On the lower energy limit of electronic stopping in simulated collision cascades in Ni, Pd and Pt

We have investigated the effect of the choice of kinetic energy threshold T_c for electronic stopping (S_e) in molecular dynamics (MD) simulations of collision cascades. We find that while the choice of T_c has only a negligible effect in low energy cascades, it has a pronounced effect on the fraction of defects found in clusters in high energy cascades. In order to gain insight into the level of energy losses expected in cascades, we have simulated a large number of cascades in Ni, Pd and Pt, with primary knock-on atom (PKA) energies between 30 eV and 200 keV. Since the energy losses affect the total atomic displacements especially in high energy cascades, we use this measure to determine a reasonable value of T_c. By directly comparing the simulated mixing efficiency to ion beam mixing experiments, we conclude that a threshold of T_c=1 eV is too low for simulations of high energy cascades in all materials considered. A value of T_c=10 eV is more realistic, although for Pd and Pt, this results in a slight over-prediction of the mixing efficiency