Stereoscopic Analysis of Dislocation Distributions from Electron Micrographs

The use of stereo pairs of electron micrographs for quantitative analysis of defect structures offers several advantages over methods which use single micrographs: stereoscopic viewing aids in comprehending complicated 3-dimensional structure. Defect densities can be measured locally, i.e. as a function of depth in the specimen rather than as an average over the foil thickness. The depth definition afforded by 3-dimensional viewing largely eliminates problems of image overlap. The depth dimension can be measured from the micrographs. In this paper, stereo techniques for analyzing dislocation distributions will be discussed along with results obtained using high voltage electron micrographs of very thick foils.Although the practice of electron stereomicroscopy with diffraction contrast images is not yet widespread, the technique is not difficult. Two different views of the same specimen detail are obtained by tilting the specimen between exposures. With diffraction contrast, the operating reflection and Bragg deviation must be kept the same so that any differences in the position and appearance of the defect images is due to the change in viewpoint.