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Adams, Stephen J. A. "Optical spectroscopy of InxGa1-xAs/GaAs quantum wells." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/816.
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Wittee, Lopes Christian. "Characterization of metallic species on porous materials by in situ XAS." Doctoral thesis, Universitat Politècnica de València, 2018. http://hdl.handle.net/10251/107953.
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El objetivo de esta tesis es estudiar la agrupación y el crecimiento de especies metálicas confinadas o soportadas en materiales porosos mediante espectroscopia de absorción de rayos X in situ. Para lograrlo, las especies de paladio y plata se han introducido en materiales porosos (¿-alúmina, carbón activo y zeolitas) mediante impregnación vía húmeda y métodos de intercambio iónico, respectivamente. Luego, el agrupamiento de estas especies metálicas se ha controlado mediante tratamientos de activación en diferentes atmósferas (inerte, oxidativa y reductiva) y seguido por XAS de manera detallada.
El objetivo principal del trabajo actual es demostrar que tanto XANES como EXAFS pueden proporcionar información valiosa y, en cierto punto, innovadora durante el control de especies metálicas (en términos de tipo y tamaño de las especies). Aprovechando los procedimientos de análisis inusuales, como el análisis de los cumulantes, el ajuste de la parte imaginaria de la transformada de Fourier y otros, es posible obtener información refinada sobre los sistemas investigados.
En la sección de introducción, se proporciona una compilación de estudios en los que se ha utilizado XAS como técnica importante para caracterizar especies metálicas en materiales porosos. Conscientes de que las personas pueden usar dicha introducción como base para estudios más complejos en el futuro, la discusión se ha dirigido tentativamente hacia este objetivo.
El capítulo 4 se centra en el estudio de la influencia de los precursores de paladio y la naturaleza del soporte en las nanopartículas resultantes. El proceso de activación completo, es decir, la transformación precursor --> nanopartícula, ha sido seguido por XAS in situ. El análisis estuvo compuesto por el punto de partida (material impregnado), calcinación en flujo de O2 y reducción posterior con H2. La consecuencia del uso de diferentes precursores metálicos y soportes se ha discutido en términos del número de coordinación promedio obtenido a partir del análisis de datos de EXAFS, que fue respaldado por técnicas de caracterización de laboratorio.
El capítulo 5 está dedicado al estudio de la agrupación de plata durante y después de los tratamientos de activación utilizando zeolitas de poro pequeño intercambiadas con plata como precursores y nanocontenedores. Se ha estudiado la influencia de la estructura y la composición química de los materiales basados en plata sobre las especies metálicas formadas en diferentes condiciones de agrupamiento y redispersión del metal (calcinación usando atmósferas distintas, reducción en H2, redispersión en O2) utilizando métodos de caracterización in situ o ex situ. Después, se discuten las consecuencias catalíticas de las zeolitas que contienen Ag en la reacción de SCO-NH3. En esta sección, la combinación de XAS in situ con varias técnicas de laboratorio ha demostrado ser fundamental para un completo entendimiento del trabajo.
Finalmente, una lista de proyectos desarrollados en paralelo a esta tesis se proporciona al final de este documento.The aim of this thesis is to study the clustering and growth of metallic species either confined or supported in porous materials by in situ X-ray absorption spectroscopy. To accomplish this task, palladium and silver species were introduced into porous materials (¿-alumina, activated carbon and zeolites) by wetness impregnation and ion-exchange methods, respectively. Then, the clustering of these metallic species was controlled by activation treatments in different atmospheres (inert, oxidative and reductive) and followed by XAS in a comprehensive way. The principal goal of current work is to demonstrate that both XANES and EXAFS can provide valuable and, at certain point, innovative information during tuning of metallic species (in terms of type and size). Taking advantage of unusual analysis procedures, such as cumulant approach, fitting of imaginary part of Fourier transform and others, it is possible to obtain refined information about the investigated systems. In the introduction section, a compilation of studies in which XAS was used as important technique to characterize metallic species in porous materials is provided. Conscious that people can use such introduction as a basis for more complex studies in the future, the discussion has been tentatively directed toward this goal. The chapter 4 is focused on the study of the influence of palladium precursors and the nature of support on the resultant nanoparticles. The whole activation process, i.e. the transformation precursor --> nanoparticle, was followed in situ by XAS. The analysis pathway was composed by the starting point (as-impregnated), calcination in O2 flow and posterior reduction with H2. The consequence of using distinct metal precursors and supports were discussed in terms of average coordination number obtained from EXAFS data analysis, which was co-supported by laboratory characterization techniques. The chapter 5 is dedicated to the study of silver clustering during and after activation treatments using Ag-containing small-pore zeolites as precursors and nanocontainers. The influence of framework structure and chemical composition of Ag-based materials on formed Ag species at different clustering and metal redispersion conditions (calcination using distinct atmospheres, reduction in H2, redispersion in O2) were studied using either in situ or ex situ characterization methods. After, the catalytic consequences of tuned Ag-containing zeolites in SCO-NH3 are discussed. In this section, the combination of in situ XAS with several laboratory techniques proved to be pivotal to have a full picture of the investigated system. Finally, a list of projects developed in parallel to this thesis is provided at the end of this document.
L'objectiu d'aquesta tesi és estudiar l'agrupació i el creixement d'espècies metàl·liques confinades o suportades en materials porosos mitjançant espectroscòpia d'absorció de raigs X in situ. Per a això, les espècies de pal·ladi i plata s'han introduït en materials porosos (¿-alúmina, carbó activat i zeolites) per mitjà de la impregnació via humida i mètodes d'intercanvi iònic, respectivament. Una vegada preparats els materials, l'agrupament de les espècies metàl·liques s'ha controlat fent ús de tractaments d'activació en diferents atmosferes (inert, oxidant i reductora) s'ha estudiat exhaustivament per XAS. L'objectiu principal del treball és demostrar que tant el XANES com l'EXAFS proporcionen informació rellevant i, en certa manera, innovadora per al control d'espècies metàl·liques (en termes de tipus i grandària d'aquestes espècies). Fent ús de procediments de tractament de dades no molt habituals com l'anàlisi de cumulants, l'ajust de la part imaginària de la transformada de Fourier i altres, és possible obtenir informació detallada sobre els sistemes estudiats. En l'apartat de la introducció, es proporciona una recopilació d'estudis en els quals s'ha utilitzat XAS com a tècnica principal per a caracteritzar les anomenades espècies metàl·liques en materials porosos. Aquesta introducció ha estat redactada per a que puga servir com a punt de partida per a futurs estudis que requereixen la utilització de XAS per a la caracterització de les espècies metàl·liques presents en els catalitzadors. El capítol 4 es centra en l'estudi de la influència dels precursors de pal·ladi i la naturalesa del suport front a les nanopartícules resultants. El procés d'activació, és a dir, la transformació precursor --> nanopartícula, ha sigut estudiat per XAS in situ. L'anàlisi per XAS va comprendre els següents passos: punt de partida (material impregnat), calcinació en flux d'O2 i reducció posterior amb H2. La utilització de diferents precursors i suports metàl·lics ha permès dur a terme una discussió, referent al nombre de coordinació mitjà obtingut a partir de l'anàlisi de dades de la zona EXAFS, que ha estat recolzat per altres tècniques de caracterització. El capítol 5 s'ha dedicat a l'estudi de l'agrupació de plata intercanviada en els catalitzadors durant i després dels tractaments d'activació. S'han utilitzat zeolites de porus xicotet, com la CHA i RHO, intercanviades amb plata. L'estudi de la influència de l'estructura zeolítica i la composició química dels materials enfront dels diferents tractaments d'activació (calcinació utilitzant diferents atmosferes, reducció en presència d'H2, re-dispersió en atmosfera d'O2) es va realitzar fent ús de mètodes de caracterització in situ o ex situ. A continuació, es discuteix la influència d'aquestes espècies metàl·liques formades, utilitzant els diferents mètodes d'activació, per a la reacció d'SCO-NH3. En aquest sentit, s'ha demostrat que la combinació de XAS in situ amb diverses tècniques habituals de laboratori és fonamental per al desenvolupament d'aquest treball. Finalment, es presenta una llista de projectes, en els quals també s'ha treballat paral·lelament, on s'ha utilitzat XAS com a tècnica de caracterització.
Wittee Lopes, C. (2018). Characterization of metallic species on porous materials by in situ XAS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107953
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Vegelius, Johan. "X-ray Spectroscopic Studies of Materials for Nuclear Technology." Doctoral thesis, Uppsala universitet, Mjukröntgenfysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160362.
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X-ray spectroscopic experiments, including X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS), were performed in a large energy range (60-9000 eV) on a variety of systems, probing different elements and orbitals. The systems can preferably be divided into three groups: Actinides, copper systems and amorphous materials. We studied oxidation states of Pu in PuO2 using a closed-source experimental setup, developed by us, to lower the safety restrictions associated with such experiments. The presence of Pu with higher oxidation state than Pu(IV) was found in polycrystalline PuO2. This is an important finding since Pu with higher oxidation states has higher solubility affecting the safety of a proposed undeground repository of spent nuclear fuel which can eventually be infiltrated by groundwater. In the proposed underground repository the molecular oxygen will vanish at some point due to microbial activity and mineral oxidation. At this stage sulfur is the most important candidate for causing copper corrosion. We studied Cu films and foils exposed to sulfide solutions at both Cu L2,3, Cu K and S L2,3 edges and found for example that S L2,3 XES is useful for distinguishing between different copper sulfides and Cu Kβ XES can be used to identify monovalent Cu compounds. Amorphous, zirconium containing alloys are potentially useful materials for future nuclear reactors. The electronic structure of such materials was also investigated.
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Jahel, Ali. "Étude de l'ajout d'un promoteur au système Pt-Sn supporté sur alumine chlorée utilisé en reformage catalytique." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20233.
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L'objectif de ce travail était d'étudier de manière approfondie l'effet de l'indium dans des catalyseurs trimétalliques de reformage catalytique à base de platine, étain et indium. Des catalyseurs ont ainsi été synthétisés selon différents protocoles de préparation et de multiples caractérisations (spectroscopies Mössbauer d'étain, XANES, EXAFS, IR-CO, MEBT, chimisportion du CO, TPR et TPD) ont été mises en oeuvre afin d'élucider l'impact de l'indium sur la nature des phases métalliques présentes au sein du catalyseur. Il a ainsi été montré que la nature des sites métalliques dépend de la méthode d'introduction de l'indium. Quand l'indium est précipité avec la source d'alumine des alliages de type PtxSn sont obtenus alors que lorsque les métaux sont imprégnés sur la surface de l'alumine des espèces subsitutionnelles Pt-Sn sont formées. Il a aussi été montré que l'augmentation de la teneur en indium entraine une augmentation de la concentration atomique d'étain dans les alliage PtxSn et un remplacement de l'étain par l'indium dans les espèces substitutionnelles. Nous avons également réussi à préparer des catalyseurs avec des quantités élevées d'alliage Pt3Sn sur la base des connaissances acquises sur l'impact de l'indium et en déposant l'étain par une réaction organométallique contrôlée de surface. D'un point de vue catalytique, les tests de reformage du n-heptane mettent en évidence l'impact positif de l'indium puisque les catalyseurs à base de Pt-Sn-In sont moins sélectifs pour les réactions parasites d'hydrogénolyse et d'hydrocraquage et plus sélectifs pour l'isomérisation que les catalyseurs à base de Pt-SnThis work consists of a detailed study on the effect of indium in alumina supported trimetallic PtSnIn-based naphtha reforming catalysts. These catalysts were reproduced using different preparation protocols and the indium effect was investigated using 119Sn Mössbauer spectroscopy, XANES, EXAFS spectroscopies, IR-CO, STEM, CO chemisorption, TPR and TPD. It appears that the nature of the metallic active centres depends on the method with which indium was introduced. When co-precipitating the indium precursor with the Al source, PtxSn alloys were formed, whereas when metals were impregnated on the surface, substitutional Pt-Sn alloys were observed. Increasing the In content in the frst type of catalysts leads to an increase in the Sn concentration in PtxSn alloys, whereas a gradual replacement of Sn by indium in susbstitutinal alloys is observed in the second type of catalysts. These results allowed preparing catalysts with high Pt3Sn alloy contents using the effect of indium in catalysts prepared by Sn organometallic controlled surface reactions (CSR). From a catalytic point of view, n-heptane reforming tests show that trimetallic PtSnIn-based catalysts are less selective to hydrogenolysis and hydrocracking reactions, and highly selective to isomerisation, compared to the bimetallic PtSn-based catalyst
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Dehlinger, Mael. "XAS-XEOL and XRF spectroscopies using near field microscope probes for high-resolution photon collection." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4048/document.
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Les microscopes en champ proche permettent d'obtenir la topographie d'un échantillon avec une résolution pouvant atteindre la résolution atomique. Les spectroscopies de rayons-X sont des méthodes de caractérisation qui permettent de déterminer la composition et la structure élémentaire de l'échantillon avec une précision inférieure à l'Ångström. Nous avons choisi de coupler ces deux techniques en collectant localement la luminescence visible issue de l'échantillon par la pointe-sonde d'un microscope à force de cisaillement, constituée d'une fibre optique effilée de faible ouverture. Cette technique a été utilisée pour caractériser des échantillons semiconducteurs micro- et nano-structurés afin d'en obtenir simultanément la topographie et la cartographie de luminescence locale. Afin de pouvoir étendre ce concept à d'autres types de matériaux, la faisabilité de la collecte de la fluorescence X locale a été évaluée avec la microsource. Pour cela la fluorescence X émise par un échantillon a été collectée par un capillaire cylindrique équipant un détecteur EDX. L'influence du diamètre du capillaire sur le niveau de signal a été mesurée. Une simulation numérique a été développée afin d'estimer le niveau de signal obtenu en utilisant un capillaire de 1 µm de diamètre et d'optimiser la géométrie du système. En couplant la microscopie en champ proche et l'analyse XRF, à la lumière de ces résultats, il sera possible d'atteindre 100 nm de résolution latérale en environnement synchrotron et moins de 1 µm à l'aide d'une source de laboratoire. Il serait alors possible de sélectionner un objet particulier sur une surface et d'en faire l'analyse élémentaireScanning Probe Microscopes allow to obtain sample topography up to atomic resolution. X-ray spectroscopies allow elemental and structural analysis of a sample with accuracy better than 1 Å. The lateral resolution is limited by the primary beam diameter, currently a few µm². We have chosen to couple this two technics. Local sample visible luminescence is collected through a low aperture sharp optical fibre, probe of a shear force microscope. This technique was used to characterize microstructured semiconducting samples to achieve simultaneously the surface topography and luminescence mapping. The results were obtained using either synchrotron radiation or a laboratory microsource equipped with a polycapillary lens. To extend this concept to a wider variety of materials, local XRF collection by an EDX detector equipped with a cylindrical X-ray capillary was tested. A cobalt sample irradiated with the microsource was used for technique evaluation. The signal magnitude dependence with the capillary diameter was measured. Modelling and numerical calculations were developed to estimate the signal magnitude that could be detected using a 1 µm diameter capillary. The optimal system geometry was determined. Scanning Probe Microscopy combined to XRF analysis could thereby lead to simultaneous acquisition of sample topography and chemical mapping. The expected lateral resolution using synchrotron radiation is 100 nm while sub 1 µm resolution is realistic with a laboratory source. This technique would allow to point a peculiar micro- or nano-object on the surface and to perform its chemical analysis
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Kristiansen, Paw. "In situ X-Ray Spectroscopy of Ethylene Epoxidation over Ag and studies of Li-ion batteries and Cu sulfidation." Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-209204.
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This thesis is based on experiments applying synchrotron based X-ray Absorption Spectroscopy(XAS) and Resonant Inelastic X-ray Scattering (RIXS) in the soft X-ray region to energy related systems. The main work of this thesis has been to develop a reaction cell that allowed for in situ XAS and RIXS investigations of the partial epoxidation of ethylene over a Ag catalyst at 1 atm and up to 250C. The developed in situ cell can be used in two sample modes: 1) the Ag catalyst is deposited directly onto the vacuum separating membrane with the reaction gases flowing beneath it or 2) a slightly compressed Ag powder sample is at a distance to the vacuum membrane with the reaction gases flowing between the Ag powder sample and the membrane.Both sample modes offers the total florescence yield, TFY, and the total electron yield, TEY, to be recorded simultaneously. By means of the developed in situ cell a number of oxygen species, residing in/on the Ag surface or in the Ag bulk, have been detected. We claim to detect adsorbed O2 under epoxidation conditions, as well as Ag–O–H groups. We are also able to monitor changes of the absorbed oxygen as we change the composition of the reaction gas feed. The first charging cycle of Li-ion batteries have been investigate by ex situ measurements on the cathode Li2-xMnSiO4 and the anode composite LixNi0:5TiOPO4/C . The initial crystalline material becomes amorphous due to lithiation during the first first charging. We find that the redox behaviors of these two states are significantly different. Sulfidation of natural copper oxides are is found to be strongly promoted when it is grown on the host metal by a disproportionation.
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Davies, Graeme John. "Optically detected X-ray absorption spectroscopy (OD-XAS) study of InGaN/GaN quantum well and quantum dot nanostructures." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516410.
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InGaN/GaN single quantum well (SQW) and quantum dot (QD) samples were studied using optically detected X-ray absorption spectroscopy (OD-XAS). This is a powerful technique, capable of linking local structural environment information with the luminescence emission processes present. Ga K-edge OD-EXAFS analysis shows this technique to be site-selective for these samples and, from the emission related to the QW or QD structure, a percentage indium value was determined for each sample. Possible reasons why this siteselectivity is observed are considered, along with the implication of the results with respect to the nature of the mechanism responsible for exciton localisation within these structures. Further investigations were performed on the QD sample, including a depth profiling study based on spectra obtained at several different excitation energies and an analysis of the OD-XANES at the N K-edge. The application of pumpprobe micro-imaging OD-XAS to these types of samples is also examined.
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Poirier, Mathilde. "Fonctionnalisation et cristallochimie de talcs synthétiques submicroniques." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30237.
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Le talc synthétique est un matériau à fort intérêt industriel du fait de sa taille submicronique, de sa large surface spécifique (> 300 m²/g), et de ses propriétés hydrophiles, qui lui offrent un large éventail d'applications dans des secteurs industriels variés (polymères, cosmétiques, papiers, peintures, médecine, ...). Dans cette thèse, les potentialités d'adsorption du matériau ont été testées vis-à-vis de différents composés organiques et/ou inorganiques à propriétés physico-chimiques souhaitées (composés colorés et/ou fluorescents, nanoparticules métalliques), afin d'élaborer de nouvelles charges minérales fonctionnelles et innovantes (e.g. talcs synthétiques fluorescents). Les résultats montrent que le matériau présente une forte capacité à adsorber les composés testés, qui est bien supérieure à celle de son homologue naturel de taille pluri-micronique. La recherche des mécanismes d'adsorption se produisant à l'interface "minéral - adsorbat" a par la suite conduit à étudier de plus près la cristallochimie du talc synthétique non fonctionnalisé, en utilisant plusieurs méthodes de caractérisation comme la Diffraction des Rayons (DRX), la spectroscopie de Résonance Magnétique Nucléaire (RMN), ou bien encore la spectroscopie d'Absorption des Rayons X (XAS). Outre le fait que de grandes avancées ont été faites sur la caractérisation cristallochimique des particules, les résultats majeurs montrent que les minéraux synthétiques ne doivent pas être regardés de la même manière que les minéraux naturels, du fait de leur taille nanométrique qui engendre obligatoirement une perturbation des signaux observés. Les résultats montrent notamment que les méthodes de caractérisation qui sont classiquement utilisées en DRX pour calculer les distances inter-réticulaires ne doivent pas être appliquées sur les nanomatériaux du fait du faible empilement des particules suivant l'axe cristallographique c*. Il faut pour cela faire appel à des méthodes de simulation numériques pour déterminer les valeurs des distances inter-réticulaires réelles. De la même manière, les résultats montrent que les signaux RMN sont également impactés par la taille nanométrique des particules du fait d'une différenciation des signaux provenant du cœur des particules, de ceux provenant des surfaces externes des particules. Ces résultats ont été mis en évidence en combinant une approche expérimentale par RMN à une approche théorique par DFT (Density Functional Theory).[;;;]Synthetic talc is a material of great industrial interest because of its submicronic size, its large specific surface area (> 300 m²/g), and its hydrophilic properties, offering a wide range of applications in the fields of polymers, cosmetics, papers, paints, or medecine. In this thesis, the adsorption capacity of the material was tested towards different organic and/or inorganic compounds of desired physicochemical properties (coloured and/or fluorescent compounds, metallic nanoparticles), to elaborate new mineral fillers with functional and innovative characteristics (e.g. fluorescent synthetic talc particles). The results show that synthetic talc particles possess a much higher adsorption capacity towards organic and inorganic compounds, compared to natural plurimicron-sized talc particles. Research on the adsorption mechanisms occuring at the " mineral - adsorbate " interface was followed by the study of the crystal-chemistry of the material, using a combination of several characterization techniques such as X-Ray Diffraction (XRD), Nuclear Magnetic Resonance spectroscopy (NMR), or X-Ray Absorption spectroscopy (XAS). Beyond the fact that a great progress was made on the overall crystal-chemistry of the particles, the main results show that " synthetic minerals " should not be considered in the same way as " natural minerals " due to their nanometric size which necessarily disturbed the observed signals. As an example, the methods conventionally used in XRD to determine the interplanar spacings should not be applied on nanomaterials because of their very low particle stacking and numerical simulations shall be used instead. Similarly, our study shows that NMR signals are also impacted by the nanometric size of the particles because of a spectral differentiation of the signals coming from the bulk of the particles versus the ones coming from the external surfaces of the particles. These results were highlighted by combining an experimental NMR approach and a theoretical DFT (Density Functional Theory). Those external surfaces, which contain crystalline defects, are probably responsible for the high adsorption capacity of the material, and may explain some of the crystallogenesis processes that have been observed by XAS spectroscopy. To conclude, nano-sized lamellar synthetic materials represent a great tool to investigate the surface crystal-chemistry of natural minerals, as they revealed new contributions which were previously undetectable in larger-sized minerals
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Helmstedt, Andreas [Verfasser]. "Probing the magnetic properties of [MnIII6CrIII]3+ single-molecule magnets by XAS, XMCD and spin-resolved electron spectroscopy / Andreas Helmstedt." Bielefeld : Universitätsbibliothek Bielefeld, 2014. http://d-nb.info/1068621702/34.
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Zamora, Torres David, and Felix Abeln. "Design of an In-situ cell, for hard X-ray spectroscopy of surfaces used in high-pressure and high-temperature experiments : Design av en In-situ cell för intensiv röntgenspektroskopi i högtryck- högtemperaturexperiment." Thesis, Malmö universitet, Institutionen för materialvetenskap och tillämpad matematik (MTM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-45607.
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This project analyzes how an in-situ cell can be developed to withstand high amounts of pressure and temperature of at least 100 bar and 500 °C. A theoretical prototype will be created as a product for Malmö University and other researchers to use or improve. To make this possible, the five step method was used to present a symmetric geometrical concept for the cell. That geometric concept was designed in PTC Creo (Version 6.0.2.0 & 7.0) in 3D and drawings in 2D. The programs GRANTA EduPack (Version 2020 \& Version 2019) along with Hephaestus was used to determine a material selection that will be able to tolerate temperature, pressure and be at least ten percent transparent, to be able for the X-ray to pass through the material and into the sample. The Finite Element Method (FEM) was used to ensure that the cell adheres to the set values of pressure and not cause a catastrophic failure. The result turn out to be a elliptical three part in-situ cell of boron carbide outer shell, a beryllium main dome and a stainless steel plate for the material sample to be on top. The Finite Element Method also showed that the designed in-situ cells meet the requirements and fulfills the goal and purpose. Further development of safety features and the equipment will be needed to minimise the risk of and dangers of beryllium dust.Detta projekt analyserar hur en in-situ cell kan utvecklas för att motstå höga mängder tryck och temperatur på minst 100 bar och 500 °C . En teoretisk prototyp kommer att skapas som en produkt för Malmö universitet och andra forskare att använda eller förbättra. För att göra detta möjligt användes femstegsmetoden för att presentera ett symmetriskt och geometriskt koncept för cellen. Det geometriska konceptet kommer att utformas 3-dimensionellt i PTC Creo (Version 6.0.2.0 7.0) och 2-dimensionella ritningar . GRANTA EduPack-programmen (Version 2020 \& Version 2019) tillsammans med Hephaestus användes för att bestämma ett materialval som kommer att kunna tolerera temperatur, tryck och vara minst tio procent transparent för att röntgenstrålningen ska kunna passera genom materialet och in i provet. Finite Element Method (FEM) kommer att användas för att säkerställa att cellen följer de inställda tryckvärdena och inte orsakar katastrofala fel. Resultatet visar sig vara en elliptisk tredelad in-situ cell av borkarbid som ett yttre skal, beryllium som huvudkupol och en rostfri stålplatta som underlag för materialprovet. Finite Element Method visade också att den designade in-situ-cellen uppfyller kraven och därför uppfyller målet och syftet. Detta innebär att vidareutveckling av säkerhetsfunktioner och utrustning kommer att behövas för att minimera risken för berusning från berylliumdammet.
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Pereira, Luis Gustavo da Silva. "Avaliação do mecanismo de oxidação de hidrogênio contaminado por monóxido de carbono em células PEMFC contendo catalisadores anódicos baseados em Pt-M/C (M=Ru, Mo, Fe e W)." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-11032010-110241/.
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A busca por fontes alternativas de energia é uma tendência mundial e, neste contexto, as células a combustível alimentadas com hidrogênio obtido pela reforma de biocombustíveis constitui uma das alternativas mais promissoras. Entretanto, o desempenho das células a combustível de membrana de troca protônica (PEMFC) com ânodos baseados em Pt é drasticamente reduzido quando se utiliza hidrogênio contaminado por CO, o qual é produzido no processo de reforma. Neste trabalho, a eletrocatálise da tolerância ao CO e a estabilidade de Pt/C, PtRu/C, PtFe/C, PtMo/C e PtW/C como eletrocatlisadores anódicos de célula a combustível PEM foram investigadas através de curvas de polarização e medidas on line de espectrometria de massas (EMS), análises de voltametria cíclica, difração de raios X (DRX) e absorção de raios X (XAS). Para todos os eletrocatalisadores bimetálicos, os quais apresentaram alta tolerância ao CO, os resultado de EMS mostraram que a produção de CO2 inicia-se a menores sobrepotenciais em relação ao eletrodo de hidrogênio quando comparado a Pt/C, confirmando a ocorrência do conhecido mecanismo bifuncional. Por outro lado, os resultados de XANES indicam um aumento de vacância da banda 5d da Pt para todos os catalisadores bimetálicos, particularmente para PtFe/C, o que leva a um enfraquecimento da ligação Pt-CO e conseqüente aumento da tolerância ao CO (efeito eletrônico). Para PtMo/C e PtRu/C alimentado com H2/CO, a formação de CO2 é observada mesmo quando a célula opera em circuito aberto, confirmando alguma eliminação de CO por um processo químico, muito provavelmente uma reação de deslocamento gás-água. Uma deterioração do desempenho de célula a combustível foi observada em uma função do tempo de operação. As causas desta degradação durante a operação a longo prazo fazem parte de um processo complexo que envolve diversos mecanismos paralelos, tais como: perda ou redistribuição do eletrocatalisador, corrosão do suporte de carbono e degradação do eletrólito (Nafion®).The search for alternative sources of energy is a global trend, and in this context, the fuel cell supplied with hydrogen obtained by biofuels reforming is one of the most promising alternative. However, the performance of proton exchange membrane fuel cells (PEMFC) with Pt-based anode is drastically lowered when using CO-contain hydrogen, as that produced by reform. In this work, the electrocatalysis of CO tolerance and the stability of Pt/C, PtRu/C, PtFe/C, PtMo/C, and PtW/C electrocatalysts at a PEM fuel cell anode has been investigated using single cell polarization and on line electrochemical mass spectrometry (EMS) measurements, and cyclic voltammetry, X-ray diffraction (XRD), and X-ray absorption near edge structure (XANES) analyses of the electrocatalysts. For all bimetallic electrocatalysts, which presented higher CO tolerance, EMS results have shown that the production of CO2 starts at lower hydrogen electrode overpotentials as compared to Pt/C, confirming the occurrence of the so-called bifunctional mechanism. On the other hand, XANES results indicate an increase in the Pt 5d-band vacancies for the bimetallic catalysts, particularly for PtFe/C, this leading to a weakening of the Pt-CO bond, helping to increase the CO tolerance (the so-called electronic effect). For PtMo/C and PtRu/C supplied with H2/CO, the formation of CO2 is observed even when the cell is at open circuit, confirming some elimination of CO by a chemical process, most probably the water gas shift reaction. A decay of the fuel cell performance was observed as a function of the operation time. The causes of degradation during long-term operation were found to be a complex process that involves several parallel mechanisms, including: electrocatalyst loss or redistribution, carbon corrosion, and electrolyte (Nafion®) degradation.
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Gråsjö, Johan. "Molecular Arrangement, Electronic Structure and Transport Properties in Surfactant Gel- and Related Systems Studied by Soft X-ray and Dielectric Spectroscopy." Doctoral thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205072.
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This thesis concerns studies of aqueous soft matter systems, especially surfactant micelle systems. The aim has been to study the molecular arrangement and electronic structure of the constituents of, as well as transport properties in such a system. The molecular arrangement and electronic structure has been studied by means of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray spectroscopy (RIXS). The transport properties have been investigated by low-frequency dielectric spectroscopy (LFDS) and small angle X-ray scattering (SAXS) as well as a theoretical modelling. The latter was based on Fick’s laws of the release from binary surfactant system and was validated by experiments. The RIXS and XAS measurements show the electronic structure in bulk water and the influence of the chemical surrounding of the water molecule in bulk water and of the water molecules confined in a micelle lattice. The spectra are highly dependent on the molecular arrangement in such systems. For glycine and sodium polyacrylate RIXS and XAS spectra show features which are unique for carboxyl and carboxylate groups and such measurements can thus be used for fingerprinting. The LFDS and SAXS measurements show a strong correlation between structure in a surfactant/poly-ion system and apparent mobility of surfactants. This conclusion is in line with earlier observations. By the theoretical modelling a predictive model for the surfactant release from a binary surfactant micelle system has been obtained and the importance of different factors for surfactant release has been further clarified.
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Bao, Zhuo. "Synchrotron Radiation Studies of Free and Adsorbed Molecules." Doctoral thesis, Uppsala University, Surface and Interface Science Division, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8610.
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This thesis contains two parts. The first part concerns the research work on free molecules using synchrotron-radiation-related techniques. Auger electron spectra of two free open-shell molecules, O2 and NO, were studied experimentally and theoretically. Photoionization experimental technique with tunable synchrotron radiation source was used to induce core-level electron ionization and obtain the KVV normal Auger electron spectra. A quantitative assignment of O2 normal Auger spectrum was obtained by applying ab initio CI calculations and LVI Auger line shape simulations including the bond length dependence of Auger transition rates. The photon energy dependence of normal Auger electron spectra was focused on with photon energies in the vicinities of core-ionization threshold energies. Consequently, the MAPCI (Molecular Auger Post Collision Interaction) theory was developed. Taking the near-threshold O2 normal Auger spectrum as an example, the two extreme cases of MAPCI effect, “atomic-like PCI” and “molecular PCI”, were discovered and discussed. The effect of shape resonance on near-threshold molecular normal Auger spectrum was discussed taking NO near threshold normal Auger spectra as example.
The second part deals with research work on the chemisorption of small epoxy organic molecules, ethylene oxide, methyl oxirane, on Si (100) surfaces. Synchrotron radiation related techniques, UPS, XPS and NEXAFS, were applied. Based on the valence photoemission spectra, C 1s and Si 2p XPS spectra, the epoxy ring opening reactions of these molecules in chemisorption process were proved. Further tentative search for the surface-adsorbate CDAD effect was performed, and no evident circular dichroism was confirmed.
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Zhang, Teng. "Synchrotron radiation study of free and adsorbed organic molecules." Licentiate thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-307787.
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In this licentiate thesis, organic molecules, namely Cobalt Phthalocyanine (CoPc) and Biphenylene, have been studied by means of synchrotron radiation-based spectroscopic methods (Photoemission Spectroscopy (PES) and X-ray Absorption Spectroscopy (XAS) in combination with Density Functional Theory (DFT) calculations. Paper I is a combined experimental and theoretical investigation of electronic structure of CoPc. addressing the atomic character of the Highest Occupied Molecular Orbital (HOMO) and the electronic configuration of the molecular ground state. Both these aspects are still under discussion since different experimental and theoretical studies have given controversial results. Previous works have indicated the CoPc ground state to either be described by the 2A1g or 2Eg, or by a mix of the two electronic configurations. Regrading the debated the atomic character of the HOMO of CoPc, it has been suggested to be either metal 3d-like and localized on the central Co atom or originating in the organic ligand of the molecule. In this thesis the valence photoemission results for CoPc in gas phase and as adsorbed films on Au(111) together with the DFT simulations, consistently indicate that the HOMO is derived only by the organic ligand, with mainly contribution from the carbon atoms with no metal character. Moreover, the good agreement between the experimental and theoretical results, confirms that the ground state of CoPc is correctly described by the 2A1g configuration. In Paper II, PES and XAS have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, XAS measurements allowed the characterizion of the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction.
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Curcio, Ana Laura [UNESP]. "Síntese e caracterização de materiais semicondutores nanoestruturados luminescentes à base de ZnS." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/138154.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Nanocristais tem sido extensivamente investigados nos últimos anos devido à sua ampla gama de aplicações em vários dispositivos tais como sensores, células solares, lasers, fotocatalisadores, fotodetectores, detectores de infravermelhos, diodos emissores de luz, materiais eletroluminescentes e outros materiais emissores de luz. Semicondutores nanocristalinos apresentam propriedades eletrônicas intermediárias entre aqueles de estrutura molecular e sólidos macrocristalinos, proporcionando uma ampla gama de aplicações. Entre estes materiais, o sulfeto de zinco (ZnS) puro ou dopado tem recebido notável atenção por causa de suas propriedades estruturais ópticas, versatilidade e potencial para várias aplicações tecnológicas. O ZnS é um típico semicondutor II-VI, com um gap direto de 3,6 eV à temperatura ambiente e aproximadamente 40 meV de energia de gap, sendo um bom material luminescente utilizado em telas, sensores e lasers. Como material de gap largo, o ZnS pode facilmente hospedar diferentes metais de transição como centros luminescentes. Entre estes íons de metais de transição para estruturas dopadas, os íons Cu2+e Mn2+ são atraentes pelas emissões de luz características e por apresentarem propriedades eficientes para aplicações como luminóforos. A inserção desses íons na estrutura do ZnS proporcionam defeitos que resultam em emissão no verde para os íons Cu2+e emissão no laranja para os íons Mn2+. Neste estudo, as amostras de ZnS pura e dopadas com Cu2+ e Mn2+ foram preparados pelo método solvotermal, que demonstra ser um processo eficaz para preparar nanopartículas. Uma vez preparadas, as estruturas das amostras nanoestruturadas foram caracterizadas e correlacionada s com propriedades fotoluminescentes. Os resultados de difração de raios X mostram que as amostras de ZnS foram cristalizadas completamente sem a presença de fases secundárias e os difratogramas correspondem à estrutura blenda cúbica de zinco com grupo espacial F-43m. Os espectros de XANES (X-ray Absorption Near Edge Structure) teóricos e experimentais na borda K do Zn indicam que a incorporação de átomos de Mn na matriz ZnS causam a formação de vacâncias de Zn e S, a qual é confirmada por ajustes de espectros EXAFS (Extended X-ray Absorption Fine Structure). Estas vacâncias estão relacionadas com um desvio para o vermelho observado no pico do espectro de fotoluminescência devido a adição de Mn na estrutura do ZnS. Para o ZnS puro, o pico é centrado em ~ 504 nm, relativo as vacâncias de S na amostra nanoestruturada. À medida que se aumenta a porcentagem de Mn na matriz ZnS, uma emissão no amarelo-laranja centrada em ~ 590 nm pode ser observada, associada com a transição 4T1-6A1 no interior de níveis 3d de Mn2+. A adição de íons Cu2+ ao ZnS resulta em um alargamento no pico do espectro de fotoluminescência decorrente de emissão no azul-verde, que está relacionada a recombinação de elétrons de níveis de defeitos mais profundos dos estados t2 do Cu próximos da banda de valência.
Nanocrystals has been extensively investigated in recent years due to its wide range of applications in various devices light emitting materials such as sensors, solar cells, lasers, photocatalysts, photodetectors, IR detectors, light emitting diodes and others. Nanocrystalline Semiconductors have electronic properties between those intermediate molecular macrocristalinos and solid structure, providing a wide range of applications. Among these materials, zinc sulfide (ZnS) pure or doped has received considerable attention because of its optical structural properties, versatility and potential for several technological applications. The ZnS is a typical II-VI semiconductor with a direct band gap of 3.6 eV at room temperature and about 40 meV in energy gap, and a good luminescent material for constrution of displays, lasers and sensors. As wide band gap material, ZnS can easily host different transition metals as luminescent centers. Among these ions of transition metal doped structures, Cu2+ and Mn2+ ions are attractive for light emission characteristics and for having effective properties for applications such as phosphors. The addition of these ions in ZnS structure provide defects that result in emission in the green for the Cu2+ ions and emission in orange for the Mn2+ ions. In this study, samples of pure ZnS and doped with Cu2+ and Mn2+ ions were prepared by solvotermal method, which demonstrate to be an effective process for preparing nanoparticles. Once prepared, the structures of the nanostructured samples were characterized and correlated with photoluminescent properties. The results of X-ray diffraction showed that the ZnS samples were completely crystallized without the presence of secondary phases and XRD patterns correspond to the structure of zinc blende to cubic space group F-43m. spectra XANES (X-ray Absorption Near Edge Structure) theoretical and experimental in the Zn K edge indicates that the inclusion of Mn atoms in the ZnS matrix cause the formation of Zn and S vacancies, which is confirmed by spectral adjustments EXAFS (Extended X-ray Absorption Fine Structure). These vacancies are associated with a red shift observed in the photoluminescence spectrum peak due to the addition of Mn in ZnS structure. For pure ZnS, the peak is centered at ~ 504 nm concerning the vacancies in the S nanostructured sample. As it increases the percentage of Mn in the ZnS matrix, in yellow-orange emission centered at ~ 590 nm can be observed, associated with the transition 4 T1- 6A1 inside 3d levels of Mn2+. Adding Cu2+ to the ZnS results in a broadening of the peak of the photoluminescence spectrum due to emission in blue-green, which is related to recombination deeper defect levels of electrons of t2 Cu states near the valence band.
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Chalker, Paul R. "The oxidation of nickel and titanium studied by XPS and XAES." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371219.
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Gomes, Washington Charles de Macedo. "Aplica??o da espectroscopia de absor??o de raios X no estudo do comportamento do ?on Cu2+ em micelas inversas." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/17615.
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Previous issue date: 2009-04-29Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
This work deals with the application of X-Ray Absorption Spectroscopy on the study of the behavior of Cu2+ ions in inverse micelles. The formation of copper nanoparticles in water-in-oil microemulsions in pseudo-ternary systems of cetyl trimethylammonium Bromide (CTAB) surfactant, butanol co-surfactant, heptane as oil phase and aqueous solutions of CuSO4.5H2O, and NaBH4. The microemulsions were prepared with a fixed percentage (60 %) of oil phase and a variable water to tensoative proportion. It was observed an increase on Cu2+ reduction by the sodium borohydride in microemulsions with 13 % of aqueous phase, independent of the reaction time. For the microemulsions in which the aqueous phase is composed only by the CuSO4 solution, it was observed that the color of the solution depends on the water to surfactant ratio. These changes in color were attributed to a competition for the hidratation water between the polar head of the tensoative and Cu2+ ions with the eventual substitution of oxygen by bromine atoms in the first coordination shell of Cu2+ ions
Neste trabalho estudou-se aplica??o da espectroscopia de absor??o de raios x no estudo do comportamento dos ?ons Cu2+ em micelas inversas. Estudou-se a forma??o de nanopart?culas de cobre em microemuls?es ?gua-em-?leo de sistemas pseudo-tern?rios tensoativo (brometo de hexadeciltrimetilam?nio, CTAB)-cotensoativo (butanol) / fase oleosa (heptano) / fase aquosa (solu??es de CuSO4.5H2O, e NaBH4). As microemuls?es foram preparadas fixando em 60% a fase ?leo (Heptano) e variando 40% de fase aquosa com tensoativo/cotensoativo na mesma propor??o, sendo que a fase aquosa do agente redutor NaBH4 foi usada em excesso de 0,4 mol.L-1 e 0,8 mol.L-1 em rela??o 0,2 mol.L-1 de fase aquosa de CuSO4.5H2O. Observou-se uma maior redu??o dos ?ons Cu2+ pelo boridreto de s?dio em microemuls?es com 13% de ?gua, independente do tempo de rea??o. Para as microemuls?es em que a fase aquosa corresponde a solu??o de CuSO4, observou-se uma depend?ncia na colora??o em fun??o da rela??o entre as concentra??es de ?gua/tensoativo. Essa mudan?a de colora??o foi atribu?da a uma competi??o pelas mol?culas de ?guas entre a cabe?a polar do tensoativo e os ?ons Cu2+ com uma eventual substitui??o do oxig?nio da primeira esfera de coordena??o por bromo
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Luo, Yun. "Crystal Chemistry of U and Th in Apatite." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1272635731.
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Bordage, Amélie. "Propriétés spectroscopiques et structure électronique du vanadium dans des matériaux complexes : implications géologiques et technologiques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00459909.
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Cette thèse a pour but d'étudier les propriétés spectroscopiques et la structure électronique du vanadium dans différents minéraux d'intérêt géologique et/ou technologique. Une approche expérimentale basée sur la spectroscopie HERFD-XAS au seuil K du vanadium a été combinée à une approche théorique. Cette dernière couple calculs ab initio et calculs multiélectroniques des spectres XANES, permettant une interprétation plus fine des spectres expérimentaux. Des développements théoriques basés sur les tenseurs sphériques et la méthode des cosets ont été effectués puis appliqués au cas de la section efficace d'absorption des rayons X, afin d'extraire les propriétés spectroscopiques du cristal à partir de celles d'un site individuel. La signature spectrale de V3+ dans le grossulaire (Ca3Al2(SiO4)3) a été déterminée grâce à la dépendance angulaire du préseuil de son spectre XANES. Ce minéral peut donc être utilisé de manière fiable comme composé de référence dans l'étude du degré d'oxydation du vanadium dans des verres, de minéraux et de composés synthétiques. Le vanadium peut être incorporé comme dopant dans l'anatase (TiO2 ) sous forme de vanadium tétravalent. Son environnement local dans l'anatase a été sondé, montrant que le vanadium n'est pas incorporé en substitution du titane. Enfin, le degré d'oxydation du vanadium dans les titanomagnétites (Fe3-xTixO4 :V) du Bushveld (Afrique du Sud) a été déterminé pour des échantillons naturels et synthétiques. La coexistence de deux degrés d'oxydation (+III et +IV) a été montrée mais les implications de leur variations relatives sur la formation des couches géantes de magnétite dans le Bushveld restent encore mal comprises.
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Glorius, M., H. Moll, G. Bernhard, A. Roßberg, and A. Barkleit. "The Mobilization of Actinides by Microbial Ligands Taking into Consideration the Final Storage of Nuclear Waste - Interactions of Selected Actinides U(VI), Cm(III), and Np(V) with Pyoverdins Secreted by Pseudomonas fluorescens and Related Model Compounds (Final Report BMBF Project No.: 02E9985)." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-27809.
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The groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m in the Äspö Hard Rock Laboratory secretes a pyoverdin-mixture with four main components (two pyoverdins and two ferribactins). The dominant influence of the pyoverdins of this mixture could be demonstrated by an absorption spectroscopy study. The comparison of the stability constants of U(VI), Cm(III), and Np(V) species with ligands simulating the functional groups of the pyoverdins results in the following order of complex strength: pyoverdins (PYO) > trihydroxamate (DFO) > catecholates (NAP, 6HQ) > simple hydroxamates (SHA, BHA). The pyoverdin chromophore functionality shows a large affinity to bind actinides. As a result, pyoverdins are also able to complex and to mobilize elements other than Fe(III) at a considerably high efficiency. It is known that EDTA may form the strongest actinide complexes among the various organic components in nuclear wastes. The stability constants of 1:1 species formed between Cm(III) and U(VI) and pyoverdins are by a factor of 1.05 and 1.3, respectively, larger compared to the corresponding EDTA stability constants. The Np(V)-PYO stability constant is even by a factor of 1.83 greater than the EDTA stability constant. The identified Np(V)-PYO species belong to the strongest Np(V) species with organic material reported so far. All identified species influence the actinide speciation within the biologically relevant pH range. The metal binding properties of microbes are mainly determined by functional groups of their cell wall (LPS: Gram-negative bacteria and PG: Gram-positive bacteria). On the basis of the determined stability constants raw estimates are possible, if actinides prefer to interact with the microbial cell wall components or with the secreted pyoverdin bioligands. By taking pH 5 as an example, U(VI)-PYO interactions are slightly stronger than those observed with LPS and PG. For Cm(III) we found a much stronger affinity to aqueous pyoverdin species than to functional groups of the cell wall compartments. A similar behavior was observed for Np(V). This shows the importance of indirect interaction processes between actinides and bioligands secreted by resident microbes.
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Leetmaa, Mikael. "Structure Modeling with X-ray Absorption and Reverse Monte Carlo: Applications to Water." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-31475.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2009.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4, 5 and 6: Submitted. Härtill 6 uppsatser.
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Åhlund, John. "Electronic and Geometrical Structure of Phthalocyanines on Surfaces : An Electron Spectroscopy and Scanning Tunneling Microscopy Study." Doctoral thesis, Uppsala universitet, Fysiska institutionen, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7802.
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Core- and Valence Photoelectron Spectroscopy (PES), X-ray- and Ultraviolet-Visible Absorption Spectroscopy (XAS and UV-Vis), Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) calculations are used to study the electronic and geometrical structure of a class of macro-cyclic molecules, Phthalocyanines (Pc), on surfaces. These molecules are widely studied due to their application in many different fields. Multilayer and monolayer coverages of Iron Phthalocyanine (FePc) and metal-free Phthalocyanine (H2Pc) deposited on different surfaces are investigated in order to get insight in the electronic and geometrical structure of the obtained overlayers, of crucial importance for the understanding of the film functionality. Sublimation of molecular thick films on Si(100) and on conducting glass results in films with molecules mainly oriented with their molecular plane orthogonal to the surface. Ex-situ deposited H2Pc films on conductive glass show different molecular orientation and morphology with respect to the vacuum sublimated films. We study the monolayer adsorption structure of FePc and H2Pc and compare our results with other Pc’s adsorbed on graphite. We find that the molecular unit cell and the superstructure is characteristic for each Pc adsorbed on graphite, even if the geometrical size of the compared molecules is the same. The PE- and XA- spectra of FePc on graphite are essentially identical for the mono- and multilayer preparations, evidencing weak intermolecular and molecular-substrate interactions of van der Waals nature. Furthermore, we characterize Pc’s on InSb (001)-c(8x2). The substrate In rows are observed to be the adsorption site for Pc’s. We find that the growth of the two-dimensional islands of FePc is prolonged in the [-110] direction, in contrast to ZnPc adsorbed on the same substrate at room temperature. We interpret this result as an indication that the adsorption is controlled by the substrate corrugation observed at 70 K.
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Gomes, Washington Charles de Macedo. "Caracteriza??o estrutural de Perovskitas Lax-1AxCoO3 (x=0 e 0,2) ,dopadas com c?lcio e bario, por espectroscopia de absor??o de raios X (XAS)." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/17779.
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Previous issue date: 2013-09-09Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
In this work, the structures of LaCoO3, La0,8Ba0,2CoO3 and La0,8Ca0,2CoO3 perovskites were characterized as a function of temperature (LaCoO3 structure being analyzed only at room temperature). The characterization of these materials were made by X-Ray Absorption Spectroscopy (XAS), in the cobalt K-edge, taking into account the correlated Einstein model X-ray absorption fine structure (EXAFS). The first part of the absorption spectrum corresponded the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). These materials were prepared by the combustion method. The combustion products were calcinated at 900 0C, for 6 hours in air. Noted that the sample LaCoO3 at room temperature and samples doped with Calcium and Barium in the temperature range of 50 K to 298 K showed greater distortion to monoclinic symmetry with space group I2/a. However, the sample doped with barium at the temperatures 50 K, 220 K, and 260 K showed a slight distortion to rhombohedral symmetry with space group R-3c. The La0,8Ca0, 2CoO3 structure was few sensitive to temperature variation, showing a higher local distortion in the octahedron and a higher local thermal disorder. These interpretations were in agreement with the information electronic structural on the XANES region and geometric in the EXAFS region
Neste trabalho foram investigados estruturas de perovskitas LaCoO3, La0,8Ba0,2CoO3 e La0,8Ca0,2CoO3 em fun??o de temperatura, sendo que a estrutura LaCoO3 foi analisada apenas em temperatura ambiente. As caracteriza??es destes materiais foram realizadas pela espectroscopia de absor??o de raios X (XAS) na borda K do cobalto levando em considera??o modelo de Einstein correlacionado na estrutura fina de absor??o (EXAFS). A primeira parte do espectro de absor??o de raios X corresponde absor??o de raios X pr?xima ? borda de absor??o (XANES) e a outra estende ? espectroscopia da estrutura fina de absor??o (EXAFS). Estes materiais foram preparados pelo m?todo de combust?o. Os produtos obtidos da combust?o foram tratados termicamente por 9000C por 6 horas nesses materiais. Observou que a amostra LaCoO3 em temperatura ambiente e as amostras dopadas com C?lcio e B?rio na faixa de temperatura entre 50 K a 298 K apresentaram uma maior distor??o com simetria monocl?nica com grupo espacial I2/a. No entanto, a amostra dopada com B?rio nas temperaturas 50 K, 220 K e 260 K mostrou uma leve distor??o com simetria rombo?drica com grupo espacial R-3c. A estrutura La0,8Ca0,2CoO3 foi pouco sens?vel com a varia??o de temperatura, apresentando uma maior distor??o local no octaedro e uma maior desordem t?rmica local. Estas interpreta??es est?o de acordo com as informa??es estruturais eletr?nica na regi?o XANES e geom?trica na regi?o EXAFS
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Travnikova, Oksana. "Structure and Dynamics of Core-Excited Species." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8904.
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Martins, Emanuel. "X-ray spectroscopic study of the electronic structure of sulfur compounds." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283717.
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Gallo, Erik. "Modification of the electronic structure of catalytic active transition-metal centers upon molecular adsorption : an XAS/XES study." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S054/document.
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Le travail de thèse "Modification of the electronic structure of catalytic active metal centres upon adsorption of molecules : a XAS and XES study" porte sur l'étude de la structure électronique des métaux de transition utilisés dans les catalyseurs par les techniques spectroscopiques d'absorption et d'émission de rayons durs (rayonnement synchrotron). Il s'agit, en particulier, d'utiliser les avancées dans les techniques spectroscopiques des rayons X pour l'étude des matériaux nanostructurés en conditions in situ. Le premier chapitre de la thèse, "X-Ray Spectroscopy: an Overview", présente brièvement les techniques spectroscopiques disponibles sur la ligne de lumière ID26 de l'Installation Européenne de Rayonnement Synchrotron (en anglais European Synchrotron Radiation Facility (ESRF), Grenoble), où toutes les mesures présentées dans ce travail ont été effectuées. Dans le deuxième chapitre, "Study of the Electronic structure of the Ti-sites in TS-1 using X-ray spectroscopy", est décrite la caractérisation électronique des centres de Ti en TS-1, qui est un important catalyseur, employé dans de nombreuses usines à travers le monde. Nous montrons que la combinaison des techniques spectroscopiques d'absorption et d'émission des rayons avec des calculs de mécanique quantique permet d'obtenir des informations importantes sur la structure électronique des centres de Ti dans des conditions in situ. Le troisième chapitre, “Identification of the Ti-Ligands in a Silica Supported Ziegler-Natta Catalyst by X-Ray Emission Spectroscopy", présente l'étude d'un catalyseur (une variante du catalyseur Ziegler-Natta), qui affiche un degré élevé/important de désordre chimique. L'utilisation de la théorie fonctionnelle de la densité des états (DFT) pour l'interprétation des données expérimentales a permis de développer des modèles possibles pour l'environnement d'un ligand Ti. Le quatrième chapitre, "Observing the dd-Excitations in CPO-27-Ni using Resonant Inelastic X-ray Scattering", conclut la partie principale de la thèse. Il présente un exemple d'utilisation de la diffusion inélastique des rayons X (RIXS) en chimie pour la détermination des excitations du champ cristallin des ions Ni dans l'oxyde de nickel et d'une cage organique autour d'un Ni métallique (CPO-27-Ni). Le chapitre explique brièvement les différentes approches théoriques qui peuvent être utilisées pour l'interprétation des caractéristiques spectrales. De plus, l'adsorption de molécules sonde, comme le CO sur les centres de Ni en CPO-27-Ni, est discutée sur la base des données expérimentales RIXS. Le dernier chapitre synthétise les résultats obtenus et indique des perspectives futures. Enfin, dans les annexes sont reportés les dispositifs expérimentaux développés dans le cadre du travail de thèse pour des mesures résolues en temps, ainsi que le curriculum vitae et les publications du candidatThe purpose of this research project was to apply advanced X-ray based spectroscopic techniques for investigating the electronic structure of transition metals within catalysts and molecular sieves under in-situ conditions. Thus, the first chapter of the thesis, "X-Ray Spectroscopy: an Overview " briefly presents the spectroscopic techniques available at ID26, beamline of the European Synchrotron Radiation Facility (Grenoble) where all the measurements reported in this work have been obtained. In the second chapter, "Study of the Electronic structure of the Ti-sites in TS-1 using hard X-ray spectroscopy", it is reported the electronic characterization of the Ti centres in titanium silicalite-1 (TS-1), that is a relevant catalyst employed in industrial plants worldwide. The chapter shows that the combination of X-ray absorption and X-ray emission spectroscopy with quantum mechanical calculations is effective to obtain important insights on the electronic structure of the Ti-centres under in-situ conditions. The third chapter entitled “Identification of the Ti-Ligands in Silica Supported Ziegler-Natta Catalyst by X- Ray Emission Spectroscopy" presents the study of a variant of the Ziegler-Natta catalyst. The chapter discusses the interpretation of the valence emission lines within the theoretical framework provided by the density functional theory (DFT) and proposes possible models for the Ti-ligand-environment. The fourth chapter, entitled "Observing the dd-Excitations in CPO-27-Ni using Resonant Inelastic X-ray Scattering", concludes the main part of the thesis. It presents the application of resonant inelastic X-ray scattering (RIXS) for obtaining the crystal field excitations of the Ni ions within nickel oxide and within a Ni- metal-organic-framework (CPO-27-Ni). The chapter briefly describes the different theoretical approaches that can be used for the interpretation of the spectral features and discusses the adsorption of probe molecules like H2O, CO and H2S on the Ni centres of CPO-27-Ni. The last chapter (Chapter five) drawn a series of conclusions concerning the performed investigations and indicates possible future research directions. In Appendix A entitled "Pump and Probe Time Resolved Experiments at ID26" it is reported the description of the experimental setup co-developed and co-realized by the candidate for time resolved experiments. The appendix also accounts for the scientific outcome of the performed pump and probe measurements. The curriculum vitae and the publications list of the candidate are respectively reported in Appendix B and C
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Borna, Marija. "On Ternary Phases of the Systems RE–B–Q (RE = La – Nd, Sm, Gd – Lu, Y; Q = S, Se)." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-94774.
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It is known that boron containing compounds exhibit interesting chemical and physical properties. In the past 50 years modern preparative methods have led to an overwhelming number of different structures of novel and often unexpected boron–sulfur and boron–selenium compounds. Among all these new compounds, there was only one which comprises rare earth metal (RE), boron and heavier chalcogen, namely sulfur, the europium thioborate Eu[B2S4] [1]. Selenoborates of rare earth metals are hitherto unknown. On the other hand, rare earth oxoborates represent a well-known class of compounds [2] with a wide range of applications, especially in the field of optical materials. In addition, well-defined boron compounds containing the heavier group 16 elements are fairly difficult to prepare due to the high reactivity of in situ formed boron chalcogenides towards most container materials at elevated temperatures. The chalcogenoborates of the heavier chalcogens are sensitive against oxidation and hydrolysis and therefore have to be handled in an inert environment. Therefore, developing and optimization of preparative routes for the syntheses of pure and crystalline RE thio- and selenoborates was needed.
In the course of this study, the application of different preparation routes, such as optimized high-temperature routes (HT), metathesis reactions and high-pressure high-temperature routes (Hp – HT), led to sixteen new rare earth thioborates. Their crystal structures were solved and/or refined from powder and single crystal X-ray diffraction data, while the local structure around rare earth metal was confirmed from the results of the EXAFS analyses. Quantum mechanical calculations were used within this work in order to investigate the arrangement of intrinsic vacancies on the boron sites in the crystal structures of rare earth thioborates. Thermal, magnetic and optical properties of these compounds are also discussed.
The rare earth thioborates discovered during this work are the first examples of ternary thioborates containing trivalent cations. These compounds can be divided into two groups of isotypic compounds: the rare earth orthothioborates with general formula REIII[BS3] (RE = La – Nd, Sm, Gd and Tb) [3] and the rare earth thioborate sulfides with general formula REIII¦9B5S21, (RE = Gd – Lu, and Y) [4].
In the crystal structure of RE[BS3] (orthorhombic, space group Pna21, Z = 4), the sulfur atoms form the vertices of corrugated kagome nets, within which every second triangle is occupied by boron and the large hexagons are centered by RE cations. The structural features of the isotypic RE[BS3] phases show great similarities to those of rare earth oxoborates RE[BO3] and orthothioborates of alkali and alkaline earth metals as well as to thallium orthothioborate, yet pronounced differences are also observed: the [BS3]3– groups in the crystal structures of RE[BS3] are more distorted, where the distortion decreases with the decreasing size of the RE element, and the coordination environments of the [BS3]3– groups in the crystal structures of RE[BS3] are different in comparison with the coordination environments of the [BO3]3– groups in the crystal structures of λ-Nd[BO3] [5] and of o-Ce[BO3] [6].
The results of the IR and Raman investigations are in agreement with the presence of [BS3]3– anions in the crystal structure of RE[BS3]. Thermal analyses revealed the thermal stability of these compounds under inert conditions up to ~ 1200 K. Analyses of the magnetic properties of the Sm, Gd and Tb thioborates showed that both Gd and Tb phases order antiferromagnetically. The magnetic susceptibility for Sm orthothioborate approximately follows the Van-Vleck theory for Sm3+. Between 50 K and 62 K a transition appears which is independent of the magnetic field: the magnetic susceptibility becomes lower. This effect might indicate a discontinuous valence transition of Sm which was further investigated by means of XANES and X-ray diffraction using synchrotron radiation, both at low temperatures.
The series of isotypic RE thioborate sulfides with composition RE9B5S21, was obtained by the application of Hp – HT conditions to starting mixtures with the initial chemical composition “REB3S6“, after careful optimization of the pressure, temperature and treatment time, as well as the composition of the starting mixtures. Their crystal structures adopt the Ce6Al3.33S14 [7] structure type (hexagonal, space group P63, Z = 2/3). The special features of the RE9B5S21 crystal structures, concerning boron site occupancies and different coordination environments of the two crystallographically independent boron sites, were investigated in more detail by means of quantum chemical calculations, electron diffraction methods, optical and X-ray absorption spectroscopy as well as by 11B NMR spectroscopy. The results obtained from these different experimental and computational methods are in good mutual agreement. The crystal structures of the RE9B5S21 compounds are characterized by two types of anions: tetrahedral [BS4]5– and trigonal planar [BS3]3– as well as [(S2–)3] units. Isolated [BS4]5– tetrahedra (all pointing with one of their apices along the polar [001] direction) represent a unique feature of the crystal structure which is observed for the first time in a thioborate compound. These tetrahedra are stacked along the three-fold rotation axes. Vacancies are located at the trigonal-planar coordinated boron site with preferred ordering –B–B––B–B–– along [001]. No superstructure is observed by means of electron diffraction methods as adjacent columns are shuffled along the c axis, giving rise to a randomly distributed vacancy pattern. Positions of the sulfur atoms within the [(S2–)3] substructure as well as planarity of the [BS3]3– units were investigated in more detail by means of quantum mechanical calculations.
Results of the IR and Raman spectroscopy, as well as of the 11B NMR spectroscopy are in agreement with the presence of the boron atoms in two different coordination environments. Thermal analyses showed that compounds RE9B5S21 are stable under inert conditions up to ~ 1200 K. In accordance with the combined results of experimental and computational investigations, the chemical formula of the RE9B5S21 compounds is consistent with RE3[BS3]2[BS4]3S3.
A short overview of investigations towards rare earth selenoborates, where in most of the cases only known binary rare earth selenides could be identified, is presented as well in this work. Investigations in the RE–B–Se systems were conducted by the application of different preparation routes by varying the experimental parameters and the initial compositions of the starting mixtures. Although no crystal structure of a ternary phase in these systems could be solved, there are indications that such phases exist, but further investigations are needed.
[1] M. Döch, A. Hammerschmidt, B. Krebs, Z. Anorg. Allg. Chem., 2004, 630, 519.
[2] H. Huppertz, Chem. Commun., 2011, 47, 131; and references therein.
[3] J. Hunger, M. Borna, R. Kniep, J. Solid State Chem., 2010, 182, 702; J. Hunger, M. Borna, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 217; M. Borna, J. Hunger, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 223; M. Borna, J. Hunger, R. Kniep, Z. Kristallogr. NCS, 2010, 225, 225.
[4] M. Borna, J. Hunger, A. Ormeci, D. Zahn, U. Burkhardt, W. Carrillo-Cabrera, R. Cardoso-Gil, R. Kniep, J. Solid State Chem., 2011, 184, 296;
[5] H. Müller-Bunz, T. Nikelski, Th. Schleid, Z. Naturforsch. B, 2003, 58, 375.
[6] H. U. Bambauer, J. Weidelt, J.-St. Ysker, Z. Kristallogr., 1969, 130, 207.
[7] D. de Saint-Giniez, P. Laruelle, J. Flahaut, C. R. Séances, Acad. Sci. Ser. C, 1968, 267, 1029.
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Näslund, Lars-Åke. "Probing unoccupied electronic states in aqueous solutions." Doctoral thesis, Stockholm University, Department of Physics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-294.
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Water is one of the most common compounds on earth and is essential for all biological activities. Water has, however, been a mystery for many years due to the large number of unusual chemical and physical properties, e.g. decreased volume during melting and maximum density at 4 °C. The origin of the anomalies behavior is the nature of the hydrogen bond. This thesis will presented an x-ray absorption spectroscopy (XAS) study to reveal the hydrogen bond structure in liquid water.
The x-ray absorption process is faster than a femtosecond and thereby reflects the molecular orbital structure in a frozen geometry locally around the probed water molecules. The results indicate that the electronic structure of liquid water is significantly different from that of the solid and gaseous forms. The molecular arrangement in the first coordination shell of liquid water is actually very similar as the two-hydrogen-bonded configurations at the surface of ice. This discovery suggests that most molecules in liquid water have two-hydrogen-bonded configurations with one donor and one acceptor hydrogen bond compared to the four-hydrogen-bonded tetrahedral structure in ice. This result is controversial since the general picture is that the structure of liquid water is very similar to the structure of ice. The results are, however, consistent with x-ray and neutron diffraction data but reveals serious discrepancies with structures based on current molecular dynamics simulations. The two-hydrogen-bond configuration in liquid water is rigid and heating from 25 °C to 90 °C introduce a minor change in the hydrogen-bonded configurations. Furthermore, XAS studies of water in aqueous solutions show that ion hydration does not affect the hydrogen bond configuration of the bulk. Only water molecules in the close vicinity to the ions show changes in the hydrogen bond formation. XAS data obtained with fluorescence yield are sensitive enough to resolved electronic structure of water molecules in the first hydration sphere and to distinguish between different protonated species. Hence, XAS is a useful tool to provide insight into the local electronic structure of a hydrogen-bonded liquid and it is applied for the first time on water revealing unique information of high importance.
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Geiger, Ernesto. "Study of Fission Products (Cs, Ba, Mo, Ru) behaviour in irradiated and simulated Nuclear Fuels during Severe Accidents using X-ray Absorption Spectroscopy, SIMS and EPMA." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS064/document.
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L’identification des mécanismes de relâchement des Produits de Fission (PF) hors de combustible nucléaire irradié lors d’un accident grave est primordiale pour le développement de codes capables d’estimer précisément le terme source (nature et quantité des radionucléides émis dans l’environnement). Parmi les différents PF, les Ba, Cs, Mo et le Ru sont particulièrement intéressants, car ils peuvent interagir entre eux ou avec d’autres éléments et donc affecter leur relâchement. Dans le cadre de cette thèse, deux axes de travail ont été mis en place avec l’objectif d’identifier les phases chimiques présentes avant l’accident et leur évolution au cours de l’accident lui-même. L’approche expérimentale a consisté à reproduire les conditions d’un accident nucléaire à l’échelle du laboratoire, en utilisant des échantillons de combustibles irradiés et des matériaux modèles (UO₂ vierge dopés en 12 PF). Le principal avantage de ces derniers est l’utilisation de méthodes de spéciation chimique comme la Spectroscopie d’Absorption des rayons X, qui n’est pas aujourd’hui encore disponible pour les combustibles irradiés. Trois échantillons de combustible irradié ont été étudies, représentatifs de l’état initial (i.e. avant l’accident), d’une étape intermédiaire en température (1773K) et d’un état avancé d’accident nucléaire (2873K). Pour les matériaux modèles, plusieurs séquences accidentelles (de 573K à 1973K) ont été réalisés. Les résultats expérimentaux ont permis d’établir un nouveau mécanisme de relâchement des PF en en fonction des conditions oxydantes et réductrices du scénario accidentel. Ces résultats ont démontré aussi l’importance des matériaux modèles pour l’étude des accidents nucléaires graves, en complémentarité aux combustibles irradiésThe identification of Fission Products (FP) release mechanism from irradiated nuclear fuels during a severe accident is of main importance for the development of codes for the estimation of the source-term (nature and quantity of radionuclides released into the environment). Among the many FP Ba, Cs, Mo and Ru present a particular interest, since they may interact with each other or other elements and thus affect their release. In the framework of this thesis, two work axes have been set up in order to identify, firstly, the chemical phases initially present before the accident and, secondly, their evolution during the accident itself. The experimental approach consisted in reproducing nuclear severe accidents conditions at laboratory scale using both irradiated fuels and model materials (natural UO₂ doped with 12 FP). The advantage of these latter is the possibility of using characterization methods such as X-ray Absorption Spectroscopy which are not available for irradiated fuels. Three irradiated fuel samples have been studied, representative to an initial state (before the accident), to an intermediate stage (1773K) and to an advanced stage (2873K) of a nuclear severe accident. Regarding to model materials, many accident sequences have been carried out, from 573 to 1973K. Experimental results have allowed to establish a new release mechanism, considering both reducing and oxidizing conditions during an accident. These results have also demonstrated the importance of model materials as a complement to irradiated nuclear fuels in the study of nuclear severe accidents
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Glorius, M., H. Moll, G. Bernhard, A. Roßberg, and A. Barkleit. "The Mobilization of Actinides by Microbial Ligands Taking into Consideration the Final Storage of Nuclear Waste - Interactions of Selected Actinides U(VI), Cm(III), and Np(V) with Pyoverdins Secreted by Pseudomonas fluorescens and Related Model Compounds (Final Report BMBF Project No.: 02E9985)." Forschungszentrum Dresden-Rossendorf, 2009. https://hzdr.qucosa.de/id/qucosa%3A21603.
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The groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m in the Äspö Hard Rock Laboratory secretes a pyoverdin-mixture with four main components (two pyoverdins and two ferribactins). The dominant influence of the pyoverdins of this mixture could be demonstrated by an absorption spectroscopy study. The comparison of the stability constants of U(VI), Cm(III), and Np(V) species with ligands simulating the functional groups of the pyoverdins results in the following order of complex strength: pyoverdins (PYO) > trihydroxamate (DFO) > catecholates (NAP, 6HQ) > simple hydroxamates (SHA, BHA). The pyoverdin chromophore functionality shows a large affinity to bind actinides. As a result, pyoverdins are also able to complex and to mobilize elements other than Fe(III) at a considerably high efficiency. It is known that EDTA may form the strongest actinide complexes among the various organic components in nuclear wastes. The stability constants of 1:1 species formed between Cm(III) and U(VI) and pyoverdins are by a factor of 1.05 and 1.3, respectively, larger compared to the corresponding EDTA stability constants. The Np(V)-PYO stability constant is even by a factor of 1.83 greater than the EDTA stability constant. The identified Np(V)-PYO species belong to the strongest Np(V) species with organic material reported so far. All identified species influence the actinide speciation within the biologically relevant pH range. The metal binding properties of microbes are mainly determined by functional groups of their cell wall (LPS: Gram-negative bacteria and PG: Gram-positive bacteria). On the basis of the determined stability constants raw estimates are possible, if actinides prefer to interact with the microbial cell wall components or with the secreted pyoverdin bioligands. By taking pH 5 as an example, U(VI)-PYO interactions are slightly stronger than those observed with LPS and PG. For Cm(III) we found a much stronger affinity to aqueous pyoverdin species than to functional groups of the cell wall compartments. A similar behavior was observed for Np(V). This shows the importance of indirect interaction processes between actinides and bioligands secreted by resident microbes.
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Yang, Weibing. "Probing electronic, magnetic and structural heterogeneity in advanced materials and Nanostructures with x-ray imaging, scattering and spectroscopic techniques." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/588064.
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PhysicsPh.D.
In this dissertation, we have used a combination of synchrotron-based x-ray spectroscopic, scattering and imaging techniques to investigate the electronic, magnetic and structural properties of materials and material systems which exhibit natural as well as engineered nanoscale structural distortions. In order to investigate the interplay between the above-mentioned degrees of freedom with spatial and depth resolution, we have utilized non-destructive techniques, such as x-ray absorption spectroscopy (XAS), polarization-dependent photoemission electron microscopy (PEEM), nanoscale scanning x-ray diffraction microscopy (nano-SXDM) and standing-wave x-ray photoemission spectroscopy (SW-XPS). The results were compared to several types of state-of-the-art first-principles theoretical calculations. In the first part of the dissertation, we have investigated the nanoscale magneto-elastic structure of the Fe3Ga magnetic alloy, which was recently reported to exhibit non-volume conserving magnetostriction. As the result of our combined PEEM and nano-SXDM study, we have discovered the structural basis for this phenomenon – periodic long-wavelength (~269 nm) elastic domain walls, with domains (regions of zero-strain) existing as narrow transition regions. Atto-scale elastic gradients and self-strain across the elastic domain walls were quantitatively measured and imaged by nano-SXDM. Our measurements revealed that the gradients inside the elastic walls are accommodated by gradually increasing/decreasing inter-planar spacing resembling a longitudinal wave. Our element-specific polarization-dependent PEEM measurements revealed that the magnetic structure of the crystal modulates with similar periodicity (~255 nm), and the resulting magneto-elastic coupling produces a ‘giant’ field-induced bulk deformation, which is equal to the measured self-strain of the elastic domain wall. In the second part of this dissertation, we utilized a combination of soft x-ray standing-wave photoemission spectroscopy (SW-XPS), hard x-ray photoemission spectroscopy (HAXPES) and scanning transmission electron microscopy (STEM) to probe the depth-dependent and single-unit-cell resolved electronic structure of isovalent manganite superlattices (Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3)15 wherein the electronic and magnetic properties are intentionally modulated with depth via engineered O octahedral rotations and A-site displacements. Standing-wave-excited spectroscopy of the Mn 2p and O 1s core-levels confirmed the isovalent nature of the Mn ions in the superlattice and revealed significant depth-dependent variations in the local chemical and electronic environment around the O atoms, consistent with the state-of-the-art theoretical calculations. Furthermore, it was shown that a surface relaxation and orbital reconstruction in the several top Eu0.7Sr0.3MnO3 atomic layers produces substantial changes in the observed electronic structure, which, according to the first-principles theoretical calculations, occur due to the establishment of orbital stripe order in the top unit cell. In summary, we have used synchrotron-based x-ray spectroscopic and microscopic techniques, in conjunction with high-resolution electron microscopy, to study the electronic, magnetic and structural properties of advanced functional materials exhibiting strong nanoscale heterogeneity. We discovered a strong coupling between the nanoscale structural and magnetic properties in the non-conventional magnetostrictive Fe3Ga single crystal. Our results suggest that this coupling provides the fundamental basis for the non-conventional magnetostriction phenomenon in this material. We have also discovered that the electronic properties of the Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3 superlattices can be epitaxially tuned via engineered A-site cation displacement, which is a result of the strong interfacial coupling between the Eu0.7Sr0.3MnO3 and La0.7Sr0.3MnO3 layers. This suggests a new way of tailoring and spatially-confining electronic and ferroic behavior in complex oxide heterostructures and creating novel ordered surface-reconstruction effects.
Temple University--Theses
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Johnson, Brian Ivins. "Preparation and Detailed X-Ray Photoelectron Spectroscopy and Spectroscopic EllipsometryAnalysis of Ultrathin Protective Coatings." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8119.
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Ultra-thin films (UTFs) are important in many applications, seen in the semiconductor industry, in chromatography, in sensing, in microfluidics, in aerospace, and in robotics. They also protect materials from corrosion, change surface energies, limit water intrusion into materials, allow material self-cleaning and self-healing, provide scratch resistance, and impart other specific chemical properties. In many cases, UTFs drastically alter surface properties and therefore their applications. It is imperative that proper and consistent characterization be performed on coatings to confirm and understand their desired properties. In Chapter two, Al oxidation under MgF2 protective layers is studied using real time X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). These tools allowed me to monitor Al oxidation for both short (hours) and long (months) periods of time. XPS revealed the chemical changes that took place in these materials as a function of time, and these changes were verified with SE. These studies help increase an understanding of aluminum changes under MgF2 protective layers. The third chapter demonstrates ab initio calculations guided X-ray photoelectron spectroscopy (XPS) analysis of surfaces functionalized with fluorinated silanes. This study addresses deficiencies in the literature where CF2:CF3 ratios from experimental XPS data do not match theoretical CF2:CF3 ratios. In a systematic approach, I developed semi-empirical models directed both by ab initio calculations and adjustable, empirical parameters. These models were effective in describing the raw data and exceeded fitting methods used in literature. In Chapter four, SiO2 UTFs with variable thicknesses deposited on Eagle XG® glass substrates are characterized. Challenges associated with this work consisted of similar optical functions of the film and substrate as well as backside reflections from the substrate. These obstacles were met using a multi-sample analysis (MSA), a variable angle spectroscopic ellipsometric approach, and mechanical abrasion/roughening of the substrate backside. With these approaches, I developed a model that precisely fit the data collected from all the samples and gave the correct optical function of the material along with thickness values for each film. Surface characterization represents a commitment of resources. It takes time to make measurements, and it takes time to analyze and understand the results. As presented in this work, I increase understanding of ultra-thin films at interfaces using both a multi-tool approach as well as using multiple analytical methods on data collected from each tool.
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Nilson, Katharina. "Phthalocyanines on Surfaces : Monolayers, Films and Alkali Modified Structures." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8209.
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Hung, Wing Wa. "FTIR and XPS of congruent and stoichiometric LiNbO3." HKBU Institutional Repository, 2003. http://repository.hkbu.edu.hk/etd_ra/442.
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Fleutot, Benoit. "Amélioration des performances des microbatteries au lithium : corrélation entre la structure locale et la conductivité ionique d’électrolytes solides amorphes." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14162/document.
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Les microbatteries sont des microsources d’énergie adaptées à l’alimentation des microsystèmes tels que l’horloge à temps réel des téléphones portables, les étiquettes intelligentes RFID…. Pour pouvoir être considéré comme un composant classique de la microélectronique, la microbatterie doit être compatible avec le processus de soudure de type solder-reflow qui atteint une température de 260 °C pendant quelques secondes. Au cours de cette thèse, nous nous sommes focalisés sur l’étude de couches minces de LiPON (oxynitrure de phosphate de lithium) utilisé comme électrolyte solide qui est le matériau limitant pour une application à basse température en établissant des relations entre sa composition, sa structure et ses performances électriques. Ayant observé une baisse des performances après traitement thermique, nous avons proposé un matériau présentant une meilleure stabilité. Nous avons également étudié la compatibilité des autres couches ainsi que l’empilement complet de la microbatterie vis-à-vis du solder-reflowMicrobatteries are energy sources well-adapted to power microsystems such as the real time clock of mobile phones, smart tags RFID. To be considered as a microelectronic component, the microbattery must be compatible with the solder-reflow process which reaches a temperature of 260 °C during few seconds. During this Ph-D, various thin films of LiPON (lithium phosphate oxynitride) used as amorphous solid electrolyte have been prepared by sputtering. As this material presents limited performances for an application of the microbattery at low temperature, we have investigated the influence of its composition and local structure on its electrical performances. In addition, a decrease of its performances has been noticed after solder-reflow. In this work, we have proposed a new material, much more thermally stable. Finally, we have studied the compatibility of other active layers as well as the all-solid-state microbattery towards the solder-reflow
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Chevreux, Sylviane. "Spéciation directe de métalloprotéines séparées sur gels d'électrophorèse : analyses XAS de la superoxyde dismutase et ICP-MS de protéines arseniées." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13880/document.
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L’analyse métalloprotéomique est un nouveau champ d’étude qui couple la détermination du protéome et l’identification, localisation et spéciation des éléments inorganiques complexés aux protéines. La faible concentration de ces hétéroéléments et la labilité possible de ceux-ci nécessite la mise en place d’outils de chimie analytique permettant une séparation des protéines à grande résolution, sans modifier la liaison protéine-hétéroélément, et une spéciation des protéines avec une technique bénéficiant d’une faible limite de détection. L’objet de cette étude est la mise en place de tels protocoles pour une application sur deux systèmes protéiques, modèles représentant les deux principales interactions métal-protéine : formation de complexes métalliques ou de liaisons covalentes. Dans une première partie, nous avons étudié la superoxyde dismutase à cuivre et zinc (CuZnSOD), protéine dont des formes mutantes sont impliquées dans une maladie neurodégénérative, la sclérose latérale amyotrophique. Les isoformes de point isoélectrique de CuZnSOD sauvage et mutante, séparées sur gel d’électrophorèse, ont été analysées par spectroscopie d’absorption des rayons X (XAS). Une analyse XAS sur des protéines séparées sur gel d’électrophorèse a ainsi pour la première fois été menée. Le traitement des spectres obtenus au seuil du Zn révèle la faisabilité de cette technique et celui au seuil du Cu met notamment en évidence des différences d’état d’oxydation Cu(I) et Cu(II) entre les isoformes. Dans une seconde partie, nous avons étudié la métabolisation de l’arsenic dans le cadre de la cancérogénicité de ce métalloïde. Les protéines extraites de cellules hépatiques exposées à l’arsenic ont été séparées par électrophorèse sur gel et chromatographie en phase liquide. L’analyse des échantillons obtenus par spectrométrie de masse a mis en évidence trois espèces protéiques complexant l’arsenicMetalloproteomic is a new discipline which ally proteome determination and the identification, location and speciation of inorganic elements bound to proteins. The low concentration of these heteroelements and sometimes their non-covalent binding to proteins need to set up analytical tools enabling the protein separation at high resolution, without any modification of the bond protein-heteroelement, and the protein speciation with a technique presenting a low detection limit. The aim of this study is to set up such protocols on two proteic systems, depicting the two main protein-heteroelement interactions: forming of metallic complexes or covalent bonds. First, we studied copper, zinc superoxide dismutase (CuZnSOD), mutants of this protein being involved in a neurodegenerative disease, the amyotrophic lateral sclerosis. Isoelectric point isoforms of wild-type and mutant CuZnSOD, separated on electrophoresis gel, were analyzed using X-ray Absorption Spectroscopy (XAS). XAS experiments on proteins separated on electrophoresis gel were performed for the first time. Data analysis at Zn K-edge demonstrated the feasibility of this technique and the ones at the Cu K-edge highlighted oxidation states Cu(I) et Cu(II) differences between isoforms. Second, we studied arsenic metabolisation to understand its carcinogenicity. Proteins extracted from hepatic cells exposed to arsenic were separated using gel electrophoresis and liquid chromatography. Samples analysis using mass spectrometry highlighted three proteic species which bind arsenic
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Morales, Ugarte Jorge Eduardo. "Etude Operando des accumulateurs au lithium par couplage spectroscopie à photoémission des rayons X et spectroscopie d’impédance." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI082.
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Face aux grands défis industriels dans les domaines du stockage électrochimique de l’énergie, un effort de recherche fondamentale sur les matériaux impliqués et leurs interfaces est aujourd'hui indispensable pour un gain en performance, durabilité, sécurité.Dans ce contexte, il est primordial de comprendre les processus interfaciaux mis en jeu qui induisent la dégradation de l’interface lithium métal-électrolyte et entrainent une baisse du rendement Coulombique et favorisent la croissance dendritique.Nous proposons ainsi dans cette thèse une étude couplant des techniques électrochimiques comme la spectroscopie d’impédance avec des techniques d’analyse de surface comme la spectroscopie à photoémission des rayons X pour étudier la réactivité chimique et électrochimiques entre les électrolytes et une électrode de lithium métal.Pour ce faire, un intérêt spécifique a été porté aux électrolytes à base de liquides ioniques, qui ont été proposés comme solvants des sels de lithium, notamment pour leur faible pression de vapeur saturante qui augmente considérablement la sécurité des batteries ainsi conçues.Enfin, ce travail a été consacré en particulier au développement de montages et de mesures operando XPS afin de suivre l’évolution chimique des interfaces à l’intérieur d’une batterie en temps réelFaced with the major industrial challenges in the field of electrochemical energy storage, a fundamental research effort on the materials involved and their interfaces is nowadays essential for a gain in performance, durability and safety.In this context, it is essential to understand the interfacial processes involved that induce the degradation of the lithium metal-electrolyte interface and lead to a decrease in Coulombic efficiency and promote dendritic growth.In this thesis, we propose a study coupling electrochemical techniques such as impedance spectroscopy with surface analysis techniques such as X-ray photo-emission spectroscopy to study the chemical and electrochemical reactivity between electrolytes and a lithium metal electrode.To this end, special attention has been paid to the ionic liquids based electrolytes, which have been proposed as solvents for lithium salts, particularly for their low saturation vapor pressure, which considerably increases the safety of the batteries thus designed.Finally, this work was devoted in particular to the development of operando XPS assemblies and measurements in order to follow the chemical evolution of the interfaces inside a battery in real time
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Haskel, Daniel. "Local structural studies of oriented high temperature superconducting cuprates by polarized XAFS spectroscopy /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9712.
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Olthof, Selina. "Photoelectron Spectroscopy on Doped Organic Semiconductors and Related Interfaces." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-38320.
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Using photoelectron spectroscopy, we show measurements of energy level alignment of organic semiconducting layers. The main focus is on the properties and the influence of doped layers. The investigations on the p-doping process in organic semiconductors show typical charge carrier concentrations up to 2*10E20 cm-3. By a variation of the doping concentration, an over proportional influence on the position of the Fermi energy is observed. Comparing the number of charge carriers with the amount of dopants present in the layer, it is found that only 5% of the dopants undergo a full charge transfer. Furthermore, a detailed investigation of the density of states beyond the HOMO onset reveals that an exponentially decaying density of states reaches further into the band gap than commonly assumed. For an increasing amount of doping, the Fermi energy gets pinned on these states which suggests that a significant amount of charge carriers is present there. The investigation of metal top and bottom contacts aims at understanding the asymmetric current-voltage characteristics found for some symmetrically built device stacks. It can be shown that a reaction between the atoms from the top contact with the molecules of the layer leads to a change in energy level alignment that produces a 1.16eV lower electron injection barrier from the top. Further detailed investigations on such contacts show that the formation of a silver top contact is dominated by diffusion processes, leading to a broadened interface. However, upon insertion of a thin aluminum interlayer this diffusion can be stopped and an abrupt interface is achieved. Furthermore, in the case of a thick silver top contact, a monolayer of molecules is found to float on top of the metal layer, almost independent on the metal layer thickness. Finally, several device stacks are investigated, regarding interface dipoles, formation of depletion regions, energy alignment in mixed layers, and the influence of the built-in voltage. We show schematic energy level alignments of pn junctions, pin homojunctions, more complex pin heterojunctions with Zener-diode characteristics, as well as a complete OLED stack. The results allow a deeper insight in the working principle of such devicesMit Hilfe der Photoelektronenspektroskopie werden in der vorliegenden Arbeit Energieniveaus an Grenzflächen von organischen Halbleitern untersucht, wobei ein Hauptaugenmerk auf dem Einfluss und den Eigenschaften dotierter Schichten liegt. Bei der Untersuchung grundlegender Eigenschaften eines p-dotierten organischen Halbleiters können Ladungsträgerkonzentrationen bis zu 2*10E20 cm-3 nachgewiesen werden. Eine Variation der Dotierkonzentration zeigt einen überproportionalen Einfluss der Ladungsträger auf die Position des Ferminiveaus verglichen mit Experimenten an anorganischen Schichten. Durch den Vergleich mit der Anzahl Dotanden in der Schicht kann gezeigt werden, dass dabei nur etwa 5% der Dotanden einen vollständigen Ladungstransfer eingehen. Eine detaillierte Untersuchungen der Zustandsdichte jenseits des HOMOs (Highest Occupied Molecular Orbital) zeigt, dass die exponentiell abfallende Flanke der Zustandsdichte weiter in die Bandlücke hineinreicht als üblicherweise angenommen. Das Ferminiveau erfährt bei steigender Dotierung ein Pinning an diesen Zuständen, was für eine signifikante Ladungsträgerkonzentration spricht. Weiterhin wurden Untersuchungen zu Metal Top- und Grundkontakten durchgeführt. Es kann gezeigt werden, dass die Ursache für die Entstehung unsymmetrischer Strom-Spannungskurven, trotz eines symmetrischen Probenaufbaus, an einer Reaktion zwischen dem Molekül und den Metallatomen liegt. Dadurch entsteht eine um 1.16eV reduzierte Injektionsbarriere für Elektronen am Topkontakt. Weitere detaillierte Untersuchungen an diesen Topkontakten zeigen, dass im Falle von Silber als Metall diese Grenzfläche von Diffusionsprozessen dominiert ist. Im Gegensatz dazu zeigt das unedle Metall Aluminium keine Diffusion und führt zu abrupten Grenzflächen. Im ersten Fall kann zudem eine Monolage vom Molekül auf dem Metallkontakt nachgewiesen werden, die unabhängig von der Metalldicke aufschwimmt. Zuletzt werden Bauelemente oder Teile solcher mit Photoelektronenspektroskopie vermessen. Hierbei werden die Grenzflächendipole, die Ausbildung von Verarmungszonen, die Energieangleichung in Mischschichten und der Einfluss der Eingebauten Spannung untersucht. Es können die Banddiagramme von pn-Übergängen, einfachen pin Homoübergängen, komplexeren pin Heteroübergänge mit Zener-Dioden Verhalten sowie eine gesamte OLED gezeigt werden. Die Ergebnisse erlauben einen tieferen Einblick in die Arbeitsweise solcher Bauelemente
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Dehlinger, Maël. "XAS-XEOL and XRF spectroscopies using Near-Field Microscope probes for high-resolution photon collection." Phd thesis, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-00880623.
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Les microscopes en champ proche permettent d'obtenir la topographie d'un échantillon avec une résolution pouvant atteindre la résolution atomique. Ces techniques permettent également d'accéder à certaines propriétés locales de la surface telles que le potentiel, l'élasticité, la densité d'états... Ces spectroscopies locales sont de type 'contraste' et ne permettent pas de dresser la cartographie chimique de la surface sans connaissance a priori des éléments qui la composent. Les spectroscopies de rayons-X sont des méthodes de caractérisation puissantes qui permettent de déterminer la composition et la structure élémentaire de l'échantillon avec une précision inférieure à l'Ångström. La résolution latérale est essentiellement limitée par la taille du faisceau primaire, couramment de plusieurs μm². Deux voies sont possibles pour l'améliorer: - réduire l'étendue du faisceau primaire excitateur; - limiter la collecte du rayonnement émis à une portion du volume excité, tout en approchant le détecteur au maximum pour garder un rapport signal/bruit suffisant. C'est cette deuxième option que nous avons choisi de développer. Pour cela nous avons collecté localement la luminescence visible issue de l'échantillon par la pointe-sonde d'un microscope à force de cisaillement, constituée d'une fibre optique effilée de faible ouverture. Cette technique a été utilisée pour caractériser des échantillons semiconducteurs micro- et nano-structurés afin d'en obtenir simultanément la topographie et la cartographie de luminescence locale. Ces résultats ont été obtenus non seulement sur une ligne synchrotron mais également à l'aide d'une microsource de laboratoire équipée d'une lentille polycapillaire. Afin de pouvoir étendre ce concept à d'autres types de matériaux, la faisabilité de la collecte de la fluorescence X locale a été évaluée avec la microsource. Pour cela la fluorescence X émise par un échantillon de cobalt a été collectée par un capillaire cylindrique équipant un détecteur EDX. L'influence du diamètre du capillaire sur le niveau de signal a été mesurée. Une simulation numérique a été développée afin d'estimer le niveau de signal obtenu en utilisant un capillaire de 1 μm de diamètre et d'optimiser la géométrie du système. En couplant la microscopie en champ proche et l'analyse XRF, à la lumière de ces résultats, il sera possible d'atteindre 100 nm de résolution latérale en environnement synchrotron et moins de 1 μm à l'aide d'une source de laboratoire. Il serait alors possible de sélectionner un objet particulier sur une surface et d'en faire l'analyse élémentaire.
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Lebrun, Delphine. "Thiolsulfinates/Thiolsulfonates formation: X-ray photoelectron spectroscopy (XPS) of oxidized thiols on flat surfaces." Thesis, Uppsala universitet, Materialfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160332.
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In order to find another way to fix peptides on surfaces we study the chemical and electro oxidation of a Silicon flat surface after silanization. Traditional experimental setup is used to make the oxidations and Xray photoelectron spectroscope (XPS) is used to analyze the surfaces. We find that chemical oxidation works well but we cannot fix the Alanine molecule on the surface, unlike the electro oxidation which works for peptides fixation. We need to focus on the electro oxidation process, use a more accurate method to analyze the samples and probably used a higher Alanine concentration.
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Lunt, Patrick Joseph Brian. "XPS studies of surface ageing and discharge processes in polymeric insulators." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/xps-studies-of-surface-ageing-and-discharge-processes-in-polymeric-insulators(2329d184-6677-4981-988e-e17b95bae229).html.
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The ageing of polymer insulation occurs under long-term exposure to high electric fields and has attracted research due its relevance to high voltage insulation. In this work, polymers that have been electrically aged via a number of methods have been investigated using X-ray photoelectron spectroscopy (XPS). Despite some use in the investigation of outdoor insulation surfaces, XPS has not been used for investigations of polymer bulk electrical ageing before now. The first XPS measurements, using both small spot analysis and XPS imaging, are presented from the exposed inner surfaces of electrically aged artificial voids and electrical breakdown channels, as well as corona discharge aged surfaces and spark discharge by-products. XPS is shown to be a valuable technique for the investigation of polymer electrical ageing. Investigations into breakdown channels are supported by data acquired using X-ray photoemission electron microscopy (XPEEM) and scanning electron microscopy (SEM).Results show that the chemistry present at these surfaces takes the form of significant oxidation over a wide area with localised production of graphitic carbon. C-O-, C=O, and O-C=O species are detected in all cases. It is found that similar ageing products are present regardless of the ageing process or material investigated. However, the level of oxidation and relative ratio of the species seen with XPS is shown to be highly dependant on oxygen availability. Greater intensity of carbon oxides, and a shift towards highly oxidised species, is observed when there is more oxygen in the system. XPS imaging of breakdown channels reveals that high concentrations of oxidised components form on the outer edges of the channel, with graphitic carbon forming in the central regions. In addition, evidence for degradation is seen to extend at least 300 μm from channels in XPS imaging and at least ~650 μm in XPS line scans. Variation with the applied discharge energy was investigated for breakdown channels and spark discharge ageing. Evidence is seen for an energy dependence on the breakdown products, with higher energies producing relatively higher graphitic carbon and reduced oxidation products. Further, the relationship between the applied voltage and graphitic carbon concentration suggests an activated process with an energy barrier before graphitic carbon formation starts. XPS observations are supported by confocal Raman microprobe spectroscopy (CRMS) results from artificial voids and electrical breakdown channels, which identify graphitic carbon on a fluorescent background as the main features. XPS data indicate oxidised species are the origin of the fluorescence seen and provides quantitative information on the levels, chemical states and spatial distribution of these species and of graphitic carbon.
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Adnan, Rohul. "Gold-based Nanomaterials: Spectroscopy, Microscopy and Applications in Catalysis and Sensing." Thesis, University of Canterbury. Chemistry, 2015. http://hdl.handle.net/10092/10507.
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The birth of nanotechnology era has revolutionized materials science, catalysis and field of optoelectronics. Novel and unique phenomena emerge when material dimensions are reduced to ultra-small size regime and enter nanometre (2-100 nm) realm. Such novel materials are expected to replace bulk materials, offering lower cost of manufacturing and enabling progress in many areas such as solar cell, drug delivery, quantum communication and computing, catalysis and sensing applications. With the progress in nanomaterial synthesis and fabrication, the need for the state-of-art characterization techniques became obvious; such techniques help to establish a complete understanding of the nature and interactions of nanosized materials.
In this thesis, the first part focuses on the synthesis of gold and ruthenium clusters, namely Au8, Au9, Au101, Ru3, Ru4 and AuRu3, using the well-established synthetic protocols in the literature. Apart from the standard lab-based characterization techniques such as nuclear magnetic resonance (NMR), UV-visible spectroscopy (UV-vis) and Fourier Transform Infra-red (FTIR), a less explored but useful technique far infra-red (far IR) spectroscopy, available at the Australian Synchrotron (AS), was employed to investigate the vibrational modes in these clusters. Peaks in the experimental far IR spectra were assigned unambiguously to specific vibrations by comparing with the ones generated via DFT calculations with the help of collaborators, group of Professor Gregory Metha, University of Adelaide. For the Au9 cluster, three significant gold core vibrations are observed at 157, 177 and 197 cm-1 in the experimental spectrum. In the case of the Ru3 cluster, only a single ruthenium core vibration is identified within the spectrum, at 150 cm-1 with the calculated force constant, k = 0.33 mdyne/Å. The Ru4 cluster exhibits two metal core vibrations at 153 and 170 cm-1 with force constants of 0.35 and 0.53 mdyne/Å, respectively. Substitution with a gold atom yielding a mixed metal AuRu3 cluster shifts the core transitions toward higher wavenumbers at 177 and 299 cm-1 with an increase in force constants to 0.37 and 1.65 mdyne/Å, respectively. This is attributed to the change in chemical composition and geometry of the metal cluster core. A combination of the DFT calculations and high quality synchrotron-based experimental measurements allowed the full assignment of the key transitions in these clusters.
Next, these clusters were fabricated into heterogeneous catalysts by depositing on different metal oxide nanopowders. Synchrotron X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were performed at the Australian Synchrotron and the Photon Factory synchrotron in Japan to investigate the electronic structure of Au8, Au9 and Au101 on TiO2 catalysts. The XPS analysis reveals that “as-deposited” Au8 and Au9 retain some un-aggregated clusters while Au101 show bulk-like gold. These findings are in line with TEM observations, where the aggregates (large particles, > 2 nm) of Au8, Au9 and Au101 are hardly seen under HRTEM. UV-visible diffuse reflectance spectroscopy (UV-vis DRS) studies show the absence of localised surface plasmon resonance (LSPR) peaks in these “as-deposited” clusters, suggesting they are below 2 nm in size. Importantly, the XAS spectrum of “as-deposited” Au9 clusters estimates that 60% of pure, un-aggregated Au9 clusters and 40% of bulk gold in the sample. Upon calcination under O2 and combined O2 and H2 (O2-H2), Au8, Au9 and Au101 clusters form larger nanoparticles (> 2 nm) with the appearance of LSPE peak in UV-vis DR spectra. In addition, majority of the phosphine ligands (that stabilise the gold core) dislodge and form phosphine oxide-like species by interacting with oxygen on the TiO2 surface.
The third part focused on testing the catalytic performance of the supported Au8, Au9, Au101, Ru3, Ru4 and AuRu3 clusters on different TiO2, SiO2, ZnO and ZrO2 in benzyl alcohol oxidation. Au101-based catalysts display the highest catalytic activity with a turn-over frequency (TOF) up to 0.69 s-1. The high catalytic activity is attributed to the formation of large Au nanoparticles (> 2 nm) that coincides with the partial removal of capping ligands. Au8 and Au9 clusters which contain NO3- counter anions are found to be inactive in benzyl alcohol oxidation. Further work shows that the presence of NO3- species diminishes the catalytic activity. Monometallic ruthenium clusters, Ru3 and Ru4, are found to be inactive yet the bimetallic AuRu3 clusters are active in benzyl alcohol oxidation, suggesting the synergistic effect between ruthenium and gold metal. Investigation of catalytic testing parameters reveals that tuning selectivity of the product is possible through manipulating the reaction temperature.
Finally, a joint experiment with Prof. Wojtek Wlodarski’s group at RMIT, Melbourne was undertaken to test the sensing ability of Au9 clusters for hydrogen detection. Au9 clusters were deposited onto radio-frequency (RF) sputtered WO3 films at two different concentrations; 0.01(S1) and 0.1(S2) mg/mL. It was found that the optimal temperatures for sensor S1 and S2 were 300 °C and 350 °C, respectively. The sensor with lower Au9 concentration (S1) displays a faster response and recovery time, and a higher sensitivity toward H2. HRTEM studies reveal that the sensor S1 contain a significant population of sub-5 nm Au nanoparticles which might be responsible for a faster rate of H2 adsorption and dissociation. The key finding in this study suggest that the addition of catalytic layer such as ultra-small Au9 clusters results in improved sensitivity and dynamic performance (response and recovery time) of H2 sensors.
In summary, this thesis demonstrated that cluster-based nanomaterials have wide range of applications spanning from catalysis to sensing. Further improvements in material synthesis and use of multiple complimentary characterization techniques allowed better understanding of the nature of the key active species (metal nanoparticles) assisting design of catalysts and sensors with enhanced performance.
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Maniš, Jaroslav. "Modifikace grafenových struktur ionty o nízké energii (E." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254316.
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Diploma thesis deals with the influence of low energy ions on graphene structures. Graphene structures were modified by nitrogen and argon ions of energies lower than 100 eV. Modified structures were analysed by Raman spectroscopy and x-ray photoelectron spectroscopy. The influence of the dose of ions on quality of graphene were investigated as well. In addition, this diploma thesis includes the literature search which focuses on modification of graphene by charged particles.
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Rochet, Amélie. "Caractérisation structurale de catalyseurs hétérogènes en conditions de fonctionnement par spectroscopie d'absorption des rayons X résolue dans le temps." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00756909.
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Les catalyseurs hétérogènes sont des matériaux complexes dont les structures peuvent être modifiées en cours de fonctionnement. Une meilleure compréhension des relations entre propriétés catalytiques et propriétés structurales est nécessaire pour répondre à de nouveaux enjeux environnementaux et économiques. Seules les caractérisations in situ résolues dans le temps i.e. dans des conditions réelles, permettent d'apporter ces informations. Dans ce travail, nous nous sommes intéressés à la caractérisation operando par spectroscopie d'absorption des rayons X (XAS) résolue dans le temps de deux types de catalyseurs hétérogènes : les catalyseurs Fischer-Tropsch et les catalyseurs d'hydrodésulfuration. Si ces catalyseurs sont connus depuis de nombreuses années, peu de caractérisations sont réalisées in situ ou operando au cours de la réaction.Etant données leurs conditions réactionnelles (haute température et haute pression), la mise en œuvre de ces caractérisations a nécessité tout d'abord la construction des outils nécessaires à la caractérisation in situ de catalyseurs hétérogènes sous haute pression de gaz. Ensuite, nous avons réuni un ensemble cohérent de techniques de caractérisation autour du catalyseur Fischer-Tropsch afin de permettre son étude structurale à différentes échelles : l'ordre local avec le Quick-EXAFS et l'ordre à grande distance avec la diffraction des rayons X. Afin d'observer l'effet de la forme cristalline de la phase active sur les propriétés catalytiques, nous avons pour un même catalyseur, activé selon deux voies d'activation, quantifié son activité au moyen de la spectroscopie Raman et la spectrométrie de masse. D'autre part, la caractérisation simultanée de deux centres métalliques, accessible par le dispositif QEXAFS installé sur la ligne de lumière SAMBA, a permis d'obtenir une description fine des processus d'activation des catalyseurs bimétalliques d'hydrodésulfuration. Notre étude s'est portée, sur la comparaison de catalyseurs de même formulation avec des prétraitements différents (séché/calciné) et de deux catalyseurs promus par des métaux différents : le cobalt et le nickel.
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Clarke, Coby James. "Ionic liquids as designer molecules for XPS peak fitting." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33303/.
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X-ray photoelectron spectroscopy (XPS) of ionic liquids (ILs) has become a valuable tool for the investigations of IL interfacial and physicochemical properties. The complex signals that result from elements which occupy a variety of chemical states, for example the C 1s photoemission, are often interpreted through chemical intuition and peak fitting parameters. This Thesis will present a new method to determine exact photoemission binding energies (B.E.s), through the comparison of multiple spectra. The designer aspect of ILs has been exploited in order to produce salts with small structural modifications. By comparing the C 1s and N 1s photoemissions of the structurally related samples, difference spectra have been produced. These spectra show the relative shifting of electron density between the two signals, revealing the initial and final locations of the changing photoemission. Using this technique, the current C 1s peak fitting models of imidazolium and pyridinium ILs have been examined. A variety of 4,4’-bipyridinium salts have also been used as a structural variation of pyridinium ILs to show how molecular symmetry and normalisation may be utilised in order to produce photoemissions equivalent to fragments of molecules. The subsequent C 1s difference spectra have provided carbon peak fitting models for mono- and di-alkylated 4,4’-bipyridinium salts. Without the use of XP difference spectra, these known fitting models would be almost impossible to determine. Finally, multiple complex difference spectra have been used to identify the exact B.E.s of C 1s photoemissions from a series of nitrile functionalised ILs. The complex difference spectra have also been analysed by inverse Gaussian fittings to show how additional information may be extracted from the characteristic shapes. The ‘construction’ of photoemissions is also demonstrated, whereby known B.E. peaks are assembled to accurately reproduce experimentally determined XP spectra.
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Jagst, Eda [Verfasser]. "Surface functional group characterization using Chemical Derivatization X-ray Photoelectron Spectroscopy (CD-XPS) / Eda Jagst." Berlin : Freie Universität Berlin, 2010. http://d-nb.info/1024743934/34.
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Svensson, Pamela. "DFT investigations of the donor-acceptor couple CuPc/C60." Thesis, Uppsala universitet, Materialteori, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297935.
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The donor-acceptor couple CuPc/C60 has been the subject of recent studies in organic solar cells due to its combined abilities in light absorption (CuPc) and charge transport (C60). By better understanding the electronic and geometric nature of the system it is possible to shed light on how the molecules act under different conditions. In this study the geometric properties for three different configurations have been studied by means of Density Functional Theory (DFT). By comparing the molecular structure of pristine CuPc with the structure of CuPc in the presence of C60, a slight elongation of the bonds is observed when the fullerene is present. This is especially true for the Cu-N bonds. By further including van der Waals interactions, no change in bond lengths is observed. This, in turn, suggests that, most likely, the interaction between the two molecules is relatively weak and the C60 will not have a major influence on the electronic structure of CuPc. The N1s X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) calculations confirm these conclusions, as only very small changes in peak positions are observed when comparing pristine CuPc with CuPc/C60.Tack vare sina egenskaper inom absorption och laddningsöverföring har CuPc och fullerenen C60 varit föremål för omfattande studier bland forskare inom organiska solceller. Genom att få större förståelse för den geometriska såväl som den elektroniska konfigurationen inom och mellan paret kan man förutse hur dessa kommer att bete sig i olika sammansättningar. I denna studie har de geometriska förutsättningarna studerats där olika konfigurationer beräknats genom täthetsfunktionalteori (DFT). Genom att mäta bindningslängderna mellan koppar, kol och de olika typer av kväve i CuPc i de olika systemen, kan det inses att bindningarna förlängs då C60 läggs till. Då van der Waals-interaktioner inkluderades observerades ingen större förändring i bindingslängderna i jämförelse med fallet utan van der Waals-interaktioner. Detta tyder på att växelverkan mellan de två molekylerna är relativt svag och att C60-fullerenen ej har någon större påverkan på elektronkonfigurationen i CuPc. Beräkningarna av N1s X-ray Photoelectron Spectroscopy (XPS) och Near Edge X-ray Absorption Fine Structure (NEXAFS) stödjer denna slutsats då endast små skiftningar i topparna observerades vid jämförelse mellan rent CuPc och CuPc/C60.
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Lemon, Christine Elizabeth. "Atmospheric Corrosion of Silver Investigated by X-ray Photoelectron Spectroscopy." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1350660429.
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Pinto, Rui Montenegro Val-do-Rio. "Photoelectron spectroscopy of nitrogen containing molecules of biological and industrial interest." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2011. http://hdl.handle.net/10362/7077.
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