Biomedical Engineering Reference
In-Depth Information
by Ebbesen and Ayajan [97] who achieved growth and purification of
high quality MWCNTs at the gram level. These synthesized MWCNTs
have lengths on the order of 10
m and diameters in the range of
5-30 nm. The nanotubes are typically bound together by strong van
der Waals interactions and form tight bundles. To achieve single-
walled nanotubes, the electrodes are doped with a small amount of
metallic catalyst particles (Ru, Rh, Pd, Os, Ir, and Pt) [45, 118-120].
The first success in producing substantial amounts of SWCNTs by
arc discharge was achieved by Bethune
µ
. [45] in 1993. They used
a carbon anode containing a small percentage of cobalt catalyst in
the discharge experiment, and found abundant SWCNTs generated
in the soot material.
et al
9.3.2
Laser Ablation
Laser ablation was first used for the initial synthesis of fullerenes.
Over the years, the technique has been improved to allow the
production of SWCNTs [91, 121, 122]. In this technique, a laser is
used to vaporize a graphite target held in a controlled atmosphere
oven at temperatures near 1200°C. To produce single-walled
nanotubes, the graphite target was doped with cobalt (Co) and nickel
(Ni) catalyst [121]. The condensed material is then collected on a
water-cooled holder. This laser ablation technique, and similarly the
arc discharge method, are limited in the volume of sample they can
produce in relation to the size of the carbon source (the anode in
the arc discharge, and the target in the laser ablation). Moreover,
next purification steps are necessary to separate the tubes from
undesirable by-products of fullerenes, graphitic polyhedrons,
enclosed metal particles, amorphous carbon. The growth of high-
quality SWCNTs at the 1-10 g scale was achieved by Smalley and
coworkers [91] using a laser ablation (laser oven) method. This
approach utilized intense laser pulses to ablate a carbon target
containing 0.5 atomic percent of nickel and cobalt. The target was
placed in a tube furnace heated to 1200°C. During laser ablation, a
flow of inert gas was passed through the growth chamber to carry the
grown nanotubes downstream to be collected on a cold finger. The
produced SWCNTs are mostly in the form of the ropes consisting of
tens of individual nanotubes closely packed into hexagonal crystals
via van der Waals interactions.
