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Most
single-walled nanotubes
(SWNT) have a diameter of close to 1 nanometer,
with a tube length that can be many thousands of times longer. The structure
of a SWNT can be conceptualized by wrapping a one-atom-thick
layer of graphite
called graphene
into a seamless cylinder. The way the graphene
sheet is wrapped is represented by a pair of indices (n,m) called the chiral
vector. The integers n and m denote the number of unit vectors along two
directions in the honeycomb crystal
lattice
of graphene.
If m=0, the nanotubes
are called "zigzag". If n=m, the nanotubes
are called "armchair".
Otherwise, they are called "chiral".Single-walled nanotubes are a very important variety of carbon nanotube
because they exhibit important electric properties that are not shared by the
multi-walled carbon
nanotube
(MWNT) variants. Single-walled nanotubes
are the most likely candidate for miniaturizing electronics
beyond the micro electromechanical scale that is currently the basis of
modern electronics.
The most basic building block of these systems
is the electric wire, and swnts can be excellent conductors.[18]
One useful application
of swnts is in the development of the first intramolecular field effect transistors
(fets). The production of the first intramolecular logic gate using SWNT fets has recently become possible as
well.[19] To create a logic gate
you must have both a p-FET and an n-FET. Because swnts are p-fets when
exposed to oxygen and n-fets when unexposed to oxygen, it is possible to
protect half of a SWNT from oxygen exposure, while exposing the other half to
oxygen. This results in a single SWNT that acts as a NOT logic gate with both p and n-type fets within the same molecule.
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