ABSTRACT
The fine structure, such as streaks and satellites, present in many electron diffraction patterns contains a great deal of information about the defect structure of the specimen. It is therefore imperative to correlate detail in the diffraction pattern with features in the image, in particular by forming dark-field images. It is also possible to detect reflections that arise from double diffraction by dark-field imaging. If the precipitate particle or twin intersects the specimen surfaces, the double-diffraction process will be confined to the interface, which will be bright in the dark-field image using a doubly diffracted spot. However, if the particle is entirely confined within the specimen, there will be no obvious differences between dark-field images with doubly diffracted or primary precipitate spots. At high temperatures, many metal alloys, minerals and ceramics have disordered structures, i.e. some or all of the atoms are randomly distributed on the atomic sites.
