AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM4
Dissociative Adsorption and Electron Stimulated Desorption of Cl on TiO@sub 2@(110) Studied by STM, AES and ISS

Thursday, November 5, 1998, 9:20 am, Room 309

Session: Oxide Surface Chemistry
Presenter: U. Diebold, Tulane University
Authors: U. Diebold, Tulane University
G. Leonardelli, TU Vienna, Austria
W. Hebenstreit, Tulane University
M. Schmid, TU Vienna, Austria
P. Varga, TU Vienna, Austria
Correspondent: Click to Email
The catalytic reactivity of a metal oxide can be significantly altered by adsorbed halogen species, but little is known about the adsorption of chlorine on well-characterized model oxide surfaces. We present a combined study of atomically-resolved Scanning Tunneling Microscopy (STM), Auger Electron Spectroscopy (AES) and Ion Scattering Spectroscopy (ISS) of chlorine adsorption on TiO@sub 2@(110). Chlorine was dosed from a calibrated electrolytic AgCl cell at room temperature. STM reveals a dissociative adsorption process. For small doses (@<=@0.01 Cl atoms/unit cell), a large average separation (26 Å) between Cl-Cl pairs indicate that adsorption energy is transformed into kinetic energy of the Cl atoms. The saturation coverage for an annealed surfaces is 0.3 Cl/unit cell. STM does not show any prefered adsorption at step edges, kink sites or oxygen defect sites. Chlorine atoms can be desorbed from the surface with STM by scanning at sample bias voltages @>=@+4 V. AES measurements are complicated by electron stimulated desorption of the Cl atoms. The desorption cross section is 3 10@super -20@cm@super 2@ for a sputtered surface and >2 10@super -17@ cm@super 2@ for a annealed surface. ISS (He@super +@ ions 1keV, scattering angle 90°) detects Cl only after adsorption on a sputtered surface, while the ISS signal of an annealed surface remains unchanged during adsorption of chlorine.