Irradiation-induced amorphization: Effects of temperature, ion mass, cascade size, and dose rate

An empirical model based on cascade ``quenching'' and epitaxial recrystallization has been developed to describe the accumulation of the amorphous fraction during ion beam irradiation experiments. The model is based on the assumption that the amorphous fraction that remains after the formation of a cascade is related to a crystallization efficiency parameter A. For low values of A, as would be expected at low temperatures, for heavy-ion irradiations, or for materials that are good glass formers, the accumulation of the amorphous fraction as a function of dose is an exponential function. For high values of A, as would be expected at elevated temperatures, for light-ion irradiations, or for materials that are poor glass formers, the accumulation of the amorphous fraction as a function of dose is a sigmoidal function. Amorphization dose varies as a function of temperature and is reflected by the temperature-dependent crystallization efficiency. The effects of ion mass and energy on critical amorphization dose and temperature are discussed in terms of the cascade size. The dose-rate effect on the critical temperature of amorphization is derived considering the thermal annealing of the damaged material.