Uses Broaden for Wonky Nanotubes
USURBIL, Spain, Nov. 1, 2013 — A light emitter based on boron nitride nanotubes emits light across much of the electromagnetic spectrum, and can easily be incorporated into current microelectronics technology and used to develop high-efficiency optoelectronic devices, new research suggests.
Defect-free nanostructures are usually most attractive to researchers, but work at the UPV/EHU-University of the Basque Country takes advantage of the structural defects in boron nitride nanotubes.
A diagram of the device proposed by the UPV/EHU’s NanoBio Spectroscopy Group. Their results have led to a patented new source of light emission; its main feature is that it emits across the visible and UV spectrums at ambient temperature, and can be produced using standard manufacturing methods. Images courtesy of UPV/EHU.
With its excellent insulating properties, resistance and 2-D structure similar to graphene, boron nitride is a promising nanotechnology material. And the properties of hexagonal boron nitride, the focus of this work by UPV/EHU’s NanoBio Spectroscopy Group, are far superior to those of other metals and semiconductors currently being used as light emitters — such as in optical storage or communications applications.
“It is extremely efficient in ultraviolet light emission, one of the best currently available on the market,” said Angel Rubio, materials physics professor and NanoBio Spectroscopy Group leader.
The problem is its UV emission is of a very limited range, meaning it cannot be used in applications requiring a broader range of frequencies and precise control, such as those based on visible light.
The NanoBio Spectroscopy Group found that, by applying an electric field perpendicular to the nanotube, they could get it to emit light across a large swath of the spectrum — from the IR to the far-UV — and also control it in a simple way. The solution could open the door to commercial applications of hexagonal boron nitride nanotubes.
Rubio has been working with boron nitride nanotubes for nearly 20 years. “We proposed them theoretically, and then they were found experimentally. So far, all our theoretical predictions have been confirmed, and that is very gratifying,” he said.
This ease of control is only found in nanotubes due to their cylindrical geometry. Once the properties of layered hexagonal boron nitride and its extremely high efficiency in light emission were known, the research sought to show that these properties are not lost in nanotubes.
“We knew that when a sheet was rolled up and a tube was formed, a strong coupling was produced with the electric field and that would enable us to change the light emission,” Rubio said. “We wanted to show that light emission efficiency was not being lost due to the fact that the nanotube was formed, and that it is also controllable.”
The end result, he said, is “a device that functions with defects, it does not have to be pure, and it’s very easy to build and control,” adding, “what is more, the more defects you have, the better it functions.”
Nanotubes can be synthesized using standard scientific methods for producing inorganic nanotubes. As a result, those structures have natural defects, and it is possible to incorporate more by means of simple, postsynthesis irradiation processes, he said.
“It has a traditional transistor configuration, and what we are proposing would work with current electronic devices,” Rubio said.
The down side is that boron nitride nanotubes are still only produced in very small quantities, with no commercial-scale synthesis process yet established. Still, Rubio has no doubt as to the long-term potential of these new materials that offer an alternative to graphene.
“It’s a field that has been active for over the last fifteen years, even though it has been less visible,” Rubio said. “We have been working with hexagonal boron nitride since 1994, it’s like our child, and I believe that it has opened up an attractive field of research, which more and more groups are joining.”
His collaborators on the work, which has resulted in a patent, are Dr. Ludger Wirtz of the University of Luxembourg, Dr. Claudio Attaccalite of the University of Grenoble and Dr. Andrea Marini of the CNR Italian Research Council in Rome.
For more information, visit: www.basqueresearch.com
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