Scientists have developed a new full-color display technology that, once refined, could be a critical component for creating artificial “squid skin”—camouflaging metamaterials that can “see” colors and automatically blend into the background.
The technology uses aluminum nanoparticles to create the vivid red, blue, and green hues found in today’s top-of-the-line LCD televisions and monitors.
The breakthrough is the latest in a string of recent discoveries by a research team working to develop materials that mimic the camouflage abilities of cephalopods—the family of marine creatures that includes squid, octopus, and cuttlefish.
“Our goal is to learn from these amazing animals so that we could create new materials with the same kind of distributed light-sensing and processing abilities that they appear to have in their skins,” says Naomi Halas, a coauthor of the study published in PNAS and director of Rice University’s Laboratory for Nanophotonics.
“We know cephalopods have some of the same proteins in their skin that we have in our retinas, so part of our challenge, as engineers, is to build a material that can ‘see’ light the way their skin sees it, and another challenge is designing systems that can react and display vivid camouflage patterns,” Halas says.
The color display technology delivers bright red, blue, and green hues from five-micron-square pixels that each contains several hundred aluminum nanorods. By varying the length of the nanorods and the spacing between them, researchers Stephan Link and Jana Olson showed they could create pixels that produced dozens of colors, including rich tones of red, green, and blue that are comparable to those found in high-definition LCD displays.
“Aluminum is useful because it’s compatible with microelectronic production methods, but until now the tones produced by plasmonic aluminum nanorods have been muted and washed out,” says Link, associate professor of chemistry at Rice and the lead researcher on the PNAS study. “The key advancement here was to place the nanorods in an ordered array.”
Olson says the array setup allowed her to tune the pixel’s color in two ways, first by varying the length of the nanorods and second by adjusting the length of the spaces between nanorods.
“This arrangement allowed us to narrow the output spectrum to one individual color instead of the typical muted shades that are usually produced by aluminum nanoparticles,” she adds.
Olson’s five-micron-square pixels are about 40 times smaller than the pixels used in commercial LCD displays. To make the pixels, she used aluminum nanorods that each measured about 100 nanometers long by 40 nanometers wide.
She used electron-beam deposition to create arrays—regular arrangements of nanorods—in each pixel.
She was able to fine-tune the color produced by each pixel by using theoretical calculations by Rice physicists Alejandro Manjavacas, a postdoctoral researcher, and Peter Nordlander, professor of physics and astronomy.
“Alejandro created a detailed model of the far-field plasmonic interactions between the nanorods,” Olson says. “That proved very important because we could use that to dial in the colors very precisely.”
Halas and Link say the research team hopes to create an LCD display that uses many of the same components found in today’s displays, including liquid crystals, polarizers and individually addressable pixels. The photonic aluminum arrays would be used in place of the colored dyes that are found in most commercial displays.
Unlike dyes, the arrays won’t fade or bleach after prolonged exposure to light, and the inherent directionality of the nanorods provides another advantage.
“Because the nanorods in each array are aligned in the same direction, our pixels produce polarized light,” he says. “This means we can do away with one polarizer in our setup, and it also gives us an extra knob that we can use to tune the output from these arrays. It could be useful in a number of ways.”
They hope to further develop the display technology and eventually to combine it with other new technologies that the squid skin team has developed both for sensing light and for displaying patterns on large polymer sheets.
For example, Halas and colleagues published a study in Advanced Materials in August about an aluminum-based CMOS-compatible photodetector technology for color sensing. In addition, University of Illinois at Urbana-Champaign co-principal investigator John Rogers and colleagues published a proof-of-concept study in PNAS in August about new methods for creating flexible black-and-white polymer displays that can change color to match their surroundings.
“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,” Halas explains.
The Department of Defense through the Office of Naval Research’s Basic Research Challenge program and the Welch Foundation funded the project.
Source: Rice University