Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 38: Halbleiteroberfl
ächen und -grenzfl
ächen
O 38.6: Vortrag
Dienstag, 8. März 2005, 12:00–12:15, TU EB301
Diffusion Pathways of Hydrogen across the Steps of a vicinal Si(001)-Surface — •P. Kratzer1, M. Lawrenz2, C. Schwalb2, M. Dürr2, and U. Höfer2 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, D-14195 Berlin — 2Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg
Surface diffusion of hydrogen on vicinal Si(001) surfaces is an interesting system to test theoretical results against experimental data, because selective hydrogen adsorption at the step sites only opens the experimental possibility to prepare a well-defined initial state. Diffusion of H away from the DB step sites has been observed by real-space STM studies at elevated temperatures. We have investigated the diffusion pathways by performing density-functional theory calculations using the gradient-corrected PW91 functional and the plane-wave+pseudopotential approach. While H atoms bind more strongly to the lower terrace sites than to the upper terrace sites, the calculated energy barriers show that H diffusion onto the upper terrace is strongly preferred, in agreement with the experimental findings. We learn from the calculations that a metastable intermediate where hydrogen binds weakly to an already four-fold coordinated Si atom at the step is responsible for the lowering of the "upward" diffusion barrier.