Étude de la croissance de nanofils de SiGe par dépôt chimique en phase vapeur et caractérisation par microscopie à force atomique. Les nanofils semi-conducteurs constituent des briques de bases au potentiel prometteur pour l'amélioration des dispositifs du futur. D'autre part, l'alliage SiGe permet de contrôler les propriétés électroniques de la matière telles que les mobilités des porteurs et la largeur de bande. Dans le cadre de ce travail de thèse, nous étudions les mécanismes de croissance catalysée de nanofils de SiGe et développons des méthodes de caractérisation de nanofils par AFM.Dans un premier temps, la croissance par CVD de nanofils de SiGe est étudiée en utilisant l'or comme catalyseur. Nous étudions l'influence du HCl en phase gazeuse qui permet un contrôle de la croissance de nanofils de SiGe et modélisons son action.Dans un deuxième temps, nous étudions la croissance de nanofils SiGe catalysée par siliciures compatibles CMOS, et la croissance de nanofils de Ge pur à basse température. Nous nous intéressons également à l'élaboration d'hétérostructures.Enfin, nous étudions le module de Young de NF unique de Si, GaN et ZnO par AFM et une nouvelle méthode de génération de potentiel piézoélectrique sur NF de GaN a été développée.

Cette thèse vise à maitriser la synthèse MPCVD de films hétéroépitaxiés de diamant de haute qualité cristalline sur substrat d'iridium pour la réalisation de dosimètres en radiothérapie. Cet objectif nous a conduits à élaborer la couche d'iridium épitaxiée sur des substrats SrtiO3 (001). Un bâti sous vide équipé d'un canon à électrons a donc été développé et calibré. Les couches obtenues ont été caractérisées par DRX et présentent une qualité structurale équivalente à l'état de l'art. Le procédé de nucléation (BEN) - MPCVD induit sur la surface de l'iridium des " domaines " spécifiques à la nucléation du diamant sur iridium. Un travail important a été mené sur l'optimisation du (BEN) - MPCVD de façon à obtenir un procédé fiable et reproductible pour obtenir des " domaines " homogènes sur une surface de 5x5mm2 d'Ir/SrtiO3. Des études de caractérisation de surface (MEB, XPS, AES) des " domaines " nous ont permis de dresser leur carte d'identité chimique et morphologique. Nous démontrons ainsi qu'ils contiennent des nuclei de diamant. De plus, la propagation de ces " domaines " semble suivre des directions préférentielles [110] induites par l'épitaxie de l'iridium au cours du temps durant l'étape de (BEN)-MPCVD. A partir de ces résultats, des films de diamant hétéroépitaxiés autosupportés de 100&#956-m ont été élaborés. La corrélation entre la qualité cristalline du diamant hétéroépitaxié et sa réponse en détection a été menée avec l'équipe dosimétrie du LCD. Des inhomogénéités de la structure cristalline due à la présence de défauts structuraux ont été mises en évidence. Afin d'étudier localement ces échantillons, une campagne de mesure par microfaisceau X a été réalisée sur la ligne Diffabs du Synchrotron Soleil. L'assemblage des différentes connaissances acquises lors de cette thèse a permis de fabriquer et de caractériser un premier détecteur à base de diamant hétéroépitaxié au LCD

Carbon forms the basis of a variety of compounds. The allotropic forms of carbon include graphene, fullerenes, graphite, carbon nanotubes and diamond. All these structures possess unique physical and chemical properties. This work focusses on the usage of carbon nanotubes (CNT), especially iron-filled CNT. An industrial application of CNT requires the understanding of the growth mechanism and the control of the synthesis process parameters. Regarding iron-filled CNT the shell formation as well as the filling process has to be understood in order to control the CNT morphology and distribution and dimension of the iron filling. The thesis involves two topics - synthesis of CNT and characterization of their mechanical properties. Chapter 2 of the present work deals with the synthesis of iron-filled CNT. In this thesis all experiments and the discussion about the growth process were conducted with respect to the demands of magnetic force microscopy probes. The experimental work was focused on the temperature profile of the furnace, the aluminum layer of the substrate, the precursor mass flow and their impact on the morphology of in-situ iron-filled CNT. By selecting appropriate process parameters for the temperature, sample position, gas flow and by controlling the precursor mass flow, CNT with a continuous filling of several microns in length were created. Existing growth models have been analyzed and controversially discussed in order to explain the formation of typical morphologies of in-situ filled CNT. In this work a modified growth model for the formation of in-situ filled CNT has been suggested. The combined-growth-mode model is capable to explain the experimental results. Experiments which were conducted with respect to the assumptions of this model, especially the role of the precursor mass flow, resulted in the formation of long and continuous iron nanowires encapsulated inside multi-walled CNT. The modified growth model and the synthesis results showed, that besides the complexity of the parameter interaction, a control of the morphology of in-situ iron-filled CNT is possible. In chapter 3 the measurements of mechanical properties of in-situ iron-filled CNT are presented. Two different experimental methods and setups were established, whereby one enabled a static bending measurement inside a TEM and another a dynamical excitation of flexural vibration of CNT inside SEM. For the first time mechanical properties and in particular the effective elastic modulus Eb of in-situ iron-filled CNT were determined based on the Euler-Bernoulli beam model (EBM). This continuum mechanic model can be applied to describe the mechanical properties of CNT and especially MWCNT in consideration of the restriction that CNT represent a macro molecular structure built of nested rolled-up graphene layers. For evaluation and determination of the elastic modulus the envelope of the resonant vibrating state was evaluated by fitting the EBM to the experimental data. The experiments also showed, that at the nanoscale the properties of sample attachment have to be taken into account. Thus, instead of a rigid boundary condition a torsion spring like behavior possessing a finite stiffness was used to model an one side clamped CNT. The extended data evaluation considering the elastic boundary conditions resulted in an average elastic modulus of Eb = 0.41 ± 0.11 TPa. The low standard deviation gives evidence for the homogeneity of the grown material. To some extend a correlation between the formation process, the morphology and the mechanical properties has been discussed. The obtained results prove the usability of this material as free standing tips for raster scanning microscopy and especially magnetic force microscopy. The developed methods provide the basis for further investigations of the CNT and the understanding of mechanical behavior in greater detail.

In the frame of this thesis, a new experimental setup for the measurement of the energy loss of carbon ions at maximum stopping power in a hot laser-generated plasma has been developed and successfully tested. In this parameter range where the projectile velocity is of the same order of magnitude as the thermal velocity of the plasma free electrons, large uncertainties of up to 50% are present in the stopping-power description. To date, no experimental data are available to perform a theory benchmarking. Testing the different stopping theories is yet essential for inertial confinement fusion and in particular for the understanding of the alpha-particle heating of the thermonuclear fuel. Here, for the first time, precise measurements were carried out in a reproducible and entirely characterized beam-plasma configuration. It involved a nearly fully-stripped ion beam probing a homogeneous fully-ionized plasma. This plasma was generated by irradiating a thin carbon foil with two high-energy laser beams and features a maximum electron temperature of 200 eV. The plasma conditions were simulated with a two-dimensional radiative hydrodynamic code, while the ion-beam charge-state distribution was predicted by means of a Monte-Carlo code describing the charge-exchange processes of projectile ions in plasma. To probe at maximum stopping power, high-frequency pulsed ion bunches were decelerated to an energy of 0.5 MeV per nucleon. The ion energy loss was determined by a time-of-flight measurement using a specifically developed chemical-vapor-deposition diamond detector that was screened against any plasma radiation. A first experimental campaign was carried out using this newly developed platform, in which a precision better than 200 keV on the energy loss was reached. This allowed, via the knowledge of the plasma and of the beam parameters, to reliably test several stopping theories, either based on perturbation theory or on a nonlinear T-Matrix formalism. A preliminary analysis suggests that the energy deposition at maximum stopping power is significantly smaller than predicted, particularly, by perturbation approaches.

No description available.

There has been growing interest in two-dimensional (2-D) crystals beyond graphene for next-generation nano-electronics. Transition metal dichalcogenides have been most widely studied, for their semiconducting characteristics and hence, potential applications. This interest has fueled many efforts to establish methods for synthesis of MoS2 layers, a most promising candidate, in controlled numbers over large areas. One of the most scalable methods is chemical vapor deposition (CVD). The current approaches to growth from the vapor phase are by and large very empirical. This thesis is hence concerned with the predictive synthesis of n-layered MoS2 using CVD uniformly over large areas and the correlation of growth parameters with the structural and electronic properties of the deposited films. A simple, relatively non-toxic and non-pyrophoric chemistry, consisting of Mo(CO)6 and H2S was first chosen for vapor phase synthesis. This chemistry allowed synthesis of MoS2 from precursors located outside of the growth reactor, a necessary condition for electronics device technology. Iterative thermodynamic modeling of the Mo-S-C-O-H system and growth was then done to identify the appropriate CVD process windows for the growth of pure MoS2, departures from stoichiometry, contamination and breakdown of equilibrium modelling. Remarkable agreement between theoretical modelling and actual growth has been observed leading to predictable deposition. Within these thermodynamic windows, the gas phase supersaturation were then reduced to obtain better kinetic control over crystal growth. It is shown that control of supersaturation at the very initial stages of growth is critical to reduce the nucleation density and hence obtain monolayers with small defect densities. In addition, it is shown that at higher temperatures the kinetics of nucleation and growth are determined by the supersaturation on the growth surface. Physico-chemical modelling reveals that this steady state supersaturation is determined by the kinetics of adsorption and desorption. All of this understanding has been used to realize a variety of structures from discrete crystalline islands- 30 nm to 150 microns- to deposits with controlled number of layers – n =1 to 6 or greater- uniformly over large areas on quartz and sapphire. Gas phase chemistry also affects the electrical characteristics of the as deposited layers. It is shown, for the first time, that by changing gas phase Mo to S ratios the stoichiometry of the deposited layers MoS2 can be made metal or chalcogen deficient. This yields MoS2 that can be either p-type or n-type. p-type and n-type MoS2 with mobilities up to 7.4 cm2/Vs and 40 cm2/Vs respectively are demonstrated. FETs fabricated on MoS(2-x) samples (increasing x) with varying stoichiometry showed a maximum on-current of 18 μA (4.5 μA/μm) in vacuum and 0.6 μA (0.15 μA/μm) in air for a drain bias Vds = 1 V. Sulphur deficiency also affect reliability. While samples with a higher concentration of sulphur vacancies have higher mobility in vacuum, the mobility degrades significantly in air and gets reversed on annealing in H2S. The details of such correlation between growth and electrical characteristics are discussed in this thesis.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第13825号 / 工博第2929号 / 新制||工||1433(附属図書館) / 26041 / UT51-2008-C741 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 藤田 静雄, 教授 三浦 孝一, 教授 川上 養一 / 学位規則第4条第1項該当

Carbon nanotubes (CNTs) were successfully grown on the surface of carbon fibre reinforcements in carbon fibre architecture through in-situ catalytic chemical vapour deposition (CCVD). Success was also implemented on powders of oxides and non-oxides, including Y-TZP powder, ball milled alumina powder, alumina grits, silicon carbide powder. Preliminary results have been achieved to demonstrate the feasibility of making ceramic composites consisting of CNTs reinforcements.

Orientador: Vitor Baranauskas / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-05T18:10:58Z (GMT). No. of bitstreams: 1 Correa_WashingtonLuizAlves_D.pdf: 3351242 bytes, checksum: 8f30a26c68d4c1e73a72d065eaedb4f9 (MD5) Previous issue date: 2004 / Resumo: Estudamos processos de dopagem do diamante crescido por deposição química a partir da fase vapor (diamante CVD) com a introdução de impurezas dopantes durante o crescimento do diamante em reatores do tipo filamento-quente. Focalizamos nossa pesquisa na dopagem do diamante com boro, ou nitrogênio, ou enxofre, visando obter diamantes com propriedades semicondutoras com condutividade eletrônica (tipo n) ou condutividade por lacunas (tipo p). Foram utilizadas contaminações intencionais utilizando: trimetil borano (B(CH3)3), ou amônia (NH3), ou dissulfeto de carbono (CS2), misturados com metano e diluídos em hidrogênio. As amostras foram caracterizadas por microscopia eletrônica de varredura (SEM), espectroscopia Raman, espectroscopia de foto-elétrons excitados por raios X (XPS), espectroscopia de emissão de raios X excitado por feixe de prótons (PIXE) e efeito Hall. As dopagens do diamante do tipo p e do tipo n foram obtidas com contaminações de boro e enxofre, respectivamente. O diamante dopado com nitrogênio não apresentou propriedades semicondutoras / Abstract: We studied the diamond doping processes with introduction of doping impurities during the diamond growth in the chemical vapor deposition (CVD) technique, using a hot-filament reactor. Our research focused the use of boron, nitrogen or sulphur atoms in order to obtain diamond films with semiconductor properties of electronic (n-type) or hole (p-type) current transport mechanisms. Trimethyl-borane (B(CH3)3), or ammonia, or carbon disulphide (CS2), mixed with methane and hydrogen were used in the feed gas mixture. The diamond samples were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Proton-induced X-ray emission (PIXE) and Hall effect. p-type and n-type diamonds have been obtained with boron and sulphur doping, respectively. However, the nitrogen doped samples do not presented semiconductor properties / Doutorado / Engenharia de Eletronica e Comunicações / Doutor em Engenharia Elétrica

Orientador: Jose Alexandre Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-05T17:29:59Z (GMT). No. of bitstreams: 1 Biasotto_Cleber_M.pdf: 4466326 bytes, checksum: 75500d469b99d21f5c40a3214a755168 (MD5) Previous issue date: 2005 / Resumo: Neste trabalho, filmes finos de nitreto (SixNy), oxido (SiOx) e oxinitreto (SiOxNy) de silicio sobre substrato de silicio, obtidos através da deposição química a partir da fase vapor auxiliada por plasma remoto (RPCVD), foram caracterizados e estudados para aplicações em micromáquinas (micromachining) ou sistemas micro-eletro-mecanico (MEMS). Os filmes de nitreto de silicio (SixNy) foram obtidos para aplicação em estruturas suspensas (pontes e membranas) e como mascara de proteção de dispositivos MOS para remoção do substrato, utilizando os processos de corrosão úmida do substrato de silicio pelas faces superior (front-side bulk micromachining) e inferior (back-side bulk micromachining), respectivamente. Os filmes de oxido de silicio (SiOx) foram aplicados como camada sacrificial em processos de obtenção de estruturas suspensas empregando a técnica de remoção de camadas sacrificiais na superfície (surface micromachining). Os filmes de oxinitreto de silicio (SiOxNy) foram obtidos como filmes alternativos para aplicação em estruturas suspensas (pontes e membranas), utilizando os processos de corrosão úmida do substrato de silicio pela face superior (front-side bulk micromachining). A fabricação destas estruturas e primordial para o desenvolvimento de micro-sensores e micro-atuadores. Neste trabalho foram revisadas as técnicas de processamento CVD (Chemical Vapor Deposition), apresentando a justificativa da escolha do reator ECR (Electron Cyclotron Resonance), que utiliza a tecnologia CVD com Plasma Remoto (RPCVD) para as deposições / Abstract: In this work, silicon nitride (SixNy), oxide (SiOx) and oxynitride (SiOxNy) thin films obtained by remote plasma chemical vapor deposition (RPCVD) on silicon substrate were studied and characterized for micromachining or micro electro-mechanical system (MEMS) applications. Silicon nitride films (SixNy) were used in suspended structures (membranes and bridges) and as MOS device protection mask against wet substrate etching, obtained by wet substrate etching processes using the front-side and back-side bulk micromachining techniques, respectively. Silicon oxide films (SiOx) were employed as sacrificial layers to obtain suspended surface structures using the surface micromachining technique. Silicon oxynitride (SiOxNy) films were used as alternative films in suspended structures (membranes and bridges), using the front-side bulk micromachining technique. The fabrication of these structures is primordial for the micro sensor and actuator development. In these work, CVD (Chemical Vapor Deposition) techniques are revised, presenting the choice justification of ECR (Electron Cyclotron Resonance) reactor, which uses RPCVD technology for the depositions / Mestrado / Mestre em Engenharia Elétrica