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

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


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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
Journal information: Nature Nanotechnology

Citation: Ultra-thin, high-speed detector captures unprecedented range of light waves (2014, September 7) retrieved 26 June 2019 from https://phys.org/news/2014-09-ultra-thin-high-speed-detector-captures-unprecedented.html
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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?

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.

Sep 07, 2014
This comment has been removed by a moderator.

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?

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