Work function of carbon nanotubes

The work functions of multi- and single-walled carbon nanotubes are found t o be 4.95 and 5.05 eV. respectively. The measurements were carried out usin g the photoelectron emission (PEE) method, which allows easy and precise me asurements to be made in air. We have found that the work function of the n anotubes is 0.1-0.2 eV larger than that of highly oriented pyrolytic graphi te (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 o f carbon nanotubes. The experimental data were well reproduced in ab-initio calculations on planar and cylindrical conjugated states. (C) 2001 Elsevie r Science Ltd. All rights reserved.