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Thin films of CuInSe2 can be completely converted into CuInS2 after annealing in elemental sulfur vapor. In this thesis, the sulfide conversion process was done in an MBE chamber and the film was exposed to a heated sulfur source. Our experiments showed that complete conversion of a 1.0 £gm-thick CuInSe2 film into CuInS2 was achieved when the film was annealed in a sulfur beam flux of 4.5x1016 atoms/cm2-sec at 450¢J for 5 minutes. This is the shortest conversion time ever reported for the same annealing temperature. The speed of conversion process depended on sulfur vapor flux, film crystallinity, and original film composition. Among them, the film composition was the most important factor. The presence of Cu2Se phase in Cu-rich CuInSe2 film enhances the sulfide conversion process and confirmed by KCN etching of a Cu-rich sample. The role of Cu2Se phase in sulfide conversion was investigated. The sulfide conversion mechanism also presented in this work.

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Understanding oxygenation throughout Earth history, particularly intervals where marine deoxygenation occurred, are crucial to investigating the changes in habitability on Earth. Marine deoxygenation events, in particular, can result in changes in the carbon, sulfur, and iron cycles on our planet. Changes in these elemental cycles lead to distinctive variation in the chemical composition of seawater that is recorded in marine sediments that are preserved into the sedimentary record. Our modern ocean is experiencing rapid deoxygenation, thus understanding the duration and extent of ancient deoxygenation events is vital to predicting future climate scenarios. Here I investigated the record of environmental change during the Early Jurassic Toarcian Oceanic Anoxic Event or T-OAE (~183 Ma). The first chapter of this dissertation investigates the record of marine anoxia across the Pliensbachian to Toarcian transition. Specifically, I investigate the temporal and geographic development of anoxia across three basins from the European Epicontinental Seaway. Through utilization of iron speciation, a local redox proxy, I identify anoxia developing before and persisting well after the negative carbon isotope excursion (NCIE) conventionally used to define the T-OAE. These data indicate an increase in the occurrence of anoxia at the Pliensbachian – Toarcian boundary, coincident with the initial phase of volcanism associated with the Karoo-Ferrar Large Igneous Province and an interval of heightened marine invertebrate extinction. Ultimately, our data support a greater temporal extent of anoxic conditions around the T-OAE, which support the greater sensitivity of marine oxygen levels to climatic change outside of the NCIE interval. The second chapter of this dissertation assesses the occurrence and extent of organic matter sulfurization (OMS), a biogeochemical feedback known to enhance the preservation and burial of OM. Because this process is accelerated when euxinic conditions develop in the water column, I investigated it as a mechanism promoting OM burial across two oceanic anoxic events of the Mesozoic. Importantly, I find that sulfurization does not occur uniformly across both events and propose a conceptual model of the depositional settings most favorable for sulfurization to occur and when throughout geologic time OMS is most likely to influence the global cycles of carbon and sulfur. / Doctor of Philosophy / Understanding past time intervals where there was widespread loss of oxygen in the oceans is crucial to understanding habitability on Earth. Since our modern oceans are experiencing a rapid loss of oxygen, understanding the duration and extent of ancient marine oxygen loss events is vital to predicting future habitability of the oceans. These ancient events can result in distinctive changes in the carbon, sulfur, and iron cycles on our planet. Variation in these elemental cycles lead to distinctive shifts in the chemical composition of seawater that is recorded in marine sediments that get preserved as rocks in the geologic record. Here, I investigated the record of environmental change during the Early Jurassic Toarcian Oceanic Anoxic Event or T-OAE (~183 Ma). The first chapter of this dissertation investigates the record of marine oxygen loss across the T-OAE. Specifically, I investigate the temporal and geographic development of oxygen loss across three ancient marine basins. Through utilization of a local tracer of water column oxygen loss (e.g. iron speciation) I identify oxygen loss developing before and persisting well after the conventional timeframe associated with the event. These data indicate oxygen loss first occurred before the T-OAE, coincident with the initial phase of volcanic eruptions from the Karoo-Ferrar Large Igneous Province and an interval of heightened marine extinction. Ultimately, these data support a longer time interval of oxygen loss around the T-OAE and the greater sensitivity of marine oxygen levels to climatic change. The second chapter of this dissertation assesses the occurrence and extent of organic matter sulfurization (OMS), a feedback known to enhance the preservation and burial of organic matter (OM). Because this process is accelerated when oxygen is lost and free sulfur builds up in the water column, I investigated its occurrence across two oceanic oxygen loss events of the Mesozoic Era. Importantly, I find that sulfurization does not occur uniformly across both events and propose a conceptual model of the settings most favorable for sulfurization to occur and also when in geologic time it is most likely to influence the global cycling of carbon and sulfur.

Cu(In,Ga)Se2 (CIGS) thin film solar cells contain a thin layer of CdS. To avoid toxic heavy-metal-containing waste in the module production the development of a cadmium-free buffer layer is desirable. This thesis considers alternative Cd-free buffer materials deposited by Atomic Layer Deposition (ALD). Conditions of the CIGS surface necessary for ALD growth are investigated and the heterojunction interface is characterized by band alignment studies of ZnO/CIGS and In2S3/CIGS interfaces. The thesis also includes investigations on the surface modification of the CIGS absorber by sulfurization. According to ALD theory the growth process is limited by surface saturated reactions. The ALD growth on CIGS substrates shows nucleation failure and generally suffers from surface contaminations of the CIGS layer. The grade of growth disturbance varies for different ALD precursors. The presence of surface contaminants is related to the substrate age and sodium content. Improved growth behavior is demonstrated by different pretreatment procedures. The alignment of the energy bands in the buffer/absorber interface is an important parameter for minimization of the losses in a solar cell. The valence band and conduction band offsets was determined by in situ X-ray and UV photoelectron spectroscopy during layer by layer formation of buffer material. The conduction band offset (ΔEc) should be small but positive for optimal solar cell electrical performance according to theory. The conduction band offset was determined for the ALD ZnO/CIGS interface (ΔEc = -0.2 eV) and the ALD In2S3/CIGS interface (ΔEc = -0.25 eV). A high temperature process for bandgap grading and a low temperature process for surface passivation by post deposition sulfurization in H2S were investigated. It is concluded that the high temperature sulfurization of CuIn(1-x)GaxSe2 leads to phase separation when x>0. The low temperature process did not result in enhanced device performance.

L’énergie photovoltaïque jouera un rôle déterminant dans la transition énergétique future. Bien que les cellules solaires à base de silicium dominent encore le marché, leur coût de fabrication et le poids des modules limitent leur développement. Depuis quelques années, les industriels s’intéressent de plus en plus aux dispositifs à base de couches minces en raison de leurs procédés de fabrication rapides et peu onéreux sur de larges substrats. Cette technologie utilise une large variété de matériaux; les chalcopyrites tels que Cu(In,Ga)Se2 sont les plus prometteurs. Le procédé de fabrication de couches chalcopyrites le plus répandu est la coévaporation mais l’utilisation de vides très poussés rende cette technique peu adaptée à la production à grande échelle de modules bon marché. La solution alternative décrite dans ce travail est un procédé en deux étapes basé sur le recuit sous atmosphère réactive de précurseurs métalliques électrodéposés. Le développement de cette technologie passe par une meilleure compréhension des mécanismes d’incorporation et d’homogénéisation du gallium dans les couches formées et par une optimisation des étapes de recuit. Le premier objectif de ce travail de thèse est une étude des mécanismes réactionnels mis en jeu lors du procédé de recuit à travers l’étude de différents types de précurseur. Par la suite ces connaissances sont utilisées pour modéliser et optimiser un recuit industriel innovant. Ce travail est réalisé à l’aide de plans d’expérience (DOE) où l’influence de certains paramètres, les plus critiques est mise en évidence. Des voies d’optimisation sont proposées et des hypothèses faites afin d’expliquer les phénomènes observés. / Solar energy is promised to be a major actor in the future of energy production. Even if silicon based solar cells remain the main product their fabrication is energy consuming and requires heavy cover glass for protection, which reduce their development. For several years, commercial interest has shifted towards thin-film cells for which manufacturing time, large scale production, fabrication costs and weight savings are the main advantages. For thin film technology, a wide variety of materials can be used but chalcopyrite such as Cu(In,Ga)Se2 is one of the most promising. The most current method used for chalcopyrite formation is co- evaporation but this process is very expensive and not well suitable for large scale production due to high vacuum requirements. One alternative solution described in this work consists of a two-step technology based on the sequential electro-deposition of a metallic precursor followed by a rapid reactive annealing. However to reach its full potential this technology needs a better understanding of the Ga incorporation mechanism and of the selenization/sulfurization step. This work focuses first on formation mechanisms through the study of several kinds of precursor. This knowledge is then used to explain and to optimize innovative annealing processes. This study is achieved by observing the impact of some process parameters using designs of experiment (DOE). A link between process parameters and properties of these thin films is obtained using electrical, structural and diffusion characterization of the devices. Finally we propose hypothesis to explain observed phenomena and also some improvements to meet the challenges of this process.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-06-07T18:11:24Z No. of bitstreams: 1 Tese Rut Díaz.pdf: 2159528 bytes, checksum: 159d73b33fae80ff4ee36bea4366ea74 (MD5) / Made available in DSpace on 2017-06-07T18:11:24Z (GMT). No. of bitstreams: 1 Tese Rut Díaz.pdf: 2159528 bytes, checksum: 159d73b33fae80ff4ee36bea4366ea74 (MD5) / Fundação de Amparo a Pesquisa do Rio de Janeiro / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Petrobras/CENPES / Agência Nacional do Petróleo / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / O presente estudo utiliza a geoquímica inorgânica das espécies reduzidas do enxofre, operacionalmente definidas como acid - volatile sulfufide (AVS) e chromium -reducible sulfur (CRS),a composição isotópica ( δ 34 S) do sulfat o da água intersticial, do CRS, e das frações orgânicas (ácidos húmicos, ácid os fúlvicos e resíduo orgânico) para avaliar a diagênese do enxofre ao longo do Holoceno (últimos 12.000 anos cal AP) no Sistema de Ressurgência de Cabo Frio (SRCF) . Também foi usada a morfologia da pirita, considerando a distribuição de tamanho dos frambóides através de microscopia eletrônica de varredura (MEV), com o objetivo de inferir o estado de oxidação do ambiente de formação. Foram coletados quatro perfis sedimentares cur tos (b ox - cores ) e três longos ( kullembers ) em um gradiente “cross - shelf” na plataforma continental de Cabo Frio. A razão C/N e o a composição isotópica ( δ 13 C) da matéria orgânica reflete uma fonte marinha durante a diagênese recente. As diferentes caracter ísticas morfológicas, como as superfícies de oxidação nos microcristais, os processos de crescimento secundário e os poliframboides encontrados nas análises morfológicas da pirita, assim como também a variabilidade na distribuição dos diâmetros dos frambói des evidenciaram uma formação sob condição redox altamente dinâmica. A razão COT/CRS indica que o fator limitante para a formação da pirita é o enxofre , devido as condições de deposição do ambiente as quais favorecem a re - oxidação do sulfeto de hidrogênio. A composição isotópica do sulfato ao longo dos perfis apresenta um valor médio de +23‰, e não foi observado um fracionamento isotópico com respeito ao sulfato da água do mar (+ 21‰), indicando a diagênese do sulfato em um sistema aberto e baixas taxas de sulfato redução. No entanto, a composição isotópica do CRS apresentou sinais altamente empobrecidos em 34 S ( - 45‰ até - 25 ‰), indicando reações de re - oxidação no ciclo do enxofre. A composição isotópica das espécies orgânicas do enxofre apresenta um enrique cimento em 32 S quando comprados com o sulfato da água intersticial , e isotopicamente pesadas comparadas com a pirita. O incremento na razão S/C dos ácidos húmicos e o empobrecimento do sinal isotópico em 34 S com o avanço da profundidade indicam a captura d o enxofre de origem diagenético pela matéria orgânica. Um balanço de massa isotópico indica a predominância de uma fonte biossintética nos ácidos húmicos e diagenética nos ácidos fúlvicos, estes resultados guardam relação com a reatividade da matéria orgân ica em cada fração. No gradiente “cross - shelf” as frações orgânicas da plataforma média apresentam os menores conteúdo de enxofre biossíntetico, indicando a presença de matéria orgânica mais reativa. Estes resultados indicam que a sulfurização da matéria o rgânica e a cumulação de pirita em Cabo Frio foi favorecida pelo ciclo re - oxidativo do enxofre devido a intensas condições óxicas na coluna de água. O processo de diagênese do enxofre ao longo do Holoceno não guarda relação aparente com as mudanças oceanog ráficas registrada na área de estudo, assim sendo, adinâmica do enxofre esteve relacionada com a intensidade dos processos de diagênese / Four box-corer and tree kullemberg were collected in a cross - shelf gradient in the continental shelf of Cabo Frio. The box-corer were used to evaluated the sulfurization of the organic matter during the early diagenesis and also, study the pyrite morphology and size distribution of framboids by scanning electron microscopy (SEM) to infer the oxidation state of the environment during the early diagenesis. This study uses the inorganic geochemistry of reduced sulfur species operationally defined as acid-volatile sulfufide (AVS) and chromium - reducible sulfur (CRS), the isotopic composition ( δ 34 S) of pore water sulfate, CRS, and the isotopic composition of difference organic fraction (humic acids, fulvic acids and organic residue to evaluated the sulfur diagenesis during the Holocene (last 12000 years cal AP) in the upwelling system of Cabo Frio. Carbon stable isotopes signatures and C/N ratios of total organic matter evidence a marine source during the early diagenesis. The observed increase in the atomic S/C ratios and t he 34 S depletion in humic acids with increasing depth evidence the diagenetic uptake of reduced sulfur species by organic matter during the early diagenesis. The different morphological characteristics observed, such as surface oxidation in the microcrysta ls, the processes of secondary growth and poliframboides found, as well as the variability in the framboids diameters distribution, show the formation under highly dyna mic redox condition. In the sedi m e nts from the Holocene the COT/CRS ratio indicates that the limiting factor for the pyrite formation is the sulfur. The isotopic composition of sulfate is around +23 ‰ , and without fractionation of sulfate with respect to sea water (21 + ‰) indicating a sulfur diagenesis in a open system and a low net sulfate r eductions. The isotopic composition of the CRS is highly depleted ( - 45 ‰ to - 35‰), indicating oxida tion reactions in the cycle of sulfur . The stable sulfur isotope composition of the organic fractions ( humic acids, fulvics acids and organic res idue ) was sub stantially enriched in 32 S when compared to bottom and pore water sulfate (δ 34 S SO4 2 - ~ +23‰), but isotopically heavier than the co - existing pyrite ( δ 34 S CRS = - 45‰ to - 35‰). The 34 S depletion in humic acids, fulvis acids and in the organic residue with increasing depth evidence the diagenetic uptake of reduced sulfur species by organic matter. A sulfur isotope mass balance indicated a predominance of biogenic sulfur in humic acids and in the organic residue, while the fulvic acids has a predominance of d iagenetic sulfur. In cross - shelf gradient, the organic fractions from the middle shlelf have the lower proportion on biosynthetic sulfur, indicating the presence of more reactive matter. The results evidenced that the sulfurization of organic matter and th e p yrite accumulation in the Cabo F rio sediments was favored by the sulfur re - oxidative cycling due to the intense oxic water conditions . The diageneses process in the sulfur cycle during the Holocene in sediments from the continental shelf don’t have rela tion with the changes in the oceanography conditions. The process of diagenesis of sulfur seem to be a continuous process

科学研究費補助金 研究種目:基盤研究(B)(2) 課題番号:10555255 研究代表者:藤澤 敏治 研究期間:1998-2000年度