Hexagonal Nanodimers as Plasmonic Metasurface for SERS Exhibiting Ultrahigh Electromagnetic Enhancement

In the era of highly sensitive single molecule detection, Surface-Enhanced Raman Spectroscopy (SERS) has proven itself one of the most promising surface-sensitive techniques, enabled due to the highly localized plasmonic field at the nanoscaled rough metallic surfaces. Here, we report a theoretical study of systematic design and analysis of SERS-based closely spaced periodic gold hexagonal nanodimers using finite difference time domain (FDTD) simulations, which induces strong localized surface plasmon resonance resulting in the highly localized hot-spots at the sharp edges of the structure and hence high order electromagnetic coupling at the center of dimers. Moreover, we explore the influence of geometric parameters such as nanopattern spacing, polarization, and surrounding environment on the SERS enhancement factor (EF) and spectral response. Through calculations, maximum EF is achieved up to the order of ~ 2.7´1011, and 1.46´1012 for incident laser wavelengths of 632 nm, and 785 nm, respectively. In addition, due to the cavity quantum electrodynamic (cQED) effect, high Purcell factor ~ 3.8´106 and corresponding EF ~ 1.5´1013 are attained facilitating the possibility of nearly single molecule detection. The proposed device is found to be highly sensitive to changing the surrounding refractive index from 1.330 to 1.400, proving its applicability for biomedical monitoring. The proposed structure showed a potential for designing SERS substrates for real-world applications, including biomedical diagnostics, environmental monitoring, chemical analysis, and quantum plasmonics.