Anisotropic displacement threshold energy and defect distribution in diamond: PKA energy and temperature effect

Diamond is a promising semiconductor material for future space exploration, owing to its unique atomic and electronic structures. However, diamond materials and related devices still suffer from irradiation damage under space irradiation involving high-energy irradiating particles. The study of the generation and evolution of point defects can help understand the irradiation damage mechanisms in diamond. This study systematically investigated the defect dynamics of diamond in 162 crystallographic directions uniformly selected on a spherical surface using molecular dynamics simulations, with primary knock-on atom (PKA) energies up to 20 keV, and temperatures ranging from 300 K to 1800 K. The results reveal that the displacement threshold energy of diamond changes periodically with crystallographic directions, which is related to the shape of potential energy surface along that direction. Additionally, the number of residual defects correlates positively with PKA energy. However, temperature has dual competing effects: while it enhances the probability of atomic displacement, it simultaneously suppresses the probability of defect formation by accelerating defect recombination. The calculation of sparse radial distribution function indicates that the defect distribution shows a certain degree of similarity in the short-range region across different PKA energies. As the PKA energy increases, defect clusters tend to become larger in size and more numerous in quantity. This study systematically investigates the anisotropy of displacement threshold energy and elucidates the relationship between various irradiation conditions and the final states of irradiation-induced defects.