High-resolution scanning transmission electron microscopy (HR-STEM) with spherical aberration correction enables researchers to peer into two-dimensional (2D) materials and correlate the material properties with those of single atoms. The maximum intensity of corrected electron beam is confined in the area having sub-angstrom size. Meanwhile, the residual threefold astigmatism of the electron probe implies a triangular shape distribution of the intensity, whereas its tails overlap and thus interact with several atomic species simultaneously. The result is the resonant modulation of contrast that interferes the determination of phase transition of 2D materials. Here, we theoretically reveal and experimentally determine the origin of resonant modulation of contrast and its unintended impact on violating the power-law dependence of contrast on coordination modes between transition metal and chalcogenide atoms. The finding illuminates the correlation between atomic contrast, spatially inequivalent chalcogenide orientation, and residual threefold astigmatism on determining the atomic structure of emerging 2D materials.

具有球面像差校正功能的高分辨率扫描透射电子显微镜（HR-STEM）使研究人员能够凝视二维（2D）材料并将材料特性与单个原子的特性相关联。校正后的电子束的最大强度被限制在具有亚埃大小的区域中。同时，电子探针的残留三倍像散意味着强度的三角形分布，而其尾部重叠并因此与几种原子种类同时相互作用。结果是对比度的共振调制会干扰2D材料相变的确定。这里，我们从理论上揭示并实验确定了对比度的共振调制的起源，以及其对违反对比度对过渡金属和硫族化物原子之间的配位模式的幂律依赖性的意外影响。这一发现阐明了在确定新兴2D材料的原子结构时原子对比度，空间上不等价的硫族化物取向和残留三倍散光之间的相关性。