Scientists have developed a novel graphene-based radiation detector which has a fast response time and works over a wide range of temperatures. With a simple design and relatively low cost, the device classified as a bolometer could be scaled up, enabling a wide range of commercial applications. The new bolometer created by researchers at Chalmers University of Technology in Sweden is based on graphene's thermoelectric properties. Radiation heats part of the device, inducing electrons to move. The displaced electrons generate an electric field, which creates a voltage difference across the device. The change in voltage thus provides an essentially direct measurement of the radiation. Other devices rely on the generation of electrical current or resistance change by incoming radiation. However, measuring changes in current or resistance requires an external power source to generate an initial current. The mechanism is much simpler than in other bolometers, according to Grigory Skoblin of Chalmers University. The piece of graphene in the new bolometer is small, so it is one of the fastest bolometers because it heats up and responds quickly. The device remains sensitive to radiation at temperatures up to 200 degrees Celsius. Conventional bolometers typically work only at cryogenic temperatures. Other researchers have previously made graphene bolometers, with better properties than this new device, but these models contain a double layer of graphene, making them more difficult to scale, Skoblin said. Another advantage of the new device is its coating. The researchers previously developed a method to coat graphene with a dielectric polymer called Parylene, which offers a good balance of performance and scalability. The prototype bolometer works only with microwave radiation at 94 gigahertz, but future designs will widen the frequency range, they said.
