Radiation Defects in Aluminum. Simulation of Primary Damage in Surface Collision Cascades

Molecular dynamics method has been applied to simulate collision cascades initiated by primary knock-on atoms (PKAs) with energy E_PKA = 5, 10, 15, and 20 keV at temperatures T = 100, 300, and 600 K on the aluminum surface. A series of 48 cascades has been simulated for each pair of parameters (E_PKA, T), providing a representative statistical sampling. The number of Frenkel pairs N_FP, the fraction of vacancies ε_vac and self-interstitial atoms (SIA) ε_SIA in clusters of point defects, the average size of vacancy 〈N_vac〉 and self-interstitial 〈N_SIA〉 clusters, the average number of vacancy 〈Y_vac〉 and self-interstitial 〈Y_SIA〉 cluster per cascade yield, and the average time τ_c of cascade relaxation as a function (Е_PKA, T) have been found. The level of primary damage, 〈ε_vac〉, 〈ε_SIA〉, 〈N_vac〉, 〈N_SIA〉, 〈Y_vac〉 and 〈Y_SIA〉 have been found to be higher in surface cascades than those in displacements cascades in the bulk of material under the same simulation conditions. The morphology of surface cascades and the spatial separation of self-interstitial atoms and vacancies has been studied. Icosahedral self-interstitial clusters have been identified in displacement cascades in aluminum for the first time.