Oxygen deficiency and excess of rutile titania (110) surfaces analyzed by ion scattering coupled with elastic recoil detection
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms(2011)
Abstract
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; 80keV He+) coupled with elastic recoil detection analysis (ERD; 150keV Ne+) can determine the numbers of bridging O (Obr) vacancies (VO) and excess O atoms adsorbed on the 5-fold Ti rows of TiO2(110) surfaces. The amounts of VO and adsorbed O were derived by H2O and 18O2 exposure followed by ERD and MEIS analyses, respectively. The present analysis revealed that only about a half of VO are filled and a comparable amount of O atoms are adsorbed on the reduced TiO2(110) surface after exposure to O2 (1000L; 1L=1×10−6Torrs) at room temperature (RT). We also detected the adsorbed O for the hydroxylated TiO2(110) after 18O2 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 VO are filled by exposing reduced surface to O2 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(110) surfaces.
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Key words
Oxygen vacancies,Oxygen adsorption,TiO2(110),Defect state,Medium energy ion scattering,Elastic recoil detection
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