Microdiffraction from antiphase domain boundaries in Cu₃Au

Electron diffraction patterns have been obtained from regions of a thin crystal of partially ordered copper-gold alloy, Cu₃Au, which have a diameter of about 15 Å and contain an antiphase domain boundary. The superlattice diffraction spots show a characteristic splitting similar to the splitting which appears in all spots, both fundamental and superlattice, when the beam irradiates a region at the edge of a crystal. By observing which of the superlattice spots are split and which are not, it is possible to deduce immediately whether the antiphase domain boundary is of the 'good' type or is one of the 'bad' types or whether more than one boundary is illuminated by the beam. The observations of split spots are in good agreement with the results of calculations made on the basis of kinematic theory. It is shown that these results remain valid in the presence of strong dynamical scattering for small specimen thicknesses.