Hierarchically Well-Ordered Array of Concentric Silver Nanorings for Highly Sensitive Surface-Enhanced Raman Scattering Substrate

We fabricated a high density array of concentric silver nanorings in a large area (over in.2) with uniform gap distance by utilizing half onion-shaped microdomains prepared by symmetric polystyrene-block-poly(methyl methacrylate) copolymers (PS-b-PMMA) confined within hemispherical cavities in anodized aluminum oxide (AAO) template. Silver nanoparticles with 6 nm height were selectively deposited only on the PS microdomains by thermal evaporation. The gap distance of two neighboring silver nanorings was controlled from 12 to 24 nm by changing the total molecular weight of PS-b-PMMAs. The substrate showed high surface-enhanced Raman scattering (SERS) enhancement factor as high as 4.3 × 107 with good reproducibility (±7%). It could be used for biosensing, detection of trace-level explosive and hazardous chemicals, and reaction monitoring.