Raman Spectra of Single-Wall Carbon Nanotube.

The Raman spectra of two G-bands and a radial breathing mode (RBM) of  single-wall semiconducting and metallic carbon nanotubes have been investigated theoretically.The 
tangential G-band in the Raman spectra of  metallic single-wall carbon nanotube shows two peaks: a higher frequency component having the Lorentzian shape and a lower-frequency component of lower intensity with a Breit-Wigner-Fano (BWF)-type lineshape. Whereas for semiconducting nanotube both the peaks in the G band has Lorentzian line shape. This interesting feature has been analyzed on the basis of phonon-plasmon coupling in a metallic nanotube. It is shown that while the gapless semi-acoustic plasmon cannot account for the observed spectra as claimed by other investigators, the low-lying optical plasmon corresponding to the tangential motion of the electrons on the nanotube surface can explain the observed features. We further studied in details the new features in the Raman spectra of metallic and semiconducting nanotubes in presence of filling atoms inside the nanotube.