Resonance Raman study of linear carbon chains formed by the heat treatment of double-wall carbon nanotubes

Abstract

We study the resonance behavior of the unusual Raman feature known as the coalescence-inducing mode (CIM), observed at $\sim 1850{\mathrm{cm}}^{-1}$, in samples of double-wall carbon nanotubes annealed at high temperatures. Resonance Raman spectra taken with different laser energies show that the intensity of the CIM band exhibits a maximum around $2.20\mathrm{eV}$. By comparing the resonance Raman experimental results with first-principles calculations for the vibrational frequency and the energy gap, we propose that the CIM feature is associated with short carbon chains with an odd number of atoms, interconnecting the nanotube surfaces.