Page 257 - Adsorbents fundamentals and applications

242 CARBON NANOTUBES, PILLARED CLAYS, AND POLYMERIC RESINS

Table 9.2. Formation of carbon nanotubes and fullerenes by graphite vaporization/con-
densation
Technique Conditions/Observation Reference

Arc discharge Graphite electrodes at near Bacon (1960)
triple point (in 92 atm Ar)
Multiwall, cylindrical,
graphitic whiskers formed on
cathode, “scroll” structure
was (mis)-identified by TEM
Laser vaporization 1 atm He over graphite C 60 Kroto et al. (1985)
(major) and C 70 fullerenes
formed
Ohmic Graphite rod resistively heated Kratschmer et al. (1990)
vaporization in glass bell jar with He at
>100 torr C 60 fullerene
formed
Arc discharge Graphite electrodes in contact, Haufler et al. (1990).
100 torr He C 60 fullerene
formed
Arc discharge Similar to Bacon’s, Ar at Iijima (1991)
100 torr was used. Multiwall
nanotubes correctly
identified
Arc discharge with (a) Fe placed on cathode to be (a) Iijima and Ichihashi
catalyst co-vaporized, in 10 torr (1993); (b) Bethune
CH 4 + 40 torr Ar. (b) Co et al. (1993)
added to anode, in
100–500 torr He.
Single-wall nanotubes
(∼1 nm) formed on cathode
in both cases.
Laser vaporization MixedCo(1at%)orNi (0.6 Guo et al. (1995)
with catalyst at %) in graphite as target, in
500 torr Ar. Single-wall
nanotubes

The role of the catalyst and the mechanism for the formation of SWNTs
during condensation of carbon vapor are not known. It is possible that the epi-
taxial matching of graphite lattice or rings on the faces of the transition metal
plays a role, as illustrated in Figures 4–6. A rationalization for the growth pro-
cess has also been given by Thess et al. (1996). In their rationalization, metal
atom(s) is attached to the carbon atoms on the open end of the tube where growth
occurs. These metal atoms prevent five-member rings from forming and keep the
end open. The tube diameter is determined by competition between the strain