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Experiment shows thin films of dealloyed nanoporous gold (NPG) spontaneously detaching from massive gold base layers. NPG can also densify near its external surface. This is naturally reproduced by kinetic Monte Carlo (KMC) simulation of dealloying and coarsening and so appears generic for nanoscale network materials evolving by surface diffusion. Near the porous layer’s external surface and near its interface with the base layer, gradients in the depth-profile of a laterally averaged mean surface curvature provide driving forces for diffusion and cause divergences of the net fluxes of matter, leading to accretion/densification or to erosion/disconnection. As a toy model, the morphology evolution of substrate-supported nanopillars by surface diffusion illustrates and confirms our considerations. Contrary to cylindrical nanowires, the ligaments in nanoporous materials exhibit pre-existing gradients in the mean curvature. The Plateau-Rayleigh long-wavelength stability criterion is then not applicable and the disconnection accelerated.

Nanoporous gold (NPG) made by dealloying takes the form of a network of nanoscale struts or “ligaments”. It is well established that the material's mechanical behavior is strongly affected by its ligament size, L and by its solid volume fraction, φ. We explore the mechanical behavior of NPG, with an emphasis on establishing a consistent data set with comparable L but covering a significant range of initial φ. Specimens are prepared from Ag-Au master alloys with their Au atom fraction, xAu0 in the range 0.20–0.35. Since dealloying replaces Ag with voids, φ may be expected to agree with xAu0. Yet, spontaneous plastic deformation events during dealloying can result in macroscopic shrinkage, decoupling φ from xAu0. This raises the question, how do φ and xAu0 separately affect the mechanical behavior? We confirm two recent suggestions, namely i) a modified Roberts-Garboczi-type scaling law for Young's modulus versus φ of the material in its as-prepared state and ii) the relevance of an apparent “load-bearing solid fraction” for Young's modulus as well as strength. Yet, remarkably, we find that stiffness and strength of the as-prepared material show a much better correlation to xAu0 as compared to φ. This can be understood as a consequence of the microstructural changes induced by shrinkage. Studying the microstructure evolution during annealing, we also confirm the suggestion that coarsening entails an enhanced loss in stiffness for samples with lesser solid fraction. This finding confirms concerns about the notion of self-similar coarsening as a general behavior of dealloying-made network materials. Deutsche Forschungsgemeinschaft (DFG)