The fluctuations of steps and the shapes of islands on metal surfaces generally depend strongly on the electrode potential, an effect that has been attributed to the interaction of local surface dipole moments with the double-layer field. In order to understand the details of this effect,we have calculated the relevant energies and dipole moments for the diffusion processes that govern the fluctuations of steps and island shapes on Ag(1 0 0). The corresponding rates have been used in kinetic Monte-Carlo simulations to explore the dynamics of these structures. Due to the field-dipole interactions the mobility of the surface becomes larger with increasing electrode potential. Fourier analysis allows us to determine the step stiffness and the kink energy, and from the shape of the islands we have obtained the line tension. All three quantities decrease with increasing double-layer field. (C) 2009 Elsevier Ltd. All rights reserved.