Electronic Structures of Single-Walled Carbon Nanotubes Studied by NMR

Abstract

ABSTRACTAn individual single-walled carbon nanotube (SWNT) has been shown [1-4] to exhibit remarkable electronic properties which depend on its diameter and chirality. In this work, the 13C nuclear magnetic resonance technique is used to measure quantitatively the electronic density-of-state (DOS) at the Fermi level in a bulk SWNT sample. Two types of 13C nuclear spins are observed with drastically different nuclear spin-lattice relaxation time (Tl). About onethird of the 13C nuclear spins with shorter Tl, are identified to reside at the metallic SWNTs and two-thirds can be associated with the semiconducting SWNTs. For the metallic SWNTs, the DOS at the Feimi level is measured quantitatively, which is about 0.022 states/(eV·atom·spin). The measured electronic DOS at the Fermi level agrees with the theoretical prediction for metallic tubes. This study also found that the semiconducting SWNTs in bundles, in fact, possess weak metallic characters. This indicates that tube-tube interactions within SWNT bundles could change the electronic properties.