Ultra-thin, high-speed detector captures unprecedented range of light waves

September 7, 2014
Top-down view of broadband, ultra-fast graphene detector capable of detecting terahertz frequencies at room temperature. Credit: Thomas Murphy

New research at the University of Maryland could lead to a generation of light detectors that can see below the surface of bodies, walls, and other objects. Using the special properties of graphene, a two-dimensional form of carbon that is only one atom thick, a prototype detector is able to see an extraordinarily broad band of wavelengths. Included in this range is a band of light wavelengths that have exciting potential applications but are notoriously difficult to detect: terahertz waves, which are invisible to the human eye.

A research paper about the new was published Sunday, September 07, 2014 in Nature Nanotechnology. Lead author Xinghan Cai, a University of Maryland physics graduate student, said a detector like the researchers' prototype "could find applications in emerging fields such as mobile communications, medical imaging, chemical sensing, night vision, and security."

The light we see illuminating everyday objects is actually only a very narrow band of wavelengths and frequencies. Terahertz light waves' long wavelengths and low frequencies fall between microwaves and infrared waves. The light in these terahertz wavelengths can pass through materials that we normally think of as opaque, such as skin, plastics, clothing, and cardboard. It can also be used to identify chemical signatures that are emitted only in the terahertz range.

Few technological applications for terahertz detection are currently realized, however, in part because it is difficult to detect light waves in this range. In order to maintain sensitivity, most detectors need to be kept extremely cold, around 4 Kelvin, or -452 degrees Fahrenheit. Existing detectors that work at are bulky, slow, and prohibitively expensive.

The new room temperature detector, developed by the University of Maryland team and colleagues at the U.S. Naval Research Lab and Monash University, Australia, gets around these problems by using , a single layer of interconnected carbon atoms. By utilizing the special properties of graphene, the research team has been able to increase the speed and maintain the sensitivity of room temperature wave detection in the terahertz range.

Using a new operating principle called the "hot-electron photothermoelectric effect," the research team created a device that is "as sensitive as any existing room temperature detector in the terahertz range and more than a million times faster," says Michael Fuhrer, professor of physics at the University of Maryland and Monash University, Australia.

Graphene, a sheet of pure carbon only one atom thick, is uniquely suited to use in a terahertz detector because when is absorbed by the electrons suspended in the honeycomb lattice of the graphene, they do not lose their heat to the lattice but instead retain that energy.

The concept behind the detector is simple, says University of Maryland Physics Professor Dennis Drew. "Light is absorbed by the electrons in graphene, which heat up but don't lose their energy easily. So they remain hot while the carbon atomic lattice remains cold." These heated electrons escape the graphene through electrical leads, much like steam escaping a tea kettle. The prototype uses two electrical leads made of different metals, which conduct electrons at different rates. Because of this conductivity difference, more electrons will escape through one than the other, producing an electrical signal.

This electrical signal detects the presence of beneath the surface of materials that appear opaque to the human eye – or even x-rays. You cannot see through your skin, for example, and an x-ray goes right through the skin to the bone, missing the layers just beneath the skin's surface entirely. Terahertz waves see the in-between. The speed and sensitivity of the room temperature detector presented in this research opens the door to future discoveries in this in-between zone.

Explore further: New 'T-ray' tech converts light to sound for weapons detection, medical imaging

More information: "Sensitive Room-Temperature Terahertz Detection via Photothermoelectric Effect in Graphene," Xinghan Cai et al. Nature Nanotechnology, dx.doi.org/10.1038/nnano.2014.182

Related Stories

Graphene may open the gate to future terahertz technologies

September 12, 2011

Nestled between radio waves and infrared light is the terahertz (THz) portion of the electromagnetic spectrum. By adding a nanoscale bit of graphene, researchers have found a better way to tune radiation for a THz transmitter.

Light pulses control graphene's electrical behavior

August 1, 2014

Graphene, an ultrathin form of carbon with exceptional electrical, optical, and mechanical properties, has become a focus of research on a variety of potential uses. Now researchers at MIT have found a way to control how ...

Ultra-thin light detectors

March 27, 2014

A new, extremely thin kind of light detectors was created at Vienna University of Technology. Two very different technologies were combined for the first time: metamaterials and quantum cascade structures.

Recommended for you

Multicolor MRIs could aid disease detection

August 16, 2017

Researchers at Case Western Reserve University School of Medicine have developed a method that could make magnetic resonance imaging—MRI—multicolor. Current MRI techniques rely on a single contrast agent injected into ...

Turning pollen into a low-cost fertilizer

August 16, 2017

As the world population continues to balloon, agricultural experts puzzle over how farms will produce enough food to keep up with demand. One tactic involves boosting crop yields. Toward that end, scientists have developed ...

Nanotechnology gives green energy a green color

August 15, 2017

Solar panels have tremendous potential to provide affordable renewable energy, but many people see traditional black and blue panels as an eyesore. Architects, homeowners and city planners may be more open to the technology ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

ChangBroot
1 / 5 (3) Sep 07, 2014
Ahh, the key word: Security. Did you see it?
"could find applications in emerging terahertz fields such as mobile communications, medical imaging, chemical sensing, night vision, and security."

Everyday they find new ways for the West's military to exploit the poor people. Another way to ease the road to "civil" war in poor countries, without directly being there. Potential for weapons is endless. Can't they just for once use these kinds of things for the benefit of the people?
Returners
1.7 / 5 (6) Sep 07, 2014
Your response is not worth of a "1". There ought to be a "zero" option on this site.

"the West" are the first on hand to deliver food and medical supplies to other nations suffering mega-disasters, you jackass.

I'm sure it will be used in weapons, but to kill godless terrorists, like Isis and Al Quaeda who deliberately target unarmed people, and NOT to harm "innocent poor people".

It's not just the Arabic muslim terrorists though, if we ever get rid of the ones in the middle east, we'll need to turn our attention to the African muslims in the sub-saharan nations which kidnap, rape, and force conversions of little girls.

They need to be summarily executed whenever they're found.

Maybe these new scanners will allow a new form of night vision goggles, or missile guidance that can be programmed to target Korans and AK-47s.

You're darn right it'll be turned into a weapon, and the more lunatic terrorists it kills the better.
Aligo
Sep 07, 2014
This comment has been removed by a moderator.
Uncle Ira
3 / 5 (4) Sep 07, 2014
Your response is not worth of a "1". There ought to be a "zero" option on this site..


Skippy, maybe you ought not to be suggesting that one. I mean, all those ones you get, are they because your postums are only worth one? Or are all those ones you get ones because they don't allow the zero or the minus numbers?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.