Scanning Electron Microscopy


We study the plural scattering of electrons in amorphous and polycrystalline films. The incident electron energy ranges from 0.1 to 3 MeV. The cross sections are obtained by measuring the transmission coefficient for targets of gold, silver, aluminium and carbon. The partial elastic cross section is calculated from Lenz's theory using a Wentzel-Yukawa model for the atomic potential of the scattering atom. In the case of inelastic interactions, we take into account either scattering by a free atom (Morse's approximation) or scattering by plasmon creation (relativistic theory of Ashley Ritchie). From these results, we solve the problem of electron transport in thin films with the aid of a Monte Carlo method. We use a single scattering model: each electron trajectory is followed through a succession of distinct scattering events in the target. For each scattering event, the direction and, if necessary, the electron energy are modified. We obtain the angular distributions of the transmitted electrons and the broadening of the electron beams in the specimen. This study sheds light on the amplitude contrast of electron microscope images.

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