Scientists have used carbon nanotubes to create compact terahertz sensors that operate at room temperature.
The technology could make screening bags and passengers at airports less intrusive. It also has the potential to inspect food and even scan for tumors.
Junichiro Kono, a physicist at Rice University, says the potential to replace magnetic resonance imaging (MRI) technology in screening for cancer and other diseases is one of the most exciting possible applications.
“The potential improvements in size, ease, cost, and mobility of a terahertz-based detector are phenomenal,” Kono says. “With this technology, you could conceivably design a handheld terahertz detection camera that images tumors in real time with pinpoint accuracy. And it could be done without the intimidating nature of MRI technology.”
Why carbon nanotubes?
Because terahertz waves are much smaller in energy than visible light, finding materials that absorb and turn them into useful electronic signals has been a challenge, Kono says.
The scientific community has long been interested in the terahertz properties of carbon nanotubes, says François Léonard, a scientist at Sandia National Laboratories. But virtually all of the research to date has been theoretical or computer-model-based.
A handful of papers, including several by Kono and his team, have investigated terahertz phenomena in carbon nanotubes, but those have focused mainly on the use of one or a bundle of nanotubes.
The problem, Léonard says, is that terahertz radiation typically requires an antenna to achieve coupling into a single nanotube, due to the relatively large size of terahertz waves.
Thin film soaks up terahertz
The researchers, however, found a way to create a small detector that is visible to the naked eye. The thin carbon nanotube film developed by Rice chemist Robert Hauge and graduate student Xiaowei He does not require an antenna, and is thus amenable to simple fabrication.
It represents one of the team’s most important achievements, Léonard says.
“Carbon nanotube thin films are extremely good absorbers of electromagnetic light,” he explains. In the terahertz range, the film, a mix of metallic and semiconducting nanotubes, soaks up all of the incoming terahertz radiation.
“Trying to do that 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,” Kono says. “But that’s what we’ve achieved with the carbon nanotubes.”
The research was reported in the journal Nano Letters.
Additional researchers from the Rice, Sandia National Laboratories, Tokyo Institute of Technology, and Carnegie Mellon University contributed to the project, which was funded by the Department of Energy, the National Institute for Nano Engineering at Sandia National Laboratories, the Lockheed-Martin Rice University LANCER program, the National Science Foundation, and the Robert A. Welch Foundation.
Source: Rice University