Diffraction Contrast Effects of Electrons Scattered Inelastically through Large Angles

Abstract

The contrast of electron microscopic images formed by inelastic scattering varies as the scattering angle of electrons which contribute to the image. At 50 kV, the electrons which are scattered inelastically by 2.8×10 -2 rad. (3θ B where θ B is the Bragg angle for 220 reflection) do not give the dislocation image due to the loss of coherence, while the electrons scattered by 9.2×10 -2 rad. (35 θ B ) still give the dislocation image at 800 kV. In the latter case contrast produced by electrons scattered through large angle is reverse to that of bright-field image. The contrast reversal and loss of coherence are discussed by the dynamical theory of electron diffraction for inelastic scattering. The contrast loss by multiple scattering in a thick crystal is briefly described.