Structural Colors - Engineered Biomimicry - page 283

to the ridge spacing on the Morpho wing. Such
arrays were produced on large substrates and
they displayed the wavelength range and the
brilliant sheen of the Morpho blue [106] . The top
half of Figure 11.20 a shows the scanning electron
micrograph of the parallel ridges on a scale of a
Morpho wing, and the bottom half of the same
figure has a similar micrograph of an array of
953-nm-diameter polystyrene spheres on a glass
slide. An artificial wing was produced as a col-
lage of photographs of the polystyrene-sphere
array of Figure 11.20 a, followed by image pro-
cessing to match the real wing's shape and size.
As shown in Figure 11.20 b, the artificial wing
displayed iridescent blue color with a brilliance
competing with that of a real Morpho wing.
However, this bioinspired attempt was success-
ful in only partially reproducing the Morpho 's
beauty. Due to the symmetry of the hexagonal
structure and the different textured surfaces, the
artificial wing displays shades of iridescent blue
(appearing more like a speckle pattern), but it
does not reproduce the color uniformity over
a wide range of viewing angles, so characteris-
tic of the Morpho blue. Although precise tuning

of the delicate blue sheen of the Morpho wing
is really challenging, this attractive approach
could be implemented to create new iridescent
materials for arts, textiles, cosmetics, and paints.
The elucidation of the physical mechanisms
for the Morpho blue [27] opened the horizons for
its successful biomimetic reproduction. Saito
and colleagues dry-etched a substrate using the
electron-beam technique to reproduce the Mor-
pho blue [28, 29, 87] . Parallel ridges, each com-
prising a large number of parallel pillars or tips,
were etched, with the ridge width and the inter-
ridge separation the same as those in the scales
of a wing. The pillar heights were chosen ran-
domly, to mimic the uneven heights of ridges in
the Morpho wing. The fabricated substrate
resembles the wing in reflectance, color, band-
width, angular dependence, and chromatic
anisotropy.
Neither of the two ways ends up mimicking
the structure of the Morpho wing itself but only
the collaboration between regularity and irregu-
larity discussed in Section 11.4.3. Using a com-
pletely different approach, Watanabe et al. [88]
successfully reproduced not only the color

FIGURE 11.20 (a) SEM showing (top area of image) parallel ridges on a scale of a Morpho wing and (bottom of image)
an array of polystyrene particles on a glass slide. (b) Comparison between a Morpho stoffeli wing (left) and an artificial wing
constructed from 953-nm-diameter polystyrene spheres on a glass slide (right). The incidence and the viewing angles are
about 60° and 90°, respectively, and the illumination is from the left of the figure [106] . Courtesy of Kuniaki Nagayama
(National Institute for Physiological Sciences, Japan). Reproduced with permission of © SYMMETRION.