Towards rapid nanoscale chemical analysis using tip-enhanced Raman spectroscopy with Ag-coated dielectric tips
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The influence of dielectric substrates on the Raman scattering activities of Ag overlayers has been investigated. Materials with low refractive indices, such as SiO2, SiOx and AlF3, were found to provide suitable supporting platforms for Ag films to give strong surface-enhanced Raman scattering for dye molecules when illuminated at 488 nm. This finding was then extended to tip-enhanced Raman scattering (TERS). Huge enhancements of 70–80×, corresponding to net enhancements of >104, were observed for brilliant cresyl blue test analyte when Ag-coated tips made from or precoated with low refractive index materials were applied. The yield of fabricated tips that significantly enhance the Raman signals was found to be close to 100%. These findings provide crucial steps towards the use of TERS as a robust technique for rapid chemical imaging with nanometer spatial resolution.
KeywordsNanoscale chemical analysis Surface-enhanced Raman spectroscopy Tip-enhanced Raman spectroscopy Refractive index Surface plasmon resonance
We would like to thank the Electron Microscopy Center at ETH Zürich (EMEZ), and Frank Krumeich for performing the SEM analyses as well as Urs Stauffer and Laure Aeschimann (University of Neuchâtel) for supplying the SiO2 AFM probes. We would also like to acknowledge the Gebert–Rüf Foundation (grant nr. P-085/03) and Deutsche Forschungsgemeinschaft (TS) for financial support of this project.
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