Water vapor interactions with polycrystalline titanium surfaces

The initial interactions of water vapor with polycrystalline titanium surfa ces were studied at room temperature. Measurements of water vapor surface a ccumulation were performed in a combined surface analysis system incorporat ing direct recoils spectrometry (DRS), Auger electron spectroscopy and X-ra y photoelectron spectroscopy. The kinetics of accommodation of the water di ssociation fragments (H, O and OH) displayed a complex behavior depending n ot only on the exposure dose but also on the exposure pressure. For a given exposure dose the efficiency of chemisorption increased with increasing ex posure pressure. DRS measurements indicated the occurrence of clustered hyd roxyl moieties with tilted O-H bonds formed even at very low surface covera ge. A model which assumes two parallel routes of chemisorption, by direct c ollisions (Langmuir type) and by a precursor state is proposed to account f or the observed behavior. The oxidation efficiency of water seemed to be mu ch lower than that of oxygen. No Ti4+ states were detected even at high wat er exposure values. It is likely that hydroxyl species play an important ro le in the reduced oxidation efficiency of water. (C) 1999 Elsevier Science B.V. All rights reserved.