Chemistry Reference
In-Depth Information
Fig. 1 Transmission electron
micrographs of MWCNTs
reported by Iijima in 1991.
Reprinted with permission
from [
3
]
Fig. 2 The way the graphene
sheet is rolled up results in
tubes with different
morphologies and electronic
behaviors. (a) Metallic
“armchair” tube.
(b) Semiconducting “chiral”
tube. (c) Conducting “zig
zag” tube. Reprinted with
permission from [
14
]
types of tubes with very different properties. For instance, depending on the
wrapping angle of the two-dimensional sheet, three types of SWCNTs can be
defined: armchair, zigzag, and chiral (Fig.
2
). The electronic behavior of the tubes
is determined by their exact structure; thus the zigzag and chiral nanotubes can be
either metallic or semiconducting while armchair nanotubes are always metallic [
9
].
In general, the available synthetic methods produce SWCNTs as a mixture of
metallic and semiconducting material while MWCNTs are regarded as metallic.
This is important, as semiconducting SWCNTs could be useful in applications that
involve charge transfer processes, including sensors and photovoltaic devices, while
metallic CNTs are preferred in electronic tools or as conductive filler in CNT-
composites [
10
,
11
].
Furthermore, nanotubes present intrinsic advantages, including high mechanical
strength, structural flexibility, and high surface area, which make them potential
