Formation and microstructures of nanoporous gold films with tunable compositions/porosities/sizes through chemical dealloying of dilute solid solution Cu-Au alloys

Structural regulation of both macro-shape (cubes, films) and microstructure (ligament size, porosity) of nanoporous metals is of central importance for their fundamental studies and practical applications. The choice of dilute solid solutions as precursors for dealloying provides great chances for structural regulation of nanoporous metals, but has received little attention. Herein, a series of dilute Cu-Au solid solution foils with 0.001-5 at% Au were dealloyed in HNO3 solutions, and monolithic nanoporous gold (NPG) films with different microstructures/compositions were fabricated. After dealloying, all the NPG films manifest a considerable degree of volume shrinkage (61.9-99.9 %), high porosity (up to 91.0 %), and low density (0.9-3.8 g cm(-3)). Furthermore, the NPG samples maintain their initial foil shape even when the atomic ratio of Au in the Cu-Au precursor is as low as 0.01 at% (that is, Cu99.99Au0.01). All the NPG samples feature an open, three-dimensional, bi-continuous ligament-channel structure at the nanoscale. The ligament size of the NPG samples shows a negative correlation with the residual amount of Cu after dealloying. We further investigated the phase transformation behavior of Cu99.9Au0.1 and surface morphology evolution of Cu99.99Au0.01 using in-situ X-ray diffraction (XRD) and ex-situ scanning electron microscopy (SEM) techniques.