Graphene is a form of carbon where a single layer of carbon atoms forms a flat sheet with a hexagonal grid arrangement. It was discovered in 2004 and thought to hold great promise. Research on graphene has uncovered a variety of interesting and potentially useful features including being light weight, strong and a good conductor. Graphene also has the ability to convert heat directly into electricity. Recently, a group of researchers developed a new type of radiation detector based on graphene.
A bolometer is an instrument that can measure electromagnetic radiation through the heating of a material in which the electrical resistance is related to temperature. The new graphene radiation detector is a type of bolometer. The graphene bolometer is able to work over a much broader range of temperatures that existing commercial bolometers. The design for the graphene bolometers is simple and the cost of production is low. There could be a lot of commercial applications for the new bolometer.
Grigory Skoblin does research at the Chalmers University of Technology in Sweden. With respect to graphene, he said, “…there are some strong fundamental limitations for this material. Nowadays, the real industrial applications of graphene are quite limited.” Most current uses of graphene are based on its mechanical properties. Skoblin says that “…our device shows that more fundamental properties can be used in actual applications.”
The graphene bolometer is based on the thermoelectric properties of graphene. Radiation heats a piece of graphene which causes electrons to move through the material. The moving electrons generate an electrical field. A voltage difference is created across the bolometer. The change in voltage can be used to directly measure the radiation.
Other bolometers also use voltage differences to measure radiation, but they need an external power source to generate the initial current. Because the graphene bolometer generates its own current under the influence of the radiation, it is much simpler than other bolometers. The piece of graphene inside the new bolometer is very small so the new bolometer is very fast because it is quickly heated by the radiation being measured.
The new bolometer can measure radiation up to temperatures of two hundred degrees Celsius. There have been other attempts to create graphene-based bolometers, but they used two layers of graphene which makes manufacturing more difficult and expensive. Current bolometers can only work at very low temperatures referred to as “cryogenic.”
An additional innovation in the new bolometers is the material used to coat the instrument. The developers use a dielectric polymer called “Parylene” for the coating. Parylene provides a good combination of performance and scalability. Hexagonal boron nitride offers better performance than Parylene but it is hard to obtain and the processed used to apply the coating would be more difficult to scale up.
The prototype for the new bolometer can only detect microwave radiation at ninety-four gigahertz but the researchers will be working to broaden the detection range of frequencies. The developers are also working on a vapor deposition process to produce bigger pieces of graphene which will help scale up production of the new bolometer.
