On the possibility of universal interstitial emission induced annihilation in metallic nanostructures

Abstract

Nano-structured metals have been explored as self-healing materials for radiation damage due to vacancy-interstitial recombination at interfaces, such as grain boundaries (GBs) in nanocrystals (NCs) and free surfaces in nanoporous metals (NPs). The annihilation in copper was recently proposed to be via the interstitial-emission (IE) from the GB. However, whether the IE is applied as a possibly universal mechanism in other NPs and NCs deserves further investigation. The interstitial is often considered to overcome a large binding energy with the GB/surface to migrate out of the GB/surface and induce annihilation. In this work, with emphasis on the IE in tungsten where the interstitial is exceptionally tightly bound to the tungsten GB/surface, we found that the interstitial only needed to migrate over a small distance from the GB/surface to recombine with the vacancy nearby at a small energy barrier. During the process, the annihilation region around a static interstitial at the GB/surface propagated or extended greatly to the adjacent bulk area. The annihilation was found to be via the IE from the GB/surface or coupled vacancy hop with the IE. The ratio of the interstitial-GB/surface binding energy to the trapping-radius of the GB/surface for the interstitial was proposed to be a better qualitative indicator for the difficulty in the IE than the binding energy. Given that the IE works in the investigated NPs and NCs tungsten, iron and copper where the interstitials of distinct configurations bind with the GBs/surfaces at diverse levels, the IE mechanism may work universally in various nano-structured metals.