Graphene-based light detector operates in the THz range

Utilising the special properties of graphene, the prototype device is claimed to be more than a million times faster than existing detectors in the terahertz range. It's also less bulky, considerably cheaper to produce and able to work at room temperature. Lead researcher Xinghan Cai believes the prototype "could find applications in emerging terahertz fields such as mobile communications, medical imaging, chemical sensing, night vision and security". To create the detector, Cai and his team made use of a principle called the hot-electron photothermoelectric effect, whereby graphene's electrons are able to absorb light and retain the resultant energy. "The concept behind the detector is simple," noted Professor Dennis Drew. "Light is absorbed by the electrons in graphene, which heat up but don't lose their energy easily. So they remain hot while the carbon atomic lattice remains cold. These heated electrons escape the graphene through electrical leads, much like steam escaping a tea kettle." The prototype uses two electrical leads made of different metals, which conduct electrons at different rates. Because of this conductivity difference, more electrons escape through one than the other, producing an electrical signal. This electrical signal detects the presence of terahertz waves beneath the surface of materials that appear opaque to the human eye – or even X-rays. "You cannot see through your skin, for example, and an X-ray goes right through the skin to the bone, missing the layers just beneath the skin's surface entirely," Prof Drew said. "Terahertz waves see the in-between. The speed and sensitivity of the room temperature detector presented in this research opens the door to future discoveries in this in-between zone."