Kinetic Monte Carlo Simulation Studies of the Shape of Islands on Close-Packed Surfaces

Abstract

Kinetic Monte Carlo simulations are used to study processes that affect the shape of islands during growth of close-packed surfaces. The difference in adatom binding energy at the two types of edges and the relative height of diffusion barriers together with the incident flux and temperature determine which of the two types of edges dominates. This in turn affects strongly whether the crystal grows layer-by-layer or forms three-dimensional islands. Several features of the energy landscape that affect the island shape are illustrated. An unexpected edge nucleation effect involving addimer formation near a corner where edges meet can strongly affect the shape of small islands especially at low flux. Since the barrier for an adatom to exit a corner site to an edge site is lowered by such dimer formation, the overall activation energy for transport from an edge with low diffusion barrier to an edge with high diffusion barrier is reduced. As a result, small islands mainly have edges for which the diffusion barrier is lower. However, for large islands, the adatom is more likely to find a kink on the edge that has smaller diffusion barrier so large islands mainly has edges where the diffusion barrier is higher.