Exploring the role of hyperbolicity in surface enhanced Raman sensing

TL;DR

This study investigates how hyperbolic metamaterial properties of gold nanorod arrays influence their effectiveness as SERS substrates for detecting low concentrations of molecules like R6G.

Contribution

It demonstrates the fabrication and comparison of HMM and non-HMM nanorod arrays, highlighting the impact of hyperbolicity on SERS performance.

Findings

HMM nanorod arrays show enhanced Raman signals compared to non-HMM arrays.

Fabrication method allows detection of lower molecular concentrations.

Simulation and mapping confirm the role of hyperbolicity in SERS enhancement.

Abstract

A plasmonic nanostructure-based substrate, serving as a surface-enhanced Raman scattering (SERS) substrate, enhances the Raman scattering of molecules. By employing an electron beam lithography followed by our recently developed nano-electroplating protocol, a gold nanorod array SERS substrate can be fabricated to detect lower molecular analyte concentrations, such as Rhodamine 6G (R6G) solution. As the critical dimensions of the nanorod array decrease, they exhibit hyperbolic metamaterial (HMM) characteristics with anisotropic permittivity behavior. In our study, we fabricated two sets of nanorod arrays: one in the HMM regime (140 nm periodicity) and the other in the non-HMM regime (400 nm periodicity), aiming to evaluate the performance of each set based on R6G detection. The obtained results are compared and analyzed using COMSOL simulation and Raman mapping and the role of hyperbolicity is discussed.