Influence of primary electron energy and take‐off angle of scanning electron microscopy on backscattered electron contrast of iron oxide

The contrasts in backscattered electron (BSE) images were studied from the cross section of a heat‐treated steel sheet using a scanning electron microscope (SEM) equipped with a conventional annular BSE detector. BSE images were taken at various primary electron energies ( E p ) and take‐off angles ( θ ; measured from the specimen surface) of the detector. Low E p and low θ improved surface information and channeling contrast, whereas high E p and high θ enhanced bulk information and reduced channeling contrast, resulting in improved material ( Z ) contrast. These results regarding channeling contrast and Z contrast can be understood by the ratio of low‐loss electrons (LLEs) to the inelastic BSE components detected; LLEs contribute to channeling contrast, and their ratio increases with decreasing E p and θ . The systematic results obtained in this study are helpful for controlling SEM conditions in order to select Z and crystallographic information separately in BSE images for practical materials of interest.