Out-of-equilibrium optical properties of pristine and functionalized carbon nanotubes
Benjamin Langlois (LPA)

Abstract

This thesis is devoted to the experimental study by femtosecond pump-probe spectroscopy of micellar solutions of carbon nanotubes.

The properties of carbon nanotubes are greatly affected by their 1D geometry. Confinement of electrons in 1D leads to enhanced coulomb interactions giving rise to strongly bound excitons. Many-body effects between excitons is investigated by the moment method analysis of the transient absorption spectra.
The relaxation of excitons is controlled by diffusion-limited collisions between excitons. The presence of excitons in the lowest subband results in a broadening and an uniform blue-shift of the excitonic energy spectrum. Intra and intersubband interactions turn out to be of the same magnitude, in agreement with a simple mean field theory of excitonic interactions.

Moreover, the one-layer structure of nanotubes results in strong interaction with the environment. We take advantage of the environmental sensitivity of nanotubes in hybrid compounds where the non-covalent functionalization with dyes opens a new extrinsic monochromatic excitation channel of the nanotubes through an efficient and ultrafast energy transfer between dyes and nanotubes. Once the exciton transferred to the nanotube, its relaxation is similar to the one observed in bare nanotubes.