Silver-coated elevated bowtie nanoantenna arrays: Improving the near-field enhancement of gap cavities for highly active surface-enhanced Raman scattering

Abstract

Improving hot-spot intensity is a key issue in surface-enhanced Raman scattering (SERS). The bowtie nanoantenna (BNA) is an effective device used to concentrate light energy into a nanoscale volume and produce strong hot spots. Nanosphere lithography (NSL) is a large-area and low-cost technique to produce BNA arrays; however, the SERS activity of NSL-fabricated BNAs is limited. In this paper, we present a simple method to improve the SERS activity of conventional NSL-fabricated BNAs by modifying their geometry. The new configuration is termed “silver-coated elevated bowtie nanoantenna” (SCEBNA). SCEBNAs perform intensive near-field enhancement in the gap cavities owing to the integrated contribution of the “lightning rod” effect, resonance coupling, and the formation of the plasmonic Fabry–Perot cavity. Experimental measurements and finite-difference time-domain simulations revealed that the hot-spot intensity and the substrate enhancement factor can be optimized by adjusting the silver thickness. The optimal sample has the capability of trace-amount detection with fine reproducibility.