Quantitative analysis of angle-selective backscattering electron image of iron oxide and steel

The contrasts in backscattered electron (BSE) images, such as topographic, channeling and mean atomic number (Z) contrasts, were investigated quantitatively from the cross section of a heat-treated steel sheet using a scanning electron microscope (SEM). High primary electron energy (EP) enhances Z contrast, whereas low EP improves channeling contrast. A high take-off angle (θ; measured from the specimen surface) also enhances Z contrast, whereas low θ improves channeling contrast. When θ becomes very low, topographic information is enhanced and superimposed on channeling contrast due to the tilt effect of BSE. The relationship of the behaviors of the Z contrast and the channeling contrast can be understood by the detection ratio of low-loss electrons (LLEs) to the inelastic BSE components emitted from the sample surface; LLEs contribute to channeling contrast, and their ratio increases with decreasing EP and θ. The systematic results obtained in this study are useful for controlling SEM conditions in order to enhance the target information in BSE images for practical materials of interest.