TIME-DEPENDENT MONTE-CARLO STUDIES OF DIFFUSION WITH SURFACE STEPS

Our initial time-dependent Monte Carlo investigations of diffusion on perfect surfaces indicated that a variety of diffusion mechanisms were operative depending on the adparticle interactions and other controlling parameters in the system. We have now extended our approach to examine diffusion in the presence of defects. We find that the diffusion coefficient and mechanism are intimately related to the concentration and nature of the defects. Surface traps have been shown to act as nucleation sites for island formation. Surface steps facilitate a number of diffusion phenomena. We observe step-mediated "corralling" or "herding" of adparticles which creates regimes of different adparticle concentrations on the lattice. Steps also directionally enhance the diffusion rate and act as nucleation sites. Our studies indicate that current mathematical interpretations of surface diffusion experiments are flawed by the 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 adparticle interactions. In the systems examined at higher adparticle interactions, defects play a less significant role in diffusion dynamics than adparticle interactions.