Aberration Determinations
- Practical Electron Microscopy and Database -
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The methods for determining the aberrations can be generally categorized by two groups based on either measuring image shifts when the illumination is tilted or diffractograms of amorphous materials. From any of the methods the aberration coefficients can be reliably determined by simple least squares fitting of the parameters that are obtained by the measurements. However, the aberration coefficients of the non-aligned EM systems are measured most effectively by the method of the diffractogram tableau introduced by Zemlin et al. [2].

The aberration correctors, e.g. double-sextupole aberration correctors, provide a number of ways to compensate for the aberrations of the entire imaging system of the microscope through the excitation of deflectors, lenses, and the coils of the poles in the corrector. The current settings of the elements in the correctors significantly depend on the aberration measurement [1].

Aberration measurement can be corrupted if the measurement is slow, for instance, when the measurement requires several images [2-6]. However, the measurement can also be performed with a single image, for instance, with a single Ronchigram of an amorphous material as suggested by Lupini et al. [7]

 

 

 

 

 

[1] Uhlemann, S. & Haider, M. (1998). Residual wave aberrations in the first spherical aberration corrected transmission electron microscope. Ultramicroscopy 72, 109–119.
[2] Zemlin F. Weiss K, Schiske P, Kunath W, and Herrmann K H (1977) Coma-free aligment of high-resolution electron microscopes with the aid of optical diffractograms. Ultramicroswpy 3, 49—60.
[3] A.F.deJong,A.J.Koster,Scanning Microscopy 6 (Suppl.)(1992) 95.
[4] M.Haider,etal., Journal of Electron Microscopy 47 (1998) 395.
[5] O.L.Krivanek, N.Dellby, A.R.Lupini, Ultramicroscopy 78 (1999) 1.
[6] W.O.Saxton, Ultramicroscopy 81 (2000) 41.
[7] A. R. Lupini, P. Wang, P. D. Nellist, A. I. Kirkland, S. J. Pennycook, Aberration measurement using the Ronchigram contrast transfer function, Ultramicroscopy 110 (2010) 891–898.

 

 

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