Low dimensional nanostructures have defined the frontier of the research in material science for the last two decades. Presented here are the results of experimental research on growth, device fabrication and application of quasi-one dimensional phthalocyanines and metal oxides to gas-sensing. The possibility of rational tuning of the growth conditions, in order to control composition, morphology, size, orientation and alignment of the grown low-dimensional nanostructures was investigated. Employing custom designed heating stages coupled with optical microscope the in situ approach of monitoring the growth of nanostructures has been realized. Using this method, the growth of VO2 nanowires and nanoplatelets have been investigated and two novel growth mechanisms were discovered and explained. A variety of phthalocyanine and metal-oxide nanowire-based chemical sensors have been proposed, fabricated and tested. The focus of our research was on the development of new sensing principles and the improvement of existing ones. In particular, nanowires of tin and titanium dioxide were proposed to be used as self-heated chemiresistors capable of operating in the absence of an external heater, thus paving the way for ultra-low power consumption sensors. For the first time VO2 nanowires were used to create a nano-Pirani gauge and a gas sensor employing a sharp temperature-driven metal-insulator transition in this material. The sensor is sensitive to both chemically active and inert gases. Its performance is modeled and optimization parameters are presented.

Mesoporous thin films are promising architectures for positive electrodes in Li-ion battery applications. A particular challenge in this field has been successful templating of vanadium-based oxides, materials known for their ability to host lithium, since their thermal instability and complex vanadium chemistry hinder templating through traditional soft-chemistry approaches. To address these technical problems we here develop the soft-templating of vanadium and niobium mixed oxides based on Evaporation Induced Micelles Packing using thermally stable polystyrene-b-polyethyleneoxide structuring agents. In-situ thermal monitoring via ellipsometry allows successful navigation of the thermal stability landscape. TEM and AFM analyses reveal homogeneous wormlike mesoporous structures whose pore and inorganic wall sizes can be tuned from 15 to 100 nm by changing the hydrophobic/hydrophilic surfactant chain lengths. Ellipsometric porosimetry shows that 100 nm thick films with a 15 nm pore size displays 30% electrolyte accessible porosity. The interconnected tridimensional mesoporous network has been highlighted by electronic tomography. Thicker films up to 1.3 µm are prepared by a multidipping process. The superiority of such nanoarchitectures compared to non porous materials in terms of electrochemical properties such as capacity are revealed using cyclic voltammetry.

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Dans les années à venir, la production d’Energie devra passer par l’utilisation de moyens plus respectueux de l’environnement tels que les énergies renouvelables. Leur caractère intermittent nécessite cependant la mise en place d’un stockage à grande échelle. Parmi les différentes technologies à disposition, les batteries Na-ion apparaissent comme une solution de choix grâce aux ressources de sodium illimitées. Dans ce contexte, nous nous sommes donc intéressés à la synthèse et la caractérisation de nouveaux matériaux d’électrodes positives pour batteries Na-ion. Les oxydes de métaux de transition et plus particulièrement le système Na-Mn-O a attiré notre attention pour les avantages que procure le manganèse en termes de non toxicité, de faible coût et d’abondance. Les phases Na4Mn2O5, lacunaire en oxygène, et Na2Mn3O7, lacunaire en cation manganèse, montrent des capacités spécifiques intéressantes par l’action de différents phénomènes redox. Na2Mn3O7 peut notamment être réduite, pour former la phase Na4Mn3O7 et oxydée, par l’action de l’activité redox de l’oxygène, donnant des capacités de 160 et 120 mAh/g, respectivement. Dans le but d’élargir l’étude à un métal de transition pouvant être oxydé à un état de valence +V, la phase isoformulaire Na2V3O7 a également été étudiée et un Na+ peut être réversiblement extrait de cette dernière. / N the coming years, the production of Energy will have to go through the use of more environmentally friendly means such as renewable energies. However, their intermittent nature requires the establishment of a large-scale storage. Among the various technologies available, Na-ion batteries appear as a solution of choice thanks to unlimited sodium resources. In this context, we are interested in the synthesis and characterization of new positive electrode materials for Na-ion batteries. The transition metal oxides, and more particularly the Na-Mn-O system, have drawn our attention to the benefits of manganese in terms of non-toxicity, low cost and abundance. The phase Na4Mn2O5 (with oxygen vacancies) and Na2Mn3O7 (with manganese vacancies) show interesting specific capacities by the action of various redox phenomena. Na2Mn3O7 may be reduced, to form the phase Na4Mn3O7 and oxidized, by the action of the oxygen redox activity, giving capacities of 160 and 120 mAh/g, respectively. In order to extend the study to a transition metal that can be oxidized to a +V valence state, Na2V3O7 has also been studied and one Na+ can be reversibly extracted from it.

Geträgerte Vanadiumoxidkatalysatoren sind wegen ihrer Vielseitigkeit bei Oxidationsreaktionen von großem Interesse. Der Schlüssel zum Verständnis der zugrunde liegenden Mechanismen ist ein weitreichendes Verständnis in die mikroskopische Struktur der Vanadiumoxide unter verschiedenen Bedingungen sowie die Art der Bindung an die Oberfläche des Trägers. In der vorliegenden Arbeit werden die Systeme Vanadiumoxid/Aluminiumoxid und Vanadiumoxid/Siliziumoxid mittels Dichtefunktionaltheorie in Kombination mit statistischer Thermodynamik untersucht. Als Modelle für Aluminiumoxid werden die stabile alpha-Al2O3 bzw. die metastabile kappa-Al2O3 Phase verwendet und ein ultradünner, epitaxialer SiO2 Film auf Mo(112) wird als Siliziumoxidsupport verwendet. Dessen einzigartige atomare Struktur, genauso wie diejenige eindimensionaler Silizumoxid-Streifen, die mit dem Film auf der Oberfläche koexistieren, wird durch kombinierte experimentelle und theoretische Untersuchungen aufgeklärt. Die Bildung einer neuen, "sauerstoffreichen" Phase des SiO2/Mo(112) Films wird vorhergesagt und deren Existenz anschließend experimentell gezeigt. Die Zielsetzung der Arbeit ist es zu Verstehen, wie Vanadiumoxidaggregate mit der Oberfläche verknüpft sind und den Einfluß des oxidischen Trägers auf die geometrische und elektronische Struktur der geträgerten Spezies zu untersuchen. Der Schwerpunkt liegt auf der Suche nach einer Korrelation von Struktureigenschaften mit der katalytischen Aktivität von Reaktionen die nach dem Mars-van Krevelen Mechanismus ablaufen. Hierzu wird die Energie für die Bildung eines Sauerstoffdefekts als Indikator für die Leistungsfähigkeit des Katalysators verwendet. Der Einfluß der Trägerstruktur auf die Schwingungsmoden des Interfacebereichs wird untersucht, um den Ursprung von charakteristischen Banden im experimentellen Spektrum von Vanadiumoxid/Siliziumoxid und Vanadiumoxid/Aluminiumoxid zu ergründen. / Supported vanadium oxide catalysts are of high interest because of their potential in a wide variety of oxidation reactions. A key step to fully understand the catalytic mechanism is a profound knowledge of the microscopic structure of the active vanadia species under various conditions and the way they are anchored to the support material. In the present work, density functional theory in combination with statistical thermodynamics is employed to investigate two vanadia-based systems, i.e., vanadia/alumina and vanadia/silica. The alumina support is modeled using the stable alpha-Al2O3 and the metastable kappa-Al2O3 phases, whereas ultrathin SiO2 film epitaxially grown on Mo(112) is employed as a silica support. The unique atomic structure of the latter as well as that of the one-dimensional silica stripes, found to coexist with the film in a perfect registry, are precisely determined based on combined theoretical and experimental studies. Moreover, the formation of a new, "O-rich" phase of the SiO2/Mo(112) film is predicted, whose existence is subsequently experimentally confirmed. The aim of the thesis is to provide an understanding on how vanadia aggregates anchor to the surface and to examine the role of the oxide support on the molecular and electronic structure of the stable VOx species. The efforts have focused on finding correlations between structural properties and catalytic activity in reactions proceeding via the Mars-van Krevelen mechanism. In accord therewith, the formation energy of a lattice oxygen defect is used as an indicator of catalytic performance. The influence of the support structure on the interface vibrational modes is analyzed in an attempt to shed light on the origin of the characteristic bands observed in the experimental spectra of vanadia/alumina and vanadia/silica model catalysts.

<p>This thesis addresses the electronic structure of vanadium and copper oxides using soft X-ray absorption (SXA) spectroscopy and resonant inelastic X-ray scattering (RIXS) at high brightness synchrotron radiation sources. In RIXS incident photons, tuned to the energy of specific absorption resonances, are inelastically scattered leaving behind a low energy valence excitation in the system studied. Effects of electron localization are reflected by the occurrence of low-energy excitations in form of dd- and charge-transfer excitations that are modelled by cluster calculations. Band-like states are dominating when the intermediate core excited state is delocalized.</p><p>RIXS at V 2p and O 1s resonances has been used to study the electronic structure of the monovalent vanadium oxides VO₂ and V₂O₃, and of the mixed valence compounds, NaV₂O₅ and V₆O₁₃. For NaV₂O₅ and V₆O₁₃ significant contributions from localized low-energy excitations reflect the partly localized character of their valence band electronic structure, whereas VO₂ and V₂O₃ appear mostly as band-like. Effects of carrier doping are addressed for the case of Mo doping into VO₂ and reveal a quasi-rigid band behavior. In the cases of VO₂ and V₆O₁₃ the temperature dependent metal-insulator transition could be monitored by following the spectral evolution of bands originating from V 3d and V 3d - O2p hybridized states. For Na₂V₃O₇ nanotubes it was possible to selectively probe states from the apical and the basal oxygen sites of VO₅ pyramids that constitute these nanotubes. Furthermore, the RIXS technique has been demonstrated to be highly valuable in characterizing the charge transfer processes that accompany lithium insertion into vanadium oxide battery cathodes. Finally, for insulating cuprates RIXS at O 1s, Cu 3p and Cu 3s resonances has been recorded at high-resolution for the detailed investigation of crystal field excitations.</p>

This thesis addresses the electronic structure of vanadium and copper oxides using soft X-ray absorption (SXA) spectroscopy and resonant inelastic X-ray scattering (RIXS) at high brightness synchrotron radiation sources. In RIXS incident photons, tuned to the energy of specific absorption resonances, are inelastically scattered leaving behind a low energy valence excitation in the system studied. Effects of electron localization are reflected by the occurrence of low-energy excitations in form of dd- and charge-transfer excitations that are modelled by cluster calculations. Band-like states are dominating when the intermediate core excited state is delocalized. RIXS at V 2p and O 1s resonances has been used to study the electronic structure of the monovalent vanadium oxides VO2 and V2O3, and of the mixed valence compounds, NaV2O5 and V6O13. For NaV2O5 and V6O13 significant contributions from localized low-energy excitations reflect the partly localized character of their valence band electronic structure, whereas VO2 and V2O3 appear mostly as band-like. Effects of carrier doping are addressed for the case of Mo doping into VO2 and reveal a quasi-rigid band behavior. In the cases of VO2 and V6O13 the temperature dependent metal-insulator transition could be monitored by following the spectral evolution of bands originating from V 3d and V 3d - O2p hybridized states. For Na2V3O7 nanotubes it was possible to selectively probe states from the apical and the basal oxygen sites of VO5 pyramids that constitute these nanotubes. Furthermore, the RIXS technique has been demonstrated to be highly valuable in characterizing the charge transfer processes that accompany lithium insertion into vanadium oxide battery cathodes. Finally, for insulating cuprates RIXS at O 1s, Cu 3p and Cu 3s resonances has been recorded at high-resolution for the detailed investigation of crystal field excitations.

In this dissertation we reported our experimental investigation of the magnetic properties of nine low-dimensional vanadium compounds. Two of these materials are completely new (Pb2V5O12 and Pb2VO(PO4)2) and were found during our search for new low-dimensional vanadium oxides. Among the other seven vanadium compounds studied, three were physically investigated for the first time (Sr2VO(PO4)2, BaZnVO(PO4)2 and SrZnVO(PO4)2). Two had hitherto only preliminary, and wrongly interpreted, susceptibility measurements reported in the literature (Sr2V3O9 and Ba2V3O9) while the remaining two (Li2VOSiO4 and Li2VOGeO4) were previously investigated in some detail but the interpretation of the data was controversial. We investigated the magnetic properties of these materials by means of magnetic susceptibility and specific heat (Cp(T)) measurements (as well as single crystal ESR measurements in the case of Sr2V3O9). We synthesized the samples necessary for our physical studies. That required a search of the optimal synthesis conditions for obtaining pure, high quality, polycrystalline samples. Single crystals of Sr2V3O9 and Pb2VO(PO4)2 were also successfully grown. Pb2VO(PO4)2, BaZnVO(PO4)2, SrZnVO(PO4)2, Li2VOSiO4 and Li2VOGeO4 were found to be experimental examples of frustrated square-lattice systems which are described by the J1-J2 model. We found that Li2VOSiO4 and Li2VOGeO4 posses a weakly frustrated antiferromagnetic square lattice while Pb2VO(PO4)2, BaZnVO(PO4)2 and SrZnVO(PO4)2 form a more strongly frustrated ferromagnetic square lattice. Pb2V5O12 is structurally and compositionally related to the two dimensional A2+V4+nO2n+1 vanadates. Its structure consists of layers formed by edge- and corner-shared square VO5 pyramids. The basic structural units are plaquettes consisting of six corner-shared pyramids pointing in the same direction, which form a spin lattice of novel geometry. / In dieser Dissertation berichteten wir über unsere experimentelle Untersuchung der magnetischen Eigenschaften von neun Niedrigdimensionalen vanadiumverbindungen. Zwei dieser Materialien sind vollständig neu (Pb2VO12 und Pb2VO(PO4)2) und wurden während unserer Suche nach neuen Niedrigdimensionalen Vanadiumoxiden gefunden. Unter den anderen sieben studierten Vanadiumverbindungen, wurden drei physikalisch zum ersten Mal nachgeforscht (Sr2VO(PO4)2, BaZnVO(PO4)2 und SrZnVO(PO4)2). Zwei hatten bisher nur einleitendes, und falsch gedeutet, magnetische Susceptibilitaet Messungen, die in der Literatur berichtet wurden (Sr2V3O9 und Ba2V3O9) während die restlichen zwei (Li2VOSiO4 und Li2VOGeO4) vorher in irgendeinem Detail aber in der Deutung der Daten waren umstritten nachgeforscht wurden. Wir forschten die magnetischen Eigenschaften dieser Materialien mittels der magnetischen Susceptibilitaet und der spezifischen Waerme (Cp(T)) nach (sowie ESR-Messungen des einzelnen Kristalles im Fall von Sr2V3O9). Wir synthetisierten die Proben, die für unsere körperlichen Studien notwendig sind. Das erforderte eine Suche der optimalen Synthesezustände für das Erreichen der reinen, hohen Qualität, polykristalline Proben. Einzelne Kristalle von Sr2V3O9 und von Pb2VO(PO4)2 wurden auch erfolgreich gewachsen. Pb2VO(PO4)2, BaZnVO(PO4)2, SrZnVO(PO4)2, Li2VOSiO4 und Li2VOGeO4 werden gefunden, um experimentelle Beispiele der frustrierten Quadrat-Gittersysteme zu sein, die durch das J1-j2 model. Wir fanden daß posses Li2VOSiO4 und Li2VOGeO4 ein schwach frustriertes antiferromagnetische quadratisches Gitter, während Pb2VO(PO4)2, BaZnVO(PO4)2 und SrZnVO(PO4)2 ein stärker frustriertes ferromagnetisches quadratisches Gitter bilden. Pb2V5O12 strukturell und zusammenhängt kreativ mit den zweidimensionalen vanadates A2+V4+nO2n+1 beschrieben werden. Seine Struktur besteht aus den Schichten, die durch Rand und Ecke-geteilte quadratische Pyramiden VO5 gebildet werden. Die grundlegenden strukturellen Maßeinheiten sind die plaquettes, die aus sechs Ecke-geteilten Pyramiden bestehen, die in die gleiche Richtung zeigen, die ein Drehbeschleunigunggitter von Romangeometrie bilden.

Die vorliegende Arbeit enthält neuartige Ergebnisse festkörperanalytischer Untersuchungen zu Synthese, Struktur und Eigenschaften von anodischen Konversionsschichten auf Vanadium und Zirkonium. Schwerpunkte sind die Darstellung anodischer Oxidschichten auf den Metallen Vanadium und Zirkonium sowie ihre Charakterisierung mit ausgewählten Methoden der Festkörperanalytik. Am Beispiel des Vanadiums wird die anodische Schichtbildung in Essigsäurebasiselektrolyten untersucht. Unter anderem wird anhand von Strom-Spannungs-Kennlinien das unterschiedliche anodische Verhalten der physikalisch ähnlichen Metalle Vanadium und Zirkonium diskutiert. Neben den Methoden der Röntgenbeugung, Infrarotspektroskopie, Photoelektronenspektroskopie und Elektronenmikroskopie wird die Ramanspektroskopie als ein geeignetes Mittel zur Unterscheidung der Oxidphasen verwendet. Die amorphen VOx-Schichten und kristallinen ZrO2- bzw. modifizierten Schichten wurden sowohl unter anodischen als auch unter elektrochemischen Plasmabedingungen erzeugt. Die Korrelation zwischen Schichtstruktur und Syntheseverfahren wird herausgearbeitet.