Made available in DSpace on 2014-10-09T12:33:41Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:35Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Orientador: Keizo Yukimitu / Banca: Ezequiel Costa Siqueira / Banca: Américo Sheitiro Tabata / Resumo: Apresentamos os resultados de estudos de cristalização de possíveis crescimentos de cristais semicondutores de óxido de telúrio (CdTe) e óxido de bismuto (Bi2O3) no sistema de vidro 20WO3-80TeO2 (TW). Estes trabalho configura-se como um estagio anterior aos estudos de crescimentos de semicondutores em dimensões nanométricas(nanocristais "NCs") em vidros teluritos. Com este objetivo foi sintetizada a amostra: dopadas com óxido de cadmio e óxido de bismuto, em diversas proporções em suas composições, e estas foram submetidas ou não a ambientes redutores. As amostras foram tratadas termicamente a diferentes temperaturas na região de transição vítrea (Tg ~ 350° C) e analisados utilizando as técnicas de DRX, DSC, FTIR e UV-Vis. Resultados de DRX mostram que acima do recozimento 400°C estimulou o crescimento de trigonal bipiramidal-estruturas conhecidas como α-TeO2 em ambas as amostras, e para as amostras TW dopadas com óxido de bismuto, o tratamento térmico induz a formação de cristais semicondutores de óxido de bismuto. Espectroscopia no infravermelho também mostrou a presença de estruturas Bi2O3. Absorção óptica UV-Vis indica que a presença de cádmio e bismuto em vidro TW sem serem submetidos a tratamento térmico não muda os valores de "gap" óptico, sendo que este corresponde a uma energia de ~2,8 eV / Abstract: The present work shows the studies of possible crystallization growth of crystals oxide semiconductors of tellurium (CdTe) and bismuth oxide (Bi2O3) in the glass system 20WO3- 80TeO2 (TW). This work consists in the first steps of initial growth of semiconductors in nanometrics dimensions (nanocrystals "NCs") in glasses teluritos. The sample was synthecized: doped with oxide of cadmium and bismuth oxide, in diverse ratios of its compositions, and these had been submitted or not it reducing enviroments. The samples had been thermally dealt with the different temperatures in the region glass transition (Tg ~ 350° C) and analyzed using the techniques of DRX, DSC, FTIR and UV-Vis. Results of DRX showed that up to the annealing 400°C it stimulated the trigonal growth known bipiramidal-structures as α-TeO2 in both the samples, and for samples TW (B), the thermal treatment induced the crystal formation bismuth oxide semiconductors. Spectroscopy in the infra-red ray also showed the presence of Bi2O3 structures in samples TW (B). Optic absorption UV-Vis indicated that the presence of cadmium and bismuth in glass TW without being submitted not dumb the thermal treatment the values of optic " gap", being that this corresponds to an energy of ~2,8 eV / Mestre

Made available in DSpace on 2014-10-09T12:42:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:21Z (GMT). No. of bitstreams: 1 05244.pdf: 7104329 bytes, checksum: 5c2e4b0cdbfa5595e3825819e43fe6fe (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:33:41Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:35Z (GMT). No. of bitstreams: 0 / Neste trabalho descreve-se o estudo do estabelecimento de uma técnica para o crescimento e preparo de cristais de HgI2, com o intuito de utilizá-los como detectores semicondutores de radiação que operam a temperatura ambiente. Três métodos de crescimento de cristais foram estudados no desenvolvimento deste trabalho: (1) Transporte Físico de Vapor (Physical Vapor Transport PVT), (2) Solução Saturada de HgI2 empregando dois solventes distintos; Dimetil Sulfóxido (DMSO) (a) e acetona (b) e (3) método de Bridgman. A fim de avaliar os cristais de HgI2 desenvolvidos pelos três métodos, medidas sistemáticas foram realizadas para determinar a estrutura, o plano de orientação, a estequiometria, a morfologia da superfície e as impurezas do cristal. A influência destas propriedades físico-químicas sobre os cristais desenvolvidos foi avaliada em termos de desempenho como detector de radiação. Os difratogramas indicaram que os cristais estão orientados preferencialmente planos (001) e (101) com estrutura tetragonal para todos os cristais desenvolvidos. No entanto, a morfologia com menor nível de deformação foi observada para o cristal obtido pela técnica de PVT. Uma uniformidade na camada de superfície do cristal de PVT foi observada, enquanto na superfície do cristal de DMSO podem ser nitidamente encontradas incrustações de elementos distintos ao cristal. A melhor resposta de radiação foi encontrada para os cristais crescidos pela PVT. Significativa melhora no desempenho do detector de radiação de HgI2 foi encontrada, purificando o cristal por meio de dois crescimentos sucessivos, pela técnica de PVT. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Elemental proxy models for temperature and seawater chemistry begin by assuming compositional signatures reflect environmental conditions of formation. The Mg/Ca ratio in marine cements and calcified skeletal structures is a widely used proxy for reconstructing past earth environments. Many studies have positively correlated Mg content in biogenic carbonates with temperature, but it is difficult to differentiate the effect of temperature from other environmental factors. Supersaturation, precipitation rate, salinity, pH, and ion concentration have also been proposed as drivers of Mg/Ca. Furthermore, it is difficult to distinguish environmental signatures from the “vital effect,” or the influences superimposed by the growth needs and metabolic activities of the organism. To construct viable paleoenvironmental proxies from biomineral compositions, we must resolve the effects of environmental conditions from the vital effects of the organism by first understanding the underlying thermodynamic and kinetic mechanisms for incorporating minor and trace elements. Using in situ Atomic Force Microscopy, controlled solution chemistries, and different ion microprobe techniques, this dissertation investigates the kinetics and thermodynamics of calcite growth to establish an inorganic baseline for uptake of Mg. I use this information to quantify the enhancement in Mg/Ca due to the presence of hydrophilic 27-mer peptides, demonstrating a possible origin of vital effects. Likewise I measure the effect of ionic strength on signatures and find that growth rate and background electrolyte proved more important than salinity in determining Mg contents. The findings contribute to the ongoing discussion regarding the relative importance of unique seawater parameters in determining Mg/Ca in calcite. Mg contents are significantly enhanced by biomolecules relative to the amounts attributed to temperature differences, while Mg content is less influenced by salinity variation than by changing supersaturation or driving force. In addition to sorting out the relative importance of environmental factors, our results begin to address the interplay of these different parameters in concert, and at different scales. At sites of calcification, the local biochemistry within an organism may shift in response to more saline waters. At a geological scale, interpreting past temperatures and particularly those of the Last Glacial Maximum depends on our ability to sort out and account for this interplay of salinity and temperature on Mg/Ca. Processes underlying inorganic and biogenic carbonate mineralization and interpretations of their formation environments are better understood by examining the influence of environmental parameters and biomolecular chemistry on kinetics and thermodynamics of calcite growth and stability. / Ph. D.

This project concerns the non-classical crystal growth of various porous and non-porous materials. In order to determine their crystal growth mechanism, the reaction was stopped at several different reaction times with the size, morphology, crystal structure and orientation of the particles analysed using scanning electron microscopy and high resolution transmission electron microscopy as the principal characterisation techniques. Other techniques used include X-ray diffraction, energy dispersive X-ray spectroscopy, selected area electron diffraction and thermal gravimetric analysis. Selected biomimetic systems include the early stage crystal growth of ZnO/gelatin composite twin-crystals and the time dependent microstructural evolution of CaCO₃/gelatin composite particles from spherulites into rods. Further investigations of the role of gelatin molecules were carried out by replacing gelatin by gum arabic. Using knowledge gained from synthetic systems, several travertine crust specimens collected from hot springs were investigated to gain an insight into the possible formation mechanisms of naturally occurring biominerals. Another form of ZnO investigated was the formation of core-shell ZnO hexagonal microdisks and selective dissolution of their core to form microstadiums followed by the selective growth of nanorods and nanocones onto the columnar surfaces of the microstadiums to generate branched-microstadiums. The formation mechanism of ultrasonically prepared BiOBr displaying a flower-like architecture was investigated. These BiOBr assemblies are found to exhibit excellent photocatalytic activity and stability during the photodegradation of Rh.B under visible-light irradiation. Finally mesoporous silicate plates displaying a single crystal-like property were re-investigated to clarify whether the previously reported mesoporous silicate plates exhibiting a single crystalline property were one-phase materials or a composite of non-crystalline mesoporous silicate and crystalline zeolite.