Increasing local field by interfacial coupling in nanobowl arrays

Abstract

An increased local field is crucial to create hotspots when applied in detections, which usually means the fabrication of nanostructure arrays with strong electromagnetic couplings. In this study, ordered monolayer Ag and Ag/SiO₂/Ag sandwich nanobowls arrays with enhanced local field are fabricated by the combination of nanosphere self-assembly lithography (NSL) technology and layer-by-layer (LBL) film deposition. The isolated nanobowls and nanohole-like nanostructures composed of connected nanobowls can be obtained by tuning the sputtering film thickness and polystyrene (PS) microsphere size. The isolated nanobowl arrays show high local surface plasmon resonance (LSPR) and surface plasmon resonance (SPR), which result in SERS enhancement. Compared to the Ag nanobowl arrays, the dielectric SiO₂ layer in Ag/SiO₂/Ag sandwich nanobowls as a spacer layer enhances the SERS signals. And the new plasmon couplings between interior and exterior Ag layers through the thin SiO₂ layer are implementated, in addition to the contributions of nanogaps in the adjacent nanobowls and the sharp edges of a single nanobowl. The finite-difference time-domain (FDTD) solution shows the field enhancement can be mainly attributed to the SPR of interparticles along the Ag–SiO₂ interfaces. The simulation results and experimental analysis indicate the important contribution of the SiO₂ layer to the enhanced SERS effects in Ag/SiO₂/Ag sandwich nanobowl arrays.