In scanning microscopy in transmission (STEM) and reflection (SEM) the spreading of the spatial distributions of the forward-and backscattered electrons, respectively, deteriorates contrast and resolution. We therefore investigate this spreading by measuring quantitatively the corresponding distributions of secondaries released by these reemerging electrons. In order to carry out this experiment we visualize these distributions by using the surface of the specimen as the source of an emission microscope.
The spreading of transmitted beams of 19.5 keV in thin films of Al and Ge 0 .2-2 μm in thickness is reported here as well as the spatial distributions of secondaries released by backscattered electrons from bulk Si-, Ge-, Ag- and Au-specimens for 20-70 keV energy of the primary probe. By evaluating these distributions we calculated an upper limit of the contrast available in SEM micrographs obtained in the secondary mode. The formation of edge brightening, flaring due to charging and the top bottom effect is demonstrated by means of emission microscopical micrographs.
"The Emission Microscope: A Valuable Tool for Investigating the Fundamentals of the Scanning Electron Microscope,"
Scanning Microscopy: Vol. 2
, Article 5.
Available at: https://digitalcommons.usu.edu/microscopy/vol2/iss1/5