Defect-Induced Water Bilayer Growth on Anatase TiO₂(101)

Abstract

Preparing\nan anatase TiO₂(101) surface with a high density\nof oxygen vacancies and associated reduced Ti species in the near-surface\nregion results in drastic changes in the water adsorption chemistry\ncompared to adsorption on a highly stoichiometric surface. Using synchrotron\nradiation excited photoelectron spectroscopy, we observe a change\nin the water growth mode, from layer-by-layer growth on the highly\nstoichiometric surface to bilayer growth on the reduced surface. Furthermore,\nwe have been able to observe Ti³⁺ enrichment at the surface\nupon water adsorption. The Ti³⁺ enrichment occurs concomitant\nwith effective water dissociation into hydroxyls with a very high\nthermal stability. The water bilayer on the reduced surface is thermally\nmore stable than that on the stoichiometric surface, and it is more\nefficient in promoting further water dissociation upon heating. The\nresults thus show how the presence of subsurface defects can alter\nthe wetting mechanism of an oxide surface.