Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 14: Poster session I (Adsorption, Epitaxy and growth, Phase transitions, Surface reactions, Organic films, Electronic structure, Methods) (sponsored by Omicron Nanotechnology GmbH)
O 14.18: Poster
Montag, 27. März 2006, 18:00–21:00, P2
Why does molecular hydrogen adsorb on SiC(001)-c(4x2) but not on SiC(001)-(3x2)? An ab-initio investigation — •X. Peng, P. Krüger, and J. Pollmann — Institut für Festkörpertheorie, Wilhelm-Klemm-Str. 10, 48149 Münster
In recent experiments (V. Derycke et al. PRB 63, 201305) the amazing observation was made that molecular hydrogen readily adsorbs on the SiC(001)-c(4×2) surface while it hardly interacts with SiC(001)-(3×2) although both surfaces are characterized by similar Si dimers.
To elucidate the origin of the very different reactivities of H2 on these surfaces we have performed ab-initio density-functional calculations for a variety of hydrogenated surface configurations. In general, we find that intradimer adsorption of H2 on top of a single surface dimer is unlikely due to a significant energy barrier. Instead, interdimer adsorption of H2 molecules between two neigboring dimers can occur without an energy barrier when the dimers are sufficiently close-by. In that case, the H2 molecule dissociates by simultaneous adsorption of the two H atoms at the dangling bonds of two neighboring dimers. At the c(4×2) surface, the distance between neigboring dimers is small enough to easily allow for interdimer adsorption of H2 without any energy barrier. This holds for both the missing row asymmetric dimer (MRAD) as well as the alternating up and down dimer (AUDD) model. Intradimer adsorption on an up dimer in the AUDD model, as conjectured before, turns out to be unlikely due to the energy barrier mentioned above. At the 3×2 surface, on the contrary, H2 adsorption is strongly hindered due to a much too large distance between neighboring dimers.