Wafer-scale low-cost complementary vertically coupled plasmonic structure for surface-enhanced infrared absorption

Abstract

A scalable nanofabrication approach for the fabrication of hexagonal packed complementary vertically coupled plasmonic (CVCP) structures for surface-enhanced infrared absorption (SEIRA) applications is reported in this study. This fabrication approach consists of nanosphere lithography, reactive ion etching, and metal deposition and can be implemented on a four-inch wafer scale with low cost and high uniformity. The CVCP structure contains dense plasmonic nanoparticles inside a three-dimensional cavity nanoantenna array. The localized surface plasmon resonance between the top-bottom metallic nanoantenna couple generates a solid localized electric field inside the cavity. A high simulated and experimental SEIRA electric-field enhancement was achieved by optimizing the height of the silicon nanopedestals. Using a representative monolayer octadecanethiol, an enhancement factor of 2.1 × 103 was demonstrated with an optimized structure geometry. When the detection area was extended to square millimeters, the limit of detection of monolayer octadecanethiol on the CVCP substrate reached 10 nM, which is four orders of magnitude lower than that on a flat gold substrate. This study demonstrates a feasible fabrication approach for producing three-dimensional nanoantenna structures with high enhancement factors in a scalable fashion, empowering the practical application of SEIRA substrates.