Enhancing the contrast of defects in lattice images

Abstract

The technique used in processing HREM images to locate atomic positions in defective area of crystal, such as grain boundaries and GP zones which often have poor contrast in a HREM image due to strain fields and, worse yet, lack of atomic columns in the projection, has been the application of ring filters in Fourier space to get rid of both high and low frequency components. There is no doubt that such technique is capable of providing useful results, but only if practiced with caution. Enough bandwidth must be kept to guarantee the claimed resolution which, one has to remember, is not simply determined by the larger diameter of the ring filter. As pointed out, a compromise, between effectively removing ‘noise’ and creating spurious atoms, exists which probably depends on specific case. Improper use can give impressive, but not necessarily reliable, results.