Ordered Nanocap Array Composed of SiO₂‑Isolated Ag Islands as SERS Platform

SERS-active substrate is fabricated by cosputtering Ag and SiO₂ onto two-dimensional polystyrene (PS) colloidal particle templates in a magnetron sputtering system. When Ag and SiO₂ are cosputtered onto ordered PS templates, the SiO₂-isolated Ag island (SiO₂–Ag) nanocap arrays with nanogaps and nanoscaled surface roughness form on PS particles, in which “hot spots” are facilely engineered on three-dimensional nanostructures. The surface-enhanced Raman scattering (SERS) activities of the SiO₂–Ag nanocap arrays vary nonmonotonically and depend on the film thickness and surface roughness strongly. Under the optimized conditions, the SERS signal intensity of 4-aminothiophenol (PATP) is employed to evaluate the SERS ability (4.41 × 10⁵). The addition of SiO₂ not only avoids photobleaching and background fluorescence but also decreases the oxidation rate of Ag and increases the stability of Ag particles. The results demonstrate the potential applications of this technique in reproducible SERS substrate.