Oxygen deficiency and excess of rutile titania (1 1 0) surfaces analyzed by ion scattering coupled with elastic recoil detection

Abstract

Oxygen deficiency and excess of rutile titania (TiO 2) surfaces are important factors for catalytic activities of metal nano-particles on the TiO 2 supports. Medium energy ion scattering (MEIS; 80 keV He +) coupled with elastic recoil detection analysis (ERD; 150 keV Ne +) can determine the numbers of bridging O (O br) vacancies (V O) and excess O atoms adsorbed on the 5-fold Ti rows of TiO 2(1 1 0) surfaces. The amounts of V O and adsorbed O were derived by H 2O and 18O 2 exposure followed by ERD and MEIS analyses, respectively. The present analysis revealed that only about a half of V O are filled and a comparable amount of O atoms are adsorbed on the reduced TiO 2(1 1 0) surface after exposure to O 2 (1000 L; 1 L = 1 × 10 −6 Torr s) at room temperature (RT). We also detected the adsorbed O for the hydroxylated TiO 2(1 1 0) after 18O 2 exposure at RT. Finally, it is shown that the O adsorbed on the Ti rows reacts with CO probably to form CO 2 at RT. Based on the results obtained here, we clarify the reason why only a half of V O are filled by exposing reduced surface to O 2 at RT and what is the primary source of subsurface excess electronic charge, which acts as a leading part of the surface electrochemistry and gives the defect state in the band gap seen in the valence band spectra for reduced and hydroxylated TiO 2(1 1 0) surfaces.