AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP17
Measurement of the Dependence of Bulk Defects on the Reactivity of the TiO@sub 2@(110) Surface

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: S.N. Thornburg, University of New Orleans
Authors: S.N. Thornburg, University of New Orleans
J.M. Burst, University of New Orleans
C.A. Ventrice, Jr., University of New Orleans
U. Diebold, Tulane University
Correspondent: Click to Email
Missing-atom point defects at metal oxide surfaces often enhance the reactivity of these surfaces towards the adsorption of simple molecules. A previous study of the adsorption of S on the TiO@sub 2@(110) surface found that the reactivity of this surface at temperatures >120°C was enhanced by the presence of bulk missing-oxygen defects.@footnote 1@ This was determined by measuring the S 2p uptake with x-ray photoelectron spectroscopy as a function of reduction time. However, this was performed on a new Ti O@sub 2@ crysta l, so the influence of bulk impurities on the uptake of S was difficult to determine. A technique for reoxidizing dark blue, bulk-reduced, TiO@sub 2@ crystals has been developed that allows us to return these crystals to a defect f ree clea r state. The degree of bulk reduction is monitored using optical spectroscopy and temperature dependent resistivity measurements with a four point probe. Optical spectroscopy measurements for both the dark blue and clear crystals show the same ab sorption edge at 3.0 eV, which corresponds to the bulk band gap of TiO@sub 2@. However, the dark blue crystals also show a strong absorption below 2.6 eV. Photoemission measurements of the S uptake, O reduction, and S peak shift at 250°C and room t emperature have been performed on both dark blue and clear crystals. At room temperature, the S saturates at approximately one monolayer coverage for both clear and bulk reduced crystals. At 250°C, the adsorbed S replaces the first few layers of oxygen atoms. The rate of S adsorption is found to depend on bulk reduction, but at a reduced rate as compared to the measurements on a new crystal. This indicates that bulk contaminants in new crystals are also influencing the S adsorption rate. @FootnoteText@ @footnote 1@E. L. D. Hebenstreit et al., Surf. Sci. 486, L467 (2001).