Researchers from Delft University of Technology in the Netherlands have discovered what could one day be a new type of display technology: bubbles of graphene that change color as they expand and contract. Scientists say that these ‘mechanical pixels’ could eventually make screens that are more flexible, durable, and energy efficient than current LED technology. They caution, though, that the work is very much in its infancy; whether these graphene bubbles can make displays of equivalent quality, or be scaled up for mass production, remains to be seen.
The discovery was made by researchers working with panels of silicon oxide covered with graphene — sheets of pure carbon just a single atom thick. (Graphene is that wonder material you probably heard of years ago, but scientists are still working on commercial applications for it.) The silicon is pockmarked with holes about ten times the width of a human hair, leaving the graphene stretched across these tiny cavities like a drum. When working with these samples, scientists noticed that the bubbles of graphene changed color depending on the pressure inside the cavities. When the pressure shifts, the bubbles became concave or convex, changing how light refracted through them and creating different colors.
A technical diagram showing how layers of graphene are stretched over silicon oxide cavities.
“Graphene in principle is transparent; it’s so thin that light doesn’t get reflected,” researcher Santiago Cartamil Bueno told The Verge. “But we were using a double layer of graphene, and that reflects more.” As the bubbles of graphene inflate or deflate, light has to travel different amounts before it hits the back of the silicon cavity. This changes which part of the light spectrum is absorbed, and which part is reflected back, altering the colors of the bubbles. “Depending on the depth of the cavity you have different interference, and from this you get different colors of light,” says Bueno.
This is the same principle used in Qualcomm’s Mirasol technology, which uses reflective membranes controlled using electrostatic. As with E Ink screens, these sorts of display are very energy-efficient, as once an image has been ‘set’ it takes no additional power to maintain it. But, the way they’re made makes backlighting impossible. You can’t read these screens in a dark room, and they look their best in bright sunlight.