The adsorption of water on r-TiO2(110) has been investigated with thermal desorption spectroscopy (TDS) and helium atom scattering. Conventional TDS using a mass spectrometer and He-TDS monitoring reflected He beam intensity consistently show the existence of a structurally well-defined monolayer as well as a highly ordered second layer of water and a disordered multilayer phase. He diffraction patterns recorded along the high symmetry [001], equation image, and equation image directions reveal a well-ordered superstructure with (1x1) symmetry, providing strong evidence for the absence of a partially dissociated monolayer on the perfect parts of the substrate. No changes in the diffraction patterns are observed after irradiation with UV-light.
Hydrogen concentrations in ZnO single crystals exposing different surfaces have been determined to be in the range of (0.02–0.04) at.% with an error of ±0.01 at.% using nuclear reaction analysis. In the subsurface region, the hydrogen concentration has been determined to be higher by up to a factor of 10. In contrast to the hydrogen in the bulk, part of the subsurface hydrogen is less strongly bound, can be removed by heating to 550°C, and reaccommodated by loading with atomic hydrogen. By exposing the ZnO(10-10) surface to water above room temperature and to atomic hydrogen, respectively, hydroxylation with the same coverage of hydrogen is observed.