Nonequilibrium effects in diffusion of interacting particles on vicinal surfaces -: art. no. 214728

We study the influence of nonequilibrium conditions on the collective diffusion of interacting particles on vicinal surfaces. To this end, we perform Monte Carlo simulations of a lattice-gas model of an ideal stepped surface, where adatoms have nearest-neighbor attractive or repulsive interactions. Applying the Boltzmann-Matano method to spreading density profiles of the adatoms allows the definition of an effective, time-dependent collective diffusion coefficient D-C(t)(theta) for all coverages theta. In the case of diffusion across the steps and strong binding at lower step edges we observe three stages in the behavior of the corresponding D-xx,C(t) (theta). At early times when the adatoms have not yet crossed the steps, D-xx,C(t) (theta) is influenced by the presence of steps only weakly. At intermediate times, where the adatoms have crossed several steps, there are sharp peaks at coverages theta < 1/L and theta > 1-1/L, where L is the terrace width. These peaks are due to different rates of relaxation of the density at successive terraces. At late stages of spreading, these peaks vanish and D-yy,C(t) (theta) crosses over to its equilibrium value, where for strong step edge binding there is a maximum at theta = 1/L. In the case of diffusion in direction along the steps the nonequilibrium effects in D-yy,C(t) (theta) are much weaker, and are apparent only when diffusion along ledges is strongly suppressed or enhanced. (c) 2005 American Institute of Physics.