The method of C-V analysis is a powerful technique to determine the parameter of MOS (metal oxide semiconductor) structure. In this study, we fabricate the MOS structure with rf magnetron sputtering of Ta2O5 on n-ZnSe surface. The n-ZnSe¡¦s with various carrier concentrations have different electrical property. Interfaces of various Ta2O5/ZnSe have different properties, for examples flatband voltage, threshold voltage, the mobile oxide charge density, and the effective oxide charge concentration and etc. We find that the interfaces of the Ta2O5/ZnSe MOS structure have low mobile charges and interface trap charges. Thus Ta2O5/ZnSe MOS structure may be worthy to develop further.

No description available.

In this study, metal-oxide-semiconductor (MOS) capacitances were prepared with rf magnetron sputtering of Ta2O5 on both n-type GaN and p-type GaN. And metal-insulator-semiconductor (MIS) capacitances were prepared with conjugated rigid-rod polymers PBT on n-type GaN. The processes of fabrication the diodes were shown, and the structures of MOS/MIS diodes were represented. Hysteresis was observed in high-frequency capacitance-voltage (C-V) measurements. And the hysteresis was changed with different scanning delay time on scanning step. They were ascribed to mobile charges and interface charges. The carrier concentration were calculated and compared with the Hall results. The flatband voltage and threshold voltage were calculated and compared with C-V curves which were measured.

Prédites en 1916 par Albert Einstein, puis détectées 100 ans plus tard par les collaborations LIGO et VIRGO, les ondes gravitationnelles constituent un outil prometteur pour observer l’univers sur des échelles toujours plus grandes. Cependant, pour accéder à de plus nombreux évènements, une des principales limitations des détecteurs provient du bruit thermique des couches minces composant leurs miroirs, couches minces non cristallines de SiO2 et Ta2O5 dopé TiO2.L’objectif de ce travail est d’étudier l’origine microstructurale du bruit thermique de ces couches en utilisant les spectroscopies vibrationnelles pour, à terme, obtenir des matériaux plus performants. Il a notamment été observé que le bruit thermique diminue lorsque les miroirs sont recuits à faible température. Dans la silice, nous observons une restructuration du matériau lors du recuit qui semble suivre la diminution du bruit thermique. En particulier, un relâchement des contraintes a été constaté. En revanche, dans le Ta2O5, matériau de structure complexe et encore mal connue, l’effet du recuit sur la structure des couches apparaît plus limité, alors que celles-ci cristallisent facilement dès que la température augmente. Pour compléter la connaissance de ce matériau, des mesures in-situ hautes pressions ont été réalisées. Finalement, le rôle du dopage des couches de Ta2O5 par du TiO2 a été exploré / Predicted in 1916 by Einstein, then detected one hundred year later by the VIRGO and LIGO collaborations, the gravitational waves are a promising tool to observe the universe at scales always bigger. However, to detect a larger number of events, one of the main limitation of the detectors originates in the mirrors coatings thermal noise, thin non-crystalline layers composed of SiO2 and TiO2-doped Ta2O5. The aim of this work is to study the micro-structural origin of the layers thermal noise, by using vibrational spectroscopies, in order to, ultimately, process more efficient materials. Studies show a decrease of the thermal noise when the mirrors are annealed at low temperature. In silica, a structural reorganization happens during the annealing, following the evolution of the thermal noise. Notably, a stress relaxation has been observed. However, in Ta2O5, oxide with a complex structure not much studied, the impact of the annealing seems to be more limited, while the structure crystallizes easily as soon as the temperature increases. To complete our knowledge of this structure, in-situ high pressure measurements were conducted. Finally, the TiO2-doping effect of the Ta2O5 structures was studied

[pt] Processos de ustulação cloretante podem ser realizados de forma direta, utilizando o Cl2 como agente cloretante, ou através de agentes cloretantes alternativos. Neste contexto, compostos organoclorados são promissores, pois além de serem facilmente volatizados, já apresentam na mesma molécula o agente cloretante e redutor. O presente estudo teve como principal objetivo a avaliação quantitativa da cinética de cloração do pentóxido de tântalo com tetracloroetileno através dos modelos do núcleo não reagido (SC) e auto catalítico (AC). Tanto o material inicial, quanto o mesmo após o processo, bem como o produto sólido depositado na saída do reator foram caracterizados via DRX e MEV/EDS. Através de simulações termodinâmicas foi possível verificar a viabilidade de cloração de amostras puras de Ta2O5 com C2Cl4 diluído em atmosfera de N2 na faixa de temperatura entre 800 a 950 graus Celsius, sendo os principais cloretos gasosos formados, TaOCl3 e TaCl5. Verificou-se ainda a possível decomposição térmica do agente cloretante no caminho entre a entrada do reator e a amostra. Os resultados provenientes das caracterizações comprovaram as tendências apontadas pelas simulações termodinâmicas, comprovando a formação exclusiva de cloretos voláteis. No que diz respeito à modelagem cinética ambos os modelos permitiram o ajuste dos dados em nível quantitativo, sendo os valores de energia de ativação global iguais a 93,8 kJ/mol (SC) e 32 kJ/mol (AC). A comparação dos valores obtidos com dados da literatura sugere que o controle é de natureza química, sendo a decomposição do C2Cl4 na superfície das nanopartículas de Ta2O5, possivelmente, a etapa controladora. / [en] Chlorination roasting can be carried out directly, using Cl2 as a chlorinating agent, or through alternative reagents. In this context, organochlorine compounds are promising, since besides being easily volatilized, they already present in the same molecule the chlorinating and reducing agents. The present study had as main objective the quantitative evaluation of the chlorination kinetics of tantalum pentoxide with tetrachlorethylene through the shrinking core (SC) and auto catalytic (AC) models. The initial material, as well as post-processed materials, and also the solid product deposited at the reactor s exit were characterized through DRX and MEV/EDS. By means of thermodynamic simulations, it was possible to verify the viability of pure Ta2O5 samples chlorination with C2Cl4 diluted in N2 in the temperature range of interest (800 - 950 Celsius Degree), thereby producing only gaseous chlorides, TaOCl3 and TaCl5. The possible C2Cl4 thermal decomposition in the path between the reactor inlet and sample was also identified. The characterization results were in accordance with the tendencies indicated by the thermodynamic simulations, proving the exclusive formation of volatile chlorides. With regard to the kinetic study, both tested models allowed quantitative adjustment of the conversion data, with overall activation energies equal to 93.8 kJ/mol (SC) and 32 kJ/mol (AC). The comparison of the values obtained with literature data suggests that the control is of chemical nature, the decomposition of C2Cl4 on the surface of the Ta2O5 nanoparticles being, possibly, the main control reaction step.

Catalisadores à base de óxidos metálicos têm sido muito utilizados nas indústrias do petróleo, de química fina e no controle de poluição. A seleção adequada do óxido metálico como suporte, do catalisador e o uso de coberturas superficiais menores que uma monocamada dos componentes ativos, onde somente espécies MOx estão presentes sobre a superfície dos óxidos suportes, pode ser uma exigência para modificar as propriedades catalíticas de modo a obter uma boa eficiência do catalisador durante a reação. Óxidos metálicos do grupo V suportados têm uma grande variedade de aplicações catalíticas, e têm sido extensivamente investigados nos últimos anos. Catalisadores à base de óxido de vanádio suportado possuem excelentes propriedades redox e são principalmente empregados como catalisadores em processos de oxidação seletiva. Óxido de tântalo mássico é um sólido ácido com propriedades catalíticas e diversas aplicações têm sido reportadas. O suporte foi preparado pelo método de coprecipitação, utilizando proporções de 15 e 30% p/p de Ta2O5 em Al2O3. A adição de V2O5 sobre o suporte Ta2O5-Al2O3 foi realizada através de impregnação úmida com excesso de solvente, água, formando catalisadores com 2, 4 e 8 átomos de vanádio/nm². A fim de alcançar o objetivo deste trabalho, as seguintes técnicas de caracterização foram utilizadas: volumetria de N2 para determinação da área específica e volume de poros, redução à temperatura programada (RTP), difratometria de raios-X (XRD), espectroscopia na região do infravermelho com transformada de Fourier (FTIR), FTIR com adsorção de piridina e espectroscopia Laser Raman. As propriedades ácidas e/ou básicas dos suportes e catalisadores foram avaliadas através da reação de decomposição do isopropanol. As propriedades texturais do suporte foram modificadas pela adição crescente do vanádio ao suporte, efeito este atribuído ao bloqueio dos microporos pelas espécies de vanádio superficiais. A metodologia empregada na preparação do suporte revelou um material amorfo ao DRX. Nos catalisadores, a adição crescente de vanádio promove a formação de cristais de V2O5 superficiais nas amostras com 4 e 8 átomos de V/nm². Nos resultados de RTP, os catalisadores apresentaram um único pico de redução do vanádio que corresponde à redução de V2O5 a V6O13. Nas análises de FTIR com adsorção de piridina verificou-se a diminuição da força dos sítios ácidos de Lewis, presentes em todos os catalisadores, com a adição de vanádio. Somente nos catalisadores com 8 átomos de V/nm² foram detectadas bandas referentes a sítios ácidos de Br?nsted. Nas análises de espectroscopia Raman não foi observada nenhuma banda característica de espécies VOx isoladas nas amostras, porém para coberturas abaixo de uma monocamada de V foram observadas bandas de espécies poliméricas. Bandas Raman de cristais de V2O5 foram características somente na amostra com 8 átomos de V/nm². A presença de sítios ácidos foi confirmada pela presença de propeno e éter diisopropílico como produtos da desidratação do isopropanol em todos os catalisadores. Com a adição de vanádio, sítios básicos ou redox também foram verificados pela presença de acetona produzida pela desidrogenação do isopropanol. / Metal oxides based catalysts have been very used in petroleum industry, fine chemical and pollution control. The adequate selection of the metal oxide as a support and catalyst, and the use of superficial covering with active compounds lower than a monolayer, where only MOx species are present on the support oxide surface, can be a requirement to modify the catalytic properties in order to have a good catalyst efficiency during the reaction. Supported metal oxides of group V have a large variety of catalytic applications, and have been widely investigated in the last years. Supported vanadium oxide based catalysts have excellent redox properties and they are mainly used as selective oxidation catalyst. Tantalum oxide is an acid solid with catalytic properties and many applications of supported tantalum oxide based catalysts have been reported. The supports were prepared by coprecipitation method, using the proportions of 15 and 30% of Ta2O5 in Al2O3. The addition of V2O5 on the support Ta2O5-Al2O3 was performed using the wet impregnation method with excess of solvent, water, forming catalysts with 2, 4 and 8 atoms of V/nm². In order to achieve the purpose of this work, the following characterization techniques were used: N2 volumetry to determine specific area and pore volume, temperature programmed reduction (TPR), X-ray difratometry, Fourier transform infrared spectroscopy (FTIR) and Laser Raman spectroscopy. The acid/ basic properties of the support and catalysts were evaluated through isopropanol decomposition reaction. The textural properties of the supported were modified by the increasing addition of vanadium, effect attributed to micropores blocked by superficial vanadium species. The used methodology in the support preparation showed an amorphous material to XRD. In the catalysts, the increasing addition of vanadium promotes the formation of V2O5 superficial crystals in the samples with 4 and 8 atoms of V/nm². In the TPR results, the catalysts presented only one reduction peak corresponding to the V2O5 a V6O13 reduction. In the FTIR analysis with adsorbed pyridine, it was observed a decrease of acidity at Lewis acid sites, which were present in all catalysts samples. In the Raman spectroscopy analysis, it was not observed any characteristic band of isolated VOx species in the sample, although covering lower than a monolayer of vanadium, it was observed V=O bands due to surface polymeric vanadium oxide species. V2O5 crystal Raman bands were characteristics only in samples with 8 atoms of V/nm². The presence of acid sites was confirmed by the production of propane and diisopropyl ether as product of isopropanol dehydratation, observed for all catalysts. With V charge, basic and redox sites were verified as well by the production of acetone at isopropanol dehydrogenation.

Catalisadores à base de óxidos metálicos têm sido muito utilizados nas indústrias do petróleo, de química fina e no controle de poluição. A seleção adequada do óxido metálico como suporte, do catalisador e o uso de coberturas superficiais menores que uma monocamada dos componentes ativos, onde somente espécies MOx estão presentes sobre a superfície dos óxidos suportes, pode ser uma exigência para modificar as propriedades catalíticas de modo a obter uma boa eficiência do catalisador durante a reação. Óxidos metálicos do grupo V suportados têm uma grande variedade de aplicações catalíticas, e têm sido extensivamente investigados nos últimos anos. Catalisadores à base de óxido de vanádio suportado possuem excelentes propriedades redox e são principalmente empregados como catalisadores em processos de oxidação seletiva. Óxido de tântalo mássico é um sólido ácido com propriedades catalíticas e diversas aplicações têm sido reportadas. O suporte foi preparado pelo método de coprecipitação, utilizando proporções de 15 e 30% p/p de Ta2O5 em Al2O3. A adição de V2O5 sobre o suporte Ta2O5-Al2O3 foi realizada através de impregnação úmida com excesso de solvente, água, formando catalisadores com 2, 4 e 8 átomos de vanádio/nm². A fim de alcançar o objetivo deste trabalho, as seguintes técnicas de caracterização foram utilizadas: volumetria de N2 para determinação da área específica e volume de poros, redução à temperatura programada (RTP), difratometria de raios-X (XRD), espectroscopia na região do infravermelho com transformada de Fourier (FTIR), FTIR com adsorção de piridina e espectroscopia Laser Raman. As propriedades ácidas e/ou básicas dos suportes e catalisadores foram avaliadas através da reação de decomposição do isopropanol. As propriedades texturais do suporte foram modificadas pela adição crescente do vanádio ao suporte, efeito este atribuído ao bloqueio dos microporos pelas espécies de vanádio superficiais. A metodologia empregada na preparação do suporte revelou um material amorfo ao DRX. Nos catalisadores, a adição crescente de vanádio promove a formação de cristais de V2O5 superficiais nas amostras com 4 e 8 átomos de V/nm². Nos resultados de RTP, os catalisadores apresentaram um único pico de redução do vanádio que corresponde à redução de V2O5 a V6O13. Nas análises de FTIR com adsorção de piridina verificou-se a diminuição da força dos sítios ácidos de Lewis, presentes em todos os catalisadores, com a adição de vanádio. Somente nos catalisadores com 8 átomos de V/nm² foram detectadas bandas referentes a sítios ácidos de Br?nsted. Nas análises de espectroscopia Raman não foi observada nenhuma banda característica de espécies VOx isoladas nas amostras, porém para coberturas abaixo de uma monocamada de V foram observadas bandas de espécies poliméricas. Bandas Raman de cristais de V2O5 foram características somente na amostra com 8 átomos de V/nm². A presença de sítios ácidos foi confirmada pela presença de propeno e éter diisopropílico como produtos da desidratação do isopropanol em todos os catalisadores. Com a adição de vanádio, sítios básicos ou redox também foram verificados pela presença de acetona produzida pela desidrogenação do isopropanol. / Metal oxides based catalysts have been very used in petroleum industry, fine chemical and pollution control. The adequate selection of the metal oxide as a support and catalyst, and the use of superficial covering with active compounds lower than a monolayer, where only MOx species are present on the support oxide surface, can be a requirement to modify the catalytic properties in order to have a good catalyst efficiency during the reaction. Supported metal oxides of group V have a large variety of catalytic applications, and have been widely investigated in the last years. Supported vanadium oxide based catalysts have excellent redox properties and they are mainly used as selective oxidation catalyst. Tantalum oxide is an acid solid with catalytic properties and many applications of supported tantalum oxide based catalysts have been reported. The supports were prepared by coprecipitation method, using the proportions of 15 and 30% of Ta2O5 in Al2O3. The addition of V2O5 on the support Ta2O5-Al2O3 was performed using the wet impregnation method with excess of solvent, water, forming catalysts with 2, 4 and 8 atoms of V/nm². In order to achieve the purpose of this work, the following characterization techniques were used: N2 volumetry to determine specific area and pore volume, temperature programmed reduction (TPR), X-ray difratometry, Fourier transform infrared spectroscopy (FTIR) and Laser Raman spectroscopy. The acid/ basic properties of the support and catalysts were evaluated through isopropanol decomposition reaction. The textural properties of the supported were modified by the increasing addition of vanadium, effect attributed to micropores blocked by superficial vanadium species. The used methodology in the support preparation showed an amorphous material to XRD. In the catalysts, the increasing addition of vanadium promotes the formation of V2O5 superficial crystals in the samples with 4 and 8 atoms of V/nm². In the TPR results, the catalysts presented only one reduction peak corresponding to the V2O5 a V6O13 reduction. In the FTIR analysis with adsorbed pyridine, it was observed a decrease of acidity at Lewis acid sites, which were present in all catalysts samples. In the Raman spectroscopy analysis, it was not observed any characteristic band of isolated VOx species in the sample, although covering lower than a monolayer of vanadium, it was observed V=O bands due to surface polymeric vanadium oxide species. V2O5 crystal Raman bands were characteristics only in samples with 8 atoms of V/nm². The presence of acid sites was confirmed by the production of propane and diisopropyl ether as product of isopropanol dehydratation, observed for all catalysts. With V charge, basic and redox sites were verified as well by the production of acetone at isopropanol dehydrogenation.

O estudo da adição de dopantes pentavalentes é uma das principais linhas de pesquisas em eletrocerâmicas para varistores de TiO2. Diversos autores têm buscado entender os efeitos destes dopantes nas propriedades elétricas e microestruturais destas cerâmicas eletrônicas. Este trabalho apresenta um estudo do comportamento eletrônico do TiO2 frente a adição de Ta2O5 em concentrações maiores das já estudas, buscando obter varistores binários para aplicação em baixa tensão. Sistemas a base de TiO2 dopados com Ta2O5 foram preparados por mistura convencional de óxidos e conformados na forma de disco. A microestrutura dos compactos contendo 0,5, 1,0, 1,5 e 2,0% em mol de Ta2O5, sinterizados a uma taxa de aquecimento de 5°C/min. em 1300°, 1350° e 1400°C por 1 hora, foram analisadas, apresentando a evolução da microestrutura frente a temperatura de sinterização. Os valores da densidade das amostras foram obtidos através do método de Arquimedes, demonstrando a contribuição do Ta2O5 na densificação dos sistemas, e através de difração de raios X, foi possível determinar a fase presente nestas cerâmicas. Para avaliar as propriedades elétricas, realizou-se medidas de tensão-corrente (CC) em temperatura ambiente e em função da temperatura, obtendo coeficiente não-linear, altura e largura da barreira de potencial. Utilizando a espectroscopia de impedância avaliou-se o comportamento dos sistemas, medindo a contribuição do grão e do contorno de grão, calculando a energia de ativação. As medidas Mott-Schottky foram obtidas, possibilitando estimar a concentração de doadores e densidade de estados eletrônico. Na temperatura mais elevada de sinterização, 1400°C, melhorou-se as características varistoras, ocorrendo aumento da densificação e redução do campo elétrico de ruptura, apresentando com um nível ideal do dopante, 1% em mol de Ta2O5, varistores com coeficiente não-linear de 5,3 e baixo campo elétrico de ruptura de 38,4 V/cm. / The study of additional pentavalent dopants is one of the main research lines in electroceramics for TiO2 varistors. Several authors have sought to understand the effect this dopants in eletrical and microstructural properties of these electronic ceramics. This work presents a study of the electronic behavior of TiO2 versus the addition of Ta2O5 in higher concentrations of those already studied, in order to obtain binary varistors for low voltage application. TiO2 based systems doped with Ta2O5 were prepared by the conventional mixture of oxides and shaped in the disk form. The microstructure of the composites containing 0.5, 1.0, 1.5 and 2.0 mol% of Ta2O5, sintered at a heating rate of 5°C/min. at temperatures of 1300°, 1350° and 1400°C for 1 hour were analyzed, showing a development of the microstructure against a sintering temperature. The density values of the samples were obtained by the Archimedes method, demonstrating a contribution of Ta2O5 in the densification of the systems; and, by means of X-ray diffraction, it was possible to determine a phase present in these ceramics. In order to evaluate electrical properties, voltage-current (DC) measurements were performed at room temperature and changing the temperature, obtaining nonlinear coefficient, height and width of the potential barrier. Using impedance spectroscopy, evaluate the behavior of the systems by measuring a contribution of the grain and the grain boundary, calculating an activation energy. As Mott-Schottky measurements were obtained, making it possible to estimate a concentration of donors and density of electronic states. At the higher sintering temperature, 1400°C, varistor characteristics were improved, increasing densification and reduction of the break down electric field, showing with the ideal level of dopant, 1.0 mol% of Ta2O5, varistors with nonlinear coefficient of 5.3 and low break down electric field of 38.4 V/cm.

Our aim was to establish a methodology for laser assisted oxidation of semiconductor and metal surfaces. One advantage of laser oxidation is the fact that radiation is heavily absorbed in a thin surface layer of the sample and the other is its ability for local oxidation. In addition to this, laser beam can be directed into some areas that other processes cannot reach. For these reasons, Nd:YAG pulsed laser working at 1064 nm wavelength is used for the oxidation purposes of Si and Ta films. First, SiO2 layer was obtained for various O2 pressures and laser powers. The thickness, refractive index, structural, dielectric, electrical and optical characteristics of the SiO2 layers have been determined. We have established that there exists an interval of laser power in which the oxidation occurs without surface melting. The oxidation process is controlled by the laser power rather than by the substrate temperature (673 &ndash / 748 K). It was found that better film quality is obtained at higher substrate temperatures and laser power greater than 3.36 J/cm2. Second, rf-sputtered Ta films were oxidized by laser, because Ta2O5 appears to be a good promising candidate to replace SiO2 because of its high dielectric constant, high breakdown voltage and relevant small leakage current values. It was found that the substrate temperature is an important parameter to obtain denser layers with reduced amount of suboxides and the most suitable substrate temperature range is around 350 C to 400 C. &amp / #946 / -orthorhombic crystal structure was obtained when the substrate temperature is 350 &ndash / 400 C for thinner films (up to 20 &ndash / 25 nm) and 300 &ndash / 350 C for thicker films (40 nm). The refractive index values of laser grown thin tantalum oxide films were between ~1.9 and 2.2 being close to those of bulk Ta2O5 (2.0 &ndash / 2.2). Oxide thicknesses in uniform Gaussian&ndash / like shapes were measured as around the twice of those initial Ta films. Effective dielectric constant values reached ~26 when the substrate temperature was increased from 250 C to around 400 C. It was shown that the leakage current density level decreases with increasing substrate temperature. However, the refractive index values of the films were smaller than those of thermally grown films. Porous structure formed during laser oxidation might be the reason for lower refractive indices and can be improved by post&ndash / oxidation annealing.

No description available.