Raman spectra of lithium doped single-walled 0.4 nm carbon nanotubes

Using the vapor phase adsorption method, we show that it is possible to intercalate lithium atoms into 0.4-nm diameter single-walled carbon nanotubes. The charge-transfer behavior is studied by resonant Raman spectra. With increasing doping concentration, the radial breathing mode of these tubes shifts to higher frequency by about 18cm^-1 because the vibration perpendicular to the tube axis is depressed. The G band exhibits conventional softening and downshift behavior. By decomposing the G band by one Breit-Wigner-Fano line shape and three Lorentzians, we found that the softening and downshift is due to the intensity competition between four components. The BWF component at 1558cm^-1 couples with the electronic continuum and survives until the saturated doping stage.