IMAGE-PROCESSING BASED ON THE COMBINATION OF HIGH-RESOLUTION ELECTRON-MICROSCOPY AND ELECTRON-DIFFRACTION

A method of crystal structure determination by electron crystallograph ic image processing based on the combination of high-resolution electr on microscopy (HREM) and electron diffraction is introduced. It consis ts of two stages: image deconvolution and resolution enhancement. In t he first stage an image taken at an arbitrary defocus condition is tra nsformed into the structure image-with the resolution depending on the resolution of the electron microscope. In the second stage the image resolution is enhanced to the diffraction resolution limit by combinin g the electron diffraction data and using the phase extension techniqu e so that in the final image most unoverlapped atoms can be resolved i ndividually. The experimental diffraction intensities are corrected fo r approximating to square structure factors. The principle of the imag e processing and the procedure of diffraction intensity correction are briefly described and the results of applications are illustrated. Si nce the method is based on the weak phase object approximation (WPOA), the validity of WPOA is discussed by introducing an approximate image contrast theory named pseudo weak phase object approximation (PWPOA) to demonstrate the image contrast change with the crystal thickness fo r very thin crystals. (C) 1998 Wiley-Liss, Inc.