Mahr Christoph, Müller-Caspary Knut, Grieb Tim, Krause Florian F, Schowalter Marco, Rosenauer Andreas
Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany; MAPEX Center for Materials and Processes, University of Bremen, Bibliothekstr. 1, D-28359 Bremen, Germany.
Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Wilhelm-Johnen-Strasse, D-52428 Jülich, Germany.
Ultramicroscopy. 2021 Feb;221:113196. doi: 10.1016/j.ultramic.2020.113196. Epub 2020 Dec 14.
Strain analysis by nano-beam electron diffraction allows for measurements of strain with nanometre resolution in a large field of view. This is done by evaluating distances between diffraction discs in diffraction patterns acquired while a focussed electron beam is scanned across the sample in a transmission electron microscope. The bottleneck of this method is a precise determination of diffraction disc positions, which suffers from the inner structure of the discs caused by dynamical diffraction. Electron beam precession is a tool that solves this problem but it is not commonly available in every microscope. Without precession significant progress has been reported recently by using patterned condenser apertures. The pattern of the aperture is reproduced in patterns of the diffraction discs allowing for a more precise position determination. In this report the accuracy of measured strain profiles using patterned apertures is investigated by evaluation of realistic simulations. This is done especially at interfaces between regions with different lattice plane spacing. It is found by evaluation of the simulations that measured strain profiles are more blurred and hence the accuracy at the interface is worse the more patterns are imprinted to the condenser aperture. An explanation of this effect is given and as a proof of principle a solution to this problem is provided applying geometric phase analysis ptychography.
通过纳米束电子衍射进行应变分析，可以在大视场中以纳米分辨率测量应变。这是通过评估在透射电子显微镜中聚焦电子束扫描样品时获得的衍射图案中衍射盘之间的距离来实现的。该方法的瓶颈在于精确确定衍射盘的位置，这受到动态衍射导致的盘内部结构的影响。电子束进动是解决这个问题的一种工具，但并非每台显微镜都普遍具备。在没有进动的情况下，最近通过使用图案化的聚光镜光阑取得了显著进展。光阑的图案会在衍射盘的图案中重现，从而可以更精确地确定位置。在本报告中，通过对实际模拟的评估，研究了使用图案化光阑测量应变分布的准确性。特别是在具有不同晶格面间距的区域之间的界面处进行了此项研究。通过对模拟的评估发现，测量的应变分布更加模糊，因此，印刻在聚光镜光阑上的图案越多，界面处的准确性就越差。文中给出了对此效应的解释，并作为原理证明，提供了一种应用几何相位分析叠层成像术解决此问题的方法。
