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.
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.
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.
Most of us are familiar with the military applications of infrared vision, which allows the soldiers to see in the dark. But the technology also has medical applications such as letting doctors monitor blood flow.