Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 197-202). Also available on the Internet.

Bacterial pathogens cause severe infections worldwide in livestock and in humans, and antibiotic resistance further increases the importance of prophylactic vaccines. Inactivated bacterial vaccines (bacterins) are usually produced via incubation of the pathogen with chemicals such as formaldehyde, which is time consuming and may cause loss of immunogenicity due to the modification of structural components. We evaluated low-energy electron irradiation (LEEI) as an alternative method to generate a bacterin. Rodentibacter pneumotropicus, an invasive Gram-negative murine pathogen, was inactivated with LEEI and formaldehyde. LEEI resulted in high antigen conservation, and LPS activity was significantly better maintained when compared with formaldehyde treatment. Immunization of mice with LEEI-inactivated R. pneumotropicus elicited a strong immune response with no detectable bacterial burden upon sublethal challenge. The results of this study suggest the inactivation of bacteria with LEEI as an alternative, fast and efficient method to generate bacterial vaccines with increased efficacy.

Résumé: Ce mémoire de maîtrise est une étude des probabilités d’interactions (sections efficaces) des électrons de basse énergie avec une molécule d’intérêt biologique. Cette molécule est le tétrahydrofurane (THF) qui est un bon modèle de la molécule constituant la colonne vertébrale de l’ADN; le désoxyribose. Étant donné la grande quantité d’électrons secondaires libérés lors du passage des radiations à travers la matière biologique et sachant que ceux-ci déposent la majorité de l’énergie, l’étude de leurs interactions avec les molécules constituant l’ADN devient rapidement d’une grande importance. Les mesures de sections efficaces sont faites à l’aide d’un spectromètre à haute résolution de pertes d’énergie de l’électron. Les spectres de pertes d’énergie de l’électron obtenus de cet appareil permettent de calculer les valeurs de sections efficaces pour chaque vibration en fonction de l’énergie incidente de l’électron. L’article présenté dans ce mémoire traite de ces mesures et des résultats. En effet, il présente et explique en détail les conditions expérimentales, il décrit la méthode de déconvolution qui est utilisée pour obtenir les valeurs de sections efficaces et il présente et discute des 4 résonances observées dans la dépendance en énergie des sections efficaces. En effet, cette étude a permis de localiser en énergie 4 résonances et celles-ci ont toutes été confirmées par des recherches expérimentales et théoriques antérieures sur le sujet des collisions électrons lents-THF. En outre, jamais ces résonances n’avaient été observées simultanément dans une même étude et jamais la résonance trouvée à basse énergie n’avait été observée avec autant d’intensité que cette présente étude. Cette étude a donc permis de raffiner notre compréhension fondamentale des processus résonants impliqués lors de collisions d’électrons secondaires avec le THF. Les valeurs de sections efficaces sont, quant à elles, très prisées par les théoriciens et sont nécessaires pour les simulations Monte Carlo pour prédire, par exemple, le nombre d’ions formées après le passage des radiations. Ces valeurs pourront justement être utilisées dans les modèles de distribution et dépôt d’énergie au niveau nanoscopique dans les milieux biologiques et ceux-ci pourront éventuellement améliorer l’efficacité des modalités radiothérapeutiques. / Abstract: This master’s thesis is a study of interactions probabilities (cross sections) of low-energy electrons with an important biomolecule. The studied molecule is tetrahydrofuran (THF) which is a good model for the DNA backbone constituent deoxyribose. Knowing the important quantity of secondary electrons generated by the radiations passage through the biological matter and knowing that these low-energy electrons are responsible for the majority of the energy deposited, the study of their interactions with DNA constituents becomes rapidly important. Cross sections measurements are performed with a high-resolution electron energy loss spectrometer. The electron energy loss spectra obtained from this spectrometer allow cross sections calculations for each vibration mode as a function of electron incident energy. The article presented in this master thesis describes in details the experimental methods, it presents energy loss spectra and it shows and discusses results obtained in this project. The energy dependence of the cross sections allows the observation of multiple resonances in many vibration modes of THF. Effectively, this study allows the energy localisation of 4 resonances, which have all been confirmed by previous experimental and theoretical studies on the electron-THF collisions. Additionally, these resonances have never been observed simultaneously in the same study and the resonance found at low incident energy has never been observed with as much intensity as this present work. This study allowed a better understanding of the fundamental processes occurring in collisions of low-energy electrons with THF. The cross sections values are highly prized by theorists and they are essential for Monte Carlo simulations. These values will be used in models for energy distribution and deposition in biological matter at nanoscopic scales, thereby they will eventually improve the efficiency of radiotherapeutic modalities.

Deposition of solid state materials span a wide variety of methods and often utilize high energy sources such as plasmas and ultra-violet light resulting in a wide variety of characteristics and applications. A fundamental understanding is essential for furthering the applications of these materials which include catalysis, molecular filtration, electronics, sensing devices, and energy storage among others. A combination of experimental and theoretical work is presented here on several materials including 2D silicates on Pd, boron oxide, and vanadium oxynitride. Silicate formation under low energy electron microscopy demonstrate film permeability to oxygen, while ab initio molecular dynamics simulations reveal the possible initial mechanisms associated with the formation of boron oxide films during atomic layer deposition. Lastly, vanadium oxynitrides have shown preferential sputtering of N over O sites and theoretical binding energies serve as a guide for assigning experimental x-ray photoelectron spectra.

No description available.

L’espace est un milieu hostile pour les équipements embarqués à bord des satellites. Les importants flux d’électrons qui les bombardent continuellement peuvent pénétrer à l’intérieur de leurs composants électroniques et engendrer des dysfonctionnements. Leur prise en compte nécessite des outils numériques 3D très performants, tels que des codes de transport d’électrons utilisant la méthode statistique de Monte-Carlo, valides jusqu’à quelques eV. Dans ce contexte, l’ONERA a développé, en partenariat avec le CNES, le code OSMOSEE pour l’aluminium. De son côté, le CEA a développé, pour le silicium, le module basse énergie MicroElec dans le code GEANT4. L’objectif de cette thèse, dans un effort commun entre l’ONERA, le CNES et le CEA, est d’étendre ces codes à différents matériaux. Pour ce faire, nous avons choisi d’utiliser le modèle des fonctions diélectriques, qui permet de modéliser le transport des électrons à basse énergie dans les métaux, les semi-conducteurs et les isolants. La validation des codes par des mesures du dispositif DEESSE de l’ONERA, pour l’aluminium, l’argent et le silicium, nous a permis d’obtenir une meilleure compréhension du transport des électrons à basse énergie, et par la suite, d’étudier l’effet de la rugosité de la surface. La rugosité, qui peut avoir un impact important sur le nombre d’électrons émis par les matériaux, n’est habituellement pas prise en compte dans les codes de transport, qui ne simulent que des matériaux idéalement plats. En ce sens, les résultats de ces travaux de thèse offrent des perspectives intéressantes pour les applications spatiales. / Space is a hostile environment for embedded electronic devices on board satellites. The high fluxes of energetic electrons that impact these satellites may continuously penetrate inside their electronic components and cause malfunctions. Taking into account the effects of these particles requires high-performant 3D numerical tools, such as codes dedicated to electrons transport using the Monte Carlo statistical method, valid down to a few eV. In this context, ONERA has developed, in collaboration with CNES, the code OSMOSEE for aluminum. For its part, CEA has developed for silicon the low-energy electron module MicroElec for the code GEANT4. The aim of this thesis, in a collaborative effort between ONERA, CNES and CEA, is to extend those two codes to different materials. To describe the interactions between electrons, we chose to use the dielectric function formalism that enables to overcome of the disparity of electronic band structures in solids, which play a preponderant role at low energy. From the validation of the codes, for aluminum, silver and silicon, by comparison with measurements from the experimental set-up DEESSE at ONERA, we obtained a better understanding of the transport of low energy electrons in solids. This result enables us to study the effect of the surface roughness. This parameter, which may have a significant impact on the electron emission yield, is not usually taken into account in Monte Carlo transport codes, which only simulate ideally flat materials. In this sense, the results of this thesis offer interesting perspectives for space applications.

Orientador: Richard Landers / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T10:50:19Z (GMT). No. of bitstreams: 1 Pancotti_Alexandre_M.pdf: 2977317 bytes, checksum: 914d690fda86677fcc9c894c6f408409 (MD5) Previous issue date: 2005 / Resumo: Nesse trabalho nos propomos a estudar a estrutura eletrônica e geométrica de ligas de superfície à partir de filmes ultra finos, da ordem de monocamada atômica , crescidos por MBE sobre substratos monocristalinos. Os filmes finos foram crescidos in situ e analizados por XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) e UPS (Ultra Violet Photoelectron Spectroscopy). As ligas de superfície estudas foram InPd, SnPd e SbPd sempre sobre um substrato de Pd(111). Os resultados das medidas PED dos sistemas InPd e SnPd foram interpretadas usando programas tipo MSCD[1]. Foi mostrado que Sn e In em baixa cobertura formam uma estrutura (raiz2 3 x raiz2 3) R 30o ( e o In mostrou uma estrutura (1x1) para filmes com mais de 2 monocamadas, provavelmente na forma de ilhas sobre a superfície do Pd. Estudos anteriores mostraram que Sb sobre Pd(111) também apresenta a fase (raiz2 3 x raiz2 3)R 30o para baixas coberturas[2]. Os modelos que melhor se adequaram aos dados sugerem fortemente que os metais sp(In, Sn,e Sb) não difundem além da segunda monocamada. Durante estes estudos foi observado que a intensidade do satélite de shake-up do Pd tendia a zero para os átomos em contato direto com os metais s / Abstract: The purpose of this report is to present a study of the electronic and geometric structure of surface alloys grown by MBE (Molecular Beam Epitaxy) on single crystal substrates in the sub monolayer regime. The films were grown "in-situ" in the analysis chamber and analyzed by XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) and UPS (Ultra Violet Photoelectron Spectroscopy). The alloys studied were InPd, SnPd e SbPd, all grown on the (111) face of a Pd crystal. The PED measurements for InPd and SnPd were analyzed using the MSCD code[3]. It was possible to show that for low coverages both metals formed a (raiz2 3 x raiz2 3) R 30o ( reconstruction and the first inter-planar distances were determined. For films with over two monolayers the In grew with a (1x1) structure probably in the form of islands separated by clean Pd. Previous studies showed that Sb[4] at low coverage also forms a (raiz2 3 x raiz2 3) R 30o ( structure. Our simulations suggest that In, Sn and Sb for the coverages studied do not diffuse beyond the second atomic layer. We also observed that the intensity of the Pd shake up satellite tends to zero for the Pd atoms in contact with these sp metals / Mestrado / Física da Matéria Condensada / Mestre em Física

The direct epitaxial growth of multilayer BN by atomic layer deposition is of critical significance forfo two-dimensional device applications. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) demonstrate layer-by-layer BN epitaxy on two different substrates. One substrate was a monolayer of RuO2(110) formed on a Ru(0001) substrate, the other was an atomically clean Ni(111) single crystal. Growth was accomplished atomic layer deposition (ALD) cycles of BCl3/NH3 at 600 K substrate temperature and subsequent annealing in ultrahigh vacuum (UHV). This yielded stoichiometric BN layers, and an average BN film thickness linearly proportional to the number of BCl3/NH3 cycles. The BN(0001)/RuO2(110) interface had negligible charge transfer or band bending as indicated by XPS and LEED data indicate a 30° rotation between the coincident BN and oxide lattices. The atomic layer epitaxy of BN on an oxide surface suggests new routes to the direct growth and integration of graphene and BN with industrially important substrates, including Si(100). XPS and LEED indicated epitaxial deposition of h-BN(0001) on the Ni(111) single crystal by ALD, and subsequent epitaxially aligned graphene was deposited by chemical vapor deposition (CVD) of ethylene at 1000 K. Direct multilayer, in situ growth of h-BN on magnetic substrates such as Ni is important for spintronic device applications. Solid-state electrolytes (SSEs) are of significant interest for their promise as lithium-ion conducting materials but are prone to degradation due to lithium carbonate formation on the surface upon exposure to atmosphere, adversely impacting Li ion conduction. In situ XPS monitored changes in the composition of the SSE Li garnet (Li6.5La3Zr1.5Ta0.5O12, LLZTaO) upon annealing in UHV and upon Ar+ ion sputtering. Trends in core level spectra demonstrate that binding energy (BE) calibration of the Li 1s at 56.4 eV, yields a more consistent interpretation of results than the more commonly used standard of the adventitious C 1s at 284.8 eV. Annealing one ambient-exposed sample to >1000 K in UHV effectively reduced surface carbonate and oxygen, leaving significant amounts of carbon in lower oxidation states. A second ambient-exposed sample was subjected to 3 keV Ar+ ion sputtering at 500 K in UHV, which eliminated all surface carbon, and reduced the O 1s intensity and BE. These methods present alternative approaches to lithium carbonate removal than heating or polishing in inert atmospheres and are compatible with fundamental surface science studies. In particular, the data show that sputtering at mildly elevated temperatures yields facile elimination of carbonate and other forms of surface carbon. This is in contrast to annealing in either UHV or in noble gas environments, which result in carbonate reduction, but with significant remnant coverages of other forms of carbon.

No description available.

A catalytic route to hydrogen production via thermochemical water splitting is highly desirable because it directly converts thermal energy into stored chemical energy in the form of hydrogen and oxygen. Recently, the Davis group at Caltech reported an innovative low-temperature (max 850°C) catalytic cycle for thermochemical water splitting based on sodium and manganese oxides (Xu, Bhawe and Davis, PNAS, 2012). The key steps are thought to be hydrogen evolution from a Na₂CO₃/MnO mixture, and oxygen evolution by thermal reduction of solids formed by Na⁺ extraction from NaMnO₂. Our work is aimed at understanding the fundamental chemical processes involved in the catalytic cycle, especially the hydrogen evolution from water. In this project, efforts are made to understand the interactions between the key components (Na, O₂, CO₂, and water) in the hydrogen evolution steps on a well-defined MnO(100) single crystal surface, utilizing x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). While some of the behavior of the catalytic system is observed with the model system developed in this work, hydrogen is only produced from water in the presence of metallic sodium, in contrast to the proposal of Xu et al. that water splitting occurs from the reaction of water with a mixture of Na₂CO₃ and MnO. These differences are discussed in light of the different operating conditions for the catalytic system and the surface science model developed in this work. / Ph. D.