Misfit dislocation patterning in thin films

Document Type

Article

Publication Date

10-1998

Department

Department of Materials Science and Engineering; Department of Mechanical Engineering-Engineering Mechanics

Abstract

The emergence of non-uniform distributions of misfit dislocations (MDs) in thin films is discussed. A three-element reaction-diffusion model for the kinetics of gliding, climbing and misfit dislocations as proposed by Romanov and Aifantis (R-A model) is used to describe the corresponding pattern. The non-local integral expression for the effective stress field at the film surface, which is the main driving force for MD patterning, is approximated by a gradient expression in the MD density. The corresponding gradient coefficients have an explicit dependence on the film thickness which, thus, defines a characteristic length for the pattern. Analytical solutions of the model are obtained which describe transient spatially uniform dislocation distributions, as well as steady-state spatially periodic dislocation distributions. Linear stability analysis around a uniform steady-state solution demonstrates the formation of MD patches as a result of a dynamical spatial instability. This instability is governed by the competition of the spatial coupling provided by the MD stress field and a diffusion-like term entering the dynamics of the gliding dislocations. A stochastic argument for the corresponding diffusion coefficient, which depends on the average spacing between MDs (thus providing a second characteristic length scale), yields an explanation for not observing MD patterns for film thicknesses below 1 μm.

Publication Title

Physica Status Solidi (B) Basic Research

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