Interfacial edge dislocation interactions with free-surfaces in nanocrystals.

The configurational force experienced by a dislocation towards a free-surface is termed as the image force. In this work we consider a combination of two cases, wherein the image force experienced by an edge dislocation is considerably altered with respect to an edge dislocation in a semi-infinite body: (i) interfacial misfit edge dislocation in an epitaxial system and (ii) edge dislocation in a 2D nanocrystal. The interaction of an edge dislocation with a free-surface in a 2D nanocrystal can be: (i) attractive with a considerably altered magnitude and direction (as compared to the theoretically calculated value), (ii) neither attractive nor repulsive or (iii) even repulsive. To compute the image force on a misfit edge dislocation in a 2D nanocrystalline epitaxial system, a finite element model is constructed and stress-free strains are imposed in appropriate regions of the domain, to simulate an epitaxial system (Nb/Sapphire) and an interfacial dislocation. The results of the simulation are contrasted with the standard theoretical formulations, which are shown to be highly inadequate to handle such cases which involve epitaxial strains, two materials in the system and considerable domain deformations.