Electronic structure at carbon nanotube tips studied by photoemission spectroscopy

The valence band and $\mathrm{C}1s$ photoemission spectra were measured from the tips and the sidewalls of multiwalled carbon nantoubes grown on Si substrates. The results show an overall spectral shift to the higher-binding-energy side, a larger density of states at the Fermi level, and a lower work function at the tips. These results can be explained by assuming that the Fermi level is slightly shifted upward and located inside the conduction band at the tips. We suggest that the electronic structure at the tips is considerably affected by defects.