Surface Plasmon Coupling in Nanotubes

To investigate the dielectric response of isolated Single‐Walled Carbon Nanotubes (SWCNTs), spatially‐resolved Electron Energy‐Loss Spectroscopy measurements have been carried out using a Scanning Transmission Electron Microscope in a near‐field geometry. Spectra have been compared with those acquired on Multi‐Walled Carbon Nanotubes (MWCNTs) made of different numbers of layers, and with simulations performed within the framework of the continuum dielectric theory, taking into account the local anisotropic character of these nanostructures. For thin MWCNTs, two polarisation modes have been identified at 15 and 19 eV, indexed as tangential and radial surface plasmon modes respectively, resulting from the coupling of the two surface modes on the internal and external surfaces of the nanotubes. We finally show that the dielectric response of a SWCNT, displaying a single energy mode at 15 eV, can be understood in the dielectric model as the thin layer limit of surface plasmon excitation of MWCNTs.