It was recalled that diffraction experiments could be easily used to measure the temporal evolution of a non-equilibrium system towards a new equilibrium state, and thereby deduce so-called non-equilibrium surface diffusion coefficients. However, it was unclear how the non-equilibrium diffusion coefficients which were deduced from such diffraction experiments should be interpreted. Monte Carlo simulations were made here of the behavior of the non-equilibrium tracer and of collective diffusion coefficients in a lattice-gas model, with attractive nearest-neighbour interactions, as the system changed from an initial random state to a (1 x 1) ordered state. Calculations were made of the time-dependence of the mean-square displacement upon time, and of collective diffusion which arose from relaxation of the non-equilibrium structure factor. Time-dependent non-equilibrium diffusion coefficients were determined, and time-dependent activation energies were deduced.

Diffusion Studies in Nonequilibrium Systems with Attractive Interactions. E.Arapaki, P.Argyrakis, M.C.Tringides: Physical Review B, 2000, 62[12], 8286-94