Shift of extinction contours due to the presence of dislocations

The deformation of prisms and elliptical cylinders, resulting Tröra-TFie presence of an arbitrary dislocation line parallel to one of the main axes of the cross-sections is discussed, it is shown that in general the specimen Is both bent and twisted. The deformation appears in the electron microscope as a shift of the extinction contours where these cross the disIocations. The sign and magnitude of the shift depend on the magnitude, the sign and the orientation of the Burgers vector with respect to the dislocation line, as weII as on the operating diffraction vector and local curvature of the foil. For a particular dislocation in tin disulfide it has been possible to verify the theory in detail.