Interstitials and their agglomerates in electron irradiated gold investigated by diffuse X-ray scattering

Abstract

Single crystals of gold have been irradiated at a temperature of 5 K with 3 MeV electrons. The radiation induced defects were investigated by measurements of the Huang diffuse scattering of X-rays, the change of the lattice parameter and the change of the electrical resistivity. Even at the lowest irradiation dose (concentration of Frenkel defects ∼ 75 ppm) no single interstitials but small interstitial clusters were observed in high purity gold. The larger clusters take the form of dislocation loops on {111} planes already at the irradiation temperature. By doping with impurities the cluster formation can be suppressed, and single interstitials trapped at copper atoms were observed in an Au (300 ppm Cu) alloy. Such behaviour can explain the absence of stage I annealing. During thermal annealing at higher temperatures a growth of the interstitial clusters is observed. The number of interstitials present in the clusters decreases during stage III (200 K < T < 400 K) and vacancy clusters are also formed. Although there is nearly complete annealing of the resistivity in stage III, final annealing of the clusters is observed after stage V (650 K).