ETHYLENE ADSORPTION AND DECOMPOSITION ON SI(100) 2 X-1 - A SEMIEMPIRICAL QUANTUM-CHEMICAL STUDY

The interaction of ethylene with the Si(100) 2 x 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) arid C2H4-induced species confirm the results of a recent HREELS study.