Recent work at Cornell University explores atomic scale electron microscopy using pixel array detection [1]. This largely model-driven paper follows up the paper two years ago announcing the EMPAD [2]. The authors emphasize the distinction between center-of-mass (CoM) and differential phase contrast (DPC) imaging. These respond differently to collection angle. Among other interesting conclusions, they observe “shape of the signal maps the derivative of the probe shape, and is more sensitive to changes in the probe shape than the underlying potential. While small changes to defocus only affected the peak height, other aberrations can have a stronger effect on the probe tails which will be reflected in the tails of the CoM image. Overall, this cautions against any interpretation that we are mapping the atomic structure or bond charge distributions with an atomic CoM/DPC signal.”
References:
[1] Cao, et al., “Theory and Practice of Electron Diffraction from Single Atoms and Extended Objects using an Electron Microscope Pixel Array Detector”, arXiv:1711.07470.
[2] Tate, et al., “High Dynamic Range Pixel Array Detector for Scanning Transmission Electron Microscopy”, arXiv:1511.03539.