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电子叠层的原理与特点

于 荣*，沙浩治，崔吉哲，杨文峰
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2023年 第42卷 第6期: 1000-6281（2023）06-767-005     下载地址：

电子叠层的原理与特点

于  荣*，沙浩治，崔吉哲，杨文峰

（清华大学材料学院，北京100084）

摘  要    即使在像差校正电镜方兴未艾之时，材料的微观结构分析也面临残余像差、带轴偏离、表面损伤和辐照损伤等问题，不仅使电镜的空间分辨率近年来一直徘徊在0.5 Å左右，而且制约了微观结构分析的可靠性和精度。电子叠层（electron ptychography）是结合扫描透射电镜和相干衍射成像的一种计算成像方法，具有高空间分辨、高相位精度、高剂量效率等特点。电子叠层包括数据采集和数值重构两个阶段。在数据采集阶段，通过像素化探测器记录电子束在样品上二维扫描时每个位置的二维衍射图，形成所谓的四维扫描透射电镜数据集（four-dimensional scanning transmission electron microscopy, 4D-STEM）。在数值重构阶段，通过合适的算法从这些数据集中提取样品的振幅和相位。作为比较，像差校正能显著减小透镜像差对成像质量的影响，而电子叠层可以消除这种影响，实现零像差成像，近乎完美地重现样品的真实结构。作者从材料微观结构分析面临的主要问题出发，简要介绍电子叠层的基本原理和算法，并通过应用实例介绍电子叠层的主要特点。

关键词   电子叠层；计算成像；电子显微学；零像差成像

中图分类号：TP391.41; TN16; TH742 文献标识码：A  doi:10.3969/j.issn.1000-6281.2023.06.010

 

Principles and characteristics of electron ptychography

YU Rong, SHA Hao-zhi, CUI Ji-zhe, YANG Wen-feng

（School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China)

Abstract    Even for aberration-corrected electron microscopy, structural analysis of a material still faces challenges including residual aberrations, misorientations, surface damages, irradiation damages, etc. These challenges have not only made the spatial resolution of electron microscopy stay around 0.5 Å, but also restricted the reliability and accuracy of microstructural analysis. Electron ptychography is a computational imaging method combining scanning transmission electron microscopy with coherent diffraction imaging. It is characterized by high spatial resolution, high phase accuracy and high dose efficiency. Electron ptychography includes two steps: data acquisition and numerical reconstruction. In the data acquisition step, two-dimensional diffraction patterns are recorded by a pixelated detector at each position when the electron beam is scanned in two dimensions on a sample, forming the so-called four-dimensional scanning transmission electron microscopy dataset (4D-STEM). In the numerical reconstruction step, the amplitude and phase of the object and the probe are extracted from the dataset by suitable algorithms. For comparison, aberration-correction significantly reduces the impact of lens aberrations on image quality, while electron ptychography is able to achieve aberration-free imaging, almost perfectly reproducing the true structure of the object. We first discuss the main challenges in the structural analysis of materials, then we briefly introduce the fundamentals, the reconstruction algorithms, and the characteristics of electron ptychography, in particular the adaptive-propagator ptychography (APP).

Keywords    electron ptychography; computational imaging; electron microscopy; aberration-free imaging

 

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