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MM: Fachverband Metall- und Materialphysik
MM 36: Topical Session: Thermodynamics at the nano scale IV - Electrochemistry and strain
MM 36.4: Talk
Wednesday, April 2, 2014, 11:30–11:45, BAR 205
Surface excess elasticity in nanostructures: fact or fiction? — •Nadiia Mameka1, Jürgen Markmann1,2, and Jörg Weissmüller1,2 — 1Helmholtz-Zentrum Geesthacht, Institut für Werkstoffforschung, Wekrstoffmechanik, Geesthacht, Germany — 2Technische Universität Hamburg-Harburg, Institut für Werkstoffphysik und -technologie, Hamburg, Germany
Solid surfaces interact with the underlying bulk via a capillary force, the surface stress, which varies as the solid is strained. This variation defines a surface excess elastic modulus, which is well documented in theory. For nanoscale structures, the excess elasticity implies a size-dependent effective elastic response of the entire structure. While experimental observations of this phenomenon have been claimed, no agreement has been reached about magnitude or even sign of the excess modulus. One may therefore ask if there is a measurable impact at all. Here, we use experiments with dynamic mechanical analysis (DMA) on nanoporous gold to probe the issue. We focus on reversible changes in the elastic response when the surface is electrically charged or adsorbate monolayers deposited and lifted in electrolyte. The results reveal a significant variation in macroscopic stiffness. This conclusively confirms the important role of the surface excess elasticity phenomena in materials with large specific surface area. As an example, the reversible variation of the elastic modulus in the presence of weakly binding ClO4− ions to the Au surface reached up to 10% for a ligament size of 40 nm in mm-sized samples.