Sign-inverted surface stress-charge response in nanoporous gold

Sign-inversion of charging-induced variation of electrical resistance of nanoporous platinum

“…Turning to the sign inversion of the charging-induced resistance variation, it should be noted at first, that a sign inversion of another charging-induced property variation has been observed recently for nanoporous Au [8] and nanocrystalline Pt [18], namely a sign inversion of the surface stress-charge coefficient. Clean metal surfaces usually are characterized by a negative value of the surface stress-charge coefficient, i.e., the surface stress in the double layer regime of charging increases with negative charging (electron excess).…”

“…Clean metal surfaces usually are characterized by a negative value of the surface stress-charge coefficient, i.e., the surface stress in the double layer regime of charging increases with negative charging (electron excess). Since concomitantly with increasing surface stress the relative volume decreases, negative charging of porous nanophase metals in the double layer regime causes volume contraction (positive strain-charge response) which is considered to arise from the increasing strength of in-plane bonds due to excess electronic charge [8,18]. Compared to this usual behavior, for oxidecovered porous nanophase metals (np-Au [8], nc-Pt [18]) the opposite behavior, namely a volume expansion with negative charging was observed.…”

“…Since concomitantly with increasing surface stress the relative volume decreases, negative charging of porous nanophase metals in the double layer regime causes volume contraction (positive strain-charge response) which is considered to arise from the increasing strength of in-plane bonds due to excess electronic charge [8,18]. Compared to this usual behavior, for oxidecovered porous nanophase metals (np-Au [8], nc-Pt [18]) the opposite behavior, namely a volume expansion with negative charging was observed. For nanoporous Au this behavior was only observed for the oxide-covered surface of the freshly dealloyed sample, whereas for nanocrystalline Pt switching from the double layer behavior (positive strain-charge response) to the oxide-layer behavior (negative strain-charge response) could be achieved reversibly by appropriate electrochemical surface treatment.…”

“…Compared to cluster-assembled nanocrystalline metals, effects associated with charging at surface-electrolyte interfaces emerge more pronounced in nanoporous metals prepared by dealloying owing to the reduced influence of interfaces between the crystallites, i.e., grain boundaries. Both charge-induced [7,8] and surface-chemistry driven actuation (i.e., length change) [9] as well as tunable mechanical strength [10] could be observed in np-Au.…”

Adsorption-driven tuning of the electrical resistance of nanoporous gold

“…6 Compared to cluster-assembled nanocrystalline metals, effects associated with charging at surface-electrolyte interfaces are expected to be enhanced in nanoporous metals prepared by dealloying owing to the reduced influence of interfaces between the crystallites, i.e., grain boundaries. Both charge-induced 7,8 and surface-chemistry driven actuation ͑i.e., length change͒ 9 could be observed in np-Au.…”