Impurity-induced step interactions: a kinetic Monte-Carlo study

TL;DR

This study uses kinetic Monte-Carlo simulations to verify how immobile impurities can induce step bunching on vicinal surfaces by affecting adatom diffusion, revealing conditions for stable step flow and impurity effects.

Contribution

It provides the first kinetic Monte-Carlo simulation validation of impurity-induced step interactions and analyzes stability conditions for step assemblies.

Findings

Impurities can induce step bunching by suppressing adatom diffusion.

Assemblies of up to 20 steps are unstable and tend to emit single steps.

An analytic estimate for the critical number of steps for stability is confirmed by simulations.

Abstract

A one-dimensional continuum description of growth on vicinal surfaces in the presence of immobile impurities predicts that the impurities can induce step bunching when they suppress the diffusion of adatoms on the surface. In the present communication we verify this prediction by kinetic Monte-Carlo simulations of a two-dimensional solid-on-solid model. We identify the conditions where quasi one-dimensional step flow is stable against island formation or step meandering, and analyse in detail the statistics of the impurity concentration profile. The sign and strength of the impurity-induced step interactions is determined by monitoring the motion of pairs of steps. Assemblies containing up to 20 steps turn out to be unstable towards the emission of single steps. This behavior is traced back to the small value of the effective, impurity-induced attachment asymmetry for adatoms. An analytic estimate for the critical number of steps needed to stabilize a bunch is derived and confirmed by simulations of a one-dimensional model.