Direct estimation and correction of residual aberrations in the reconstructed exit-wavefunction of a crystalline specimen

Measuring residual aberrations up to second order using a crystalline specimen in transmission electron microscope is challenging. Here, we show by good examples of both experimental and simulated images that it is feasible to measure aberrations up to the second-order, using minimum amplitude contrast criterion for the exit wave function reconstructed. We propose a two-steps strategy for the task: (i) Firstly measuring defocus and twofold astigmatism simultaneously to avoid error accumulation and to reduce the number of dimensions in parameters space. (ii) Then, with minimized misleading effects (or errors) in defocus and two-fold astigmatism, estimations of three-fold astigmatism and coma can be conducted more efficiently and effectively. Influences of other factors such as specimen structure, resolution and specimen thickness on the validity of the method are also discussed in detail. Our study provides a practical procedure for correcting residual aberrations in image wave using crystalline materials, which can then facilitate application of exit wave reconstruction technique to materials research.

Automated summary

This study demonstrates the feasibility of measuring second-order residual aberrations in a transmission electron microscope using the minimum amplitude contrast criterion for exit wave function reconstruction. The study proposes a two-step strategy of simultaneously measuring defocus and twofold astigmatism, followed by more efficient estimation of threefold astigmatism and coma after minimizing misleading effects. The influences of specimen structure, resolution, and specimen thickness on the validity of the method are also discussed.