Pristine monocrystalline
molybdenum disulfide (MoS2)
possesses high mechanical strength comparable to that of stainless
steel. Large-area chemical-vapor-deposited monolayer MoS2 tends to be polycrystalline with intrinsic grain boundaries (GBs).
Topological defects and grain size skillfully alter its physical properties
in a variety of materials; however, the polycrystallinity and its
role played in the mechanical performance of the emerging single-layer
MoS2 remain largely unknown. Here, using large-scale atomistic
simulations, GB structures and mechanical characteristics of realistic
single-layered polycrystalline MoS2 of varying grain size
prepared by confinement-quenched method are investigated. Depending
on misorientation angle, structural energetics of polar-GBs in polycrystals
favor diverse dislocation cores, consistent with experimental observations.
Polycrystals exhibit grain-size-dependent thermally induced global
out-of-plane deformation, although defective GBs in MoS2 show planar structures that are in contrast to the graphene. Tensile
tests show that presence of cohesive GBs pronouncedly deteriorates
the in-plane mechanical properties of MoS2. Both stiffness
and strength follow an inverse pseudo Hall–Petch relation to
grain size, which is shown to be governed by the weakest link mechanism.
Under uniaxial tension, transgranular crack propagates with small
deflection, whereas upon biaxial stretching, the crack grows in a
kinked manner with large deflection. These findings shed new light
in GB-based engineering and control of mechanical properties of MoS2 crystals toward real-world applications in flexible electronics
and nanoelectromechanical systems.