Surface-enhanced Raman scattering from silver ellipsoidal particles

The wavelength dependence of surface-enhanced Raman scattering from molecules adsorbed on the dry surfaces of silver ellipsoids has been measured. Several substrates were employed during the measurements: silver coated, random arrays of silicon dioxide posts, silver coated polystyrene spheres, and silver metal island films. The Raman active compounds used were phthalic acid and benzoic acid. The data for the silicon dioxide posts are representative of the data for all of the substrates; therefore, only the post data is presented. Since these substrates consist of submicron sized particles of silver which are known to have surface plasmon resonances for optical energies, it was logical to assume that SERS could be explained in terms of the field enhancement due to the surface plasmons. The data, however, indicates that there is a significant chemical dependence in the SERS that cannot be correlated with the generation of surface plasmon resonances of the surface particles. The SERS peak positions and widths do not correspond to those of the surface plasmon resonances of the surface particles; therefore, there is not good agreement with the theory. SERS data was obtained with several laser wavelengths throughout the visible portion of the spectrum. The optical properties of the surface particles were obtained by measuring the optical absorbance of the substrates.