AVS 50th International Symposium
    Nanotubes Wednesday Sessions
       Session NT-WeA

Invited Paper NT-WeA1
Photoemission Spectromicroscopy and Spectroscopy of Carbon Nanotubes

Wednesday, November 5, 2003, 2:00 pm, Room 317

Session: Properties of Carbon Nanotubes
Presenter: S. Suzuki, NTT Basic Research Laboratories, NTT Corporation, Japan
Authors: S. Suzuki, NTT Basic Research Laboratories, NTT Corporation, Japan
Y. Watanabe, NTT Basic Research Laboratories, NTT Corporation, Japan
T. Ogino, NTT Basic Research Laboratories, NTT Corporation, Japan
Y. Homma, NTT Basic Research Laboratories, NTT Corporation, Japan
S. Heun, Sincrotrone Trieste, Italy
L. Gregoratti, Sincrotrone Trieste, Italy
A. Barinov, Sincrotrone Trieste, Italy
B. Kaulich, Sincrotrone Trieste, Italy
M. Kiskinova, Sincrotrone Trieste, Italy
W. Zhu, Bell Laboratories, Lucent Technologies
C. Bower, University of North Carolina at Chapel Hill
O. Zhou, University of North Carolina at Chapel Hill
Correspondent: Click to Email
Investigating the electronic structure of carbon nanotubes, especially their tips, is important for understanding the electron-field-emission properties of nanotubes. A specific electronic structure is expected at the hemispherical tips of nanotubes, where the graphene cylinders are believed to be closed by insertion of the five-member rings in the graphene network. The localized states in the vicinity of the Fermi level would largely contribute to the field emission properties for close-end nanotubes. For open-end nanotubes or nanotubes having imperfect structures, dangling bond states may significantly contribute to the field-emission properties. Moreover, the edge state, which is a characteristic electronic structure formed at a zigzag-type graphene edge, and has a large density of states at the Fermi level, may also play a key role. By means of scanning photoemission spectromicroscopy, we studied the local electronic structure at the tips of aligned multi-walled carbon nanotubes grown using microwave plasma-enhanced chemical vapor deposition. The valence band and the C 1s spectra, measured systematically from spatially selected regions along the tube axes, were the fingerprint for lateral variations in the electron density of states and in the band bending, respectively. The spatially selected photoemission spectra revealed that the tips have a larger density of states in a binding energy range of 0 to about 1 eV, whereas band bending, which would explain such a spectral difference, was not observed. It is suggested that the different density of states near the Fermi level is due to a larger dangling bond density at the tips. We also studied the electronic structure and work function of alkali-metal-doped carbon nanotubes. Drastic change in the electronic structure caused by the doping will also be presented.