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-dislocationnucleation at this scale. 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.

Light, strong, and stable nanoporous aluminum with native oxide shell

“…Similarly, surface modification-induced strengthening has been observed in other nano-objects (62,63). Since the alumina layer in this study is substantially thicker (and harder to break through by dislocations) than monolayer oxide as shown in previous studies (9,(62)(63)(64), the additional strengthening effect from surface oxide could be even more pronounced, particularly for the densified alumina layer, as will be discussed below.…”

The Mechanical Effect of MnO2 Layers on Electrochemical Actuation Performance of Nanoporous Gold

“…The nanoporous gold (npg) samples in use were prepared by electrochemical dealloying under potentiostatic control (AUTOLAB PGSTAT302N) in 1 M HClO 4 in a three-electrode electrochemical cell. The detail about the preparation of npg can be found in previous reports [ 10 , 31 , 33 , 34 , 35 ]. The reference electrode used in this study was a pseudo Ag/AgCl electrode, whose potential with respect to the standard hydrogen electrode (SHE) was 0.53 V [ 35 ].…”

“…The detail about the preparation of npg can be found in previous reports [10,31,[33][34][35]. The reference electrode used in this study was a pseudo Ag/AgCl electrode, whose potential with respect to the standard hydrogen electrode (SHE) was 0.53 V [35].…”

“…Zhang and Jin reported an interesting strategy from the viewpoint of the structural composite to improve the linear actuation of nanoporous gold (npg) by forming Au/npg multilayer composites [ 33 ]. More and more new-style efficient strategies for the improvement in the electrochemical actuation of nanoporous metals are still under exploration and investigation [ 34 , 35 , 36 ].…”

“…In this work, we introduce a common supercapacitive material, MnO 2 , using the electrochemical deposition technique to improve the actuation behavior of nanoporous metal materials. Since the electrochemical actuation performance of nanoporous gold has been well-investigated in the past decade and the sample preparation process is standard [ 19 , 20 , 21 , 31 , 33 , 34 , 35 ], this work chose nanoporous gold as a typical case to study the strategy. Our work found that the deposited MnO 2 thin layer could change the electrochemical actuation phase of npg (i.e., from expansion to contraction) as well as the actuation magnitude.…”