TRANSIENT THERMAL-PROCESS AFTER A HIGH-ENERGY HEAVY-ION IRRADIATION OF AMORPHOUS METALS AND SEMICONDUCTORS

Following a description used to explain a phase transformation observed after pulsed femtosecond laser irradiation, a transient thermal process is used to describe latent-track formation after high electronic excitation induced by energetic (GeV) heavy ions. The transient thermal calculation is restricted to the amorphous materials a-Ge, a-Si, and a-Fe85B15, for which nearly all latent-track radii and/or macroscopic thermodynamic properties are known. The heat-flow equation is solved numerically in cylindrical geometry. The time-dependent heat-generation term is assumed to be due to the electron-atom interaction. The characteristic length lambda of the energy transport by secondary electrons is taken as the only free parameter and the maximum diameter of the cylinder of liquid matter is considered as the diameter of the observed latent track. Using the single value lambda = 14 nm, we have been able to calculate these diameters in a-Si and a-Ge in reasonable agreement with experimental track diameters, taking into account the large differences between the macroscopic thermodynamic parameters of both materials. This lambda value is less than that for the crystalline state. In the case of a-Fe85B15, the diameters calculated with use of lambda = 19 nm are in agreement with the ones determined recently by electrical-resistivity change.