Navy Scientists Discover New Approach to Use Carbon Nanotubes in Electronics and Bio-Chemical Sensors

4/15/2003 - 27-03r
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Scientists are studying carbon nanotubes because of the promise they hold for a range of applications in electronics and sensors. The single-wall carbon nanotubes possess unique structural, mechanical and electrical properties that contribute to their usefulness. However, in the past scientists have faced two major problems that prevent the fabrication and use of carbon nanotubes for commercial applications. Now scientists working in the Institute for Nanoscience at the Naval Research Laboratory, have found an alternative approach that circumvents the potential problems in using carbons nanotubes for commercial applications.

One of the problems scientists faced in the past has been the lack of position and orientation control. The other problem has been the lack of control of the precise atomic structure of the carbon nanotubes that results in a wide variety of electronic properties ranging from semiconducting to metallic behavior. Dr. Eric Snow and a team of researchers from NRL's Electronics Science and Technology Division have found that these problems can be avoided by using random networks of single-wall carbon nanotubes. The networks are chemically and mechanically robust and can be patterned into electronic devices using conventional photolithographic techniques. When devices are fabricated using the random networks, Dr. Snow explains, the problems of position and structural control are circumvented because the device properties are determined by the averaged properties of the individual carbon nanotubes. At the right density the network behaves like a semiconducting thin film that maintains the functionality and sensitivity found in individual semiconducting carbon nanotubes.

The NRL scientists have developed electronic devices and chemical and biological sensors that use random networks of carbon nanotubes as the active electronic material. These networks have exhibited a value of mobility that is an order of magnitude larger than the mobility found in commercial thin-film transistors. In addition, Dr. Snow explains, the carbon nanotube networks can be deposited or grown onto a wide range of noncrystalline substrates. "The ability to deposit electronically active materials onto arbitrary substrates opens new possibilities for electronic applications. For example, carbon nanotubes network electronics on plastic substrates would offer the potential of lighter, less breakable, and higher performance flat panel displays. In addition, these networks are flexible and can conform to arbitrary geometries," Dr. Snow said.

In addition to the electronic applications, carbon nanotubes have also demonstrated potential for sensor applications by serving as a sensitive electronic transducer of chemical or biological recognition events. In these situations, the NRL researchers determined that sensors fabricated using networks of carbon nanotubes can detect sub-part-per-billion levels of a simulant for chemical nerve agents. For biosensing, the researchers are exploring the operation of sensors in an aqueous saline solution. They have used this approach to electronically detect the adsorption of a protein from solution onto a carbon nanotube network.

Since the useful properties of the carbon nanotubes devices can be achieved without the precision assembly that was required in the past, then the NRL scientists are hopeful that the random carbon nanotube networks may be a viable material for commercial thin-film transistor and sensor applications in the future.

In addition to Dr. Snow, the other researchers on the team are Drs. James Novak, Paul Campbell, and Doe Park, from NRL's Electronics Science and Technology Division and Dr. Eric Houser from the Materials Science and Technology Division. A paper on this research was published in the March 31, 2003 issue of Applied Physics Letters. This research is funded by the Office of Naval Research.

Optical micrograph of a C nanotube device. The inset is an atomic force microscope image of the nanotube network that makes up the conducting region. The individual nanotubes average 1.5 nm in diameter and 2 mm in length.

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