Page 137 - Carbon Nanotubes

Electronic properties of carbon nanotubes 127
termediate field regime (around 0.5 T), x is probably model developed by Ajiki and Ando[%]. From the tem-
sensitive to the fact that the sample consists of a mix- perature dependence of the electrical resistance of this
ture of semiconducting and metallic tubes. Further- microbundle, it appears that the measured nanotubes
more, the tubes in that mixture have different diameters are semimetallic and behave like rolled-up graphene
and, thus, go from the low-field to the high-field re- sheets. Below 1 K, the results are puzzling and yet un-
gime at different fields. Figure 10 shows a summary explained. Susceptibility was measured on 20-mg sam-
of the a.c. susceptibilities of various forms of carbon, ples containing a large variety of tubes. Free carrier
as an easy ready reference. The values for diamond contributes to the diamagnetic behavior of nanotubes,
and the basal plane of graphite represent the atomic which is similar to that of graphite when the magnetic
contributions, and the c-axis of graphite and the sus- length is smaller than the tube diameter. The low-field
ceptibilities of nanotubes are dominated by free car- diamagnetism contains more information about the
rier contributions. specific band structure of the tubes.

5. CONCLUSIONS Acknowledgements-The authors gratefully acknowledge
much help from M.S. Dresselhaus and G. Dresselhaus in the
The purpose of this work is to review experimen- preparation of this article.
tal data on the electronic properties of carbon nano-
tubes. Although most of the theoretical work has been
focused on single-walled individual tubes, performing REFERENCES
transport and other measurements on such entities is
1. S. Iijima, Nature (London) 354, 56 (1991).
extremely difficult and remains unachieved. Combined 2. S. Iijima, Mater. Sci. Eng. B19, 172 (1993).
STM and STS measurements access single tubes within 3. S. Iijima, T. Ichihashi, and Y. Ando, Nature (London)
bundles containing a few a tubes. They provide exper- 356, 776 (1992).
imental evidence that graphite nanotubes behave as 4. T. W. Ebbesen and P. M. Ajayan, Nature (London) 358,
nanowires, with a density of states and an energy gap 220 (1992).
dependence on inverse diameter as predicted. Studies 5. T. W. Ebbesen, H. Hiura, J. Fujita, Y. Ochiai, S. Mat-
sui, and K. Tanigaki, Chem. Phys. Lett. 209, 83 (1993).
in ultra-high vacuum are needed to provide more quan- 6. J. C. Charlier and J. P. Michenaud, Phys. Rev. Lett. 70,
titative data on the dependence of the gap on diameter. 1858 (1993). J. C. Charlier, Carbon Nunotubes and Ful-
No electrical resistance measurements are currently lerenes. PhD thesis, Catholic University of Louvain, May
1994.
available on a well-characterized single nanotube. 7. C. T. White, D. H. Roberston, and J. W. Mintmire,
However, electrical resistivity measurements performed Phys. Rev. B 47, 5485 (1993).
at low temperature on a large nanotube bundle were 8. R. Saito, G. Dresselhaus, and M. S. Dresselhaus, J.
interpreted in terms of a 2D WL. On the other hand, Appl. Phys. 73, 494 (1993). M. S. Dresselhaus, G. Dres-
MR data obtained for a single microbundle were con- selhaus, and R. Saito, Solid State Commun. 84, 201
(1992).
sistent with the formation of Landau levels using the 9. R. Saito, M. Fujita, G. Dresselhaus, and M. S. Dressel-
haus, In Electrical, Optical and Magnetic Properties of
Organic Solid State Materials, MRS Symposia Proceed-
ings, Boston (Edited by L. Y. Chiang, A. E Garito, and
D. J. Sandman), vol. 247, page 333. Materials Research
Society Press, Pittsburgh, PA (1992).
10. 2. Zhang and C. M. Lieber, Appl. Phys. Lett. 62,2792
(1993).
11. C. H. Olk and J. P. Heremans, J. Mater. Res. 9, 259
(1994).
12. N. Venkateswaran, K. Sattler, U. Muller, B. Kaiser, 6.
J Raina, and J. Xhie, J. Vac. Sci. Technol. B9, 1052 (1991).
M. Jobin, R. Emch, F. Zenhausern, S. Steinemann, and
P. Descouts, J. Vac. Sci. Technol. B9, 1263 (1991). 2.
Zhang, C. M. Lieber, D. S. Ginley, R. J. Baughman, and
B. Morosin, J. Vac. Sci. Technol. B9, 1009 (1991). H.
4- - Enomoto, H. Ozaki, M. Suzuki, T. Pujii, and M.
I Grappite, H in-plane Yamaguchi, J. Vac. Sci. Technol. B9, 1022 (1991).
7)- 0-0 -0-
k*+++ 13. M. S. Dresselhaus, R. A. Jishi, G. Dresselhaus, and Ri-
Diamond’ - ichiro Saito, Fullerenes (1994). St. Petersburg, Russia
Fullerene workshop, October 1993.
I **,,, , 14. R. Heyd, A. Charlier, J. F. Marechi, E. McRae, and
<-C60
I I I
10 100 1000 0. V. Zharikov, Solid State Commun. 89, 989 (1994).
Temperature (K) 15. R. Seshardi, H. N. Aiyer, A. Govindaraj, and C. N.
Rao, Solid State Commun. 91, 195 (1994).
Fig. 10. Temperature dependence of the magnetic suscepti- 16. S. N. Song, X. K. Wang, R. P. H. Chang, and J. B. Ket-
bility of various carbon-based materials. The data on HOPG terson, Phys. Rev. Lett. 12, 697 (1994).
(H//c) are taken at 200 Oe. The data reported for nanotubes, 17. K. Noto and T. Tsuzuku, Jpn. J. Appl. Phys. 14, 46
graphite (H in-plane), and diamond, were taken at 4 kOe, (1975).
those on diamond at 8 kOe. The ordinate axis is negative (af- 18. L. Stockman, G. Neuttiens, C. Van Haesendonck, and
ter Heremans et ai. [26]). Y. Bruynseraede, Appl. phys. Lett. 62, 2935 (1993).