Biomedical Engineering Reference
In-Depth Information
Fig. 7.16
(continued) (
b
) Natural photonic structure,
Papilio blumei
butterfly. (
i
) The bright green
wings of the
P. blumei
butterfly resulted from the mixing of the different
colors
of light from
different regions of the wing scales. (
ii
,
iii
), Optical micrographs (scale bar: 20
m) showing that
the concavities reflect
yellow
and
blue colors
under normal incident light. (
vi
) Scanning electron
micrograph showing that the surface of a wing scale is covered with concavities (diameter
5-
10
m). (
v
) The transverse cross section of concavities consists of 21 alternative cuticle and
air layers with a thickness of 120 nm. Reflectance spectra under normally incident light and
45
ı
incident light, and the overlapping of the spectra confirm the non-iridescent property of the
green wing scales of
P. blumei
(From [
148
]). (
c
) Mimicking by surface structural engineering. (
i
)
Deposition of polystyrene colloids on a gold-coated silicon substrate. (
ii
) Growth of platinum or
gold in the interstices of the colloidal array by electroplating. The metal deposition is terminated
when the thickness of the deposited film equals the microsphere radius. (
iii
) Removal of the
polystyrene spheres from the substrate by ultrasonication in acetone. (
iv
) Sputtering of a thin
carbon film and ALD of a stack of 11 alternating TiO
2
and Al
2
O
3
layers (
arrows
indicate the
precursor gas flow). (
e
,
f
) In a second route, the colloids are molten to cover the cavities with a
homogeneous film, (
v
) which is covered by a TiO
2
-Al
2
O
3
multilayer [
141
](
vi
). (
a
,
b
) Reprinted
with permission from [
30
] © 2012 Wiley-VCH Verlag GmbH & Co. (
c
) Reprinted with permission
from [
172
] ©2010, Nature publishing group