Nanopixels that are 1 million times smaller than those being used in smartphones have been constructed from gold nanoparticles encapsulated in a conductive polymer shell. The tiny pixels, developed by scientists at the University of Cambridge, could be used to create large-scale flexible displays at lower cost than existing technologies. Key to the nanopixel design is the use of plasmonic metasurfaces. The metasurface is constructed using a bottom-up solution process that controls the plasmonic gaps and fills them with an active medium. Electrochromic gold nanoparticles are coated onto a metallic mirror and encapsulated in a thin polymer coating that changes chemically when electrically switched, causing the pixel to change color across the spectrum. Electrochromic nanoparticle-on-mirror constructs (eNPoMs) formed from gold nanoparticles (Au NPs) encapsulated in a conductive polymer shell. Courtesy of NanoPhotonics Cambridge/Hyeon-Ho Jeong, Jialong Peng. To produce the nanopixels economically, the team coated vats of the gold nanoparticles with an active polymer and then sprayed them onto flexible mirror-coated plastic. “We started by washing them over aluminized food packets, but then found aerosol spraying is faster,” said researcher Hyeon-Ho Jeong. The pixels can be produced using roll-to-roll fabrication on flexible plastic films. The nanopixels show strong scattering colors and are electrically tunable across >100-nm wavelength ranges. Their bistable behavior and ultralow energy consumption offer vivid, uniform, nonfading color that can be tuned at high refresh rates and optical contrast. The scientists said that the nanopixels can scale from the single nanoparticle level to multicentimeter-scale films in subwavelength thickness devices, which are a hundredfold thinner than current displays. Because the nanopixels do not need constant power to keep their set color, they can maintain performance at a level that could make large display areas feasible and sustainable. “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. “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. 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.” In addition to building-size display screens, the nanopixels could enable new application possibilities such as architecture that could switch off solar heat load, active camouflage clothing and coatings, and tiny indicators for Internet of Things devices. The research was published in Science Advances (https://doi.org/10.1126/sciadv.aaw2205).