Incoherent imaging using dynamically scattered coherent electrons

We use a Bloch wave approach to show that, even for coherent dynamical scat tering from a stationary lattice with no absorption, annular dark-field ima ging in a scanning transmission electron microscope gives a direct incohere nt structure image of the atomic-column positions of a zone-axis-aligned cr ystal. Although many Bloch waves may be excited by the probe, the detector provides a filtering effect so that the 1s-type bound states are found to d ominate the image contrast for typical experimental conditions. We also fin d that the column intensity is related to the transverse kinetic energy of the 1s states, which gives atomic number, Z, contrast, The additional effec ts of phonon scattering are discussed, in particular the reasons why phonon scattering is not a prerequisite for transverse incoherence. (C) 1999 Else vier Science B.V. All rights reserved.