Electron Microscopy Centre, AIIM Building, Innovation Campus, University of Wollongong, Fairy Meadow, New South Wales, Australia.
Microsc Res Tech. 2022 Jul;85(7):2708-2713. doi: 10.1002/jemt.24124. Epub 2022 Apr 9.
Electron diffraction patterns obtained on a TEM contain elliptical distortion resulting from column defects. This distortion can be corrected by applying offsets to the objective lens stigmators to cancel distortions occurring further down the column. In this work, a DigitalMicrographTM script-based method has been developed to identify the optimum objective stigmator settings which produce a distortion minimum in diffraction. Initially, a manual (by eye) correction is used to determine the stigmator values necessary to bring the pattern distortion below the threshold at which it is no longer visible to the naked eye (<1%). Thereafter, an automated acquisition script is used to acquire matrices of diffraction patterns while varying the stigmator values about the values which were identified as producing a distortion minimum in the preceding step. This analysis can be applied iteratively to refine the location of the distortion minimum, using progressively finer step changes in objective stigmator values. The optimum stigmator values producing the distortion minimum in diffraction are very different to those in imaging. These imaging and diffraction stigmator values can be saved to script and subsequently recalled at the click of a button, making their application very simple. Using this method, diffraction pattern elliptical distortion in a newly installed TEM was reduced from 1.6% to 0.3%, on a measurement precision of 0.3%, effectively producing distortion-free diffraction. The relevant scripts can be freely downloaded from the internet. RESEARCH HIGHLIGHTS: This paper reports a DigitalMicrograph script-based method to identify and subsequently apply optimized objective stigmator values in diffraction mode. These effectively eliminate elliptical distortion inherent to this diffraction technique.
在 TEM 上获得的电子衍射花样会由于柱缺陷而产生椭圆变形。这种变形可以通过对物镜消像散器施加偏移量来校正，以抵消柱进一步向下延伸时产生的变形。在这项工作中，开发了一种基于 DigitalMicrographTM 脚本的方法来确定最佳物镜消像散器设置，以在衍射中产生最小的变形。最初，使用手动（通过眼睛）校正来确定使花样变形低于肉眼可见阈值（<1%）所需的消像散器值。然后，使用自动采集脚本来获取衍射花样矩阵，同时在产生最小变形的前一步骤确定的消像散器值附近改变消像散器值。可以迭代应用这种分析方法来细化变形最小值的位置，使用物镜消像散器值的逐步更细的步长变化。在衍射中产生最小变形的最佳消像散器值与成像时的非常不同。这些成像和衍射消像散器值可以保存到脚本中，并在点击按钮时随时调用，使其应用非常简单。使用这种方法，新安装的 TEM 中的衍射花样椭圆变形从 1.6%降低到 0.3%，测量精度为 0.3%，有效地产生了无变形的衍射。相关脚本可以从互联网上免费下载。研究亮点：本文报道了一种基于 DigitalMicrograph 脚本的方法来识别和随后在衍射模式下应用优化的物镜消像散器值。这些值有效地消除了该衍射技术固有的椭圆变形。
