G′ band in double- and triple-walled carbon nanotubes: A Raman study

Double- and triple-walled carbon nanotubes are studied in detail by laser energy-dependent Raman spectroscopy in order to get a deeper understanding about the second-order ${\mathrm{G}}^{\ensuremath{'}}$ band Raman process, general nanotube properties, such as electronic and vibrational properties, and the growth method itself. In this work, the inner nanotubes from the double- and triple-walled carbon nanotubes are produced through the encapsulation of fullerene peapods with high-temperature thermal treatments. We find that the spectral features of the ${\mathrm{G}}^{\ensuremath{'}}$ band, such as the intensity, frequency, linewidth, and line shape are highly sensitive to the annealing temperature variations. We also discuss the triple-peak structure of the ${\mathrm{G}}^{\ensuremath{'}}$ band observed in an individual triple-walled carbon nanotube taken at several laser energies connecting its Raman spectra with that for the ${\mathrm{G}}^{\ensuremath{'}}$ band spectra obtained for bundled triple-walled carbon nanotubes.