Kinetic Monte Carlo simulations of adatom island decay on Cu(111)

Abstract

Kinetic Monte Carlo simulations are used to investigate the recent scanning tunneling microscopy (STM) measurements of fast decaying adatom islands on Cu(111). First, reduced potential barriers for adatom migration along close-packed 〈011\ifmmode\bar\else\textasciimacron\fi{}〉 step edges having {100} or {111} step risers are shown to be very important to obtain close-to-monotonic decay of the island top layer, in correspondence to STM measurements. The best correspondence is obtained for fully suppressed one-dimensional Ehrlich-Schwoebel barriers. Second, for encounters between steps in adjacent atomic layers it is demonstrated that a moderately reduced step-edge potential energy barrier for adatom crossing of these steps is sufficient to obtain correspondence between simulations and experiments provided that the step-edge diffusion is increased. The step-step-interaction-related activation energy for step-edge crossing is found to be significantly lower than what was previously reported. This work shows that concerted atomic motion is not necessary to explain the rapid top-island decay if the low-coordinated step-edge transition states are properly modeled. Moreover, no critical step-step distance larger than one atomic row, for which rapid top-island decay occurs, is obtained in the simulations. Furthermore, the simulations are interesting because they show that dramatic macroscopic effects can be generated by just small changes of the potential-energy barriers that are controlling the surface diffusion rates.