From tungsten hexacarbonyl adsorption on TiO2(110) surface to supported tungsten oxide phases

Abstract: Synchrotron-based photoemission spectroscopies were used to study the adsorption of tungsten hexacarbonyl on (110) TiO2 surfaces: experiments using W4f and Ti2p intensities variations show that, at 140K, the hexacarbonyl growth proceeds via a layer-by-layer mode. Moreover, it was evidenced using both core levels and valence band experiments that, after back to room temperature, W(CO)6 desorbs without significant decomposition. However, low energy (500eV) ion (Ar+) irradiation can allow partial decomposition of tungsten hexacarbonyl molecules leading to sub-carbonyl tungsten molecules. The bonding of sub-carbonyl species to the TiO2 surface was then stronger than the one of hexacarbonyl: these chemisorbed species do not desorb when going back to room temperature allowing a higher amount of metal to remain on the surface. Subsequent annealing gets rid of remaining carbonyl groups. This phenomenon leaves tungsten atoms at the TiO2 surface. The annealing organizes these W atoms in the 400–600K temperature range leading to WO x phases, which are almost free of carbon. The oxidation degree of these phases is strongly related to tungsten amount remaining at the surface. [Copyright &y& Elsevier]