Laser-heating effect on Raman spectra of individual suspended single-walled carbon nanotubes

We studied the Raman spectra of 21 individual suspended single-walled carbon nanotubes (SWNTs) using different excitation laser powers. The results indicate that the laser-heating effect is more significant for suspended SWNT than nanotubes sitting on a substrate. The spectral variations of these individual SWNTs induced by different laser power shed new light on the temperature dependence of Raman spectra and electronic properties of SWNTs. By analyzing the frequency downshift of each nanotube induced by increased laser power, the temperature coefficient of radial breathing mode (RBM) frequency omega(RBM) is supposed to be diameter and chirality-dependent, whereas that of the G-band frequency omega(+)(G) is not. The behaviors of full width at half-maximum (fwhm) and intensity ratio between anti-Stokes and Stokes spectra (I-AS/I-S) of RBM with increasing laser power reflected the temperature increase and the consequent variation in the electronic density of states (DOS) of SWNT. The variation of resonance intensity with laser power showed interesting dependence on E-ii > E-laser or E-ii < E-laser, suggesting downshift of E-ii with increased temperature, which offers the possibility of utilizing the optical/thermal response of SWNT to modulate the electronic property of nanotubes.