在透射电子显微镜中从暗场强度提取莫尔尺度应变的考量
Considerations for extracting moiré-level strain from dark field intensities in transmission electron microscopy
AI总结：
本文分析了基于4D-STEM的布拉格干涉测量法在提取莫尔尺度应变时的采集参数限制与计算后处理瓶颈，并提出改进方法以提升空间分辨率和扩展对扭曲结构的探测能力。
摘要：
布拉格干涉测量法（BI）是一种基于四维扫描电子显微镜（4D-STEM）的成像技术，其中选定重叠布拉格盘的强度在简单三角方程的背景下被拟合或更定性分析，以确定局部堆叠顺序。在基于4D-STEM的方法中，在扫描探针的每个实空间位置收集完整衍射图案，允许使用比传统暗场成像中使用的更小且形状更多变的精确虚拟光阑，因此甚至可以针对与其他层略微扭曲的埋藏界面。作为暗场叠层成像的一种粗粒度形式，BI使用简单的物理推导拟合函数来提取照明区域内的平均结构，因此在大视场下是可行的。BI在选择性研究复杂多层结构中的双层界面的层间堆叠及相关的莫尔重构方面显示出特别的优势。这使得研究通过封装六方氮化硼的双层中的重构和衬底效应以及三层堆叠中选定双层界面成为可能。然而，该技术可以改进以提供更高的空间分辨率并探测更广泛的扭曲结构，对于这些结构，当前采集参数的限制可能导致大的照明区域，并且计算密集的后处理可能失败。在这里，我们更深入地分析这些限制和计算处理，提出一些相对于先前工作的改进方法，讨论进一步扩展的潜在领域，并说明这种方法在提取莫尔尺度应变方面的当前能力。
英文摘要：
Bragg interferometry (BI) is an imaging technique based on four-dimensional scanning electron microscopy (4D-STEM) wherein the intensities of select overlapping Bragg disks are fit or more qualitatively analyzed in the context of simple trigonometric equations to determine local stacking order. In 4D-STEM based approaches, the collection of full diffraction patterns at each real-space position of the scanning probe allows the use of precise virtual apertures much smaller and more variable in shape than those used in conventional dark field imaging, such that even buried interfaces marginally twisted from other layers can be targeted. A coarse-grained form of dark field ptychography, BI uses simple physically derived fitting functions to extract the average structure within the illumination region and is therefore viable over large fields of view. BI has shown a particular advantage for selectively investigating the interlayer stacking and associated moiré reconstruction of bilayer interfaces within complex multi-layered structures. This has enabled investigation of reconstruction and substrate effects in bilayers through encapsulating hexagonal boron nitride and of select bilayer interfaces within trilayer stacks. However, the technique can be improved to provide a greater spatial resolution and probe a wider range of twisted structures, for which current limitations on acquisition parameters can lead to large illumination regions and the computationally involved post-processing can fail. Here we analyze these limitations and the computational processing in greater depth, presenting a few methods for improvement over previous works, discussing potential areas for further expansion, and illustrating the current capabilities of this approach for extracting moiré-scale strain.
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