World's smallest pixels may help create building-sized flexible displays

Scientists have created the world's smallest pixels, by trapping particles of light under tiny rocks of gold, that could be used for new types of large-scale flexible displays, big enough to cover entire buildings.

The colour pixels, developed by scientists from the University of Cambridge in the UK, are compatible with roll-to-roll fabrication on flexible plastic films, dramatically reducing their production cost. It has been a long-held dream to mimic the colour-changing skin of octopus or squid, allowing people or objects to disappear into the natural background.

However, making large-area flexible display screens is still prohibitively expensive because they are constructed from highly precise multiple layers. According to the research developed in the journal Science Advances, at the centre of the pixels is a tiny particle of gold a few billionths of a metre across. The grain sits on top of a reflective surface, trapping light in the gap in between. Surrounding each grain is a thin sticky coating which changes chemically when electrically switched, causing the pixel to change colour across the spectrum. "These are not the normal tools of nanotechnology, but this sort of radical approach is needed to make sustainable technologies feasible," said Jeremy J Baumberg, a professor at University of Cambridge, who led the research. "The strange physics of light on the nanoscale allows it to be switched, even if less than a tenth of the film is coated with our active pixels," Baumberg said in a statement. "That's because the apparent size of each pixel for light is many times larger than their physical area when using these resonant gold architectures," he said.

The pixels could enable a host of new application possibilities such as building-sized display screens, architecture which can switch off solar heat load, active camouflage clothing and coatings, as well as tiny indicators for coming internet-of-things devices. The team of scientists, from different disciplines including physics, chemistry and manufacturing, made the pixels by coating vats of golden grains with an active polymer called polyaniline and then spraying them onto flexible mirror-coated plastic, to dramatically drive down production cost. The pixels are the smallest yet created, a million times smaller than typical smartphone pixels. They can be seen in bright sunlight and because they do not need constant power to keep their set colour, have an energy performance that make large areas feasible and sustainable. "We started by washing them over aluminised food packets, but then found aerosol spraying is faster," said Hyeon-Ho Jeong from Cambridge. The team is currently working at improving the colour range and are looking for partners to develop the technology further.