Mawson T, Nakamura A, Petersen T C, Shibata N, Sasaki H, Paganin D M, Morgan M J, Findlay S D
School of Physics and Astronomy, Monash University, Victoria 3800, Australia.
JEOL Ltd., Akishima, Tokyo 196-8558, Japan.
Ultramicroscopy. 2020 Dec;219:113097. doi: 10.1016/j.ultramic.2020.113097. Epub 2020 Aug 28.
It is well known that dynamical diffraction varies with changes in sample thickness and local crystal orientation (due to sample bending). In differential phase contrast scanning transmission electron microscopy (DPC-STEM), this can produce contrast comparable to that arising from the long-range electromagnetic fields probed by this technique. Through simulation we explore the scale of these dynamical diffraction artefacts and introduce a metric for the magnitude of their contribution to the contrast. We show that precession over an angular range of a few milliradian can suppress this contribution to the contrast by one-to-two orders of magnitude. Our exploration centres around a case study of GaAs near the [011] zone-axis orientation using a probe-forming aperture semiangle on the order of 0.1 mrad at 300 keV, but the trends found and methodology used are expected to apply more generally.
众所周知，动态衍射会随着样品厚度和局部晶体取向的变化而变化（由于样品弯曲）。在差分相衬扫描透射电子显微镜（DPC-STEM）中，这会产生与该技术探测的长程电磁场产生的对比度相当的对比度。通过模拟，我们探索了这些动态衍射伪像的尺度，并引入了一个度量来衡量它们对对比度贡献的大小。我们表明，在几毫弧度的角度范围内进行进动可以将这种对对比度的贡献抑制一到两个数量级。我们的探索围绕着一个案例研究展开，该案例研究使用了在300keV下约0.1mrad的探针形成孔径半角，研究[011]晶带轴取向附近的GaAs，但所发现的趋势和使用的方法预计将更广泛地适用。
