Heat treatment effects on dissociative adsorbates from methane on an Ar-ion sputtered single crystal of LiNbO 3

Abstract

The dissociative adsorbed states of methane and the effects of heat treatments have been studied on an Ar-ion sputtered single crystal of LiNbO 3 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 LiNbO 3 reacted with O −, 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 400°C 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 H 2O during TPD up to 400°C. 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 100°C up to 400°C, we suspected that some part of the produced methanol dissociated again to CH 3 and OH − during heating. This OH − was desorbed as H 2O during heating up to 400°C.