Electronic States of Chemisorbed Oxygen Species and Their Mutually Related Studies on SnO2Thin Film

Abstract

Not only the clarification of chemisorbed oxygen species on oxides but also the variation of electronic states of these oxygen species under reaction condition are quite important to both science and applications. We proved the presence of four kinds of chemisorbed oxygen species (Ob, O22-, O-, O2-) on the topmost layer of SnO2 thin film with X-ray photoelectron spectroscopy (XPS). Ob was assigned to be O2- ion at the bridging site on the topmost layer of SnO2 (110) surface without oxygen vacancies around it by comparison between the binding energy values of the peak in XPS spectra and that obtained from the convoluted partial electronic density of states which were calculated using the density functional theory (DFT). The intensity variation of Ob during heat treatment up to 773 K with evacuating was weakly and inversely related to that of O22- and O-. The proportion of Ob and O- decreased after CH4 exposure at 473 K. We considered that highly reactive oxygen species, O- reacted with CH4 at 473 K, then oxygen vacancies at the topmost bridging site were produced. Some of Ob species coupled with these vacancies, and the electronic states of Ob modified to O- from O2-. This newly produced O- reacted with CH4 at 473 K.