On the core structures of misfit dislocations in grain boundaries

The core widths of grain boundary misfit dislocations in [001] twist boundaries close to coincidence site lattice misorientations have been studied by transmission electron microscopy on thin-film bicrystals of gold. Matching of experimental dark-field weak-beam images with profiles computed using the dynamical theory of electron diffraction shows that the core width for the 36·9°, σ = 5 boundary is ∼ 5 nm and may be even greater for the 22·6°, σ = 13 and 28·1°, σ = 17 boundaries. The results suggest that the coincidence site lattice plus dislocation network model of high-angle grain-boundary structures is applicable only to small angular ranges of misorientation close to angles corresponding to coincidence site lattice boundaries with relatively low energies.