Scientists have demonstrated for the first time a visible light source using graphene as a filament.
“We have created what is essentially the world’s thinnest light bulb,” said Prof James Hone of Columbia University, a co-author of the paper reporting the results in the journal Nature Nanotechnology today. “This new type of 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.”
Prof Hone and his colleagues from South Korea and the United States attached small strips of graphene to metal electrodes, suspended the strips above a silicon chip and passed a current through the filaments to cause them to heat up.
They used a special form of the same material that Thomas Edison used when he invented the incandescent light bulb. Edison used carbon as a filament for his light bulb. The new light source uses graphene, an allotrope of carbon discovered by Prof Andre Geim’s research group at the University of Manchester, UK.
The researchers then measured the light output of the tiny devices while applying a range of voltages.
“It was exciting to be able to see such bright, visible light from this device with my own eyes,” said co-author Yujin Cho, a doctoral student at the University of Texas at Austin.
By measuring the spectrum of the light emitted from the graphene, the scientists were able to show that it was reaching temperatures above 4,500 degrees Fahrenheit (2,500 degrees Celsius), hot enough to glow brightly.
“The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification,” said lead author Young Duck Kim of Columbia University.
The ability of graphene to achieve such high temperatures without melting the substrate or the metal electrodes is due to another interesting property: as it heats up, graphene becomes a much poorer conductor of heat. This means that the high temperatures stay confined to a small ‘hot spot’ in the center. This increases the energy efficiency of the new light source 1,000 times, as compared with graphene on a solid silicon chip.
Interestingly, the spectrum of the emitted light showed peaks at specific wavelengths, which the researchers discovered was due to interference between the light emitted directly from the graphene and light reflecting off the silicon substrate and passing back through the graphene.
“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,” Kim said.
The scientists also demonstrated the scalability of their technique by constructing large-scale arrays of chemical-vapor-deposited graphene light emitters.
They currently working to further characterize the performance of these devices and to develop techniques for integrating them into flexible substrates.
Young Duck Kim et al. Bright visible light emission from graphene. Nature Nanotechnology, published online June 15, 2015; doi: 10.1038/nnano.2015.118