THEORY OF SURFACE ELECTROMIGRATION ON METALS - APPLICATION TO SELF-ELECTROMIGRATION ON CU(111)

We present a calculation of the force, due to electron scattering, act ing upon an adatom at the surface of a current-carrying metal, i.e., t he so-called ''wind'' force in surface electromigration. The force is calculated from the Feynman-Hellmann theorem in which the electron sca ttering states are computed with full multiple scattering corrections by a layer-KKR method. In contrast to previous jellium models, this ap proach allows the proper treatment of electron scattering by both the surface barrier and the substrate and its effect upon the current-carr ying states at the surface. The electron scattering force is computed for the self-electromigration of Cu adatoms on Cu(111). At room temper ature, the effective valence of the adatom is found to be almost-equal -to -21. We conclude that surface electromigration of Cu on Cu(111) is dominated by the electron scattering force and that any direct force originating from charge transfer to the adatom is likely to be unimpor tant in this case. The implications of the computed value of the wind force for the mass transport at a current-carrying metal surface are d iscussed.