Preservation of electron microscope image contrast after inelastic scattering

Abstract

Abstract Observations of the effect of thermal diffuse scattering, single electron excitations and plasmon excitation on the quality of electron microscope images of crystals are presented and discussed. Preservation of image contrast after thermal diffuse scattering seems to be poor in practice but only a small fraction of the electrons accepted by the aperture are affected in this way. To a first approximation, contrast appears to be preserved after single electron excitation or plasmon excitation especially at small scattering angles where no evidence of interband transitions of the fast electron has been found. At larger scattering angles some loss of contrast occurs so that the size of the aperture can be important. The significance of the results is discussed with reference to electron microscopy of thick crystals, direct resolution of atomic positions and out-of-focus images.