The publication of a paper in a scientific journal is a significant moment for any research group. This was certainly the case when Professor Geoffrey Nash and his team, including undergraduate students Hannah Barnard and Katya Zossimova, succeeded in publishing their paper entitled “Boron nitride encapsulated graphene infrared emitters” in the well-respected and highly competitive scientific journal, Applied Physics Letters. This achievement was made even more impressive by the fact that not only was the paper accepted for publication, but it was also chosen as the “Editor’s Pick of the Week”! The success of the paper has not gone unnoticed; just over a week after the publication of the paper, a press release was posted on the Exeter University website, praising both the paper and the research team. (The press release can be found under the College of Engineering, Maths, and Physical Sciences, and contains a link to the paper itself).
The paper lays out a ground-breaking new method for making infrared emitters, by using sheets of graphene, and boron nitride. Infrared (IR) radiation has a wavelength of roughly 10-5 metres, giving it a slightly higher wavelength than visible light, and meaning that it cannot be seen with the naked eye. However, it is still often produced in a similar way, using incandescent sources that are reminiscent of standard light bulbs. Professor Nash and his team have succeeded in making a device that emits IR radiation, by passing a current through a device made of layers of graphene encapsulated with boron nitride. This is a vast improvement on the current method, as it can emit a broader range of wavelengths, is more efficient, has a longer lifespan, and could be cheaper to manufacture.
Infrared emitters are used in the detection of a wide range of gasses, such as mono-nitrogen oxides (NO, NO2). These gases are highly toxic, yet are produced in copious amounts from power plants, car exhausts, and energy generation plants, making it important to develop accurate detectors. NOx gases absorb light in the infrared region, and so if an IR emitter is used to produce light in this region, and the light is absorbed, it is a sign that the NOx gasses could be present. However, there are some problems with the IR emitters currently in use. These generally use fragile light bulbs, not too dissimilar to the ones used in lamps or on wall lightings, whose filaments break frequently and need replacing. Furthermore, they are slow, and have a limited range of wavelengths over which they can emit.
“At the time that the paper was written, one of the tests had already been running for 1000hrs, without showing signs of breaking”
In order to overcome these problems, significant interest has been placed on the idea of using graphene as a source of IR emission. Made of a single layer of carbon atoms, graphene boasts, amongst other properties, incredible strength, flexibility, and conductivity. As a result of this, it has been used widely across science and engineering, to great effect, on everything from efficient solar panels to durable display screens to lightweight speakers. However, when used to produce an IR emitter, there was a problem; the emitter could only be made to function in a vacuum. In order to solve this problem, Professor Nash and his team used a protective boron nitride sheath to prevent the device from breaking. Using this method, they were able to keep the device stable in air for longer than even a light bulb-based device. At the time that the paper was written, one of the tests had already been running for 1000hrs, without showing signs of breaking. Furthermore, the resulting device is believed to be stronger, more sustainable, and more cost effective to manufacture than existing devices.
Although Professor Nash and his team have been focusing on the uses of IR emitters for gas detection, there is a seemingly endless range of uses for IR emitters, from reflectors for solar cells, and manufacturing textiles, to detecting explosive devices! One thing’s for sure; if all goes well, research from the labs of Exeter will soon be making a very significant impact on the world around us.