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Terahertz detector holds imaging promise

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Researchers at Sandia National Laboratories, along with collaborators from Rice University and the Tokyo Institute of Technology, are developing new terahertz detectors based on carbon nanotubes that could lead to significant improvements in medical imaging, airport passenger screening, food inspection and other applications.

Researchers at Sandia National Laboratories, Rice University and the Tokyo Institute of Technology developed a terahertz detector using several nanoscopic-sized tubes, creating a macroscopic thin film that contains a mix of metallic and semiconducting carbon nanotubes.

Researchers at Sandia National Laboratories, Rice University and the Tokyo Institute of Technology developed a terahertz detector using several nano-scopic-sized tubes, creating a macroscopic thin film that contains a mix of metallic and semiconducting carbon nanotubes.  (Courtesy of Sandia Labs)

Researchers at Sandia National Laboratories, Rice University and the Tokyo Institute of Technology developed a terahertz detector using several nano-scopic-sized tubes, creating a macroscopic thin film that contains a mix of metallic and semiconducting carbon nanotubes. (Courtesy of Sandia Labs)

A paper in Nano Letters journal, “Carbon Nanotube Terahertz Detector,” debuted in the May 29 edition of the publication’s “Just Accepted Manuscripts” section. The paper describes a technique that uses carbon nanotubes to detect light in the terahertz frequency range without cooling.

Historically, the terahertz frequency range – which falls between the more conventional ranges used for electronics on one end and optics on another – has presented great promise along with vexing challenges for researchers, said Sandia’s François Léonard, one of the authors.

“The photonic energy in the terahertz range is much smaller than for visible light, and we simply don’t have a lot of materials to absorb that light efficiently and convert it into an electronic signal,” said Léonard. “So we need to look for other approaches.”

Researchers need to solve this technical problem to take advantage of the many beneficial applications for terahertz radiation, said co-author Junichiro Kono of Rice University. Terahertz waves, for example, can easily penetrate fabric and other materials and could provide less-intrusive ways for security screenings of people and cargo. Terahertz imaging could also be used in food inspection without adversely impacting food quality.

Perhaps the most exciting application offered by terahertz technology, said Kono, is as a potential replacement for magnetic resonance imaging (MRI) technology in screening for cancer and other diseases.

“The potential improvements in size, ease, cost and mobility of a terahertz-based detector are phenomenal,” he said. “With this technology, you could conceivably design a hand-held terahertz detection camera that images tumors in real time, with pinpoint accuracy. And it could be done without the intimidating nature of MRI technology.”

Sandia, its collaborators and Léonard, in particular, have been studying carbon nanotubes and related nanomaterials for years. In 2008, Léonard authored “The Physics of Carbon Nanotube Devices,” which looks at the experimental and theoretical aspects of carbon nanotube devices.

Carbon nanotubes are long, thin cylinders composed entirely of carbon atoms. While their diameters are in the 1- to 10-nanometer range, they can be up to several centimeters long. The carbon-carbon bond is very strong, so it resists any kind of deformation.

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