Optimum rotationally symmetric detector configurations for phase-contrast imaging in scanning transmission electron microscopy

A configured STEM detector yields simultaneously several signals which can be arbitrarily combined. We have calculated the optimum annular subdivision of the detector which maximizes the signal-to-noise ratio in the image of weak scatterers. The optimum detector doubles the signal-to-noise ratio as compared to the conventional STEM detector, increases the resolving power of the instrument and enhances the contrast of strong scatterers located on a supporting foil.