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 O2-exposed SnO2 thin film have been studied with X-ray photoelectron spectroscopy (XPS) from room temperature up to 473 K. Adsorbed oxygen species O2−2, O−2 and O− were observed in the O 1s level spectra after O2 exposure. With the rise of O2 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 O2-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.