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Graphene light detector could put heat vision tech in a contact lens

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April 13, 2014

The Zhong group from U-M responsible for pioneering a new graphene-based photodetector (Ph...

The Zhong group from U-M responsible for pioneering a new graphene-based photodetector (Photo: University of Michigan)

Thermal imaging has already found its way onto smartphones, but a team of researchers from the University of Michigan (U-M) have gone even further with the creation of an ultrathin graphene-based light detector. Being only slightly thicker than two sheets of graphene, the approach has the potential to put infrared heat detecting technology into a contact lens.

Under ordinary conditions, it is impossible to detect certain light frequencies, such as infrared light, with the naked eye. However, technology has long been in use that grants us the ability to extend the spectrum of visible light. One such example of this technology being the use of infrared light detectors as a method of night vision.

The infrared spectrum, that begins just beyond the wavelengths of visible light, is made up of near, mid, and far infrared radiation. Traditionally, devices that allow for the detection of the full range of infrared frequency light require bulky cooling systems in order to function, as the device must generally be kept at very cold temperatures to allow the sensors to function properly. However, the new graphene-based technique pioneered by the U-M research team works at room temperature without requiring a cooling system, and thus can be easily miniaturized.

“We can make the entire design super-thin,” states Zhaohui Zhong, assistant professor of electrical engineering and computer science at U-M, "It can be stacked on a contact lens or integrated with a cell phone."

How does it work?

The team created the compact light detector by utilizing graphene, a wonder material with the ability to detect the entire infrared spectrum. Whilst researchers have attempted to use graphene for infrared imaging applications in the past, until the breakthrough by the U-M research team, the material had not been suitable for the task.

"The challenge for the current generation of graphene-based detectors is that their sensitivity is typically very poor," stated Zhong. In basic terms, the one-atom-thick graphene is unable to absorb enough light to produce an electric signal, rendering the material useless as a sensor.

The team solved this problem by finding a different way in which to create the electrical signal. Instead of directly measuring the electrons freed from the graphene when the light hits its surface, (the method of observation used in the past), the researchers magnified the signal by observing how the electrical charges on the graphene affected a nearby current.

The device itself was created by placing an insulating layer between two sheets of graphene, with an electrical current running through the bottom sheet. As infrared light impacted on the upper layer, electrons were freed from the graphene, creating holes that acted as a positive charge between the electrons. The electrons were then able to slip through the insulating barrier and on to the bottom layer of graphene where the team was then able to observe changes in the flow of the current running through the bottom layer of graphene. From this, the team was able to deduce the brightness of the light impacting on the upper layer and thus create a viable method for detecting infrared light that is only slightly thicker than two sheets of graphene.

The future uses of this light detecting technology could span from military applications – replacing the clunky infrared gear sported by special forces around the world – to medical innovation – aiding doctors in monitoring the blood flow of patients. There's also a possibility the technology could find more general commercial applications.

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

The team's research appears in the journal Nature Nanotechnology.

Source: University of Michigan

About the Author
Anthony Wood Anthony is a recent law school graduate who also has a degree in Ancient History, for some reason or another. Residing in the UK, Anthony has had a passion about anything space orientated from a young age and finds it baffling that we have yet to colonize the moon. When not writing he can be found watching American football and growing out his magnificent beard.   All articles by Anthony Wood
6 Comments

How about a nice windshield application? Something that might save a few lives and pets.

VoiceofReason
14th April, 2014 @ 01:15 am PDT

I would love a similar device that operates at the other end of the spectrum and allowed me to see U.V. I have no idea what practical use it would, but there again lasers were a solution looking for a problem when they were being developed.

Mel Tisdale
14th April, 2014 @ 03:29 am PDT

"...near, mid, and far infrared radiation...[existing devices] require bulky cooling systems [but] the new graphene-based technique ... at room temperature." This implies, but does not QUITE say, that a room temperature (or if in a contact lens, a BODY temperature) device can detect far infrared light. But at either room or body temperature the device will glow in the far infrared. It's only possible to image in the same wave lengths that the device, itself, emits, if the source is far brighter that the device. But the great value of far infrared imaging comes from the warm body glow that all the normal objects around us have. Thus the uncooled device will be useless unless you carry around a near or mid infrared light source.

piperTom
14th April, 2014 @ 08:33 am PDT

@piperTom, I have no experience or knowledge of any sort on this, BUT it would seem to me that as thin as this can be it wouldn't require much in the way of cooling to allow for the near/mid ranges (maybe not applicable on contact lenses, but still a significant reduction in size).

Benjamin Clements
14th April, 2014 @ 10:19 am PDT

The idea of the detector being mounted on a contact lens makes no sense at all. Without a lens in front of it, how can it focus on a subject in front of it?, And with it on the surface of your eye how can the image be in focus on your retina after going through the lens in your eye (which is focused on things far in front of you, not on its surface)?

I can only hope that there was a translation problem or something.

Michaelc
14th April, 2014 @ 03:59 pm PDT

I have joked any number of times just how useful it would be to see in IR,

the potential applications are amazing.

From engineers being able to see at a glance hot spots in machinery (bearings failing), electrical engineers overloaded cables, junction boxes with failing connections. Doctors sites of infection, Psychologists patients lying (skin response)

Glider/Paragliding pilots able to see thermals and "core" them.

Volcanologists' spotting imminent eruptions (magma nearing the surface)

Potential boyfriend/girlfriend emotional response.

The list is endless, I want some. Now.

Pat Pending
15th April, 2014 @ 06:01 am PDT
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