Abstract
The structural modification caused by the high-energy-beam irradiation of single-crystalline β-cristobalite was simulated by the molecular dynamics method. As the initial condition, high thermal energy was supplied to the individual atoms within a cylindrical region of nanometer-order radius located in the center of the specimen. The supplied thermal energy was first spent to change the crystal structure into an amorphous one within a short period of about 0.3ps, then it dissipated in the specimen. The amorphous track radius Ra was determined as a function of the effective stopping power gSe, i.e., the thermal energy per unit length created by ion irradiation. It was found that the relationship between Ra and gSe follows the relation Ra2=alog(gSe)+b. Compared to the case of Si single crystal, it was easier to produce amorphous track because of the weakness of the bonding between SiO4 tetrahedra. It was also found that the mechanism of structural transition changes at Ra = 1 nm.
