Electronic properties of carbon nanotubes: Experimental results

• Published in: Carbon (New York) Vol. 33; no. 7; pp. 941 - 948
• Main Authors: Issi, J.-P., Langer, L., Heremans, J., Olk, C.H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1995
• Subjects: Carbon nanotubes; electrical resistivity; magnetic susceptibility; magnetoresistance; scanning tunneling microscopy; spectroscopy; magnetoresistance; Carbon nanotubes; magnetic susceptibility; spectroscopy; scanning tunneling microscopy; electrical resistivity
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/0008-6223(95)00023-7

Band structure calculations show that carbon nanotubes exist as either metals or semiconductors, depending on diameter and degree of helicity. When the diameters of the nanotubes become comparable to the electron wavelength, the band structure becomes noticeably one-dimensional. Scanning tunneling microscopy and spectroscopy data on nanotubes with outer diameters from 2 to 10 nm show evidence of one-dimensional behavior: the current-voltage characteristics are consistent with the functional energy dependence of the density-of-states in 1D systems. The measured energy gap values vary linearly with the inverse nanotube diameter. Electrical resistivity and magnetoresistance measurements have been reported for larger bundles, and the temperature dependence of the electrical resistance of a single microbundle was found to be similar to that of graphite and its magnetoresistance was consistent with the formation of Landau levels. Magnetic susceptibility data taken on bundles of similar tubes reveal a mostly diamagnetic behavior. The susceptibility at fields above the value at which the magnetic length equals the tube diameter has a graphite-like dependence on temperature and field. At low fields, where electrons sample the effect of the finite tube diameter, the susceptibility has a much more pronounced temperature dependence.