The adsorption of liquid and vapor water on TiO2(110) surfaces: The role of defects

The adsorption of liquid and vapor water on defective and nearly defect-free TiO2(110) surfaces has been studied using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). The study focuses on examining electronic defects as created in vacuum and after exposure to both liquid and vapor water. Defective surfaces were prepared by electron-beam exposure and Ar+ bombardment. With exposure up to 10(4) L low vapor pressure (< 10(-5) Torr) water to defective surfaces, little change on Ti3d defect intensity was observed. However, defect intensities were greatly reduced after exposing defective surfaces to similar to 10(8) L higher vapor pressure (0.2-0.6 Torr) water for 5 min. More significantly, XPS and UPS spectra showed that electron-beam induced defects were completely removed upon liquid water exposure, while defects created by Arf bombardment were only partially removed. Surface defects created by Ar+ bombardment were removed more readily than sub-surface defects. Water adsorption on the surface has been quantified using the OH signal from the O 1s photopeak. For a nearly defect-free surface, water coverage was similar to 0.02 ML at 10(4) L exposure to low vapor pressure water, similar to 0.07 ML at 10(8) L exposure to higher vapor pressure water, and similar to 0.125 ML with liquid water exposure, respectively.