Mechanisms of He escape during implantation in CuNb multilayer composites

CuNb multilayer composites with layer thicknesses as small as 4 nm have shown remarkable resistance to radiation damage at room temperature. The technological importance of these materials, however, depends on their radiation damage resistance properties at elevated temperatures. We investigated the degree of retention of 33 keV ⁴He⁺ implanted at temperatures ranging from 490 °C to 660 °C in CuNb multilayer composites with layer thicknesses from 4 nm to 100 nm. Analysis by elastic recoil detection (ERD) with 12 MeV ¹²C³⁺ beam demonstrates that the fraction of retained He decreases with increasing temperature and decreasing layer thickness, suggesting that interfaces between neighboring Cu and Nb layers serve as pathways for fast diffusion of implanted He out of the CuNb multilayer composites. Atomic-scale simulations of radiation damage cascades indicate that this property stems from the ability of CuNb interfaces to quickly absorb defects created during these cascades.