Heavy ion irradiation and annealing of lead: atomistic simulations and experimental validation

We simulated the evolution of the defect microstructure resulting from irradiation of lead with 180 keV Er + at liquid Nitrogen temperature followed by an isochronal anneal up to 350 K. The results were validated by comparison with experiments. The simulation consists of a coupled molecular dynamics (MD) and kinetic Monte Carlo (KMC) calculation that follows the production and migration of defects during irradiation and subsequent isochronal annealing. Defect diffusivities and cluster energetics were calculated by MD simulations with and embedded atom-like potential for Pb, or obtained from experiments whenever available. The primary stage of the damage produced by the energetic recoils was also calculated using MD. These calculations show the formation of dense interstitial and vacancy clusters after the cooling of the cascade. The ions are implanted at a temperature of 94 K and the damage is annealed by increasing the temperature on a stepwise fashion by 50 K every 5 min. The time–temperature evolution of the density of point defects and defect clusters is calculated in this simulation. The results are compared with experimental observations for the same irradiation and annealing conditions. The experiments consist of a set of transmission electron microscope (TEM) micrographs taken at different times during the anneal. The micrographs show the presence of loops after irradiation at 94 K, the increase in loop density with temperature, and the disappearance of all the loops at temperatures of ∼340 K. These results are in good agreement with the simulations, which help us understand the underlying processes occurring during irradiation and annealing.