Reducible transition metal oxides are key components in many catalytic, sensing and device systems however relatively little quantitative information exists on the nature of non-stoichiometric phases. In this study, we show how substrates can be prepared in a controlled manner with designed levels of non-stoichiometry. These in turn will facilitate quantitative studies of the interaction of non-stoichiometric oxide materials with adsorbates, reactants and supported metallic particles. We grow stoichiometric ultrathin films of TiO 2 in the rutile phase and (110) orientation on W(100) which represent our baseline material. Films are then doped with submonolayer excess Ti and annealed to create films with quantified levels of non-stoichiometry. The study relies heavily on previous scanning tunnelling microscopy work, which shows the dominant nature of Ti interstitial defects in the surface chemistry of TiO 2 , combined with detailed and quantitative X-ray photoelectron spectroscopy measurements.
We have determined the structure of a complex rhodium carbonyl chloride [Rh(CO)2Cl] molecule adsorbed on the TiO2(110) surface by the normal incidence x-ray standing wave technique. The data show that the technique is applicable to reducible oxide systems and that the dominant adsorbed species is undissociated with Rh binding atop bridging oxygen and to the Cl found close to the fivefold coordinated Ti ions in the surface. A minority geminal dicarbonyl species, where Rh-Cl bond scission has occurred, is found bridging the bridging oxygen ions forming a high-symmetry site.
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