Metallic Polymers of $C_{60}$ Inside Single-Walled Carbon Nanotubes

Doping induced polymerization of ${\mathrm{C}}_{60}$ inside single-walled carbon nanotubes is reported using Raman spectroscopy and resistivity measurements as a probe. The resistivity changes from semiconducting for the undoped system to metallic for the doped system. For full intercalation, we observe a chemical reaction inside the nanotubes which leads to a one-dimensional polymeric ${\mathrm{C}}_{60}^{-6\mathrm{}}$ chain which has metallic character. The resonance and the oscillations of the radial breathing mode are lost suggesting an up-shift of the Fermi level to beyond the third Van Hove singularity in the semiconducting tubes. The linewidth of the radial breathing mode now represents directly the Gaussian distribution of tube diameters.