An analysis of the symmetries in electron microscope images of a sloping dislocation and its application as a method for dislocation characterization

The conditions are established under which a sloping dislocation in a thin-foil crystal may produce a symmetric dynamical contrast electron microscopic image. The contrast symmetries are deduced purely by geometrical considerations from the criteria of Howie and Whelan, and Pogany and Turner. This analysis is, in fact, the basis of a new approach for characterizing dislocation parameters. Unlike the computer simulated picture method of Head this method does not necessitate resort to the digital computer. Furthermore, the symmetric nature of a diffraction contrast image is shown to be invariant of the degree of elastic anisotropy.