Non-stoichiometric oxide surfaces and ultra-thin films:: Characterisation of TiO2

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 ultra-thin films of TiO2 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 TiO2, combined with detailed and quantitative X-ray photoelectron spectroscopy measurements.