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. The precise and independent determinations of both structure and Raman features of semiconducting and metallic SWNTs allow to answer at several questions: 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. The unprecented study of large diameter tubes (1.4-3 nm) showed that the RBM frequency was not simply inversely proportional to the nanotube diameter [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 SWCNT. 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]. On the other hand the profile of the G-modes for metallic tubes is shown 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 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 the ES33 and ES44 [4] transitions. [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