NANOTUBE'05 Conference:
NANOTUBE'05 Conference:
Structure and vibrations of the same individual single-walled carbon nanotube
J.-L. SauvajolContact e-mail: sauva@lcvn.univ-montp2.fr
Despite the large number of prior works devoted to Raman scattering in nanotubes, there are still answers about the Raman response of individual metallic and semiconducting isolated single-walled carbon nanotubes (SWNT). Up to now, the Raman response of an isolated SWNT has been mainly understood in the framework of different modelizations of the electronic and vibrational features. By contrast, the ultimate goal of our "complete experimental" approach is to relate the Raman response of an individual SWNT to its (n,m) structure determined from an independent way. In this aim a procedure including the preparation of substrates, the sample preparation, atomic force microscopy imaging (AFM), transmission electronic microscopy (TEM), electronic diffraction and Raman spectroscopy experiments has been developed. The following results can be pointed out:
1) A comparison between the Raman spectra measured on well characterized thin bundles and isolated tubes clearly highlights the dependence of the profile of the TM of metallic tubes with the size of the bundles. We state that the observation of a Breit-Wigner-Fano component in the profile of the the tangential modes is an intrinsic feature of metallic SWNT bundles, this latter component vanishing in the Raman response of an individual metallic tube.
2) We demonstrate the determination of the structural indices (n,m) by electron diffraction and of the frequencies of the vibrational modes by Raman spectroscopy on the very same single nanotube. The precise and independent determination of both structure and frequencies allows for direct and unambiguous verification of molecular dynamical calculations. The relation between diameter (d) and the radial breathing mode frequency (nRBM) is thus determined in a direct way. It is found to be close of nRBM= 273 (cm-1 nm)/d. The pre-factor of this expression is significantly higher than that predicted in different modelizations. The accuracy of this relation is discussed. On the other hand, the profile of the tangential modes with the respect to the structure of the tube is reported and discussed in relation with previous modelizations. Finally, some clarifications of the resonant process involved in the Raman scattering from SWNTs are shown.
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