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The purpose of this thesis is to make a broadband antireflection coating configuration known as a quarter-wave stack consisting of one layer of titania and of one layer of silica nanoparticles. We utilize much that is already known about silica nanoparticle deposition. The first objective of this thesis is deposition and characterization of titania nanoparticle films deposited on glass microscope slides by a technique known as Ionic Self-Assembled Multilayers or ISAM deposition. This technique takes advantage of the electrostatic attraction between oppositely charged materials and ideally results in a uniform nanoparticle film whose thickness and optical properties can be tightly controlled. Deposition of a quarter-wave stack based on ISAM deposition of silica and titania nanoparticles is significantly simpler and less expensive than alternative deposition methods. Initial attempts to deposit titania films were unsuccessful because of excess diffuse scattering due to inhomogeneities in the film. In order to reduce diffuse scattering, two approaches were considered. The first approach was to improve the deposition process itself by experimenting with different values of deposition parameters such as solution pH and solution molarity. The other approach focused on removing the large nanoparticle aggregates from the colloidal solutions of titania nanoparticles that were suspected to be responsible for rough film surfaces resulting in diffuse scattering. This approach was successful. In addition, evidence suggested that surface roughness contributed more to diffuse scattering than the bulk of the films. After minimizing diffuse scattering from titania nanoparticle films, we used known results from research on silica nanoparticle films to deposit quarter-wave stacks consisting of one layer of titania nanoparticles with high refractive index and one layer of silica nanoparticles with low refractive index. This contrast in refractive indices is a desirable characteristic of quarter-wave stacks. The thicknesses and refractive indices of the two layers in the quarter-wave stacks were measured by ellipsometry and compared to the nominal thicknesses of these layers. Finally, the reflectance was derived from a model of the quarter-wave stack and was compared to the measured reflectance. It was found that construction of a quarter-wave stack by ISAM is possible but that it will be necessary to acquire data from more experiments. / Ph. D.

Dans cette thèse nous considérons deux problèmes d'optimisation combinatoire.Le premier s'appelle problème du double voyageur de commerce avec contraintes de piles. Dans ce problème, un véhicule doit ramasser un certain nombre d'objets dans une région pour les livrer à des clients situés dans une autre région. Lors du ramassage, les objets sont stockés dans les différentes piles du véhicule et la livraison des objets se fait selon une politique de type last-in-first-out. Le ramassage et la livraison consistent chacune en une tournée Hamiltonienne effectuée par le véhicule dans la région correspondante.Nous donnons une formulation linéaire en nombres entiers pour ce problème. Elle est basée sur des variables de précédence et sur des contraintes de chemins infaisables. Nous donnons par la suite des résultats polyédraux sur l'enveloppe convexe des solutions de notre formulation. En particulier, nous montrons des liens forts avec un polytope associé au problème du voyageur de commerce et des liens avec un polytope de type set covering. Cette étude polyédrale nous permet de renforcer la formulation initiale et de développer un algorithme de coupes et branchements efficace. Le deuxième problème que nous considérons consiste à trouver la description des polytopes lexicographiques. Ces derniers sont les enveloppes convexes des points entiers lexicographiquement compris entre deux points entiers fixés. Nous donnons une description complète de ces polytopes en termes d'inégalités linéaires. Nous démontrons que la famille des polytopes lexicographiques est fermée par intersection. / In this thesis we consider two problems arising in combinatorial optimization.The first one is the double traveling salesman problem with multiple stacks. In this problem a vehicle picks up a given set of items in a region and subsequently delivers them to demanding customers in another region. When an item is picked up, it is put in a stack of the vehicle. The items are delivered observing a last-in-first-out policy. The pickup phase and the delivery phase consist in two Hamiltonian circuits, each performed by the vehicle in the corresponding region. We give a new integer linear programming formulation for this problem. Its main features are the presence of precedence variables and new infeasible path constraints. We provide polyhedral results on the convex hull of the solutions to our formulation. In particular, we show strong links with a specific TSPpolytope and a specific set covering polytope. We deduce strengthening inequalities for the initial formulation, subsequently embedded in an efficient branch-and-cut algorithm. The second problem we consider consists in finding the description of the lexicographical polytopes. These are convex hulls of the integer points lexicographically between two given integer points. We give a complete description of these polytopes by means of linear inequalities. We show that the lexicographical polytope family is closed under intersection.

Energy traps at the silicon surface originating from discontinuities in the lattice is detrimental to the performance of solar cells. Acting as recombination centers, they offer a location where the charge carriers may easily return to their original energy band after excitation. Surface passivation is an effective method to combat this and can be done either by suppressing traps (lowering trap density) or by forming an electric field, preventing the carriers from reaching the defect states. Silicon oxide, SiO2, and aluminum oxide, Al2O3, are two materials which have previously been shown to provide good passivating qualities. In this thesis, SiO2 and Al2O3 have been used both as single layers and in a stack configuration to passivate the surface of crystalline silicon (c-Si). Using a response surface methodology approach, temperature optimization with respect to deposition and annealing temperature has been conducted for SiO2/Al2O3 stacks deposited with plasma-enhanced atomic layer deposition, PEALD. It was shown that the same deposition temperature (Tdeposition = 140 °C, Tanneal = 395 °C) could be used for both materials and provide good passivation with an effective surface recombination velocity, Seff, of 5.3 cm/s (1Ωcm n-type Si wafers). From FTIR measurements, an increase in hydroxyl groups was seen as the SiO2 deposition temperature increased while the opposite was observed for Al2O3 which also showed fewer carbon related impurities with increasing temperature. Increasing the SiO2 temperature strongly affected the fixed charge density, causing it to decrease and even switch polarity. The fixed charge density could also be controlled by varying the thickness of the intermediate SiO2 layer. At a thickness of 1-2 nm, a minimum in the effective lifetime was observed and was correlated to Si close to flat-band conditions. N-type wafers showed a larger negative fixed charge density than p-type wafers which results in stronger field-effect passivation. For phosphorous doped emitters (200 Ω/sq on 10 Ωcm p-type wafer), it was seen that SiO2/Al2O3 stacks with a SiNx anti-reflection coating performed better than SiO2 or Al2O3 single layers. By depositing SiO2 at 130 °C in SiO2/Al2O3 stacks and annealing at 450 °C, an implied open circuit voltage (iVoc) of 710 mV was measured (AM1.5G) together with an implied fill factor (iFF) of 84.1% and a recombination parameter (J0) of 19.2 fA/cm2. Al2O3 single layer showed an extremely low J0 of 10 fA/cm2 but suffered from a decreased iFF and strong injection dependent lifetimes which originates from an inversion layer. ALD ozone processes were successfully developed for SiO2 and Al2O3.  The deposition rate per cycle for SiO2 was found to be only ~0.175 Ǻ/cycle (PEALD ~1.1 Ǻ/cycle), making it rather unpractical for use outside of research. Single layer SiO2 deposited with ozone showed, similarly to a plasma process, almost no surface passivation. Al2O3 however proved to be highly passivating on its own with a τeff = 3.8 ms, Seff = 1.2 cm/s (1 Ωcm n-type) after depositing at 250 °C. Studies on the effect of annealing showed that an annealing temperature of 450 °C is necessary to completely activate the passivation. The low Seff values were attributed to a very high negative fixed charge density ~1013 cm-2 together with strong chemical passivation.

This thesis discusses the growth of thin-film silicon layers suitable for solar cells using liquid phase epitaxy and the behaviour of oxide LPCVD silicon nitride stacks on silicon in a high temperature ambient.¶ The work on thin film cells is focussed on the characteristics of layers grown using liquid phase epitaxy. The morphology resulting from different seeding patterns, the transfer of dislocations to the epitaxial layer and the lifetime of layers grown using oxide compared with carbonised photoresist barrier layers are discussed. The second half of this work discusses boron doping of epitaxial layers. Simultaneous layer growth and boron doping is demonstrated, and shown to produce a 35um thick layer with a back surface field approximately 3.5um thick.¶ If an oxide/nitride stack is formed in the early stages of cell processing, then characteristics of the nitride may enable increased processing flexibility and hence the realisation of novel cell structures. An oxide/nitride stack on silicon also behaves as a good anti- reflection coating. The effects of a nitride deposited using low pressure chemical vapour deposition on the underlying wafer are discussed. With a thin oxide layer between the silicon and the silicon nitride, deposition is shown not to significantly alter effective life-times.¶ Heating an oxide/nitride stack on silicon is shown to result in a large drop in effective Lifetimes. As long as at least a thin oxide is present, it is shown that a high temperature nitrogen anneal results in a reduction in surface passivation, but does not significantly affect bulk lifetime. The reduction in surface passivation is shown to be due to a loss of hydrogen from the silicon/silicon oxide interface and is characterised by an increase in Joe. Higher temperatures, thinner oxides, thinner nitrides and longer anneal times are all shown to result in high Joe values. A hydrogen loss model is introduced to explain the observations.¶ Various methods of hydrogen re-introduction and hence Joe recovery are then discussed with an emphasis on high temperature forming gas anneals. The time necessary for successful Joe recovery is shown to be primarily dependent on the nitride thickness and on the temperature of the nitrogen anneal. With a high temperature forming gas anneal, Joe recovery after nitrogen anneals at both 900 and 1000oC and with an optimised anti-reflection coating is demonstrated for chemically polished wafers.¶ Finally the effects of oxide/nitride stacks and high temperature anneals in both nitrogen and forming gas are discussed for a variety of wafers. The optimal emitter sheet resistance is shown to be independent of nitrogen anneal temperature. With textured wafers, recovery of Joe values after a high temperature nitrogen anneal is demonstrated for wafers with a thick oxide, but not for wafers with a thin oxide. This is shown to be due to a lack of surface passivation at the silicon/oxide interface.

Contribution à l’étude de la réflectance et du confinement des modes dans les systèmes optiques stratifiés Résumé : Ce travail prolonge les études du changement de réflectivité des systèmes optiques stratifiés sous des contraintes mécanique et électrique. D’abord, nous quantifions le déplacement de la bande interdite photonique suite à une modification de l’angle d’incidence. Il en dérive une technologie bio-inspirée. Ensuite, c’est un champ électrique externe qui contrôle les propriétés de réflexion et de polarisation d’une multicouche construite à partir de cristaux liquides. Enfin, nous distinguons deux manières de confiner l’énergie électromagnétique. Ce travail s’attache à comprendre la nature des modes qui se propagent à la surface des milieux stratifiés. Par ailleurs, il montre que l’association de matériau gauche et de matériau droit pour former un guide d’onde permet de réduire la vitesse de la lumière de plusieurs ordres de grandeur. Contribution to the study of the reflectance and the mode confinement in optical stratified systems Abstract : This work extends the studies of change in reflectance in optical stratified systems under mechanical and electrical constraints. In the first part, we quantify the shift of the photonic bandgap following, a modification in the angle of incidence. We define the tools for the design of bio-inspired Bragg mirrors. In the second part, we adjust the reflection properties of a multilayer stack made of liquid crystals with an external electric field. Furthermore, we examine two distinct ways of producing light confinement. First, we contribute to the understanding of the nature of electromagnetic modes propagating at the surface of stratified media. Second, we show that a waveguide made of left- and right-handed materials can reduce the speed of light by several orders of magnitudes.

The express wood volume in meter estere (mst) sometimes need to be converted into cubical meters (m3). This is possible estimating a cubication factor (Fc). With the objective to determine the Fc for Eucalyptus grandis and its variation in pieces of wood of different lengths of 1 and 2,3m of length in reason of the time of exposure to the enviroment, in the summer and the winter. Six stacks of wood pieces 3X2X1m (width, height and depth) dimensions had been prepared and six stacks of wood pieces in the dimensions 3X2X2,3m, installed in the summer and winter. The Fc was obtained by volume reason, with CV of 4,2 to 9,5% and by angular counting with CV of 10,9 to 17%. Thus, continued analysis with Fc s average obtained by reason of volumes because they had presented minor variation. The analysis statistics for factorial experiment(2X2X6), indicated significant difference (α<5%) in the variations of principal effect, that is, in the climatic station (F=18,72) , in the time of exposure (F=6,51) and in the length of the different pieces of wood (F=35,18) .The analysis of the correlation of Pearson indicated that the Fc was also influenced by the cracks on top, the humidity of the wood and the atmospheric variable, in the two observed seasons. Evidenced variation of the Fc of the stacks in exposition, equation with use of Stepewise procedure was shaped for the independent variable: T, T2, T3, T4, T5, 1/T, 1/T2, 1/T3, 1/T4, 1/T5, log(T), log(1/T), log(lnT), 1/lnT, 1/log(T), the equation with the best adjustment was decurrent of short pieces of wood of winter for an initial period until 90 days after installation. Adjusted the equation Fc=0,70385+0,00000961(T2), with values of F and R2 equal 17,22 (Pr>F=0,2%) e 0,63, respectively. However the averages of the value of the Fc obtained by observation and the estimator are the same (0,74) and the model was more accurate, then was opted to using the average gathered by each month. The conversion chart of the volume estere in cubical volume was completed since specific average values of the Fc for the climatic stations summer and winter and for the two lengths of pieces of wood, obtained by reason of volumes. The average values of the Fc s had indicated a stabilization after ninety days of the installation of the stacks, with this subdivided the time of exposure in two periods: one from zero to ninety days and another one from ninety to one hundred and eighty days, these compared with the total of the observations (180 days), the average values of these observations had not presented significant difference by the Tukey test (α<5%). However, pieces of wood of Eucalyptus grandis had presented dimensional variation when displayed in inclement weather for a period of one hundred and eighty days (six months) making the cubication factor Fc to vary in elapsing of the period of exposition. / O volume de madeira expresso em metro estere (mst) algumas vezes necessita ser convertido em metro cúbico (m3). Isso é possível estimando-se um fator de cubicação (Fc). Com o objetivo de determinar o Fc para Eucalyptus grandis e sua variação em toretes de 1 e de 2,3m de comprimento em razão do tempo de exposição ao ambiente, no verão e no inverno. Foram confeccionadas 6 pilhas de toretes nas dimensões 3x2x1m (largura, altura e profundidade) e 6 pilhas nas dimensões 3x2x2,3m, instaladas no verão e no inverno. O Fc foi obtido por razão de volume, com CV de 4,2 a 9,5% e por contagem angular com CV de 10,9 a 17%. Assim, prosseguiu análise com Fc s médios obtidos por razão de volumes pois apresentaram menor variação. A análise estatística para experimento fatorial (2x2x6), indicou diferença significativa (α<5%) nas variáveis do efeito principal, isto é, na estação climática (F=18,72), no tempo de exposição (F=6,51) e no comprimento do torete (F=35,18). A análise da correlação de Pearson indicou que o Fc também foi influenciado pelas rachaduras de topo, pela umidade da madeira e pelas variáveis atmosféricas, nas duas estações observadas. Constatada variação do Fc das pilhas em exposição, modelou-se equação com uso de procedimento Stepewise para as variáveis independentes: T, T2, T3, T4, T5, 1/T, 1/T2, 1/T3, 1/T4, 1/T5, log(T), log(1/T), log(lnT), 1/lnT, 1/log(T), a equação com o melhor ajuste foi a decorrente de toras curtas de inverno para um período inicial até 90 dias após a instalação. Ajustada a equação Fc=0,70385+0,00000961(T2), com valores de F e R2 iguais a 17,22 (Pr>F=0,2%) e 0,63, respectivamente. No entanto as médias do valor do Fc obtidas das observações e do estimador é a mesma (0,74) e o modelo foi tendencioso, optou-se por utilizar a média obtida a cada mês, a partir da exposição. A tabela de conversão do volume estere em volume cúbico foi confeccionada a partir dos valores médios do Fc específicos para as estações climáticas verão e inverno e para os dois comprimentos dos toretes, obtidos por razão de volumes. Os valores médios dos Fc s indicaram uma estabilização após noventa dias da instalação das pilhas, com isso subdividiu-se o tempo de exposição em dois períodos: um de zero a noventa dias e outro de noventa a cento e oitenta dias, esses comparados ao total das observações (180 dias) os valores médios dessas observações não apresentaram diferença significativa pelo teste Tukey (α<5%). No entanto, os toretes de Eucalyptus grandis apresentaram variação dimensional quando expostos as intempéries por um período de cento e oitenta dias (seis meses) fazendo o fator de cubicação (Fc) variar no decorrer do período de exposição.

Made available in DSpace on 2014-10-09T12:35:00Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:32Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:35:00Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:32Z (GMT). No. of bitstreams: 0 / Este trabalho apresenta a contribuição obtida no desenvolvimento de um Gerador de Eletricidade Híbrido (HYBRIDGEN), com tecnologia nacional, focado nos sistemas de terceira geração de energia elétrica híbrido, composto por um módulo de células a combustível tipo PEMFC, associado a um acumulador chumbo ácido. Mostra-se também a sua capacidade de operar em modo contínuo, carga com demanda variável e fator de carga inferior a 50%. Foram abordados quatro temas principais. O primeiro refere-se a um estudo para a melhoria da eficácia na conversão de energia em corrente contínua (cc), ao regular o potencial de saída do conversor cc-cc. A energia é proveniente do módulo de célula a combustível de 1 kWe, equipado com sistema térmico de refrigeração e sistema de alimentação de gases, aqui denominados MCC1. Para tal, foi construído o modelo matemático do sistema conversor de corrente contínua (sistema conversor cc-cc), com solução suportada em equações diferenciais algébricas, ensaios no MCC1, bem como em simulação computacional no programa MATLAB7®. O segundo tema refere-se ao desenvolvimento do projeto e montagem do protótipo do HYBRIDGEN devido à inexistência no mercado brasileiro de um equipamento com as características necessárias tanto para a pesquisa, quanto para uso comercial. Desenvolveu-se uma placa controladora para o acumulador (PCC), os esquemas elétricos, os barramentos e o sistema de relés. Também foi utilizado o MCC1 em desenvolvimento pelo IPEN e ELECTROCELL® com tecnologia 100% nacional. O HYBRIDGEN foi instalado em um sistema móvel. O terceiro tema refere-se à análise de estabilidade do modelo matemático do sistema conversor cc-cc. Utilizou-se de quatro testes de estabilidade, sendo: 1 - pela Resposta em Frequência ao utilizar o Teorema do Mapeamento, de Nyquist; 2 - Lugar das Raízes, de Nyquist; 3 - função de teste Degrau, em pontos de operação e, 4 - função de teste Impulso, em pontos de operação. Por fim, apresentaram-se os resultados dos ensaios de potencial e corrente de uma célula a combustível unitária de 25 cm2, do MCC1, e do HYBRIDGEN. No desenvolvimento dos primeiros testes o MCC1 atingiu 704,55 We, (potência considerada condição predominante de operação). A seguir, demonstrou-se a capacidade do HYBRIDGEN para simultaneamente: alimentar cargas em corrente contínua; carregar o acumulador de 45 Ah; alimentar o inversor de 2 kWe e o autotransformador, para fornecer energia a equipamentos em 12Vcc, 127 Vac e 220Vac, 60 Hz, todos num total de 819,52 We. Esses resultados foram obtidos mesmo com limitações na refrigeração ventilada do MCC1, observadas no decorrer dos testes. Assim, o HYBRIDGEN se mostrou viável tecnicamente, e com grande potencial de uso. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP