Distance dependence of surface-enhanced resonance Raman enhancement in Langmuir-Blodgett dye multilayers.

Monolayers of a surface-active dye incorporated into inert matrix material were transferred onto structurally defined silver island films by the Langmuir-Blodgett technique. The dye-containing monolayers were spaced from the surface by accurately known increments by deposition of inert spacer monolayers. Surface-enhanced resonance Raman spectra were observed from dye molecules spaced as distant as six spacer increments (ca. 16 nm) from the silver surface. These results indicate an electromagnetic mechanism is operative in this system in contradiction to a chemical mechanism which would require direct contact between the Raman-active species and the metal surface.