BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 11

have shown extremely high modulus, greater than 1 TPa (the elastic modulus of
diamond is 1.2 TPa) and reported strengths 10-100 times higher than the stron-
gest steel at a fraction of the weight. Indeed, if the reported mechanical properties
are accurate, carbon nanotubes may result in an entire new class of advanced
materials [58, 62].
In addition to the exceptional mechanical properties associated with carbon
nanotubes, they also possess superior thermal and electric properties such as
thermally stableup to 2800°C in vacuum, thermal conductivity about twice as
high as diamond, electric current carrying capacity 1000 times higher than copper
wires. These exceptional properties of carbon nanotubes have been investigated
for devices such as field emission displays, scanning probe microscopy tips and
microelectronic devices. Carbon nanotubes present significant opportunities to
basic science and nanotechnology, and pose significant challenge for future work
in this field. The approach of direct growth of nanowires into ordered structures
on surfaces is a promising route to approach nanoscale problem and create novel
molecular scale devices with advanced electrical, electromechanical and chemical
functions [54].

1.1.5.1 STRUCTURE AND PROPERTIES

1.1.5.1.1 ELECTRICAL PROPERTIES

The Unique Electrical Properties of carbon nanotubes are to a large extent derived
from their 1-D character and the peculiar electronic structure of graphite. They
have extremely low electrical resistance. Resistance occurs when an electron col-
lides with some defect in the crystal structure of the material through which it is
passing. The defect could be an impurity atom, a defect in the crystal structure,
or an atom vibrating. Such collisions deflect the electron from its path, but the
electrons inside a carbon nanotube are not so easily scattered. Because of their
very small diameter and huge ratio of length to diameter a ratio that can be up
in the millions or even higher. In a 3-D conductor, electrons have plenty of op-
portunity to scatter, since they can do so at any angle. Any scattering gives rise to
electrical resistance. In a 1-D conductor, however, electrons can travel only for-
ward or backward. Under these circumstances, only backscattering (the change in
electron motion from forward to backward) can lead to electrical resistance. But
backscattering requires very strong collisions and is thus less likely to happen.
So the electrons have fewer possibilities to scatter. This reduced scattering gives
carbon nanotubes their very low resistance. In addition, they can carry the highest
30 current density of any known material, measured as high as 109 A/cm 2 . One
use for nanotubes that has already been developed is as extremely fine electron
guns, which could be used as miniature cathode ray tubes (CRTs) in thin high-
brightness low-energy low-weight displays. This type of display would consist
of a group of many tiny CRTs, each providing the electrons to hit the phosphor