Researchers at the University of Central Florida (UCF) have devised a strategy for uncooled, tunable, multispectral infrared (IR) detection. The team showed that room-temperature photodetection using 2D monolayer graphene is possible through the interplay of tunable, enhanced IR absorption induced by localized Dirac plasmonic excitations, graphene mobility engineering, and excitation of asymmetric hot carriers and the resulting electronic photothermoelectric effect. The key to developing the new highly sensitive, but uncooled IR detector was engineering the 2D nanomaterial graphene into a material that could carry an electric current. The researchers achieved this by designing the material to be asymmetric, so that the temperature difference created from absorbed light hitting the different parts of the material caused electrons to flow from one side to another, thus creating a voltage. The asymmetric graphene channel design facilitates the generation of a high-temperature gradient, which the team said is critical to the detector’s photoresponse. Debashis Chanda, an associate professor at the University of Central Florida’s NanoScience Technology Center, demonstrates improved infrared night-vision capabilities. Courtesy of Karen Norum, University of Central Florida Office of Research. The detector’s ability to capture an image was tested one pixel at a time. The researchers identified various processes contributing to the photoresponse, which indicated that the detector’s fast, high responsivity could be attributed to the photothermoelectric effect. The UCF team worked with wavelengths extending to about 16,000 nm to build a detector that can discern different wavelengths within the invisible IR domain and select different objects emitting different IR wavelengths. “With the infrared detector we’ve developed, you can extract more information from the object you’re looking at in the dark,” professor Debashis Chanda said. The researchers said that current night-vision cameras can’t isolate different objects based on their distinct IR wavelengths and instead lump the wavelengths all together, so that what may be several separate objects are seen as one object through the IR lens. “Say you’re looking at somebody at night through night-vision goggles. You’re looking at his infrared signature, which is coming all over his body. He may have a hidden weapon that emits a different wavelength of infrared light, but you cannot see that even with a presently available, expensive, cryogenically cooled camera,” Chanda said. “This is one of the first demonstrations of actually dynamically tuning the spectral response of the detector or, in other words, selecting what infrared ‘color’ you want to see,” Chanda said. The UCF detector can assign additional infrared “colors” to represent items that reflect different wavelengths of IR light, in addition to the standard colors seen in night-vision cameras. The frequency-tunable graphene detectors proposed by the UCF team offer spectroscopic detection and could be step toward dynamic multispectral imaging in the IR. The ability to enhance night-vision capabilities could improve what scientists can see in space, in chemical and biological disaster areas, and on the battlefield. The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-11458-5).