Il y a un énorme intérêt dans la construction de lasers à l'état solide capables d'atteindre les niveaux de petawatt (PW) et au-delà. Afin d'atteindre ce niveau de puissance, des amplificateurs Ti: Al2O3 d'un diamètre maximum de 20 cm ou plus sont nécessaires et il est donc nécessaire de développer des boules de cristaux Ti:Al2O3 de grand diamètre. Le procédé de croissance de Kyropoulos a été identifié par la société RSA le Rubis SA comme la technique la plus productive car elle permet de croître des cristaux massifs sous un faible gradient de température et donc de bonne qualité.La croissance de cristaux pesant environ 30 kg s'accompagne de complications qui affectent gravement la morphologie cristalline et donc sa qualité cristalline. Pour étudier les problèmes de morphologie, une étude détaillée de l'effet des paramètres de croissance a été réalisée en analysant le processus des cristaux cultivés dans l'installation industrielle. Les facteurs pour les problèmes critiques d'une formation de plaque plate et les zones refondues dans le cristal ont été identifiés et un ensemble idéal de paramètre pour le taux de tirage et le taux de croissance de masse a été proposé. Ceux-ci ont conduit à des améliorations marquées dans le volume productif du cristal et ont permis la croissance de cristaux avec des morphologies prévisibles.Pour aller plus loin, un système de croissance cristalline totalement autonome a été envisagé qui permettrait à l'opérateur de surveiller en temps réel la forme du cristal et de contrôler ses paramètres de croissance radiale. Ceci est basé sur la mesure in situ simultanée du poids cristallin et du niveau de liquide restant. Une étude mathématique est présentée pour expliquer la relation entre toutes les forces de pesage agissant sur le cristal en croissance et pour étudier la faisabilité de ce système de contrôle. On montre qu'il pourrait être utile pour la régulation du diamètre pendant la croissance de Kyropoulos.Les cristaux ont été caractérisés et contrôlés pour détecter les défauts qui affecteraient leurs propriétés optiques. Un tel défaut était la présence d'une bande translucide dans le cristal autrement transparent, appelé "défaut laiteux". La qualité cristalline en termes de densité de dislocation due à la déformation induite a été analysée en utilisant des techniques de diffraction des rayons X, ainsi que des caractérisations optiques et des analyses chimiques. Aidé du transfert de chaleur et des simulations numériques thermomécaniques du système de croissance, une explication de l'origine de ce défaut en termes de contrainte thermique agissant et de dynamique de croissance cristalline associée est proposée.Le dopage du titane dans le cristal de saphir est nécessaire pour l'application Laser, mais il y a ségrégation du dopant au cours de la croissance, ce qui conduit à une distribution inhomogène des cristaux développés, comme le montre la caractérisation optique de la distribution du titane dans ses états Ti3 + et Ti4 + . Des idées pour améliorer l'homogénéité des échantillons laser sont proposées. / There is a huge interest in construction of solid state lasers capable of reaching petawatt (PW) levels and beyond. In order to achieve this level of power, Ti:Al2O3 amplifiers up to 20 cm in diameter or larger are required and hence there is the need for the growth of large diameter Ti:Al2O3 crystal boules. The Kyropoulos growth process has been identified by the company RSA le Rubis SA as the most productive technique because it allows growing massive crystals under a low temperature gradient and hence of good quality.Growing crystals weighing about 30 kg comes with its share of complications which gravely affect the crystal morphology and hence its crystalline quality. To address the issues of morphology, a detailed study of the growth parameters effect was carried out by analysing the process of crystals grown in the industrial setup. The factors for the critical issues of a flat plate formation and re-melted zones in the crystal were identified and an ideal set of parameter for the pulling rate and mass growth rate was proposed. These led to marked improvements in the productive volume of the crystal and enabled growth of crystals with predictable morphologies.To take a step further, a completely autonomous crystal growth system was envisioned which would allow the operator live monitoring of the crystal shape and give control over its radial growth parameters. This is based on the simultaneous in situ measurement of crystal weight and remaining liquid level. A mathematical study is presented to explain the relationship between all the weighing forces acting on the growing crystal and to study the feasibility of this control system. It is shown that it could be useful for the diameter regulation during the Kyropoulos growth.Crystals were characterised and checked for defects which would affect its optical properties. One such defect was the presence of a translucent band in the otherwise transparent crystal, called “milky defect”. The crystalline quality in terms of dislocation density due to induced strain was analysed using X-ray diffraction techniques, along with optical characterisation and chemical analyses. Aided with heat transfer and thermo-mechanical numerical simulations of the growth system, an explanation for the origin of this defect in terms of acting thermal stress and associated crystal growth dynamics is proposed.Titanium doping in the sapphire crystal is needed for the Laser application, but there is segregation of the dopant during growth and this leads to an inhomogeneous distribution in the grown crystals, as shown by optical characterisation of the distribution of titanium in its Ti3+ and Ti4+ states. Ideas in order to improve the laser samples homogeneity are proposed.

Dans le domaine de la cristallisation des fibres monocristallines par la technique de la micro-pulling down (µ-PD), les résultats récents sur les performances des fibres monocristallines (optique, laser, scintillateur) ont montré l’étendue des champs d’applications ouverts aux fibres cristallines. La course à la croissance cristalline, la fabrication de fibres cristallines performantes et la maitrise des procédés sont des enjeux de recherche dans un nombre important de laboratoires à travers le monde. Les fibres monocristallines de saphir et du YAG dopées Cérium (Ce3+) sont des formats à forte valeur ajoutée. Elles sont susceptibles d’être utilisées dans un large domaine d’applications, d’où la nécessité de contrôler et de maitriser la technologie de fabrication. En fonction des conditions de tirage (gradient de température, orientations cristallographiques des germes, vitesses de tirage), nous nous sommes intéressés à l’étude des bulles et des contraintes résiduelles dans le saphir tiré par µ-PD. La ségrégation du Cérium et la propagation de la lumière ainsi que l’atténuation dans les fibres YAG-dopées Cérium (Ce3+) ont été étudiées en fonction des vitesses de tirage. Nous avons étudié tous ces phénomènes ainsi que les mécanismes mis en jeu. La variation de la vitesse de tirage est en corrélation avec la distribution des bulles, la ségrégation du Ce et l’atténuation. A travers ce travail, on est en mesure de dire que les phénomènes à l’origine de la présence, de la répartition des bulles dans les fibres saphir et la ségrégation du Cérium dans le YAG ont été significativement éclaircis et que, à partir de ces résultats, des améliorations peuvent être apportées aux procédés technologiques de tirage par µ-PD / In the field of crystallization of single crystal fibers by micro-pulling down (µ-PD) technique, the recent results on the performance of single crystal fibers (optical, laser, scintillator) have shown the wide range of applications open to crystalline fibers. The race for crystal growth, the manufacture of high-performance crystal fibres and process control are research challenges in a large number of laboratories around the world. Cerium-doped monocrystalline sapphire and YAG fibres (Ce3+) are high value-added formats. They are likely to be used in a wide range of applications, hence the need to control and master manufacturing technology. Depending on the growth conditions (temperature gradient, crystallographic orientations of the germs, growth speeds), we were interested in studying the bubbles and residual stresses in the sapphire pulled by µ-PD. The segregation of Cerium and the propagation of light as well as the attenuation in YAG-doped Cerium fibres (Ce3+) were studied as a function of growth speeds. We have studied all these phenomena and the mechanisms involved. The variation in the growth rate is correlated with the distribution of bubbles, the segregation of Ce and the attenuation. Through this work, it can be said that the phenomena at the origin of the presence, distribution of bubbles in sapphire fibres and the segregation of Cerium in the YAG have been significantly clarified and that, from these results, improvements can be made to the technological processes of pulling by µ-PD

GaN-based High Electron Mobility Transistors (HEMT) are appealing because of their large breakdown field, high saturation velocity, and superior thermal conductivity. They work at high temperature without much degradation. HEMTs have a few drawbacks despite many positives. The cost of developing GaN HEMTs on a native substrate is high. It would be cost effective to fabricate HEMTs on an alternative substrate without affecting their performance. The goal of this project is to characterise GaN HEMTs on various substrates like Si, SiC and Sapphire. This thesis focuses mainly on DC measurements for threshold voltage, leakage current, and breakdown voltage of these transistors. It is observed that HEMT devices grown on Si substrate provides maximum saturation current, however, the breakdown voltage is about 650 V. The breakdown voltage for HEMTs grown on SiC is superior showing about 1410 V with saturation drain current of 0.49 A/mm making it a good fit for power electronic applications. The threshold voltage for the devices on SiC substrate is -8.5 V. Additionally, different device architectures with different gate lengths, gate widths, and gate to drain distances are also evaluated and compared. It is noticed that the gate length of 1.5 μm and gate-drain length of 20 μm showed the best results for devices on all the substrates. / Hög elektronmobilitetstransistorer (HEMT) baserade på galliumnitrid (GaN) är mycket aktuella på grund av materialets höga genombrottsfält, hög mättnadshastighet för elektroner och bra termisk ledningsförmåga. Dessutom kan komponenter också användas vid höga temperaturer, men det finns även nackdelar. En nackdel är att kostnaden för GaN-substrat är mycket stor och man letar därför efter mer kostnadseffektiva substratmaterial. I detta projekt jämförs därför prestanda för HEMT-komponenter tillverkade på tre olika alternativa substrat som bedöms vara mer kostnadseffektiva än GaN, kisel (Si), kiselkarbid (SiC) och safir (Al2O3). Projektet fokuseras på DC mätningar av tröskelspänning, läckströmmar och genombrottsspänning för att utröna om komponenternas elektriska prestanda påverkas av dessa substratmaterial. Resultaten visar att HEMT-komponenter på Si-substrat uppvisar något högre mättnadsström, men genombrottsspänningar på bara ca 650 V. Genombrottsspänningar på HEMT-komponenter tillverkade på SiC-substrat ligger däremot på över 1400 V och har mättnadströmmar på omkring 0.50A/mm, vilket gör dom klart bättre än komponenter på Si och safir. Tröskelspänningen för HEMT-komponenter på SiC uppmäts till -8.5 V. Ytterligare mätningar gjordes också av komponenter med olika gemoetrier, som grindbredd och längd, samt olika avstånd mellan grind och utlopp (drain), och det kan konstateras att en grindlängd på 1.5 μm och ett avstånd mellan grind och utlopp på 20 μm uppvisar de bästa resultaten oberoende av substratmaterial.

La recherche présentée dans le cadre du présent mémoire porte sur la traduction vers le français de trois romans écrits - partiellement ou complètement - en vernaculaire noir américain (VNA), un sociolecte propre à la communauté formée par les Afro-Américains issus de l'esclavage. Les romans à l'étude sont : Their Eyes Were Watching God (1937), de Zora Neale Hurston, traduit en 1993 par Françoise Brodsky sous le titre Une femme noire; The Color Purple (1982), d'Alice Walker, traduit en 1984 par Mimi Perrin sous le titre La couleur pourpre; et Push (1996), de Sapphire, traduit en 1997 par Jean-Pierre Carasso sous le titre homonyme Push. Ces œuvres littéraires partagent, en plus de l'usage intensif du VNA, de nombreuses caractéristiques : il s'agit dans tous les cas de la quête émancipatoire d'une femme afro-américaine, qui s'accomplit grâce au langage - récit, écriture, alphabétisation. Les revendications culturelle, politique et féministe de ces textes sont-elles rendues fidèlement dans la traduction? La méthodologie et la grille d'analyse que j'utiliserai sont inspirées de l'œuvre d'Antoine Berman, un théoricien de la traduction littéraire qui s'est penché sur le phénomène de la traduction ethnocentrique, dans le cadre de laquelle les normes culturelles, littéraires et linguistiques de la culture d'arrivée sont privilégiées au détriment de la spécificité étrangère du texte. Les critères que Berman propose pour l'évaluation des traductions sont l'éthique et la poétique, qui concernent, pour l'un, la valeur du projet de traduction, et pour l'autre, la présence ou non de tendances déformantes propres à la traduction ethnocentrique. Puisque l'interprétation - quelquefois biaisée ou inexacte, ou bien heureuse - du traducteur l'influence sans conteste dans son travail, je pourrai déterminer par l'analyse la position idéologique des traducteurs et les associer aux courants théoriques identifiés par Inês Oseki-Dépré. Enfin, rassemblant les données obtenues lors de l'analyse des différentes traductions, je me prononcerai sur les conditions de possibilité de la traduction du VNA, un sociolecte fortement ancré culturellement et politiquement dans la communauté d'où il émerge. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Traduction littéraire, vernaculaire noir américain, littérature afro-américaine, féminisme noir (womanism), littérature américaine, Zora Neale Hurston, Alice Walker, Sapphire, Françoise Brodsky.

Si nanowires have potential applications in a variety of technologies such as micro and nanoelectronics, sensors, electrodes and photovoltaic applications due to their size and specific surface area. Au particle-assisted vapour-liquid-solid or VLS growth method remains the dominant process for Si nanowire growth. A comprehensive kinetic model that addresses all experimental observations and provides a physico-chemical model of the VLS growth method is thus essential. The work done as part of this research is divided into two sections. A steady state kinetic model was first developed for the steady state growth rate of Si nanowires using SiCl4 and SiH4 as precursors. The steady state refers to a balance between the rates of injection and ejection of Si into the Au droplet. This balance results in a steady state supersaturation under which wire growth proceeds. In particular evaporation and reverse reaction of Si from the Au droplet and modes of crystal growth for wire growth have been considered in detail for the first time. The model is able to account for both, the radius independent and radius dependent growth rates reported in the literature. It also shows that the radius dependence previously attributed to purely thermodynamic considerations could also as well be explained just by steady state kinetics alone. Expressions have been derived for the steady state growth rate that require the desolvation energy, activation energy for precursor dissociation and supersaturation prevalent in the particle as inputs for calculation. In order to evaluate this model the incubation and growth of Si nanowires were studied on sapphire substrates in an indigenously built automated MOCVD reactor. Sapphire was chosen as the substrate, as opposed to Si which is commonly used, so as to ensure that the vapour phase is the only source of Si. A classical incubation period for nucleation, of the order of 4-8 minutes, was experimentally observed for the first time. Using the change in this incubation period with temperature a value of 15kT was determined to be the desolvation energy for growth using SiH4. The steady state growth rate of Si nanowires were measured and compared with the predictions of the model using the values of activation energies so determined. The thesis based on the current research work is organized as follows: Chapter 1 introduces the research area followed by a brief outline of the overall work Chapter 2 provides a summary of current literature, and puts the research described in this thesis in perspective. The diameter dependent growth rate of NWs which was initially solely attributed to the Gibbs-Thomson effect is first summarized. Experimental observations to the contrary are then highlighted. These contradictions provided the incentive for the research described in this thesis. Following a summary of the growth rate theories, the experimental observations on incubation available in the literature are summarized. All the other variants of the VLS method are also discussed. Chapter 3 describes the design, construction and working of an indigenously built semi- automated CVD reactor. This CVD reactor was used to conduct the Si NW growth experiments over sapphire substrates. Chapter 4 develops the physical chemistry model for Au catalyzed Si nanowire growth using SiCl4 and SiH4 precursors. The model originated from the contradictions present in the literature over the rate limiting step of the VLS growth mechanism and the steady state growth rate dependence on wire diameter. The development starts with explaining the thermodynamics of the steady state VLS process. The significance of the model lies in the detailed analysis of the all the atomistic process occurring during the VLS growth. In particular the evaporation and reverse reaction of Si from Au-Si droplet is explained in detail and possibly for the first time. Expressions for steady state growth rate by various modes, such as layer by layer growth (LL), by multilayer growth (ML) and growth by movement of a rough interface at the L-S growth interface are derived and presented. Chapter 5 discusses the results which emerge out the kinetic model from the previous chapter. Under a single framework of equations, the model is successful in explaining both the diameter independent and diameter dependent growth of NWs. As one of the major outcomes of the model, the growth rates of Si NWs are predicted and trends in growth rate are found to agree with those experimentally observed. Growth rate dependencies on pressure and temperature are implicitly included in the equations derived. An estimate of supersaturation has been extracted for the first time using the framework of equations. Chapter 6 contains the experimental results of the Si NW growth over sapphire substrates. An incubation period in the order of 3-8 minutes has been observed for Si NW growth on sapphire. The data has been compared with existing literature data and interpreted using classical transient nucleation theory. The incubation period data has been utilized to extract the kinetic parameter, QD, which is the desolvation enegy. These parameters and the measured steady state growth rates have been used to estimate the supersaturation existing in the droplet using the framework developed in chapters 4 and 5. Chapter 7 summarizes the outcome of the current research and highlights the future directions for the research problem addressed in this thesis.

The master’s thesis deals with a design of a radial journal bearing simulator, which is ready to implement a transparent sapphire journal bearing to an optical observation of the oil film. The first part of this thesis contains a short review of a few currently used journal bearing test rigs. The next part of the work deals with a discussion of concept variants and a definition of important parameters. The last part contains a detailed description of the designed radial journal bearing simulator. Limitations of the designed simulator and recommendations for future improvements are also discussed. The result of the presented work is the designed journal bearing simulator which will allow observing of the oil film. The work also consists a complete design documentation.

This diploma thesis deals with the optimization of ultra-high vacuum scanning electron microscope - UHV SEM, which is developed within the Amispec project in cooperation with BUT, Institute of Scientific Instruments of the Czech Academy of Science and Tescan Brno, s.r.o. The theoretical part deals with the description of the actual state of the developed equipment and the research of competing systems. The next part describes the optimization of the sample holder and the pallet receptor for studying nanostructures over a wide range of temperatures. Part of the optimization is the sapphire thermal diode development and experimental verification of the functionality of the designed components. This is followed by the verification of the functionality of the whole system for the transport of samples to the UHV area, deposition with effusion cell and in-situ observations.

We report the possibility to control the tilting of nanoneedles and nanowires by using structured sapphire substrates. The advantage of the reported strategy is to obtain well oriented growth along a single direction tilted with respect to the surface normal, whereas the growth in other directions is suppressed. In our particular case, the nanostructures are tilted with respect to the surface normal by an angle of 58°. Moreover, we demonstrate that variation of the nanostructures shape from nanoneedles to cylindrical nanowires by using SiO2 layer is observed.

No description available.

Conceptual design is an early stage in the design process, in which functional requirements of a design problem are transformed into solution concepts for satisfying the requirements. It is regarded as a crucial step in design, because decisions made in this stage will strongly affect all the subsequent stages of the design process. Research evidence suggests that inspiration is useful for exploration and discovery of new solution spaces, and exploration of a wide variety of concepts increases the chances of developing more novel, and hence more creative solutions. There are various approaches to providing inspiration, e.g., creativity techniques such as trigger word technique, biomimetics such as Idea-Inspire, and computational synthesis approaches such as compositional synthesis. Computational synthesis tools are used for automated generation of concepts, which can be offered to the designer as triggers for inspiring ideation. The advantage of using solutions from computational synthesis as triggers are the following: the solutions can be produced in a relatively unbiased manner, allowing a variety of directions to be explored, and the solutions are exhaustive within the constraints of the databases or rules used, allowing a multitude of possibilities to be offered. However, computational synthesis has been traditionally used for automating solution generation, rather than creating triggers for designers’ ideation. Notwithstanding their potential for inspiring ideation, current computational synthesis approaches rarely focused on this task. One exception is FuncSION, a compositional synthesis tool, which can automatically synthesize solution concepts for mechanical devices, where a set of input and output characteristics i.e. functional requirements are provided by the user and the computer generates solutions by combining building blocks from a library to satisfy the requirements; these solutions are then used as stimuli for ideation by designers. The focus of this thesis is on evaluating and improving the effectiveness of computational synthesis in triggering ideation during conceptual design, in terms of improving the fluency and variety of the concept space produced. FuncSION has been used as the example synthesis approach on which the work has been focused. In order to evaluate the effectiveness of FuncSION in terms of fluency and variety, a method for assessing variety of a concept space is proposed, and a tool for supporting the assessment process has been developed. However, compositional synthesis research has always assumed that the building blocks are given, and has confined its focus on the process of combining the building blocks. It has not been investigated as to how such building blocks can be automatically identified. If new building blocks can be automatically identified, the resulting change in the library of building blocks would have a substantial effect on the outcomes of compositional synthesis, i.e. the triggers that can be offered to the designers for ideation, with a resulting effect on the concepts generated by the designers. Therefore, in this thesis, an automated method for building blocks synthesis has been proposed, and has been implemented as a computational tool.