A prototype graphene photodetector is capable of detecting terahertz frequencies quickly and at room temperature, possibly enabling a new generation of see-through imaging. The device operates on the hot-electron photothermoelectric effect, making it “as sensitive as any existing room-temperature detector in the terahertz range and more than a million times faster,” according to Dr. Michael Fuhrer, a professor of physics at the University of Maryland, College Park, and Monash University in Australia. Conventional detectors must be kept extremely cold, -452 °F. Those that operate at room temperature are slow, bulky and expensive. In the new detector, “Light is absorbed by the electrons in graphene, which heat up but don’t lose their energy easily,” said Dr. Dennis Drew, a Maryland physics professor. “So they remain hot while the carbon atomic lattice remains cold.” Heated electrons escape the graphene through electrical leads. The new prototype uses two electrical leads made of different metals, which conduct electrons at different rates and produce an electrical signal. A top-down view of a prototype broadband, ultrafast graphene photodetector capable of detecting terahertz frequencies at room temperature. Courtesy of Thomas Murphy/University of Maryland. That signal detects the presence of terahertz waves beneath the surface of materials that appear opaque to the human eye. Conventional methods, such as x-rays, image through to the bone, missing the layers just beneath the skin’s surface. Terahertz waves allow such layers to be seen via devices like the prototype detector. The new device “could find applications in emerging terahertz fields such as mobile communications, medical imaging, chemical sensing, night vision and security,” said Xinghan Cai, a Maryland graduate student. The work was funded by the U.S. Office of Naval Research, the National Science Foundation and the Intelligence Advanced Research Projects Activity. The research was published in Nature Nanotechnology (doi: 10.1038/nnano.2014.182). For more information, visit www.umd.edu.