Size effect of amorphous layers on radiation resistance in Cu/Nb multilayers

Utilizing multilayer engineering to connect crystalline and amorphous can not only improve the mechanical properties but also enhance the radiation resistance of multilayers. However, the non-monotonic dependence of radiation resistance on the amorphous thickness necessitates an in-depth investigation into the size effect of the amorphous layer. Taking the Cu-Nb system as the prototype, we reveal the radiation resistance of Cu/Nb multilayers with varying thicknesses of the CuNb amorphous layer. After irradiation, multilayers with 0, 0.8, and 2 nm amorphous show flat or non-flat interface structures due to distinct crystalline growth processes during amorphous crystallization. Notably, multilayers with 0.8 nm amorphous exhibit the optimal radiation response, because the ultra-thin amorphous layer shows better thermal stability and slower crystallization rate that can annihilate more radiation defects and effectively inhibit defects growth. Furthermore, a quantitative analysis elucidates the reasons for hardness changes, which are attributed to amorphous crystallization, dislocation nucleation-induced softening, and radiation defects-induced hardening.