RESUMEN
Atomic-scale chemical modification of surface-adsorbed ethyl groups on Si(001) was induced and studied by means of scanning tunneling microscopy. Tunneling at sample bias >+1.5 V leads to tip-induced C-H cleavage of aß-hydrogen of the covalently bound ethyl configuration. The reaction is characterized by the formation of an additional Si-H and a Si-C bond. The reaction probability shows a linear dependence on the tunneling current at 300 K; the reaction is largely suppressed at 50 K. The observed tip-induced surface reaction at room temperature is thus attributed to a one-electron excitation in combination with thermal activation.
RESUMEN
The reaction dynamics of methanol and water on Si(001) were investigated by means of molecular beam techniques. The initial sticking probability s0 was determined as a function of the kinetic energy of the incoming molecules, Ekin, and surface temperature, Ts. For both, methanol and water, a nonactivated reactional channel was observed; the dynamics were found to be determined by the reaction into the datively bonded intermediate state. A low conversion barrier was deduced for the conversion from this intermediate into the final state. It is attributed to the reaction mechanism, which proceeds via proton transfer from the OH-group of the datively bonded molecules to a Si surface atom. Despite this low conversion barrier, adsorption into the intermediate and further reaction via proton transfer were found to be largely decoupled.