Non-equilibrium effects in profile evolution measurements of surface diffusion

In this work, we use the Boltzmann-Matano method to determine the collective diffusion coefficient, D-C(theta), as a function of coverage, theta, from scaled coverage profiles obtained from Monte Carlo simulations using a lattice-gas model of O/W(110). We focus on the temporal behavior of D-C(theta) as the system approaches equilibrium. We demonstrate that the effective D-C(theta) obtained in this fashion depends strongly on the time regime chosen for analysis of the density profiles, and thus may differ significantly from results obtained from equilibrium simulations within ordered phases and close to phase boundaries. This is due to the interplay between spreading and phase-ordering kinetics and is reflected in enhanced particle number fluctuations with respect to the equilibrium case, Also, both the effective diffusion barriers of D-C and the location of phase boundaries, as extracted from the data, depend on time. (C) 2000 Elsevier Science B.V. All rights reserved.