Probing Atomic-Scale Fracture of Grain Boundaries in Low-symmetry 2D Materials

Grain boundaries (GBs) play a central role in the fracture of polycrystals. However, the complexity of GBs and the difficulty in monitoring the atomic structure evolution during fracture greatly limit the understanding of the GB mechanics. Here, in situ aberration-corrected scanning transmission electron microscopy and density functional theory calculations are combined to investigate the fracture mechanics in low-symmetry, polycrystalline, 2D rhenium disulfide (ReS₂ ), unveiling the distinctive crack behaviors at different GBs with atomic resolution. Brittle intergranular fracture prefers to rip through the GBs that are parallel to the Re chains of at least one side of the GBs. In contrast, those GBs, which do not align with Re chains on either side of the GBs, are highly resistant to fracture, impeding or deflecting the crack propagation. These results disclose the GB type-dependent mechanical failure of anisotropic 2D polycrystals, providing new ideas for material reinforcement and controllable cutting via GB engineering.