Chemical Sensors from Carbon Nanotubes

There exists a clear need in the Department of Defense for small, sensitive, and rapid response sensors of dangerous chemicals and explosives. To address this need, we are developing devices based on random networks of single-walled carbon nanotubes SWNTs. The carbon nanotube, a carbon phase that can be described as a hollow tube one nanometer in diameter, one atom thick, and several microns long, is very nearly an ideal material for sensor applications it is highly nonreactive while at the same time all of the electronically active area is at the surface. We have found that SWNT network-based transducers rapidly and reversibly respond to a wide spectrum of dilute chemical vapors. We are working with colleagues in the Materials Science and Technology Division to improve the specificity of the devices and to turn this novel transducer design into a fieldable and useful sensor technology. Carbon nanotubes were initially discovered about a dozen years ago. Demonstration of sensitivity of single nanotube conductance to ambient species was only six years ago. However, such single nanotube devices are difficult and expensive to fabricate. A key innovation of our laboratory is the use of networks of randomly grown nanotubes as the active sensor material. Such SWNT network sensors can be fabricated with high yield by using conventional microfabrication technology. Additionally, the use of SWNT networks dramatically reduces the level of 1f noise, a critical factor for sensor applications, but an intrinsic feature of nanoscale electronic materials.