Pressure-Driven Atomic Reconstruction Governs Strength Collapse in Slightly Twisted Moiré Diamane Nanostructures.

The advent of moiré engineering and twistronics has unlocked new possibilities for tailoring the structure and properties of diamane. Using molecular dynamics (MD) simulations, we investigate the pressure-driven phase transition from hydrogenated twisted bilayer graphene (tBLG) to moiré diamane at ambient temperature. We reveal that atomic reconstruction in small-angle tBLG (θ < 10°) under out-of-plane pressure produces distinct microstructures, comprising covalently bonded AA-diamane domains separated by metastable, weakly interacting graphene boundaries. Decreasing twist angles significantly enhances interlayer covalent bonding, reaching a bonding ratio of 82.5% at 2.005° compared to only 11.7% at 9.430°. Paradoxically, fracture strength weakens despite increased reinforcement by the AA-diamane phase (88.0 GPa), dropping to 28.2 GPa at θ = 2.005°. This counterintuitive trend arises from interior stress concentrations at unbonded graphene boundaries, which promote crack initiation and propagation. Stress distribution analysis, based on the first principal stress, reveals distinct patterns at various angles. These findings reveal a surprising phenomenon where interlayer-bonded reinforcing domains reduce mechanical strength, offering new mechanistic insights for tailoring the properties and applications of emerging twisted 2D materials.