Magnetron sputtered metallic multilayers such as Cu-Nb and V-Ag with a range of individual layer thickness from approximately 2 nm to 50 nm and the corresponding 1000 nm thick single layer films were implanted with helium ions at room temperature. Elastic Recoil Detection (ERD) and Nuclear Reaction Analysis (NRA) were used to measure the helium concentration profile in the ion implanted films. Cross-sectional Transmission Electron Microscopy (TEM) was used to measure the distribution of helium bubbles and correlated with the measured helium concentration profile to obtain the helium concentration at which bubbles are detected in TEM. It was found that in multilayers the minimum helium concentration to form bubbles (approximately 1 nm in size) that are easily resolved in through-focus TEM imaging was several atomic %, orders of magnitude higher than that in single layer metal films. This observation is consistent with an increased solubility of helium at interfaces that is predicted by atomistic modeling of the atomic structures of fcc-bcc interfaces. At helium concentrations as high as 7 at.%, a uniform distribution of 1 nm diameter bubbles results in negligible irradiation hardening and loss of deformability in multilayers with layer thicknesses of a few nanometers. The control of atomic structures of interfaces to produce high helium solubility at interfaces is crucial in the design of nano-composite materials that are radiation damage tolerant.

This research is funded by US DOE, Office of Basic Energy Sciences, Energy Frontier Research Center.

Amit Misra, Los Alamos National Lab, United States
Dhriti Bhattacharyya, , 
Nan Li, , 
Qiangming Wei, , 
Yongqiang Wang, , 
Mike Demkowicz, , 
Mike Nastasi*, , 

*presenting author