Abstract
Carbon-based nanostructures, particularly carbon nanotubes, represent a critically important field of research in nanoscale electronics and optics. Among these nanostructures, metallic carbon nanotubes offer exceptional technological potential as the smallest metallic wires at the nanoscale, possessing remarkable electrical properties. However, despite their significant potential, metallic carbon nanotubes have been relatively less explored in optics compared to their semiconductor counterparts, which have garnered interest as light sources in the near-infrared range. This thesis focuses on determining the optical properties of metallic carbon nanotubes across a broad spectral range, from ultraviolet to far-infrared. This work involved the meticulous preparation and characterization of sorted samples of metallic and semiconductor carbon nanotubes, utilizing various techniques such as optical absorption, atomic force microscopy, Raman spectroscopy, and thermogravimetric analysis. A pivotal aspect of our research was the determination of the complex dielectric constant of metallic carbon nanotube films, a fundamental parameter for understanding their optical behavior. To achieve this, we established a robust numerical method based on Kramers-Kronig relations applied to the phase of the Fresnel coefficient. The measurable quantity enabling the extraction of the dielectric constant was reflectance, measured using a Fourier-transform infrared spectrometer and a UV-visible spectrometer. We particularly investigated intraband transitions, which induce a Drude-like behavior in the mid-infrared. By determining the screened plasma frequency, we characterized the threshold below which a film of metallic carbon nanotubes behaves as a metal. Our experimental results were compared with two widely used theoretical models: the surface conductivity model and ab-initio calculations based on density functional theory. This comparison revealed significant discrepancies between the two theoretical predictions, especially concerning the evolution of the plasma frequency with the diameter of the nanotubes. The dielectric constants obtained from the models were compared with experimental measurements, confirming excellent agreement with ab-initio calculations and refuting predictions from the surface conductivity model. Additionally, we observed a p-type doping of carbon nanotube films, induced by adsorbed molecules, before annealing. This doping was confirmed by a Drude-like behavior of the dielectric constant and was associated with the observation of characteristic electron-phonon interaction signatures. In summary, this comprehensive study of the optical properties of metallic carbon nanotubes paves the way for innovative applications in the fields of physics and biology. Furthermore, it enables precise and quantitative predictions, contributing significantly to the advancement of our understanding of these exceptional nanostructures.