Abstract :
What is a CARBON
NANOTUBE?
Carbon
nanotubes are wires of pure carbon with nanometer diameters and lengths of many
microns. A single-walled carbon nanotube (SWNT) may be thought of
as a single atomic layer thick sheet of graphite (called graphene) rolled into
a seamless cylinder. Multi-walled carbon nanotubes (MWNT) consist of
several concentric nanotube shells.
Understanding
the electronic properties of the graphene sheet helps to understand the
electronic properties of carbon nanotubes. Graphene is a zero-gap
semiconductor; for most directions in the graphene sheet, there is a bandgap,
and electrons are not free to flow along those directions unless they are given
extra energy. However, in certain special directions graphene is
metallic, and electrons flow easily along those directions. This property
is not obvious in bulk graphite, since there is always a conducting metallic
path which can connect any two points, and hence graphite conducts
electricity.
However,
when graphene is rolled up to make the nanotube, a special direction is
selected, the direction along the axis of the nanotube. Sometimes this is
a metallic direction, and sometimes it is semiconducting, so some nanotubes are
metals, and others are semiconductors. Since both metals and
semiconductors can be made from the same all-carbon system, nanotubes are ideal
candidates for molecular electronics technologies.
In addition
to their interesting electronic structure, nanotubes have a number of other
useful properties. Nanotubes are incredibly stiff and tough mechanically
- the world's strongest fibers. Nanotubes conduct heat as well as diamond
at room temperature. Nanotubes are very sharp, and thus can be used as
probe tips for scanning-probe microscopes, and field-emission electron sources
for lamps and displays.
Carbon
nanotubes are the next step in miniaturizing electronic circuits, replacing
silicon transistors and diodes, which are fast reaching the theoretical limits
of size and speed of operation. Using CNTs, nanochips can be made with entire
circuits on it. Ideal diodes can be made from CNTs, resulting in highly
efficient electronic circuits. Further, CNTs have a number of other uses other
than in the electronic industry, as seen here.
Download :
Download :