Collective diffusion on strongly correlated heterogeneous surfaces

Collective diffusion coefficients are studied for heterogeneous bivariate s urfaces with two different topographies, namely the random patches and the chessboard-like ordered distributions. The topography is shown to affect st rongly the coverage dependence of the transport coefficients. Various diffu sion quantities like the chemical D, jump D-J and tracer D* diffusion coeff icients are analyzed by means of Monte Carlo simulations in the framework o f the fluctuation and the Kubo-Green theory. The behavior of diffusion coef ficients in small patches is mainly affected by the mobility of the particl es in the border vacancies, and a simple law is obtained for the ratio D(1) /D(0). For large patches the behavior is dominated by the mobility of parti cles in the central vacancies. In the limit of very large patches the diffu sion coefficients become independent of the energetic topography. (C) 1999 Elsevier Science B.V. All rights reserved.