Surface plasmon enhanced Raman spectra of monolayer assemblies

Abstract

This paper describes the systematics of using plasmon surface polariton (PSP) fields to enhance the Raman spectra of monolayer assemblies deposited on silver metal gratings by the Langmuir–Blodgett deposition technique. The intensity of the incident light is enhanced by grating coupling to the PSP mode, likewise, the intensity of the outcoupled Raman light is enhanced by emission via radiative PSP modes. It is shown how the various spectral regions corresponding, e.g., to C–C and C–H stretching vibrations are individually enhanced by selecting the appropriate scattering angle for the light collected from the grating. Results are presented that demonstrate how the gaps in the PSP dispersion curve at the center and the boundary of the Brillouin zone can be shifted to preselected frequency ranges using assemblies of different thickness. It is also shown that the dispersion gap width and intensities of the Raman vibrational bands depend on the number of monolayers making the assembly.