Efficient large field of view electron phase imaging using near-field electron ptychography with a diffuser

Frederick Allars,Peng-Han Lu,Maximilian Kruth,Rafal E Dunin-Borkowski,John M Rodenburg,Andrew M Maiden

doi:10.1016/j.ultramic.2021.113257

Frederick Allars, Peng-Han Lu + Show 4 more

Open Access

https://doi.org/10.1016/j.ultramic.2021.113257

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Abstract

Most implementations of ptychography on the electron microscope operate in scanning transmission (STEM) mode, where a small focussed probe beam is rapidly scanned across the sample. In this paper we introduce a different approach based on near-field ptychography, where the focussed beam is replaced by a wide-field, structured illumination, realised through a purpose-designed etched Silicon Nitride window. We show that fields of view as large as 100 μm2 can be imaged using the new approach, and that quantitative electron phase images can be reconstructed from as few as nine near-field diffraction pattern measurements.

Highlights

Ptychography is a computational imaging technique first described in 1970 by Hoppe for electron microscopy [1], which has been developed into a popular form of coherent diffractive imaging in the last decade [2]
The microscope is a probe-corrected STEM instrument, it was operated as an uncorrected transmission electron microscope (TEM) for these experiments
This paper demonstrates a novel form of near-field ptychography in the TEM that employs a structured diffuser located in the microscope selected area aperture strip

Summary

Introduction

Ptychography is a computational imaging technique first described in 1970 by Hoppe for electron microscopy [1], which has been developed into a popular form of coherent diffractive imaging in the last decade [2]. The detector records the intensity of the new diffraction pattern, the process repeats until an area of interest on the sample has been illuminated by an overlapping patchwork of probe positions. The overlap between probe positions means ptychography is robust and insensitive to noise, compared to other forms of coherent diffractive imaging, whilst the lateral translation at the heart of the technique naturally extends the field of view. These benefits, combined with ptychography’s simple, single-optical path experimental process, have led to its wide adoption in both optical [9,10] and x-ray [11] microscopy. The advent of high speed direct-detection cameras has recently sparked great interest in applying the technique for ultra-high resolution imaging [12] as well as low dose imaging of biological samples [13]

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