The formation of point defect clusters in 5N-purity material, under bombardment with 5keV He+, was studied by means of in situ transmission electron microscopy. Conventional transmission electron microscopic techniques showed that the clusters which were introduced by bombardment were interstitial-type dislocation loops at 85 to 770K, and cavities at 300 to 770K. Most of the interstitial-type loops lay on {100} planes, and their Burgers vectors were determined to be a[100]. Temporal variations in the volume-density of the interstitial-type loops were measured by means of stereomicroscopy at various temperatures. The volume-density of the interstitial-type loops was about 2 orders of magnitude higher, when compared with the effect of high-energy electron irradiation to the same dpa-rate. It was therefore deduced that He atoms had the effect of enhancing the nucleation of interstitial-type loops. The depth distribution of the loop densities broadened above about 235K, where vacancies became thermally mobile. The dependence of loop formation upon the He+ beam flux was weak. It was suggested that He-vacancy complexes acted as trapping sites for self-interstitial atoms, so that interstitial-type loop nucleation was enhanced.

Evolution of Point Defect Clusters in Pure Iron under Low-Energy He+ Irradiation. K.Arakawa, R.Imamura, K.Ohota, K.Ono: Journal of Applied Physics, 2001, 89[9], 4752-7