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Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 166-167). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2007. / Title from PDF t.p. (viewed on Apr. 16, 2009) Includes bibliographical references. Also issued in print.

Exploring the properties of layered materials as a function of thickness has largely been limited to semiconducting materials as thin layers of metallic materials tend to oxidize readily in atmosphere. This makes it challenging to further understand properties such as superconductivity and charge density waves as a function of layer thickness that are unique to metallic compounds. This dissertation discusses a set of materials that use the modulated elemental reactants technique to isolate 1 to 3 layers of VSe2 in a superlattice in order to understand the role of adjacent layers and VSe2 thickness on the charge density wave in VSe2. The modulated elemental reactants technique was performed on a custom built physical vapor deposition to prepare designed precursors that upon annealing will self assemble into the desired heterostructure. First, a series of (PbSe)1+δ(VSe2)n for n = 1 – 3 were synthesized to explore if the charge density wave enhancement in the isovalent (SnSe)1.15VSe2 was unique to this particular heterostructure. Electrical resistivity measurements show a large change in resistivity compared to room temperature resistivity for the n = 1 heterostructure. The overall change in resistivity was larger than what was observed in the analogous SnSe heterostructure. v A second study was conducted on (BiSe)1+δVSe2 to further understand the effect of charge transfer on the charge density wave of VSe2. It was reported that BiSe forms a distorted rocksalt layer with antiphase boundaries. The resulting electrical resistivity showed a severely dampened charge density wave when compared to both analogous SnSe and PbSe containing heterostructures but was similar to bulk. Finally, (SnSe2)1+δVSe2 was prepared to further isolate the VSe2 layers and explore interfacial effects on the charge density wave by switching from a distorted rocksalt structure to 1T-SnSe2. SnSe2 is semiconductor that is used to prevent adjacent VSe2 layers from coupling and thereby enhancing the quasi two-dimensionality of the VSe2 layer. Electrical characterization shows behavior similar to that of SnSe and PbSe containing heterostructures. However, structural characterization shows the presence of a SnSe impurity that is likely influencing the overall temperature dependent resistivity. This dissertation includes previously published and unpublished co-authored materials.

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Les polyoxovanadates fonctionalisés (POVs) présentent des structures de type cœur – cluster super-octahédral à l’échelle nanométrique, des propriétés électroniques et magnétiques facinantes, de nombreux isomers possédant des propriétés thermodynamiques de type réduction – oxydation et des applications catalytiques prometteuses. Parmi ces différentes propriétés, nous nous sommes intéressées aux propriétés de transfert de charge et de fluorescence. Cependant, comprendre des comportements de transfert de charge, et des mécanismes de fluorescence de ces héxavanadates fonctionnalisées est un encore véritable challenge.La diffraction des rayons X haute résolution permet l’analyse des propriétés électroniques et topologiques, et représente une méthode performante pour étudier les liaisons chimiques et la réactivité chimique, basées sur la détermination des propriétés électroniques et électrostatiques. Par conséquent ces propriétés ont été déterminées pour des polyoxovanadates et sont discutées au niveau atomique.Dans ce manuscrit, nous présentons les résultats de : i) la densité électronique expérimentale, la topologie et les propriétés électrostatiques de deux hexavanadates fonctionnalisées (V6), [(C4H9)4N]2[V6O13{(OCH2)3CCH2OCCH2CH3}2] (V6-C3) and Na2[V6O13{(OCH2)3CCH2OH}2]·3.5H2O (V6OH) ; ii) les calculs théoriques ab initio, d’une série de composés fonctionnalisées (V6) et du décavanadate (V10). Les informations chimiques déduites de l’analyse de la densité électronique sont utilisées pour une meilleure compréhension de la distribution de la densité de charge, des propriétés de fluorescences, du comportement en terme de fonctionnalisation, et des propriétés biologiques. / The functionalized polyoxovanadates (POVs) exhibit nanoscale superoctahedral cluster-core structures, fascinating electronic and magnetic properties, various thermodynamically stable redox isomers, and potential catalytic capabilities. Among of the various properties, we are interested in the charge transfer and fluorescent properties. However, understanding such a charge transfer behavior and fluorescence mechanism of these functionalized hexavanadates is still a formidable challenge.High resolution X-ray crystallography allows the analysis of the electronic and topological properties, and provides a method to study the chemical bonding and chemical reactivity based on charge density and the electrostatic properties determination. Experimental and theoretical charge density analysis of functionalized polyoxovanadates has been carried out and the related properties have been discussed at the atomic level.In this manuscript, we present the results of: i) experimental charge density and related electronic and topological properties of two functionalized hexavanadates (V6), [(C4H9)4N]2[V6O13{(OCH2)3CCH2OCCH2CH3}2] (V6-C3) and Na2[V6O13{(OCH2)3CCH2OH}2]·3.5H2O (V6OH); ii) theoretical calculations on a series of functionalized V6 compounds, and decavanadate (V10). The chemical information from charge density analysis is used for a better understanding of the charge density distribution, charge transfer, fluorescent properties, functionalization behavior, and biological activities.

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The value of the surface charge density of polypropylene reported in literature has a three order of magnitude discrepancy. Nauruzbayeva et al report a 0.7nCcm−2 as the surface charge density of polypropylene as measured using the charge of electrified droplets[1]. Meagher and Craig reported result 111nCcm−2 as estimated by electric double layer theory from colloidal probe Atomic force microscopy (AFM) force spectroscopy [2]. We show that oxidation of hydrophobic surfaces as a potential mechanism in origin of these surface charges. Using colloidal probe AFM We measured the surface charge densities of Teflon AF, perfluorodecanethiol, Perfluorodecyltrichlorosilane(FDTS), Octadecyltrichlorosilane, polystyrene, and polypropylene. Also, The pH dependence of the surface charge density for FDTS was studied and it shows the behavior expected of a weak acid in response to pH. We suspect that the origin of the surface charges is mostly likely impurities or surface oxidation. We conclude that the electrometer and dispensed droplets approach cannot detect these charges because of the process of de-wetting all the surface be neutralized to maintain charge neutrality. This explanation supports Nauruzbayeva et al claims about surface bound charges[1].

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Recentemente foi descoberto que diversos calcogenetos de metais de transição podem ter o estado charge density waves (CDW) suprimido a partir de pressão hidrostática e dopagens, e, por conseguinte, o estado supercondutor emerge. Nesse contexto, este trabalho apresenta um estudo sistemático de propriedades físicas de amostras poli e monocristalinas de dois compostos do sistema Nb-Te, NbTe2 e NbTe4. Com relação ao composto NbTe2, os resultados aqui apresentados demonstram que esse composto é mais um exemplo de material que exibe ambos os estados a pressão atmosférica e sem dopagens. No que tange as propriedades do NbTe4, este trabalho demonstra que amostras deficientes em telúrio tem a anomalia na curva de resistividade elétrica relacionada a formação do estado CDW amplificada e, a deficiência em telúrio é também capaz de fazer emergir supercondutividade em 5.5 K. Este trabalho também sugere algumas mudanças no diagrama de equilíbrio de fases Nb-Te publicado na base de dados da sociedade americana de metalurgia (ASM). As fases Nb5Te4 e Nb3Te4 foram identificadas como sendo fases de altas temperaturas que são formadas a partir de reações eutetóides. Além do mais, nossos resultados demonstram que a região entre as fases NbTe2 e NbTe4 consiste, na verdade, de uma região bifásica. Durante a realização deste trabalho, outro composto foi investigado, o NiTe2. Nesse composto, nossos resultados demonstram que a intercalação de Ti faz emergir um estado supercondutor em 4.5 K e cuja temperatura de transição parece insensível a pressão hidrostática. Cálculos de estrutura de bandas sugerem fortemente que o composto NiTe2 intercalado com Ti pode ser mais um exemplo de supercondutor com aspectos topológicos em sua superfície de Fermi. / Recently was demonstrated that it is possible to suppress the charge density waves (CDW) ground states while, simultaneously, a superconductor state emerges in several transition metal chalcogenides (TMC), by means of hydrostatic pressure or chemical doping. Within this context, this work presents a systematic study on physical properties of two Nb chalcogenides, NbTe2 and NbTe4. Our results demonstrate that NbTe2 is another example of a TMC which exhibit both stabilities at atmospheric pressure and without doping. Regarding the physical properties of NbTe4, we have demonstrated that Te deficiency increases significantly the anomaly in the electrical resistivity as function of temperature behavior related with the CDW formation. At the same time, Te deficiency can also cause a SC state to emerge at 5.5 K. This work also presents a review of the binary phase diagram, Nb-Te, and some changes are proposed. Nb5Te4 and Nb3Te4 were identified as high temperature phases originated from eutectoid reactions. Furthermore, our results demonstrated that the region between the phases NbTe2 and NbTe4 are, in fact, a two-phase region, differently from what is proposed in the actual version of the phase diagram. Also, during this work, another chalcogenide was investigated, NiTe2. Our results demonstrate that Ti can be intercalted between the Van der Waals gaps of the structure and consequently a superconductor state emerges at 4.5 K. The critical temperature is found to be insensitive to hydrostatic pressure. Band structure strongly suggests that NiTe2 could be another example of a superconductor with topological aspects in its Fermi surface.