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Journal of Electron Microscopy
Year: 2009  |  Volume: 58  |  Issue: 6  |  Page No.: 341 - 347

Correction of higher order geometrical aberration by triple 3-fold astigmatism field

H Sawada, T Sasaki, F Hosokawa, S Yuasa, M Terao, M Kawazoe, T Nakamichi, T Kaneyama, Y Kondo, K Kimoto and K. Suenaga    

Abstract:

A new concept of a spherical aberration correction system using three dodecapoles is proposed. The system compensates for higher order aberration of 6-fold astigmatism, which generally limits a uniform phase area for image forming and probe forming in an electron microscope with a conventional two-hexapole corrector. Triple 3-fold astigmatism field is used to correct the spherical aberration of the objective lens, and the total 3-fold astigmatism is eliminated by their combination. The optimum azimuth relationship among three dodecapoles is calculated to eliminate the 6-fold astigmatism. The principle of the method was verified using a mathematically complex representation. This new concept was experimentally tested with a scanning transmission electron microscope at 60 kV acceleration. The 6-fold astigmatism was certainly compensated and the coherent convergent angle became almost twice compared to a conventional double hexapole system.

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