March 18, 2014
The Future Of Contact Lenses May Have You Seeing Infrared
Lee Rannals for redOrbit.com - Your Universe Online
A new device developed by researchers at the University of Michigan could make it possible for contact lenses to give the wearer infrared vision.The engineering researchers developed the first room-temperature light detector that can sense the full infrared spectrum without the need for bulky cooling equipment.
"We can make the entire design super-thin," Zhaohui Zhong, assistant professor of electrical and computer engineering at UMich, said in a statement. "It can be stacked on a contact lens or integrated with a cell phone."
Graphene is able to detect the entire infrared spectrum, as well as visible and ultraviolet light. However, because it is only one-atom thick it can only absorb 2.3 percent of the light that hits it.
"The challenge for the current generation of graphene-based detectors is that their sensitivity is typically very poor," Zhong said. "It's a hundred to a thousand times lower than what a commercial device would require."
Instead of directly measuring the electrons that are freed when light hits the graphene, the team amplified the signal by looking at how the light-induced electrical charges in the graphene affect 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."
In order to create the device, the researchers put an insulating barrier layer between two graphene sheets. When light strikes the top layer, it frees electrons to create positively charged holes. After this, the electrons use quantum mechanical tricks to get past the barrier and into the bottom layer of graphene.
Positively charged holes that are left behind in the top layer produce an electric field that affects the flow of electricity through the bottom layer. The team measured the change in current to deduce the brightness of the light hitting the graphene.
The researchers said the new approach allows the sensitivity of a room-temperature graphene device, instead of a device that requires cooled mid-infrared detectors.
"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."
A contact lens that sees in infrared could allow doctors to monitor blood flow, scientists to identify chemicals in the environment and art historians to see the sketches under Paul Gauguin's layers of paint.
The team wrote about their research in a paper titled "Graphene photodetectors with ultra-broadband and high responsivity at room temperature” in the journal Nature Nanotechnology.