*Letter* **Comparison of Vacancy Sink E**ffi**ciency of Cu**/**V and Cu**/**Nb Interfaces by the Shared Cu Layer**

**Huaqiang Chen 1, Jinlong Du 1, Yanxia Liang 1, Peipei Wang 1, Jinchi Huang 2, Jian Zhang 2,\*, Yunbiao Zhao 1, Xingjun Wang 3,\*, Xianfeng Zhang 4, Yuehui Wang 4, George A. Stanciu <sup>5</sup> and Engang Fu 1,\***


Received: 18 June 2019; Accepted: 8 August 2019; Published: 18 August 2019

**Abstract:** This paper provides a new method to compare and then reveal the vacancy sink efficiencies quantitively between different hetero-interfaces with a shared Cu layer in one sample, in contrast to previous studies, which have compared the vacancy sink efficiencies of interfaces in different samples. Cu-Nb-Cu-V nanoscale metallic multilayer composites (NMMCs) containing Cu/V and Cu/Nb interfaces periodically were prepared as research samples and bombarded with helium ions to create vacancies which were filled by helium bubbles. A special Cu layer shared by adjoining Cu/V and Cu/Nb interfaces exists, in which the implanted helium concentration reaches its maximum and remains nearly constant with a well-designed incident energy. The results show that bubble-denuded zones (BDZ) close to interfaces exist, and that the width of the BDZ close to the Cu/V interface is less than that of Cu/Nb interface. This result is explained by one-dimensional diffusion theory, and the ratio of vacancy sink efficiency between Cu/V and Cu/Nb interfaces is calculated. Conclusively, Cu/Nb interfaces are more efficient than Cu/V interfaces in eliminating vacancies induced by radiation.

**Keywords:** radiation damage; sink efficiency; multilayer composite; interface; vacancy
