The general trend for reducing the energies of primary electrons in electron microscopy has been faced with a gradual deterioration of the image resolution. Biasing the sample to a high negative voltage and making the electrons arbitrarily slow solely on and inside the sample has shown itself to be far more feasible than originally expected. The fundamental aberration coefficients (spherical and chromatic) of a combination of an objective lens and an immersion electrostatic lens formed by the biased sample decrease with the decreasing landing energy of the electrons. As a result, the spot size in scanning systems may become nearly independent of the landing energy of the electrons. The requirements placed on samples are strict but feasible, and detection of signal electrons is greatly facilitated by the acceleration of both reflected and transmitted electrons in the field of the biased sample and their collimation toward the optical axis. The interaction of slow electrons is not only more intensive than that at standard energies but even scattering phenomena appear which are not otherwise observed. Several application examples are presented. The benefits of very low energy EM are still being uncovered after its having been in routine use for several years.
Part of the book: Modern Electron Microscopy in Physical and Life Sciences