Dislocation interactions and strain relaxation

The issue of dislocation formation in a strained epitaxial heterostructure was the focus of attention in the preceding chapter. Residual stress was assumed to originate from the combination of a mismatch in lattice parameters between the materials involved and the constraint of epitaxy. The discussion in Chapter 6 led to results in the form of minimal conditions which must be met by a material system, represented by a geometrical configuration and material parameters, for dislocation formation to be possible. Once the values of system parameters are beyond the point of fulfilling such minimal conditions, dislocations begin to form, propagate and interact. The ensemble behavior is usually termed strain relaxation. 

Progress toward resolving such questions is summarized in this chapter. The discussion begins with the issue of fundamental dislocation interaction phenomena and nonequilibrium behavior of interacting dislocations. Attention is then shifted from consideration of films with low dislocation density to the modeling of inelastic deformation of thin films with a relatively high densities of dislocations. For this purpose, constitutive models for time-independent and time-dependent deformation of thin films are examined by appeal to continuum plasticity theory. Overall features of material behavior captured by such theories are then compared with available 

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