Table Of ContentBiomimetic Architectures
by Plasma Processing
About the Cover
Cicada
The cover image shows a photograph (Canon EOS 7D, Canon
100 mm, f 2.8, macro, flash) of a , collected dead, placed in
front of a polished silicon wafer (right) and a black silicon nanotip
wafer (left). The cicada wing is highly transparent, indicating low
reflection, due to the presence of conical burls on their wings. The
cicada
efficacy of such conical structures in anti-reflection is demonstrated
in this image. The part of the in front of the polished wafer
produced crisp and clear image of the cicada since the wafer is
highly reflecting and mirror-like. However, the part of the insect
in front of the black silicon nanotip (similar to the anti-reflecting
nanostructures in cicada wings or the moth eyes) produced no
image at all, even under a strong camera flash, demonstrating the
anti-reflection property of the silicon nanotips (discussed in Chapter
2 of this book).
Next, as we know, the conical nanostructures in the cicada wings
make their wings highly hydrophobic with water contact angles
around 150°. This is demonstrated in the near-spherical water
droplets that sit on its wings and stick to it even when the wing is
not horizontal. In fact, the cicada wing can hold the water droplets in
its near-perfect spherical shape even when it is turned upside down.
However, if the water droplets make an impact with the wings with
some velocity, as in raindrops, they bounce off the wings keeping it
perfectly dry. Such wetting properties are discussed in Chapter 4 of
this book.
In short, the image shows, in a single photographic shot, how
nature designs nanostructures for certain specific functionalities
and how we are able to mimic them in the laboratories to a certain
extent.
Pan Stanford Series on Renewable Energy — Volume 2
Biomimetic Architectures
by Plasma Processing
Fabrication and Applications
editors
Preben Maegaard edited by
Anna Krenz
Surojit Chattopadhyay
Wolfgang Palz
The Rise of Modern Wind Energy
Wind Power
for the World
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Contents
Preface
Introduction
ix
1. Photon i c Structures in the Animal Kingdom: Valuable xi
Inspirations for Biomimetic Applications 1
Bodo D. Wilts and Doekele G. Stavenga
1.1 Introduction 1
1.2 Principles of Animal Colouration 3
1.2.1 Pigmentary Colouration 3
1.2.2 Structural Colouration 4
1.2.2.1 Note on Order and Disorder 7
1.3 One-Dimensional Photonic Structures 7
1.3.1 Thin Films 7
1.3.2 Multilayers 9
1.3.3 Iridescence 10
1.4 Two-Dimensional Photonic Structures 13
1.5 Three-Dimensional Photonic Structures 14
1.5.1 Iridescence 16
1.6 Quasi-Ordered Photonic Structures 18
1.7 Combination of Pigmentary and Structural
Colouration 19
1.7.1 Increasing the Optical Contrast 20
1.7.2 Increasing the Chromatic Contrast 20
1.7.3 Spectral Tuning 21
1.8 Biological Relevance of Animal Colouration 22
1.8.1 Sex Recognition and Mate Choice 24
1.8.2 Warning Colouration 24
1.8.3 Camouflage 25
1.9 Bio-Inspired Applications 25
1.10 Conclusion: Design Principles for Bio-Inspired
Photonic Structures 26
vi Contents
2. Anti-Reflecting Nanostructures 35
Abhijit Ganguly, Surojit Chattopadhyay,
Pradip Kumar Roy, Li-Chyong Chen, and
Kuei-Hsien Chen
2.1 Introduction 36
2.2 Anti-reflective Coating 39
2.2.1 Layer-Structured AR Coating 40
2.2.2 Gradient Refractive Index AR Coating 42
2.2.3 Towards Perfect AR Coating 43
2.3 Anti-reflective Surfaces 43
2.3.1 Porous AR Surfaces 45
2.3.2 ‘Moth-Eye’ AR Surfaces 45
2.3.3 Surface-Relief Grating AR Surfaces 47
2.3.4 Textured AR Surfaces 50
2.4 Anti-reflecting Nanostructures 50
2.4.1 Fabrication of AR Nanostructures 51
2.4.1.1 Bottom-up technology 51
2.4.1.2 Top-down technology 53
2.4.1.3 Fabrication of wafer scale
AR surfaces 56
2.4.2 Biomimetic Photonic Nanostructures 56
2.4.3 Silicon Nanotips for Broadband,
Omnidirectional AR 60
2.4.4 Non-Silicon AR Nanostructures 67
3. P2l.5as ma-FPurotuceress Terde Bnidosm ainmde Ctiocn Ncalunsoi-o ann d 73
Micro-Structures 91
Choonsup Lee
3.1 Introduction 92
3.2 Silicon Nanotips Formation 94
3.2.1 Two-Step Technique 95
3.2.2 Single-Step Techniques 101
3.2.2.1 Room-temperature etching
using an ICP-RIE 103
3.2.2.2 Cryogenic-etching using
an ICP-RIE 105
3.4 Conclusions 106
Contents vii
4. Wetting Properties of Natural and Plasma-Processed
Biomimetic Surfaces 111
Pradip Kumar Roy and Surojit Chattopadhyay
4.1 Introduction 111
4.2 Theoretical Approach 114
4.2.1 Young’s Equation 115
4.2.2 The Wenzel State 115
4.2.3 The Cassie and Baxter State 115
4.2.4 Droplet Evaporation 120
4.2.5 Impact Velocity 121
4.2.6 Contact Angle Hysteresis and
Self-Cleaning 123
4.3 Natural Surfaces 124
4.3.1 Lotus Leaf 124
4.3.2 Salvinia auriculata and Lady’s Mantle 126
4.3.3 Fish Scale Antifouling Effect 127
4.3.4 Pond Skater 128
4.3.5 Dove’s Feather and Sandfish Skink 129
4.4 Adhesion Properties of Surface 130
4.5 Fabrication of Hydrophobic and Hydrophilic
Surface 133
4.5.1 Hydrophilic Surface 133
4.5.2 Hydrophobic Surface 137
4.6 Conclusion 143
5. BiomimeAtcick nSouwpelerhdygdermopehnot bic Surface by Plasma 142
Processing 151
Anyarat Watthanaphanit and Nagahiro Saito
5.1 Introduction 152
5.2 Superhydrophobic Surfaces 152
5.2.1 Superhydrophobic Surfaces in Nature 153
5.2.2 Surface Wettability 154
5.3 General Introduction to Plasma 157
5.4 Strategies to Generate Superhydrophobic
Surfaces by Plasma Processing 161
5.4.1 Etching 162
5.4.2 Functionalization 162
viii Contents
5.4.3 Polymerization 163
5.5 Recent Achievements in the Generation of
Superhydrophobic Surfaces with Different
Plasma Strategies 164
5.5.1 Etching Strategy 164
5.5.2 Functionalization Strategy 166
5.5.3 Polymerization Strategy 170
5.5.4 Superhydrophobic Surfaces with
Tuning Wettability 172
6. 5B.i6o mimCetoinc cInlutseirofanc es of Plasma-Modified Titanium 174
Alloy 181
Shuilin Wu and Paul K. Chu
6.1 Introduction 182
6.2 Plasma-Induced Biomimetic Interfacial
Structure and Coatings 182
6.2.1 Gas PIII&D 184
6.2.2 Metal PIII&D 191
6.2.3 Dual PIII&D 198
6.3 Plasma-Induced Biomimetic Interphases 201
6.3.1 Plasma Spraying 201
6.3.2 Reactive Plasma-Aided RF Sputtering
Deposition 206
6.3.3 Plasma Polymerization 209
6.3.4 Combined Plasma Treatment 214
Index6.4 Conclusion and Outlook 218
227
Contents ix
Preface
Mr. Stanford Chong of Pan Stanford Publishing house seemed to
have taken an interest in our work on ‘plasma-processed biomimetic
nanostructures’ that demonstrated extraordinary anti-reflection
behaviour. It was his suggestion to write a book on this topic, which
we kept rejecting only because the task seemed to be too daunting.
Exhaustive Google searches indicated something which I did not
know before. Abundant literature is available on ‘plasma-processed
nanostructures’ and also on ‘biomimetic nanostructures’; however,
the sub-set of ‘plasma-processed biomimetic nanostructures’ was
insignificantly small compared with those bigger sets. Hence, the
motivation behind this book, with an associated challenge of finding
contributing authors from the limited pool available out there.
Positive responses to the feeler mails sent out to the prominent
authors in the field ultimately convinced us. Stanford’s perseverance
won.
As a researcher, I know how difficult it is to find time for a
book chapter amidst one’s busy schedule where ‘original’ research
articles claim priority. I must thank my contributors, eminent in
their respective fields, for their insightful chapters. These chapters
outline natural nanostructures that are found aplenty around us
but we are either ignorant of or are indifferent to them. However,
when the visual or the functional aspects of these nanostructures
are properly explained, even a kid, as young as my seven-year-old
daughter, Oorja, would take keen interest in them. This book intends
to give the readers a general tour of these illuminating details of
nature. For the more advanced and avid readers, students, teachers,
and researchers alike, technical details and the science thereof has
been included to increase the depth of the subject of this book.
As I read the contributed chapters, I understood the
mathematical descriptions of these nanostructures more than I
ever did before. I also learnt various plasma-based techniques of
mimicking these natural structures in the laboratory. It provided
me with a perspective of my own research, a different viewpoint
to look at the tiny insects and creatures with which we co-exist. It
