We present results of optical measurements that yield clear evidence of localized-plasmon resonances of uniformly sized, submicroscopic structures on a continuous metal surface. Reflectance and inelastic-light-scattering spectra were measured for a silver surface that has randomly located projections, or “bumps,” 60 nm high and 60 nm wide. The reflectance spectra exhibit two absorption bands corresponding to localized plasmons of the silver bumps, which oscillate in directions parallel and perpendicular to the surface. Addition of Rhodamine-dye molecules to the surface yields marked changes in the reflectance spectra. The intensities of the luminescence and the Raman scattering from the dye layer at the surface increase in approximate proportion to the number density of bumps, confirming the role of these bumps as signal amplifiers in the enhancements of the inelastically scattered light. The intensity and the shape of the luminescence spectra depend on the incident and emitted polarizations in a manner that can be qualitatively understood in terms of the polarization dependence of the localized plasmons.
© 1985 Optical Society of AmericaPDF Article