Development of the microstructure of 2D graphene sheets in the molecular dynamics simulation of irradiation damage cascades

Two-dimensional graphene is widely used in the nuclear industry, computer simulation of the physical process of graphene irradiation damage can assist the study of microscopic dynamic processes that cannot be directly observed in irradiation experiments. The irradiation-induced microstructural change of 2D graphene sheets was studied using molecular dynamics simulations with a maximum primary knock-on atoms (PKA) energy of 180keV. The results show that using direct observation, the defects generated during the cascade collision process can be divided into three types according to the generation mechanism: defects by PKA damage (DPD), instantaneous defects by shock wave rippling (DSR), and permanent defects by shock wave overlapping (DSO). The atomic configuration of the final stage consists of various topological polygons; in general, octagons and polygons with fewer than eight sides are bulged, while polygons with more than eight sides are depressed. The largest topological polygon found by the simulation is a 13-sided polygon. In addition to atoms with a coordination number of 3 (originating from the perfect lattice structure of graphene), atoms with coordination numbers of 2 and 4 are produced. Atoms with a coordination number of 4 are generally enclosed by four polygons that have no more than six sides, while atoms with a coordination number of 2 are generally located between two polygons that have at least six sides.