Surface diffusion mechanism for step bunching

Abstract

The influence of local atomic interactions on step bunching and step debunching of vicinal fcc(111) surfaces inclined in the [2\ifmmode\bar\else\textasciimacron\fi{}11] direction is modeled by kinetic Monte Carlo simulations under annealing conditions. Different local interactions give rise to characteristic step bunch configurations. By using transition probabilities describing 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-packed 〈011\ifmmode\bar\else\textasciimacron\fi{}〉 step edges, a quasiequilibrium configuration consisting of large (100) and (111) terraces evolves. On the other hand, for a system with strongly enhanced surface diffusion along the 〈011\ifmmode\bar\else\textasciimacron\fi{}〉 step edges, but for all other directions local isotropic diffusion 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 〈011\ifmmode\bar\else\textasciimacron\fi{}〉 step edges is also shown to be necessary for the stability of step bunches for the investigated system. Finally, we show that the step bunching can be completely quenched for compact steps, by means of an increased step-edge barrier for mass transport across the 〈011\ifmmode\bar\else\textasciimacron\fi{}〉 step edges. This shows that step bunching cannot occur without mass transport between adjacent terraces.