Structure of the σ = 9,11 symmetrical tilt grain boundaries in germanium Electron microscopy observations

The structure of the [011] σ = 9 and σ = 11 symmetrical tilt grain boundaries in germanium, very close to the exact coincidence orientation, has been studied using the α-fringe and electron diffraction techniques. Diffraction patterns from the grain boundary at various inclinations were recorded, those at normal incidence examined in detail, and fine matrix and double-diffracted spots identified. The boundary zones are dilated, and from the results of both techniques we can conclude that there is no rigid body translation parallel to the grain boundary. The σ = 9 periodicity is that of the coincidence site lattice, while that of the σ = 11 bicrystal is double. In both cases there is a glide-reflection plane parallel to the grain boundary which leads to the existence of favourable, symmetrically alternated atomic arrangements. Five-ring and seven-ring units and “boat-shaped” six-ring units are combined in geometrical models without dangling bonds.