A team of Dutch scientists have used color changing bubbles of graphene to create a pixel.
Researchers from Delft Univeristy of Technology have found yet another use for graphene, the mono-atomic structure of carbon often cited as a wonder-material: It may one day power the displays of the future. The scientists have managed to create ‘bubbles’ of graphene which change color as they’re put under tension. These ‘mechanical pixels’ could one day replace conventional LED technology, with the potential of producing screens more durable, flexible and energy efficient. The technology is still very much in its infancy however, and the researchers warn that any assumptions about the pixels’ practical applications are unreliable at this point.
The discovery was made during an experiment involving silicon oxide coated in graphene. The surface of the silicone sample was covered in cavities about ten times the thickness of a human hair, and the graphene layer was stretched across these holes like a drum. The scientists noticed that the color reflecting off of the holes would change depending on the pressure of the test chamber. Altering the pressure would flex the graphene layer, changing how light refracted through it and thus resulting in a different hue.
Schematic of the experimental setup, with images of the memberanes under tension.
“Graphene in principle is transparent; it’s so thin that light doesn’t get reflected,” says researcher Santiago Cartamil-Bueno. “But we were using a double layer of graphene, and that reflects more.” When the graphene layer flexes, it changes how far light has to travel beyond the graphene before it hits the back wall of the cavity. This in turn changes which part of the light spectrum is absorbed, and as a result, when the light reflects back out of the cavity, it has a different color. This same principle is used in Qualcomm’s Mirasol technology, where thin membranes are stretched using electrostatics. Such displays are very energy efficient, and like E-ink, do not require any additional power to maintain color after they’ve been set.
The difficulties facing a potential graphene-bubble screen are many. For one, the bubbles are so small that hundreds of thousands would be required to create even a small screen. In addition, the pixels tend to create a rainbow-effect since some parts of the membrane flex more than other parts – the scientists have yet to observe any pure colors like solid blue or green during their research. The next step for the team is to figure out how to control an individual graphene bubble with precision. One idea is to do it electrostaticallly, just like with the Mirasol screens.
source: Delft University of Technology