Electron microscope images of twin boundaries. II. Contrast mechanisms

An analysis of the contrast obtained in electron microscope images of twin boundaries in wedge crystals is given in terms of interbranch scattering of Bloch waves. The analysis is based on the assumption that there are two strong beams in the matrix and two in the twin. The results show that spacings of the two sets of fringes obtained in the image are related to the extinction distances in the twin and the matrix. The fringes associated with the matrix reflection are shown to be parallel to the surface adjacent to the matrix, while the fringes associated with the twin reflection are parallel to the surface adjacent to the twin.