Tong Hoi Yee. / "July, 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 237-253). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Thesis (Ph.D.)--Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 197-202). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 197-202). Also available on the Internet.

Orientador: Fernando Alvarez / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T01:14:15Z (GMT). No. of bitstreams: 1 OchoaBecerra_ErikaAbigail_M.pdf: 6414208 bytes, checksum: be25f7cebf36f2d96cfd208deecb449a (MD5) Previous issue date: 2003 / Resumo: Apresente tese trata sobre a implantação de nitrogênio em sistemas baseados em ferro. Duas técnicas de nitretação são utilizadas, plasma pulsado e feixe iônico por canhão de íons. Os parâmetros de nitretação são otimizados com a finalidade de obter um melhoramento na dureza superficial destes sistemas, isto é, em algumas dezenas de mícron. Tal melhoramento é relacionado com a concentração de nitrogênio em profundidade correspondente a uma sucessão de nitretos formados. A estabilidade destas fases é observada qualitativamente pela dependência com os processos de nitretação. A formação de camadas de nitretos é estudada a partir de um modelo de difusão e determinadas através de caracterização por raios-X, microscopia eletrônica de varredura (MEV) e espectroscopia de fotoelétrons de raios-X (XPS). A dureza em profundidade, de amostras submetidas a diferentes processos de implante de nitrogênio, foi determinada mediante nanoindentação. Amostras portadoras de um alto grau de dureza foram empregadas: aço AISI 4140. O polimento destas amostras, para caracterização em diferentes profundidades, foi processado mediante iesputteringl, com íons de argônio. Os efeitos da erosão foram estudados com auxilio de um perfilômetro. Coeficientes de difusão de nitrogênio em diferentes tipos de nitretos foram determinados e a uma correlação entre a dureza e concentração de nitrogênio em profundidade foi verificada explicitamente / Abstract: This thesis deals about the nitrogen implantation in iron - based systems. Two techniques to nitriding were used, either pulsed plasma or ionic beam by use of a cannon. The nitriding parameters were optimized with the purpose to get an improvement in the superficial hardness of these systems; this is, in a few dozen of micrometers. Such improvement is related with the in-depth nitrogen concentration corresponding to a set of layered phases. The stability of these phases is observed qualitatively because the dependece with the processes of nitriding. The layered phases containing nitrides is studied from a difusion model and determined through X-ray, scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). The hardness in depth, of samples subjected to different processes of nitrogen implantation, was determined by means of nano-indentation. Samples showing a high degree of hardness were used: steel AISI 4140. The polishment of these samples, for characterization in different depths, was processed by means of sputtering with argon ions. The effect of erosion had been studied by means of a perfilometer. Difusion coefficients of nitrogen in the different types of layered nitrides had been determined and a correlation between hardness and nitrogen concentration in depth was verified explicitly / Mestrado / Física da Matéria Condensada / Mestre em Física

Les oxydes de métaux de transition sont d'un grand intérêt en raison du large éventail de propriétés qu'ils présentent. Ils ont potentiellement de nombreuses applications technologiques dans le domaine de l'électronique, reposant en partie sur le développement de dispositifs pour la technologie de l'information nécessitant de les contacter avec des métaux. Ce travail de thèse, basé principalement sur l'utilisation de la spectroscopie de photoémission, porte sur une étude détaillée de l'interface Fe/SrTiO₃ réalisée à température ambiante, dans laquelle nous nous sommes intéressés en particulier aux propriétés structurales et électroniques. Nous montrons que le fer est épitaxié, que sa croissance est en îlots et que les films couvrent entièrement le substrat pour le dépôt de quelques monocouches atomiques. Nous mettons en évidence une réaction du métal avec le substrat lors de la formation de l'interface qui se manifeste par la présence de titane réduit à l'interface. Nous associons cette réduction du titane à la présence de lacunes d'oxygène à l'interface Fe/SrTiO₃. Alors que la hauteur de barrière Schottky attendue pour une jonction abrupte Fe/SrTiO₃(001) est d'environ 1 eV pour les électrons, nous montrons que la présence des lacunes d'oxygène à l'interface abaisse la hauteur de barrière Schottky à environ 0,05 eV. La création de lacunes d'oxygène lors du dépôt de fractions de monocouche de fer sur le SrTiO₃ conduit aussi à une métallisation de la surface du semi-conducteur. Ce mécanisme est relié à la création d'états donneurs chargés positivement associés aux lacunes d'oxygène pendant le dépôt. Pour déterminer le profil de bande dans le substrat nous avons résolu l'équation de Poisson à une dimension dans une approche de la théorie de la fonctionnelle de la densité modifiée, en tenant compte de la couche d'accumulation d'électrons. Confrontant ces calculs avec nos résultats de photoémission nous trouvons que le potentiel de surface présente des inhomogénéités spatiales parallèlement à la surface. / Transition metal oxides are of great interest because of the wide range of properties they exhibit. They have potentially many technological applications in the field of electronics, especially based on the development of devices for information technology requiring contacting these oxides with metals. This thesis work, mainly based on photoemission spectroscopy, is a detailed study of the Fe/SrTiO₃ interface grown at room temperature in which we focus in particular on structural and electronic properties. We show that iron has an epitaxial growth with an island morphology and that films completely cover the substrate for the deposition of few atomic monolayers. We demonstrate that the metal reacts with the substrate during the formation of the interface which results in the presence of reduced titanium at the interface. We associate this reduction of titanium with the presence of oxygen vacancies at the Fe/SrTiO₃ interface. While the expected Schottky barrier height for a Fe/SrTiO₃(001) abrupt junction is about 1 eV for electrons, we show that the presence of oxygen vacancies at the interface lowers this Schottky barrier height to about 0.05 eV. The creation of oxygen vacancies during the deposition of fractions of iron monolayer on SrTiO₃ also leads to the metallization of the semiconductor surface. This mechanism is related to the creation of positively charged donor states associated with oxygen vacancies during deposition. To determine the band profile in the substrate, we solved the one-dimensional Poisson equation in a modified approach of the density functional theory taking into account the electron accumulation layer. By comparing these calculations with our photoemission results, we find that the surface potential has spatial inhomogeneities parallel to the surface.

Orientador: David Mendez Soares / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-06T09:05:00Z (GMT). No. of bitstreams: 1 Pinto_EdilsonMoura_M.pdf: 2421703 bytes, checksum: 4f88cfbf1bf972bc5ed1991a06982550 (MD5) Previous issue date: 2004 / Resumo: Neste trabalho, a QCM (Quartz Crystal Microbalan e) Microbalança de Cristal de Quartzo, como ténica alternativa para o estudo da corrosão /inibição do metal cobre. Estudamos a proteção anti-corrosão de superfícies de cobre mediante a adsorção de inibidores voláteis de corrosão (VCI-CHAB,Ciclohexilamina-Benzoato). Utilizamos uma QCM, composta de um cristal de quartzo de 6MHz, recoberto por um filme de ouro depositado por sputtering. Utilizamos Técnicas eletroquímicas para caracterizar a corrosão. Para isto, estudamos a corrosão do metal cobre em diferentes ambientes, básicos e ácidos, na presença e ausência dos inibidores. Aplicamos a QCM acoplada à um potenciostato (EQCM), como método de determinação de variação de massa e e carga de correntes da corrosão/inibição. A presença dos filmes VC I sobre a superfície de cobre, também foi demonstrada pela técnica Reflection-Absorption Infra-Red Spectros opy (RAIRS), através da Micros copia de infravermelho razante, esta técnica é indicada para situações em que os filmes formados são Ultra-finos. Baseado nos resultados das medidas feitas, propomos e des revemos um modelo para a dsorção dos filmes VCI sobre a superfície metálica, incluindo a formação da corrosão por pitting / Abstract: In this work we used the QCM (Quartz Crystal Microbalance) as an alternative technique for the studying of the corrosion/inhibition of cooper. We studied the protection of cooper surfaces due to the adsorption of a volatile corrosion inhibitor, (VCI-Cyclehexilamine-Benzoate). We used electrochemical techniques to characterize the corrosion in different environments. We applied the QCM together with the potentiostat as a method of determination of charge and mass variations. In this work the QCM has been used as a complementary technique for investigating the corrosion of copper with and without adsorbed inhibitors. The protection of copper surfaces due to the adsorption of a volatile corrosion inhibitor (VCI) ¿ Cyclohexylamine Benzoate ¿ has been studied by electro chemical techniques to characterise the corrosion in aqueous environments over a wide range of pH values. The presence of VCI films on the copper surface was also shown by Reflection-Absorption Infra-Red Spectroscopy (RAIRS), a technique indicated for situations when very thin films are formed. The EQCM, which used 6 MHz gold-sputtered quartz crystals coated with electrodeposited copper films, was applied to the simultaneous determination of the charge and frequency variations associated with the corrosion process, with and without adsorbed inhibitor. Based on the measurements, a model has been developed to describe the dynamics of adsorption of the VCI on the metalli surface, including the formation of pits on the surface / Mestrado / Superfícies e Interfaces ; Peliculas e Filamentos / Mestre em Física

Orientador: Richard Landers / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T10:50:19Z (GMT). No. of bitstreams: 1 Pancotti_Alexandre_M.pdf: 2977317 bytes, checksum: 914d690fda86677fcc9c894c6f408409 (MD5) Previous issue date: 2005 / Resumo: Nesse trabalho nos propomos a estudar a estrutura eletrônica e geométrica de ligas de superfície à partir de filmes ultra finos, da ordem de monocamada atômica , crescidos por MBE sobre substratos monocristalinos. Os filmes finos foram crescidos in situ e analizados por XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) e UPS (Ultra Violet Photoelectron Spectroscopy). As ligas de superfície estudas foram InPd, SnPd e SbPd sempre sobre um substrato de Pd(111). Os resultados das medidas PED dos sistemas InPd e SnPd foram interpretadas usando programas tipo MSCD[1]. Foi mostrado que Sn e In em baixa cobertura formam uma estrutura (raiz2 3 x raiz2 3) R 30o ( e o In mostrou uma estrutura (1x1) para filmes com mais de 2 monocamadas, provavelmente na forma de ilhas sobre a superfície do Pd. Estudos anteriores mostraram que Sb sobre Pd(111) também apresenta a fase (raiz2 3 x raiz2 3)R 30o para baixas coberturas[2]. Os modelos que melhor se adequaram aos dados sugerem fortemente que os metais sp(In, Sn,e Sb) não difundem além da segunda monocamada. Durante estes estudos foi observado que a intensidade do satélite de shake-up do Pd tendia a zero para os átomos em contato direto com os metais s / Abstract: The purpose of this report is to present a study of the electronic and geometric structure of surface alloys grown by MBE (Molecular Beam Epitaxy) on single crystal substrates in the sub monolayer regime. The films were grown "in-situ" in the analysis chamber and analyzed by XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) and UPS (Ultra Violet Photoelectron Spectroscopy). The alloys studied were InPd, SnPd e SbPd, all grown on the (111) face of a Pd crystal. The PED measurements for InPd and SnPd were analyzed using the MSCD code[3]. It was possible to show that for low coverages both metals formed a (raiz2 3 x raiz2 3) R 30o ( reconstruction and the first inter-planar distances were determined. For films with over two monolayers the In grew with a (1x1) structure probably in the form of islands separated by clean Pd. Previous studies showed that Sb[4] at low coverage also forms a (raiz2 3 x raiz2 3) R 30o ( structure. Our simulations suggest that In, Sn and Sb for the coverages studied do not diffuse beyond the second atomic layer. We also observed that the intensity of the Pd shake up satellite tends to zero for the Pd atoms in contact with these sp metals / Mestrado / Física da Matéria Condensada / Mestre em Física

Orientador: Fernando Alvarez / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-04T02:41:56Z (GMT). No. of bitstreams: 1 Figueroa_CarlosAlejandro_D.pdf: 23603712 bytes, checksum: 9d788dfc54dde973a5d614fc546e3311 (MD5) Previous issue date: 2004 / Resumo: A compreensão da radiação cósmica -a saber: os mecanismos de produção / aceleração e os processos de propagação - passa pela determinação de três grandezas: a energia dessa radiação, sua direção de chegada e sua composição química. Essas três "frentes de trabalho"desafiam a experiência, a capacidade e a responsabilidade de vários grupos de físicos de partículas do mundo todo. Este trabalho se refere à composição do primário da radiação cósmica no âmbito da Colaboração Auger. Ele não tem a ambição de encontrar uma técnica definitiva para a obtenção deste parâmetro. Aliás, determinar a composição química do primário é algo difícil, tendo em vista a dependência de modelos de interação hadrônica e a impossibilidade (atual) de sua caracterização evento a evento. Dos vários parâmetros usados para se estimar essa composição, tentamos analisar cinco deles: Xmax, tlO-50, t50-90, tlO-90, rlocal. Estes foram obtidos por meio de simulação de Monte Carlo, através dos códigos CORSIKA e AIRES. A rede de detectores de superfície foi simulada usando-se o programa SAMPLE. Os resultados das simulações foram comparados, quando possível, a dados experimentais fornecidos pelo Engineering Array do sítio sul do Observatório Auger / Abstract: The understanding of cosmic radiation -the production/ acceleration mechanism and the propagation processes -involves the determination of three parameters: the energy of this radiation, its arrival direction and the chemical composition. These three tasks have challenged the experience, the skill and responsibility of several groups of particle physicists over the whole world. This work refers to the primary cosmic ray composition in the scope of the Auger Collaboration. It does not intend to present a definite technique to obtain this parameter. As a matter of fact, to determine the primary composition is something difficult, considering the hadronic model dependence and the impossibi1ity (nowadays) of its description event by event. Among the several parameters used to estimate the composition, we attempted to investigate five of them: Xmax, tl0-50, t50-90, tl0-90, rlocal. They were obtained through Monte Carlo simu1ation with two different codes: CORSIKA and AIRES. The surface array was simulated by the SAMPLE program. The simu1ation results were compared, when possible, to experimental data from the Engineering Array of the Auger Observatory / Doutorado / Física da Matéria Condensada / Doutor em Ciências

<p align="justify">This work is a theoretical contribution to the study of thermo-hydrodynamic instabilities in fluids submitted to surface-tension (Marangoni) and buoyancy (Rayleigh) effects in layered (Benard) configurations. The driving constraint consists in a thermal (or a concentrational) gradient orthogonal to the plane of the layer(s).</p><p><p align="justify">Linear, weakly nonlinear as well as strongly nonlinear analyses are carried out, with emphasis on high Prandtl (or Schmidt) number fluids, although some results are also given for low-Prandtl number liquid metals. Attention is mostly devoted to the mechanisms responsible for the onset of complex spatio-temporal behaviours in these systems, as well as to the theoretical explanation of some existing experimental results. </p><p><p align="justify">As far as linear stability analyses (of the diffusive reference state) are concerned, a number of different effects are studied, such as Benard convection in two layers coupled at an interface (for which a general classification of instability modes is proposed), surface deformation effects and phase-change effects (non-equilibrium evaporation). Moreover, a number of different monotonous and oscillatory instability modes (leading respectively to patterns and waves in the nonlinear regime) are identified. In the case of oscillatory modes in a liquid layer with deformable interface heated from above, our analysis generalises and clarifies earlier works on the subject. A new Rayleigh-Marangoni oscillatory mode is also described for a liquid layer with an undeformable interface heated from above (coupling between internal and surface waves).</p><p><p align="justify">Weakly nonlinear analyses are then presented, first for monotonous modes in a 3D system. Emphasis is placed on the derivation of amplitude (Ginzburg-Landau) equations, with universal structure determined by the general symmetry properties of the physical system considered. These equations are thus valid outside the context of hydrodynamic instabilities, although they generally depend on a certain number of numerical coefficients which are calculated for the specific convective systems studied. The nonlinear competitions of patterns such as convective rolls, hexagons and squares is studied, showing the preference for hexagons with upflow at the centre in the surface-tension-driven case (and moderate Prandtl number), and of rolls in the buoyancy-induced case.</p><p><p align="justify">A transition to square patterns recently observed in experiments is also explained by amplitude equation analysis. The role of several fluid properties and of heat transfer conditions at the free interface is examined, for one-layer and two-layer systems. We also analyse modulation effects (spatial variation of the envelope of the patterns) in hexagonal patterns, leading to the description of secondary instabilities of supercritical hexagons (Busse balloon) in terms of phase diffusion equations, and of pentagon-heptagon defects in the hexagonal structures. In the frame of a general non-variational system of amplitude equations, we show that the pentagon-heptagon defects are generally not motionless, and may even lead to complex spatio-temporal dynamics (via a process of multiplication of defects in hexagonal structures).</p> <p><p align="justify">The onset of waves is also studied in weakly nonlinear 2D situations. The competition between travelling and standing waves is first analysed in a two-layer Rayleigh-Benard system (competition between thermal and mechanical coupling of the layers), in the vicinity of special values of the parameters for which a multiple (Takens-Bogdanov) bifurcation occurs. The behaviours in the vicinity of this point are numerically explored. Then, the interaction between waves and steady patterns with different wavenumbers is analysed. Spatially quasiperiodic (mixed) states are found to be stable in some range when the interaction between waves and patterns is non-resonant, while several transitions to chaotic dynamics (among which an infinite sequence of homoclinic bifurcations) occur when it is resonant. Some of these results have quite general validity, because they are shown to be entirely determined by quadratic interactions in amplitude equations.</p><p><p align="justify">Finally, models of strongly nonlinear surface-tension-driven convection are derived and analysed, which are thought to be representative of the transitions to thermal turbulence occurring at very high driving gradient. The role of the fastest growing modes (intrinsic length scale) is discussed, as well as scalings of steady regimes and their secondary instabilities (due to instability of the thermal boundary layer), leading to chaotic spatio-temporal dynamics whose preliminary analysis (energy spectrum) reveals features characteristic of hydrodynamic turbulence. Some of the (2D and 3D) results presented are in qualitative agreement with experiments (interfacial turbulence).</p><p><p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished