Axial Coma (B2) Correction with Ronchigram in STEM
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Figure 3339a shows the change of Ronchigram taken at overfocus of 50 nm during axial coma C2,1 (B2) correction. The characteristic feature of the aberration marked by white broken lines disappeared after the aberration correction.
Figure 3339a. Change of Ronchigram taken at overfocus of 50 nm during axial coma C2,1 (B2) correction. Adapted from 
The changes of A1 and B2 from underfocus (UF) to overfocus (OF) are shown in Figure 3667d. At focus (F), the probed area is the smallest and the image blows-up to "infinity" magnification, while the images reverses from UF to OF.
Figure 3339b. Changes of A1 and B2 from underfocus (UF) to overfocus (OF). Adapted from 
 H. Akima, Y. Hirayama and T. Yoshida, Automated Alignment Cs Correction System for STEM (II): Installation of
Reinforcement Learning, www.microscopy.org, 2011 .
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