Optical in situ study of de-alloying kinetics in nanoporous gold sponges

Abstract

Nanoporous gold sponges are useful for a variety of applications but the kinetics of the dissolution process used to make them is not well understood. Here we show how optical transmittance can be used to determine the rate at which sponges form from thin film precursors. The technique also provides a means by which de-alloying can be terminated at a target thickness. Analysis revealed three stages during the de-alloying process: initial depassivation, bulk dissolution and, finally, delamination. The dissolution rate is linear with hydroxide concentration, and exponential with temperature, with an activation energy of approximately 0.5 eV.