Antenna-free THz Detector Uses Nanotube Thin Films

Carbon nanotube-based detectors that reveal light in the terahertz frequency range without cooling could lead to significant improvements in medical imaging, airport screening and food inspection.

A team from Sandia National Labs has begun developing the detectors in collaboration with Rice University and the Tokyo Institute of Technology.

A newly developed carbon nanotube-based terahertz detector shows potential for imaging improvements. Courtesy of Sandia National Labs.

“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 François Léonard, a researcher of nanophotonics and nanoelectronics at Sandia. “We need to look for other approaches.”

In the search for more efficient tactics, researchers industry-wide have long studied THz sensing technology that uses carbon nanotubes, specifically focusing on the use of single or single bundle nanotubes. However, to achieve coupling in a single nanotube, the relatively larger size of THz waves requires an antenna.

Now, the researchers have created a detector invisible to the naked eye that uses carbon-nanotube thin films without the need for an antenna.

“Carbon nanotube thin films are extremely good absorbers of electromagnetic light,” Léonard said, adding that such thin films will soak up incoming radiation in the THz range.

The new technique allows the researchers to combine several nanoscopic tubes to form a macroscopic thin film that contains both metallic and semiconducting carbon nanotubes.

With the new detector, terahertz radiation is captured by a carbon nanotube thin film contacted by two gold electrodes. Courtesy of Rice University.

These nanotubes possess effective terahertz absorption properties.

“Trying to do this with a different kind of material would be nearly impossible, since a semiconductor and a metal couldn’t coexist at the nanoscale at high density,” said Junichiro Kono, a professor of electrical and computer engineering, physics and astronomy, and a co-author of the study. “That’s what we’ve achieved with the carbon nanotubes.”

Development of such terahertz detectors could potentially benefit several applications, such as laser imaging and MRI technology.

“The potential improvements in size, ease, cost and mobility of a terahertz-based detector are phenomenal,” Kono said. “With this technology, you could conceivably design a hand held terahertz detection camera that images tumors in real time, with pinpoint accuracy.”

Development and improvement of the detector and related technology are ongoing.

The research is published in Nano Letters (doi: 10.1021/nl5012678).

For more information, visit www.sandia.gov.