THE ROLE OF ELECTRON-PHONON COUPLING IN THE FORMATION OF CLUSTERED VACANCY DEFECTS IN ELEMENTAL METALS FROM HEAVY-ION IRRADIATION

The role of electron-phonon coupling in reducing the lifetime of the thermal spike of a collision cascade has been examined by calculating the power absorbed by the electronic system of the lattice and comparing the data with published results for the defect yield in a wide variety of elemental metals. A modified version of TRIM has been used to calculate the cascade energy density for all the irradiation conditions and materials considered. A strong dependence of the efficiency of dislocation loop production (defect yield) on the cascade energy density was determined, and only at constant cascade energy density were variations in the defect yield for different materials compared. Good correlation was found between the strength of electron-phonon coupling and the defect yield data for those materials that exhibit strong electron-phonon coupling. As the strength of this coupling decreased, other factors which influence the molten zone lifetime, such as the melting temperature, were found to become more significant. However, from the data examined, it was not possible to determine which parameters controlled the thermal spike lifetime in those metals for which the power absorbed by the electronic system was negligible; a correlation between a long thermal spike lifetime and low melting temperature was noted.