Traditional devices for thermal imaging are relatively bulky, because the mechanisms that detect the mid- and far-infrared radiation need to be cooled significantly. A team of engineers from the University of Michigan have made a sensor that can detect the infrared spectrum at room temperature. Because the sensor is made of graphene and therefore extremely small, the team could potentially put this technology into all sorts of things, including heat vision contact lenses. The technology has been described in the journal Nature Nanotechnology.
Graphene is a honeycomb-shaped arrangement of carbon that is only one atom thick. Previous attempts to use graphene as a light sensor have failed, as the material is not able to absorb enough light to trigger the necessary electrical signal, as they only absorb about 2.3% of the light it comes into contact with. One of the researchers, Zhaohui Zhong, described traditional graphene sensors as about one thousand times less sensitive than current commercially available sensors.
Zhong and his collaborators were able to remedy the problem by thinking about it backwards. Instead of trying to bolster the amount of electricity produced by the graphene, they focused on how the electric current produced by the light is affected by the material.
The sensor works by putting a insulator between two sheets of graphene, the bottom of which was charged. When light hits the top layer, it frees electrons that are able to slip through the insulation down to the bottom layer. The electrons leave positively-charged holes in the upper layer, which affect the charged bottom layer and create the signal needed to identify light. The operation is based on certain principles of quantum mechanics that the team was able to exploit.
The result was a new way to detect light that may not just work with graphene; it could have a host of practical applications with other materials. Zhong reports that the sensor, which is currently the size of a fingernail, could easily be made smaller. While not everyone would have a need for thermal vision contact lenses, the technology could also be integrated into cell phones or other devices.
Though the obvious uses for this technology would be military applications, there are many other uses for thermal imaging, including scanning for cancers, mapping energy losses in buildings, studying volcanoes, finding faults in electrical circuits, aiding firefighters, and detecting several metabolic, musculoskeletal, or inflammatory medical conditions.
