A kinematical theory of diffraction contrast of electron transmission microscope images of dislocations and other defects

Abstract

This paper describes a kinematical theory of electron microscope images of dislocations observed by transmission in thin crystalline foils. The contrast is essentially phase contrast in the Bragg diffracted beams, the phase differences being due to the displacements of the atoms from their positions in the ideally perfect crystal. The theory explains many of the characteristic features of the observed images, such as the dependence of the contrast on orientation, the reversal of contrast on bright and dark field images, the fact that dislocations are generally dark on bright field images, the position and width of the images, the general nature of the profile, the occurrence of dotted dislocations, the invisibility of some dislocations, the dependence of contrast on the inclination of the dislocation, and the occurrence of double images. The theory also accounts satisfactorily for the nature and width of the dislocation images obtained with X-rays.