Temperature-dependent vibrational spectra of carbon nanotubes

The complete Raman spectra of carbon tubules at various temperatures are compared with those of graphite and fullerene C₆₀. The band at 1470 cm^-1 as well as those in the range 100--600 cm^-1 in tubules attest to the presence of pentagon-containing hemispherical surfaces on both the end caps and the inside terminations of the cylindrical structures of nanotubes. Raman microspectroscopy is also used to observe a temperature-dependent and reversible shift of the stretching frequencies corresponding to changes in the carbon-carbon distances in tubules. This could result in a temperature dependence of the diameters of the multilayer carbon nanotubes and could ultimately lead to a tuning method for structure-sensitive properties, such as the band gaps of individual tubes.