The measurement of work function of carbon nanotubes

The work function of multi-walled carbon nanotubes (MWNTs) is found to be about 5 eV by the photo-electron emission method. For comparison, the work function of highly oriented pyrolytic graphite (HOPG) was also measured and it was determined that the work function of MWNT is larger than that of HOPG. MWNT has σ-π non-orthogonal valence state, while HOPG has an orthogonal state. Because of this non-orthogonality, HOMO level of MWNT is deeper, which gives a larger work function. To check the validity of this experimental result, the first principle ab-initio calculation was carried out and the result shows the validity of the experiment.