Bilder lokaler Aufladungen im Elektronen-Spiegelmikroskop

Two characteristic types of spots which are frequently found in electron mirror microscope images are interpreted as caustic cross sections caused by local surface charges. Negative charges produce dark circular spots with a bright edge while the caustic cross sections produced by positive charges are of the type well known from the caustic surfaces of electron lenses suffering from spherical aberration and astigmatism. The bright edge in the negative caustic is accompanied by a second edge which in all practical cases is much less intense and consequently invisible.