Computer simulation of high-energy-beam irradiation of single-crystalline silicon

The structural relaxation caused by the high-energy-beam irradiation of single-crystalline silicon was simulated by the molecular dynamics method. As the initial condition, high thermal energy was supplied to the individual silicon atoms within a cylindrical region of nanometer-order radius located in the center of the specimen. The Tersoff potential was assumed as the interaction mechanism between silicon atoms. The supplied thermal energy was first spent to change the crystal structure into an amorphous one within a short period of about 0.3 ps; then it diffused in the specimen by an ordinary thermal dissipation process. The amorphized track radius Ra was determined as a function of the energy density of the thermalized region. It was found that the relationship between Ra and the effective stopping power gSe follows the relation Ra2=alog(gSe)+b, which is similar to the formula derived on the basis of the thermal spike model [G. Szenes, J. Nucl. Mater. 336 (2005) 81]. It was also found that the mechanism of structural transition changes at the thermalized region of 1 nm radius.