Chromatic and Spherical Aberration Correction with Hexapole and Quadrupole Fields

Abstract: We report the development of a chromatic and spherical aberration corrector based on a combination of hexapole and quadrupole fields. Thick hexapole fields are used to generate negative spherical and to correct residual axial and off-axial aberrations. However, instead of using round transfer lenses placed between the hexapoles, a quadrupole multiplet producing superimposed electric and magnetic quadrupole fields is used to produce negative chromatic aberration. The quadrupole multiplet also functions as a transfer doublet within the corrector. In this paper, the simultaneous correction of chromatic and spherical aberrations using this corrector design is described and we demonstrate a resolution improvement in cases where the energy spread is limiting.