This study measures the electron-induced luminescence (cathodoluminescence) for various samples of fused silica. With a band gap of ~8.9 eV, visible and near-IR (NIR) luminescence occurs only if there are states (localized defect or trap states) within the forbidden band gap for electrons to occupy. A model is presented based on the electronic band structure and defect density of states—used to explain electron transport in highly disordered insulating materials—which has been extended to describe the relative cathodoluminescent intensity and spectral bands as a function of incident beam energy and current density, sample temperatures, and emitted photon wavelength. Tests were conducted on two types of disordered SiO2 samples, the first type containing two variations: (i) thin (~60 nm) coatings on reflective metal substrates, and (ii) ~80 μm thick bulk samples. Luminescence was measured using a visible range SLR CCD still camera, a VIS/NIR image-intensified video camera, a NIR video camera, and a UV/VIS spectrometer. Sample temperature was varied from ~295 K to 40 K. The results of these tests were fit with the proposed model using saturation dose rate and mean shallow trap energy as fitting parameters and are summarized below. First, each incident energy has a corresponding penetration depth, or range, which determines the fraction of energy absorbed in the material. In the thinner samples, the range exceeds the thickness of the sample; therefore, the intensity decreases with increasing energy. However, for the thicker samples, the range is less than the sample thickness and the intensity increases linearly with incident energy. Next, at low current densities, luminescent intensity is linearly proportional to incident current density through the dose rate. At very high current densities, saturation is observed. Finally, the overall luminescent intensity increased exponentially as T decreased, until reaching an optimum temperature, where it falls off to zero (as the model predicts). The spectra show four distinct bands of emitted photon wavelengths, corresponding to four distinct energy distributions of defect states within the band gap, each behaving differently with temperature. The response of each band to temperature is indicative of the extent to which it is filled.

Ce travail de thèse porte sur l'étude d'oxydes (ZnO et SiO2) fabriqués par voie sol-gel. Dans un premier temps, nous avons étudié la cinétique de croissance des nanoparticules de ZnO en milieu aqueux. L'étude in-situ de la croissance d'oxyde de zinc par la technique de croissance en milieu aqueux (ACG) a été réalisée grâce à la radiation synchrotron de l'ESRF sur la ligne ID10B. Nous avons réalisé la diffraction de rayons X en incidence rasante sur un substrat plongé dans une solution constituée de nitrate de zinc hexahydraté [Zn(NO3)2,6H2O], d'hexamethylenetetramine (HMT) (C6H12N4) et de l'eau dé-ionisée comme solvant. Nous avons réussi à mettre en évidence l'existence de nanoparticules de ZnO dans la solution et suivre la cinétique de formation. La deuxième partie de ce travail est consacrée à l'étude des films minces de silice mésoporeux structurés par un tensioactif connu sous l'acronyme Brij58. Nous avons commencépar établir le diagramme de phase du Brij58 par la diffusion centrale des rayons X (SAXS), complété par l'établissement d'un diagramme d'état solide-liquide par la rhéologie. Grâce à ce diagramme de phase nous avons pu fabriquer des films minces de silice. L'étude de la structuration des films a été réalisée par la diffusion des rayons X en incidence rasante (GISAXS) et la réflectivité des rayons X. Nous avons finalisé ce travail par l'utilisation des films mésoporeux comme matrice hôte à deux fluides : l'eau et le CO2, et par l'insertion de nanocristaux de ZnO dans les pores de la matrice mésoporeuse.

The diploma thesis deals with the experimental study of shielding effect of oxide isolating layer on surface potential measured by Kelvin Probe Force Microscopy. For the study of surface potential were created Au/SiO2 based nanostructures by Electron Beam Lithography, Atomic Layer Deposition and Multilayer Deposition. Surface potential was measured depending on the relative humidity and thickness of oxide isolating layer.

Gas source molecular beam epitaxy (GSMBE) has been used to grow InGaAs/lnP epitaxial layers in selected areas defined by SiO2-masked InP substrates, with the goal of obtaining controlled in-plane variations in the bandgap of the InGaAs wells. The ability to alter the bandgap of the semiconductor spatially over the surface in one growth procedure is desirable for integrating laser, waveguide and detector devices. To form the masked substrates, stripes (ranging in width from 2 pm to 50 pm) were opened up in SiO2 by standard photolithography. The crystal growths were carried out at various substrate temperatures (ranging from 460 °C to 510 °C) and arsenic fluxes (V/lll ratios ranging from 1.2 to 3.4). The properties of the epitaxial layers were investigated by using such analytical techniques as photoluminescence, electroluminescence and transmission electron microscopy (TEM). Photoluminescence measurements performed on waveguide stripes of decreasing width reveal an increasing red-shift of the e1-hh1 transition in InGaAs wells. The maximum red-shift occurred when growing at a high substrate temperature and a low arsenic flux. For example, a decrease in slit width from 50 pm to 10 pm resulted in a 25 meV shift of the photoluminescence peak. From cross-sectional TEM measurements, the wavelength shift observed can be attributed primarily to an increase in thickness of the InGaAs well, due to incorporation of additional indium and gallium migrating from the material on the masked regions. The interfaces in the centre of the stripe region are defect free; however, stacking faults and thickness variations are evident 1-2 pm from the edges. These results are confirmed by scanning photoluminescence, in which the maximum intensity occurs at the centre of the stripe and decreases to zero at the edges. Mapping of the peak wavelength across the stripe reveals a diffusion profile, with the edges being additionally red shifted by 10 nm. Reactive ion etching of the edge and the polycrystalline material results in a much improved spectral photoluminescence scan, in both increased intensity of the bandgap peak and elimination of lower energy peaks assumed to be correlated with edge effects. Finally, a stripe contact light emitting device, with a single 50 A quantum well InGaAs/lnP structure, was fabricated and electrically pumped. The device exhibited spectral peak wavelength shifts between narrow stripes (10 pm) and wide stripes (50 pm) of 22 nm, similar to the value observed by photoluminescence studies. / Thesis / Master of Engineering (ME)

No description available.

Les travaux présentés dans ce manuscrit, sont basés sur l'étude de l'auto-organisation de la matière à l'échelle nanométrique. A cette échelle, les énergies de surfaces jouent un rôle prépondérant dans cette organisation. Pour comprendre au mieux ses mécanismes nous avons étudié plusieurs types de structures à base de Silicium et de Germanium. Nous avons expérimentalement étudié la croissance cristalline ou amorphe sur différents types de substrats (amorphe : SiO2 et cristallins Si ou SOI). Certain de ces substrats furent nano-structurés en utilisant un faisceau d'ions focalisés de type Gallium ou Or-Silicium. De plus nous avons pu utiliser des surfaces différentes telle que le TiO2 ou le Silicium poreux, afin d'étudier l'organisation de la matière sur des pores de petites tailles (inférieurs à 50nm). / The following works are base on the study of self assembly structures at the nanometric scale. At this scale the surface energy have a major impact in this organization. For a better understanding of this mechanism we studied different Silicon-Germanium base structures. We experimentally studied the crystalline or amorphous growth on different types of substrates (amorphous: SiO2, crystalline: Si or SOI). Some of these substrates were nano-structured using a focused ion beam using gallium source or gold-silicon source. In addition, we were able to use different surfaces such as TiO2 or porous silicon to study the organization of the material small size pore(less than 50nm).

Neste trabalho foi estudado o efeito dos parâmetros de síntese na resposta de polarização de híbridos Nafion-SiO2 como eletrólitos em células a combustível poliméricas (PEMFC) em elevadas temperaturas (até 130 °C). A fase inorgânica foi adicionada à matriz polimérica com o objetivo de aumentar a retenção de água na membrana em elevadas temperaturas (acima de 100 °C); melhorar as propriedades mecânicas do Nafion e favorecer cineticamente as reações eletródicas. As membranas foram preparadas a partir da incorporação in-situ de sílica em membranas comerciais de Nafion por rota sol-gel acompanhada de catálise ácida. Os parâmetros de síntese, tais como: concentração do catalisador ácido, natureza do solvente, temperatura e tempo de reação e concentração do precursor de silício (Tetraetil-Ortosilicato TEOS) foram avaliados em função do grau de incorporação e resposta de polarização. Os híbridos Nafion-SiO2 foram física e quimicamente caracterizados por gravimetria, termogravimetria (TG), microscopia eletrônica de varredura e espectroscopia de energia dispersiva de raios X (MEV-EDX), espectroscopia de impedância eletroquímica (EIS) e espalhamento de raios X em baixos ângulos (SAXS). Por fim, os híbridos sintetizados foram avaliados diretamente como eletrólitos em células PEM unitárias alimentadas com hidrogênio (H2) e oxigênio (O2) no intervalo de temperatura de 80 ºC a 130 ºC e a 130 ºC em condições de umidade relativa reduzida (75 e 50%). Resumidamente, o desempenho dos híbridos se mostrou fortemente dependente dos parâmetros de síntese, principalmente, o tipo de álcool utilizado e concentração inicial de TEOS. / In this work, the effect of sol-gel synthesis parameters on the preparation and polarization response of Nafion-SiO2 hybrids as electrolytes for proton exchange membrane fuel cells (PEMFC) operating at high temperatures (130 oC) was evaluated. The inorganic phase was incorporated in a Nafion matrix with the following purposes: to improve the Nafion water uptake at high temperatures (> 100 oC); to increase the mechanical strength of Nafion and; to accelerate the electrode reactions. The hybrids were prepared by an in-situ incorporation of silica into commercial Nafion membranes using an acid-catalyzed sol-gel route. The effects of synthesis parameters, such as catalyst concentration, sol-gel solvent, temperature and time of both hydrolysis and condensation reactions, and silicon precursor concentration (Tetraethylorthosilicate TEOS), were evaluated as a function on the incorporation degree and polarization response. Nafion-SiO2 hybrids were characterized by gravimetry, thermogravimetric analysis (TGA), scanning electron microscopy and X-ray dispersive energy (SEM-EDS), electrochemical impedance spectroscopy (EIS), and X-ray small angle scattering (SAXS). The hybrids were tested as electrolyte in single H2/O2 fuel cells in the temperature range of 80 130 oC and at 130 oC and reduced relative humidity (75% and 50%). Summarily, the hybrid performance showed to be strongly dependent on the synthesis parameters, mainly, the type of alcohol and the TEOS concentration.

Afin de répondre aux problématiques écologique et économique du traitement des Matériaux Contenant de l’Amiante (MCA), un procédé complet permettant de traiter de manière optimale ces déchets a été proposé. Pour cela, trois types de déchets ont d’abord été analysés par plusieurs techniques de caractérisation complémentaires (diffraction des rayons X, microscopie électronique à balayage, infrarouge et RMN du solide). Ces analyses ont permis l’identification des différentes phases présentes au sein des déchets. Cette identification est nécessaire, car elle permet d’adapter de manière optimale le procédé de destruction au déchet. La première étape de ce procédé est le traitement en température des MCA dans une solution d’acide nitrique. Elle permet la dissolution de la matrice du déchet et la dénaturation des fibres de chrysotile qui sont présentes dans 95 % des déchets amiantés. Deux phases sont alors récupérées à l’issue de ce traitement : une phase solide composée de silice pure et une phase liquide contenant, notamment, du calcium, du magnésium et du fer. Si les déchets contiennent des fibres de type amphibole (5 % des MCA) ils sont ensuite traités par voie hydrothermale dans un autoclave contenant une solution de soude. Cette étape mène à la dissolution complète du déchet. Une solution basique contenant du silicium est ainsi récupérée. Différentes voies de valorisations ont été développées. Les ions présents dans la solution acide sont récupérés par précipitation sélective des hydroxydes. Une autre voie consiste à synthétiser une zéolithe à partir de la silice pure et de la solution basique. Les isothermes d’adsorption de cette dernière ont été tracés afin de déterminer sa capacité d’adsorption de certains cations métalliques polluants. Pour terminer, une étude fondamentale a été menée sur les nanotubes de silice obtenus avec le traitement de fibres d’amiante pures et différentes applications de ces nanotubes de silice ont été évoquées. / To answer the ecological and economic problems of the treatment of Materials Containing Asbestos (MCA), a complete process allowing to handle in an optimal way these waste was proposed. For that purpose, three types of waste were analyzed by several complementary techniques of characterization (X-rays diffraction, Scanning Electron Microscopy, infrared and NMR spectroscopy). These analyses allowed the identification of the present various phases within waste. This identification is necessary, because it allows to adapt in the optimal way for the destruction of the waste. The first stage of the process is a treatment in temperature of the MCA in a solution of nitric acid leading to the dissolution of the matrix of the waste and the denaturation of the fibers of chrysotile which are present in 95 % of MCA. Two phases are then got back at the end of this treatment: a solid phase of pure silica and a liquid phase containing, in particular, calcium, magnesium and iron ions. If previous waste contains fibers of amphibole type (5 % of the MCA) they are then treated through a hydrothermal process in an autoclave containing a solution of soda. This stage leads to the complete dissolution of the waste. The basic solution containing some silicon is so got back. Various ways of valuations were then developed. The present ions in the acid solution are chemically sorted out by a selective precipitation of hydroxides. Another way consists in synthesizing a zeolite from the pure silica coming from the acid treatment and from the basic solution after hydrothermal treatment. The isotherms of adsorption of this synthesized zeolite were established to determine its capacity of adsorption of certain polluting metallic cations. To finish, a fundamental study was led on the nanotubes of silica obtained after the acid treatment of pure asbestos fibers and diverse applications of these nanotubes of silica were evoked.

In this study we used a different route, simple and economical: the dissolution of the SiO2 powder DGEBA with a hardener to base polymercaptan ( aradur 90 ). Analysis was performed micro hardness in different percentages of the concentration of SiO2. The hardness of multicomponent solid is approximately equal to the average hardness of the material composition and is also related to the fraction of crystalline phase present in these materials. Since the hardness of the material a decisive factor for its implementation, it is interesting to see how this property varies depending on the composition of multicomponent solid. Was used to DGEBA Araldite GY 279 and hardener aradur 90 provided by Huntsman. We prepared several samples with different concentrations of SiO2 (3%, 5%, 10%, 20%, 30%, 40% and 50%) compared to the total mass of Araldite-Aradur Mixtures spent 24 hours at ambient temperature and then became a cure at 100 ° C, 120 ° C, 140 ° C, 160 ° C and 180 ° C for 4 h in an oven at ambient pressure. For the determination of hardness, we used a Shimadzu micro hardness tester equipped with an indenter Vickers. Several tests were performed and it was observed that the micro hardness was a sharp increase with increasing temperature and the concentration of SiO2. This behavior is associated mainly to the oxidation of the surface and also due to the higher concentration of SiO2, forming a kind of composite with a thermosetting characteristics of high rigidity. There was a significant growth type reaching a 500 % increase in Vickers hardness between the sample with 50 % SiO2 and pure to a cure of 180 °C. Were also carried out measurements of elastic modulus and pure sample was obtained a score of 1.65 x107 Pa for the sample with 50 % had a value of 8x107 Pa. The growth of the elastic modulus accompanied the growth of the hardness, around 480 %. The presence of SiO2 in the epoxy resin causes a change in the mechanical properties of DGEBA and a concentration of 50% at 180 ° C for a cure for 4 h, a significant increase of the same. It was also observed at high homogeneity powder of silicon oxide to Araldite and Aradur These results indicate that the composite DGEBA/SiO2 can be a good candidate to be used in covering of metals, for example, duct that demand a good hardness. / Neste trabalho foi utilizado uma rota diferente, simples e econômica: a dissolução do pó de SiO2 na DGEBA com um endurecedor a base de polimercapitana. Foi feita análise de microdureza nos diferentes percentuais da concentração de SiO2. A dureza em sólidos multicomponentes é aproximadamente igual à média aritmética das durezas dos materiais constituintes e está ainda relacionada com a fração da fase cristalina presentes nestes materiais. Sendo a dureza do material um fator decisivo para a aplicação do mesmo, torna-se interessante verificar como esta propriedade varia em função da composição em sólidos multicomponentes. Foi utilizado a DGEBA Araldite GY 279 e o endurecedor Aradur 90 fornecido pela Huntsman. Foram preparadas diversas amostras com concentrações diferentes de SiO2 (3 %, 5 %, 10 %, 20 %, 30 %, 40 % e 50 % ) em relação a massa total de Araldite-Aradur. As misturas passaram 24 h à temperatura ambiente e depois fez-se uma cura a 100 °C, 120 °C, 140 °C, 160 °C e 180 °C, durante 4 h em uma estufa em pressão ambiente. Para a determinação da microdureza, utilizou-se um microdurômetro da Shimadzu equipado com um identador Vickers. Diversas análises foram realizadas e foi observado que a microdureza teve um crescimento acentuado em função do aumento da temperatura e da concentração de SiO2. Este comportamento está associado, principalmente, à oxidação da superfície e também devido à maior concentração de SiO2, formando uma espécie de compósito com características de um termofixo de alta rigidez. Encontrou-se um crescimento tipo significante chegando a um aumento de 500% na dureza Vickers entre a amostra com 50% de SiO2 e a pura a uma cura de 180 °C. Foram realizadas também medidas do módulo elástico e para amostra pura obteve-se um resultado de 1,65x107 Pa e para a amostra com 50% apresentou um valor de 8x107 Pa. O crescimento do módulo de elasticidade acompanhou o crescimento da dureza, em torno de 480%. A presença do SiO2 na resina epóxi causa alteração nas propriedades mecânicas da DGEBA e que numa concentração de 50 % a 180 °C, durante uma cura de 4 h, houve um aumento significante das mesmas. Foi observado também a alta homogeinidade do pó de óxido de silício com o Araldite e o Aradur. Estes resultados indicam que o compósito DGEBA/SiO2 pode ser um bom candidato para ser utilizado em revestimento de metais, por exemplo, dutos que exijam uma boa dureza.

In this study we used a different route, simple and economical: the dissolution of the SiO2 powder DGEBA with a hardener to base polymercaptan ( aradur 90 ). Analysis was performed micro hardness in different percentages of the concentration of SiO2. The hardness of multicomponent solid is approximately equal to the average hardness of the material composition and is also related to the fraction of crystalline phase present in these materials. Since the hardness of the material a decisive factor for its implementation, it is interesting to see how this property varies depending on the composition of multicomponent solid. Was used to DGEBA Araldite GY 279 and hardener aradur 90 provided by Huntsman. We prepared several samples with different concentrations of SiO2 (3%, 5%, 10%, 20%, 30%, 40% and 50%) compared to the total mass of Araldite-Aradur Mixtures spent 24 hours at ambient temperature and then became a cure at 100 ° C, 120 ° C, 140 ° C, 160 ° C and 180 ° C for 4 h in an oven at ambient pressure. For the determination of hardness, we used a Shimadzu micro hardness tester equipped with an indenter Vickers. Several tests were performed and it was observed that the micro hardness was a sharp increase with increasing temperature and the concentration of SiO2. This behavior is associated mainly to the oxidation of the surface and also due to the higher concentration of SiO2, forming a kind of composite with a thermosetting characteristics of high rigidity. There was a significant growth type reaching a 500 % increase in Vickers hardness between the sample with 50 % SiO2 and pure to a cure of 180 °C. Were also carried out measurements of elastic modulus and pure sample was obtained a score of 1.65 x107 Pa for the sample with 50 % had a value of 8x107 Pa. The growth of the elastic modulus accompanied the growth of the hardness, around 480 %. The presence of SiO2 in the epoxy resin causes a change in the mechanical properties of DGEBA and a concentration of 50% at 180 ° C for a cure for 4 h, a significant increase of the same. It was also observed at high homogeneity powder of silicon oxide to Araldite and Aradur These results indicate that the composite DGEBA/SiO2 can be a good candidate to be used in covering of metals, for example, duct that demand a good hardness. / Neste trabalho foi utilizado uma rota diferente, simples e econômica: a dissolução do pó de SiO2 na DGEBA com um endurecedor a base de polimercapitana. Foi feita análise de microdureza nos diferentes percentuais da concentração de SiO2. A dureza em sólidos multicomponentes é aproximadamente igual à média aritmética das durezas dos materiais constituintes e está ainda relacionada com a fração da fase cristalina presentes nestes materiais. Sendo a dureza do material um fator decisivo para a aplicação do mesmo, torna-se interessante verificar como esta propriedade varia em função da composição em sólidos multicomponentes. Foi utilizado a DGEBA Araldite GY 279 e o endurecedor Aradur 90 fornecido pela Huntsman. Foram preparadas diversas amostras com concentrações diferentes de SiO2 (3 %, 5 %, 10 %, 20 %, 30 %, 40 % e 50 % ) em relação a massa total de Araldite-Aradur. As misturas passaram 24 h à temperatura ambiente e depois fez-se uma cura a 100 °C, 120 °C, 140 °C, 160 °C e 180 °C, durante 4 h em uma estufa em pressão ambiente. Para a determinação da microdureza, utilizou-se um microdurômetro da Shimadzu equipado com um identador Vickers. Diversas análises foram realizadas e foi observado que a microdureza teve um crescimento acentuado em função do aumento da temperatura e da concentração de SiO2. Este comportamento está associado, principalmente, à oxidação da superfície e também devido à maior concentração de SiO2, formando uma espécie de compósito com características de um termofixo de alta rigidez. Encontrou-se um crescimento tipo significante chegando a um aumento de 500% na dureza Vickers entre a amostra com 50% de SiO2 e a pura a uma cura de 180 °C. Foram realizadas também medidas do módulo elástico e para amostra pura obteve-se um resultado de 1,65x107 Pa e para a amostra com 50% apresentou um valor de 8x107 Pa. O crescimento do módulo de elasticidade acompanhou o crescimento da dureza, em torno de 480%. A presença do SiO2 na resina epóxi causa alteração nas propriedades mecânicas da DGEBA e que numa concentração de 50 % a 180 °C, durante uma cura de 4 h, houve um aumento significante das mesmas. Foi observado também a alta homogeinidade do pó de óxido de silício com o Araldite e o Aradur. Estes resultados indicam que o compósito DGEBA/SiO2 pode ser um bom candidato para ser utilizado em revestimento de metais, por exemplo, dutos que exijam uma boa dureza.