Secondary Electron (SE) and Backscattered Electron (BSE)
Secondary electrons are used to produce the classic topographic images that are most familiar. ISAAC's field-emission SEM's yield secondary electron images with very high spatial resolutions.
Backscattered electrons are primary electrons that have been scattered by sample atoms. As the intensity of backscattering is proportional to the mean atomic number of the atoms, images developed from them provide information on variations in sample composition.