Raman spectroscopy on the nanoscale: An investigation of silver triangle arrays, polymer laminates and gold-loaded mesoporous titania films

Raman scattering experiments can be performed on samples in any phase to provide both qualitative and quantitative information. Near-field scanning optical microscopy (NSOM) allows for samples to be imaged at a resolution of approximately 100 nm by coupling the excitation light into a tapered optical fiber that is scanned in the near-field (10 nm) of the sample. Raman scattering was coupled with NSOM (R-NSOM) which permits simultaneous topography and fluorescence imaging with high spatial resolution and chemical specificity. This technique has been applied to characterize various systems. Triangular-shaped silver nanoparticles (200 nm) fabricated via nanosphere lithography have shown dramatic enhancement (106--1010) of the resonance Raman spectrum of rhodamine 6G (R6G), which was attributed to the shape of the Ag triangles. In addition to the large surface-enhanced resonance Raman spectroscopy (SERRS) enhancement, we have also observed enhanced luminescence from the Ag nanoparticle films. In order to further understand the shape dependence of the electric-field enhancement we have used R-NSOM to map both the SERRS and luminescence for individual Ag nanotriangles. The enhancement is largest for the apex of the triangle or near sharp points.;Raman scattering from thin PEN and PET films and laminates have been examined with high resolution using R-NSOM. Comparison of Raman spectra taken with both confocal and NSOM indicated that it was not only possible, but beneficial to perform near-field measurements on these samples. In NSOM spectra, laminate samples displayed a shoulder, as well as shifts in the Raman bands, which proves helpful in characterizing the polymer thicknesses and/or interfacial region.;Gold nanoparticles on metal oxide supports have displayed excellent performance as catalysts for the low temperature oxidation of carbon monoxide, but complete characterization of the gold environment and the gold-titania interaction remains elusive. Gold-loaded free-standing mesoporous titania films were synthesized using two different methods and characterized using Raman scattering and confocal optical microscopy to compare to the more common x-ray diffraction technique. Initial work determined that Raman was sensitive to the titania crystallite size and to the gold-loading method providing more local information than powder XRD studies.