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 defec t-free TiO2(110) surfaces has been studied using X-ray photoelectron s pectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). Th e study focuses on examining electronic defects as created in vacuum a nd after exposure to both liquid and vapor water. Defective surfaces w ere prepared by electron-beam exposure and Ar+ bombardment. With expos ure up to 10(4) L low vapor pressure (< 10(-5) Torr) water to defectiv e surfaces, little change on Ti3d defect intensity was observed. Howev er, defect intensities were greatly reduced after exposing defective s urfaces to similar to 10(8) L higher vapor pressure (0.2-0.6 Torr) wat er for 5 min. More significantly, XPS and UPS spectra showed that elec tron-beam induced defects were completely removed upon liquid water ex posure, while defects created by Arf bombardment were only partially r emoved. Surface defects created by Ar+ bombardment were removed more r eadily than sub-surface defects. Water adsorption on the surface has b een quantified using the OH signal from the O 1s photopeak. For a near ly 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.