Oriented chemical overgrowths and surface topography

Abstract
The growth of thin halide tarnish layers on silver crystals has been studied. The substrate surfaces were prepared in various ways, so that their topography could be varied. By a careful analysis of electron-diffraction patterns from the specimens, it has been possible to deduce the true contact planes between silver and halide for many of the observed orientations of silver halide. The contact planes were often not parallel to the macroscopic surface of the substrate. To a large extent, the orientation of the halide on the (hkl) type silver facets was independent of the position of those facets with respect to the macroscopic surface. There is evidence, however, that certain orientations on a given (hkl) facet only occur provided that facet contains some irregularities (probably steps or cracks), along which the growth can originate. Some unexplained disorientation effects are observed, and some examples of orientations corresponding to large percentage misfit between substrate and overgrowth are also given.

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