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Figure 5
Results from a numerical simulation of the effect from a voltage bias on the objective lens aperture. (a) Electrostatic potential distribution around the objective lens polepiece gap caused by applying voltage to the objective lens aperture. The potential is confined mostly between the bottom of the cryo-box and the lower polepiece. (b) Axial magnetic field (green) and electrostatic potential (red) distributions along the optical axis, and electron trajectories for a paraxial illumination ray (orange) and an image ray (blue). The zero of the horizontal axis corresponds to the sample position. (c) Numerical results for the defocus change caused by biasing the objective lens aperture. The results indicate a linear relation between defocus and bias voltage with a modulation strength of 4.69 nm V−1.

IUCrJ
Volume 7| Part 3| May 2020| Pages 566-574
ISSN: 2052-2525
https://doi.org/10.1107/S205225252000408X