Monolayer oxide enhanced flow stress in nanoporous gold: The size dependence

Abstract

Compression of nanoporous gold in situ under electrochemical control reveals that its flow stress can be enhanced by surface coverage of monolayer oxide. Here we present a study on the monolayer oxide induced changes in flow stress of an nanoporous gold, while the ligament size is varied by more than 2 orders of magnitude. The increase percentage of flow stress (of nanoporous gold and nano-ligaments) induced by surface monolayer oxide is negligible when the ligament size (L) exceeds ∼ 2 µm, increases with decreasing L for ∼ 200 nm < L < ∼ 2 µm, and then saturates at ∼ 27% for L < ∼ 200 nm. These results indicate a transition from bulk-like to surface-mediated deformation behavior of nano-ligaments as L decreases from ∼ 2 µm to ∼ 200 nm. Our observation at L < ∼ 200 nm support the notion that the deformation is dominated by the surface-dislocation-nucleation at this scale. (Images presented) IMPACT STATEMENT This study shows that the surface-modification induced hardening in nanoporous Au doesn’t increase monotonically with decreasing structure size as usually thought, providing new clues to the understandings of nano-crystal plasticity.