Long-period patterns (LPPs) are widely observed by transmission electron microscopy (TEM) in the study of nanoscale materials. Identifying the origin of LPPs is of significant importance when interpreting TEM images, and for an in-depth understanding of material characteristics. However, the two most common LPP categories, modulated structure and moiré patterns, are not easily differentiated by conventional TEM (CTEM). In this work, an LPP was observed in Cu2-xSe nanoplates by CTEM. And then the depth sectioning with an aberration-corrected scanning transmission electron microscope (AC STEM) has been performed to determine the LPP type. Two misorientated layers were recognized from the depth-series of atomic resolution images of an LPP region, confirming the LPP is a moiré pattern caused by two twisted stacked crystal flakes which commonly exists in nanosized materials. This depth sectioning method is generally applicable for structural characterization of layered systems, and is a powerful approach for the in-situ structural probe of nanomaterials. It is promising to be extended to fast three-dimensional (3D) reconstruction.

中文翻译：

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使用像差校正的扫描透射电子显微镜通过深度切片洞察长周期模式

在纳米材料的研究中，透射电子显微镜 (TEM) 广泛观察到长周期模式 (LPP)。在解释 TEM 图像和深入了解材料特性时，确定 LPP 的起源非常重要。然而，两种最常见的 LPP 类别，调制结构和莫尔图案，传统 TEM (CTEM) 不容易区分。在这项工作中，通过 CTEM 在 Cu2-xSe 纳米片中观察到 LPP。然后使用像差校正的扫描透射电子显微镜 (AC STEM) 进行深度切片以确定 LPP 类型。从 LPP 区域的原子分辨率图像的深度系列中识别出两个方向错误的层，确认 LPP 是由通常存在于纳米材料中的两个扭曲堆叠的晶体薄片引起的莫尔图案。这种深度切片方法通常适用于层状系统的结构表征，是纳米材料原位结构探针的有力方法。它有望扩展到快速三维（3D）重建。