Graphene-Based Materials Could Help Make Infrared Contact Lenses

University of Michigan engineering researchers have demonstrated that graphene could be used to develop contact lenses to help people see infrared.

Researchers used a new approach to make a graphene-based device that doesn't require bulky cooling systems used in current infrared vision technologies.

The most obvious use of the lenses would be to see heat-emitting objects in the dark. However, the latest technology could also be used in hospital settings where doctors could monitor blood flows and in environmental studies where researchers could detect chemicals in the atmosphere.

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

Thermal imaging works by capturing infrared spectrum. There are several problems with the current thermal imaging devices. Different wavelengths of visible light can be captured by a single device, but detecting near-, mid- and far-infrared radiation requires a combination of technologies. Also, mid and far infrared radiation require cooling systems to work.

The idea that Graphene could help make better heat-sensing equipment has been around for some time now. Researchers at IBM's Nanoscale Science and Technology had shown that grapheme- a strong, thin, conductive material made of carbon-has certain photoconductive qualities that could make it a good candidate for infrared spotting devices.

One major problem with graphene is that it is one-atom thick and absorbs just 2.3 percent of the light that falls on it. The electrical signal produced by the material is too weak to be used in devices that detect heat.

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

In the present study, researchers increased the electrical signals by measuring light-induced electrical charges in the presence of 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."

Their device was made of two graphene layers separated by a layer of insulator. The bottom graphene layer has a current flowing through it. When light falls on the top layer, the electrons are released and generate positively charged holes. The electrons then reach the bottom layer via a phenomenon called quantum tunneling effect.

The top layer, thus, has positively charged holes. These holes generate an electric field that affects the flow of current in the bottom layer. Researchers could estimate the brightness of light hitting the top layer by measuring changes in the current running in the bottom layer.

The sensitivity of this room-temperature graphene device matches with that of mid-infrared devices.

The study "Graphene photodetectors with ultra-broadband and high responsivity at room temperature," is published in the journal Nature Nanotechnology. The study was supported by National Science Foundation.