Does the Latent Track Occurrence in Amorphous Materials Result from a Transient Thermal Process?

Abstract

ABSTRACTHeavy ion irradiations in the electronic stopping power (Se.) regime have been performed in amorphous materials. Latent tracks have been observed in amorphous semiconductors (a-Ge, a-Si) and their radii have been deduced from a phenomenological analysis in an amorphous metallic alloy, in vitreous silica and “polymer” like amorphous carbon. A transient thermal model is developed describing the energy diffusion by the electron gas, by the atomic lattice and the energy exchange between the two subsystems. According to Fick's law, the classical equations of heat flow in the two subsystems (electrons and atoms) are numerically solved in a cylindrical geometry taking into account the temperature dependence of all the parameters. A simulation of annealing of nuclear collisions induced defects in crystalline iron allows to determine a local temperature. Electronic defect creation occurs when Se. increases and becomes larger than a threshold which is correlated with the appearance of a molten phase. Using such a criterion, the radii of latent tracks are reproduced in both a - Ge and a - Si with the same value of the electron-phonon coupling despite large differences in their lattice thermodynamic parameters. Such a model is applied to amorphous metallic alloy Fe85B15, vitreous silica and amorphous carbon.