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 Å 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 Å 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.