The fine structure of spots in electron diffraction resulting from the presence of planar interfaces and dislocations

Abstract

AbstractA theory is developed which accounts for the fine structure of electron diffraction spots due to the presence of imperfections of different types in thin foils. The method consists essentially of considering the diffraction pattern to result from the image (i.e. from the amplitudes of transmitted and scattered beams at the exit surface of the foil) by Fourier transformation. The image is described by the expressions given by the two‐beam column approximation assuming the symmetrical Laue case to be realized. The use of the method for the present problem is justified. The geometry of the fine structure and the intensities of the different components of the transmitted and scattered beams are then calculated for a general planar interface taking anomalous absorption into account in the usual phenomenological way. A detailed discussion is given for the special case of a stacking fault. In particular the relation between the properties of the fringe patterns and the fine structure of the transmitted and scattered beams is emphasized. In part II observations will be reported on crystals containing stacking faults which lend support to the theory developed here. In part III crystals containing domain boundaries will be discussed and part IV will be devoted to the study of the diffraction effects of other types of geometrical imperfections.