Recoil ranges in ion-induced collision cascades

Using molecular-dynamics simulation, we study the recoil atom ranges in collision cascades as a function of the recoil energy. We focus on cascades initiated by 1 keV ions in Cu and Cu-related model metals, in which the cohesive energy has been changed with respect to that of Cu. At high energies, E > 100 eV, the recoil range follows the prediction of linear cascade theory. At lower energies, the ranges are still considerable. In particular, we observe a 15% probability of atom relocation at the nominal displacement threshold; the relocation probability does not vanish even for 1 eV recoils. We attribute this feature to the moderate collision spike existing in the system. The cohesive energy of the material affects the ranges considerably; a decrease of the cohesive energy increases low-energy recoil ranges. On the other hand, the recoil density is only moderately influenced by the cohesive energy. We hence conclude that the strong mixing observed in ion-bombarded materials with small cohesive energy is due to the increased recoil ranges.