electrical properties of these Schottky contacts can be attributed to combined effects of interfacial reactions and phase transformation during the annealing process. The barrier height distribution in identically prepared Schottky contacts on n-Ge (100) showed that the barrier heights and ideality factors varied from diode to diode even though they were identically fabricated. The properties of the n-Ge Schottky contacts have revealed a strong dependence on temperature. The current transport mechanism has been shown to be predominantly thermionic emission at high temperatures while at low temperatures, the Schottky contacts have exhibited the dominance of the generation-recombination current mechanism. The variation of the Schottky barrier heights at low temperatures have been attributed to barrier inhomogeneities at the metal-semiconductor (MS) interface. Results from defect characterization by DLTS show that the E-centre is the dominant defect introduced in n-Ge by electron beam deposition during contact fabrication and substitutional related defects are induced during the annealing process. The identification of some of the defects was achieved by using defect properties, defect signature, annealing mechanisms and annealing behaviour and comparing these properties to the results from theoretical defect models. Annealing showed that defects in Ge can be removed by low thermal budget of between 250–350°C. Finally, structural characterization of these samples was performed by scanning electron microscopy (SEM) and Rutherford backscattering spectrometry (RBS) techniques. From the SEM images it can be observed that the onset temperature for agglomeration in the 30 nm Ni/n-Ge (100), and Pt/-, Ir/- and Ru/n-Ge (100) systems occur at 500–600°C and 600–700°C, respectively.
Thesis (PhD)--University of Pretoria, 2011.
Physics
unrestricted

Thesis (Ph.D.)--Worcester Polytechnic Institute.
Keywords: composite Pd and Pd/Ag membranes, alloying, Pd/Ag barrier, intermetallic diffusion, bi-metal multi-layer BMML deposition, electroless plating kinetics, high temperature x-ray diffraction, aluminum hydroxide surface grading, porous sintered metal supports, hydrogen separation. Includes bibliographical references (leaves 279-296 ).

In this thesis we report on the metal-mediated-thermally induced changes of the structural and optical properties of hydrogenated amorphous silicon deposited by hot-wire CVD, where aluminium and nickel were used to induce crystallization. The metal-coated amorphous silicon was subjected to a thermal annealing regime of between 150 and 520°
C. The structural measurements, obtained by Raman spectroscopy, show partial crystallization occurring at 350 °
C. At the higher annealing temperatures of 450°
C and 520°
C complete crystallization occurs. Reflection and transmission measurements in the UV-visible range were then used to extract the optical properties. By adopting the effective medium approximation a single optical model could be constructed that could successfully model material that was in different structural phases, irrespective of metal contamination. Changes in the absorption of the material in various stages of transition were confirmed with a directly measured absorption technique, and the modelled absorption closely followed the same trends This study forms part of the larger overall solar cell research project, of which the primary aim is to eventually develop a silicon solar panel that optimises the characteristics for best performance.

Deformation and annealing texture in the cold rolled low carbon steels is important for sheet metal forming operations and service performance. The aim of this study is to non-destructively investigate the effect of texture on magnetic anisotropy. Various samples having different textures and residual stress states, due to different % reduction in thickness, annealing and stress relieving treatment, were prepared. Texture maps were obtained by Magnetic Barkhausen noise measurements performed with 100 steps between the ranges of 00-3600 on the surface. Microstructure investigation by optical &
scanning electron microscopy
hardness and tension tests were performed
and texture was determined by X-Ray diffraction method. The results were compared, evaluated and discussed to establish relationship between texture and magnetic Barkhausen Noise emission.

>Magister Scientiae - MSc
Solar cells offer SA an additional energy source. While Si cells are abundantly available they are not at an optimal efficiency and the cost is still high. One technology that can enhance their performance is SiNW. However, material properties such as the diameter, porosity and length determine their effectiveness during application to solar cell technology. One method of growing SiNW uses Sn catalysts on a Si substrate. As the properties of the Sn nanoparticle govern the properties of the SiNW, this thesis investigates their formation and properties by depositing a Sn layer on a Si wafer and then subjecting it to different temperatures, during process the layer forms into nanoparticles. At each temperature the morphology, composition and crystallinity will be determined using XPS, SEM, TEM and EDS. Thus, in Chapter 1 there is an overview, Chapter 2 deals with techniques used in this study, Chapter 3 will give the quantitative and qualitative results on the XPS analysis and Chapter 4 will illustrate the structural behaviour of the annealed Sn film samples.

Metal oxide thin films serve as critical components in many modern technologies, including microelectronic devices. Industrial state-of-the-art production utilizes vapor-phase techniques to make high-quality (dense, smooth, uniform) thin film materials. However, vapor-phase techniques require large energy inputs and expensive equipment and precursors. Solution-phase routes to metal oxides have attracted great interest as cost-effective alternatives to vapor-phase methods and also offer the potential of large-area coverage, facile control of metal composition, and low-temperature processing. Solution deposition has previously been dominated by sol-gel routes, which utilize organic ligands, additives, and/or solvents. However, sol-gel films are often porous and contain residual carbon impurities, which can negatively impact device properties. All-inorganic aqueous routes produce dense, ultrasmooth films without carbon impurities, but the mechanisms involved in converting aqueous precursors to metal oxides are virtually unexplored. Understanding these mechanisms and the parameters that influence them is critical for widespread use of aqueous approaches to prepare microelectronic components. Additionally, understanding (and controlling) density and composition inhomogeneities is important for optimizing electronic properties. An overview of deposition approaches and the challenges facing aqueous routes are presented in Chapter I. A summary of thin film characterization techniques central to this work is given in Chapter II. This dissertation contributes to the field of solution-phase deposition by focusing on three areas. First, an all-inorganic aqueous route to high-κ metal oxide dielectrics is developed for two ternary systems. Chapters III and IV detail the film formation chemistry and film properties of lanthanum zirconium oxide (LZO) and zirconium aluminum oxide (ZAO), respectively. The functionality of these dielectrics as device components is also demonstrated. Second, the impact of steam annealing on the evolution of aqueous-derived films is reported. Chapter V demonstrates that steam annealing lowers processing temperatures by effectively reducing residual counterion content, improving film stability with respect to water absorption, and enhancing dielectric properties of LZO films. Third, density and composition inhomogeneities in aqueous-derived films are investigated. Chapters VI and VII examine density inhomogeneities in single- and multi-metal component thin films, respectively, and show that these density inhomogeneities are related to inhomogeneous metal component distributions. This dissertation includes previously published coauthored material.

Mise en evidence d'un nouvel ensemble de raies dans le spectre de photoluminescence du silicium recuit a 600**(o)c pendant une centaine d'heures. Observation d'energie de localisation faible et d'une raie a zero phonon. Proposition d'un modele prenant en compte les variations de potentiel aux interfaces entre les precipites d'oxygene generes par le recuit et le substrat

Etude de l'effet getter au voisinage des surfaces de silicium bicristallin. Caracterisation des especes segregees a la surface par spectrometrie electronique auger permettant de connaitre les concentrations atomiques et les liaisons chimiques existant entre atomes. Analyse des trois facteurs principaux d'effet getter: role d'une couche d'oxyde; role des recuits thermiques, role d'une impurete a grande diffusivite, l'or

Etude des effets de dopage par implantation de bore et de phosphore. Etude du role des defauts d'irradiation dans des couches implantees au silicium. Les couches implantees et non implantees sont cristallisees en phase solide par recuit thermique a basse temperature. Etude de la taille des grains, de la texture, de la morphologie de surface et de la conductivite electriques des couches en fonction de la concentration d'ions implantes

Etude de la degradation de la surface plane si(111) par implantation d'ions ar**(+) a temperature ambiante. Lorsque la dose d'ions implantes augmente, l'intensite des taches du diagramme de diffraction diminue progressivement et les marches atomiques, observees en microscopie electronique par reflexion, disparaissent. Lorsque l'energie incidente des ions ar**(+) augmente, la vitesse de degradation de la surface diminue. Apres disparition complete des marches atomiques, un recuit thermique "in situ" de quelques minutes a 575**(o)c permet de retrouver la topographie de la surface initiale. Le recuit provoque la desorption complete de l'argon implante et de retour en sites des atomes de la surface

Etude quantitative , par la methode ebic, de la recombinaison des porteurs minoritaires dans des bicristaux de silicium en fonction des traitements thermiques, entre 450 et 950**(o)c. Un developpement des phenomenes physiques regissant la creation de differentes theories conduisant au traitement quantitatif du signal ebic est presente. Selon le traitement thermique, le contraste des deux types de joints de grains evolue avec la temperature: vitese de recombinaison et longueur de diffusion varient avec la temperature de recuit

Etude des mecanismes d'interaction joint de grain dislocations lors de la deformation du bicristal, mettant en evidence la dissociation des dislocations entrant dans le joint, leur perte d'identite et l'interaction entre eux des residus. Determination des structures des dislocations residuelles. Apparition de precipites lors du recuit du bicristal deforme

L’industrie microélectronique est régie depuis plusieurs années par la loi de miniaturisation. En particulier, en technologie CMOS, les procédés de fabrication de l’oxyde permettant l’isolation électrique entre les transistors nécessitent sans cesse d’être améliorés pour répondre aux défis de cette loi. Ainsi, on est passé du procédé d’isolation par oxydation localisée de silicium (LOCOS) au procédé d’isolation par tranchées (STI). Cependant, ce dernier a montré pour les technologies en développement des limitations liées au remplissage non parfait par la silice de tranchées de moins en moins larges (Voiding) et au ‘‘surpolissage’’ des zones les plus larges (Dishing). Le procédé FIPOS (full isolation by porous oxidation of silicon) a été donc proposé comme solution alternative. Il est basé sur la formation sélective et localisée du silicium poreux qui est transformé ensuite en silice par un recuit oxydant. Cette piste prometteuse a constitué le point de départ de ce travail. Dans ce contexte, la thèse s’est focalisée sur deux axes principaux qui concernaient d’une part la maîtrise du procédé d’anodisation électrochimique pour la formation du silicium poreux et d’autre part l’optimisation du procédé d’oxydation. Dans une première partie de notre travail, l’analyse des caractéristiques courant-tension I-V menée sur le silicium durant son anodisation électrochimique a permis de montrer que la formation du silicium poreux dépend fortement de la concentration en dopants. Cette propriété nous a permis de développer une technique simple d’extraction du profil de dopage dans le silicium de type p par voie électrochimique. On a montré que la résolution en profondeur de cette technique est liée au niveau du dopage et s’approche de celle du SIMS (spectroscopie de masse d'ions secondaires) pour les fortes concentrations avec une valeur estimée à 60 nm/décade. Dans une deuxième partie, nous avons mis en évidence la formation localisée du silicium poreux oxydé. En effet, un choix judicieux du potentiel d’anodisation permet de rendre poreux sélectivement des régions fortement dopées implantées sur un substrat de silicium faiblement dopé. Ces régions sont ensuite transformées en oxyde par un recuit oxydant. Par ailleurs, les conditions optimales des processus d’oxydation et d’anodisation permettant d’obtenir un oxyde final de bonne qualité diélectrique sont analysées
The microelectronic industry is still ruled up to now by the law of miniaturization or scaling. In particular, in CMOS (complementary metal-oxide semiconductor) technology, the oxide allowing electric isolation between p- and n-MOS transistors has also been scaled down and has then exhibited different technological processes going from LOCOS (local oxidation of silicon) to STI (shallow trench isolation) and arriving to FIPOS (full isolation by porous oxidation of silicon). The latter seems to be the most promising alternative solution that can overcome actual limitations of voiding and dishing encountered in the STI process. The approach, which is based on selective formation of porous silicon and its easy transformation to silicon dioxide, has aroused our motivation to be well studied. In this context, the PhD project has first focused on the understanding of electrochemical porous silicon formation, and then on the study of porous silicon oxidation. In a first part of our work, we emphasize the dependence of porous silicon formation with the silicon doping concentration through the investigation of current-voltage I-V characteristics measured on p- and n-type silicon electrodes during electrochemical anodization. Taking advantage of this dependence, we have developed a very simple electrochemical method allowing an accurate determination of doping profiles in p-type silicon. It has been shown that the depth resolution of the technique is readily linked to the doping level and it approaches that of the secondary ion mass spectroscopy (SIMS) analysis for high doping concentrations with an estimated value of 60 nm/decade. In a second step, we highlight the selective formation of oxidized porous silicon. In fact, with a correct choice of the applied potential during anodization, only highly doped regions implanted on a lightly doped silicon wafer are preferentially turned into porous silicon and subsequently oxidized. Furthermore, we give the optimum conditions for oxidation and anodization processes which result in an insulating oxide of reliable dielectric properties

This report collects selected outstanding scientific and technological results obtained within the frame of the European project "FLASiC" (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.

Abstract The qualitative and quantitative characteristics of each component layer constituting the structure of organic bulk heterojunction solar cells (OSC-BHJ) contribute significantly towards its overall performance. One of the prevalent issues resulting in reduced device efficiency is due to the conformational inhomogeneities in the active and buffer layers. The mechanical stress, extended thermal exposure and presence of mutually reactive component layers etc., affects negatively on the device stability. Effective methods to address these issues will be extensively benefited by the industry since the current commercialisation of the technology is hindered owing to the lower efficiency and stability of these devices. This dissertation focuses on methods to coherently enhance the performance and longevity of the OSC-BHJ devices. The efficiency enhancements of the devices in this work were achieved through two main routes. The first route was through morphological improvement of the active layer. The second route was through boosting the electrical characteristics of hole transporting conducting polymer layer (HTL) by controlled annealing conditions. The introduction of a suitable additive in the active layer was found to reduce unfavourable phase segregation thus resulting in enhanced morphology. Further, the annealing conditions in different atmospheres (air, nitrogen and vacuum) were found to have a clear influence on the optimum functioning of the HTL in the device. Regarding the stability improvement study done in this work, a method of employing suitable interlayer was developed to effectively abate the internal degradation occurring in the device due to etching reaction on the indium tin oxide (ITO) anode by the HTL. Moreover, experimental investigations were carried out for drawing fundamental understanding of stability degenerating issues such as the influence of mechanical defects on transparent conducting metal oxide (ITO) anode on the performance of the device and heat induced degradations in the low band gap polymer-fullerene active layer. The highlight of this research is that the discovered methods are inexpensive, efficient, and easy to adopt. The results of the study could help the technology to overcome some of its limitations and accelerate its progress towards commercialisation
Tiivistelmä Orgaanisten heteroliitosaurinkokennojen kerrosrakenteen ominaisuudet ja laatu vaikuttavat merkittävästi aurinkokennojen toiminnallisuuteen. Erityisesti rakenteelliset epähomogeenisuudet aktiivi- ja puskurikerroksissa heikentävät kennon hyötysuhdetta. Kennojen stabiilisuutta tarkasteltaessa myös mekaanisella rasituksella, pitkittyneellä lämpöaltistuksella ja materiaalien reagoinneilla keskenään kerrosten välillä, on selkeä negatiivinen vaikutus kennojen stabiilisuuteen. Orgaanisen aurinkokennoteknologian kaupallistamisen rajoitteina ovat kennojen heikko hyötysuhde ja stabiilisuus, joten menetelmät jotka tarjoavat ratkaisuja edellä mainittuihin ongelmiin, ovat erittäin tärkeitä teknologiaa kaupallistavalle teollisuudelle. Tämä väitöskirja keskittyy johdonmukaisesti selvittämään tapoja, joilla voidaan parantaa heteroliitosaurinkokennojen hyötysuhdetta ja elinikää. Hyötysuhteen tehostamiseksi valittiin kaksi eri lähestymistapaa, joista ensimmäisessä keskityttiin aktiivikerroksen morfologian parantamiseen ja toisessa aukkoja kuljettavan kerroksen sähköisten ominaisuuksien parantamiseen lämpökäsittelyprosessin avulla. Sopivan lisäaineen avulla aktiivikerroksen ei-toivottua kiteytymistä voidaan pienentää ja parantaa näin kerroksen morfologiaa. Lisäksi työssä todettiin, että lämpökäsittelyn aikaisella ympäristöolosuhteella (ilma, typpi, tyhjiö) on merkittävä vaikutus puskurikerroksen optimaaliseen toimintaan aurinkokennossa. Stabiilisuuden parantamiseksi kehitettiin välikerroksen hyödyntämiseen perustuva menetelmä, jolla voidaan tehokkaasti vähentää kennojen sisäisessä rakenteessa tapahtuvaa toiminnallisuuden heikkenemistä, joka aiheutuu aukkoja kuljettavan kerroksen syövyttävästä vaikutuksesta indiumtinaoksidi (ITO) pohjaiseen anodiin. Tämän lisäksi työssä tutkittiin kokeellisesti stabiilisuuteen heikentävästi vaikuttavia tekijöitä, kuten mekaanisen rasituksen aiheuttamia vaurioita metallioksidi (ITO) anodissa ja lämpöaltistuksesta aiheutuvia vikoja polymeeri-fullereeni rakenteeseen perustuvassa aktiivikerroksessa. Tutkimuksen keskeisin tulos on, että esitellyt keinot aurinkokennojen hyötysuhteen ja stabiilisuuden parantamiseen ovat edullisia, tehokkaita ja helppoja hyödyntää. Tulokset voivat merkittävästi edistää orgaanisten aurinkokennojen teknistä kehitystä ja kiihdyttää niiden tuloa kaupallisiksi tuotteiksi

This report collects selected outstanding scientific and technological results obtained within the frame of the European project "FLASiC" (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.

Presentation d'une methode de calcul de la distribution des defauts nes par implantation ionique dans une cible cristalline et inventaire des modeles decrivant la transition cristal amorphe par implantation ionique. Il est montre comment ces travaux theoriques peuvent etre adaptes a la localisation de couches amorphes continues grace a ce calcul de la distribution de defauts. Etude par microscopie electronique en transmission de l'amorphisation a temperature ambiante de si et etude par microscopie electronique par reflexion de la degradation de surfaces atomiquement planes de si par implantation de gaz rares

Etude des variations de l'effet hall dans les rubans amorphes en effectuant des substitutions sur un ruban proche du metglas 260553 en fonction de leurs compositions et de leur temperature. Determination a temperature ambiante des constantes de hall extraordinaires et des resistivites en l'absence d'induction. Extrapolation des valeurs des temperatures de curie et des constantes de hall ordinaires. Mesures des constantes de hall extraordinaires apres recuit. Le mecanisme du saut lateral semble etre preponderant et un rearrangement des atomes aurait lieu durant le recuit

Caracterisation de couches minces cozr et co(zr,nb) deposes par pulverisation cathodique en radio-frequences. Etude de l'anisotropie developpee aux faibles et fortes pressions de depot. Discussion relative a l'origine de ces anisotropies. Etude du controle de la direction et de l'intensite du champ d'anisotropie par application de recuits sous champ magnetique tournant suivis de recuits sous champ magnetique fixe

Dans ce travail nous avons etudie experimentalement l'evolution des microstructures et des contraintes internes au cours de la restauration des alliages al-mg. Nous avons etudie une large gamme de deformation par laminage a froid et une gamme de temperature de recuit de restauration qui nous ont permis de degager les grands mecanismes du processus ainsi que les evolutions microstructurales associees. Au niveau microstructural, nous avons employee des techniques traditionnelles telle que la microscopie electronique en transmission, ainsi que des mesures originales de l'evolution de l'energie stockee par calorimetrie, de la resistivite electrique, et de l'elargissement des pics de diffraction par rayons x. Ces dernieres techniques permettent de caracteriser au niveau mesoscopique les microstructures de dislocations. Parallelement, les proprietes mecaniques des alliages ont ete caracterisees avec des essais de traction (mesure de la limite d'elasticite et du durcissement d'ecrouissage), ainsi que par des tests de mise en forme (emboutissage et anisotropie de la limite d'elasticite des toles laminees). La modelisation des resultats experimentaux permet d'aborder des questions de fond de la plasticite: nous avons ainsi verifie la loi reliant la contrainte d'ecoulement a la racine carree de la densite de dislocations quelle que soit la microstructure. Pour decrire la restauration statique, nous avons mis en evidence l'importance du rayon de coupure des interactions elastiques qui constitue une grandeur mesoscopique pertinente pour decrire l'organisation des dislocations. Enfin une esquisse de l'approche du phenomene de restauration statique par le developpement d'une simulation numerique 3d des dislocations est donnee

Etude par mesure de resistivite electrique, de l'influence de la teneur en chrome sur la production et la migration des defauts ponctuels dans les alliages fe-25%ni-8 a 16%cr(% en poids) et fe-5 a 15%atcr soumis a une irradiation par electrons a 21k. Influence d'un recuit sur ces defauts d'irradiation. Interpretation des resultats par un modele de restauration

Rappel de généralités sur l'analyse de la diffusion diffuse dans le cas d'un alliage binaire. Description détaillée de l'appareillage. Présentation des résultats des mesures de diffusion diffuse sur l'échantillon Au(70)Cu(30) recuit près de la température de transition ordre-désordre. Mesures de la résistivité et de l'allongement sous contrainte axiale, par diffusion diffuse. Etudes à partir de ces mesures, des cinétiques de mise en ordre local dans les alliages Au(75)Cu(25), Au(70)Cu(30) et Au(65)Cu(35). Analyse du rôle des lacunes.

Détermination de la composition pour laquelle l'alliage nickel-argent devient amorphe et ferromagnétique, à partir de l'étude de l'effet Hall et de la structure par microscopie électronique. On montre que la température de Curie reste constante dans la phase désordonnée. Apparition d'une phase superparamagnétique au sein de la matrice initiale par recuits successifs

Etude des effets de l'implantation d'ions fers dans y::(3)al::(5)o::(12),gd::(3)ga::(5)o::(12) et y::(3)fe::(5)o::(12) par differentes techniques (microscopie electronique en transmission, retrodiffusion rutherford, diffraction rx). Les changements structuraux et les modifications des proprietes magnetiques dus a l'implantation sont etudies avant et apres recuit

Etude d'aimants frittés Sm (Co, Fe, Cu, Zr)(7,29) ayant subi des traitements thermiques différents. Mesure de la coercivité et observation de la microstructure par microscopie électronique en transmission. Corrélation entre les microstructures avant et après recuit a 830°C et les propriétés magnétiques, à partir d'un modèle basé sur la répartition des éléments d'addition