Callister - An introduction - 8th edition

Another molecular form of carbon has recently
been discovered that has some unique and
technologically promising properties. Its structure
consists of a single sheet of graphite, rolled into a
tube, both ends of which are capped with C 60
fullerene hemispheres. This carbon nanotube is
represented schematically in Figure 12.19. The
nano prefix denotes that tube diameters are on the
order of a nanometer (i.e., 100 nm or less). Each
nanotube is a single molecule composed of millions
of atoms; the length of this molecule is much
greater (on the order of thousands of times
greater) than its diameter. Multiple-walled carbon
nanotubes consisting of concentric cylinders have
also been found to exist.
These nanotubes are extremely strong and
stiff and relatively ductile. For single-walled nanotubes,
tensile strengths range between 50 and
200 GPa (approximately an order of magnitude
greater than for carbon fibers); this is the strongest
known material. Elastic modulus values are on the
order of one tetrapascal [TPa (1 TPa 10 3 GPa)],
with fracture strains between about 5% and 20%.
Furthermore, nanotubes have relatively low densities.
On the basis of these properties, the carbon
nanotube has been termed the “ultimate fiber”
and is extremely promising as a reinforcement in
composite materials.
Carbon nanotubes also have unique and
structure-sensitive electrical characteristics. Depending
on the orientation of the hexagonal units
in the graphene plane (i.e., tube wall) with the tube
axis, the nanotube may behave electrically as
MATERIALS OF IMPORTANCE
Carbon Nanotubes
12.4 Carbon • 471
either a metal or a semiconductor. It has been
reported that flat-panel and full-color displays (i.e.,
TV and computer monitors) have been fabricated
using carbon nanotubes as field emitters; these
displays should be cheaper to produce and will
have lower power requirements than CRT and
liquid crystal displays. Furthermore, it is anticipated
that future electronic applications of carbon
nanotubes will include diodes and transistors.
An atomically resolved image of a carbon nanotube
that was generated using a scanning tunneling
microscope (a type of scanning probe microscope,
Section 4.10). Note the dimensional scales (in the
nanometer range) along the sides of the micrograph.
(Micrograph courtesy of Vladimir K. Nevolin,
Moscow Institute of Electronic Engineering.)
Figure 12.19 The structure of a carbon nanotube. (Reprinted by permission from American
Scientist, magazine of Sigma Xi, The Scientific Research Society. Illustration by Aaron
Cox/American Scientist.)