Modification of defects induced by nuclear collisions in Fe and Ni in electronic stopping power regime

Abstract

Electronic energy loss (Se) induced modification of collisional defects in Fe and Ni was theoretically studied under the framework of thermal spike model. The initial spatial density of defects created by nuclear collisions was calculated by use of binary collision theory with charge screen. Taking into account the characteristics of defect annealing substages, temperature dependent atomistic jumps and migrations, the modification of collisional defects in Fe and Ni caused by Se was simulated in a cylindrical geometry. For iron, the theoretical damages were deduced from calculations and compared with experiments. It was found that the number z of quasi-free electrons in iron participating Se induced thermal spike process is about 1.5 per atom and, by use of z=1.5, the deduced defect recombination cross section values in iron are in agreement with experiments. Furthermore, three regions characterized by the concentrations of interstitials and vacancies are proposed. Similar variation tendency of damage efficiency in nickel was observed from numerical calculations. Thus, the Se induced defect modification in pure metals may be due to a transient thermal process.