The wonder material graphene has enabled researchers to create an on-chip visible light source, the world’s smallest light bulb, for the first time, heralding a major breakthrough in photonics.
In an article published on the Nature Nanotechnology web site, a team from the Columbia University School of Engineering, the Seoul National University and the Korea Research Institute of Standards and Science described how they achieved the impossible by attaching small strips of graphene to metal electrodes and allowing currents to pass through them.
The one-atom thick filaments suspended above the chip substrate heated up to 2,500°C, producing bright visible light.
“We've created what is essentially the world's thinnest light bulb,' said James Hone, Professor of Mechanical Engineering at Columbia University and co-author of the study. “This new type of 'broadband' light emitter can be integrated in to chips and will pave the way towards the realisation of atomically thin, flexible and transparent displays and graphene-based on-chip optical communications.”
Creating light in small structures on the surface of a chip is crucial for developing fully integrated photonic circuits that do with light what is now done with electric currents in semiconductor integrated circuits.
The development of such technology has so far been limited precisely by the problem of creating an efficient on-chip light source.
As light bulb filaments need to be extremely hot in order to glow in a visible spectrum, metal wires thin enough to fit on a chip have not been able to withstand such a thermal load. Moreover, the heat transfer from such a filament to its surroundings is extremely efficient at the microscale, which means the heat from the light would actually damage the chip.
The one atom-thick graphene filaments were able to solve both issues, surviving temperatures above 2,500°C as well as protect the surrounding substrate and electrodes from melting. The protection from melting is due to one intriguing property of graphene, which becomes a much poorer conductor of heat the hotter it gets. Eventually, the heat stays confined within a small spot in the centre.
“The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification,” said Young Duck Kim from the Columbia University School of Engineering, the lead author of the study.
The researchers found that the spectrum of the emitted light showed peaks at specific wavelengths, which the team 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,” explained Kim.
The team also demonstrated the scalability of their technique by creating large-scale arrays of chemical vapour-deposited graphene light emitters.
The group is currently working to further characterise the performance of these graphene-based light bulbs, trying to determine how fast they can be turned on and off to create 'bits' for optical communications.
Graphene was first isolated in 2003 by Manchester University researchers Konstantin Novoselov and Andre Geim and has been hailed for its out-of-this-world properties. Two hundred times stronger than steel and allowing electrons to travel across its surface two to three orders of magnitude faster than silicon, graphene is widely believed to be the next big thing in electronics. Geim and Novoselov were awarded the Nobel Prize in Physics for their discovery in 2010.