High-resolution structure imaging of partially disordered atomic columns in binary alloy systems

An investigation of the high-resolution imaging of partially disordered columns in binary alloy systems has been performed both on a theoretical basis and by means of computer image simulations. The theoretical analysis predicts that the composition of the column and/or the distribution of the atoms along the column largely determine the image features of the partially disordered column. The computer simulations confirm the validity of the projection approximation for thin foils, showing only very little distribution dependence and yielding a monotonic composition-contrast relation, which is lost for somewhat thicker foils. For thick foils, the distribution dependence of the image contrast can become significant, but it cannot be distinguished from the effect of composition, so an unambiguous interpretation of the experimental images is hardly possible. Moreover, the distribution dependence turns out to be much more complicated than a simple top-to-bottom effect.