Synthesis of nanoporous gold by chemical dealloying of co-sputtered gold-silver thin films and study of its variability

In the past two decades, nanoporous metals have attracted wide attention in the areas of energy storage, biomedicine and catalysis. Compared to other metals, nanoporous gold exhibits superior chemical stability, high catalytic activity, and its synthesis is facile and well documented. While many studies elaborate on the dealloying kinetics to understand process-structure relationships, its process variability is known to be large and yet not well documented. In this study, nanoporous gold was synthesized by chemical dealloying of co-sputtered gold-silver thin film. By controlling temperature and time during dealloying, its porosity characteristics, such as ligament diameter and solid area fraction, were controlled. Further, the time evolution of structural and elemental characteristics of nanoporous gold were examined including its correlation to silver residual content. It is found that mean diameters grow as a function of etch time from 25 to 60 nm. The large standard deviation (18.6 nm) of multiple dealloying attempts at any given temperature and dealloying time points to the lack of control in the kinetics of the dealloying reaction and variability in its substrate preparation and processing protocols. A comprehensive analysis of these parameters might provoke a better understanding of nanoporous gold synthesis in terms of the structure evolution kinetics.