推动原子分辨率成像的剂量极限：NaCl的4D-STEM案例研究

中文摘要 AI 辅助

束致损伤从根本上限制了扫描透射电子显微镜（STEM）对束敏感材料的表征，因为结构信息必须在电子束不可逆地改变样品之前被记录。本文以氯化钠（NaCl）作为模型束敏感离子晶体，研究束致结构演化以及可在显著损伤前恢复有用结构信息的低剂量区域。使用Timepix3直接电子探测器在200 kV下采集四维STEM（4D-STEM）数据集，并通过实时积分质心（riCoM）成像进行重构。我们首先确定了NaCl在高电子剂量下的特征损伤行为。在不同的停留时间和光栅扫描方向上，损伤可重复地发展为方形刻面空洞，其边界与岩盐晶格的100晶向对齐，表明形态主要由内在晶体学而非扫描几何决定。然后，我们使用剂量分次采集研究低剂量成像区域。在每帧130 e-A-2下，相对于第一帧的归一化互相关定量追踪渐进的结构退化，并能够识别可测量损伤的起始作为累积剂量的函数。随后在每帧32 e-A-2下进行的采集表明，原子尺度空间信息仍可在该损伤阈值以下恢复。这些结果证明了剂量高效的4D-STEM采集结合riCoM成像如何能够扩展高束敏感离子材料的可成像区域，同时保留原子尺度信息。

英文摘要

Beam-induced damage fundamentally limits the characterization of beam-sensitive materials by scanning transmission electron microscopy (STEM), since structural information must be recorded before the electron beam irreversibly modifies the specimen. Here, sodium chloride (NaCl) is employed as a model beam-sensitive ionic crystal to investigate beam-induced structural evolution and the low-dose regime in which useful structural information can be recovered prior to significant damage. Four-dimensional STEM (4D-STEM) datasets were acquired at 200 kV using a Timepix3 direct electron detector and reconstructed using real-time integrated centre of mass (riCoM) imaging. We first establish the characteristic damage behavior of NaCl under high electron doses. Across different dwell times and raster scan orientations, damage develops reproducibly into square-faceted voids whose boundaries align with the 100 crystallographic directions of the rock-salt lattice, indicating that the morphology is governed predominantly by the intrinsic crystallography rather than the scan geometry. We then investigate the low-dose imaging regime using dose-fractionated acquisitions. At 130 e-A-2 per frame, normalized cross-correlation with respect to the first frame quantitatively tracks progressive structural degradation and enables the onset of measurable damage to be identified as a function of accumulated dose. A subsequent acquisition at 32 e-A-2 per frame demonstrates that atomic-scale spatial information can still be recovered below this damage threshold. These results demonstrate how dose-efficient 4D-STEM acquisition combined with riCoM imaging can extend the accessible imaging regime of highly beam-sensitive ionic materials while preserving atomic-scale information.

发表机构

• University of Antwerp（安特卫普大学）

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