Raman spectroscopy for investigation of growth process of carbon nanotubes

Raman spectroscopy (RS) is soft technique to study the vibronic, and electronic properties of material. Single-walled carbon nanotubes (SWCNTs) have unique chemical and physical properties. The chemical functionalization methods such as filling, intercalation, substitution of carbon atoms in walls, covalent, noncovalent modifications allow changing precisely the electronic properties. Raman spectroscopy investigates these modifications. Raman spectrum of pristine SWCNTs includes four regions: radial breathing mode (RBM) at 50-300 cm^-1, D-band at 1350 cm^-1, G-band at 1590 cm^-1, and 2D-band at 2700 cm^-1. There are five main modifications upon charge transfer: shift of peaks, change of peak shape, decreasing or increasing in the intensity of peaks, disappearance of peaks, change of band profile. In the typical p-doped spectrum of SWCNTs, i.e. the spectrum of metal halogenide-filled SWCNTs, peaks are positioned at 50-300 cm^-1 (RBM), 1350 cm^-1 (D-band), 1600 cm^-1 (G-band), and 2700 cm^-1 (2D-band), depending on the laser wavelength (458-1064 nm). These changes are observed in the spectra of filled SWCNTs, which are encapsulated with n-dopant substances, too. The mechanisms of Raman spectra modifications are different for p, and n doping, which is discussed here.