Thermal vision: Graphene light detector first to span infrared spectrum

Mar 16, 2014
Credit: University of Manchester

The first room-temperature light detector that can sense the full infrared spectrum has the potential to put heat vision technology into a contact lens.

Unlike comparable mid- and far-infrared detectors currently on the market, the detector developed by University of Michigan engineering researchers doesn't need bulky cooling equipment to work.

"We can make the entire design super-thin," said Zhaohui Zhong, assistant professor of and computer science. "It can be stacked on a contact lens or integrated with a cell phone."

Infrared starts at wavelengths just longer than those of visible red light and stretches to wavelengths up to a millimeter long. Infrared vision may be best known for spotting people and animals in the dark and heat leaks in houses, but it can also help doctors monitor blood flow, identify chemicals in the environment and allow art historians to see Paul Gauguin's sketches under layers of paint.

Unlike the visible spectrum, which conventional cameras capture with a single chip, infrared imaging requires a combination of technologies to see near-, mid- and far-infrared radiation all at once. Still more challenging, the mid-infrared and far-infrared sensors typically need to be at very cold temperatures.

Graphene, a single layer of carbon atoms, could sense the whole —plus visible and ultraviolet light. But until now, it hasn't been viable for infrared detection because it can't capture enough light to generate a detectable electrical signal. With one-atom thickness, it only absorbs about 2.3 percent of the light that hits it. If the light can't produce an electrical signal, graphene can't be used as a sensor.

"The challenge for the current generation of graphene-based detectors is that their sensitivity is typically very poor," Zhong said. "It's a hundred to a thousand times lower than what a commercial device would require."

To overcome that hurdle, Zhong and Ted Norris, the Gerard A. Mourou Professor of Electrical Engineering and Computer Science, worked with graduate students to design a new way of generating the . Rather than trying to directly measure the electrons that are freed when light hits the graphene, they amplified the signal by looking instead at how the light-induced electrical charges in the graphene affect a nearby current.

"Our work pioneered a new way to detect light," Zhong said. "We envision that people will be able to adopt this same mechanism in other material and device platforms."

To make the device, they put an insulating barrier layer between two graphene sheets. The bottom layer had a current running through it. When light hit the top layer, it freed electrons, creating positively charged holes. Then, the electrons used a quantum mechanical trick to slip through the barrier and into the bottom layer of graphene.

The positively charged holes, left behind in the top layer, produced an electric field that affected the flow of electricity through the bottom layer. By measuring the change in current, the team could deduce the brightness of the light hitting the graphene. The new approach allowed the sensitivity of a room-temperature device to compete with that of cooled mid-infrared detectors for the first time.

The device is already smaller than a pinky nail and is easily scaled down. Zhong suggests arrays of them as infrared cameras.

"If we integrate it with a or other wearable electronics, it expands your vision," Zhong said. "It provides you another way of interacting with your environment."

While full-spectrum infrared detection is likely to find application in military and scientific technologies, the question for the general tech market may soon be, "Do we want to see in infrared?"

The device is described in a paper titled "Graphene photodetectors with ultra-broadband and high responsivity at room temperature," which appears online in Nature Nanotechnology.

Explore further: Graphene sheets could make effective transparent electrodes in certain types of photovoltaic cells

More information: Graphene photodetectors with ultra-broadband and high responsivity at room temperature, Nature Nanotechnology, 2014, DOI: 10.1038/nnano.2014.31

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User comments : 7

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h20dr
1 / 5 (1) Mar 16, 2014
X-ray vision coming soon...
Wolf358
5 / 5 (2) Mar 16, 2014
I have worked with building HVAC systems including steam-heat, exchangers, pumps, etc, and I would _love_ to have an infrared contact lens. Being able to see, at a distance, which pipes are hot and how hot would be an incredible troubleshooter's tool. Yes, Please! :-)
Eikka
5 / 5 (1) Mar 16, 2014
"If we integrate it with a contact lens or other wearable electronics, it expands your vision,"


But that's not how vision works.

You can't just put a sensor on top of the lens in your eye and see infrared. You have to project the image onto the sensor with optical lenses, and then convert the image from the sensor to visible light, and then project that image onto the retina at the back of the eye to see it. The sensor doesn't just magically convert infrared light to visible light.

Good luck miniaturizing the optics to within the thickness of a contact lens, when the wavelenght of the light you're trying to focus is longer than the thickness of the whole device.
gjbloom
5 / 5 (1) Mar 16, 2014
"If we integrate it with a contact lens or other wearable electronics, it expands your vision,"

So let's think about how that would have to work. It would need to be an array of small diode lasers, arranged in a raster that is interconnected by a mesh that is either transparent or so fine that it doesn't interfere with most of the light passing through the lens. Then you'd need some short-distance wireless connection to provide the data-stream being projected onto the retina. With such a general-purpose graphic overlay system, one could overlay whatever they're looking at with other meaningful indications, including infra-red imaging.

Manufacture would have to be fully automated. Perhaps a very accurate, very small six-axis robot could extrude this very thin mesh of diode lasers and conductors onto a contact that is molded half as thick as needed. Then the other half could be molded onto it to encapsulate the emitter mesh.

Doable?
h20dr
2 / 5 (1) Mar 16, 2014
If you can imagine it it will happen. Eventually...
Shabs42
not rated yet Mar 16, 2014
Hard to imagine it in a contact lens, but it would be a great accessory for a Google Glass type product.
alfie_null
not rated yet Mar 17, 2014
As these sensors are wide spectrum, an interesting next step would be to outfit a sensor array with cells of dyes (or whatever) that pass different wavelengths - create something that can easily see in infrared "color".