Characterization of SPR and cavity modes in one-dimensional (1D) gold nanograting chips: figure of merit analysis and implications for Raman signal enhancement.

The optical properties of the 1D nanograting chip have been explored based on computational and experimental studies. Dispersion curve analysis demonstrates cavity and surface plasmon modes in the 1D nanograting chips with periods of 400 nm and 800 nm. In this grating period range, the cut-off period is at a grating period of 644 nm under excitation with a wavelength of 670 nm. Among the two investigated chips, the chip with a grating period of 800 nm is more promising for application as a dual-mode sensor based on SPR/Raman. By using the angle interrogation method, this chip has a figure of merit (FOM), which is 3.23 times higher than the 1D nanograting chip with a period of 400 nm. In the same system, Raman measurements have also been performed using Rhodamine 6 G (R6 G) as the standard material. The experimental results show that the Raman signal measured at the grating resonance angle shows higher intensity than the Raman measurement without Surface Plasmon Resonance (SPR) sensor. SPR-induced electromagnetic enhancement plays an important role in amplifying Raman signals in surface-enhanced Raman scattering (SERS) and this approach is very promising to be further developed to obtain sensors that are not only sensitive but also accurate.