CRYSTALLOGRAPHIC IMAGE-PROCESSING APPROACH TO CRYSTAL-STRUCTURE DETERMINATION

It is shown that the crystallographic image-processing technique based on the weak-phase object approximation and on the combination of high -resolution electron microscopy and electron diffraction is applicable to crystal structure determination, The technique consists of two sta ges: image deconvolution and phase extension. In the first stage an im age taken at an arbitrary defocus condition can be transformed into th e structure image with the resolution limited by the resolution of the electron microscope. In the second stage the image resolution is enha nced to the diffraction resolution limit so that most unoverlapped ato ms can be resolved individually in the final image, Although the exper imental diffraction intensities are available for the image deconvolut ion, they must be corrected for the phase extension. The proposed empi rical method of electron diffraction intensity correction seems effect ive for obtaining a set of corrected diffraction intensities which are approximately equal to square structure factors. When the crystal str ucture under examination belongs to a known typical type, it is easy t o propose the structure model by referring to the deconvoluted image w hich reveals the low-resolution structure, and the high-resolution str ucture can also be determined by image simulation.