CHEMICAL SURFACE-DIFFUSION COEFFICIENT AND ORDERED C(2X2) ADSORBATE LAYER

Using the lattice gas model and transition-type-dependent type Monte C arlo method, we calculated the chemical surface diffusion coefficient with nearest-neighbour repulsion (epsilon(nn)) and next-nearest-neighb our attraction (epsilon(nnn)) (epsilon(nn) = 2.0\epsilon(nnn)\ = epsil on(int)) directly from Pick's first law. Our results show that the che mical diffusion coefficient depends on the structure of the adsorbate layer. When epsilon(int)/k(B)T greater than or equal to 1.20, the orde red lattice gas phase c(2 x 2) is established near c = 0.50. The prese nce of the ordered domains will greatly reduce the chemical surface di ffusion coefficient.