Diffraction contrast from the displacement field of antiphase-domain-boundary tubes

Abstract

Abstract In a transmission electron microscope, antiphase-domain-boundary (APB) tubes have been found to produce contrast not only in superlattice reflections satisfying g · R ¦ integer, as previously known, but also in a range of reflections, superlattice or fundamental, which contain large components normal to the tube axis. This observation is explained by a continuous lattice distortion in and around the tube caused by the surface tension of the APB. The displacement field associated with a circular APB tube is calculated using isotropic elasticity under the assumption of isotropic APB energy. The image contrast formed by this displacement field in dark-field Bragg reflections in the transmission electron microscope is calculated using the two-beam dynamical theory. The image contrast of an APB tube is shown to be substantially weaker than that of a dislocation owing to its much smaller lattice distortions. This contrast mechanism is shown to explain the images of APB tubes observed in deformed L12 ordered Ni3Ga single crystals. Effects caused by this displacement field on the interaction between APB tubes and other defects are discussed.