Graphene In The Spotlight Again With World’s Thinnest Lightbulb

For the first time, scientists have demonstrated an “on-chip” white light source using graphene. Published this week in Nature Nanotechnology, this atomically thin lightbulb opens the door to ultra-thin, transparent and flexible displays; picture a smartphone that you can wrap around your wrist like a bracelet, t-shirts with integrated computers, or Google Glass-style eyewear that is indistinguishable from regular glasses. Not only that, but this new light source also paves the way to integrated photonic circuits, one of the most exciting ways to dramatically increase computing speeds.

Graphene light source: taking adavantage of graphene's unique thermal properties allows for the first on-chip visible light source. Image screenshot from video below.Graphene light source: taking adavantage of graphene's unique thermal properties allows for the first on-chip visible light source. Image screenshot from video below.

To create the light source, the Columbia University Engineering led team suspended a single sheet of graphene between two metal electrodes above a silicon substrate. In analogy to a typical incandescent bulb, the graphene acts as the filament. As in a standard bulb, a very high current was then passed through the graphene causing it to heat up and emit visible light. While the principle seems simple, there is a good reason why an on-chip light source such as this has only just been demonstrated for the first time. In order to produce light in the visible region of the spectrum, lightbulb filaments must be extremely hot – on the order of thousands of degrees Celsius. While this level of heat is manageable for the large wires of a lightbulb you might find on your desk lamp, it simply melts the microscale wires used in tiny computer chips, as well as damaging the other surrounding components of the chips. Graphene turns out to be a material uniquely suited to solving this problem.

Upon passing of a strong current, the graphene sheet heats to a measured 2500 °C and emits light bright enough to be visible to the naked eye! A remarkable feat for a light source that would be dwarfed by a human hair. There are two distinctive aspects of graphene that make this possible. The first is its transparency, a feature not possessed by any other filament material. The researchers discovered that the broadband nature of the emitted light was partially due to light reflecting off the silicon substrate and passing back and forth through the graphene. This gave them the idea that the emitted wavelengths could actually be tuned by changing the distance between the graphene and silicon allowing unparalleled control over the emission. The second key property of graphene is that as it heats up, its ability to conduct heat actually diminishes. This leads to the formation of a super “hot spot” in the center of the graphene filament and prevents melting of the metal electrodes at either end. Indeed, the researchers reported that they were able to heat the graphene to “half the temperature of the sun”.

While the development of an on-chip light source is a significant breakthrough in itself, the researchers involved are already dreaming up a multitude of applications to take advantage of graphene’s exceptional thermal properties. For example, Prof. James Hone suggests “micro-hotplates that can be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.” With each new development it becomes clear we have only just scratched the surface of graphene’s potential technological applications.

Via Columbia University, Science Daily and Nature Nanotechnology.