Observation of monolayer steps on {111}, Σ = 3 twin boundaries in chemically vapour-deposited polycrystalline diamond

A cross-section through a thick, chemically vapour-deposited polycrystalline diamond sample has been studied by transmission electron microscopy. In one region of the specimen a {111}, = 3 twin boundary was found that was almost parallel to the plane of the section. This boundary, which contained the growth direction, had a remarkable dislocation structure that has been analysed by diffraction contrast techniques and by electron diffraction experiments. It is concluded that these dislocations terminate monolayer steps on the grain boundary.