Sapphires could become a nanotech engineer's
Carbon nanotubes -- rolled-up sheets of carbon atoms that can
be narrower than a single nanometer -- have the potential to be ready-made
electrical components at the molecular scale. A nanometer is one millionth
of a millimeter, or the span of 10 hydrogen atoms.
One key to enabling this potential is finding ways to place nanotubes
where they are needed.
Researchers from the Weizmann Institute of Science in Israel have
found that it is possible to grow carbon nanotubes along atom-size steps
on a sapphire surface.
These arrays of carbon nanotubes could eventually be used as electronic
circuits, according to the researchers. The combination of aligned nanotubes
on a sapphire base could also find use as a transparent conducting material.
Sapphire is transparent and resists high temperatures.
Growing the arrays is only the first step in eventually using
them as electronic circuits. The researchers must also devise ways of
producing the junctions required for the nanotubes to act as transistors,
and wiring the nanotubes to electrodes.
Key to the method is the structure of a crystal like sapphire.
When the crystal is cut in a plane that is slightly tilted from one of
its main faces, the surface contains parallel steps of one-atom height.
The researchers were able to grow one-nanometer-wide carbon nanotubes
along these steps to produce dense arrays of parallel, separated tubes.
The direction and shape of the atomic steps can be controlled
by the crystal cut, according to the researchers. Deliberately introduced
defects in the crystal could be used to produce kinks and other useful
shapes in the nanotubes, which could lead to nanotube architectures constructed
from the bottom up.
The work appeared in the November 15, 2004 issue of Angewandte
Chemie International Edition.
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