Theory of the production and depth distribution of helium defect complexes by ion implantation

The complex defect formations and migrations occurring under helium ion bombardment of Cu have been modeled by a system of coupled equations, including diffusion. Atomistic binding and migration energies were determined from two-body calculations. A new mathematical scheme was developed in order to take diffusion into account in a self-consistent fashion. The calculations were applied to the low temperature implantation and annealing experiments of Bauer and also to the (proton backscattering) profiling experiments of Blewer. The calculations indicate that the ~0° C release peak of Bauer may be due to helium interstitial migration. When applied to the Blewer experiments, the calculations indicate that the dominant defect after room temperature implantation is six helium atoms in a vacancy (He₆V). The shape and position of the total helium distribution is not altered by isochronal annealing (because of the trapping of vacancies by the helium), but the helium is released directly from the damage which traps it.