A group of researchers, from Columbia University, Korea Research Institute of Standards and Science (KRISS) and Seoul National University (SNU), has created what is likely the world’s thinnest light bulb, using graphene. A one-atom-thick allotrope of carbon, graphene is known to have a plethora of impressive properties and uses. Although invisible to the naked eye, the contraption, containing tiny strips of graphene affixed to metal electrodes, produces light so bright that it can be easily detected by the unaided eye.
The study, titled “Bright Visible Light Emission from Graphene”, was recently published in Nature Nanotechnology’s Advanced Online Publication (AOP). A crucial step towards the development of fully-equipped nanoscopic photonic circuits, the breakthrough marks the first time that an on-chip light source has been created using graphene. In case of traditional incandescent light bulbs, the filaments heat up to incredibly high temperatures, of several thousand degrees Celsius, at which the risk of damaging the micro-scale circuitry increases manifold. Graphene, on the other hand, exhibits certain remarkable properties, thus making it the ideal alternative. Speaking about the project, James Hone, professor at Columbia’s Mechanical Engineering department, said:
We’ve created what is essentially the world’s thinnest light bulb. This new type of ‘broadband’ light emitter can be integrated into chips and will pave the way towards the realization of atomically thin, flexible, and transparent displays, and graphene-based on-chip optical communications.
Led by postdoctoral researcher, Young Duck Kim, the team built the device by carefully attaching graphene strips to metal electrodes and then, suspending the strips over a specially-designed silicon substrate. According to the scientists, passing electric current through the filaments actually caused the graphene to reach temperatures of around 2,500° C (4,500° F) and in turn produce bright, visible light. Kim said:
The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification… This is only possible because graphene is transparent, unlike any conventional filament, and allows us to tune the emission spectrum by changing the distance to the substrate.
Despite attaining exceptionally high temperatures, the graphene lattice actually manages to protect the substrate as well as the metal electrodes from any significant damage. This is primarily because, at higher temperatures, graphene reportedly becomes a poorer conductor of heat, rendering it incapable of transmitting the heat away from itself. This creates a tiny “hot spot” at the center, which in turn prevents the melting of the surrounding chip and metal wires. Speaking about this unusual ability of the carbon allotrope, Myung-Ho Bae, of KRISS, said:
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 unique thermal properties allow us to heat the suspended graphene up to half of the temperature of the sun, and improve efficiency 1000 times, as compared to graphene on a solid substrate.
According to the researchers, the technology can also be applied in the case of large-scale chemical-vapor-deposited (CVD) graphene light emitters. Currently, the team is working on enhancing the overall efficiency of the contraption, especially with regard to how quickly it can be turned on and off for the purpose of optical communications. Furthermore, they are looking for ways to integrate different types of flexible substrates into the original design. Talking about the potential uses of the technology, Hone notes:
We are just starting to dream about other uses for these structures—for example, as micro-hotplates that can be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.
Interestingly, the research uses the same set of materials that Edison used, some 130 years ago, to develop the first commercial incandescent light bulb. Yun Daniel Park, of the Seoul National University, said:
Edison originally used carbon as a filament for his light bulb and here we are going back to the same element, but using it in its pure form—graphene—and at its ultimate size limit—one atom thick.
Source: Columbia University