Shape of Heteroepitaxial Island Determined by Asymmetric Detachment

TL;DR

This study uses kinetic Monte Carlo simulations of lattice gas models to explore how asymmetric detachment rates influence the anisotropic shape of heteroepitaxial islands, aligning with experimental observations.

Contribution

It demonstrates that orientation-dependent detachment rates can produce anisotropic island shapes, explaining experimental anisotropy in heteroepitaxial growth.

Findings

Island shape becomes anisotropic with orientation-dependent detachment.

Dense steps on vicinal substrates enhance shape anisotropy.

Irreversible cluster formation leads to ramified shapes, while detachment smooths edges.

Abstract

Square lattice gas models for heteroepitaxial growth are studied by means of kinetic Monte Carlo simulations, in order to find a possible origin of anisotropic island shape observed in growth experiments of long organic molecules. When deposited molecules form clusters irreversibly at their encounter during surface diffusion, islands grow in a ramified dendritic shape, similar to DLA. Introduction of molecular detachment from edges makes islands compact with smooth edges. Tilting of adsorbed long molecules or steps in a vicinal substrate may induce orientation-dependence in the detachment rate of edge molecules from an island. In simulations with orientation-dependent detachment rates, a clear anisotropy in an island shape is observed. Shape anisotropy on a vicinal substrate is enhanced as steps get dense, in agreement to the experimental observation.