Molecular Dynamics Simulation of High-Energy Beam Irradiation of SiO₂ Single Crystal with Three Different Morphologies: No Free Surface, with a Free Surface, and Thin Films

High-energy beam irradiation of SiO 2 crystal with the α -quartz structure was simulated by the molecular dynamics method. Three types of specimen structures were examined: a single crystal without a free surface, a single crystal with a free surface, and a thin film. After structural relaxation at room temperature, a cylindrical region with diameter of 3.0 nm was set at the center of the specimen and high-thermal energy of S eff = 0.1–4.0 keV nm −1 was added to that region, where S eff is the effective stopping power. Atomic motions were calculated by the molecular dynamics method using the large-scale atomic/molecular massively parallel simulator. Vashishta potential was used for the atomic interaction. The single crystal structure of α -quartz without the free surface was stable up to 1.0 keV nm −1 and it gradually became amorphous with increasing thermal energy. In contrast, the single crystal structure with the free surface was stable up to 0.5 keV nm −1 and was amorphous at higher thermal energy. In particular, the atomic structures for the thermal impact S eff ≥ 2.0 keV nm −1 had a facet-like structure at the impacted surface, which corresponds to actual experimental results. Nano-hole formation was observed in the irradiation process of the film structure.