It sounds like something from a spy thriller movie: putting on a contact lens that gives you infrared vision without a bulky contraption that covers your face. But now, thanks to research at the University of Michigan, such a contact lens is a real possibility.
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 a electrical signal, and without 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, in a press release. “It’s a hundred to a thousand times lower than what a commercial device would require.”
In research that was published in the journal Nature Nanotechnology (“Graphene photodetectors with ultra-oadband and high responsivity at room temperature”), 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.