Single atom image contrast: conventional dark-field and bright-field electron microscopy.

Single atom inage intensities are calculated for bright-field and various dark-field modes, including the ideal beam stop, a wire beam stop, tilted illumination and a displaced aperture. Comparisons of scattering amplitudes and elastic scattering cross-sections are made with different object potentials and scattering formulations. The image contrast for one mercury atom (Z equals 80) on a column of carbon atoms (Z equals 6) as the substrate is also discussed for both the bright-field and the various dark-field situations.