In situ nanomechanical characterization of multi-layer MoS2 membranes: from intraplanar to inter-planar 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 similar to 100 to similar 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.