Surface adsorbate diffusion was examined using a numerical algorithm which incorporated a kinetic treatment in conjunction with a time-dependent Monte Carlo formalism. The method was based upon a probabilistic description of ad particle jump events. The diffusion rate was determined by the energetics of interactions among ad-particles, the surface substrate atoms, and surface defects. The rare event problem associated with other theoretical treatments of diffusion was overcome by highly efficient algorithms. Consequently, it was possible to observe events, including adsorbate overlayer ordering and island formation, which occurred over time scales which were longer by orders of magnitude than those for simple adsorbate diffusion. The initial investigations of perfect surfaces indicated that a variety of diffusion mechanisms were operative depending on the ad particle interactions and other controlling parameters in the system. The effects of surface traps on adsorbate diffusion dynamics were then examined. It was found that, at low attractive ad particle interactions, the surface traps became titrated after which diffusion proceeds as it might otherwise. At higher ad particle interactions, diffusion was found to be strongly affected by the surface traps, even beyond the range of direct influence of the trap sites. In fact, it was found that traps may act as nucleation sites for both cluster formation and long range island formation. It was concluded that no comprehensive analysis of surface diffusion could fail to address the effects of imperfections such as these on the diffusion rate and mechanism.

Time-Dependent Monte Carlo Studies of Diffusion with Surface Traps. A.M.Bowler, E.S.Hood: The Journal of Chemical Physics, 1992, 97[2], 1250-6