In situ nanomechanical characterization of multi-layer MoS₂ membranes: From intraplanar to interplanar fracture

Layered molybdenum disulfide (MoS₂) exhibits rich electronic and optical properties and possesses vastly differing characteristic dimensions. A multi-layer MoS₂ membrane represents the critical hierarchical structure which bridges the length-scale of monolayer and bulk material architectures. In this study, the in-plane mechanical properties of MoS₂ membranes were investigated by in situ SEM tensile testing. Under the uniaxial tensile loading, brittle fracture caused failure in a highly localized region of the MoS₂ membranes and their mechanical properties showed a thickness effect: the strengths of the relatively thicker MoS₂ membranes (thickness around hundreds of nanometers) distribute from ∼100 to ∼250 MPa, while the corresponding values of the MoS₂ nanosheets (thickness around tens of nanometers) increase significantly to more than 1 GPa. Upon molecular dynamics (MD) simulations on the fractures of MoS₂ with various thicknesses/layers, the thicker MoS₂ membranes show interplanar fracture, and the typical MoS₂ nanosheets demonstrate the transition from interplanar to intraplanar fractures, while monolayer and few-layer MoS₂ are dominated by intraplanar fracture. Our study provides some critical insights into the mechanical properties and fracture behavior of layered MoS₂ 2D materials, which could be of value for their flexible electronic, optoelectronic and nano-electro-mechanical system (NEMS) applications.