Blackburn Arthur M, McLeod Robert A
Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada.
Nano Accessories Product Group, Hitachi High Technologies Canada, Inc., Etobicoke, ON M9W 6A4, Canada.
Microscopy (Oxf). 2021 Feb 1;70(1):131-147. doi: 10.1093/jmicro/dfaa055.
Ptychography is a coherent diffractive imaging technique that can determine how an electron wave is transmitted through an object by probing it in many small overlapping regions and processing the diffraction data obtained at each point. The resulting electron transmission model describes both phase and amplitude changes to the electron wave. Ptychography has been adopted in transmission electron microscopy in recent years following advances in high-speed direct electron detectors and computer algorithms which now make the technique suitable for practical applications. Its ability to retrieve quantitative phase information at high spatial resolution makes it a plausible alternative or complement to electron holography. Furthermore, unlike off-axis electron holography, it can provide phase information without an electron bi-prism assembly or the requirement of a minimally structured region adjacent to the region of interest in the object. However, it does require a well-calibrated scanning transmission electron microscope and a well-managed workflow to manage the calibration, data acquisition and reconstruction process to yield a practical technique. Here we detail this workflow and highlight how this is greatly assisted by acquisition management software. Through experimental data and modelling we also explore the similarities and differences between high-resolution ptychography and electron holography. Both techniques show a dependence of the recovered phase on the crystalline orientation of the material which is attributable to dynamical scattering. However, the exact nature of the variation differs reflecting fundamental expectations, but nonetheless equally useful information is obtained from electron holography and the ptychographically determined object transmission function.
叠层成像术是一种相干衍射成像技术，它可以通过在许多小的重叠区域对电子波进行探测，并处理在每个点获得的衍射数据，来确定电子波是如何透过物体的。由此得到的电子透射模型描述了电子波的相位和幅度变化。近年来，随着高速直接电子探测器和计算机算法的发展，叠层成像术已被应用于透射电子显微镜中，这些技术进步使得该技术适用于实际应用。它在高空间分辨率下获取定量相位信息的能力，使其成为电子全息术的一种可行替代方法或补充方法。此外，与离轴电子全息术不同，它无需电子双棱镜组件，也不需要在物体感兴趣区域附近有一个结构最少的区域就能提供相位信息。然而，它确实需要一台经过良好校准的扫描透射电子显微镜和一个管理完善的工作流程，以管理校准、数据采集和重建过程，从而形成一种实用技术。在这里，我们详细介绍这个工作流程，并强调采集管理软件对此有多大的帮助。通过实验数据和建模，我们还探讨了高分辨率叠层成像术和电子全息术之间的异同。这两种技术都表明，恢复的相位依赖于材料的晶体取向，这归因于动态散射。然而，变化的确切性质有所不同，反映了基本预期，但尽管如此，从电子全息术和叠层成像术确定的物体透射函数中获得的信息同样有用。
