PolyU researchers unveil novel strategy to achieve both strength and toughness in 2D materials design, advancing applications in electronic and photonic devices (IMAGE)
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a, Schematic showing the fracture processes of untwisted and twisted bilayers, respectively. The cracks in both 1st layer and 2nd layer of the untwisted bilayer propagate along the same direction. However, the cracks in the twisted bilayer are along different directions and follow the cleavage planes (the zigzag motifs of TMDs). Along with continuous crack propagation, the cracked edges of different layers can be healed to form a GB after interlayer sliding, and a screw dislocation will form at the crack tip between the GB and stacked bilayer. GBs add resistance to further crack propagation until a secondary fracture occurs. The screw dislocation will then be destroyed, and the crack propagates continuously until the GB is totally broken. b, Morphology of crack propagation in twisted bilayer MoS2. The pre-crack is induced by the e-beam. The section (stage) of the crack can be classified into the complete crack, bilayer stack section, GB section and intact twisted bilayer. c–e, In situ STEM observations of the fracture process in one crack tip of twisted bilayer MoS2. With crack propagation, the overlapped (stacked) area of the two layers continuously shrinks (c) and then the edges of the 1st layer and 2nd layer heal back to form a new GB with sequential dislocation structure (d). e, Finally, the GB breaks in a secondary fracture as the crack propagates further. f–h, MD snapshots of the fracture process at different tensile strains (ε) in twisted bilayer MoS2, where the twisted bilayer MoS2 is bridged by a GB formed across the layers. f, Equilibrated atomic-level structures of the GB-bridged twisted bilayer MoS2 (θ = 30°) corresponding to the experimental observation. g, Crack initiation from the screw dislocation area near the crack tip. h, Cracks advance through the bilayer along different paths. The insets in f–h show the detailed structures of the GB. Scale bars, 100 nm (b); 1 nm (c–e).
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