Barnard Jonathan S, Johnstone Duncan N, Midgley Paul A
Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom.
Ultramicroscopy. 2017 Mar;174:79-88. doi: 10.1016/j.ultramic.2016.12.018. Epub 2016 Dec 25.
Methods are presented for aligning the pivot point of a precessing electron probe in the scanning transmission electron microscope (STEM) and for assessing the spatial resolution in scanning precession electron diffraction (SPED) experiments. The alignment procedure is performed entirely in diffraction mode, minimising probe wander within the bright-field (BF) convergent beam electron diffraction (CBED) disk and is used to obtain high spatial resolution SPED maps. Through analysis of the power spectra of virtual bright-field images extracted from the SPED data, the precession-induced blur was measured as a function of precession angle. At low precession angles, SPED spatial resolution was limited by electronic noise in the scan coils; whereas at high precession angles SPED spatial resolution was limited by tilt-induced two-fold astigmatism caused by the positive spherical aberration of the probe-forming lens.
本文介绍了在扫描透射电子显微镜（STEM）中对准进动电子探针的枢轴点以及在扫描进动电子衍射（SPED）实验中评估空间分辨率的方法。对准过程完全在衍射模式下进行，将探针在明场（BF）会聚束电子衍射（CBED）盘内的漂移降至最低，并用于获得高空间分辨率的SPED图。通过分析从SPED数据中提取的虚拟明场图像的功率谱，测量了进动引起的模糊随进动角度的变化。在低进动角度下，SPED空间分辨率受扫描线圈中的电子噪声限制；而在高进动角度下，SPED空间分辨率受由探针形成透镜的正球差引起的倾斜诱导的二次像散限制。
