Smallest pixels ever created could light up color-changing buildings



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The color pixels, developed by a team of scientists led by the University of Cambridge, are compatible with roll-to-roll fabrication on flexible plastic films, dramatically reducing their production cost. The results are reported in the journal Science Advances.

It has been a long-held dream to paint the color-changing skin of octopus or squid, allowing people or objects to disappear into the natural background, but making large-area flexible display screens is still prohibitively expensive because they are constructed from highly precise multiple layers.

At the center of the pixels developed by the Cambridge scientists is a tiny particle of gold and few billionths of a meter 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 color across the spectrum.

The team of scientists, from different disciplines including physics, chemistry and manufacturing, made the pixels by 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 color, have an energy performance that makes large areas feasible and sustainable. "We started washing them on aluminized food packets, but then found aerosol spraying is faster," said co-lead author Hyeon-Ho Jeong from Cambridge's Cavendish Laboratory.

"These are not the normal tools of nanotechnology, but this sort of radical approach is needed to make sustainable technologies feasible," said Professor Jeremy J Baumberg of the NanoPhotonics Center at Cambridge's Cavendish Laboratory, who led the research. “The strange physics of light on the nanoscale allow it to be switched, even if less than a tenth of the film is coated with our active pixels. That's because the actual size of each pixel for light is many times larger than their physical area when using these resonant gold architectures.

The pixels could be a host of new applications, 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 is currently working to improve the color range and are looking for partners to develop the technology further.

The research is funded as part of the UK Engineering and Physical Sciences Research Council (EPSRC) investment in the Cambridge NanoPhotonics Center, as well as the European Research Council (ERC) and the China Scholarship Council.

Reference:

Jialong Peng et al. "Scalable electrochromic nanopixels using plasmonics." Science Advances (2019). DOI: 10.1126 / sciadv.aaw2205

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