Nondisturbing and stable SERS-active substrates with increased contribution of long-range component of Raman enhancement created by high-temperature annealing of thick metal films

High-temperature annealing of thick silver films (TSFs) deposited onto a smooth dielectric substrate leads to high-order self-organization of metal clusters on the film surface. A comparative atomic force microscopic (AFM) analysis of ''as-deposited'' and annealed TSFs (aTSFs) shows that uniform ellipsoidal roughness similar to 41 x 25 mn in lateral cross section and similar to 45 mn in height results after annealing. These metal clusters are mutually oriented so that the main lateral axes of the ellipsoids are nearly parallel. UV-visible data demonstrate a similar to 300 nm hypsocromic shift of the bands corresponding to the collective surface plasmon modes. Additionally, a new (similar to 350 nm) band related to the normal component of the plasmon oscillations appears after annealing. This band was found to be strongly angle-dependent for p-polarized light. The aTSFs appeared extremely time-and organic solvent-stable versus as-deposited films. The aTSFs were found to be nondisturbing surface-enhanced Raman scattering (SERS)-active substrates in the application to studies of complexation of crown ether styryl dyes with metal ions, A pronounced SERS signal of the analyte rhodamine 6G was observed with aTSFs, even when the analyte was separated from the silver surface with five Langmuir-Blodgett monolayers of stearic acid. At the same time, depositing only a monolayer of stearic acid on the as deposited film completely suppressed the SERS signal of the analyte. Finally, the self-assembling of Ag clusters on the surface of the aTSF, stimulated by the high-temperature annealing, results in the creation of a time-and organic solvent-stable SERS substrate with nanometer-scale quasi-periodical roughness, and this substrate exhibits an increased contribution of the electromagnetic component to the overall Raman enhancement.