Plasmo-photonic NanopilJar Array for Large-Area Surface-Enhanced Raman Scattering Sensors

摘要

The remarkably high electromagnetic fields that can be induced by the optical stimulation of surface plasmons in plasmonic nanostructures can induce large enhancements to Raman scattering. The Surface-enhanced Raman Scattering (SERS) effect offers great potential for the development of molecular sensors with low false alarm rates and high sensitivity. Although research in this field has grown at a very fast pace in recent years, most of this work has focused on attaining the highest enhancements at highly localized hot-spots, which while providing large peak enhancements, exhibit very low average enhancement factors, making their use for most sensing applications unlikely. Here we report on Au-coated Si nanopillar arrays where we probe the dependence of the SERS enhancement on both the nanopillar diameter and the interpillar gap over a range extending from 30 to 245 nm and 20 to 165 nm, respectively. This approach allows for the optimization of the SPR condition relative to the incident laser wavelength chosen, enabling an optimized SERS sensor. As the interparticle gaps approach 20 nm, we also explored arrays of nanopillars where interparticle plasmonic coupling should exist, however, it remains unclear if any such collective effects are present. The arrays created do illustrate very large highly uniform (<30% deviation) SERS enhancement factors (G), with G in excess of lxl0~7 being reported. In addition, we explored the role of the nanoparticle geometry, where we determined that a higher G is observed for circle in comparison to square nanopillars of similar dimensions. The SERS enhancement was found to have a very distinct dependence on the nanopillar diameter, while only a monotonic increase was observed with increasing interpillar gap. These results suggest great suitability of plasmo-photonic large-area nanopillar arrays for SERS vapor and liquid sensor applications.