Measurement of the molecule–silver separation dependence of surface enhanced Raman scattering in multilayered structures

Abstract

We report details and results of experiments in which surface enhanced Raman scattering from molecules is studied as a function of their spacing from a rough silver enhancing layer. Two types of experiments were performed. In the first, an organic monolayer chemisorbed on aluminum oxide is covered with a smooth low Raman cross section polymer spacer layer and rough silver is placed on top of the spacer. The Raman scattering from the monolayer is studied as a function of the spacer layer thickness. As a result of our diffusion and tunneling experiments, we conclude that direct contact of the molecules with scattering from the molecules. We observe an enhancement of roughly 106 for no polymer spacer thickness, and a fall-off of the enhancement by a factor of 10 with each subsequent 35–50 Å spacer thickness. We also observe a similar drop off of the broadband background under the Raman scattering. In the second type of experiment, the Raman scattering from a high Raman cross section polymer is studied as a function of its thickness in similar multilayered structures. The results of these variable thickness experiments are consistent with those of the spacer experiments. We conclude that in our samples, the major cause of surface enhanced Raman scattering is electromagnetic in nature.