SURFACE-DIFFUSION MECHANISM FOR STEP BUNCHING

The influence of local atomic interactions on step bunching and step d ebunching of vicinal fcc(111) surfaces inclined in the [<(2)over bar 1 1>] direction is modeled by kinetic Monte Carlo simulations under anne aling conditions. Different local interactions give rise to characteri stic step bunch configurations. By using transition probabilities desc ribing local atomic interactions where both the initial and the final number of atomic bonds are involved in the surface diffusion process, and in addition strongly enhanced surface diffusion along the close-pa cked [01(1) over bar] step edges, a quasiequilibrium configuration con sisting of large (100) and (111) terraces evolves. On the other hand, for a system with strongly enhanced surface diffusion along the [01(1) over bar] step edges, but for all other directions local isotropic di ffusion where only the initial number of atomic bonds before a hop is considered, a quasiequilibrium surface configuration is formed with a step bunch consisting of alternating (021) and (012) facets surrounded by large (111) terraces. Strongly enhanced surface diffusion along [0 1(1) over bar] step edges is also shown to be necessary for the stabil ity of step bunches for the investigated system. Finally, we show that the step bunching can be completely quenched for compact steps. by me ans of an increased step-edge barrier for mass transport across the [0 1(1) over bar] step edges. This shows that step bunching cannot occur without mass transport between adjacent terraces.