Molecular dynamics simulations were made of adatom diffusion along 2 close-packed steps on the (111) surfaces. Both metals were modelled by using many-body potentials which had been derived within the second-moment approximation to the tight-binding model. The simulation results predicted very different behaviors for the 2 metals. In the case of Au, diffusion was much faster along the step with (111) micro-facets (step B) whereas, in the case of Ag, diffusion was faster along the step with (100) micro-facets (step A). The difference between the diffusion coefficients along the steps was more marked in Au and, in both metals, the Arrhenius plots reflected a dynamic lowering of the activation barriers with respect to the static potential barriers. No evidence for an inversion of the anisotropy of diffusion was obtained. As the diffusion along steps was quasi 1-dimensional, the results of the simulations were compared with some which were based upon the Fokker-Planck equation for a 1-dimensional periodic potential. The agreement between the model and the simulations was remarkable for B steps on Au or Ag. The model predicted the temperature dependence of the rate, the correct proportion of long jumps, and the detailed behavior of the mean-square displacement. In the case of A steps, the agreement was satisfactory for Ag and was qualitative for Au. In the latter case, the diffusion path was rather different from a straight line and thus the use of a 1-dimensional model was questionable.

R.Ferrando, G.Tréglia: Physical Review B, 1994, 50[16], 12104-17