Anti-Reflecting Nanostructures - Biomimetic Architectures by Plasma Processing - page 36

their guiding principles, to predict a logical trend for future research
in this field.

2.1 Introduction

The 'colourful' nature around us has always fascinated the literary
world as much as it has baffled the scientists. The nature's 'colour'
is typically judged by our sense of 'seeing', relies on the science
beneath the interactions of light with an optical surface.
When light is incident on an optical surface, adsorption,
reflection, transmittance, diffraction, interference, scattering and
emission occur at each interface, resulting in 'colour' production,
'glazing' or 'dull' appearance of the observed surface. For instance,
The structural colour produced on soap bubble surface and
that of peacock's tail feather have been attributed to the optical
interference, the colour of sky to Rayleigh scattering and the rainbow
to diffraction phenomena [1]. Practical implementation of nature's
optical strategy into man-made systems requires studying the
ways to control light when it leaves a surface so as to gauge its anti-
reflecting properties. For example, a 'non-motion structural' green
colour in the peacock's feather (interference effects) appears such
due to its anti-reflecting property to other non-green wavelengths
[2]. Such physical colours are common in nature and can be found in
the butterfly wings, the cuticle of arthropods such as beetle, feathers
of peacock or hummingbird, Indigo snake skin, or crystals such as
Opal [1,3].
Morphological studies on a range of certain biological species
mentioned above have revealed a strange commonality [4], that is,
the natural coloured surfaces possess nicely ordered micro- or even
nano-structures (Fig. 2.1) as a special way of imparting roughness to
achieve selective optical property. A relevant example is the wings of
butterflies that exploit submicron scale photonic structures to bring
about the metallic appearance and iridescence [3,5]. In iridescent
blue

butterflies (Fig. 2.1a), their ultralong-range
visibility of up to half a mile relies on these submicron photonic
structures formed by discrete multi-layer of cuticle and air
(Fig. 2.1b,c).
The one that is most pertinent to this chapter are the eyes of
certain moths and butterflies [6-10] that benefit from the micro-

Morpho rhetenor