42 Micro- and Nanomanufacturing
assembled monolayers. The process is likely to be developed into a
nanomanufacturing process with the addition of many contacting
probes containing reservoirs of colloidal fluids. One of the major
uses of this technique is the deposition and positioning of carbon
nanotubes and other structures of carbon in order to produce elec-
tronic components and other functional and structural products made
from the new forms of carbon.
Nanofabrication Using Carbon Nanomaterials
A carbon nanotube is based on a two-dimensional graphene
sheet. With reference to Fig. 1.47, (a) the chiral vector is defined on
the hexagonal lattice as Ch = wal + ma2, where al and a2 are unit
vectors, and n and m are integers. The chiral angle, q, is measured
relative to the direction defined by al. This diagram has been con-
structed for (n, m) = (4, 2), and the unit cell of this nanotube is
bounded by OAB'B. To form the nanotube, imagine that this cell is
rolled up so that O meets A and B meets B', and the two ends are
capped with half of a fullerene molecule. Different types of carbon
nanotubes have different values ofn and m.
With reference Fig. 1.47, (b) zigzag nanotubes correspond to (n,
0) or
{0,
m) and have a chiral angle of 0°, armchair nanotubes have
{n,
n) and a chiral angle of
30°,
while chiral nanotubes have general
{n,
m) values and a chiral angle of between 0° and 30°. According
the theory, nanotubes can either be metallic (green circles) or semi-
conducting (blue circles). Simple construction of a one-dimensional
carbon nanotube is shown in Fig. 1.48.
Carbon nanotubes can be manufactured by arc discharge, laser
ablation, and chemical vapor deposition methods in the form of mul-
tiwall carbon nanotubes (MWCNT), or single-wall carbon nanotubes
(SWCNT). Figure 1.49 shows the structure of a multi-wall carbon
nanotube. The properties of such CNT's are shown in Tables 1.1
and 1.2.