Carbon nanotubes at the Graphene/hBN interface abnormally enhance its fracture toughness

Abstract

Different from Van der Waals heterojunction, defects often appear at the interface of the planar heterostructures due to the low-dimensional structure characteristics. These defects lead to complex mechanical problems, and seriously affect application of planar heterostructures in flexible electronics devices. The most commonly used method to improve the toughness is to reduce/eliminate the interfacial structural defects. Using a defective Graphene/hBN interface, we show surprisingly that Carbon Nanotubes (CNTs) are able to enhance the toughness at the interface. It is found that interlayer stress transfer, bonding strain energies and energy release rate of the defective Graphene/hBN interface with CNTs are higher than those of free-defect Graphene/hBN interface, which is in strong contrast to the general view that interfacial defects reduce toughness. By combining the analysis of atomic mechanics and fracture mechanics theory, we find that the abnormal enhancement in interfacial toughness comes from the stress field localization arising from sp2 + sp3 hybrid state and out-of-plane deformation at the interface. In addition, the stress field at the distal end of the simulated models gradually decays with the CNTs height, resulting in the stress fields to be controlled at the interface. This abnormal mechanism provides a new dimension for enhancing toughness in two-dimensional heterostructures.