Interaction between carbon nanotubes and their physicochemical environment : towards the control of the optical properties
Fabien Vialla (LPA)

Abstract

This thesis deals with an experimental study on pristine and functionalized single-wall carbon nanotubes by means of photoluminescence spectroscopy. Due to nanotubes original one-layer structure, the physico-chemical environnement can greatly alter their optical properties, introducing in the same time a way to control these properties. Luminescence signals from single substrate deposited nanotubes are studied with a home-made confocal microscope at cryogenic temperatures. The large variety of observed spectral profiles is interpreted in term of an unified coupling between localized excitons and unidimensionnal acoustic phonons. In particular, a local gap in the low energy phonon spectrum leads to narrow lines with width lower than 500 µeV. Nanotubes non-covalently functionalized with dye molecules (porphyrins) show an original absorption feature at 2.8 eV involving a very efficient energy transfer. Molecules coverage and affinity on the nanotube wall are evaluated from the adsorption thermodynamic equilibrium. A polarized photoluminescence study at the single compound scale reveals that the energy transfer shows strong anisotropy owing to antenna effects in the vicinity of the nanotube. Finally, the dye molecule can be used as an absorptive unit cell to calculate the absorption cross section of carbon nanotubes. A clear evolution is found at the 22 optical resonance with respect to the chiral angle of the species.