Low-dimensional materials usually exhibit mechanical properties from those of their bulk counterparts. Here, we show in two-dimensional (2D) rhenium disulfide (ReS₂) that the fracture processes are dominated by a variety of previously unidentified phenomena, which are not present in bulk materials. Through direct transmission electron microscopy observations at the atomic scale, the structures close to the brittle crack tip zones are clearly revealed. Notably, the lattice reconstructions initiated at the postcrack edges can impose additional strain on the crack tips, modifying the fracture toughness of this material. Moreover, the monatomic thickness allows the restacking of postcrack edges in the shear strain–dominated cracks, which is potentially useful for the rational design of 2D stacking contacts in atomic width. Our studies provide critical insights into the atomistic processes of fracture and unveil the origin of the brittleness in the 2D materials.

低维材料通常表现出与其大块材料不同的机械性能。在这里，我们在二维 (2D) 二硫化铼 (ReS ₂ ) 中表明，断裂过程主要由各种先前未识别的现象主导，而这些现象在块状材料中不存在。通过原子尺度的直接透射电子显微镜观察，脆性裂纹尖端区域附近的结构清晰可见。值得注意的是，在裂纹后边缘开始的晶格重建可以对裂纹尖端施加额外的应变，从而改变该材料的断裂韧性。此外，单原子厚度允许在剪切应变主导的裂纹中重新堆叠裂纹后边缘，这对于原子宽度的二维堆叠接触的合理设计可能有用。我们的研究为断裂的原子过程提供了重要的见解，并揭示了二维材料脆性的起源。