Upper limits for the residual aberrations of a high-resolution aberration-corrected STEM

The development of correctors for electron optical systems has already brou ght the improvement of resolution for a low-voltage scanning electron micro scope and a commercially available transmission electron microscope and is anticipated in the near future for a dedicated scanning transmission electr on microscope (STEM). The resolution attainable especially of a probe-formi ng system at 200 kV cannot only be estimated from calculations ignoring all non-rotationally symmetric axial aberrations in an electron optical system . For a certain resolution, one would like to attain, the influence of the deviations from the ideal, aberration-free system has to be investigated. T herefore, in the following we have carried out the evaluation of the requir ed accuracy for the compensation of the various residual aberrations in ord er to achieve a resolution in the sub-Angstrom regime with a probe-forming system. (C) 2000 Published by Elsevier Science B.V. All rights reserved.