Formation mechanism and characterization of immiscible nanoporous binary Cu-Ag alloys with excellent surface-enhanced Raman scattering performance by chemical dealloying of glassy precursor
Nanoporous binary alloys with designable microstructure and unique properties are demanded for engineering applications in nanotechnology. In this work, three-dimensional immiscible nanoporous Cu-Ag (NPCA) with tunable porosity has been fabricated by dealloying Cu-Zr-Al-Ag metallic glasses. The relationship between composition, dealloying time and temperature, and nanoporosity was systematically investigated. It is found that addition of Ag substantially slows down the dealloying process, and there exists a composition threshold (~10 at.% Ag) to form a uniform nanoporous structure for the Cu-Zr-Al-Ag glassy precursor. The evolution of ligament size of NPCA with dealloying time and temperature can be well described by a diffusion-based growth kinetic model. Moreover, it is also found that addition of Ag can effectively enhance the surface enhanced Raman scattering (SERS) performance of the resultant nanorporous materials. The highest SERS enhancement factor (EF) of the NPCA resulted from the precursor with 10 at.% Ag content is 6×106, which is about 60 times over that of the nanoporous copper (NPC) without Ag, and the limit of detection (LOD) is 10-11 mol/L to R6G. Our findings not only provide new insight into the formation mechanism of immiscible nanoporous alloys, but also are helpful for developing inexpensive SERS substrates with multiple metallic elements.