Team of researchers from Columbia University, Seoul National University and Korea Research Institute of Standards and Science have created the thinnest light bulb in the world. And this record is here to stay – it is unlikely that anyone will ever beat this record, as scientists have used graphene, which is one atom thick.
Even though experiments like this are still at their dawn, scientists say that they will pave the way towards the realization of atomically thin, flexible, and transparent displays, and graphene-based on-chip optical communications.
Scientists reached this achievement by attaching small strips of graphene to metal electrodes, suspending the strips above the substrate, and passing a current through the filaments to cause them to heat up. This experiment was needed, because scientists are trying to create fully integrated “photonic” circuits that do with light what is now done with electric currents in semiconductor integrated circuits. Because graphene is transparent, light reflects from the substrate and travels back through it, which allows scientists to tune the emission spectrum by changing the distance between graphene filament and the substrate.
Different scientists have taken different approaches to this problem, but no one up until now has managed to put the incandescent light bulb onto a chip. This was difficult, because filaments in the light bulb must reach thousands of degrees Celsius in order to glow in the visible range, but micro-scale metal wires cannot withstand such temperatures. Extremely high temperatures may damage the surrounding chip as well. However, interesting properties of grapheme makes it a perfect filament for such a small light source.
During the experiments graphene was reaching temperatures of above 2500 degrees Celsius, hot enough to glow brightly. In fact, so brightly that light was visible even to the naked eye, without any additional magnification. Graphene is capable of reaching such high temperatures needed for glowing, but does not melt the substrate or the metal electrodes, because of one curious property.
At higher temperatures grapheme is a much poorer conductor of heat, which means that the high temperatures stay confined to a small “hot spot” in the centre. Myung-Ho Bae, co-author of the study, said that “At the highest temperatures, the electron temperature is much higher than that of acoustic vibrational modes of the graphene lattice, so that less energy is needed to attain temperatures needed for visible light emission”. These properties allow scientists heating graphene up to half of the temperature of the sun, and improve efficiency 1000 times, as compared to graphene on a solid substrate.
This method of lighting up grapheme is scalable and larger parts could be made as well. Scientists point out that they are working with the same material that Thomas Edison used when he invented the incandescent light bulb. Originally he used carbon as a filament for his light bulb and now scientists are using pure form of it – graphene.
However, it is just the beginning of the research, even though the achievement is quite significant in itself. Now scientists are working to further characterize the performance of these devices. They will try to figure out how fast they can be turned on and off to create “bits” for optical communications and to develop techniques for integrating them into flexible substrates.
This discovery may lead to a variety of different inventions and scientific advancements, not just for flexible and transparent displays. Scientists hope to create micro-hotplates, which could be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.
Graphene is amazing material and science is still trying to figure out all possible uses for it. World’s thinnest light bulb is unexpected yet significant achievement that may leave to other important discoveries.