Wafer-scale silver nanoislands with ∼5 nm interstitial gaps for surface-enhanced Raman scattering

Abstract

Nanogap-rich silver nanoislands with fascinating optical properties are desirable substrates for surface-enhanced Raman scattering (SERS). Here, we propose a simple and high-throughput approach through the laser molecular beam epitaxy (LMBE) technique for preparing silver nanoislands containing large numbers of intra-nanogaps on a silicon wafer (6×6 cm2). By optimizing the deposition time, the enlarged silver nanoislands with ∼5 nm interstitial gaps of abundance and homogeneity were formed. Remarkably, the optimized SERS substrate with high-density hotspots demonstrated a high analytical enhancement factor (AEF) as large as 1.17×105, excellent reproducibility with relative standard deviation (RSD) of 7.76% over the entire substrate, and good stability after storage for 21 days. The electromagnetic field distribution of the optimized SERS substrate was simulated using the software COMSOL Multiphysics based on the actual SEM image of the fabricated sample, and the calculated enhancement factor (EF) is as high as 109. Furthermore, it can enable sensitive and quantitative detection of malachite green at concentrations as low as 10−8 M. This simple fabrication of silver nanoislands with homogeneous ∼5 nm interstitial gaps provides a practical solution for wafer-scale, sensitive, and reproducible SERS substrates.