Precise measurement of third-order spherical aberration using low-order zone-axis Ronchigrams.
A method for the measurement of third-order spherical aberration coefficients (C(s)) is suggested, using low-order zone-axis Ronchigrams of a crystalline material. The validity of the method is confirmed using simulated and experimental Ronchigrams taken with various probe-forming lens configurations. The precision of the measured C(s) value is drastically improved compared with that obtained from the power spectrum-analysis method. In addition, a method for roughly estimating defocus values is presented.
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