Energetics and atomic mechanisms of dislocation nucleation in strained epitaxial layers

TL;DR

This study uses atomistic simulations to analyze the energetics and atomic mechanisms behind dislocation nucleation in strained epitaxial layers, revealing how energy barriers vary with misfit and potential form.

Contribution

It introduces a systematic method combining repulsive potential minimization and Nudged Elastic Band to study dislocation nucleation pathways and barriers.

Findings

Energy barrier decreases with increasing misfit.

Strong tensile-compressive asymmetry observed in nucleation.

Asymmetry depends on the form of the interatomic potential.

Abstract

We study numerically the energetics and atomic mechanisms of misfit dislocation nucleation and stress relaxation in a two-dimensional atomistic model of strained epitaxial layers on a substrate with lattice misfit. Relaxation processes from coherent to incoherent states for different transition paths are studied using interatomic potentials of Lennard-Jones type and a systematic saddle point and transition path search method. The method is based on a combination of repulsive potential minimization and the Nudged Elastic Band method. For a final state with a single misfit dislocation, the minimum energy path and the corresponding activation barrier are obtained for different misfits and interatomic potentials. We find that the energy barrier decreases strongly with misfit. In contrast to continuous elastic theory, a strong tensile-compressive asymmetry is observed. This asymmetry can be understood as manifestation of asymmetry between repulsive and attractive branches of pair potential and it is found to depend sensitively on the form of the potential.