Raman modes of metallic carbon nanotubes

Abstract

The anomalous resonant behavior of the tangential Raman modes of carbon nanotubes has been studied in the critical region of laser energies 1.7‐2.2 eV. The special enhancement of the Raman modes is explained by a model that takes into account the transition between the singularities in the one-dimensional density of electronic states for the metallic nanotubes and the distribution of diameters in the sample. The results agree with direct measurements of the electronic density of states for the metallic nanotubes and establish their association with the specially enhanced high frequency, first-order Raman modes. @S0163-1829~98!50848-X# Resonant Raman spectroscopy is a very useful tool for the characterization of the one-dimensional ~1D! properties of carbon nanotubes. It has been used to study multiwall nanotubes ~MWNT!, 1 single-wall nanotubes ~SWNT!, 2‐5 and was recently examined theoretically. 6 We show here evidence that special tangential phonon modes of metallic carbon nanotubes are enhanced in a narrow range of laser energies between 1.7 and 2.2 eV by electronic transitions between the first singularities in the 1D electronic density of states ~DOS! in the valence and conduction bands v 1!c 1 . This result establishes the association of the specially enhanced highfrequency, tangential modes with the metallic carbon nanotubes.