5.4. CARBON NANOTUBES
115
(c)
Figure 5.11. Illustration of some possible structures of carbon nanotubes, depending on how
graphite sheets are rolled: (a) armchair structure; (b) zigzag structure; (c) chiral structure.
target are heated to 1200°C. Contained in the tube, but somewhat outside the
furnace, is a water-cooled copper collector. The graphite target contains small
amounts of cobalt and nickel that act as catalytic nucleation sites for the formation
of the tubes. An intense pulsed laser beam is incident on the target, evaporating
carbon from the graphite. The argon then sweeps the carbon atoms from the hightemperature zone to the colder copper collector on which they condense into
nanotubes. Tubes 10-20 nm in diameter and 100 pm long can be made by this
method.
Nanotubes can also be synthesized using a carbon arc. A potential of 20-25 V is
applied across carbon electrodes of 5-20 pm diameter and separated by 1 nun at
500 torr pressure of flowing helium. Carbon atoms are ejected from the positive
electrode and form nanotubes on the negative electrode. As the tubes form, the length
of the positive electrode decreases, and a carbon deposit forms on the negative
electrode. To produce single-walled nanotubes, a small amount of cobalt, nickel, or
iron is incorporated as a catalyst in the central region of the positive electrode. If no
catalysts are used, the tubes are nested or multiwalled types (MWNT), which are
nanotubes within nanotubes, as illustrated in Fig. 5.13. The carbon arc method can
produce single-walled nanotubes of diameters 1-5 nm with a length of 1 pm.
115
(c)
Figure 5.11. Illustration of some possible structures of carbon nanotubes, depending on how
graphite sheets are rolled: (a) armchair structure; (b) zigzag structure; (c) chiral structure.
target are heated to 1200°C. Contained in the tube, but somewhat outside the
furnace, is a water-cooled copper collector. The graphite target contains small
amounts of cobalt and nickel that act as catalytic nucleation sites for the formation
of the tubes. An intense pulsed laser beam is incident on the target, evaporating
carbon from the graphite. The argon then sweeps the carbon atoms from the hightemperature zone to the colder copper collector on which they condense into
nanotubes. Tubes 10-20 nm in diameter and 100 pm long can be made by this
method.
Nanotubes can also be synthesized using a carbon arc. A potential of 20-25 V is
applied across carbon electrodes of 5-20 pm diameter and separated by 1 nun at
500 torr pressure of flowing helium. Carbon atoms are ejected from the positive
electrode and form nanotubes on the negative electrode. As the tubes form, the length
of the positive electrode decreases, and a carbon deposit forms on the negative
electrode. To produce single-walled nanotubes, a small amount of cobalt, nickel, or
iron is incorporated as a catalyst in the central region of the positive electrode. If no
catalysts are used, the tubes are nested or multiwalled types (MWNT), which are
nanotubes within nanotubes, as illustrated in Fig. 5.13. The carbon arc method can
produce single-walled nanotubes of diameters 1-5 nm with a length of 1 pm.