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. / Physics

L'hydrotraitement est un procédé catalytique important dans le raffinage du pétrole qui utilise des catalyseurs bimétalliques sulfurés NiWS ou NiMoS (ou CoMoS) supportés sur alumine. Leur mode conventionnel de préparation implique l’imprégnation d'une solution aqueuse de sels de Mo/W et de Ni/Co, puis l’activation par un agent sulfo-réducteur (H2S/H2). Pour répondre aux exigences environnementales et améliorer l'efficacité de l'hydrotraitement, des améliorations permanentes de la performance de ces systèmes catalytiques sont attendues. Ce travail se concentre sur la préparation de catalyseurs d'hydrotraitement hautement actifs par une approche de chimie de surface contrôlée (CSC) qui implique l'imprégnation successive de précurseurs moléculaires de MoV et NiII en solvant organique sur un support silice-alumine traité thermiquement. Dans la première partie de cette thèse, la genèse de la phase active du catalyseur CSC et conventionnel Mo et NiMo est étudiée par quick-XAS combinée à d’autres techniques (chimiométrie, XPS, RPE, STEM-HAADF, modélisation moléculaire). Nous proposons ainsi des structures moléculaires depuis les précurseurs oxydes de Mo et Ni supportés jusqu’aux nombreuses espèces intermédiaires (oxysulfure et sulfures) en fonction de la température. Cette analyse multi-technique permet d'abord de révéler les spécificités de la genèse des catalyseurs CSC et conventionnels qui peuvent expliquer leurs différentes activités catalytiques. Ensuite, elle révèle également de nouvelles connaissances sur les mécanismes d’insertion du Ni dans la phase NiMoS en fonction de la préparation. Dans la seconde partie, la possibilité de remplacer Co et Ni comme promoteurs est explorée. Ceci est entrepris en synthétisant des catalyseurs alternatifs de type XYMoS, où X et Y sont des métaux de transition 3d. Comme suggéré par des études de modélisation quantiques antérieures, certaines formulations XYMoS peuvent présenter un effet de synergie analogue à ceux des phases actives CoMoS et NiMoS. L’étude des formulations les plus prometteuses méritent d'être approfondies afin de mieux comprendre leur fonctionnement. / Hydrotreating is an important catalytic process in petroleum refining which uses sulfided bimetallic catalysts NiWS or NiMoS (or CoMoS) supported on alumina. Their conventional preparation involves an incipient wetness impregnation of an aqueous solution of Mo/W and Ni/Co salts, and then activation by a sulfo-reductive agent (such as H2S/H2). To meet environmental regulations and improve the energy efficiency of hydrotreatment, permanent improvements on the performance of these catalytic systems are expected. This work is thus focused on the preparation of highly active hydrotreating catalysts through a controlled surface chemistry (CSC) approach; which involves the successive impregnation of Mo5+ and Ni2+ molecular precursors in an organic solvent on a thermally treated silica-alumina support. In the first part of this thesis, the active phase genesis of CSC and conventional Mo and NiMo catalysts is studied by in situ quick-XAS combined with various other techniques (chemometrics, XPS, EPR, STEM-HAADF, molecular modeling). We thus propose molecular structures from the oxide of supported Mo and Ni precursors up to the numerous intermediate sulfided species as a function of temperature. This multi-technique analysis enables first to reveal the specific features of the genesis of CSC and conventional catalysts which may explain their different catalytic activities. Then, it also reveals new insights into the mechanisms of Ni promoter incorporation into the NiMoS phase as a function of the preparation. In the second part, the feasibility of replacing Co and Ni as promoters is explored. Using the CSC method, we attempted to synthesize alternative catalysts of the form XYMoS ternary sulfides, where X and Y are 3d transition metals. As suggested by previous quantum simulations, certain XY formulations possibly reveal a synergy effect as observed in CoMoS and NiMoS active phases. The most promising formulations merit further investigations.

La micro-algue verte Chlamydomonas reinhardtii est considérée comme un modèle dans l’étude du stress métallique chez les organismes photosynthétiques. Les mécanismes de tolérance au stress induit par le cadmium ne sont pas encore clairement établis. Afin de déterminer ces mécanismes, la localisation subcellulaire et la spéciation chimique in situ du cadmium ont été déterminées chez trois souches de C. reinhardtii exposées au cadmium en condition mixotrophe (CO2 + Acétate) : (i) une souche de type sauvage (wt), (ii) la souche cell-wall less (cw15) qui est déficiente en paroi cellulaire, (iii) la souche pcs1 qui surexprime la phytochélatine synthase (PCS), enzyme ordinairement cytosolique, directement dans son chloroplaste. Pour ce faire, la toxicité du cadmium a été déterminée en mesurant la croissance ainsi que la teneur en chlorophylle et en amidon des micro-algues. Puis, la localisation du cadmium au niveau subcellulaire a été réalisée par trois techniques complémentaires (fractionnement subcellulaire, µXRF, TEM/X-EDS). La spéciation chimique in situ du cadmium a été effectuée par µXAS et XAS. Enfin, l’imagerie élémentaire et isotopique par nanoSIMS a permis de compléter les distributions élémentaires dans la cellule et de déterminer l’impact du cadmium sur les mécanismes d’assimilation du carbone. (i) Les résultats de ce travail montrent que la souche wt est la plus sensible au cadmium des trois avec une diminution de la croissance et de la teneur en chlorophylle. Lorsqu’elle ne présente pas ces signes de toxicité, le cadmium est séquestré dans l’ensemble de la cellule par des ligands thiolés et de façon mineure par les granules de polyphosphates. Suite à l’exposition à de fortes concentrations en cadmium, le cadmium intracellulaire est lié majoritairement à des ligands carboxylés probablement induits par le stress oxydatif. De plus, la présence du cadmium dans le pyrénoïde bloque l’assimilation du carbone inorganique (CO2), au profit de l’assimilation du carbone organique (acétate), qui est stocké sous forme d’amidon. (ii) La surexpression de la PCS de la souche pcs1 provoque une production d’amidon importante autour du pyrénoïde et protège la chlorophylle du stress lié au cadmium. Bien que la synthèse de phytochélatines soit potentiellement élevée, la moitié du cadmium intracellulaire est séquestrée par les granules de polyphosphates et l’amidon. (iii) La souche cw15 est la plus tolérante des trois souches et n’accumule pas la totalité du cadmium disponible, contrairement aux cellules possédant une paroi cellulaire. Similairement au wt, le cadmium intracellulaire est séquestré majoritairement par des ligands thiolés et de façon mineure par les granules de polyphosphates. L’observation de granules de polyphosphates excrétées par les micro-algues permet l’hypothèse de l’excrétion du cadmium vacuolaire induisant un flux constant de cadmium à travers la cellule. En conclusion, la séquestration du cadmium via des ligands soufre, potentiellement par des polypeptides thiolés, est le mécanisme de tolérance majoritaire mis en place par C. reinhardtii. Néanmoins, la séquestration du cadmium par les granules de polyphosphates semble apporter une plus grande tolérance vis-à-vis du stress lié au cadmium. / The green micro-alga Chlamydomonas reinhardtii is commonly used as a model for the study of the metallic stress in photosynthetic organisms. Tolerance mechanisms against stress induced by cadmium are not well understood. In order to determine these mechanisms, subcellular location and in situ speciation have been determined in three C. reinhardtii strains exposed to cadmium in mixotrophic conditions (CO2 + Acetate) : (i) a wild type strain (wt), (ii) a cell-wall less strain (cw15) which is deficient in cell-wall, (iii) the pcs1 strain which overexpresses the cytosolic enzyme phytochetlatin synthase (PCS) directly in the chloroplast. Cadmium toxicity has been determined by the monitoring of growth and chlorophyll, starch content in micro-algae. Then, cadmium location at subcellular level has been performed using three complementary techniques (subcellular fractionation, µXRF and TEM/X-EDS). In situ cadmium speciation has been studied by µXAS and XAS. Finally, elemental and isotopic imaging by nanoSIMS has allowed to complete elemental distribution in the cells and to determine the impact of cadmium on the assimilation of carbon. (i) The results of this work show that the wt strain is the most sensitive strain to cadmium stress among the three studied strains with a growth and chlorophyll content decrease. When wt cells do not show signs of toxicity, cadmium is mainly sequestered in the whole cell by thiolated ligands and in polyphosphate granules. After an exposure to high concentration of cadmium, intracellular cadmium is mainly bound to carboxylated ligands, probably induced by oxidative stress. Moreover, cadmium located in the pyrenoid blocks inorganic carbon (CO2) assimilation and increases organic carbon (acetate) assimilation which is stored as starch. (ii) The overexpresssion of PCS in the pcs1 strain induces a strong production of starch around the pyrenoid and proctects the chlorophyll against cadmium stress. Although the synthesis of phytocheltins was potentially strong, half of the intracellular cadmium is sequestered in polyphosphate granules and in starch. (iii) Unlike cell-walled cells, the cw15 strain is the most tolerant strain and does not accumulate the totality of available cadmium. Similarly to wt strain, intracellular cadmium is mainly sequestered by thiolated ligands and in polyphosphate granules. The observation of polyphosphate granules excreted by the micro-algae allows the hypothesis of the excretion of vacuolar cadmium, inducing a constant flux of cadmium through the cells. In conclusion, cadmium sequestration by sulfur ligands, potentially by thiolated polypeptides, is the main tolerance mechanism implemented by C. renhardtii. However, cadmium sequestration in polyphosphate granules seems to allow a better tolerance against cadmium stress.

Notre étude porte sur des matériaux à effets relativistes importants. L'hamiltonien semi-relativiste, couplé aux équations de Maxwell (EM), permet de déduire les sources de courant et de densité, incluant des termes de second ordre (polarisations de spin et de Darwin). Différents modèles sont développés par expansion des EM. L'étude ab initio montre que (1) le désordre atomique peut produire le ferrimagnétisme (FM) dans GaFeO3 (GFO) multiferroïque, (2) les états 3d Fe des octaèdres déformés ont une levée de dégénérescence tétraédrique (théorie du champ cristallin), (3) la polarisation électrique concorde avec l'expérience, (4) le mécanisme magnétoélectrique (ME) direct est insuffisant pour expliquer le ME observé. Pour Cr2O3, le calcul de l'état massif sous contraintes biaxiales n'explique pas son FM, la taille de l'échantillon ou l'excès d'oxygène pourrait de fait être important. Enfin, nous avons développé le XAS et le XMCD dans le code VASP et calculé ces spectres pour GFO. / We studied the physics of materials where relativistic effects are important. We first coupled the semi-relativistic Hamiltonian with the Maxwell's equations, and derived the current and density sources, which included second-order terms like the spin and Darwin polarizations. Different models were developed, by expanding the Maxwell's equations. We then performed ab initio studies to explain (1) site disorders as the origin of ferrimagnetism in multiferroic GaFeO3 (GFO), (2) crystal-field theory where the Fe 3d states at the deformed octahedra have tetrahedral splittings, (3) the electric polarization as a function of temperature, and (4) the insufficiency of the direct magnetoelectric (ME) mechanism to explain observed ME behavior. For Cr2O3, bulk calculations for different biaxial strains failed to explain its ferromagnetism, indicating that size or excess-O effects might be important. Finally, we implemented XAS and XMCD in VASP and computed these spectra for GFO.

The discovery of an unexpectedly large thermopower accompanied by low resistivity and low thermal conductivity in NaxCoO2 raised significant research interest in these materials and let to a number of experimental and theoretical investigations. This interest has strongly been reinforced by the discovery of superconductivity in the hydrated compound Na0.35CoO2 •1.3H2O in 2003, and thus, NaxCoO2 experiences an again increasing attention. The similarity of the Na cobaltates to the high temperature superconductors (HTSC) - both are transition metal oxides and adopt a layered crystal structure with quasi-two-dimensional (Cu,Co)O2 layers - is an important aspect of the research activities. In contrast to the HTSC cuprates however, the CoO2 layers consist of edge sharing CoO6 octahedra which are distorted in such a way that the resulting local symmetry is trigonal. The trigonal coordination of the Co sites results in geometric frustration which favours unconventional electronic ground states. The geometrically frustrated CoO2 sublattice also exists in the nonhydrated parent compound NaxCoO2, which has been investigated in this work. The intercalation of water into the parent compound is expected to have little effect on the Fermi surface beside the increase in two dimensionality due to the effect of expansion. Upon lowering the symmetry from cubic to trigonal, the t2g states split into states with eg_and a1g symmetry. Measurements of polarisation and temperature dependent soft X-ray absorption have been performed on a wide doping range of NaxCoO2 single crystals. Beside the Co L_2,3-edges, the O K-edge and the Na K-edge have been measured. These measurements show strong polarisation dependencies especially for the excitations into the lower lying a1g energy level. In addition to that, also an unexpected polarisation dependence for higher energies has been observed, which should be absent in trigonal symmetry. These results point towards a deviation of the local trigonal symmetry of the CoO6 octahedra, which is temperature independent in a temperature range between 25 K and 372 K. This deviation was found to be different for Co3+ and Co4+ sites, which leads to a polaronic electron transport. Furthermore, a strong hybridisation between the Co and O ions has been found. In order to shed further light on the electronic structure of NaxCoO2, the electronic spectrum of a CoO6 cluster has been calculated including all interactions between 3d orbitals as well as hopping processes between Co and O and O and O ions. The ground state for two electronic occupations in the cluster (i.e. Co3+ and Co4+) that correspond nominally to all O in the O−2 oxidation state, and Co+3 or Co+4 has been obtained. Then, all excited states obtained by promotion of a Co 2p electron to a 3d electron, and the corresponding matrix elements are calculated. A fit of the observed experimental spectra is good and points out a large Co-O covalence and cubic crystal field effects, that result in low spin Co 3d configurations. The results indicate that the effective hopping between different Co atoms plays a major role in determining the symmetry of the ground state in the lattice. Remaining quantitative discrepancies with the XAS experiments are expected to come from composition effects of itineracy in the ground and excited states. Beside these points, results of photoemission spectroscopy, magnetisation measurements as well as resonant and non-resonant X-ray diffraction using high energy X-rays are shown and discussed. / Die Entdeckung unerwartet großer Thermokraft bei gleichzeitigem niedrigem Widerstand und niedriger thermischen Leitfähigkeit in NaxCoO2 führte zu einem großen wissenschaftlichem Interesse an diesen Materialien und zu einer großen Anzahl an experimentellen und theoretischen Arbeiten. Dieses Interesse steigerte sich noch einmal nach der Entdeckung von Supraleitung in der hydrierten Verbindung Na0.35CoO2 •1.3H2O im Jahre 2003. Die Ähnlichkeit der Na Kobaltate zu den Hochtemperatur-Supraleitern (HTSL) – beides sind Übergangsmetalloxide mit einer geschichteten Kristallstruktur in der quasi zwei dimensionale (Cu,Co)O2 Ebenen enthalten sind – ist ein wichtiger Aspekt moderner wissenschaftlicher Arbeiten. Im Gegensatz zu den HTSL Kupraten bestehen die CoO2 Ebenen aus CoO6 Oktaedern die über ihre Kanten verbunden sind und in der Art verzerrt sind, dass die resultierende Symmetrie trigonal ist. Die trigonale Anordnung der Co Plätze führt zu einer geometrischen Frustration und unkonventionellen elektronischen Grundzuständen. Diese geometrisch frustrierten CoO2 Untergitter existieren ebenfalls in den nicht hydrierten Mutterverbindungen NaxCoO2, welche in dieser Arbeit untersucht wurden. Interkalierung von Wasser in die Mutterverbindung hat nur einen kleinen Einfluss auf die Fermi Oberfläche und führt zu einem Anstieg des zwei dimensionalen Charakters durch den Effekt der Ausdehnung. Durch Verminderung der Symmetrie von kubisch zu trigonal splitten die vormals entarteten t2g Zustände auf in Zustände mit eg und a1g Symmetrie. Zur Bestimmung der elektronischen Struktur von NaxCoO2 wurden polarisations- und temperaturabhängige Messungen der Röntgenabsorption im weichen Röntgenbereich für einen großen Dotierungsbereich durchgeführt. Neben den Co L_2,3-Kanten wurden auch die O K-Kante und die Na K-Kante gemessen. Sie zeigen eine starke Polarisationsabhängigkeit speziell für Anregungen in die niederenergetischen a1g Level. Zusätzlich wurde eine unerwartete Polarisationsabhängigkeit bei höheren Energien gefunden, die für trigonalen Symmetrie so nicht auftauchen dürfte. Diese Ergebnisse weisen auf eine Abweichung von der lokalen trigonalen Symmetrie der CoO6 Oktaeder hin, welche Temperatur unabhängig ist in einem Temperaturbereich zwischen 25 und 372 Kelvin. Diese Abweichung ist unterschiedlich für Co3+ und Co4+ Ionen was wiederum auf einen polaronischen Transport hinweist. Zusätzlich wird deutlich, dass eine starke Co-O Hybridisierung existieren muss. Um weiteres Informationen über die elektronische Struktur von NaxCoO2 zu erhalten, wurde das elektronische Spektrum eines CoO6 Oktaeders berechnet in dem alle Wechselwirkungen zwischen 3d Orbitalen sowie Hüpfprozesse zwischen Co und O sowie O und O Ionen enthalten sind. Der Grundzustand für zwei elektronische Besetzungen in einem Cluster (d.h. Co3+ und Co4+) wurde bestimmt für O Ionen mit einer nominellen O-2 Oxidation sowie Co3+ und Co4+ Ionen. Im angeregten Zustand werden die entsprechenden Anregungen eines Co 2p Elektrons in einen unbesetzten 3d Zustand berücksichtigt und die entsprechenden Matrixelemente berechnet. Ein Fit an den experimentellen Daten ist gut und weist auf eine starke Co-O Kovalenz und auf einen starken Einfluss des kubischen Kristallfeldes hin, der zu einer Low-Spin Co 3d Konfiguration führt. Die Ergebnisse zeigen, dass ein effektives Hüpfen zwischen benachbarter Co Ionen eine große Rolle für die Symmetrie des Grundzustandes im Gitter spielt. Quantitative Unterschiede zwischen den experimentellen und theoretischen Daten kommen anscheinend von itineranten Effekten im Grund- und angeregten Zustand. Zusätzlich zu den oben kurz beschriebenen Ergebnissen werden in dieser Arbeit weitere Ergebnisse der Photoemissionsspektroskopie, der Magnetisierung sowie aus resonanter und nicht resonanter Röntgenbeugung mit harter Röntgenstrahlung gezeigt und diskutiert.

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.

Die Mitwirkung bei dem Sonderforschungsbereich 1333 (SFB 1333) eröffnete die exklusive Gelegenheit, eingehende Kenntnisse über Theorie und Praxis der Röntgenabsorptions-spektroskopie (XAS) zu erwerben. Diese Expertise fand im Rahmen eigenständig geleiteter Kooperationsprojekte auf dem Gebiet der Rh- und Ru-Koordinationschemie vielseitige Anwendung: Neben der Untersuchung Lösungsmittel-bedingter Ligandensubstitutionen zählten auch mechanistische Studien homogen-katalysierter Transformationen sowie die spektroskopische Evaluierung verschiedener Immobilisierungsstrategien zu dem Anwendungs-Portfolio der XAS-Analyse. Für die Forschungsgruppe Plietker erwies sich XAS als ein geeignetes Instrument, um die Entwicklung des Konzepts der molekularen heterogenen Katalyse in definierten, dirigierenden Geometrien zu unterstützen. Das flexible Anwendungsspektrum dieser Spektroskopie-Methode gestattete, das positive Resultat der Immobilisierung eines Ru-basierten H2-Autotransfer¬katalysators auf spektroskopischem Niveau zu verifizieren. Eingehende XANES- und EXAFS-Analysen untermauerten dabei, dass dessen Fixierung innerhalb des Porensystems eines SBA-15-Materials lediglich mit einer marginalen strukturellen oder elektronischen Beeinflussung des Ru-Zentralatoms einherging. Außerdem ließen sich die chemischen Auswirkungen einer variierenden Distanz zwischen immobilisiertem Ru-Komplex und Porenwand auf das Zentralatom analysieren sowie die katalytisch aktive Spezies des recyclierten Ru-Komplexes mit hoher Wahrscheinlichkeit identifizieren. In der parallelen Untersuchung einer bis dato nur oberflächlich erforschten Kategorie kationischer Fe-Diazo-Komplexe erwies sich XAS zudem als Schlüsselmethode für die Veranschaulichung des Elektronendichte-abhängigen Equilibriums zwischen trigonal-bipyramidalem und oktaedrischem Bindungsisomer. Ferner wurden bei dieser Untersuchung deutliche Hinweise auf die Empfindlichkeit dieser Gleichgewichtslage gegenüber einer fortwährenden Exposition mit harter Röntgenstrahlung sowie der CLICK-Chemie-basierten Immobilisierung in mesoporösem Trägermaterial offensichtlich. Neben der Analyse homogener und immobilisierter Übergangsmetall-Komplexe wurde das Spektrum der in der Forschungsgruppe Plietker bisher einzig in Mikrowellen-Reaktoren praktizierten C H-Aminierungen um die bei Raumtemperatur stattfindende, TBA[Fe]-katalysierte Sultambildung erweitert. Deren Anwendungsbreite ließ sich durch die Erarbeitung eines synthetischen Zugangs zu verschiedenen o-monofunktionalisierten, aber auch asymmetrisch 2,6-difunktioanlisierten Arylsulfonylaziden, über das bisher in der Literatur bekannte Maß ausdehnen. Neben präparativen Untersuchungen, als Teil der für diese Insertionsreaktion durchgeführten Mechanismusstudie, erfolgten im Rahmen eines Forschungsaufenthaltes an der University of Rochester erste Mössbauer-Analysen des postulierten TBA[Fe]-Nitren-Intermediats. Darüber hinaus erwies sich der bereits in der homogenen H2-Autotransferkatalyse etablierte Ru(NNNN)-Komplex ebenfalls als ein wirkungsvoller Katalysator für die intramolekulare C H Aminierung aromatischer Sulfonylazide. Der Einsatz seines immobilisierten Analogons erlaubte schlussendlich die Kombination der Fachgruppen-intern bisher ausnahmslos homogen-katalysierten C-H-Aminierung mit dem neuartigen Konzept der molekularen heterogenen Reaktionsführung in definierten, dirigierenden Geometrien. / Participating in the Collaborative Research Center 1333 (CRC 1333) offered the exclusive opportunity to accumulate detailed knowledge in theory and application of X-ray Absorption Spectroscopy (XAS). This expertise was afterwards used in independently managed cooperation projects focusing on solvent-based ligand substitutions, mechanistic studies of homogeneously catalyzed transformations as well as the spectroscopic evaluation of different immobilization strategies. Within the Plietker research group, XAS became an adequate tool to support the development of the concept of molecular heterogeneous catalysis in confined geometries. XAS was applied to verify the successful immobilization of the Ru(NNNN)-based H2-autotransfer catalyst spectroscopically. XANES- and EXAFS analysis thereby proved the attachment of this complex in SBA-15 support with only small electronic and steric influence on the Ru-center. Furthermore, XAS provided valuable information about possible structural consequences for the ligand sphere caused by different distances between immobilized complex and pore wall as well as probably disclosed the catalytic active species that is immobilized in recycled solid support. In a parallel exploration of a so far only rudimentarily investigated category of cationic Fe-diazo complexes, XAS turned out to be the key method for visualizing the electron density dependent equilibrium between their trigonal-bipyramidal and octahedral coordination mode. In addition, this study also gathered information about the sensitivity of the underlying isomerization reaction to continuous exposition to hard X-rays as well as to the CLICK-chemistry based immobilization in mesoporous material. Beyond the analysis of these homogeneous and immobilized transition metal-complexes, the portfolio of the in the Plietker group so far only microwave-based C-H-amination reactions was expanded by a room temperature TBA[Fe]-catalyzed sultame formation. In order to increase its substrate scope, a new synthetic strategy for asymmetric 2,6-disubstituted arenesulfonyl azides was created guaranteeing the introduction of various carbon-based substituents. Next to preparative experiments as part of mechanistical studies for this insertion reaction, MÖSSBAUER analysis of the postulated TBA[Fe]-nitrene intermediate was performed during a research stay at the University of Rochester. Additionally, the homogeneous Ru(NNNN)-complex applied in H2-autotransfer reactions proved to efficiently catalyze the intramolecular C-H-amination of aromatic sulfonyl azides as well. The usage of its immobilized analogue finally culminated in the fusion of the group-intern only homogeneously catalyzed C-H-amination reactions with the novel concept of molecular heterogeneous catalysis in confined geometries.

L’alumine est un support important en catalyse hétérogène. Le contrôle de ses propriétés physiques et texturales permet d’en améliorer les performances comme support pour des applications en catalyse. Les catalyseurs à base de cobalt sont connus pour présenter d’excellentes performances pour la réaction de reformage de l’éthanol (RRE) du fait de leur grande affinité à cliver les liaisons C-H et C-C.De nombreuses études ont visé à corréler les propriétés de l’alumine avec celles des catalyseurs. L’alumine présente une chimie de surface plutôt complexe qui peut être contrôlée par le mode de préparation. Dans ce travail,des alumines possédant des méso- et macropores ont été obtenues par voie sol-gel dans un mode de préparation « one-pot » accompagnée par une séparation de phases. Dans cette stratégie intégrative, les deux procédés,gélification et séparation de phases, surviennent spontanément dans les systèmes contenant un inducteur de séparation de phase.Les différentes alumines ont été synthétisées à partir d’isopropoxyde oude chlorure d’aluminium et de polyethylène oxyde ou polypropylène oxydeutilisés comme inducteur de séparation de phases. Le choix approprié des compositions des réactifs permet le contrôle de la taille et volume des pores. La formation des macropores résulte du processus de séparation de phase après décomposition par calcination de l’inducteur alors que l’espace entre particules formant le squelette du xerogel constitue la structure mésoporeuse.Les différentes alumines poreuses ainsi préparées et une alumine commerciale ont été utilisées comme supports de catalyseurs de cobalt par imprégnation par voie humide. Les précurseurs oxydes du catalyseur obtenu après calcination sont composés de phases de type Co ₃ O ₄ et CoAl₂O ₄ , cette dernière étant en quantité plus importante dans les alumines synthétiques.Comme les alumines sol-gel sont caractérisées par une plus grande proportion d’aluminium en site octaédrique et de groupement hydroxyles de surface que l’alumine commerciale, nous avons proposé que ces caractéristiques facilitent la migration du Cobalt dans le réseau alumine et explique la formation plus importante de phase de type CoAl₂O ₄ .Les catalyseurs ont été caractérisés pendant l’activation et en conditions réelles de fonctionnement RRE par EXAFS rapide pour suivre l’évolution de l’ordre local du cobalt et par spectroscopie Raman et spectrométrie de masse résolues dans le temps pour l’analyse des produits de réaction. Si l’espèce active est indiscutablement Co0, nous avons montré que les performances catalytiques dépendent aussi du rapport Co ² ⁺ /Co ⁰ obtenu après activation, dans le sens où de faibles rapports Co ² ⁺ /Co ⁰ ne permettront pas de nettoyer la surface du catalyseur par oxydation du coke formé lorsque la réaction de reformage de l’éthanol opère. Une conclusion importante de ce travail est la mise en évidence du rôle joué par l’oxyde cobalt (CoO) dans la stabilité du catalyseur à travers la promotion de l’oxydation des espèces carbonées déposées en surface. Ainsi le contrôle du rapport Co ² ⁺ /Co ⁰ apparaît comme un élément capital pour la conception de catalyseurs performants à base de cobalt pour la réaction de reformage de l’éthanol, le choix du support étant essentiel / Alumina is an important support for heterogeneous catalysts. Thematching of appropriate alumina physical properties and controlled texturalproperties can improve its performance as support in catalysis applications.Cobalt based catalysts have been reported to have a good ethanol steamreforming (ESR) performance due to their high activity for the cleavage of C-Hand C-C bonds.Many studies have been conducted about the effects of aluminaproperties on the cobalt catalysts properties. Alumina exhibits a rather complexsurface chemistry which can be controlled by the preparation procedure. In thiswork alumina samples with macro and mesoporous structure were obtainedusing the one-pot sol-gel synthesis accompanied by phase separation. In thisintegrative strategy both processes, gelation and phase separation,spontaneously occur in system containing the presence of the phase separationinducer.The different aluminas were produced by using as aluminum reactants,aluminum isopropoxide and chloride and PolyEthylene Oxide or PolyPropyleneOXide as phase separation inducer. Appropriate choice of the startingcomposition allows the control the pore size and volume. Macroporous areformed as a result of phase separation after burning the phase separationinducer, while voids between particles of the xerogel skeletons form amesoporous structures.The different alumina porous alumina and commercial alumina wereused as supports for preparing by wetness impregnation cobalt-based catalyst.The oxidic catalyst precursors obtained after calcination are composed of Co ₃ O ₄ and CoAl₂O ₄ -like phases, the latter being in higher proportions in the sol-gelalumina than in the commercial one. As the sol-gel alumina presents a largeramount of octahedral AlVI sites and surface hydroxyl groups than thecommercial alumina, it was assumed that these features can facilitate themigration of Co ions into the alumina network leading to formation of thegreatest amount of CoAl₂O ₄ .The catalysts were characterized under realistic activation and reactionconditions by the combination of Quick-XAS (X-ray Absorption Spectroscopy)for monitoring the change of the local order around Co with time-resolvedRaman and Mass spectroscopy for monitoring reaction products. If the Co(0)species is undoubtedly the active species for ESR, the catalytic performancehas been clearly shown to be affected by the Co ² ⁺ /Co ⁰ ratio obtained afteractivation, getting lower Co ² ⁺ /Co ⁰ ratios will not allow to clean the surface of thecatalyst by oxidation of C* as ESR is running. As an important conclusion of thework reported herein, we have evidenced that the cobalt oxide (CoO) plays akey role in the stability over time of the catalyst through oxidation of adsorbedand reactive carbon atoms. Then the control of the Co ²⁺ /Co ⁰ ratio appears to beone of the key issues in the design of efficient cobalt alumina-supported ethanolsteam reforming catalysts and the choice of the support is essential forcontrolling this ratio of active cobalt species.

Adsorption of monolayers and multilayers of metal-free and metal phthalocyanines molecules on metal surfaces has been investigated using complementary microscopic and synchrotron-based spectroscopic techniques. It was observed by STM measurements that at monolayer coverage the adsorption direction of the metal-free phthalocyanine molecules with respect to the gold surface vary as a function of temperature, i.e. at room temperature (RT) and low temperature (LT). It was explained by the difference in strength of intermolecular and adsorbate-substrate interactions at room and low temperatures. Nature of the interaction between adsorbed species and the surfaces as a function of coverage has been further characterized by XPS measurements. Binding energy shifts as a function of coverage have been attributed to initial- and final-state effects, the latter being due to different core-hole screening for the different molecular coverage. The alignment of molecular films at both monolayer and multilayer coverages, which has been determined by XAS measurements in several cases, is also dependent upon the relative strength of molecule-molecule versus molecule-substrate interaction. Parallel alignment of the molecular film with respect to the surface is the result of significant interaction between the adsorbate and the substrate, whilst standing geometry of the molecular film is due to more significant intermolecular interactions. DFT simulations have provided further information on the nature of the adsorbate-substrate interaction as well as contribution of different molecular orbitals in XPS and XAS spectra. Moreover, investigation of alkali interaction with the phthalocyanine films revealed a significant modification in their geometric and electronic structures due to charge transfer from the alkali metal to the molecular film. However, no sign of metallization of the molecules has been observed by spectroscopic and microscopic studies.

<p>The electronic structures of the nucleobases, 5-fluorouracil compounds, DNA, metallic DNA, and samples of boron nitride are investigated. Soft X-ray absorption (XAS) and emission (XES) spectroscopy using synchrotron radiation are used to probe the unoccupied and occupied partial densities of electronic states, respectively. Hartree-Fock and density functional theory calculations have been included to compare with experimental results.</p> <p>A systematic approach to understanding the complicated electronic structure of DNA and metallic DNA systems is to initially examine smaller components. Detailed experiment and theory for both absorption and emission spectroscopy was. performed for the nucleobases and 5-fluorouracil compounds. Main transitions in the XAS and XES spectra are identified. X-ray spectroscopy has proven to be extremely sensitive to changes in the environment of various DNA samples. The local chemical environment plays an important role in determining the electronic structure of DNA. In agreement with previous results indicating metallic DNA is more efficient at the transfer of electrons than DNA, XES measurements reveal that there are a higher number of charge carriers in the metallic system. Both liquid and powder samples of (Ni)·M-DNA are found to have a high spin Ni(II) configuration. The drying process significantly alters the electronic structure of the metallic DNA sample. A comparison of high quality single crystals and thin films of boron nitride found that differences between the electronic structures of the nanocrystalline films and the single crystal samples exist, and the surface roughness of the substrate plays an important role in determining the structure of the resulting deposited film.</p>