In 1991, Sumio Iijima noticed novel structures in the byproduct soot created during fullerene
production by electric arc-discharge.1 Investigation revealed the tubular nature of these
interesting structures, now known as carbon nanotubes, which have likely existed for years,
but remained undiscovered up to this point. A carbon nanotube may be described as a
graphene sheet rolled up to form a tube, with half-fullerene caps, for closed tubes. The caps
are fairly reactive due to curvature strain, and are readily destroyed during processing,
yielding open tubes.2 Nanotubes are formed in a range of diameters and may be singlewalled
or multi-walled, depending on the reaction conditions. The single-walled variety exist
as a bundle made up of strands, like a rope, in which each strand is a single-walled nanotube
(SWNT); each bundle contains typically 10 – 50 strands and is 5 – 20 nm in diameter.3 The
diameter of SWNTs is on the order of a nanometer (~ 1.4 nm), and the intertube spacing
within the bundle has been determined to be ~ 0.3 nm, at closest approach.3 Multi-walled
nanotubes (MWNT) are comprised of several graphene sheets rolled up, resulting in
concentric tubes with successively larger radii. Multi-walled nanotubes also aggregate, due to
significant van der Waals forces. The diameter of MWNTs is typically 10 – 20 nm, and the
interlayer spacing has been determined to be ~ 0.34 nm).3
Carbon nanotubes range in electrical conductivity from metallic conductors to
semiconductors; the electronic properties depend on the diameter and the helicity, or chirality
(degree of twist of the tube), that are determined by the chiral vector, Ch, which connects
crystallographically equivalent sites (see Figure 1)
In 1991, Sumio Iijima noticed novel structures in the byproduct soot created during fullerene
production by electric arc-discharge.1 Investigation revealed the tubular nature of these
interesting structures, now known as carbon nanotubes, which have likely existed for years,
but remained undiscovered up to this point. A carbon nanotube may be described as a
graphene sheet rolled up to form a tube, with half-fullerene caps, for closed tubes. The caps
are fairly reactive due to curvature strain, and are readily destroyed during processing,
yielding open tubes.2 Nanotubes are formed in a range of diameters and may be singlewalled
or multi-walled, depending on the reaction conditions. The single-walled variety exist
as a bundle made up of strands, like a rope, in which each strand is a single-walled nanotube
(SWNT); each bundle contains typically 10 – 50 strands and is 5 – 20 nm in diameter.3 The
diameter of SWNTs is on the order of a nanometer (~ 1.4 nm), and the intertube spacing
within the bundle has been determined to be ~ 0.3 nm, at closest approach.3 Multi-walled
nanotubes (MWNT) are comprised of several graphene sheets rolled up, resulting in
concentric tubes with successively larger radii. Multi-walled nanotubes also aggregate, due to
significant van der Waals forces. The diameter of MWNTs is typically 10 – 20 nm, and the
interlayer spacing has been determined to be ~ 0.34 nm).3
Carbon nanotubes range in electrical conductivity from metallic conductors to
semiconductors; the electronic properties depend on the diameter and the helicity, or chirality
(degree of twist of the tube), that are determined by the chiral vector, Ch, which connects
crystallographically equivalent sites (see Figure 1)
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