Degradation behavior of DLC thin film under gamma-rays irradiation using molecular dynamics simulation

Abstract

γ-rays have high energy, thus, when irradiated on the materials, lead to the degradation process of the materials which means the durability and efficiency of the system decrease. Therefore, analysis of the effect of γ-rays on the materials is important, despite this, little work has so far been undertaken to predict the irradiation effect. Furthermore, because the previous theoretical equations have many assumptions, the accuracy of the prediction is low. For these reasons, molecular dynamics simulation was used to analyze and predict the effect of γ-rays on the DLC thin film in this study. This study investigates the degradation process, bond distribution, and radical creation during γ-rays irradiated on the DLC thin film. The primary knock-on atoms (PKA) method was applied which can be mimicked first excited atoms by γ-rays. Also, to analyze the chemical change of the irradiated DLC, ReaxFF potential was selected. The dose rate condition covered various environments where the γ-rays were irradiated such as space, nuclear, medical, etc. The degradation mechanisms of DLC were different by the dose rate. For low dose rate conditions, the energy of excited atoms was converted by physical collisions between atoms. However, in the case of high dose rate conditions, radical production rapidly increased, resulting in physical and chemical energy dissipation. Within this paper, we present a fundamental numerical analysis of the degradation process that combines the PKA method and MD simulation to achieve improved accuracy. These findings could provide fundamental insight into the degradation phenomenon of surface-protective coatings for various applications with γ-ray irradiation environment.