Initial time-dependent Monte Carlo investigations of diffusion on 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 approach was extended to examine diffusion in the presence of defects. It was found that the diffusion coefficient and mechanism were intimately related to the concentration and nature of the defects. Surface traps were shown to act as nucleation sites for island formation. Surface steps facilitate a number of diffusion phenomena. Step-mediated "corralling" or "herding" of ad-particles was observed which created regimes of different ad particle concentrations on the lattice. Steps also directionally enhance the diffusion rate and acted as nucleation sites. The studies indicated that current mathematical interpretations of surface diffusion experiments were flawed in their inability to explicitly account for diffusion dynamics in the presence of step features. Surface steps and traps exert roughly the same influence on diffusion rates at low ad particle interactions. In the systems examined at higher ad particle interactions, defects play a less significant role in diffusion dynamics than ad particle interactions.

Time-Dependent Monte Carlo Studies of Diffusion with Surface Steps. A.M.Bowler, E.S.Hood: The Journal of Chemical Physics, 1992, 97[2], 1257-65