发表机构
School of Applied and Engineering Physics, Cornell University; Department of Chemistry and Chemical Biology, Cornell University; Kavli Institute at Cornell for Nanoscale Science（康奈尔大学应用工程物理学院; 康奈尔大学化学与化学生物学系; 康奈尔纳米科学卡弗里研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文揭示4D-STEM中视差编码的三维信息与断层扫描及光场摄影的关联，提出基于4D FFT的快速非迭代深度切片方法，并验证像差校正明场成像在多层样品三维重建中的优势。
AI 中文摘要
三维（3D）信息通过每个探测器像素处形成的虚拟图像之间的视差编码在四维扫描透射电子显微镜（4D-STEM）中。本文将4D-STEM中深度依赖信息的编码与检索与另外两种广泛使用的三维成像方法——断层扫描和光场摄影——联系起来，并推导了其三维相位衬度传递函数。将四维数据视为角切片集合可得到一系列正弦图，为三维信息传递提供了直观的视觉表示。在小角度近似下，倾斜校正明场（tcBF）深度切片等效于非迭代断层重建。或者，四维数据也可映射到光场（或全光）成像，后者利用透镜阵列并行获取空间分辨的衍射数据。通过采用一种光场成像算法，我们表明可以从数据集的单一四维快速傅里叶变换（4D FFT）中提取二维切片来获得tcBF深度切片，从而在重建大量深度切片时实现显著加速。这些不同的视角将深度分辨率的几何方面与相位衬度成像中存在的波动光学效应区分开来。深度分辨像差校正明场（acBF）成像相比tcBF可获得改进的三维重建，消除了衬度振荡并减少了响应随深度的变化。我们使用模拟和实验数据演示了acBF深度切片，并分辨了堆叠氧化物薄膜和纳米颗粒组装体中的不同层。这种从单一4D-STEM数据集进行的非迭代体积重建，为厚而弱散射样品的改进成像以及低剂量采集的重建展现了前景。
英文摘要
Three-dimensional (3D) information is encoded in four-dimensional scanning transmission electron microscopy (4D-STEM) through parallax between the virtual images formed at each detector pixel. In this paper we connect the encoding and retrieval of depth-dependent information in 4D-STEM to two other widely-used 3D imaging methods, tomography and light-field photography, and derive its 3D phase contrast transfer function. Viewing the 4D data as a collection of angular slices yields a collection of sinograms, providing an intuitive visual representation of the 3D information transfer. Within the small-angle approximation, tilt-corrected bright-field (tcBF) depth sectioning is equivalent to non-iterative tomographic reconstruction. Alternatively, the 4D data also can be mapped to light-field (or plenoptic) imaging, which acquires spatially resolved diffraction data in parallel using an array of lenslets. Adapting a light-field imaging algorithm, we show that tcBF depth sections can be obtained by extracting two-dimensional slices from a single four-dimensional fast Fourier transform (4D FFT) of the dataset, yielding a substantial speedup when reconstructing a large number of depth slices. These differing perspectives distinguish the geometric aspects of depth resolution from wave-optical effects that are present in phase-contrast imaging. Depth-resolved aberration-corrected bright-field (acBF) imaging yields improved 3D reconstructions compared to tcBF, removing contrast oscillations and reducing the variation in response with depth. We demonstrate acBF depth sectioning using simulated and experimental data and resolve distinct layers in stacked oxide films and nanoparticle assemblies. These non-iterative volumetric reconstructions from a single 4D-STEM dataset show promise for improved imaging of thick, weakly-scattering samples and for reconstructing low-dose acquisitions.
Comments65 pages, 16 figures
