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d
n
3
r
4
n
g
|
6
Figure 3.1
Structure and morphology of carbon nanotubes. (A) Schematic represen-
tation of a graphene sheet and a carbon nanotube roll-up vector. The
roll-up vector is perpendicular to the axis of carbon nanotube. (B) A 3D
model of a single-wall carbon nanotube. (C) A SEM image of a vertically-
aligned array of multi-wall carbon nanotubes grown on a silicon sub-
strate. (D, E) TEM images of single-wall (E) and multi-wall (D) carbon
nanotubes.
.
(SEM and TEM images: Lawrence Livermore National
Laboratory).
diameter, and most importantly, its electronic properties. For example, an
(n,m) carbon nanotube has an inner diameter, d
in
, of:
2
d
in
¼
a
p
n
2
þ
m
2
þ
nm
2r
c
(3
:
1)
p
where a is the lattice parameter of graphene (2.5 Å) and r
c
is the van der
Waals radius of the carbon atom (1.7 Å).
A carbon nanotube can have one (as in the case of a single-walled carbon
nanotube, Figure 3.1E), or several concentric graphitic shells (as in the case
of multi-walled nanotubes, Figure 3.1D). Remarkably, despite its nanometre
diameter, the length of a single nanotube can reach or exceed a centimetre,
giving it an aspect ratio of greater than 10
7
. Typically, nanotubes have
lengths in the range of several microns, which still represents an aspect ratio
of 10
3
or greater. Typically, carbon nanotubes are synthesized in three forms:
loose powders, densely-packed vertical ''forest'' arrays (Figure 3.1C), or
individual nanotubes grown on prepatterned surfaces.
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