Diffraction contrast of electron microscope images of crystal lattice defects. III. Results and experimental confirmation of the dynamical theory of dislocation image contrast

Abstract

Numerical solutions for the transmitted and diffracted wave intensities when electrons pass through a thin foil containing a dislocation, are obtained by the use of a previously derived formulation of dynamical diffraction theory which takes account of anomalous absorption effects. The results for a variety of cases of physical interest are compared with transmission electron micrographs and the theory appears capable of explaining most of the observed effects. The theory also confirms many of the predictions of an earlier kinematical diffraction theory about the visibility and width of dislocation images seen by transmission microscopy, and shows that the oscillation effects observed at some images and not understood on the earlier theory are purely a diffraction phenomenon. The application of the condition for the invisibility of dislocations—that the Burgers vector should lie in the Bragg reflecting planes—still seems to be the best way of determining Burgers vectors but needs modification for edge or mixed dislocations and for partial dislocations. Other effects discussed include the occurrence of double images, the determination of the sense of Burgers vectors and some aspects of slip trace contrast.