Graphene imaging technology could make it possible for humans to see in infrared or UV wavelengths one day soon. Infrared vision would allow people to see heat signatures given off by objects, especially warm-blooded animals like humans.
University of Michigan researchers led by Zhaohui Zhong connected two layers of graphene, creating an image sensor. This simple device is able to "see" over a wide range of frequencies, from ultraviolet, though the violet and blue end of the rainbow, all the way to red, and the normally invisible infrared wavelengths that lay beyond. Best of all, this new design operates at normal room temperatures, making it possible to use in a contact lens.
Graphene is just one atom thick, and when it is struck by a photon of light, electrons gain enough energy to become "hot carriers." These subatomic particles are now able to tunnel through materials that would normally be impenetrable. This effect can be measured, and recorded as an image.
Because graphene is so thin, it is nearly transparent, absorbing just 2.3 percent of the light hitting the material. That means very few hot carriers are ever produced, making imaging difficult.
To get around this lack of hot carriers, researchers used two layers of graphene in the new device. In between the sheets, they put a dielectric layer. This would act as in insulator to electrons at most times, until the front of the chip becomes exposed to light. This creates hot carriers, that are able to penetrate the dielectric barrier. This acts as a switch, turning on the flow of electrons on the bottom layer, where the charge is recorded as an image.
This new graphene chip has 100 times the sensitivity of previous chips of this type. The quality of the images that could be produced using this tri-layer system is now nearly identical to sensors in commercial digital cameras.
"If we integrate it with a contact lens or other wearable electronics, it expands your vision. It provides you another way of interacting with your environment," Zhong said.
Such a smart contact lens could be integrated to work with web-enabled phones. Applications can extend from rescue workers to soldiers. Google has recently started a new project, aimed at developing a fully-functional electronic contact lens. Their design measures concentrations of body fluids. Healthcare workers could use the device to easily see blood vessels.
If this new eye wear goes into production, people may soon be seeing more than nature ever intended. Advertising that is invisible to most people may appear for people wearing the device.
Design of the new, versatile chip was profiled in the journal Nature.
