Cornell University researchers have devised
a simple way to position conducting polymer nanowires on an electrode,
and have made a prototype high-speed chemical detector that is capable
of sensing minuscule amounts of ammonia gas.
The researchers are working on other polymer materials that are
able to detect other gasses. The method could ultimately be used to make
a device that has an array of wires sensitive to different chemicals.
Such a device would be able to rapidly detect and analyze the composition
of gasses in the air, according to the researchers.
Key to the method was finding a way to precisely orient individual
nanowires parallel to the electrodes. The researchers' scan-tip electrode
spinning deposition method involves electrostatically moving a droplet
of solution from an arrow-shaped microscopic tip to the surface. The polymer
solution dries in transit to the substrate, producing nanowires oriented
in one direction. The researchers completed the device by positioning
patterned gold electrodes on the substrate perpendicular to the nanowires.
The nanowires had diameters of 100 to 500 nanometers. As the nanowires
absorbed ammonia, their electrical conductance decreased. The response
times of the nanowires corresponded to the differences in diameter and
the resulting diffusion time of ammonia gas into the wires. The researchers'
prototype quickly detected ammonia gas at concentrations as low as 500
parts per billion.
The method makes it easy to integrate nanowires with conventional
electronics, according to the researchers.
Polymer nanowire sensor devices could be practical in three or
four years, according to the researchers. The work appeared in the February
27, 2004 issue of Nano Letters.
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