Influences of temperature on the Raman spectra of single-walled carbon nanotubes

The Raman spectra for single-walled carbon nanotubes (SWNTs) at different temperatures are studied. We find that the G peak position shifts to low frequency with increasing temperature. The variation rate of the peak frequency as a function of temperature is a factor of 2similar to3 larger than the corresponding G peak frequency variation rates of multiwalled carbon nanotubes and highly ordered pyrolytic graphite from room temperature to 673 K. The line shapes of the RBM features are also found to be sensitive to temperature. The softening of the interatomic force constant due to thermal expansion of C-C bonds and the relaxation of the weak van der Waals interaction between the SWNTs in a bundle with increasing temperature are suggested to be the main origins of the reversible spectral variations.