Comparative fracture toughness of multilayer graphenes and boronitrenes.

We report the comparative in situ fracture toughness testing on single-edge V/U-notched multilayer graphenes and boronitrenes in a high-resolution transmission electron microscope (HRTEM). The nanostructures of notch tips and fracture edges of the tested specimens are unambiguously resolved using HRTEM. By analyzing the notch tip stresses using finite element method, the fracture toughness of multilayer graphenes and boronitrenes is determined to be 12.0 +/- 3.9 and 5.5 +/- 0.7 MPa root m, respectively, taking into account the notch tip blunting effects.