Semiconductor-to-metal transition of double walled carbon nanotubes induced by inter-shell interaction

Nuclear magnetic resonance measurements on isotope engineered double walled carbon nanotubes (DWCNT) suggest a uniformly metallic character of all nanotubes. This effect can only be explained by the interaction between the inner and outer shell. Here we study the DWCNTs by density functional theory and inter-molecular Huckel model. We present a study of the density of states of DWCNTs which clearly shows that two layers of semiconducting single walled nanotubes can indeed form a metallic DWCNT in many cases, but not necessarily in every case. For most metallic DWCNTs, a high density of states can be expected at the Fermi level. (c) 2006 WILEY-VCH Verlag GmbH & Co. KG&A, Weinheim.