ELECTRIC-FIELD INHIBITION AND PROMOTION OF EXCHANGE DIFFUSION ON PT(001)

Direct observations of a Pt adatom migrating on the Pt(001) plane in the presence of an externally applied electric field show that a positive field raises, and a negative field lowers, the activation barrier for the adatom-substrate-atom exchange process. At field strengths of 1.5 V/angstrom and above, inhibition of the exchange mechanism is sufficient to change the diffusion mode from exclusively exchange displacements to a mode that includes hops. The effect of the electric field is explained by an electron-transfer process which changes the bonding of the adatom to neighboring surface atoms.