Symmetry breaking and dynamic characteristics of post-buckling in bilayer van der Waals structures

The van der Waals (vdW) interaction plays a crucial role in the mechanical properties, including bending and buckling, of layered 2D materials, directly affecting their performance as flexible devices. This study systematically investigates the symmetry breaking and dynamic characteristics of post-buckling in bilayer vdW structures caused by the local atomic positions’ dependence of vdW interactions. Our observations reveal that the buckling configuration of bilayer molybdenum disulfide (MoS₂) exhibits a significant dependence on the direction of applied load. When compressed along the zigzag direction, the post-buckling configuration is symmetric. In contrast, compression along the armchair direction results in a significant asymmetric post-buckling configuration. Additionally, the asymmetric buckling configuration strongly correlates with the length of the structure and the magnitude of compressive strain. Combining molecular dynamics simulations and a continuum-discrete model, it is found that this symmetry breaking in buckling results from anisotropic and non-uniform shear and sliding between atomic layers. Moreover, under biaxial compression, bilayer circular MoS₂ demonstrates post-buckling configurations and thermal vibration modes markedly distinct from monolayer MoS₂. These configurations are closely associated with the initial stacking orders of bilayer MoS₂. In particular, effective modulation of asymmetry is achieved by twisting the bilayer structure, offering insights into controlling buckling behavior. These findings provide novel perspectives for describing and addressing buckling issues in layered vdW structures and offer guidance for designing and optimizing vdW structure devices.