Contrast within images of locally charged dielectrics in scanning electron microscopy

Investigations of dielectric materials via a scanning electron microscope are accompanied by definite difficulties associated with their charging under the action of electron irradiation. Certain aspects intrinsic to the formation of the contrast within images of locally charged regions of dielectric targets are discussed. Tertiary electrons, which are generated on the surface of the microscope's lens by the accelerated field of charges of true secondary electrons emitted from an irradiated sample, is shown to play a significant role. The contrast of locally charged dielectric images is demonstrated to invert at small electronbeam energies corresponding to an emission coefficient of greater than unity. The origin of this effect is also explained.