TEMPERATURE-DEPENDENCE OF THE RAMAN-SPECTRA OF CARBON NANOTUBES

We report on a temperature dependence of the frequency of all the majo r peaks in the Raman spectra of carbon nanotubes, using different exci tation laser powers at the sample. The frequency decreases with increa sing temperature for all peaks, and the shifts in Raman frequencies ar e linear in the temperature of the sample. In comparison, a similar de pendence is found in active carbon, but no shift is observed for the h ighly ordered pyrolytic graphite within the same range of variation in laser power. A lowering of frequency at higher temperature implies an increase in the carbon-carbon distance at higher temperature. The rel atively strong temperature dependence in carbon nanotubes and active c arbon may be due to the enhanced increase in carbon-carbon distance. T his enhancement may originate from the heavy defects and disorder in t hese materials. (C) 1998 American Institute of Physics. [S0021-8979(98 )05219-0].