Fluence-dependent radiation damage in helium (He) ion-irradiated Cu/V multilayers

We have explored the capacity of Cu/V interfaces to absorb helium ion radiation-induced defects spanning a peak damage range of 0.6-18 displacements per atom (dpa). The study provides evidence of alleviated nucleation of He bubbles in the multilayer films from Cu/V 50 nm to Cu/V 2.5 nm. Layer interfaces are retained in all irradiated specimens. Peak bubble density increases monotonically with fluence, and is lower in multilayers with smaller individual layer thickness. Radiation hardening decreases with decreasing layer thickness and appears to reach saturation upon peak radiation damage of 6 dpa. Size-and fluence-dependent radiation damage in multilayers is discussed.