Morphology evolution and defect distribution in irradiated graphite from molecular dynamics

Abstract

Molecular dynamics is carried out to study the morphology evolution and point defect distribution in irradiated graphite. Collision cascade processes are simulated in a wide PKA energy range (0.5–2.5 keV) by using the AIREBO potential. The formation process of a hillock (bump) defect that frequently observed in radiation experiments is repeated at atomic level and two formation mechanisms are proposed qualitatively. One light spot of this work is the quantitative analysis of defect distribution involving total vacancy defects and classified vacancy types (monovacancy, divacancy and vacancy loop). Our data is in good agreement with other theoretical calculations and the broadly accepted Norgett-Robinson-Torrens model. An evidence of the transform between different vacancy types is provided from a statistical view, which can be illustrated that monovacancy tends to form vacancy loops by transition of divacancy. The simulations help to provide a deep insight into the cascade procedure in graphite and associate surface features with the generation of defects due to the impact of energetic particles.