Regensburg 2007 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 15: Poster Session
DS 15.44: Poster
Dienstag, 27. März 2007, 15:00–17:00, Poster B
The structure and composition of oxidized and reduced tungsten oxide films — •Christoph Rameshan, Simon Penner, Bernhard Klötzer, Xianjie Liu, and Frederik Klauser — Institut für Physikalische Chemie Universität Innsbruck, Innrain 52a, A-6020 Innsbruck
The structure, morphology and composition of pure WO3 thin films deposited onto vacuum-cleaved NaCl(001) single crystals were studied at substrate temperatures up to 580 K and under different oxidative and reductive treatments in the temperature range 373-873 K by transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and x-ray photoelectron spectroscopy (XPS). A transition from an amorphous structure obtained after deposition at 298 K to a more porous structure with small crystallites at the highest substrate temperatures was observed. XPS spectra reveal the presence of W6+ irrespective of the preparation procedure. Significant changes in the film structure were only observed after an oxidative treatment in 1 bar O2 at 673 K, which induces crystallization of a monoclinic WO3 structure. After raising the oxidation temperature to 773 K, the film shows additional reconstruction and a hexagonal WO3 structure becomes predominant. This hexagonal structure persists at least up to 873 K oxidation temperature. However, these structural transformations observed upon oxidation were almost completely suppressed by mixing the WO3 thin film with a second oxide, e.g. Ga2O3. Reduction of the WO3 films in 1 bar H2 at 723-773 K induced the formation of the β -W metal structure, as evidenced by SAED and XPS.