Optical selected-area diffraction patterns of high-resolution electron-microscope images for crystal analysis

Abstract

Optical selected-area diffraction patterns made from high-resolution electron micrographs of crystals have been used as a source of diffraction information from areas as small as a single unit cell of the crystal. The intensities of the electron diffraction pattern of the specimen crystal and the optical diffraction patterns of high-resolution electron-microscope images have been discussed by electron optical image formation theory taking account of spherical aberration and defocusing of the objective electron lens and it is concluded that the optical diffraction pattern may be identical with the electron diffraction pattern if the electron micrograph is photographed under optimum conditions. Optical diffraction patterns from areas of 80, 30 and 10 Å in diameter of labradorite feldspar have been taken and the orientation of two adjoining grains, 30 Å in diameter, has been determined. The diffraction pattern from a unit-cell area has also been taken and compared with the calculated intensity.