Impact of the morphology and composition on the dealloying process of co‐sputtered silver–aluminum alloy thin films

Dealloying has been widely employed lately for the fabrication of nanoporous metals. However, in case of thin films, the impact of the initial morphology on the final porosity is still not well understood. In this work, we report on the influence of the initial morphology of silver–aluminum (Ag–Al) thin films on the dealloying process in hydrochloric acid. The films deposition was performed by a DC co-sputtering process of silver and aluminum targets in a cofocal geometry using pure argon plasma; by tuning the deposition conditions such as the electrical powers applied to the targets and the deposition temperature, films with various compositions and morphologies can be obtained. The dealloying is then carried out using a free corrosion process applied in diluted (2 wt.%) hydrochloric acid in order to leach preferentially aluminum leaving behind a nanoporous skeleton of silver. We show that the dealloying process becomes faster when decreasing the initial silver content within the films. We further demonstrate that the dealloying kinetic is also dependent on the initial morphology of the Ag–Al films: it increases when decreasing the size of the columns forming the Ag–Al films. Top-view SEM image of Ag–Al alloy thin film with 23 at.% of initial Ag content dealloyed for 5 min in 2 wt.% hydrochloric acid.