New Gas Sensors Patterned with Conducting Polymer

April 12, 2005
These colorized scanning electron micrographs show a portion of the NIST microheater device before (left) and after (right) appl

A n improved method for depositing nanoporous, conducting polymer films on miniaturized device features has been demonstrated by researchers at the National Institute of Standards and Technology (NIST).
Described in the April 6 issue of the Journal of the American Chemical Society,* the method may be useful as a general technique for reproducibly fabricating microdevices such as sensors for detecting toxic chemicals.

These colorized scanning electron micrographs show a portion of the NIST microheater device before (left) and after (right) application of the sponge-like polyaniline coating.

Unlike most polymers, conducting polymers have the electrical and optical properties of metals or semiconductors. These materials are of increasing interest in microelectronics because they are inexpensive, flexible and easy to synthesize.

Polyaniline is a particularly promising conducting polymer for microelectronics applications, but it is difficult to process because it doesn't dissolve in most solvents. NIST researchers have circumvented this problem by dispersing nanoscale particles of polyaniline into a mild solvent.

Two NIST microheater devices
Two NIST microheater devices, each about 100 micrometers wide. On the left is a microheater coated with a conducting polymer, polyaniline, which is naturally green in color. On the right is an identical microheater with no coating.

"The beauty of the method,” says NIST guest researcher Guofeng Li, “is that the polyaniline chain carries a natural positive charge.” Once the particles are formed, electrostatic repulsion prevents them from clumping together. Moreover, the positively charged particles then can be manipulated and patterned on complex device structures by applying an electrical field.

The process produces a sponge-like coating that efficiently captures gaseous molecules. So far NIST researchers have demonstrated that such coatings can detect the difference between methanol and water vapor. Additional tests will be needed before the polymer devices could be used for detecting toxic gases.

NIST holds patents for previous work using microheaters coated with nanostructured tin oxide films. As the microheaters cycle through a series of temperatures, changes in electrical resistance are used to detect toxic gases at part per billion levels. Ultimately, NIST researchers hope to develop inexpensive arrays of microheater sensors coated with both polymer and inorganic oxide films optimized to identify the components of gas mixtures.

*G. Li, C. Martinez, S. Semancik. Controlled electrophorectic patterning of polyaniline from a colloidal suspension. Journal of the American Chemical Society, April 6, 2005.

Source: NIST

Related Stories

Recommended for you

Metacognition training boosts gen chem exam scores

October 20, 2017

It's a lesson in scholastic humility: You waltz into an exam, confident that you've got a good enough grip on the class material to swing an 80 percent or so, maybe a 90 if some of the questions go your way.

Two teams independently test Tomonaga–Luttinger theory

October 20, 2017

(Phys.org)—Two teams of researchers working independently of one another have found ways to test aspects of the Tomonaga–Luttinger theory that describes interacting quantum particles in 1-D ensembles in a Tomonaga–Luttinger ...

Dawn mission extended at Ceres

October 20, 2017

NASA has authorized a second extension of the Dawn mission at Ceres, the largest object in the asteroid belt between Mars and Jupiter. During this extension, the spacecraft will descend to lower altitudes than ever before ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.