Nonlocal Electrodynamic Effect on the Enhancement Factor for Surface Enhanced Raman Scattering

The electromagnetic enhancement factor for surface enhanced Raman scattering is reexamined taking into account the nonlocal dielectric response of the substrate surface. Surface roughness is represented typically by a spherical island and nonlocal effect is introduced via a simple phenomenological model which makes possible a closer quantitative comparison with experiments. It is found that the nonlocal effect can lead to significantly lower values for the enhancement factor compared to the results calculated in the literature ignoring this effect. A sample calculation shows that, for scattering frequencies much below the surface plasmon frequency of the substrate, the nonlocal correction decreases the enhancement effect by up to 10%; and for frequencies close to the surface plasmon frequency, the difference could be by orders of magnitude. Possible experimental observation of this effect is discussed.