Fracture fingerprint of polycrystalline C₃N nanosheets: Theoretical basis

Polycrystalline carbon nanosheets are composed of several randomly rotated monocrystalline regions facing each other in grain boundaries-the cause of stress concentration-that affects the mechanics of 2D carbon nanostructures. They have been widely used in different fields, particularly in electronic devices. Herein, heterogeneous graphitic carbon nitride (C₃N) was considered as typical of polycrystalline carbon nanosheets for modelling its fracture behavior. The number of grains with random configuration, temperature, and crack length were systematically changed to track the mode and the intensity of failure of model nanosheets. Molecular dynamics simulations predictions unraveled the interatomic interaction in the C-C and C-N bonds. An increase in the number of grain boundaries from 3 to 25 as well as the length of crack led to more than 70% fall in the Young's modulus of polycrystalline carbon platelets. Stress intensity factor decreased against temperature, but increased by crack length enlargement demonstrating higher fracture toughness of small cracks. This theoretical approach can be generalized to capture the unique fracture fingerprint of polycrystalline carbon structures of different types.