Heat treatment effects on dissociative adsorbates from methane on an Ar-ion sputtered single crystal of LiNbO3

The dissociative adsorbed states of methane and the effects of heat treatments have been studied on an Ar-ion sputtered single crystal of LiNbO3 with X-ray photoelectron spectroscopy XPS.and a temperature programmed desorption TPD. method. It was found that the exposed methane on the Ar-ion sputtered single crystal of LiNbO3 reacted with Oy, and produced the partly dissociated C–H hydrocarbon species and the oxygenates such as methoxy and methanol at room temperature. Since the dissociated and produced C–H products were not desorbed from the surface even if the sample was heated at 4008C for 1 h in a vacuum chamber, the adsorbates on the Ar-ion sputtered sample seem to be adsorbed strongly. The slight increase of intensity of mass spectroscopy was observed only on H2O during TPD up to 4008C. Since the ratio of the carbon from the produced methanol to niobium ion and that of the adsorbed oxygen to niobium ion, measured by XPS, decreased during heating from 1008C up to 4008C, we suspected that some part of the produced methanol dissociated again to CH3 and OHy during heating. This OHy was desorbed as H2O during heating up to 4008C. q1998 Elsevier Science B.V. All rights reserved.