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.