Rice researchers tune the color output of each array both by varying the length of the nanorods and by adjusting the length of the spaces between nanorods. Credit: J. Olson/Rice University
Rice researchers tune the color output of each array both by varying the length of the nanorods and by adjusting the length of the spaces between nanorods. Credit: J. Olson/Rice University

Researchers from Rice University in the US have developed full color display technology using aluminum nanorods that are able to identify colors and blend automatically into the background. The camouflage approach, based on metamaterials that can mimic the ability of how cephalopods camouflage themselves, offers a vivid color display of red, green and blue hues found in current high-definition LCD televisions and monitors.

The study, as reported in the Proceedings of the National Academy of Sciences (PNAS) [Olson et al. Proc. Natl. Acad. Sci. U.S.A. (2014) DOI: 10.1073/pnas.1415970111], extended the team’s work into the development of artificial “squid skin” with similar distributed light-sensing and processing abilities in an attempt to create materials that can “see” light the way their skin sees it, and to design systems that can react and display bright camouflage patterns.

The new technology offers vivid hues from five-micron-square pixels that are around 40 times smaller than normally used in commercial LCD displays, with each pixel containing several hundred aluminum nanorods. With the nanorods being only 100 nanometers long by 40 nanometers wide, electron-beam deposition produces their regular arrangement for each pixel. When the length or the spacing between the nanorods is altered, the array set-up allowed them to tune the pixels to create a range of colors.

Using a detailed model of the far-field plasmonic interactions between the nanorods, it was possible to fine-tune the color from each pixel very specifically using theoretical calculations. The ordered array also meant they could reduce the output spectrum to one individual color instead of the usual muted shades produced by aluminum nanoparticles.

Such photonic aluminum arrays could replace the colored dyes usually found in commercial displays, and has the advantage that they do not fade or bleach after prolonged exposure to light. With the nanorods in each array being aligned in the same direction, the pixels produce polarized light so that it was possible to omit one polarizer, thus providing greater opportunity for tuning the output from these arrays.

The scientists are now looking to further develop the display approach, as well as to combine it with other new technologies for sensing light and to display patterns on large polymer sheets. As co-author Naomi Halas said “We hope to eventually bring all of these technologies together to create a new material that can sense light in full color and react with full-color camouflage displays”.