Electronic states of chemisorbed oxygen species and their mutually related studies on SnO2 thin film

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 (O-b, O-2(2-), O-, O-2(-)) On the topmost layer of SnO2 thin film with X-ray photoelectron spectroscopy (XPS). O-b, was assigned fo be O-2(-) 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 O-2(2-) and O-. The proportion of O-b 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 the electronic states of O-b modified to O- produced. Some of O-b species coupled with these vacancies, and from O2-. This newly produced O- reacted with CH4 at 473 K.