Tiny balloons are basis of mechanical pixels

Mechanical pixels, formed of tiny, balloon-like structures, could form the basis of future flexible displays in a further development in research into graphene for display applications. This latest development comes from researchers at TU Delft university in the Netherlands and Graphenea, a graphene producer based in Spain.

The pixels, measuring about 13 micrometers wide, do not emit light but are visible in sunlight. They are cut into silicon and covered by a double layer of graphene that is two atoms thick. 

Santiago Cartamil-Bueno, a PhD student at TU Delft, carried out the experimental work initially found the change in colour as an accident while carrying out research into sensors. 

“Seeing the colours under a microscope, I realised that the devices were not homogeneous, which is bad if you are trying to create a sensor,” he noted.  

After observing membrane-covered cavities for a longer period of time, researchers saw that their colours were not constant. Dr Samer Houri, a researcher at TU Delft, led the work. “We observed Newton rings and noticed their colour changing over time,” he said. 

Researchers concluded that the devices were behaving like tiny balloons. In some of them, pressure differences between the cavity and the outside atmosphere caused the graphene membrane to be pressed downwards, towards the bottom of the cavity. By having more pressure inside than outside, the membrane was pushed upwards. 

They determined that the colour change effect came from the interference between light waves reflected from the bottom of the cavity and the membrane on top and adding up or cancelling out different parts of the spectrum of white light. The application of pressure therefore changed the colour of the pixel. 

Researchers hope the development could find uses in displays with low power consumption requirements such as smart watches and ebooks and intend to have a screen prototype in places for the Mobile World Conference 2017 in Barcelona.
The research paper was co-authored by Santiago J. Cartamil-Bueno, Prof. Peter G. Steeneken, Prof. Herre van der Zant and Dr. Samer Houri from TU Delft and researcher Alba Centeno and scientific director Amaia Zurutuza from Graphenea.