Tip-Induced $\beta$-Hydrogen Dissociation in an Alkyl Group Bound on Si(001)

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 > +1.5V leads to tip-induced C-H cleavage of a $\beta$-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.