Vibrational Analysis of Organic Molecules Encapsulated in Carbon Nanotubes by Tip-Enhanced Raman Spectroscopy
Tip-enhanced Raman spectroscopy revealed the nanoscale chemical properties of organic molecules encapsulated in single-wall carbon nanotubes (SWNTs). Our approach is based on an enhanced electric field near a laser-irradiated metal tip functioning as a Raman excitation source. The enhanced field can successfully act on encapsulated molecules through the walls of the SWNTs to extract molecular vibrational information. β-carotene, which exhibits several active Raman modes under visible light illumination, was used as the encapsulated molecule. Tip-enhanced Raman spectra measured at seven different positions on SWNT bundles showed that β-carotene molecules inside the tubes were not uniformly distributed. We also found that the filling rate and peak position of the radial breathing mode of the SWNTs are linearly correlated.