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ideal structural member for designing nanostructural instruments. It has reported
that nanotubes could become as familiar as silicon in this century and the full
development of the nanotubes would be around 2010. In order to familiarize the
uses and applications of the nanotubes and their related products, an understand-
ing of the structure, characterization and properties of the nanotubes is essential.
The nanotubes possess conducting properties ranging from metallic to moderate
band gap semiconductor. In general, the nanotubes could be specified in terms of
the tube diameter (d) and the chiral angle (θ). The chiral vector (Ch) is defined as
a line connected from two crystallo graphically equivalent sites on a two-dimen-
sional graphene structure. The chiral vector can be defined in terms of the lattice
translation indices (n, m) and the basic vectors a
1
and a
2
of the hexagonal lattice
(a layer of grapheme sheet). The chiral angle (θ) is measured as an angle between
the chiral vector Ch with respect to the zigzag direction (n, 0), where θ = 0°and the
unit vectors of a
1
and a
2
. The armchair nanotube is defined as the θ = 30° and the
translation indices is (n, n). All other types of nanotubes could be identified as a
pair of indices (n, m) where n ≠ m. The electronic conductivity is highly sensitive
to a slight change of these parameters, which cause a changing of materials be-
tween metallic and semiconductor statues. Recently, it has been reported that the
scanning tunneling microscopy (STM) and spectroscopy could be used to observe
the electronic properties and atomic arrangement of SWNTs [55-57].
1.1.5.2.1
MULTI AND SINGLE WALL NANOTUBES
Multi-walled carbon nanotubes were first reported by Iijima in 1991 in carbon
made by an arc-discharge method4. About two years later, he made the observa-
tion of single-walled nanotubes (SWNTs). A SWNT is a graphene sheet rolled
over into a cylinder with typical diameter of the order of 1.4 nm
Similar to that of a C
60
Bucky ball, a MWNT consists of concentric cylinders
with an interlayer spacing of 3.4Å and a diameter typically of the order of 10-20
nm. The lengths of the two types of tubes can be up tohundreds of microns or
even centimeters. A SWNT is a molecular scale wire that has two key structural
parameters. By folding a graphene sheet into a cylinder so that the beginning and
end of a (m, n) lattice vector in the graphene plane join together, one obtains an
(m, n) nanotube. The (m, n) indices determine the diameter of the nanotube, and
also the so-called chirality [55].
1.1.5.3 SYNTHESIS METHODS OF CNT
1.1.5.3.1
SYNTHESIS OF CNT
The MWNT were first discovered in the soot of the arc-discharge method by
Iijima. This method had been used long before in the production of carbon fi-
bers and fullerenes. It took two more years for Iijima and Ichihashito synthesize
SWNT by use of metal catalysts in the arc-discharge method in 1993.Significant
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