Direct imaging of surface cusp evolution during strained-layer epitaxy and implications for strain relaxation

Abstract

We have directly imaged the evolution of surface cusps during strained-layer epitaxy. The cusps arise naturally as a result of gradients in the surface chemical potential. High stress concentrations at the cusp tip have important implications for strain relaxation in the film via dislocation nucleation.

High resolution transmission electron microscopy studies of metal/ceramics interfaces

“…On the other hand, if the substrate is dislocation-free or has a very low density of dislocations, then fresh dislocations need to nucleate in the film, at the film/substrate interface, or at the film surface. In low-mismatched systems, including the cases of two-dimensional growth, a likely mechanism is dislocation nucleation at some heterogeneity in the film, usually at its surface (Matthews et al, 1970); this includes surface sites where contaminations (say, dirt particles or oxides/carbide precipitates) (Perovic et al, 1989) are present, and possibly at the valleys of surface undulations (Cullis et al, 1992(Cullis et al, , 1994Jesson et al, 1993Jesson et al, , 1994 caused by morphological instabilities (Grinfel'd, 1986). On the other hand, in large-mismatched systems, where film deposition is invariably by (two-or three-dimensional) island growth, dislocations often nucleate at the edges of the islands (Vincent, 1969).…”

Alloying of self-organized semiconductor 3D islands

“…Further pathways to strain relaxation emerge when the constraint of perfectly coherent heterostructures is dropped. In this case, the formation of point-and particularly line-like defects of the lattice, as vacancies or interstitials and dislocations, can be very efficient ways of releasing the accumulated strain energy [47][48][49]. Here we shall however confine our discussion to the case of strict epitaxial coherence.…”

Thin Film Evolution Equation for a Strained Anisotropic Solid Film on a Deformable Isotropic Substrate

“…In experimental study of the nonlinear evolution of the stress-driven instability of thick films the formation of deep, cusp-like grooves was observed [12] [13]. In [14] this instability was studied numerically and they showed that the surface instability creates a groove that sharpens as it grows deeper.…”