Raman Scattering Enhanced by Surface Plasmon Polaritons on Ag and Al Gratings

This paper describes the development and characterization of surface-enhanced Raman spectroscopy (SERS) substrates that employ the excitation of surface plasmon polaritons (SPPs) on periodic metal diffraction gratings to amplify the Raman signal of an analyte. The gratings were fabricated via interference photolithography on As40S40Se20 thin films. The resulting surface relief was subsequently coated with either aluminium (Al gratings) or aluminium followed by silver (Ag gratings). The ratio of the relief depth to the grating period (h/a) was optimized to maximize SPP excitation efficiency. For both types of gratings, a strong angular dependence of the Raman scattering intensity of the analyte molecule (Rhodamine 6G) was observed, which anticorrelates with the angular dependence of the specularly reflected light intensity. The enhancement factor is 2 × 102 for the aluminium grating and 1 × 103 for the silver grating. This finding suggests that aluminium-based SERS substrates may serve as a cost-effective alternative to those coated with noble metals. Although the overall amplification is significantly lower than that achieved by SERS substrates based on localized surface plasmon (LSP) excitation, the grating-based SPP substrates offer a crucial advantage for quantitative measurements due to their uniform enhancement across the entire substrate area.