Superior tolerance of Ag/Ni multilayers against Kr ion irradiation: an in situ study

Abstract

Monolithic Ag and Ni films and Ag/Ni multilayers with individual layer thickness of 5 and 50 nm were subjected to in situ Kr ion irradiation at room temperature to 1 displacement-per-atom (a fluence of 2 × 10¹⁴ ions/cm²). Monolithic Ag has high density of small loops (4 nm in diameter), whereas Ni has fewer but much greater loops (exceeding 20 nm). In comparison, dislocation loops, ∼4 nm in diameter, were the major defects in the irradiated Ag/Ni 50 nm film, while the loops were barely observed in the Ag/Ni 5 nm film. At 0.2 dpa (0.4 × 10¹⁴ ions/cm), defect density in both monolithic Ag and Ni saturated at 1.6 and 0.2 × 10²³/m³, compared with 0.8 × 10²³/m³ in Ag/Ni 50 nm multilayer at a saturation fluence of ∼1 dpa (2 × 10¹⁴ ions/cm²). Direct observations of frequent loop absorption by layer interfaces suggest that these interfaces are efficient defect sinks. Ag/Ni 5 nm multilayer showed a superior morphological stability against radiation compared to Ag/Ni 50 nm film.

Keywords:

• Ag/Ni
• in situ radiation
• Kr
• interface

Acknowledgements

We acknowledge financial support by US Army Research Office – Materials Science Division, under contract no. W911NF-09-1-0223. Radiation effort was partially supported by DOE-NEUP under contract no. DE-AC07-05ID14517-00088120. Y. Liu and a portion of TEM work were supported by NSF-DMR metallic materials and nanostructures program, under grant no. 0644835. We also thank Edward A. Ryan and Peter M. Baldo at Argonne National Laboratory for their help during in situ experiments. The IVEM facility at Argonne National Laboratory is supported by DOE-BES.