Aberration analysis of Cs‐corrector system with twin hexapoles and transfer lens doublet in scanning transmission electron microscope by simple ray tracing based on geometrical optics

Abstract

AbstractOptical properties of scanning transmission electron microscopes with aberration correction systems, called Cs‐correctors, were simply calculated from the viewpoint of the geometrical optics. Here, we focused on the Cs‐corrector consisting of twin hexapoles and two round lenses. Although the above system has already been investigated theoretically and developed successfully, we attempted to interpret its properties by a simple ray tracing technique to understand them more intuitively. The aberrations on the Gaussian image plane of an objective lens were calculated. Analyses of the aberrations up to the fifth order indicated that hexapoles and round lenses could eliminate up to third‐order aberrations in the total optical system, including the objective lens, when these four elements are arranged properly. The fourth‐ and fifth‐order aberrations could also be suppressed by adding one and two round lenses, respectively. As these results agreed well with those of previous theoretical studies, our simple method is useful for designing an actual aberration correction system. Copyright © 2008 John Wiley & Sons, Ltd.