ANNULAR DARK-FIELD IMAGING - RESOLUTION AND THICKNESS EFFECTS

Simulations of annular dark-field zone-axis crystal images that explore the dependence of images with thickness are reported. Earlier work with digitally acquired experimental images and diffraction patterns provide excellent agreement with multi-slice-based, ''frozen phonon'' simulations and thus provide a foundation for this work. Additional experiments at 60 kV add support. Simulations of indium phosphide at 300 kV and 1.3 angstrom resolution show evidence that the phosphorus image is weak. The results of the currently reported thickness simulations suggest that while the electron beam probe channels for long distances in low-Z-element materials such as silicon or phosphorus, the channeled probe travels only about 100 angstrom in heavier elements such as germanium or indium. Such an effect has serious implications for quantitative analysis using annular dark-field imaging, electron energy loss spectroscopy and X-ray microanalysis.