ANN ARBOR, Mich., Feb. 6, 2013 — Peacock feathers have a beautiful iridescence — a sheen that shifts color depending on a viewer’s perspective. But, for engineers trying to reproduce the birds’ unique color mechanism to develop high-resolution, reflective color display screens, the task has proved difficult.
A study from the University of Michigan has revealed a simple way to lock in so-called structural color, which is created from texture rather than from chemicals.
Precisely arranged hairline grooves reflect light of certain wavelengths in a peacock’s mother-of-pearl tail, resulting in colors that appear different depending on the movement of the animal or the observer. Attempting to imitate this system without the rainbow effect has been a leading approach to next-generation reflective display development.
Precisely arranged hairline grooves reflect light of certain wavelengths in a peacock’s tail, resulting in brilliant colors that look different depending on the movement of the animal or the observer. Imitating this system — minus the rainbow effect — could lead to advanced color e-books and electronic paper, new research out of the University of Michigan reveals. Courtesy of ©iStockphoto.com/AndreasReh.
The UM findings could lead to advanced color e-books and electronic paper as well as to other color reflective screens that don’t need their own light to be readable. Backlit screens on laptops, tablet computers, smartphones and TVs require much more power than reflective displays. Other applications of this new technology could include data storage, cryptography and counterfeit prevention of documents.
The researchers harnessed the ability of light to funnel into nanoscale metallic grooves and become trapped inside. Using this approach, they found that the reflected hues stay true regardless of the viewer’s angle.
“That’s the magic part of the work,” said Jay Guo, a professor of electrical engineering and computer science. “Light is funneled into the nanocavity, whose width is much, much smaller than the wavelength of the light. And that’s how we can achieve color with resolution beyond the diffraction limit. Also counterintuitive is that longer wavlength light gets trapped in narrower grooves.”
Scientists have long thought that the diffraction limit was the smallest point on which you could focus a beam of light. Other research groups have broken this limit as well, but the UM team did so with a simpler technique that also produces stable and relatively easy-to-make color, Guo said.
“Each individual groove — much smaller than the light wavelength — is sufficient to do this function,” he said. “In a sense, only the green light can fit into the nanogroove of a certain size.”
The researchers determined what size slit would catch what color light. Using the standard print industry framework of cyan, magenta and yellow, they concluded that, at a groove depth of 170 nm and spacing of 180 nm, a slit 40 nm wide can trap red light and reflect a cyan color. A slit 60 nm wide can trap green and make magenta, and one 90 nm wide traps blue and produces yellow.
“With this reflective color, you could view the display in sunlight,” Guo said. “It’s very similar to color print.”
White paper is a reflective surface, and to create color, printers arrange pixels of cyan, magenta and yellow in such a way that they appear to our eyes as the colors of the spectrum. An electronic display using Guo’s approach would work in a similar manner.
To demonstrate their device, the researchers etched nanoscale grooves in a plate of glass with the technique commonly used to make integrated circuits. The plate was then coated with a thin layer of silver. When light hits the grooved surface, its electric component creates a polarization charge at the metal slit surface. This boosts the local electric field near the slit, which pulls in a particular wavelength of light.
The device currently creates only static pictures, but the researchers hope to develop a moving picture version in the near future.
The study appeared in Scientific Reports
For more information, visit: www.umich.edu