Crystallography of domain formation and dislocations in bilayers and multilayers

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Abstract
The physical properties of multilayer materials are intriguing (e.g., see Reference l), and much enterprise is currently directed toward the scientific understanding and technological application of these structures. Similar to the situation for crystalline materials in general, the presence of dislocations and other defects in these layered composites is likely to profoundly influence their properties. Moreover, the interaction of such defects with the array of interfaces present in a multilayer may be a key issue. The present article is concerned with a particular aspect of this latter topic, namely, the geometrical nature of line defects which can reside in multilayer interfaces. This is thought to be a timely contribution to the discussion of multilayer properties because, over the last few years, advances in the appreciation of interfacial defects have occurred, many of which are pertinent to multilayer applications. For example, we show that the range of dislocation types that can arise in interfaces is broader than had been recognized previously using arguments based on the concept of crystal misfit. In addition, we consider the possibility that interfacial disclinations might arise and compare their elastic properties to those of dislocations. We also discuss the interaction of domain boundaries, separating crystallographic domains within the layers, with interfaces; in particular, we show how the character of line defects delineating the intersections of domain boundaries with interfaces can be established. This discussion is relevant, for example, to the issue of domain formation during layer deposition and the stabilization of domains which may subsequently form by prqcesses such as ordering.