Selective probe of the morphology and local vibrations at carbon nanoasperities

摘要

We introduce a way to selectively probe local vibration modes at nanostructured asperities such astips of carbon nanohorns. Our observations benefit from signal amplification in surface-enhancedRaman scattering (SERS) at sites near a silver surface. We observe nanohorn tip vibration modes inthe range 200–500 cm−1, which are obscured in regular Raman spectra. Ab initio density functionalcalculations assign modes in this frequency range to local vibrations at the nanohorn cap resemblingthe radial breathing mode of fullerenes. Careful interpretation of our SERS spectra indicates presenceof caps with 5 or 6 pentagons, which are chemically the most active sites. Changes in the peakintensities and frequencies with time indicate that exposure to laser irradiation may cause structuralrearrangements at the cap.