Graphenea, the Spain-based graphene producer, has teamed up with scientists from the Delft University of Technology in the Netherlands to design graphene-based "mechanical pixels" that could, among other applications, be someday used as colored pixels in e-readers and other low-powered screens.

In these "graphene balloons", a double layer of graphene (two atoms thick) is deposited on top of circular indents cut into silicon. The graphene membranes enclose air inside the cavities, and the position of the membranes can be changed by applying a pressure difference between the inside and the outside. When the membranes are closer to the silicon they appear blue; when the membranes are pushed away they appear red.

The new method uses simple optical interference measured under a modified microscope to resolve the deflection of graphene membranes. The deflection is measured by looking at the optical interference between the light reflected off the drum and a silicon substrate. A simple fitting algorithm is applied to extract the exact deflection at the center of the drum.

What causes the color change effect is the interference between light waves reflected from the bottom of the cavity and the membrane on top. These reflected waves interfere constructively or destructively depending on the position of the membrane – either adding up or cancelling out different parts of the spectrum of white light. This interference enhances or reduces certain colors in the reflected light.



According to the team, "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". This interferometry modulation is the technology already used in some colored e-reader displays and smartwatches. 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 device's performance could get a major 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.

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