The surface mobility of silver electrodes - a kinetic Monte Carlo study

HARALD IBACH; NOELIA LUQUE; PAOLA QUAINO; WOLFGANG SCHMICKLER

Lausanne

Workshop; Ab Initio Electrochemistry - CECAM - HQ- EPFL; 2010

CECAM - ISE - ESF-SimBioMa

The fluctuations of steps and the shapes of islands on metal surfaces generallydepend 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(100). 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; both decrease with increasing double-layer field. The same method has been used to investigate Ostwald ripening of metal islands. On Au(100) this process was found to be kinetically hindered at ambient temperatures. In contrast, small islands on Ag(100) decayed readily at uncharged and at positively charged surfaces. The rate of ripening increases both with temperature and with the surface charge. The results  of the simulation have been compared with those of an analytic theory; substantial deviations have been observed. However, the same kind of systematic  deviations from the theory have been observed in experiments.Thus our simulations agree with experiments, while the analytic theory fails.