Improved terahertz technology to benefit passenger screening, food inspection, MRIs
nanotubes, said Léonard, but virtually all of the research to date has been theoretical or computer-model based. A handful of papers have investigated terahertz sensing using carbon nanotubes, but those have focused mainly on the use of a single or single bundle of nanotubes.
The problem, Léonard said, is that terahertz radiation typically requires an antenna to achieve coupling into a single nanotube due to the relatively large size of terahertz waves.
The Sandia, Rice University, and Tokyo Institute of Technology research team, however, found a way to create a small but visible-to-the-naked eye detector, developed by Rice researcher Robert Hauge and graduate student XiaoweiHe, that uses carbon nanotube thin films without requiring an antenna. The technique is thus amenable to simple fabrication and represents one of the team’s most important achievements, Léonard said.
“Carbon nanotube thin films are extremely good absorbers of electromagnetic light,” he explained. In the terahertz range, it turns out that thin films of these nanotubes will soak up all of the incoming terahertz radiation. Nanotube films have even been called “the blackest material” for their ability to absorb light effectively.
The researchers were able to wrap together several nanoscopic-sized tubes to create a macroscopic thin film that contains a mix of metallic and semiconducting carbon nanotubes.
“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,” explained Kono.
“But that’s what we’ve achieved with the carbon nanotubes.”
The technique is key, he said, because it combines the superb terahertz absorption properties of the metallic nanotubes and the unique electronic properties of the semiconducting carbon nanotubes. This allows researchers to achieve a photodetector that does not require power to operate, with performance comparable to existing technology.
A clear path to performance improvement
The next step for researchers, Léonard said, is to improve the design, engineering and performance of the terahertz detector.
For instance, they need to integrate an independent terahertz radiation source with the detector for applications that require a source, Léonard said. The team also needs to incorporate electronics into the system and to further improve properties of the carbon nanotube material.
“We have some very clear ideas about how we can achieve these technical goals,” said Léonard, adding that new collaborations with industry or government agencies are welcome.
“Our technical accomplishments open up a new path for terahertz technology, and I am particularly proud of the multidisciplinary and collaborative nature of this work across three institutions,” he said.
The release notes that in addition to Sandia, Rice, and the Tokyo Tech, the project received contributions from researchers taking part in NanoJapan, a 12-week summer program that enables freshman and sophomore physics and engineering students from U.S. universities to complete nanoscience research internships in Japan focused on terahertz nanoscience.
— Read more in Xiaowei He et al., “Carbon Nanotube Terahertz Detector,” Nano Letters, Article ASAP (29 May 2014) (DOI: 10.1021/nl5012678)
