Résumé
For long time, the resonance Raman responses of isolated SWNTs were only measured on SWNTs grown (deposited) on a substrate and on SWNTs wrapped in a surfactant and dispersed in aqueous solution. The responses have been mainly understood in the framework of different models of the electronic and mechanical properties. The goal of our “complete experimental” approach was to relate the Raman response of an individual freestanding SWNT to its (n,m) structure determined from an independent way. In this aim, a procedure including transmission electronic microscopy (TEM), Raman spectroscopy, and electron diffraction experiments on the same freestanding nanotube has been developed. In this communication we review the main results obtained up to now by using this procedure. 1- From the radial breathing mode (RBM) frequencies (RBM) measured on precisely identified nanotube structures, we obtained an RBM vs diameter relationship that does not depend on any modelization of nanotube electronic or mechanical properties[1]. The comparison with previous RBM vs d relations obtained on SWNTs grown on a substrate, or wrapped in a surfactant allowed us to discuss the role of the environmental conditions on the Raman response of SWNT. 2- The dependence of the frequency of the tangential modes (LO and TO) with the diameter of semiconducting tubes was found and compared with the predictions of different models [2]. For metallic nanotubes, the specific lineshape of the LO mode is identified and discussed. 3- The comparison between the incident excitation energies, for which an intense Raman signal is observed, and the calculated transition energies [3] allowed us to determine precisely the values of the optical transition energies EM11, ES33 and ES44 for SWNTs in the 1.3-2.4 nm diameter range [2]. A good agreement with the transition energies measured by Rayleigh scattering [4] was found. 4-These latter results question the origin of the correction, usually considered as related to the electron-electron correlation and exciton binding energy, the so-called Kane and Mele correction [Kane and Mele. Phys. Rev. Lett. 93, (2004), 197402], to explain the differences between the experimental and calculated transition energies. For semiconducting tubes, a possible explanation is that the exciton binding is very small or missing for the higher transitions ES33 and ES44, contrary to the lower transitions ES11 and ES22 [5,6]. [1] J.C. Meyer et al., Phys. Rev. Lett. . 95 (2005) 217401 [2] M. Paillet, et al.,, Phys. Rev. Lett. 96 (2006) 257401 [3] V. Popov and L. Henrard, Phys. Rev. B 70, (2004) 115407 [4] M. Y. Sfeir et al., Science 312 (2006) 554 [5] T. Michel, Phys. Rev. B 75 (2007) 155432 [6] T. Michel, Phys. Stat. solid b (2007, in press)