Structure et proprietes electroniques de nanotubes de carbone en solution polyelectrolyte

This Ph.D. work is dedicated to the studies of the structural and electronic properties of single-wall carbon nanotubes in polyelectrolyte solution.;Keywords: Doping, Work function, Neutrality level, Charge density, Raman Spectroscopy, Electrochemistry, Redox titration, Exfoliation.;Carbon nanotubes were first n doped by a chemical reduction reaction with polyaromatic radical-anions and alkali cations. The resulting nanotube salt was then spontaneous dissolved in a polar aprotic solvent in order to obtain the polyelectrolyte solution. The structural organization of the nanotube salt and of the polyelectrolyte solution were determined and characterized using X-ray diffraction and simulations and completed with Atomic Force Microscopy measurements. These studies revealed that the nanotube bundles appear expanded in the salt and the nanotubes are individualized in the polyelectrolyte solution. The characteristics of the charge transfer complexes were also studied using X-ray photoelectron and Raman spectroscopies. Comparison of pristine, doped and air oxidized doped nanotubes gave qualitative and quantitative estimates of the doping states. Characteristic signatures obtained using these measurements were identified as a function of doping level. The XPS study indicated a doping level of 1 electron per 15 carbon atoms for nanotubes in polyelectrolyte solution. Characteristic Raman signatures were identified for doped nanotubes in polyelectrolyte solution: upshift and broadening of tangential modes (TM), loss of intensity of radial breathing modes (RBM) with a wide envelope of all nanotubes RBM. These Raman signatures were then monitored in-situ during well-controlled charge transfer experiments on the nanotubes polyelectrolyte solution using both redox titration and electrochemistry. The evolution of the TM and the RBM were followed, which allowed measurements of the doping signatures and potentials during the evolution from n- to p-type doping. An original study of electronic properties of individual nanotubes was finally carried out by comparing RBM intensities with the calculated charge densities of carbon nanotubes. The study provided estimate of the work function in many identified semiconducting and metallic nanotubes and indicated that there is no clear dependence of work function with nanotube diameter.