Researchers at the Center for Nanophysics and Advanced Materials at the University of Maryland have developed a new type of thermal electron radiant calorimeter. This infrared photodetector can be widely used in the field of safety imaging technology such as long-range detection of biological and chemical weapons, airport security scanners And promote research on the structure of the universe.
Scientists developed this bolometer using double-layer graphene. Graphene has a completely zero energy consumption band gap, so it can absorb photons in any form of energy, especially photons with extremely low energy, such as terahertz or infrared and submillimeter waves. The so-called photonic band gap means that waves in a certain frequency range cannot propagate in this periodic structure, that is, there is a "forbidden band" in this structure itself. The photonic band gap structure can make electromagnetic waves in certain wave bands completely unable to propagate in it, so a band gap is formed in the frequency spectrum.
The other characteristic of graphene also makes it very suitable as a photon absorber: electrons that absorb energy can still maintain their own high efficiency, and will not lose energy due to the vibration of material atoms. At the same time, this characteristic also makes graphene have extremely low resistance. The researchers designed a thermoelectron bolometer based on these two characteristics of graphene. It can work by measuring the change in resistance. This change is caused by the heat of the electron after it absorbs light.
Generally speaking, the resistance of graphene is hardly affected by temperature, and it is not suitable for bolometers. Therefore, the researchers adopted a special technique: when the double-layer graphene is exposed to an electric field, it has a moderate band gap, which can not only link the resistance and temperature, but also maintain its ability to absorb low-energy infrared photons .
The researchers found that at 5 degrees Kelvin, the new bolometer can achieve the same sensitivity as the existing bolometer, but the speed can be increased by more than 1,000 times. They speculate that it can surpass all current detection technologies at lower temperatures.
The new device is particularly promising as a fast, sensitive and low-noise submillimeter wave detector. Sub-millimeter wave photons are emitted by relatively cool interstellar molecules, so they are difficult to detect. By observing these interstellar molecular clouds, astronomers can study the early stages of star and galaxy formation. Sensitive submillimeter wave detectors can help build new observatories and determine the redshift and mass of very distant young galaxies, thus advancing research on the development of dark energy and the structure of the universe.
Although some challenges still exist, for example, the double-layer graphene can only absorb a small part of the incident light, which makes the new bolometer have a higher resistance than similar devices using other materials, making it difficult to normalize at high frequencies. Working, but the researchers say they are working hard to improve their design to overcome the above difficulties, and they also have great confidence in the bright future of graphene as a photoelectric detection material.
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