Theoretical investigation of superlattice-fringe images of ordered alloys

Abstract
A computer simulation of lattice-fringe imaging of ordered Fe-Al and Cu-Au alloys has been carried out, using multiple-beam dynamical diffraction theory. This study corrects and extends results presented earlier for an Fe-Al alloy and provides additional results to those of Sinclair et al. for Cu3Au.Systematic-row calculations were carried out in which eight or nine beams were excited, depending on whether two or three beams, respectively, were allowed to contribute to the image. The computed parameters of the dynamical theory (Bloch wave amplitudes and vectors) were used to compute superlattice-fringe images, taking into account the effects of lens aberrations as described by Sinclair et al. (4). Four different diffraction geometries (imaging modes) were employed in the study, as indicated in Figure 1 (Only the beams allowed to contribute to the image are shown.).