Probing the influence from residual Ti interstitials on water adsorption on TiO2(110)

Reduced, stoichiometric and oxidized TiO2(110) surfaces have been compared using valence photoelectron spectroscopy. The results show that the intensity from the band-gap state carries contributions from both oxygen surface vacancies and residual Ti interstitials, present after the sample cleaning procedure. The density of Ti interstitials was found to be 0.05 +/- 0.02 monlayers (ML), while the density of oxygen vacancies was estimated to 0.09 +/- 0.01 ML. Both these values are in good agreement with previous STM studies. O 1s core-level photoelectron spectra show that oxidation of the interstitials had negligible effect on the OH-H2O balance within the first water layer. The characteristic OH-H2O balance found on a surface free from oxygen vacancies previously reported [Walle et al., Phys. Rev. B 80, 235436 (2009)] is therefore an inherent property of the TiO2(110) surface; that is, the primary mechanism leading to partial dissociation is not related to the presence of residual Ti interstitials.