Biomedical Engineering Reference
In-Depth Information
leads to the formation of iron particles that can catalyze the growth
of SWCNTs. With this approach, amorphous carbon generation could
be a problem, as benzene pyrolysis is expected to be significant at
1200°C.
[139] reported the growth of the CNTs by pyrolysis
methods with promising results in the large-scale synthesis.
Endo
et al.
9.4 
Gas Sensors Based on Carbon Nanotubes
Nanotechnology is sometimes used to refer to any process or product
that involves sub-micrometer dimensions, but a more concise
definition is “any fabrication technology in which objects are built
by the specification and placement of individual atoms or molecules
or where at least one dimension is less than 100 nm” (1 nm = 10
−9
m;
100 nm = 0.1
m) [140]. The first unequivocal nanofabrication
experiment that complied with this definition took place in 1990,
with the deposition of individual xenon atoms on a nickel substrate
to spell the logo of the computer company IBM. For future capabilities
provided by nanotechnologies, new high-performance materials
designed and engineered at nanoscale with advanced properties and
novel functionalities are necessary.
One of the most widely studied new nanomaterials is the carbon;
not as we conventionally know it in the form of thin films or bulk
materials but in the form of hexagonal lattices of carbon atoms
arranged in one-dimensional nanotubes. CNTs are effectively rolled
sheets of graphite with a few nanometers in diameter and up to tens
or hundreds of micrometers in length.
The exceptional mix of the physical properties of the CNTs for
instance the large surface area as high up to 1600 m
µ
, the high
chemical reactivity of the caps and walls, the bandgap of semicon-
ducting nanotubes tailored by diameter, the excellent mechanical
strength but ultra-lightweight, the high thermal stability, the high
electron mobility, the rich electronic properties and ballistic trans-
port characteristics, the high aspect ratio ranging from 10 to 1000,
the hollow nanostructure with tube diameter of a few nanometers,
make CNTs an ideal platform for many chemical micro/nanosensor
systems with capability of real applications. These one-dimensional
carbon nanostructures have been applying to explore their potential
in chemical gas sensors [29, 32, 141-153] and biosensors [16, 154-
158] with the different morphological structures and geometries
of ultrathin films consisting of SWCNTs and MWCNTs, networked
2
g
−1
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