Applications of `limited projection topographs' and `direct beam topographs' in diffraction topography

Abstract

The method of projection topographs can be modified so that images are recorded only from imperfections which lie within a chosen range of depths in the crystal specimen. This technique of `limited projection topographs' allows easier study of internal imperfections by eliminating images of surface damage. It can also be applied in studying imperfections just below a crystal surface, as in correlating dislocation outcrops with surface features. Another modification uses multiply scattered radiation leaving the crystal in the direction of the direct beam to produce `direct beam topographs' which have different contrast characteristics from the usual diffracted beam topographs.