Soon you may be putting on contact lenses that give you infrared vision without the need for a contraption covering your face. And the new technology also has medical applications, such as letting doctors monitor blood flow. So will night vision contact lens become a reality at last? Thanks to research at the University of Michigan, such a contact lens is a real possibility, says the March 21, 2014 news release, "New Sensor Could Make Night Vision Contact Lenses A Reality." The new study is "Graphene photodetectors with ultra-broadband and high responsivity at room temperature," published online March 16, 2014 in the journal Nature Nanotechnology. A team of researchers recently embedded an inorganic light-emitting diode directly into an off-the-shelf contact lens, explains the article, "This contact lens could eventually make Google Glass obsolete."
The ability to detect light over a broad spectral range is central to several technological applications in imaging, sensing, spectroscopy and communication. But Graphene is a promising candidate material for ultra-broadband photodetectors, as its absorption spectrum covers the entire ultraviolet to far-infrared range.
The only issue is that the responsivity of graphene-based photodetectors has so far been limited due to the small optical absorption of a monolayer of carbon atoms
Integration of colloidal quantum dots in the light absorption layer can improve the responsivity of graphene photodetectors. What happens is that the spectral range of photodetection is reduced because light absorption occurs in the quantum dots. In the new study, researchers reported how an ultra-broadband photodetector design based on a graphene double-layer heterostructure, according to the study's abstract.
The detector is a phototransistor consisting of a pair of stacked graphene monolayers (top layer, gate; bottom layer, channel) separated by a thin tunnel barrier. Under optical illumination, photoexcited hot carriers generated in the top layer tunnel into the bottom layer, leading to a charge build-up on the gate and a strong photogating effect on the channel conductance.
The devices demonstrated room-temperature photodetection from the visible to the mid-infrared range, with mid-infrared higher responsivity is required by most applications. These results of the new study address key challenges for broadband infrared detectors, and are promising for the development of graphene-based hot-carrier optoelectronic applications. For the average consumer, this means contact lens could eventually be made that would let you have night vision.
Infrared contact lens that lets you have night vision?
The Michigan researchers turned to the optical capabilities of graphene to create their infrared contact lens. IBM last year demonstrated some of the photoconductivity mechanisms of graphene that make it an attractive infrared detector. Graphene is capable of detecting the entire infrared spectrum, with visible and ultraviolet light thrown in. But where graphene giveth, it also taketh away. Because graphene is only one atom thick, it can absorb only 2.3 percent of the light that hits it. This is not enough to generate an electrical signal, and without a signal, it can't operate as a infrared sensor.
"The challenge for the current generation of graphene-based detectors is that their sensitivity is typically very poor," said Zhaohui Zhong, assistant professor at the University of Michigan, according to the press release. "It's a hundred to a thousand times lower than what a commercial device would require."
In research that was in the journal Nature Nanotechnology, the Michigan researchers devised a new method for generating the electrical signal. Instead of trying to measure the electrons that are released when the light strikes the material, they amplified an electrical current that is near the electrical signals generated by the incoming light.
To achieve this amplification, the researchers started by sandwiching an insulator between two sheets of graphene
The bottom sheet has an electrical current running through it. When light hits the top sheet, electrons are freed and positively charged electron holes are generated. The electrons are able to perform a quantum tunneling effect through the insulator layer, which would be impenetrable in classical physics.
The electron holes that are left behind in the top layer generate an electric field that impacts the way electricity flows through the bottom layer. By measuring this change in the flow of current in the bottom layer, the researchers could derive just how much light hit the top layer.
The device's sensitivity
This device has very nearly the same sensitivity as cooled mid-infrared detectors, but achieves it at room temperature. The researchers have already been able to produce infrared sensors the size of a pinky nail, or a standard contact lens.
"If we integrate it with a contact lens or other wearable electronics, it expands your vision," Zhong said in the news release. "It provides you another way of interacting with your environment."
Military infrared vision lets soldiers see in the dark
Most of us are familiar with the military applications of infrared vision, which allows soldiers to see in the dark. But the technology also has medical applications, such as letting doctors monitor blood flow, the news release explains.
Whether the ability to see in the infrared is an attractive feature for the rest of us remains to be seen. But that may become a possibility since the fundamental mechanism underlying the technology could become a mechanism for other material and device platforms. Is infrared vision mode for Google Glass in the offing? This story originally appeared on IEEE Spectrum. You also may wish to check out articles such as "Superpower vision lets cats and dogs see in ultraviolet," and "Most animals can see the flashing and glowing of power lines."