By using bilayer Researchers at the Center for Nanophysics and Advanced Materials of the University of Maryland have developed a new type of hot electron bolometer, a sensitive detector of infrared light, that can be used in a huge range of applications from detection of chemical and biochemical weapons from a distance and use in security imaging technologies such as airport body scanners, to chemical analysis in the laboratory and studying the structure of the universe through improved telescopes.
The UMD researchers, led by Research Associate Jun Yan and Professors Michael Fuhrer and Dennis Drew, developed the bolometer using bilayer graphene–two atomic-thickness sheets of carbon. Due to graphene’s unique properties, the bolometer is expected to be sensitive to a very broad range of light energies, ranging from terahertz frequencies or submillimeter waves through the infrared to visible light.
The graphene hot-electron bolometer is particularly promising as a fast, sensitive, and low-noise detector of submillimeter waves, which are particularly difficult to detect. Because these photons are emitted by relatively cool interstellar molecules, submillimeter astronomy studies the early stages of formation of stars and galaxies by observing these interstellar clouds of molecules. Sensitive detectors of submillimeter waves are being sought for new observatories that will determine the redshifts and masses of very distant young galaxies and enable studies of dark energy and the development of structure in the universe.
The Maryland team’s findings are published in the June 3 issue of Nature Nanotechnology.
Graphene, a single-
Normally, graphene’s resistance is almost independent of temperature, unsuitable for a bolometer. So the Maryland researchers used a special trick: when bilayer graphene is exposed to an electric field it has a small band gap, large enough that its resistance becomes strongly temperature dependent, but small enough to maintain its ability to absorb low-energy infrared photons.
The researchers found that their bilayer graphene hot-electron bolometer operating at a temperature of 5 Kelvin had comparable sensitivity to existing bolometers operating at similar temperatures, but was more than a thousand times faster. They extrapolated the performance of the graphene bolometer to lower temperature and found that it may beat all existing technologies.
Some challenges remain. The bilayer graphene bolometer has a higher electrical resistance than similar devices using other materials which may make it difficult to use at high frequencies. Additionally, bilayer graphene absorbs only a few percent of incident light. But the Maryland researchers are working on ways to get around these difficulties with new device designs, and are confident that a graphene has a bright future as a photodetecting material.
Reference: “Dual-gated bilayer graphene hot-electron bolometer” by Jun Yan, M-H. Kim, J. A. Elle, A. B. Sushkov, G. S. Jenkins, H. M. Milchberg, M. S. Fuhrer and H. D. Drew, 3 June 2012, Nature Nanotechnology.
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