Diffraction Contrast in TEM Images

Abstract

This chapter explains the origin of features observed in TEM images of crystalline materials. These microstructural features, having sizes from nanometers to microns, control many important properties of materials. TEM often provides information about these microstructural features with greater detail and clarity than any other experimental technique. There are subtleties, however, in the interpretation of images such as those from the dislocation segments running from top to bottom of the sample in the figure above. The dislocations themselves do not have the modulations in width seen in the image, and the dislocation images are displaced horizontally from the actual positions of the cores of the dislocations. By changing the tilt of the incident beam on the Bragg planes of the crystal, i.e., changing the “diffraction condition,” the images of the dislocations can shift in position, split in two, or disappear entirely.