Photoemission study of dissociatively adsorbed methane on a pre-oxidized SnO2 thin film

The interactions between oxygen and an argon-ion etched SnO2 thin film and between methane and an O-2-exposed SnO2 thin film have been studied with X-ray photoelectron spectroscopy (XPS) from room temperature up to 473 K. Adsorbed oxygen species O-2(2-), O-2(-) and O- were observed in the O 1s level spectra after O-2 exposure. With the rise of O-2 exposure temperature, the presence of O- species was clearly observed. Methane adsorbed molecularly on an argon-ion etched SnO2 thin film at a room temperature. Methoxide species and/or methanol were observed in the C 1s level spectra after methane exposure on the O-2-exposed SnO2 surface. With the rise of CH4 exposure temperature, the proportion of methanol to methoxide increased. The subsequent reactions of adsorbed methane to methoxide and/or methanol progressed selectively depending on the kinds of oxygen species adsorbed on the SnO2 surface. (C) 2000 Elsevier Science B.V. All rights reserved.