First-principles values were reported for the electrical dipole moment and for the formation and activation energies of adatoms and vacancies migrating on (100) surfaces. The effect of the electrical dipole energy of these point defects upon the rate of mass transport along charged metal-electrolyte interfaces was considered. It was found that adatoms and vacancies exhibited positive surface dipole moments which, for positive electrode potentials, tended to reduce the formation and activation energies and increased the mobility of the point defects. Atom migration via an exchange process which involved the intermediate formation of dimers was also considered, and it was found that the surface dipole moment of Cu and Ag dimers was negative. This implied that they tended to become more mobile for negative potentials. However, because of their large activation energies, it was concluded that an exchange process was unlikely to provide an energetically favorable mechanism for migration. The Au dimer had a small positive dipole moment, which implied that the exchange process could contribute to surface transport, but only on neutral surfaces.

Migration of Point Defects at Charged Cu, Ag and Au (100) Surfaces. J.E.Müller, H.Ibach: Physical Review B, 2006, 74[8], 085408 (10pp)