Robust Ptychographic Reconstruction with an Out-of-Focus Electron Probe

TL;DR

This paper advances out-of-focus electron ptychography by developing a robust calibration method that improves reconstruction accuracy and stability, enabling atomic-scale imaging over large fields of view despite experimental challenges.

Contribution

The study extends the Fourier calibration method for out-of-focus ptychography, enhancing robustness and accuracy in probe and scan position initialization, and provides optimized experimental parameters.

Findings

Enhanced robustness of out-of-focus ptychographic reconstruction.

Reliable initialization of scan positions and probes.

Comparison shows advantages of defocused probes in low-dose imaging.

Abstract

As a burgeoning technique, out-of-focus electron ptychography offers the potential for rapidly imaging atomic-scale large fields of view (FoV) using a single diffraction dataset. However, achieving robust out-of-focus ptychographic reconstruction poses a significant challenge due to the inherent scan instabilities of electron microscopes, compounded by the presence of unknown aberrations in the probe-forming lens. In this study, we substantially enhance the robustness of out-of-focus ptychographic reconstruction by extending our previous calibration method (the Fourier method), which was originally developed for the in-focus scenario. This extended Fourier method surpasses existing calibration techniques by providing more reliable and accurate initialization of scan positions and electron probes. Additionally, we comprehensively explore and recommend optimized experimental parameters for robust out-of-focus ptychography, includingaperture size and defocus, through extensive simulations. Lastly, we conduct a comprehensive comparison between ptychographic reconstructions obtained with focused and defocused electron probes, particularly in the context of low-dose and precise phase imaging, utilizing our calibration method as the basis for evaluation.