More pop might be in store for e-readers thanks to colorful graphene balloons

Depending on how the graphene is curved over the cavities, it can be made to display different colors(Credit: Delft University of Technology)

E-ink displays have made the consumption of no-frills digital media like text and cartoons a decidedly low-energy affair, but new research might soon allow for some more decorative elements, too. Scientists have discovered a way to warp graphene membranes to control the color that they display, raising the possibility of using these "mechanical pixels" to add some color to the e-reader mix.

Scientists from the Delft University of Technology in the Netherlands teamed up with Spanish graphene company Graphenea in developing what is described as graphene balloon devices. These consist of tiny slabs of silicon with neat rows of circular cavities throughout, each measuring 10 μm. Two graphene sheets are then laid down on top, which creates an arrangement of suspended graphene membrane circles atop the cavities.

The team discovered that depending on how the graphene curved over these holes, it could be made to display different colors. They manipulated the shape by applying different pressure to the inside and outside of the cavities, and found that when the membranes were sagged inwards and pulled outwards just enough, they began to display what are known as Newton's rings.

These circular rings take their name from Sir Isaac Newton who studied the phenomenon in 1717, and are the result of interference between the light waves bouncing off the bottom of the cavity and the material stretched over the top. Depending on where the membrane cuts through the wave, it will boost certain colors on the spectrum and reduce or cancel out others. In this case, blue resulted when the membrane was close to the silicon underneath and red showed up when the membrane was made to balloon outward.

"Not only does this provide the colorimetry technique for characterizing suspended graphene, which is useful for companies developing graphene mechanical sensors, but it also provides a means to implement display technology based on interferometry modulation," says Cartamil-Bueno, the Ph.D. student at TU Delft who first noticed the changing colors.

This interferometry modulation is the technology already used in some colored e-reader displays and smartwatches, like the Qualcomm Toq from 2013. These types of displays require little energy and use a reflective membrane and a cavity to present individual mechanical pixels, just like the process outlined above, though they use silicon materials.

By using graphene instead, a material that boasts a long list of superior qualities not least of which is an electrical conductivity 1,000 times that of silicon, it could give a device's performance a huge boost, and possibly enable new types of flexible displays. The researchers are now working out a way to manipulate the colors using electricity, and are aiming to have a screen prototype to show off at next year's Mobile World Congress in Barcelona.

The research was published in the journal Nano Letters, while the video below provides an overview of the work (credit: Ana Cartamil).

Source: Delft University of Technology via Phys.org

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