Using surface enhanced Raman scattering to study vibrations of adsorbates on thin metallic overlayers on silver

We have studied the surface enhanced Raman scattering from molecules adsorbed on thin gold overlayers on silver island films. The Raman scattering of gold cyanide species adsorbed on gold overlayers decreases in intensity with gold overlayer thickness between 0.5 - 10A. This intensity decrease is consistent with a simple model which takes into account the damping of the electromagnetic resonances of the silver islands by the absorbing gold over-layer. Implications of these findings for the enhancement of Raman scattering from adsorbates on other metals deposited as overlayers on silver will be discussed.