Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 18: Adsorption an Oberflächen I

O 18.4: Vortrag

Dienstag, 9. März 2004, 12:00–12:15, H38

Angular dependence of H2 dissociation at DB steps of Si(001) — •C. Stanciu and U. Höfer — Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg

The dynamics of dissociative adsorption of molecular hydrogen at the DB steps of Si(001) was investigated by performing angular dependent measurements of the initial sticking coefficient for different kinetic energies of H2 from a supersonic molecular beam. Optical second-harmonic generation (SHG) was used as a sensitive monitor of hydrogen coverage at the steps sites. For Ekin = 350 meV, a kinetic energy that considerably exceeds the mean barrier height of Ea = 80 meV, the polar distribution is strongly forward-peaked (∼ cos7.8θ) whereas for Ekin < Ea, H2-momentum parallel to the step edges was found to enhance dissociation, giving rise, e.g., to a broad polar distribution (∼ cos1.2θ) for Ekin = 30 meV. This behaviour contrasts the one previously observed for H2 adsorption on the terraces [1]. A sharp angular distribution, directed along the direction of the dangling bonds, was observed in that case for Ekin < Ea, indicating a strong lateral corrugation of the barrier height due to the high directionality of the dangling bonds. The behaviour at the steps, however, suggests the dominant influence of a geometric corrugation. Possible origins of such a lateral variation of the barrier position parallel to the step edges, and effects the steering of low energetic molecules will be discussed.

[1] M. Dürr and U. Höfer, Phys. Rev. Lett. 88, 076107 (2002)

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