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Résumé |
The tangential vibrational modes of metallic single-walled carbon nanotubes (SWNTs) are thought to be characterized by Kohn anomalies, due to the combination of their one-dimensional nature with a significant electron-phonon coupling. These properties are modified by the doping-induced tuning of the Fermi energy level f. We present a density-functional theory (DFT) study of the vibrational properties of a ( n, n) metallic SWNT as a function of electronic doping, and explore non-adiabatic effects using the Born-Oppenheimer (BO) approximation, and a time-dependent perturbation theory beyond this approximation. A comparison with existing measurements is done and further experiments are suggested.
The structural organization of inserted alkali atoms inside SWNT bundles is then discussed. First of all, I present x-rays and neutrons diffraction experiments in Rb inserted carbon nanotubes (n-doping). These diffraction spectra are used to discuss the possible insertion sites of the Rb atoms in the nanotube bundle and are compared to diffraction simulations and ab initio DFT calculations.
The main outcome of our combined experimental and theoretical study is that: i) up to saturation, the spectra show no lattice expansion; ii ) the extinction of the (10) peak is only compatible with Rb insertion inside the tubes; iii) DFT calculations show that the insertion within the tubes is energetically favored with respect to insertion between the tubes.
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