HOUSTON (Dec. 9, 2013) Carbon nanotubes carry plasmonic signals in the terahertz range of the electromagnetic spectrum, but only if they're metallic by nature or doped.
In new research, the Rice University laboratory of physicist Junichiro Kono disproved previous theories that dominant terahertz response comes from narrow-gap semiconducting nanotubes.
Knowing that metallic or doped nanotubes respond with plasmonic waves at terahertz frequencies opens up the possibility that the tubes can be used in a wide array of optoelectronic amplifiers, detectors, polarizers and antennas.
The work by Kono and his Rice colleagues appeared online recently in the American Chemical Society journal Nano Letters.
Scientists have long been aware of a terahertz peak in nanotubes, the tiny cylinders of rolled-up carbon that show so much promise for advanced materials. But experiments on batches of nanotubes, which generally grow in a willy-nilly array of types, failed to reveal why it was there.
The origin of the peak was not explainable because researchers were only able to experiment on mixed batches of nanotube types, said Qi Zhang, a graduate student in Kono's group and lead author of the paper. "All the previous work was done with a mixture of semiconducting and metallic tubes. We are the first to clearly identify the plasmonic nature of this terahertz response," he said.
Rice's growing expertise in separating nanotubes by type allowed Kono and his group to test for terahertz peaks in batches of pure metallic nanotubes known as "armchairs" as well as nonmetallic, semiconducting tubes.
"Metallic carbon nanotubes are expected to show plasmon resonance in the terahertz and infrared range, but no group has clearly demonstrated the existence of plasmons in carbon nanotubes," Zhang said. "Previously, people proposed one possible explanation -- that the terahertz peak is due to interband absorption in
|Contact: David Ruth|