On the optimum probe in aberration corrected ADF-STEM

New aberration correctors present new challenges in optimizing (minimizing) the probe size in the STEM (Scanning Transmission Electron Microscope). A small probe is important for high resolution imaging and analytical microscopy. Some effects of aperture size, corrector accuracy, and higher order aberrations on probe size and image artifacts are calculated. Accumulated small errors in the aberration corrector can produce a significant decrease in image contrast, which may be important in quantitative image comparisons of theory and experiment. It is important to match the objective aperture to the accuracy of the corrector instead of just the (third order) spherical aberration of the objective as in the commonly used Scherzer conditions.

► Model the image and probe in ADF-STEM with an aberration corrector. ► Optimize the optical conditions to minimize probe size at 60 kV and 100 kV. ► Accumulated small errors in the aberration corrector may cause quantitative changes in image contrast in normal operation.