Ethylene adsorption and decomposition on Si(100) 2*1: a semi-empirical quantum chemical study

Abstract

The interaction of ethylene with the Si(100) 2*1 surface has been studied by a semi-empirical molecular orbital theory using a four-layer silicon cluster model Si₂₉H₂₄-C₂H₄. Ethylene is shown to create a di- sigma bond with the surface dimer sites, and to rehybridize to a near sp³ state. Its initial C-C double bond is reduced to nearly a single bond, while its C-H bonds are almost not weakened. Both the ethylene pi donation to the surface and the substrate back-donation to the ethylene pi * orbital result in the equilibrium di- sigma bonding geometry. The C₂H₄ decomposition behaviour is somewhat different from that for C₂H₂(ads) on Si(100), and C₂H₄(ads) on transition metals. Ethylene favours C-C bond scission first, and then dehydrogenation. The calculated vibrational properties of the C₂H₄(ads) and C₂H₄-induced species confirm the results of a recent HREELS study.