Orientador: Ivan E. Chambouleyron / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-03T23:11:41Z (GMT). No. of bitstreams: 1 Origo_FabioDondeo_D.pdf: 2612005 bytes, checksum: 49cccd9932debc21d33d8d86b82f22d2 (MD5) Previous issue date: 2004 / Resumo: Neste trabalho se estudou pela primeira vez a cristalização e a epitaxia por laser pulsado para a obtenção de filmes de SixG e1-x(x = 0, 0.1, 0,25, 0,5, 0,75 e 1) sobre substratos de GaAs. Foram utilizados pulsos de laser de Nd:Yag ¿ l =532 nm ¿ com duração de 7ns e spot size de 2 a 3 mm. Camadas ou multicamadas amorfas de Ge, Si ou SiGe foram depositadas por , Ion Beam Sputtering sobre substratos epiready e não epiready de GaAs (100) à temperatura de 200 ºC. A espessura total dos filmes depositados era da ordem de 100 nm. Mostramos a eficácia da remoção de óxidos superficiais do GaAs (Ga2O3, As2O3 e As2O5) e contaminantes (C) através do bombardeamento do GaAs por feixe de H2+ (30 eV) após aquecimento a 350ºC. Demonstramos que filmes de a-Si0.1Ge0.9:H depositados com gás Kr são mais compactos que aqueles produzidos com Ar devido ao efeito de bombardeamento por partículas refletidas no alvo e por essa razão todos os filmes preparados para cristalização foram produzidos com Kr. Após irradiação com pulso entre 70 e 170 mJ, os filmes de Ge depositados sobre GaAs foram completamente liquefeitos por intervalo de até 20 ns e foram cristalizados. Dentro da área irradiada, quatro regiões foram identificadas, em ordem crescente da fluência ¿F- do laser: A) material que permaneceu amorfo (F<400 mJ/cm2), B) região policristalina (400 mJ/cm2 <F<900 mJ/cm2 ), C) região epitaxial com pouca mistura com o substrato (900 mJ/cm 2 <F<1100 mJ/cm2 ), região epitaxial com muita mistura (1100 mJ/cm2 <F<1300 mJ/cm2). O bombardeamento de uma certa região por múltiplos pulsos gera aumento da mistura com o substrato e a cristalização na forma policristalina. Os filmes multicamadas Si/Ge foram uniformemente misturados após a irradiação do laser, se transformando em filmes de SixGe1-x, com a composição esperada (x=0,25, 0,50, 0,75). Os filmes de SiGe cristalizados por laser apresentam as mesmas quatro regiões observadas em Ge. Observamos epitaxia para ligas com até 25% de Si. Para x=0,5 o material resultante é policristalino com grãos seguindo preferencialmente a orientação do substrato. Para maiores valores de x o material resultante é policristalino / Abstract: In this work we studied, for the first time, the pulsed laser crystallization and epitaxy of SixGe1-x films (x = 0, 0.1, 0,25, 0,5, 0,75 and 1) on GaAs substrates. Nd:Yag laser pulses ( g =532 nm), 7 ns wide and 2 to 3 mm spot size, were applied. Amorphous layers and multilayers of Ge, Si or SiGe were deposited, by Ion Beam Sputtering, on epiready and nonepiready GaAs (100) substrates at 200ºC. The total thicknesses are close to 100 nm. We have shown the efficacy of superficial oxide removal (Ga2O3, As2O3 and As2 O5) and contaminants (C) bombarding the substrate surface with H2+ beam (30 eV) after heating at 350ºC. We demonstrated that a-Si0.1Ge0.9:H films deposited with Kr are more compact than those produced with Ar due to the bombardment effect by particles reflected on the target; therefore, all the films prepared for laser crystallization were deposited with Kr. After laser irradiation with 70mJ-170 mJ pulses, the SiGe films were completely liquefied up to 20 ns and crystallized. Inside the irradiated area, four different regions were identified according to the increasing of laser fluency - F: A) amorphous material (F<400 mJ/cm2 ); B) polycrystalline material (400 mJ/cm2 <F<900 mJ/cm2 ); C) epitaxial material presenting low mixture with the substrate (900 mJ/cm2 <F<1100 mJ/cm2 ); D) epitaxial material presenting high mixture with the substrate (1100 mJ/cm2 <F<1300 mJ/cm2). The multiple irradiation of an area produces an increase in the mixture with the substrate components (Ga, As) and generates polycrystalline material. The Si/Ge multilayers were completely mixed after laser irradiation, forming SixGe1-x films with the expected composition (x=0,25, 0,50, 0,75).The SixGe1-x laser crystallized films present the same four regions as observed in Ge films. Epitaxial films were obtained for x up to 0,25. For x=0,5, crystallized films are polycrystalline with highly oriented grains. For higher Si content, laser crystallized SiGe films are polycrystalline / Doutorado / Física / Doutor em Ciências

For selected YAG:Ce sample the temperature dependent absorbtion and emission spectra were measured and used to simulate white LED behavior. Various CIE-xy dependencies were observed. Sample surface scaterring parameters were calibrated using a custom-made automated goniospektrometer, which provided measured data with fine accuracy. Finally, the measured data were used to construct a Geant4 simulation to optimize two light devices for output intensity and target CIE-xy coordinates. Powered by TCPDF (www.tcpdf.org)

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Orientador: Edmea Rita Temporini Nastari / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-07T02:25:27Z (GMT). No. of bitstreams: 1 Senne_FirmaniMelloBentode_D.pdf: 2133397 bytes, checksum: 05da70735ad5bd1022b72b3f03385933 (MD5) Previous issue date: 2006 / Resumo: Realizou-se um estudo transversal com intervenção com os objetivos de identificar a influência da capsulotomia posterior unilateral com Neodímio: Ítrio-Alumínio-Granada (Nd:YAG) laser na função visual e em relação à percepção de dificuldades nas atividades diárias, e verificar a relação entre as medidas subjetivas e objetivas da função visual após a intervenção. A amostra, prontamente acessível, foi composta por 48 pacientes entre 40 e 80 anos, média de 68 anos, mediana de 70 anos, pseudofácicos uni ou bilaterais, com opacificação de cápsula posterior e acuidade visual menor ou igual a 0,30 (logMAR) em um olho, atendidos consecutivamente em um hospital universitário no Brasil. Todos os pacientes foram submetidos a capsulotomia posterior com Nd:YAG laser. Um questionário, elaborado a partir de estudo exploratório, foi aplicado antes e depois da intervenção. Após a capsulotomia posterior, a acuidade visual e a estereoacuidade melhoraram significativamente. Na percepção dos sujeitos, houve redução das dificuldades relacionadas às atividades diárias ligadas à visão, exceto passar roupas, tomar banho sem ajuda e pentear os cabelos. As medidas objetivas e a auto-avaliação da visão apresentaram congruência de resultados e todos os pacientes declararam ter valido a pena a realização do procedimento laser / Abstract: An interventional survey was conducted to assess the influence of Neodymium: Yttrium-Aluminium-Garnet (Nd: YAG) laser unilateral posterior capsulotomy on visual function and perception of difficulties with vision-related daily life activities, and to verify the association between objective and subjective measures of visual function after intervention. The readily accessible sample comprised 48 patients aged between 40 and 80 years, with uni- or bilateral pseudophakia, posterior capsule opacification and visual acuity equal to or less than 0,30 (logMAR) in one eye, consecutively seen at a Brazilian university hospital. All the patients were submitted to posterior capsulotomy by Nd:YAG laser. Before and after intervention, patients were asked to answer a questionnaire developed from data obtained in an exploratory study. After posterior capsulotomy, visual acuity and stereoacuity improved significantly. According to the subjects' perception, they found less difficulty in vision-related daily activities, except for ironing, bathing without help and combing the hair. Objective measures of visual function and self-rated visual function showed congruent results after intervention. All the subjects interviewed stated that the posterior capsulotomy procedure had been ¿worthwhile¿ / Doutorado / Oftalmologia / Doutor em Ciências Médicas

Les céramiques polycristallines transparentes de YAG (Yttrium Aluminium Garnet, Y3Al5O12) et de YAG dopé par des lanthanides (Nd, Er, Ho, etc.) ont des propriétés optiques comparables aux monocristaux et peuvent être utilisées comme milieu laser solide dans les lasers solides à haute capacité calorifique. L’utilisation de ces céramiques polycristallines transparentes présente de nombreux avantages comparés aux monocristaux. Ces matériaux ont une meilleure conductivité thermique et sont fabriqués à plus faible coût tout en présentant des propriétés mécaniques améliorées et ce, sur des pièces de plus grandes dimensions. De plus, il est possible d’atteindre de plus forts taux de dopage avec une répartition uniforme du dopant. Le dopage du YAG par l’erbium (0.25 %at.) permet une émission laser « eye-safe » de 1645nm. De plus, un faible taux de dopage permet d’éviter le phénomène d’upconversion lors de l’effet laser.Les conditions pour obtenir la transparence sont, entre autres, l’absence de défauts, une très grande pureté (>99.9%), une répartition de taille de grains homogène et une densité très élevée (>99.9%).Les céramiques transparentes sont obtenues par la voie métallurgie des poudres. La synthèse par voie chimique (co-précipitation, sol-gel, voie hydrothermale…) permet la production de poudres très pures, avec une taille de particules homogène et nanométrique, comparée à la synthèse par voie mécanique (broyage d’oxydes). Le frittage SPS (Spark Plasma Sintering) permet quant à lui une densification rapide, à plus basse température, empêchant ainsi une croissance excessive et anormale des grains lors de la densification. L’application d’un courant électrique de forte intensité associée à une charge uniaxiale permet d’accélerer la cinétique de frittage comparé aux méthodes de frittage conventionelles.Ce travail porte sur l’élaboration de céramiques polycristallines transparentes Er:YAG par la voie métallurgie des poudres. La synthèse de poudre est réalisée par co-précipitation inverse d’une solution de nitrates dans l’hydrogénocarbonate d’ammonium. L’influence des paramètres de synthèse tels que le pH, la concentration, le temps de maturation ou encore le cycle de calcination a été étudiée. Après optimisation des conditions de synthèse, des particules d’Er:YAG pur présentant une taille moyenne de 50nm ont été obtenues. L’étude des mécanismes réactionnels a été menée en associant différentes techniques de caractérisations en température telles que la spectrométrie IR, la diffraction des rayons X, ainsi que des analyses thermo-gravimétriques et différentielles. La formation de la phase YAG à 1050°C passe par la formation d’une phase intermédiaire, le YAP (Yttrium Aluminium Perovskite, YAlO3) à 900°C.Les poudres synthétisées ont ensuite été frittées par frittage flash SPS. L’étude de l’influence du cycle de frittage (température, charge, rampe, maintien) sur la microstructure et son optimisation a été réalisée à partir de poudre commerciale et a permis l’obtention de céramiques transparentes de diamètre 30mm et d’épaisseur 3mm. Un changement d’échelle a également été réalisé permettant la réalisation d’échantillons de diamètre 60mm d’une part, et d’épaisseur 6mm d’autre part / Yttrium aluminium garnet (YAG, Y3Al5O12) transparent ceramics have attracted much attention since it can replace single crystals as host materials in solid state heat capacity lasers. These polycrystalline ceramics present improved mechanical and spectroscopic properties, as well as a better heat conductivity, lower fabrication costs for larger size materials. Furthermore, it is possible to reach higher doping concentrations as well a uniform distribution. Doping YAG with Erbium (Er:YAG) allows eye-safe emission at 1645nm. Moreover, a low doping rate (0.5%at.) enables upconversion process during laser operation. Conditions for transparency are amongst others, the absence of defects, a high purity (>99.9%), an homogeneous grain size as well as a high density (>99.9%).Transparent polycrystalline ceramics can be obtained by powder metallurgy route. Powders, synthesized by chemical reactions such as sol-gel process, co-precipitation or hydrothermal methods, present some advantages like high purity, homogeneity and nano-sized particles compared to those obtained by solid-state reactions. A recent process called Spark Plasma Sintering (SPS) is presented to be a promising technique for the densification of nanostructured materials. Indeed, high current and pressure allow sintering at lower temperatures in shorter sintering time than in regular processes. Besides, rapid heating enables to limit excessive grain growth.In this study, Er:YAG nanopowders have been synthesized by co-precipitation using nitrates as precursors and ammonium hydrogen carbonate as precipitant. The influence of precipitation parameters such as pH, concentration, aging time, or even calcination temperature, has been studied. Er:YAG nanoparticles, with an average grain size of 30nm have been successfully synthesized. The reaction mechanisms have been investigated using different techniques such as infrared spectroscopy, x-ray diffraction, thermal analyses… The YAG phase is formed around 1050°C passing through an intermediate phase called YAP (Yttrium Aluminium Perovskite, YAlO3) at 900°C.Synthesized and commercial powders have been sintered to transparency using SPS device. Optimisation of the sintering conditions (temperature, load, heating rate, dwell time) have been realized using commercial powder. Transparent polycrystalline ceramic specimens with a 30mm diameter and 3mm thickness have been successfully obtained. A scale-up study enabled to produce samples with a diameter up to 60mm and also with 6mm thickness

Dans le domaine de la cristallisation des fibres monocristallines par la technique de la micro-pulling down (µ-PD), les résultats récents sur les performances des fibres monocristallines (optique, laser, scintillateur) ont montré l’étendue des champs d’applications ouverts aux fibres cristallines. La course à la croissance cristalline, la fabrication de fibres cristallines performantes et la maitrise des procédés sont des enjeux de recherche dans un nombre important de laboratoires à travers le monde. Les fibres monocristallines de saphir et du YAG dopées Cérium (Ce3+) sont des formats à forte valeur ajoutée. Elles sont susceptibles d’être utilisées dans un large domaine d’applications, d’où la nécessité de contrôler et de maitriser la technologie de fabrication. En fonction des conditions de tirage (gradient de température, orientations cristallographiques des germes, vitesses de tirage), nous nous sommes intéressés à l’étude des bulles et des contraintes résiduelles dans le saphir tiré par µ-PD. La ségrégation du Cérium et la propagation de la lumière ainsi que l’atténuation dans les fibres YAG-dopées Cérium (Ce3+) ont été étudiées en fonction des vitesses de tirage. Nous avons étudié tous ces phénomènes ainsi que les mécanismes mis en jeu. La variation de la vitesse de tirage est en corrélation avec la distribution des bulles, la ségrégation du Ce et l’atténuation. A travers ce travail, on est en mesure de dire que les phénomènes à l’origine de la présence, de la répartition des bulles dans les fibres saphir et la ségrégation du Cérium dans le YAG ont été significativement éclaircis et que, à partir de ces résultats, des améliorations peuvent être apportées aux procédés technologiques de tirage par µ-PD / In the field of crystallization of single crystal fibers by micro-pulling down (µ-PD) technique, the recent results on the performance of single crystal fibers (optical, laser, scintillator) have shown the wide range of applications open to crystalline fibers. The race for crystal growth, the manufacture of high-performance crystal fibres and process control are research challenges in a large number of laboratories around the world. Cerium-doped monocrystalline sapphire and YAG fibres (Ce3+) are high value-added formats. They are likely to be used in a wide range of applications, hence the need to control and master manufacturing technology. Depending on the growth conditions (temperature gradient, crystallographic orientations of the germs, growth speeds), we were interested in studying the bubbles and residual stresses in the sapphire pulled by µ-PD. The segregation of Cerium and the propagation of light as well as the attenuation in YAG-doped Cerium fibres (Ce3+) were studied as a function of growth speeds. We have studied all these phenomena and the mechanisms involved. The variation in the growth rate is correlated with the distribution of bubbles, the segregation of Ce and the attenuation. Through this work, it can be said that the phenomena at the origin of the presence, distribution of bubbles in sapphire fibres and the segregation of Cerium in the YAG have been significantly clarified and that, from these results, improvements can be made to the technological processes of pulling by µ-PD

O desenvolvimento de materiais nanoestruturados tem se destacado devido a necessidade de miniaturização de dispositivos e a procura por novos efeitos físicos e químicos capazes de gerar novas tecnologias. Um importante composto com aplicações principalmente em óptica é o YAG (Y3Al5O12) presente no sistema cerâmico alumina-ítria (\'AL IND.2\'O IND.3\'-\'Y IND.2\'O IND.3\'). O YAG apresenta estrutura cristalina cúbica, expansão térmica isotrópica e não apresenta efeitos de birrefringência, o que possibilita a produção de cerâmica transparente para uso como material hospedeiro de íons terras-raras para o desenvolvimento de lasers de estado sólido. O ponto de partida em processamento cerâmico começa com o conhecimento das características físico-químicas do pó do composto. Em nosso trabalho, o objetivo foi o desenvolvimento de uma metodologia para a obtenção de nanopós de YAG de tamanhos médios diferenciados. Para isso foram realizados distintos processos químicos de síntese, e também, foram utilizados diferentes processos de separação, como a centrifugação e a sedimentação. Na produção das nanopartículas foram utilizados três métodos de síntese: Método de Pechini, Rota Glicerol e Método de Coprecipitação. No método de Pechini avaliou-se o efeito de diferentes valores de pH (1, 4, 7, 9 e 11) e procurou-se correlacionar com os tamanhos médios das nanopartículas. Após a obtenção do pó precursor foram realizadas medidas de decomposição térmica (DSC e TG), observando as principais transformações físico-químicas do material decorrentes dos diferentes métodos de síntese. A formação da fase cristalina do YAG foi determinada por difração de raios X e uma análise estrutural foi efetuada por espectroscopia de infravermelho. Medidas de área superficial específica (BET) foram usadas para avaliar o tamanho médio das partículas. Nanopós de YAG com diferentes intervalos de tamanhos foram produzidos, e o rendimento para cada intervalo de tamanho definido. / Nanostructured materials has emerged because the intense interest for miniaturization of devices and crescent demand for new physical and chemical effects that can generate new technologies. An important compound with applications mainly in optics is the YAG (Y3Al5O12). It\'s present in the alumina-yttria ceramic system (\'AL IND.2\'O IND.3\'-\'Y IND.2\'O IND.3\'). The YAG has a cubic crystaline structure, isotropic thermal expansion and it has no birefringence effects, which allows the production of transparent ceramics to use as host of solid-state lasers. The starting point in ceramic processing begins with the knowledge of the characteristics and physical and chemical properties of the powder. In our work, the goal was the development of a methodology for obtaining YAG nanopowders of different average sizes. To do this we performed distinct chemical synthesis, and we also used different separation processes such as centrifugation and sedimentation. For production of nanoparticles we used three synthesis methods: Pechini, glycerol route and coprecipitation. In the Pechini method we evaluated the effect of different pH values (1, 4, 7, 9 and 11) and tried to correlate with the average sizes of nanoparticles. After obtain the precursor powders we studied the decomposition thermal (DSC and TG) process, arising from the different synthesis methods. The crystalline phase of YAG was determined by x-ray diffraction and the structural analysis was carried out by infrared spectroscopy. Specific surface area measurements (BET) were used to evaluate the average particle size.YAG nanopowders with different average sizes were produced.

Dans cette étude de doctorat, de la poudre de Y3Al5O12 (YAG) a été synthétisé avec plusieurs méthodes: atomisation, synthèse de réaction et co-précipitation. Le procédé de synthèse le plus prometteur, la co-précipitation, a été optimisé pour obtenir une poudre hautement frittable, présentant une phase pure. Le traitement approprié avant frittage, comprenant calcination, efficace dispersion et séchage homogène, a été réalisé. La poudre de YAG a été dispersée avec plusieurs méthodes, avant frittage. Grâce à la technique Spark Plasma Sintering (SPS) une évaluation très rapide de l'influence des différents traitements a été réalisée. Il a été constaté que, pour une poudre obtenue avec une telle synthèse, la méthode de dispersion est cruciale afin de obtenir une transparence élevée du materiaux fritté. En raison de l'aptitude au frittage de la poudre, du traitement approprié avant frittage et de la basse température du cycle effectué par SPS, un matériau à grains fins a été obtenu. Des mesures de spectroscopie de photoélectrons (XPS) ont été effectuées sur la poudre de YAG et sur le matériaux fritté, et plusieurs differences ont été mises en évidence. Quelques hypothèses ont été faites pour expliquer les differences observées, et certains preuves supplémentaires pour les vérifier ont été mises en avant. Une poudre composite alumine-zircone-YAG a été synthétisé à partir d'une poudre d'alumine commerciale, qui a été fonctionnalisé avec chlorures de yttrium et de zirconium. Les traitements de pré-frittage appropriées ont été effectués, comprenant une calcination à basse température et une calcination "rapide", pour favoriser la germination des petits cristallites. Deux méthodes de mise en forme, coulage et pressage, ont été réalisées. Il a été constaté que le coulage permet la production de matériaux céramiques beaucoup plus homogènes. Une caractérisation mécanique préliminaire a été effectuée. Une caractérisation spectroscopique des poudres d'alumine-YAG, traités à basse et haute température, a été réalisée. Il a été mis en évidence que l'état d'hydratation des poudres varie avec la fonctionnalisation par les chlorures. La présence de sites Y sur la surface des poudres composites a été mise en évidence par XPS et à partir des spectres infrarouges (spectroscopie infrarouge par transformée de Fourier, FTIR) des échantillons soumis à des différentes pressions de monoxide de carbone (CO). / In this PhD study, Yttrium aluminum garnet (Y3Al5O12, YAG) powder was synthesised with several methods, i.e. spray drying, reaction synthesis and co-precipitation. The most promising synthesis method, i.e. co-precipitation, was optimized to obtain a pure phase, highly sinterable powder. The appropriate pre-sintering processing, i.e. calcination treatment, e fficient dispersion, homogeneous drying, were performed. YAG powder was dispersed with several methods, prior to sintering. Through Spark Plasma Sintering (SPS) a very fast assessment of the influence of the various treatments was performed. It was found that, for the synthesised powder, the dispersion method is crucial to obtain a high transparency. Due to the high sinterability of the powder and to the appropriate pre-sintering treatment, a low temperature SPS cycle was performed, and a fine-grained material was obtained. X-ray Photoelectron Spectroscopy (XPS) measurements were performed on YAG powder and on the sintered material, and several di fferences were evidenced. Some hypothesis were made to explain the observed di fferences, and some additional proofs to verify them were put forward. A composite Alumina-YAG-Zirconia powder was synthesized, starting from a commercial alumina powder, which was functionalised with Yttrium and Zirconium chlorides. The appropriate pre-sintering treatments were performed, comprising a low temperature calcination and a "fast" calcination, to favour the germination of small crystallites. Two shaping methods, i.e. slip casting and pressing, were performed. It was found that slip casting allows the production of much more homogeneous ceramic materials. A preliminary mechanical characterization was performed. A spectroscopic characterization of Alumina-YAG powders, heat-treated at low and high temperatures, was performed. It was evidenced that the hydration state of the powders changes with chlorides functionalization. The presence of Y sites on the surface of the composite powders was evidenced by X-ray Photoelectron Spectroscopy and from the di fference spectra of powdered samples subjected to various CO pressures.

Le développement de lasers solides de puissance-moyenne élevée doit faire face à des problèmes très spécifiques. La gestion de la thermique et de l'amplification de l'émission spontanée (ASE) pour de larges amplificateurs lasers deviennent des points clés lorsque l'augmentation de l'énergie de vient conséquente. Lucia est une chaîne laser de forte puissance moyenne qui repose sur le concept du miroir actif avec un cristal ou une céramique d'Yb:YAG comme milieu à gain. Comme pour d'autres systèmes lasers comparables, la distribution des ions actifs du milieu à gain est homogène en volume. Un profil variable du taux de dopage présente des avantages significatifs en termes de gain et par conséquent ouvre le chemin à une minimisation efficace des effets délétères de l'ASE et de l'échauffement. Cette thèse concerne la fabrication de tels milieux à gain. La méthode de croissance cristalline Bagdasarov, grâce à plusieurs de ses particularités, a permis d'obtenir plusieurs cristaux d'Yb:YAG avec profils de dopage variables contrôlés jusqu'à des valeurs de gradient de 3 at%/cm. Les résultats expérimentaux sont en bon accord avec les modèles mathématiques. Des simulations complémentaires de la température et du profil de gain montre que même avec des gradients plus faibles, les performances énergétiques des amplificateurs Lucia peuvent être améliorées jusqu'à 30%. Il est aussi alors possible d'utiliser des milieux à gain plus fins ce qui a pour conséquence positive une meilleure extraction de la chaleur. De larges cristaux d'Yb:YAG de 90 mm de diamètre ont été produits.

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