Sub-wavelength Raman spectroscopy on isolated silver islands

Surface Enhanced Raman Spectroscopy (SERS) is a valuable analytical tool fo r the investigation of molecules adsorbed on roughened noble metal surfaces . The shape, size, and surrounding of the metal protrusions play an importa nt role in the Raman scattering enhancement. By combining scanning near-fie ld optical microscopy (SNOM) with Raman spectroscopy the spatial resolution suffices for investigating isolated silver islands on SERS,active substrat e We demonstrate an optical resolution below 70 nm for recording spectra on specifically prepared and fully characterized SERS substrates. For a quant itative evaluation of the SERS signal the spatial distribution of Rhodamine 6G (R6G) deposited on the SERS substrate was determined by friction force measurements. By comparing the Raman intensities of the SERS substrates wit h those of unmetallized support plates absolute SERS enhancement factors at specific locations on top and in the vicinity of the silver islands were d etermined directly. (C) 2000 Elsevier Science B.V. All rights reserved.