Theory of Raman Spectra of Unfilled and Filled Carbon Nanotube

Abstract

The Raman spectra of two G‐bands and a radial breathing mode (RBM) of unfilled and filled single‐wall semiconducting and metallic carbon nanotubes have been investigated in the presence of electron‐phonon and phonon‐phonon interactions. Excitation of low frequency optical plasmons in the metallic nanotube is shown to be responsible for the asymmetric band known as the Breit‐Wigner‐Fano (BWF) line shape in the G‐band Raman spectra. In a filled nanotube there is an additional peak due to excitation of the phonon of the filling atom or molecule. Positions, shapes and relative strengths of these Raman peaks depend on the phonon frequencies of the nanotube and that of the filling atoms, and strengths and forms of the electron‐phonon and phonon‐phonon interactions. Raman spectra of semiconducting unfilled and filled nanotubes have similar behavior as those of metallic nanotubes except that normally they have Lorentzian line shapes and do not show a BWF line shape. However, if a semiconducting nanotube is filled...