AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS-TuP

Paper SS-TuP19
Dissociative Adsorption of Molecular Hydrogen on Si(001): Energy Dependence, Angular Distribution and Reaction Mechanism

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: M. Duerr, Max Planck Institut fuer Quantenoptik, Germany
Authors: M. Duerr, Max Planck Institut fuer Quantenoptik, Germany
M.B. Raschke, Max Planck Institut fuer Quantenoptik, Germany
U. Hoefer, Max Planck Institut fuer Quantenoptik, Germany
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The dissociative adsorption of molecular hydrogen on Si(001) surfaces was investigated by means of supersonic molecular beam techniques and optical second harmonic generation (SHG). Sticking on the flat surfaces shows strong activation with beam energy as well as surface temperature.@footnote 1@ Preparing single-domain surfaces by selectively passivating the step sites of vicinal Si(001) surfaces, polar and azimuthal distributions of the sticking coefficient could be measured. The polar distributions are found to be peaked towards the surface normal. However there is a strong azimuthal dependence, the distribution is considerably narrower (cos@super 12@) for incident angles perpendicular than parallel to the dimers (cos@super 3.5@). For multi-domain surfaces, the reduction of the sticking coefficients is more pronounced than it is to be expected by the reduction of normal energy. Therefore the energetic corrugation dominates the adsorption process. Temperature dependence of the sticking coefficient, deviation from normal energy scaling and azimuthal anisotropy result from the covalent bindings on the semiconductor surface, which lead to a strong corrugation of the potential energy surface and the strong influence of lattice vibrations on reaction dynamics. Proposed defect mediated mechanism, leading to an enhancement of sticking under glancing incidence can be excluded. @FootnoteText@ @footnote 1@ M. Duerr, M. B. Raschke, and U. Hoefer, J. Chem. Phys. (submitted).