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    Surface Science Wednesday Sessions
       Session SS+SC-WeM

Paper SS+SC-WeM8
Electronegative Adsorbates on TiO@sub 2@: Reducing Effects of S and Cl

Wednesday, October 31, 2001, 10:40 am, Room 122

Session: Adsorption on Semiconductor and Metal Oxide Surfaces
Presenter: E.L.D. Hebenstreit, Tulane University
Authors: E.L.D. Hebenstreit, Tulane University
W. Hebenstreit, Tulane University
H. Geisler, Xavier University of Louisiana
C.A. Ventrice, Jr., University of New Orleans
D.A. Hite, Louisiana State University
P.T. Sprunger, Louisiana State University
U. Diebold, Tulane University
Correspondent: Click to Email
TiO@sub 2@(110) is a well-studied model catalyst with an abundance of technical applications. Sulfur and chlorine are common impurities in many catalytic systems which poison catalytic reactions. The adsorption of molecular S and Cl on TiO@sub 2@(110)(1 x 1) has been studied with scanning tunneling microscopy (STM), x-ray and ultraviolet photoelectron spectroscopy (XPS, UPS), and low energy electron diffraction (LEED). At room temperature both adsorbates bind dissociatively to 5-fold coordinated Ti atoms and oxygen vacancies. At elevated temperatures (120°C - 440°C), S and Cl replace surface oxygen atoms. S forms different types of superstructures in dependence on coverage and adsorption temperature. No long-range ordering was found in the a dsorbed layer for Cl. Both adsorbates reduce the surface but S leads to a stronger oxygen depletion than Cl. In photoemission experiments, adsorption of either S or Cl at elevated temperatures cause additional emission at the high binding energy side of t he valence band and increases emission from the defect state. Adsorption of S leads to band gap states which fill the band gap completely. Evidence was found that the reduction state of TiO@sub 2@ crystals strongly affects the surface coverage of S and Cl at elevated temperatures. The rate of the site exchange of the adsobates between a weakly bound precursor state on Ti and the replacement of oxygen is kinetically limited by the arrival of diffusing bulk defects at the surface.