Surface-Stress Induced Macroscopic Bending of Nanoporous Gold Cantilevers

We report the preparation of composite foils consisting of two layers, one solid gold and one nanoporous gold. Tip displacements of several millimeters are observed when the foils are immersed in aqueous electrolytes and the electrochemical potential varied. This suggests that nanoporous metals could be used as the active component in actors, and it demonstrates for the first time that changes in the surface stress f of the metal−electrolyte interface can induce a macroscopic strain, orders of magnitude larger than the amplitudes which are reached in conventional cantilever bending experiments used to measure f.