Crystallographic image processing approach to crystal structure determination

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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 stages: image deconvolution and phase extension. In the first stage an image taken at an arbitrary defocus condition can be transformed into the structure image with the resolution limited by the resolution of the electron microscope. In the second stage the image resolution is enhanced to the diffraction resolution limit so that most unoverlapped atoms can be resolved individually in the final image. Although the experimental diffraction intensities are available for the image deconvolution, they must be corrected for the phase extension. The proposed empirical method of electron diffraction intensity correction seems effective for obtaining a set of corrected diffraction intensities which are approximately equal to square structure factors.

When the crystal structure under examination belongs to a known typical type, it is easy to propose the structure model by referring to the deconvoluted image which reveals the low-resolution structure, and the high-resolution structure can also be determined by image simulation.

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