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

Oxygen deficiency and excess of rutile titania (TiO2) surfaces are important factors for catalytic activities of metal nano-particles on the TiO2 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 TiO2(1 1 0) surfaces. The amounts of V-O and adsorbed O were derived by H2O and O-18(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 TiO2(1 1 0) surface after exposure to O-2 (1000 L; 1 L = 1 x 10(-6) Torr s) at room temperature (Rh). We also detected the adsorbed O for the hydroxylated TiO2(1 1 0) after O-18(2) exposure at RT. Finally, it is shown that the O adsorbed on the Ti rows reacts with CO probably to form CO2 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 TiO2(1 1 0) surfaces. (C) 2011 Elsevier B.V. All rights reserved.