Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 17: Poster Session I (Nanostructures at Surfaces; Metal Substrates: Epitaxy and Growth; Methods: Scanning Probe Techniques; Phase Transitions)
O 17.74: Poster
Montag, 26. März 2007, 17:30–20:30, Poster C
Adsorption of ethylene and acetylene on the SiC(001)-(3×2) surface — •Jürgen Wieferink, Peter Krüger, and Johannes Pollmann — Institut für Festkörpertheorie, Universität Münster
Most studies on the adsorption of small hydrocarbons on semiconductor surfaces have been focused on Si(001). Here, we present a complementary investigation of the adsorption on the silicon rich SiC(001)-(3×2) surface. This surface is characterized by two partial Si adlayers and a buckled Si dimer in the top adlayer which is remarkably similar to the Si(001) surface dimer.
Ethylene (C2H4) only adsorbs in an on top position above this dimer. Due to the saturation of the Si dangling bonds the buckling of the Si dimer is removed. Our calculations reveal that a twist in the C-C axis with respect to the Si dimer is energetically slightly favorable. This behavior is well known from C2H4 on Si(001) at saturation coverage and has been explained by intermolecular hydrogen Pauli repulsion. The existence of a twist on the more isolated dimers on SiC(001)-(3×2) strongly indicates that also intramolecular Pauli repulsion may play a vital role.
Acetylene (C2H2), on the other hand, may additionally adsorb on lower adlayers, though also in this case the on top structure is energetically favored. We show that on top acetylene impedes adsorption of acetylene on other layers due to a shift of the Fermi level. Thus, our studies suggest that the on top sites will rapidly become occupied while very high exposures would be needed for further acetylene adsorption.