Large Elastic Deformation and Defect Tolerance of Hexagonal Boron Nitride Monolayers

Monolayer hexagonal boron nitride can serve in optoelectronics or as a dielectric in graphene and other two-dimensional (2D) electronics due to its ultra-wide band gap. As there is no center of symmetry, monolayer hexagonal boron nitride (h-BN) also shows piezoelectricity. However, these applications require h-BN to sustain large uniform elastic deformation, which has yet to be demonstrated. Here, we report, by tensile testing, that a large elastic strain up to 6.2% is achieved for defect-scarce polycrystalline h-BN monolayers, with corresponding 2D Young’s modulus ∼200 N/m, close to the ideal value measured by atomic force microscopy (AFM). Furthermore, samples containing voids of ∼100 nm can be strained up to 5.8%. Atomistic and continuum simulations show that compared to the imperfections introduced during sample preparation, the elastic limit of h-BN is virtually immune to naturally occurring atomistic defects and is gradually lowered by submicrometer voids. The mechanical robustness of h-BN monolayers, along with the large uniform elasticity, is encouraging for strain engineering and piezoelectronics applications.