These rings (20 µm across) have color created by the width of
the slits (see black and white inset). For example, yellow is
produced with slits that are each 90 nm wide. The technique uses
light funneling to catch and trap particular wavelengths.
Researchers at the University of Michigan (U.S.A.) have found a
way to lock in structural color using sub-wavelength structures
(Scientific Reports 3, 1194). If the technique can be developed
further, it could be used with e-readers and other reflective
displays, as well as for sensors and hyperspectral imagers.
Diffraction gratings provide structural color, but the
predominant color changes with viewing angle. Instead of using
gratings on the order of the wavelengths, and on the surface of
the material, the researchers went vertical. Group leader Jay
Guo explains, "Light is funneled into the nanocavity, whose
width is much, much smaller than the wavelength of the light."
Surprisingly the longer wavelengths of light get trapped in
narrower grooves. To demonstrate the