People use electromagnetic energy
every day—watching television, listening to the radio, popping corn with a
microwave, taking an X-ray, or using a cellphone. This energy travels in the
form of waves, which are widely used in electronic and wireless devices.
One of the hottest areas of the
electromagnetic spectrum being explored today is the terahertz (THz) range.
Terahertz waves, lying between microwave and optical frequencies, offer
improved performance for a variety of applications in everyday life. For
instance, THz waves can carry more information than radio/microwaves for
communications devices. They also provide medical and biological images with
higher resolution than microwaves, while offering much smaller potential harm
of exposure than X-rays.
Researchers at the University of
Notre Dame have shown that it is possible to efficiently manipulate THz
electromagnetic waves with atomically thin graphene layers. This achievement,
which was recently published in Nature
Communications, sets the stage for development of compact, efficient and
cost-effective devices and systems operating in the THz band.
“A major bottleneck in the
promise of THz technology has been the lack of efficient materials and devices
that manipulate these energy waves,” says Berardi Sensale-Rodriguez, a graduate
student in the Department of Electrical Engineering at Notre Dame. “Having a
naturally two-dimensional material with strong and tunable response to THz
waves—for example, graphene— gives us the opportunity to design THz devices
achieving unprecedented performance.”
The terahertz team—graduate
students Sensale-Rodriguez, Rusen Yan, Kristof Tahy, and Tian Fang; research
assistant professors Michelle M. Kelly, through Center for Nano Science and
Technology (NDnano), and Lei Liu, in conjunction with Advanced Diagnostics and
Therapeutics at Notre Dame (AD&T); visiting research assistant professor
Wan Sik Hwang, with Midwest Institute for Nanoelectronics Discovery (MIND); associate professor Debdeep Jena and John Cardinal
O’Hara, C.S.C., Associate Professor Huili (Grace) Xing—has demonstrated the
first proof of concept prototype of a graphene-based THz modulator, a device
enabled solely by intraband transitions in graphene.
Graphene, an atom-thick
semiconductor material, has shown promising electrical, mechanical, and thermal
properties leading to the recent demonstration of fast transistors,
flexible/transparent electronics, optical devices, and now terahertz active
components.
“Graphene has been touted as an
ideal platform to discover new, as well as prove/dispute existing, physical
phenomena since 2004,” Xing said. “That is what two physicists in the
United Kingdom,
Andre Geim and Konstantin Novoselov, were awarded the Nobel Prize for in 2010.
However, very few real-world applications of graphene have emerged to date.
Using graphene to manipulate THz waves is one of such applications. This Nature
Communication paper documented our first experimental effort to realize the
predictions in our paper published in Applied
Physics Letters last year. Devices with better performance continue rolling
out of our laboratories.
“Though Professor Jena and I
formed the vision to use two-dimensional electron gas to manipulate THz waves
back in 2006, it was not until Michelle, Lei and Berardi joined us that this
piece of work was possible,” Xing added.
