High-resolution imaging of the atomic structures of twist and general grain boundaries was carried out on samples which had been prepared by using a thin-film technique in which [011]- and [001]-oriented grains were grown side by side epitaxially, thus permitting the investigation of a wide range of grain boundary geometries. It was noted that boundaries with tilt, as well as twist, components typically had structural modulations along the interface and often exhibited a surprising amount of coherence between lattice planes crossing the interface. The coherent connection between lattice planes was, in one case, found to extend over quite a large range of grain-boundary inclinations. This exemplified the strength of the interatomic interactions within the planes and the ability of the lattice to accommodate large elastic strains. It was demonstrated that general grain boundaries were well-structured at the atomic scale, in that the lattices retained their identity right up to the grain boundary core, which often displayed features that were related to tilt grain boundary structures; such as the tendency to misfit localization and the formation of low-index facets. As in the case of tilt grain boundaries, these features appeared to be associated with a lowering of grain boundary energy by maximizing the overall structural order in the grain boundary. Thus, the [110] 90º symmetrical twist grain boundary did not remain planar, but reconstructed into atomic-scale micro-facets.

High-Resolution Electron Microscopy of Twist and General Grain Boundaries. K.L.Merkle, L.J.Thompson: Physical Review Letters, 1999, 83[3], 556-9