Iridium Nanopillars with Multilayered, Uniformly Distributed Hot Spots for Highly Reproducible Surface-Enhanced Raman Scattering

The detection of ultralow levels of species with the surface-enhanced Raman scattering (SERS)-based sensors has been hindered by difficulties in realizing SERS substrates that provide uniform, reproducible SERS response over the active area. Here we report on the periodic arrays of high aspect-ratio iridium nanopillars that feature rich and evenly distributed plasmonic hot spots within the pillars. Working as the SERS substrate, we demonstrate that the ordered and well defined plasmonic nanopillars offer the variability less than 5% (relative standard deviation), in SERS response over the patterned area. By using iridium atomic layer deposition to overcoat high aspectratio SiO2 nanopillars, the width of interpillar gaps goes down to 10 nm, leading to an order of magnitude increase in the SERS response in comparison to conventional SERS substrates. The smallest variability in SERS response that has ever been obtained, together with the large enhancement factor, suggest the structure an ideal SERS-based sensor for species with low concentrations, paving the way for single-molecule detection.