A new graphene-based ultra-thin light detector could change the way we look under the surface of some things.
The prototype of the device, created by researchers at the University of Maryland, uses the special properties of graphene that absorb light to see terahertz waves. These waves are normally invisible to the naked eye. Terahertz waves pass through opaque materials, such as skin and plastic. This makes it possible to see through those materials.
Graphene is a pure form of carbon in an ultra-thin sheet, usually only about one atom thick. However, it is stronger than steel and can conduct both heat and electricity. Its two-dimensional nature gives it special properties when it interacts with light. Because of its unique properties, it is often dubbed a "wonder" material.
In the light-detector prototype, graphene allowed the detector to operate at higher speeds, while still maintaining its sensitivity. This is a breakthrough, as other similar detectors could only work in extremely cold temperatures, close to absolute zero, which is below 452 degrees Fahrenheit. This detector, though, works at room temperature.
The research team worked with a simple concept when building the prototype.
"Light is absorbed by the electrons in the graphene, which heat up, but don't lose their energy easily," says Professor Dennis Drew. "So they remain hot while the carbon atomic lattice remains cold."
The electrons escape from the lattice through two metal electrodes. Because of the detector's construction, more electrons go out of one electrode more than the other, which creates an electrical signal. The electrical signal picks up the terahertz waves beneath the surface of opaque materials.
This research could lead to better imaging of the human body. X-rays look way past the skin and straight to the bone, but this light detector can see that layer just underneath the skin that we're missing. This could lead to medical breakthroughs for an area of the human body we still know little about.
"Terahertz waves see the in-between," writes the researchers. "The speed and sensitivity of the room temperature detector presented in this research opens the door to future discoveries in this in-between zone."
However, the detector has other applications. It could also be used for identifying chemicals in compounds, as well as remote bomb detection and better night vision tools. The technology would also be useful for public transportation security scanning tools, safely looking underneath clothing without invading body privacy.
