Ning Shoucong, Xu Wenhui, Ma Yinhang, Loh Leyi, Pennycook Timothy J, Zhou Wu, Zhang Fucai, Bosman Michel, Pennycook Stephen J, He Qian, Loh N Duane
Department of Materials Science and Engineering, National University of Singapore, Singapore117575, Singapore.
Center for Bio-Imaging Sciences, National University of Singapore, Singapore117557, Singapore.
Microsc Microanal. 2022 Mar 9:1-11. doi: 10.1017/S1431927622000320.
Accurate geometrical calibration between the scan coordinates and the camera coordinates is critical in four-dimensional scanning transmission electron microscopy (4D-STEM) for both quantitative imaging and ptychographic reconstructions. For atomic-resolved, in-focus 4D-STEM datasets, we propose a hybrid method incorporating two sub-routines, namely a J-matrix method and a Fourier method, which can calibrate the uniform affine transformation between the scan-camera coordinates using raw data, without a priori knowledge of the crystal structure of the specimen. The hybrid method is found robust against scan distortions and residual probe aberrations. It is also effective even when defects are present in the specimen, or the specimen becomes relatively thick. We will demonstrate that a successful geometrical calibration with the hybrid method will lead to a more reliable recovery of both the specimen and the electron probe in a ptychographic reconstruction. We will also show that, although the elimination of local scan position errors still requires an iterative approach, the rate of convergence can be improved, and the residual errors can be further reduced if the hybrid method can be firstly applied for initial calibration. The code is made available as a simple-to-use tool to correct affine transformations of the scan-camera coordinates in 4D-STEM experiments.
在四维扫描透射电子显微镜（4D-STEM）中，扫描坐标与相机坐标之间精确的几何校准对于定量成像和叠层成像重建都至关重要。对于原子分辨率、聚焦的4D-STEM数据集，我们提出了一种结合两个子程序的混合方法，即J矩阵法和傅里叶法，该方法可以使用原始数据校准扫描相机坐标之间的均匀仿射变换，而无需事先了解样品的晶体结构。结果发现，该混合方法对扫描畸变和残余探针像差具有鲁棒性。即使样品中存在缺陷或样品相对较厚时，该方法也有效。我们将证明，使用混合方法成功进行几何校准将在叠层成像重建中更可靠地恢复样品和电子探针。我们还将表明，尽管消除局部扫描位置误差仍需要迭代方法，但如果首先应用混合方法进行初始校准，则可以提高收敛速度，并进一步降低残余误差。该代码作为一个简单易用的工具提供，用于校正4D-STEM实验中扫描相机坐标的仿射变换。
