Improved Three-Dimensional Reconstructions in Electron Ptychography through Defocus Series Measurements

TL;DR

This paper introduces multi-focus ptychography with defocus series measurements to improve 3D electron microscopy reconstructions, outperforming existing methods in accuracy for thick specimens.

Contribution

The paper presents a novel multi-focus ptychography technique using defocus series, enhancing 3D reconstruction quality over traditional methods.

Findings

Multi-focus ptychography achieves higher accuracy in 3D reconstructions.

The method outperforms conventional and regularized ptychography.

Enhanced surface and interface detail reconstruction in thick specimens.

Abstract

A detailed analysis of ptychography for 3D phase reconstructions of thick specimens is performed. We introduce multi-focus ptychography, which incorporates a 4D-STEM defocus series to enhance the quality of 3D reconstructions along the beam direction through a higher overdetermination ratio. This method is compared with established multi-slice ptychography techniques, such as conventional ptychography, regularized ptychography, and multi-mode ptychography. Additionally, we contrast multi-focus ptychography with an alternative method that uses virtual optical sectioning through a reconstructed scattering matrix ($\mathcal{S}$-matrix), which offers more precise 3D structure information compared to conventional ptychography. Our findings from multiple 3D reconstructions based on simulated and experimental data demonstrate that multi-focus ptychography surpasses other techniques, particularly in accurately reconstructing the surfaces and interface regions of thick specimens.