Nanoscale strain mapping by four-dimensional scanning transmission electron microscopy (4D-STEM) relies on determining the precise locations of Bragg-scattered electrons in a sequence of diffraction patterns, a task which is complicated by dynamical scattering, inelastic scattering, and shot noise. These features hinder accurate automated computational detection and position measurement of the diffracted disks, limiting the precision of measurements of local deformation. Here, we investigate the use of patterned probes to improve the precision of strain mapping. We imprint a "bullseye" pattern onto the probe, by using a binary mask in the probe-forming aperture, to improve the robustness of the peak finding algorithm to intensity modulations inside the diffracted disks. We show that this imprinting leads to substantially improved strain-mapping precision at the expense of a slight decrease in spatial resolution. In experiments on an unstrained silicon reference sample, we observe an improvement in strain measurement precision from 2.7% of the reciprocal lattice vectors with standard probes to 0.3% using bullseye probes for a thin sample, and an improvement from 4.7% to 0.8% for a thick sample. We also use multislice simulations to explore how sample thickness and electron dose limit the attainable accuracy and precision for 4D-STEM strain measurements.

中文翻译：

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用于高精度 4D-STEM 布拉格测量的图案化探头

四维扫描透射电子显微镜 (4D-STEM) 的纳米级应变映射依赖于确定一系列衍射图案中布拉格散射电子的精确位置，该任务因动态散射、非弹性散射和散粒噪声而变得复杂。这些特征阻碍了衍射盘的准确自动计算检测和位置测量，限制了局部变形测量的精度。在这里，我们研究了使用图案探针来提高应变映射的精度。我们通过在探针形成孔中使用二元掩模将“靶心”图案压印到探针上，以提高峰值寻找算法对衍射盘内强度调制的鲁棒性。我们表明，这种印记以空间分辨率略有下降为代价，显着提高了应变映射精度。在无应变硅参考样品的实验中，我们观察到应变测量精度从使用标准探针的倒易晶格矢量的 2.7% 提高到使用靶心探针测量薄样品的 0.3%，以及从 4.7% 提高到 0.8% 的测量精度。厚样品。我们还使用多层模拟来探索样品厚度和电子剂量如何限制 4D-STEM 应变测量的准确度和精度。3% 使用靶心探针检测薄样品，将厚样品从 4.7% 提高到 0.8%。我们还使用多层模拟来探索样品厚度和电子剂量如何限制 4D-STEM 应变测量的准确度和精度。3% 使用靶心探针检测薄样品，将厚样品从 4.7% 提高到 0.8%。我们还使用多层模拟来探索样品厚度和电子剂量如何限制 4D-STEM 应变测量的准确度和精度。