Electric-Field-Induced Depolarization of Si-C Bond Leads to a Strongly Reduced Barrier for Alkyl-Hopping on Si(001)

Tip-induced hopping of the ethyl fragment (-C2H5) of diethyl ether molecules reacted on Si(001) was shown to be a field-driven process. Although the hopping rate increases continuously with increasing bias voltage, it remains constant when varying the tunneling current. No hopping events are observed at 50 K. The process is thus concluded to be thermally activated with the respective energy barrier being reduced by the applied electric field. At a positive sample bias, the field in the tunneling gap is strong enough to effectively depolarize and thus weaken the covalent Si-C bond. The effect of this depolarization on the hopping barrier is quantified and compared to the strength of the electric field.