Work function of carbon nanotubes

The work functions of multi- and single-walled carbon nanotubes are found to be 4.95 and 5.05 eV. respectively. The measurements were carried out using the photoelectron emission (PEE) method, which allows easy and precise measurements to be made in air. We have found that the work function of the nanotubes is 0.1-0.2 eV larger than that of highly oriented pyrolytic graphite (HOPG) of which the valence state is sigma-pi orthogonal. This result is ascribable to reflection of the sigma-pi mixed valence state in the case of carbon nanotubes. The experimental data were well reproduced in ab-initio calculations on planar and cylindrical conjugated states. (C) 2001 Elsevier Science Ltd. All rights reserved.