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RESEARCH PRODUCT

Structure et croissance de nanophases supportées d'oxyde de tungstène

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Tungsten trioxide nanorods can be elaborated on muscovite mica substrate through simple vapor deposition method. Growth of rods seems to follow a Stranski-Krastanov model. Their crystallography was investigated by TEM and reveals the presence of hexagonal phase. Such a metastable structure occurs from an interfacial hexagonal tungsten bronze which grows epitaxially on the substrate. This bronze phase contains potassium atoms coming from mica. Concerning the thickest rods, a monoclinic phase grows on the top of the hexagonal one. The hexagonal structure is thermally very stable: after annealing at 600°C, this phase is still detected whereas the rod morphology is destroyed. This point seems to indicate that processes which stabilize the hexagonal structure are different than those which are responsible of the rod shape. Potassium plays a major role in the formation of hexagonal WO3 phase. Additional tungsten oxide phase were elaborated on other substrates containing potassium atoms. Elaboration was then followed in situ by photoemission and SEXAFS and high affinity between potassium and tungsten was evidenced. Such an affinity can cause partial decomposition of tungsten hexacarbonyl molecule simply adsorbed at cryogenic temperature on substrate. Moreover, potassium atom presence leads to more oxidized phases than when this alkali metal is absent.