Formation mechanism of plasmonic silver nanohexagonal particles made by galvanic displacement reaction

Abstract

The galvanic displacement reaction (GDR) is a powerful method for the preparation of various plasmonic nanostructures within several minutes. However, the formation mechanism of the nanostructures, which retain plasmonic hotspots, still remains unclear. In this work, X-ray photoelectron spectroscopy (XPS) is applied to silver nanostructures made by newly-discovered GDR between Ag complex solutions and Cu alloy substrates, whose nanostructures form characteristic nanoscale hexagonal columns (NHCs) and generate strong surface-enhanced Raman scattering (SERS) signals of adsorbates. Detailed depth profiles by multi-element XPS analysis revealed that NHCs are made of Ag metallic cores covered with surface layers composed of copper sulfates and copper oxides, which prevent NHCs from fusion, resulting in highly concentrated stable hotspots. These findings explain why NHCs exhibit reproducible SERS signals and the proposed methodology gives new insights for efficient creation of plasmonic nanostructures in a few minutes.