NEAR-FIELD SURFACE-ENHANCED RAMAN-SPECTROSCOPY OF DYE MOLECULES ADSORBED ON SILVER ISLAND FILMS

We report the combined use of scanning near-field optical microscopy a nd surface-enhanced Raman scattering (SERS) to obtain spectral, spatia l and chemical information of molecular adsorbates with subwavelength lateral resolution. Near-field SERS spectra of cresyl fast violet and rhodamine 6G on silver substrates are obtained with short exposure tim es (less than 100 s) and a signal-to-noise ratio of > 20. Spectra from as few as approximate to 300 molecules or less than 10(-2) monolayers adsorbed on about ten silver nanoparticles can be recorded using 200 nm tip apertures. For the near-field spectra, a local Raman enhancemen t factor of 10(-3) or greater can be derived from a comparison with fl uorescence measurements. (C) 1998 Elsevier Science B.V.