13C NMR investigation of carbon nanotubes and derivatives

We report on nuclear magnetic resonance on single wall carbon nanotubes. Depending on the chemical preparation the electronic and dynamical properties of carbon nanotubes are presented and discussed. From a room temperature study of the spin lattice relaxation of carbon nanotubes prepared with various catalysts we clearly identified two components. In agreement with previous NMR studies and theoretical predictions, one-third of the intensity of the signal is found with a short relaxation time (about 5 s) attributed to metallic nanobutes while the rest of the signal presents a relaxation time of about 90 s corresponding to semiconducting nanotubes. In the case of oxidized or cut nanotubes only one relaxation time is observed with characteristics similar to the slow component. The disappearance of the fast relaxing component is associated with the absence of metallic nanotubes damaged by the chemical or mechanical treatments. In this case, the T dependence of the spin lattice relaxation reveals the effect of thermally activated small amplitude motions (twistons) of the nanotube in ropes. If diffusion of twistons might induce movement of C-13 sites and local magnetic field fluctuations, orientational order could appear below the transition temperature of 170 K. In the last part, we present the theoretical predictions of chemical shift tensor in carbon nanotubes. (c) 2001 Elsevier Science B.V. All rights reserved.