New contrast mechanism for scanning electron microscope

With normal electron incidence, the resolution of the backscattered electron image in the scanning electron microscope (SEM) is approximately equal to the classical electron pentration depth. With oblique electron incidence, a significant number of plurally scattered electrons leave the specimen in an apparently specular direction after penetrating for a distance that is an order of magnitude smaller than this. Thus with 15-keV electrons incident onto Al at 45°, a significant number of backscattered electrons leave the specimen after penetrating to less than 500-a.u. depth. These electrons can be collected over an angle that is close to the plane of the specimen surface. Other electrons leave the specimen more nearly at right angles to the surface, and these have been scattered from a greater depth. The image in the SEM can change completely if the position of the collector is changed. © 1970 The American Institute of Physics.