O objetivo deste trabalho é avaliar o processo atual de preparação de superfície para aderência de isolantes térmicos em envelopes motores foguetes de 1.000 mm de diâmetro, visando sua utilização no aço Maraging 18Ni300, tendo como parâmetros de comparação a rugosidade superficial e a resistência mecânica adesiva, obtida atualmente na interface colada metal/isolante térmico do aço 300MESR. Para isso, foram realizados experimentos de campo, com uma abordagem quantitativa, por meio da medida de rugosidade (Ra) nas superfícies de amostras de aços, submetidas a tratamento superficial mecânico de jateamento abrasivo a seco com granalha de aço de perfil angular, sendo posteriormente selecionadas e utilizadas como substrato em juntas adesivadas que, por fim, foram submetidas a ensaio mecânico de cisalhamento, para verificação da resistência mecânica adesiva. A utilização de métodos de análise estatísticos (análise de variância, teste de tukey, intervalo de confiança) aplicados aos dados coletados, permitiram estabelecer, para o processo atual uma faixa de resistência mecânica adesiva para cada aço pesquisado. Os resultados obtidos confirmam, com boa margem de segurança, que o processo atual de preparação de superfície para aderência de isolantes térmicos pode ser aplicado ao aço Maraging 18Ni300, sem que ocorra perda significativa de resistência mecânica adesiva na interface colada metal/isolante térmico. / The aim of this work is to evaluate the current process of preparing the surface for adherence of thermal insulation in rocket motor of 1,000 mm diameter, seeking their use in Maraging18Ni300 steel, taking as parameters comparison the of surface roughness and mechanical adhesive strength obtained, currently, in the bonded interface metal /heat insulator 300M-ESR steel. A field experiment was conducted with a quantitative approach, by measuring surface roughness (Ra) on the surfaces of steel samples, subjected to mechanical surface treatment of dry abrasive blasting, with steel shot with angular profile and which were, subsequently, selected and used in bonded joints that were finally submitted to mechanical shear tests to verify the mechanical adhesive strength. The use of statistical methods of analysis (variance analysis, Tukey test, confidence interval), applied to selected data, allowed to establish for the current process, a range of mechanical adhesive strength for each steel investigated. The results confirm, with a good safety margin, that the current process of preparing the surface for adhesion of thermal insulation can be applied to the Maraging18Ni300 steel, without significant loss of mechanical adhesive strength in the metal /heat insulator bonded interface.

Nesta dissertação estudaremos sistemas de bósons ultrafrios armadilhados em uma rede ótica quadrada bidimensional sem levar em consideração o confinamento harmônico. A dinâmica desses sistemas é bem descrita pelo modelo de Bose-Hubbard, que prevê uma transição de fase quântica de um superfluido para um isolante de Mott a temperaturas baixas, e pode ser induzida variando a profundidade do potencial da rede ótica. Apresentaremos o diagrama de fases dessa transição construído a partir de uma aproximação de campo médio e também com um cálculo numérico usando um algoritmo de Monte Carlo Quântico, denominado algoritmo Worm. Encontramos o ponto crítico para o primeiro lobo de Mott em ambos os casos, concordando com trabalhos anteriores. / This work study the two-dimensional ultracold bosonic atoms loaded in a square optical lattice, without harmonic confinement. The dynamics of this system is described by the Bose-Hubbard model, which predicts a quantum phase transition from a superfluid to a Mott-insulator at low temperatures that can be induced by varying the depth of the optical potential. We present here the phase diagram of this transition built from a mean field approach and from a numerical calculation using a Quantum Monte Carlo algorithm, namely the Worm algorithm. We found the critical transition point for the first Mott lobe in both cases, in agreement with the standard literature.

Neste trabalho de mestrado apresentamos um estudo sobre a manifestação do efeito Rashba em isolantes topológicos na ausência de simetria de inversão estrutural. Os cálculos das propriedades atomísticas, energéticas e as estruturas eletrônicas são abordados através de métodos de primeiros princípios baseados na teoria do funcional da densidade. E seus resultados foram utilizados para o desenvolvimento de hamiltoniana efetiva baseado no modelo de Zhang. Realizamos o estudo de dois sistemas: 1) Bi$_2$Se$_3$ com átomos de Sn depositados na superfície: Este sistema pode ser entendido através da manifestação do efeito Rashba sobre um isolante topológico dada a quebra de simetria de inversão estrutural. Para um sítio de deposição específico, os átomos de Sn causam uma reconstrução da superfície e um terceiro cone de Dirac é observado na estrutura eletrônica. Este terceiro cone é não localizado na superfície e pode ser entendido como a manifestação do efeito Rashba. 2) PbBiI: Reportado aqui como um novo isolante topológico 2D com efeito Rashba. Descobrimos este sistema por um estudo sistemático sobre uma família de materiais formados por átomos tipo IV, V, e VII, cuja estrutura cristalina é hexagonal e não centrossimétrica. Mostramos que o PbBiI possui: i) Estabilidade mecânica, ii) Spin-splitting Rashba de 60 meV, iii) um gap de energia não trivial de 0.14 eV, iv) retroespalhamento proibido entre os estados de borda e v) retroespalhamento proibido entre os estados do bulk no entorno do nível de Fermi. Estas propriedades fazem do PbBiI um candidato para construção de dispositivos de spintrônica que atenua a perda de energia. / In this work, were studied the Rashba effect in topological insulators without structural inversion symmetry. We performed a first principles study based on density functional theory to calculate the atomistic properties, formation energy and electronic structure. These results were used to development a effective Hamiltonian based on Zhang model. They were studied two systems: 1) Bi$_2$Se$_3$ with Sn atoms deposited on the surface: This system can be seen as the Rashba effect manifestation on a topological insulator due to the structural inversion symmetry breaking. For a specific deposition site, the Sn atoms cause a reconstruction of the surface and display a third Dirac cone in the electronic structure. This third cone is not located on the surface and can be understood as the giant Rashba effect manifestation. 2) We propose a new non-centrosymmetric honeycomb-lattice QSH insulator family formed by the IV, V, and VII elements. The system formed by Bi, Pb and I atoms is reported here as a new 2D topological insulator with Rashba effect. We show that this system has: i) Mechanical stability, ii) spin-splitting Rashba of 60 meV, iii) nontrivial energy gap of 0.14 eV, iv) backscattering forbidden for both edge and bulk conductivity channels in the nanoribbon band structure. These properties make PbBiI a good candidate to construct spintronic devices with less energy loss.

Integrated Silicon Photonics has emerged as a powerful platform in the last two decades amongst high-bandwidth technologies, particularly since the adop- tion of CMOS compatible silicon-on-insulator(SOI) substrates. Microring res- onators are one of the fundamental blocks on a photonic integrated circuit chip o ering versatility in varied applications like sensing, optical bu ering, ltering, loss measurements, lasing, nonlinear e ects, understanding cavity optomechanics etc. This thesis covers the design and modeling of microring resonators for biosensing applications. The two applications considered are : homogeneous biosensing and wrist pulse pressure monitoring. Also, the designs have been used to fabricate ring resonator device using three different techniques. The results obtained through characterization of these devices are presented. Following are the observations made in lieu of this: 1) Design modeling and analysis - The analysis of ring resonator requires the study of both the straight and bent waveguide sections. Both rib and strip waveguide geometries have been considered for constructing the device as a building block by computing their respective eigen modes for both quasi-TE and quasi-TM polarizations. The non-uniform evanescent coupling between the straight and curved waveguide has been estimated using coupled mode theory. This method provided in estimating the quality-factor and free spec- tral range (FSR) of the ring-resonator. A case for optimizing the waveguide gap in the directional coupler section of a ring resonator has been presented for homogeneous biosensing application. On similar lines, a model of applying ring resonator for arterial pulse-pressure measurement has been analyzed. The results have been obtained by employing FD-BPM and FDTD including semi- vectorial eigen mode solutions to evaluate the spectral characteristics of ring resonator. The modeling and analytical results are supported by commercial software tools (RSoft). 2) Fabrication and Characterization - For the fabrication, we employ the design of ring resonator of radius 20 m on SOI substrate with two different waveguide gaps of 350 and 700 nm. Three different process sows have been used for fabricating the same device. The rst technique involved using negative e-beam resist HSQ which after exposure becomes SiO2, acts as a mask for Reactive-Ion Etching (RIE); helping in eliminating an additional step. The second technique involved the use of positive e-beam resist, PMMA for device patterning followed by metal deposition with lift-o . The third tech- nique employed was Focussed Ion-beam (FIB) which is resist-less patterning by bombarding Ga+ ions directly onto the top surface of the wafer with the help of a GDS le. The characterization process involved estimation of loss and observing the be- havior of optical elds in the device around the wavelength of 1550 nm using near-field scanning optical microscopy (NSOM) measurement. The estimation of roughness-induced losses has been made by performing Atomic Force Microscopy (AFM) measurements. In summary, the thesis presents novel design and analysis of SOI based microring resonators for homogeneous biosensing and wrist pulse pressure sensing applications. Also, the fabrication and characterization of 20 m radius ring- resonator with 500 500 nm rib cross-section is presented. Hence, this study brings forth several practical issues concerning application of ring resonators to biosensing applications.

Cette thèse concerne l’étude de l’effet du dopage au chrome sur les propriétés structurales, électriques et optiques des films de dioxyde de vanadium. Ces films V(1-x)CrxO2 (x allant de 0 à 25%) de 110 nm d’épaisseur ont été déposés par dépôt par ablation laser (PLD) multicibles sur substrat saphir c. Ils ont été caractérisés grâce à des techniques d’analyse morphologique, structurale, électrique et optique. Les différentes phases présentes dans les films V(1-x)CrxO2 ont été identifiées par DRX, spectroscopie Raman et comparées au diagramme de phase du matériau massif. Les phases M1, M2 et M3, un mélange M2 + M3 et la phase R ont été identifiées. En revanche la phase M4 n’a pas été détectée pour des dopages supérieurs à 8%, montrant une réelle différence entre diagrammes de phase du matériau massif et des films. Le dopage au chrome a permis d’augmenter la température de transition isolant-métal de 68 à 102°C. En revanche, la dynamique de cette transition, déterminée par mesure de transmission optique ou par mesure de résistivité électrique, est souvent diminuée. Enfin, des dispositifs à deux terminaux à base de films V(1-x)CrxO2 ont été réalisés. Leurs caractérisations courant-tension montrent que le dopage au chrome influence fortement le seuil d’activation de la transition entre les états isolant et métallique. / This thesis presents a study of the effect of chromium doping on structural, electrical and optical properties of thin films of vanadium dioxide. These V(1-x)CrxO2 thin films (x from 0 to 25%) of 110 nm thick have been deposited on c sapphire substrate by multi target Pulsed Laser Deposition method. Their morphological, structural, electrical and optical properties have been studied. Different phases for V(1-x)CrxO2 have been identified by XRD and Raman analysis and compared to those of bulk material. M1, M2, M3, a mixture M2 + M3 and R phases are present. The M4 phase has not been detected for doping above 8%, showing a real difference between phase diagram of bulk and thin films. Chromium doping also increases the metal-insulator transition temperature from 68°C to 102°C. Moreover, the transition dynamics, determined using optical transmission and electrical resistivity measurements, decreases. Finally, two terminal switches based on V(1-x)CrxO2 thin films have been fabricated. Their current-voltage characterization showed that chromium doping affects the activation threshold voltage of the metal to insulator transition.

This paper presents a methodology for optimizing the distribution transformers project, considering the capitalized cost, employing concurrently in your project amorphous core and insulating vegetable oil. The use of amorphous core technology provides a significant reduction of the load losses as the use of the insulating vegetable oil which is a non-toxic fluid and rapidly biodegradable when in contact with the environment, it allows increasing the machine's operating temperature . The use of these two materials have provided considerable percentage improvements in efficiency and cost / power compared to conventional distribution transformers manufactured. The methodology is aimed to create and select designs that have a lower total cost, namely the sum of the transformer manufacturing cost capitalized cost of losses during the useful life envisaged for the equipment. In addition, it presents the case study of a 75 kVA designed distribution transformer and manufactured with amorphous core and insulating vegetable oil, routine employed optimization (developed in VBA Excel), the theoretical results obtained from the optimized design and the experimental results. / Este trabalho apresenta uma metodologia de otimização do projeto de transformadores de distribuição, considerando o custo capitalizado, que empregam concomitantemente em seu projeto núcleo amorfos e óleo vegetal isolante. O emprego da tecnologia de núcleo amorfo proporciona significativa redução das perdas em vazio, enquanto a utilização do óleo vegetal isolante, que é um fluído não tóxico e de rápida biodegradação quando em contato com o meio ambiente, possibilita o aumento da temperatura de operação do equipamento. A utilização desses dois materiais propiciaram melhoras percentuais consideráveis na eficiência e na relação custo/potência em comparação aos transformadores de distribuição convencionalmente fabricados. A metodologia visa criar e selecionar projetos que tenham um menor custo total, ou seja, a soma do custo de fabricação do transformador com o custo capitalizado das perdas durante a vida útil considerada para o equipamento.Além disso, é apresentado o estudo de caso de um transformador de distribuição de 75 kVA projetado e fabricado com o núcleo amorfo e óleo vegetal isolante, a rotina de otimização empregada (desenvolvida em VBA Excel), os resultados teóricos obtidos a partir do projeto otimizado e os resultados experimentais.

Dans cette thèse, j’étudie la compressibilité électronique de deux isolants topologiques tridimensionnels : Le tellurure de mercure (HgTe) sous contrainte et le séléniure de bismuth (Bi2Se3).Je présente des mesures d’admittance électronique à basse température résolues en phase sur une large gamme de fréquence. Cela permet d’extraire la capacité quantique associé à la densité d’états et la résistivité des matériaux étudiés.Nous montrons qu’un isolant topologique intrinsèque présente une réponse dominée par les états de surface topologiques sur une large gamme d’énergie qui s’étend au-delà du gap de transport du matériau massif. Ce régime, appelé « écrantage de Dirac », est caractérisé par une compressibilité électronique proportionnelle à l’énergie de surface et une haute mobilité.Dans la suite, nous nous intéressons à la limite de ce régime. Nous observons qu’à haute énergie et sous l’influence de forts champs électriques perpendiculaires, des états excités massifs de surface sont peuplés ce qui se manifeste expérimentalement de différentes façons : Une chute dans la constante de diffusion électronique, un pic de conductivité ainsi que l’apparition d’un deuxième type de porteurs en magnéto-transport et de métastabilité dans la relation charge-tension.Un modèle théorique basé sur un traitement quasi-relativiste du Hamiltonien de surface est présenté. Il permet d’identifier la dépendance en énergie et champ électrique des états massifs de surface.Cette thèse est complémenté par des résultats expérimentaux sur Bi2Se3 obtenu par croissance sur nitrure de bore mettent en évidence l’importance de la pureté des interfaces d’isolants topologiques. / This thesis discusses the electronic compressibility of two representative three dimensional topological insulators: Strained mercury telluride (HgTe) and bismuth selenide (Bi2Se3).I present low temperature phase-sensitive electron admittance data over a broad frequency range. This allows to extract the quantum capacitance related to the density of states and the resistivity of the investigated materials.We show that the response of an intrinsic topological insulator is dominated by topological surface states over a large energy range exceeding the bulk material’s transport gap. This regime, named “Dirac screening” is characterized by an electron compressibility proportional to the surface Fermi level and a high mobility.Subsequently, we investigate the limits of this regime. At high energy and large perpendicular electric fields we observe the population of excited massive surface states. Experimentally, these manifest themselves in multiple signatures: A drop in the electronic diffusion constant, a peak in the conductivity, appearance of a second carrier type in magneto-transport and meta-stability in the charge-voltage relation.A theoretical model based on a quasi-relativistic treatment of the surface Hamiltonian is presented. It allows to identify the electric field and energy dependence of the massive surface states.This thesis is complemented by experimental results on Bi2Se3 grown on boron nitride, where we demonstrate the importance of clean surfaces for the study of electronic properties in topological insulators.

L'émergence d'une une nouvelle classe de matériaux, des isolants topologiques, a stimulé un vaste champ de recherche. Bismuth, un élément du groupe V du tableau périodique, est un des ingrédients clé d'une famille d'isolants topologiques. Pour des applications dans la technologie des composants électroniques, il est essentiel de maîtriser la préparation des matériaux en couches minces. Dans ce travail de thèse, nous avons étudié la croissance et la structure électronique de bismuth sur les surfaces (100) et (111) de semi-conducteur III-V InAs.Déposition de Bi sur la surface InAs(100) résulte en une auto-organisation de Bi qui forme des lignes de taille atomique. On montre que le bismuth interagit extrêmement faiblement avec la surface car la structure d'origine de la surface propre de l'InA(100) reste intacte. L'étude de la bande valence montre la présence d'états résonants fortement dépendants de l'énergie de photons et de la polarisation de la lumière, en cohérence avec la structure quasi unidimensionnelle de la surface.La spécificité de la surface InAs(111) est qu'elle a deux terminaisons différentes: par In, (face A) et par As, (face B). Les deux faces présentent des reconstructions différentes. Par la photoémission des niveaux de coeur nous avons montré une différence de réactivité chimique entre les faces A et B. La croissance de Bi sur la face A résulte en un monocristal de haute qualité pour les films à partir de 10 monocouches. Par contre, lors du dépôt de premières couches, la face B montre une croissance en îlots et un bon monocristal est obtenu seulement pour des films d'au moins de 50 monocouches.Pour la même face, A ou B, nous avons observé des différences de croissance plus subtiles entre les surfaces préparées soit par le bombardement ionique et des recuits soit par l'épitaxie par jets moléculaires.La photoémission résolue en angle a permit de caractériser la dispersion des bandes dans les films de Bi. La dispersion est tout à fait comparable au cristal massif de Bi. La dernière étape consistait à étudier la structure électronique d'un monocristal de Sb déposé sur le film de Bi.Les surfaces propres de InAs(111)A et InAs(111)B présentent une courbure de bande qui résulte en formation d'une couche d'accumulation d'électrons. En déposant le Bi sur ces surfaces, la couche d'accumulation est préservée, elle est même amplifié, car Bi agit comme le donneur dans l'InAs.La couche d'accumulation se traduit par un confinement quantique des électrons, mesurable par la photoémission résolue en angle.Mots clés :Structure électronique de surface, ARPES, semimétal, courbure de bande, Gaz-2D, Bismuth, Sb, InAs(111)A, InAs(111)B, puits quantique, surface Fermi, couches minces. / A new class of material is coming up, Topological Insulators, have opened a wide field of research. Bismuth, an element of group V of periodic table, is one of the key ingredient of this Topological Insulators family. With the aim of improving technological applications, especially the electronic compounds, it is of most importance to control the preparation of thin films materials. Within this Phd work, we studied the growth and Bismuth electronic structure on (100) and (111) semiconductor III-V InAs surfaces.Bi deposition on InAs(100) surface result of a Bi self-assembly which forms lines at atomic scale. We show Bi interact extremely weakly with the surface because the beginning structure of clean InAs(100) surface stay unharmed. The study of valence band sheds light on the existence of resonant states strongly photon energy dependent and also depend on the light polarization, consistent with almost one dimensional structure surface.InAs(111) surface specific feature is that it has both surface ending different : In ending, (face A) and As ending, (face B). The both faces pointed out distinguishable reconstructions. By the core-level photoemission we identified a chemical reactivity difference taking place between A and B faces. Bi growth on A-face tend to be a high quality monocrystal for those films from a thickness of 10 monolayers. On the other hand, during the deposition of first layers, the B-face show an island growth and a good monocrystal is obtained only available for films with 50 monolayers at least.For the same face, A or B, we have seen some growth discrepancies more subtle between prepared surfaces either by ionic bombardment and annealing (IBA) either by molecular beam epitaxy (MBE).The angular resolved photoemission allowed to identify the band dispersion inside of this Bi films. The dispersion is absolutely relative to the bulk Bi crystal. The final step involved the study of Sb monocrystal electronic structure deposited onto Bi film.Clean InAs(111)A and InAs(111)B surfaces indicate a band bending which result in the accumulation electron charge formation. With depositing Bi onto these surfaces, the accumulation layer would be kept, it is also increased, given that Bi acts as a donor-like in InAs. The accumulation layer is characterized by an electron quantum confinement, measurable by angle resolved photoemission.Keywords:Electronic structure surface, ARPES, semimetal, band bending effect, 2DEG, Bismuth, Sb, InAs(111)A, InAs(111)B, quatum wells, Fermi surface, thin films.

Magneto-transport study on high mobility electron systems in both 2D- and 3D- case has attracted intense attention in past decades. This thesis focuses on the magnetoresistance behavior in 3D topological insulator Bi2Te3 and GaAs/AlGaAs 2D electron system at low magnetic field range 0.4T the first drop at T~3.4K to tndium superconductor and considered the second drop at lower temperature as the proximity effect that occurred near the interface between these two materials. On the other hand, GaAs/AlGaAs heterostructure, as a III-V semiconductor family, has been extensively studied for exploring many interesting phenomena due to the extremely high electron mobility up to 10^7 cm^2/Vs. In this thesis, two interesting phenomena are present and discussed in a GaAs/AlGaAs system, which are the electron heating induced tunable giant magnetoresistance study and phase inversion in Shubnikov-de Haas oscillation study, respectively. By applying elevated supplementary dc current bias, we found a tunable giant magnetoresistance phenomenon which is progressively changed from positive to giant negative magnetoresistance. The observed giant magnetoresistance is successfully simulated with a two-term Drude model at all different dc biases, I_{dc}, and temperature, T. In addition, as increasing the dc current bias, a phase inversion behavior was observed in Shubnikov-de Haas oscillation, which was further demonstrated by the simulation with an exponential damped cosine function. This thesis also presents an ongoing project, which is the observation and fabrication of 2D layered materials. The studied 2D layered materials includes graphene, biron nitride, Molybdenum disulfide, etc. At the end, a future work about fabrication of the 2D layered materials devices as well as the suggestion about the measurement are discussed.

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