Electrical properties of nanotubes
The electrical properties of carbon nanotubes depend on how the
hexagons are orientated along the axis of the tube. The following figure
shows the three orientations that are possible: armchair, zigzag, and
Electrical properties depend on the orientation of the hexagons.
Carbon nanotubes with the hexagons orientated in the configuration
labeled armchair (hexagons are lined up parallel to the axis of the
nanotube) have electrical properties similar to metals. When you apply a
voltage between two ends of an armchair nanotube, a current will flow.
An armchair carbon nanotube is, in fact, a better conductor than the
copper normally used in electrical wire, or any other metal.
Researchers are developing methods to spin carbon nanotubes together
to make low-resistance electrical wires that could transform the
electrical power grid, as we discuss in Chapter 5, as well as reduce the
power consumed and weight of wiring in such power- and weight-sensitive
uses as spacecraft and airplanes. Another use that these armchair carbon
nanotubes are being considered for is to connect devices in integrated
circuits. As devices in integrated circuits become smaller, it may not
be possible to pattern narrow enough metal lines, so researchers are
considering using armchair carbon nanotubes to replace the metal lines.
The next two possible orientations of hexagons in carbon nanotubes
share electrical properties similar to semiconductors. Those with the
hexagons oriented in a circle around the nanotube have a configurations
labeled zigzag. Those with a twist to the nanotube so the hexagons do
not form any line are called chiral. These two configurations of
nanotubes will only conduct an electric current when extra energy in the
form of light or an electric field is applied to free electrons from the
carbon atoms. Semiconducting nanotubes could be useful in building the
ever smaller transistors used by the hundreds of millions in integrated
circuits for all kinds of electronic devices.
Another interesting property of carbon nanotubes is that their
electrical resistance changes significantly when other molecules attach
themselves to their carbon atoms. Companies are using this property to
develop sensors that can detect chemical vapors such as carbon monoxide
or biological molecules.
Excerpted from Nanotechnology For Dummies (2nd edition), from Wiley Publishing