Defects at surfaces and interfaces

This chapter discusses the crystallographic features of dislocations, with emphasis on their topological characteristics as constrained by the symmetry of their hosts. Microscopic observations of metallic, ceramic, semiconducting, superconducting, and composite materials have confirmed that dislocations are ubiquitous features in interfaces, occurring both as isolated discrete defects and in organized arrays. The chapter presents several crystallographic tools and methodology. It reviews several important (infinite) crystal structures and their space groups and outlines the assignment of space groups to (1) crystals exhibiting a planar surface and (2) bicrystals. The chapter also discusses the topological properties of defects in single crystals together with surface discontinuities and isolated interfacial defects. Only line defects arise in the class of manifest symmetry, namely, dislocations, disclinations, and dispirations. A broad range of defect types can arise in the broken symmetry class, and it is convenient to subdivide these into surface-like features (steps, demisteps, and facet junctions), and bulk-like defects (dislocations, disclinations, and dispirations). Finally, the chapter discusses several interface structures modeled by dislocation arrays. © 1994 Academic Press, Inc.