Relationships between the elastic and fracture properties of boronitrene and molybdenum disulfide and those of graphene.

A consistent set of 2D elastic and fracture properties of hexagonal boron nitride (h-BN) monolayers (boronitrene) and molybdenum disulfide (MoS2 ) nanosheets is derived. Reported literature values for Young's moduli and fracture strengths, based on experiments and DFT calculations, were used to estimate the line or edge energy with a local 2D bond-breaking model. Consistent information was obtained for intrinsic fracture properties. The basic mechanical properties of boronitrene are roughly 25% lower than the corresponding graphene values. This is consistent with the tensile bond force model, and the lower ionic-covalent bonding energy of sp2 -hybridized B-N bonds in comparison with sp2 -hybridized carbon bonds. While the intrinsic stiffness and strength of MoS2 correlate with the strength of its constituent chemical bonds, DFT calculations of the line or edge energy scale with roughly two times the Mo-S bonding energy, whereas the 2D bond-breaking model yields a correlation similar to that found for h-BN. Additional failure properties such as the fracture toughness and strain energy release rate were determined. Together with the intrinsic strengths a Griffith plot of the effective strength of defective h-BN and MoS2 versus the square root of half the defect size of single defects such as (multi)vacancies and micro-cracks exhibits a slope similar to that of the graphene plot.