二维单层过渡金属硫族化合物材料中缺陷结构的精确表征及分析

二维单层过渡金属硫族化合物（TMDC）以其新颖的电学、光学、磁学等性质，近年来引起了广泛的关注。由于热扰动、电子束辐射、掺杂等因素导致的缺陷结构的影响，TMDC的扫描透射电子显微镜（STEM）图像呈现出与标准晶格不同的明暗变化和结构畸变。本文聚焦不同TMDC单层材料高分辨STEM图像的数据分析，通过对原子（柱）投影位置、亮度、形状等图像信息的量化处理，挖掘图像中明暗变化和结构畸变背后的物理意义。本论文主要包括三方面工作：（1）基于单一STEM的二维投影图像对单层MoSe₂结构进行精确三维重构。利用Se₂原子柱投影在低采集角度（MAADF）下呈现出衬度明暗变化的特性，通过多层切片模拟和量子散射理论的计算的方法，我们证明了上下两层硒原子的微小错位是明暗变化的主要原因。结合硒原子错位导致投影图样形状变化的特点，Se₂原子柱的错位位移可以被精确重构。该位移来自于材料起伏结构的性质，MoSe₂的三维起伏结构因此可以被重构。（2）WTe₂各向异性的起伏结构的表征。WTe₂的STEM图像显示WTe₂晶格存在畸变，通过量化晶格畸变程度并统计大范围的畸变分布，我们揭示了WTe₂在畸变-非畸变区域存在的明显的边界，该现象来源于WTe₂各向异性的起伏结构。（3）钒掺杂的硒化钨（W_x V_(1-x) Se₂）中的一维钒原子链结构的表征。STEM图像显示出钒原子倾向于聚集并形成链状结构，我们精确定位了钒原子链的位置并且对其长度、宽度以及链间距等参数做统计，证明该链状结构是导致材料磁性的重要原因。该系列工作为TMDC的STEM图像信息的深入挖掘提供了新的方法，推动了TMDC各个维度的缺陷结构的精确表征及重构的研究。

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