According to researchers from the Cambridge Graphene Centre, graphene can be harnessed into a sensor that could be used for sensitive security screening to detect explosives and other hazardous substances.
Combining the single-atom-thick carbon with pyroelectric materials, which generate electric fields when heated or cooled, the team has produced a sensor that can detect temperature changes down to a few tens of µK.
The research team, as part of the Graphene Flagship, described devices based on pyroelectric substrates, on to which a graphene layer is deposited. On top of this a type of electrode known as a ‘floating gate’ is placed, which concentrates the temperature change-induced electric field produced by the substrate on to the graphene. This changes the electrical resistance of the material.
Devices that measure changes in resistance due to heating are known as bolometers, and the team claims that the combination of pyroelectricity and bolometer activity means that these sensors could be used as pixels in a high-resolution thermal imaging camera.
One particular advantage of using graphene in this system is that it acts as a built-in amplifier for the pyroelectric signal from the substrate.
Dr Alan Colli, co-author of the work, said: “We can build the amplifier directly on the pyroelectric material. So, all the charge that it develops goes to the amplifier. There is nothing lost along the way.”
The electrical conductivity of the graphene also helps with integrating the sensor with the external readout integrated circuit, Colli added, ensuring that the sensor signal is transmitted as efficiently as possible.
The temperature change detected by the sensor is around 1,000 times smaller than that induced by a human hand placed in close proximity. This sensitivity means that the sensor can be used for spectroscopy, detecting the narrow bands of the infrared spectrum that are absorbed or emitted by specific chemical groups.
Colli said: “With a higher sensitivity detector, you can restrict the band and still form an image just by using photons in a very narrow spectral range, and you can do multi-spectral IR imaging. This can be useful while looking for explosives, hazardous substances, or anything of the sort,”
The paper is published in Nature Communications.