© Delft University of Technology
© Delft University of Technology

Graphene colours aid screen pixels

Researchers from the Graphene Flagship have found a new potential application for graphene in mechanical pixels.

By applying a pressure difference across graphene membranes, the perceived colour of the graphene can be shifted continuously from red to blue. This effect could be exploited for use in coloured pixels in e-readers and other low-powered screens.

In graphene balloon devices, 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 and when they are pushed away they appear red.

The colour change effect arises from interference between light waves reflected from the bottom of the cavity and the membrane on top.

Project leader Dr Samer Houri, a researcher at TU Delft, the Netherlands, said: “At the beginning, we did not pay attention to the colours of the membranes because graphene is ‘colourless’ when isolated.

“However, we observed Newton rings and noticed their colour changing over time.”

When the membranes are extremely deformed, their colour is no longer homogeneous, but instead circular rings appear. These rings are called Newton rings in honour of Sir Isaac Newton, who studied them in 1717.

Santiago Cartamil-Bueno, a student at TU Delft, added: “Not only does this provide the colourimetry technique for characterising suspended graphene, which is useful for companies developing graphene mechanical sensors, it also provides a means to implement display technology based on interferometry modulation.”

The research was a collaborative effort from researchers at TU Delft and Graphenea, Spain. The study has recently been published in the journal Nano Letters.