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This thesis is a sandwich thesis composed of three papers that are published in refereed journals or conferences. The first paper is a systematic experimental study conducted to identify the first phase to form during cobalt germanidation. Hexagonal β-Co5Ge3 was the first phase to form at temperatures as low as 227°C followed by monoclinic CoGe as the second phase at the same temperature. We also report for the first time that both phases that formed were highly ordered partial epitaxial crystal orientations suggesting that both of those low-temperature phases could potentially serve as high quality contacts for germanium based devices with a very low thermal budget which is advantageous for the process design. Those results contributed to a better understanding of cobalt germanidation leading to the first multiphase technology computer aided design model presented in the second paper. This kinetic model for cobalt germanide growth can predict the resulting phase based on anneal time, temperature, and ambient. The model has been calibrated to experimental results. This predictive model can help in the design of cobalt germanide contacts with low resistance and can serve as a general modeling framework for multiphase solid state reaction binary systems. A comprehensive survey of the experimental results for formation of cobalt germanides is discussed and the data are reconciled in the third paper. Factors affecting the resulting phases and their quality are identified and some optimum choices for the experimental parameters are pointed based on the survey. The role of germanium crystal orientation in ohmic and Schottky properties of the contact is analyzed. Fermi level pinning plays a role mainly on metal/(100) n-type Ge interfaces and its role is minimal on p-type Ge and other crystalline orientations. Schottky Barrier Heights for cobalt germanide contacts reported in the literature are surveyed. Crystalline cobalt germanides, forming when Co is deposited at high temperatures, are expected to have lower interface resistivities compared to those reported. The work is important because contact resistance has become one of the most important factors in advanced complementary metal oxide semiconductor (CMOS) technology and advanced devices already include germanium (Ge) in the source/drain regions of devices. It is also important because heating at the interface due to contact resistance is one of the key challenges in power devices and cobalt germanide can be used both for Si and Ge based devices as well as for gallium nitride (GaN) devices. The latter application is possible because cobalt germanide is lattice-matched to GaN. / Thesis / Doctor of Philosophy (PhD) / The main goal of this thesis is to create predictive empirical, mathematical, and physical models to help the designer of the semiconductor process technology to design high quality electric contacts, namely cobalt germanides, to their semiconductor devices, germanium based. The choice of cobalt germanides is motivated by their expected superior quality given the possibility of growing them in crystalline form. We settled a theoretical and experimental controversy regarding the first phase to form by conducting experiments demonstrating that low-temperature forming cobalt germanide phases are highly ordered and could serve as high quality contacts. A predictive physical based mathematical model was developed to assist the designer in obtaining the desired cobalt germanide phase for its needed electrical properties by design. Factors affecting the quality of the germanide were identified based on an extensive survey and the optimum choices for the parameters to obtain high quality contact were pointed.

The economic incentive to restrict supply in the cobalt market is analyzed. The economic framework for supply restriction and associated conditions for revenue maximization and profitability in a dominant firm price leadership market is presented. The major focus of the economic framework presented is the magnitude of net demand elasticity faced by a producer considering supply restriction. Elasticities of market demand and competitive supply and the market share of the producer considering supply restriction are derived as the components of net demand elasticity. The potential for total revenue and profit maximization by dominant firm supply restriction in the cobalt market is estimated for a range of net demand elasticities. Cobalt market demand price elasticity is derived from cobalt market demand estimates. Preceding the market demand and price elasticity estimatation is a review of factor demand and an analysis of cobalt market demand. Market share of the dominant producer in the cobalt market is estimated from historical data. A range of competitive supply elasticities that would result in increasing the dominant producer's total revenue and profit is derived. / Master of Arts

Das Element Cobalt gewinnt als Technologiemetall und kritischer Rohstoff zunehmend an Bedeutung. Weitgehend in Vergessenheit geraten ist hingegen die Bedeutung des Cobalts für den historischen Erzbergbau im Erzgebirge. Auch die Weiterverarbeitung der Kobalterze in den historischen Blaufarbenwerken ist ein nahezu vergessenes Kapitel der sächsischen Wirtschaftsgeschichte. Es existiert keine zusammenfassende Literatur, die sich mit allen Facetten des historischen Kobalterzbergbaus im Erzgebirge befasst. Das Ziel dieser Masterarbeit ist ein Desiderat, das einen zusammenfassenden und integrativen Überblick über den historischen sächsischen Kobalterzbergbau und der eng damit verknüpften Blaufarbenindustrie schafft. Es wird der Frage nachgegangen, in welchen Lagerstättentypen Kobalterze mineralisierten und wie sich deren räumliche Verbreitung im Erzgebirge beschreiben lässt. Durch Auswertung von Akten des Bergarchivs Freiberg und anderen historischen Quellen erfolgt eine qualitative als auch quantitative Beurteilung der historischen erzgebirgischen Kobaltlagerstätten. Unter Anwendung analytischer Methoden (XRD, REM-EDX) und weiterführenden Literaturauswertungen wurde unter Zuhilfenahme von Sammlungsproben des Museums für Mineralogie und Geologie in Dresden (MMGDD) die mineralogische Zusammensetzung des bedeutendsten Kobalterzes, dem Skutterudit, analysiert. Darauf aufbauend werden die Besonderheiten der Kobalterzverarbeitung in den Blaufarbenwerken dargestellt. Standortgeographische Voraussetzungen werden ebenso erläutert, wie regionale und überregionale Handelsbeziehungen. Des Weiteren wird die Bedeutung der Blaufarbenindustrie für das Glasmacher- und Keramikhandwerk aufgezeigt. Angedeutet wird ebenfalls, wie sich der historische Kobalterzbergbau und Wissenschaft und Technik gegenseitig beeinflussten und so die sächsischen Blaufarbenwerke trotz Erfindung des kostengünstigeren Ultramarins um 1828 noch bis zu Beginn des 20. Jhd. marktbeherrschend blieben. Darüber hinaus werden die heutigen global bedeutendsten Kobaltlagerstätten und die Relevanz dieses Technologiemetalls vorgestellt. / Cobalt is becoming increasingly important as a technology metal and critical raw material. Largely forgotten, however, is the important role of cobalt for the historical ore mining and the subsequent industrial processing in the historical cobalt blue industries in the Erzgebirge mountains of Saxony. In the absence of a comprehensive modern literature the aim of this Master thesis is a desideratum that provides an overview of the historic cobalt ore mining and the closely related cobalt blue industries in the Saxon Erzgebirge. It examines the question in which types of mineral deposits cobalt was mineralised and how their spatial distribution can be described. As a result of evaluating documents of the Bergarchiv Freiberg and other historical sources, a qualitative as well as quantitative assessment of the historical cobalt deposits in the Erzgebirge is carried out. The most important cobalt ore, Skutterudite, was analyzed by using analytical methods (XRD, REM-EDX) and further literature reviews. For this purpose, collection samples from the Museum of Mineralogy and Geology in Dresden (MMGDD) were available. In addition, the peculiarities of further industrial processing of cobalt ore in the cobalt blue industries are presented, as well as their specific geographic prerequisites. Furthermore, the importance of the cobalt blue industry for the old crafts of glassmaking and ceramics is shown, just as the mutual influence with science and technology. Last but not least, the todays world's most important cobalt deposits and the relevance of this technology metal are presented.

The novel compound, [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4] was synthesized. Crystal structures of [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4]·2NCC6H5 and Ba1.5[Fe(C10H13N2O7)][Co(CN)6]·9H2O were determined employing a Rigaku Mercury375R/M CCD (XtaLAB mini) diffractometer with graphite monochromated Mo-Kα radiation. For [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4]·2NCC6H5, the space group was P-421c(#114) with unit cell dimensions: a =11.0169(14)Å, c =21.499(3)Å, V = 2609.4(6)Å3. Each rhodium had approximately octahedral coordination and was bound to another rhodium atom, two nitrogens (trans to each other), two oxygens (trans to each other), and one benzonitrile nitrogen (trans to rhodium). For Ba1.5[Fe(C10H13N2O7)][Co(CN)6]·9H2O the space group was: P-1(#2) with unit cell dimensions: a=13.634Å, b=13.768Å, c=17.254Å and α=84.795°, β=87.863°, γ=78.908°, V=3164.5Å3. The iron atom (nearly octahedral) was coordinated to one chelating ligand (derived from ethylenediaminetetraacetic acid) and the nitrogen of a cyanide ligand. The carbon of the cyanide ligand was bound to cobalt (octahedral). Thus, the cyanide ligand serves as a bridge between the two metals.

The goal of this thesis is to study the microstrucutre and texture of Yttrium-Nickel- Borocarbide and Samarium-Cobalt thin film heterostructures prepared by Pulsed Laser Deposition and to establish structure-property relations for these materials in order to improve their properties and design new structures. Coincidence site lattice epitaxy was explored in most of these heterostructures (substrate, buffer and film) and studied in detail for each case. Epitaxial thin films of the superconducting borocarbide compound YNi2B2C were grown on single crystal MgO (100) substrates without and with Y2O3 buffer layer using pulsed laser deposition (PLD). In both cases YNi2B2C grows with [001] normal to the substrate. However, the in-plane texture depends on the starting condition. For samples without buffer layer, oxygen from the substrate diffuses into the film and forms an Y2O3 reaction layer at the interface. As a consequence, a deficiency of Y is generated giving rise to the formation of secondary phases. On the other hand, using an artificial Y2O3 buffer layer secondary phases are suppressed. The texture of the Y2O3 layers determines the texture of the YNi2B2C film. The superconducting properties of the borocarbide films are discussed with respect to texture and phase purity. To prevent the formation of an impurity phase at the interface, it was the aim of this preliminary investigation to study YNi2B2C films deposited onto single crystal MgO (100) substrates with an Ir buffer layer. The Ir buffer layer shows a strong cube-on-cube texture onto MgO(100) and also prevents the formation of an Y2O3 interlayer. However, during deposition of YNi2B2C the buffer layer disappears by Ir diffusion into the borocarbide film. The YNi2B2C film exhibits a c-axis texture consisting of four components. As a consequence of these effects, the superconducting transition Tc90 equals up to 13K, but with a transition width of 4K. In the second part of this work, hard magnetic Sm-Co/Cr films were epitaxially grown on MgO(100) and (110) substrates. They were characterized by X-ray pole figure measurements and transmission electron microscopy. For films deposited on MgO(100) at 700ºC, orientations are found with the c-axis aligned in-plane and out-of-plane. By lowering the deposition temperature to 370ºC, the out-of-plane orientations disappeared. Further lowering to 350ºC leads to the formation of amorphous regions in the SmCo5 film. For films grown on MgO(110) the Cr buffer deposition temperature plays an important role. When deposited at 700°C Cr(211) and (100) growth is observed leading to two different types of SmCo5 in-plane orientations. By lowering the Cr-buffer deposition temperature to 300ºC only one buffer and one SmCo5 orientation exists: Cr(-211)[0-11] and SmCo5(10-10)[0001]. The exact orientation relationships between substrate, buffer and films are explained and their correlation with magnetic properties are discussed.

Durant ce travail de thèse, d’importants paramètres concernant la synthèse de matériaux catalytiques nanostructurés à base de manganèse et d’oxydes de cobalt ont été établis. La corrélation entre les propriétés structurales du catalyseur et l’activité catalytique, ainsi que le mécanisme d’oxydation du CO ont été analysé au moyen d’une grande variété de méthodes expérimentales physico-chimiques.<p>De l’oxyde de manganèse non-stœchiométrique (MnOx) a été préparé par décomposition spinodale d’oxalate de manganèse trihydraté en ayant recours à la technique d’oxydation programmée en température (TPO). Tant l’analyse quantitative relatives à ces données TPO que les résultats obtenus par spectroscopie de structure au front d’absorption des rayons X (XANES), ainsi que par spectroscopie des photoélectrons X (XPS) ont permis d’estimer la stœchiométrie de l’oxyde avec un x situé entre 1.61 et 1.67. En accord avec à la fois la surface spécifique élevée et la combinaison d’isothermes d’adsorption/désorption de type I et IV, la microscopie électronique à transmission à haute résolution (HRTEM) démontre la présence de micro-bâtonnets caractéristiques et « imbriqués » les uns dans les autres, accompagné de particules nanocristalline à l’extrémité de ces bâtonnets.<p>Les découvertes faites par spectroscopie infra-rouge de réflexion diffuse par transformée de Fourier (DRIFTS), par études isotopiques et cinétiques suggère que l’adsorption des deux molécules, CO et O2, est suivie par leur réaction en surface via des intermédiaires de type carbonate/formate, pour finalement produire du CO2. Nous supposons un mécanisme de type Mars-van Krevelen où l’oxygène appartenant à la structure de type MnOx prend part dans l’oxydation catalytique du CO à basse température. Cependant, ces espèces mobiles d’oxygènes ne faisaient pas partie du cœur de phase du réseau d’oxyde, et de ce fait, ont été capables de « sauter » sur la surface et approvisionner les espèces oxygénées nécessaires à l’oxydation du CO déjà adsorbé.<p>Une structure spinelle d’oxyde de cobalt Co3O4 dans lequel le cobalt présente deux états de valence (+2 et +3) a été choisie pour élucider l’effet de la taille des particules sur l’activité lors de la réaction d’oxydation du CO. Tout d’abord, des nanoparticules monodispersées de cobalt métallique présentant une déviation standard en taille inférieure à 8% ont été synthétisées à partir de carbonyle de cobalt (Co2(CO)8) par une méthode optimisée «d’injection chaude». Un contrôle de la taille des nanoparticules dans la gamme 3 à 11 nm a pu être obtenu en variant la température d’injection du carbonyle de cobalt dans une solution de dichlorobenzène et d’acide oléique. La microscopie électronique à transmission (TEM) nous montre que ces particules de cobalt sont quasiment hémisphériques. Ensuite, de la silice poreuse (de type MCF-17) a été imprégnée par des nanoparticules de cobalt, et ensuite activée par TPO menant à des nanoparticules d’oxyde de cobalt. Des études par diffraction des rayons X (XRD) et spectroscopie des photoélectrons X (XPS) ont démontré la structure spinelle Co3O4. Finalement, l’activité des catalyseurs obtenus vis-à-vis de l’oxydation du monoxyde de carbone fut mesurée à 423 K et ce en fonction de la taille des particules. Les particules de Co3O4 présentant une taille allant de 5 à 8 nm se sont révélées les plus actives. Ceci peut s’expliquer par une plus grande mobilité des atomes d’oxygène en surface des nanoparticules d’oxyde de cobalt.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The goal of this thesis is to study the microstrucutre and texture of Yttrium-Nickel- Borocarbide and Samarium-Cobalt thin film heterostructures prepared by Pulsed Laser Deposition and to establish structure-property relations for these materials in order to improve their properties and design new structures. Coincidence site lattice epitaxy was explored in most of these heterostructures (substrate, buffer and film) and studied in detail for each case. Epitaxial thin films of the superconducting borocarbide compound YNi2B2C were grown on single crystal MgO (100) substrates without and with Y2O3 buffer layer using pulsed laser deposition (PLD). In both cases YNi2B2C grows with [001] normal to the substrate. However, the in-plane texture depends on the starting condition. For samples without buffer layer, oxygen from the substrate diffuses into the film and forms an Y2O3 reaction layer at the interface. As a consequence, a deficiency of Y is generated giving rise to the formation of secondary phases. On the other hand, using an artificial Y2O3 buffer layer secondary phases are suppressed. The texture of the Y2O3 layers determines the texture of the YNi2B2C film. The superconducting properties of the borocarbide films are discussed with respect to texture and phase purity. To prevent the formation of an impurity phase at the interface, it was the aim of this preliminary investigation to study YNi2B2C films deposited onto single crystal MgO (100) substrates with an Ir buffer layer. The Ir buffer layer shows a strong cube-on-cube texture onto MgO(100) and also prevents the formation of an Y2O3 interlayer. However, during deposition of YNi2B2C the buffer layer disappears by Ir diffusion into the borocarbide film. The YNi2B2C film exhibits a c-axis texture consisting of four components. As a consequence of these effects, the superconducting transition Tc90 equals up to 13K, but with a transition width of 4K. In the second part of this work, hard magnetic Sm-Co/Cr films were epitaxially grown on MgO(100) and (110) substrates. They were characterized by X-ray pole figure measurements and transmission electron microscopy. For films deposited on MgO(100) at 700ºC, orientations are found with the c-axis aligned in-plane and out-of-plane. By lowering the deposition temperature to 370ºC, the out-of-plane orientations disappeared. Further lowering to 350ºC leads to the formation of amorphous regions in the SmCo5 film. For films grown on MgO(110) the Cr buffer deposition temperature plays an important role. When deposited at 700°C Cr(211) and (100) growth is observed leading to two different types of SmCo5 in-plane orientations. By lowering the Cr-buffer deposition temperature to 300ºC only one buffer and one SmCo5 orientation exists: Cr(-211)[0-11] and SmCo5(10-10)[0001]. The exact orientation relationships between substrate, buffer and films are explained and their correlation with magnetic properties are discussed.

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Call number: LD2668 .T4 1952 J61 / Master of Science