A new graphene-based device could yield improved communication systems and thermal imaging technologies.
A team led by researchers from Yale University and the Institute of Photonic Sciences (ICFO) in Spain has created a device that utilizes graphene to detect mid-infrared light and convert it to electrical signals at room temperature.
Mid-infrared radiation at eight to 14 micrometers aids in thermal imaging and enables molecular-specific spectroscopic information to be revealed. Radiation within that range can also propagate in the air without significant loss, indicating that it can be used in free-space communications and remote sensing.
However, conventional room-temperature mid-infrared infrared detectors are usually too slow for large thermal capacity, leading to a long-time constant for heat dissipation.
The highly conductive and atomically thin properties of graphene and its plasmon—a quantum of its collective electron oscillations—enable the new device to operate at room temperature efficiently.
“Graphene is a kind of material that can convert mid-infrared light into plasmons and then subsequently the plasmons can convert into heat,” Qiushi Guo, a PhD student and first author of the study, said in a statement. “What is truly unique about graphene is that the electron temperature rise caused by plasmon decay is much higher than that of other materials.”
Graphene usually cannot be integrated into useable devices because its resistance is insensitive at room temperature, making it difficult to electrically detect mid-infrared light except at extremely cold temperatures.
However, the new device features graphene disk plasmonic resonators that are connected by quasi-one-dimensional nanoribbons, which allows it to effectively detect mid-infrared light at room temperature.
“Our device has artificial nanostructures that convert light into plasmons, and subsequently into electronic heat,” Guo said. “Its resistance is also very sensitive to the temperature rise. Unlike that in graphene sheet, in narrow graphene nanoribbons, electron transport depends strongly on electron’s thermal energy.”
The device also responds quickly to the mid-infrared radiations.
“Existing room-temperature thermal sensors in general have a large heat capacity and well-designed thermal insulation structures,” Guo said. “They usually take milliseconds to heat up. But for graphene, it can be superfast—one nanosecond, or just 1 billionth of a second.”
The speed enable the detector to be usable in high-speed free-space communication applications in mid-infrared, which conventional microbolometers are unable to reach at room temperature.
According to the researchers, the device can be scalable and has a footprint that can be made even smaller than the wavelength of light.
“It offers many new opportunities in mid-infrared photonics,” Fengnian Xia, the Barton L. Weller Associate Professor in Engineering and Science at Yale, said in a statement. “Building a high resolution mid-infrared camera with subwavelength pixels, for example, or to be integrated on photonic integrated circuits to enable mid-infrared spectrometers on a single chip.”
The study was published in Nature Materials.