Metastability and Size Effect during Transformation from Dislocation to Ripplocation in Bilayer Graphene

Compression strain-induced dislocation and ripplocation structures are crucial for the unique properties of van der Waals layered materials. While previous studies have primarily focused on the dislocation-ripplocation transformation under thermodynamic equilibrium, the metastability of this transformation remains underexplored. This work theoretically reports the existence of a metastable region for the dislocation-ripplocation structural transformation in bilayer graphene under uniaxial compression. Using nudged elastic band calculations, we identify a nonzero energy barrier between the two structures, indicating metastability within a specific strain range ε_i ≤ ε₀ ≤ ε_e. Outside this range, only one local minimum exists: dislocation at ε₀ < ε_i and ripplocation at ε₀ > ε_e. Furthermore, we investigate the size dependence of the two critical strains that bound the metastable region, finding that the difference between them, ε_e - ε_i, increases with the sample length. This structural transformation profoundly affects the material's physical properties, such as tribological behavior. These findings reveal the metastable nature of dislocation-ripplocation transformation and offer valuable insights into strain-engineered morphologies of layered materials, with implications for the mechanical behavior and design of nanodevices.