The first on-chip visible light source using graphene as a filament has been developed by a team of scientists from Columbia Engineering, Seoul National University (SNU), and Korea Research Institute of Standards and Science (KRISS).

The scientists attached small strips of graphene to metal electrodes, suspended the strips above the silicon substrate, and passed a current through the filaments to cause them to heat up. The study was published in the Advance Online Publication (AOP) on the Nature Nanotechnology website.

“We’ve created what is essentially the world’s thinnest light bulb,” says James Hone, Wang Fon-Jen Professor of Mechanical Engineering at Columbia Engineering and coauthor of the study. “This new type of ‘broadband’ [works at near-infrared-to-visible-range wavelengths] 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.”

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. Researchers have developed many approaches to do this, but have not yet been able to put the oldest and simplest artificial light source — the incandescent light bulb — onto a chip.

This is primarily because light bulb filaments must be extremely hot — thousands of degrees Celsius — in order to glow in the visible range and micro-scale metal wires cannot withstand such temperatures. In addition, heat transfer from the hot filament to its surroundings is extremely efficient at the microscale, making such structures impractical and leading to damage of the surrounding chip.



Myung-Ho Bae/KRISS | Bright visible light emission in graphene

By measuring the spectrum of the light emitted from the graphene, the team was able to show that the graphene was reaching temperatures of above 2500 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,” explains Kim, first and co-lead author on the paper.

The ability of graphene to achieve such high temperatures without melting the substrate or the metal electrodes is due to the fact that 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. That makes graphene an ideal material to serve as a nanoscale light emitter.

“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,” Myung-Ho Bae, a senior researcher at KRISS and co-lead author, observes. “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.”

The team also demonstrated the scalability of their technique by realizing large-scale arrays of chemical-vapor-deposited (CVD) graphene light emitters.

Yun Daniel Park, professor in the Department of Physics and Astronomy at Seoul National University and co-lead author, notes that they are working with the same material that Thomas Edison used when he invented the incandescent light bulb: “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.”

The group is currently working to determine how fast the device they can be turned on and off to create bits for optical communications and to develop techniques for integrating them into flexible substrates.

Another potential application is micro-hotplates that can be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.

Scientists at Konkuk University, Sogang University, Sejong University, University of Illinois at Urbana-Champaign, and Stanford University were also involved in the research.

Abstract of Bright visible light emission from graphene