Nucleation and growth process of defect clusters in copper during helium ion irradiation

Abstract

The formation process of interstitial dislocation loops in copper under He + ion irradiation has been studied by using transmission electron microscopy. Wedge shaped specimens of pure copper are subjected to irradiation with 5 to 100 keV He + ions at irradiation temperatures between 300 to 570 K. The minimum thickness were interstitial loops are formed increases with increasing He + ion energy and irradiation temperature, although this thickness scarcely depends on He + ion dose rate. The density of loops shows a linear increase against dose for irradiation with 20 and 30 keV He + ions but has a higher order dependence with respect to doses greater than 2 under irradiation with 5 and 10 keV He + ions. On the basis of the results induced by He + ion irradiation, we have concluded that a low fraction of high energy PKAs play an important role for the nucleation of interstitial loops for energies higher than about 20 keV.