Surface enhanced Raman imaging: periodic arrays and individual metal nanoparticles

Surface enhanced Raman scattering (SERS) from Rhodamine 6G homogenously adsorbed on both periodic arrays of and individual gold nanoparticles is investigated using high-resolution Raman imaging with polarized excitation. Rectangular 50-nm-high nanoparticles of different sizes chosen to ensure the presence of localized surface plasmon resonances close to the 532-nm excitation wavelength are fabricated with electron-beam lithography on the surface of a smooth gold film and arranged both individually (i.e., placed sufficiently far apart) and in 740-nm-period arrays. Linear reflection spectra and high-resolution Raman images obtained from arrays of nanoparticles are compared revealing good correspondence in the spectral dependences of reflection and local SERS enhancements (measured at the top of nanoparticles). The latter are related to those observed with individual nanoparticles. The results obtained emphasize the importance and quantify the influence of particle dimensions, polarized excitation, collctive resonances and SERS locations.