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Morpho Butterfl y-Inspired Nanostructures
Haider Butt ,* Ali K. Yetisen , Denika Mistry , Safyan Akram Khan ,
Mohammed Umair Hassan , and Seok Hyun Yun
DOI: 10.1002/adom.201500658
1. Nanoarchitecture of Morpho Wing Scales
Tropical Morpho butterfl ies are known for their irides-
cence.
[ 1 ]
Extensive research has been dedicated to analyzing
the nanoscale architecture of Morpho butterfl y wings to
understand their brilliant blue or white–purple iridescence
The wing scales of Morpho butterfl ies contain 3D nanostructures that
produce blue iridescent colors. Incident light is diffracted from multilay-
ered nanostructures to create interference effects and diffract narrow-band
light. The intensity of the diffracted light remains high over a wide range of
viewing angles. Structural coloration originating from the scales of Morpho
wing nanostructures has been studied to analyze its optical properties and
to produce scalable replicas. This review discusses computational and
experimental methods to replicate these nanoarchitectures. Analytical and
numerical methods utilized include multilayer models, the fi nite element
method, and rigorous coupled-wave analysis, which enable the optimiza-
tion of nanofabrication techniques involving biotemplating, chemical vapour
deposition, electron beam lithography, and laser patterning to mimic the wing
scale nanostructure. Dynamic tunability of the morphology, refractive index,
and chemical composition of the Morpho wing scales allows the realization of
a numerous applications.
Dr. H. Butt, D. Mistry
Nanotechnology Laboratory
School of Engineering
University of Birmingham
Birmingham B15 2TT , UK
E-mail: [email protected]
Dr. A. K. Yetisen, Prof. S. H. Yun
Harvard Medical School and Wellman Center for Photomedicine
Massachusetts General Hospital
65 Landsdowne Street , Cambridge , Massachusetts 02139 , USA
Dr. A. K. Yetisen, Prof. S. H. Yun
Harvard-MIT Division of Health Sciences and Technology
Massachusetts Institute of Technology
Cambridge , Massachusetts 02139 , USA
Dr. S. A. Khan
Center of Excellence in Nanotechnology
King Fahd University of Petroleum & Minerals
Dhahran , Saudi Arabia
Dr. M. U. Hassan
Department of Physics
COMSATS Institute of Information Technology
Islamabad , Pakistan
(see Figure 1 a).
[ 2–5 ]
Although many
hypotheses have been proposed about
the nanostructure of the Morpho butterfl y
wing scales, the fi rst electron microscope
study of the Morpho cypris was carried out
by Anderson and Richards in the 1940s.
[ 6,7 ]
Further electron microscope studies led to
the classifi cation of the morphological fea-
tures and the discovery of blue iridescence
based on structural color.
The bright blue color irradiated from
the Morpho butterfl y is a combination of
diffraction based on multilayer interfer-
ence and pigmentation (in certain spe-
cies).
[ 6,10 ]
Under different incident or
viewing angles, the color of the Morpho
butterfl y wing slightly changes, sug-
gesting that the blue color does not solely
arise from pigmentation, but a nanostruc-
ture. Morpho species have ‘ground’ and
‘glass’ scales.
[ 9,11 ]
The ground scales are
the basis of the bright blue color, and lie on the dorsal sur-
face of the wing, where the majority of the interference occurs
(Figure 1 b).
[ 9 ]
However, the glass scales are highly transparent
and situated above the ground scales, acting as an optical dif-
fuser and resulting in a glossy fi nish to the surface of the wing,
while exhibiting relatively low iridescence (Figure 1 c). The vari-
ation in the nanoarchitecture of scales in different Morpho spe-
cies affects the appearance of the blue intensity displayed.
The scales of a Morpho butterfl y are composed of periodic
ridges made of cuticle, which lie parallel to the edge of the scale
and to each other (Figure 1 d). The gap separating the ridges
is less than 1 µm, and one scale may feature hundreds of
these ridges.
[ 12 ]
A single ridge consists of a stack of nanoscale
multilayered thin fi lms called lamellae (Figure 1 e). Hence,
these types of scale were categorized as “ridge lamella”. This
elaborate structure is the foundation of the bright blue irides-
cence of Morpho butterfl ies.
[ 13 ]
The origin of the blue color
is the multilayer interference caused by the stack of lamellae
( Figure 2 a).
[ 14,15 ]
The blue Morpho scale is wavelength selective,
since it only scatters the blue region of light from its Christmas
tree-resembling structure.
[ 12 ]
This is due to the vertical spacing
between lamellae, which is ≈200–300 nm, and approximately
equal to half the wavelength of the color that is irradiated from
the wing surface.
Each ridge consists of alternating cuticle and air layers,
which form the lamellar structure.
[ 6 ]
However, the cuticle
layers are randomly distributed over the scale, where the ridges
have irregular height differences, and these ridges run parallel
to the scale surface.
[ 17,18 ]
This is responsible for the second
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optical phenomenon. The narrow width of the ridges diffracts
light, but interference among neighboring ridges is canceled
out by the irregularities in height differences, since the light
diffracted in these regions superimposes with the interference
from the multilayer stacks, resulting in wide-angle diffraction
(Figure 2 b).
[ 6,19 ]
Additionally, the multilayer is almost ideal
since it features two media with a large difference in refractive
indices, producing enhanced diffraction effects (Figure 2 c).
[ 6 ]
Some Morpho species have pigments underneath their scales.
By analyzing diffraction, transmission, and absorption proper-
ties, the role of these pigments was studied.
[ 5,6 ]
For example,
the Morpho sulkowskyi and the Morpho didius have identical
structures; however, they irradiate different colors. The Morpho
sulkowskyi features a pearly white wing, whereas the Morpho
didius has a strong blue color. Although the Morpho sulkowskyi
has high refl ectivity, the strong presence of pigment in the
Morpho didius absorbs complementary colors, which enhances
the contrast of the blue despite its low refl ectivity (Figure 2 d).
The diffraction of colors from Morpho butterfl ies are angle
dependent.
[ 16 ]
Figure 2 e shows angle-resolved measurements
of the back-scattered light from Morpho rhetenor , showing the
angular dependence of the diffracted light.
2. Computational Analyses
Simulations are a low-cost solution to analyze the operation of
photonic structures, and offer a range of optimization options
to improve performance. Many numerical electromagnetic and
optical approaches have been used to analyze the phenomenon
of light scattering from butterfl y scale nanostructures. Before
numerical methods, most approaches were analytical, limiting
research to basic geometries. For example, the transfer matrix
method had been utilized to model a simplifi ed structure
consisting of thin fi lms.
[ 5 ]
Another approach included the
lamellar grating theory, where the structure is an x -invariant
and each grating layer is y -periodic featuring two regions with
differing refractive indices.
[ 20 ]
The fi nite difference time domain (FDTD) method has
become a practical approach for solving electromagnetic and
optical problems. It has the capability to model 3D structures to
analyze light interactions within original and fabricated Morpho
nanostructures; however, some simulations favor analyses in
2D form. The earliest FDTD simulations of Morpho structures
allowed the classifi cation of their practices as nonstandard
fi nite difference time domain methods (NS-FDTD).
[ 4,21 ]
The
algorithm used in NS-FDTD is slightly different than for typical
FDTD methods, and a steady state can be reached with fewer
iterations. The optical properties of a Morpho -inspired com-
puter-generated structure ( Morpho didius ) were investigated to
analyze the refl ectance spectra.
[ 4,21 ]
Standard FDTD was also
utilized for 3D analyses of light scattering by a Morpho rhetanor
ridge.
[ 22 ]
Recently, the standard form was adopted to analyze the
refl ectance spectra of an idealized 2D model, and the effect of
different parameters on diffraction characteristics.
[ 23 ]
A different approach to simulate Morpho butterfl y structures
is the fi nite element method (FEM). In comparison to
standardized FDTD, FEM analysis for Morpho applications is
new; however, it is based on a comparable simulation operation.
Haider Butt is a lecturer
(assistant professor) in
the School of Engineering,
University of Birmingham,
UK. Previously, he was a
Henslow Research Fellow at
the University of Cambridge,
UK, where he received his PhD
in 2012. His research focusses
on photonic devices based
on nanostructures like carbon
nanotubes, graphene, and
plasmonic nanostructures. He has secured several pres-
tigious research awards and has poineered the research
on carbon nanotubes based holograms and holographic
nanofabrication.
Ali K. Yetisen researches
nanotechnology, photonics,
biomatercials, government
policy, entrepreneurship,
and arts. He also lectures
at Harvard-MIT Division
of Health Sciences and
Technology. He holds a PhD
in Chemical Engineering
and Biotechnology from the
University of Cambridge,
where he also taught at
Judge Business School. He has served as a policy advisor
for the British Cabinet Offi ce.
Seok-Hyun (Andy) Yun
received his PhD in physics
from the Korea Advanced
Institute of Science and
Technology in 1997. His
thesis research led to a
startup company in Silicon
Valley, where he managed the
engineering to produce fi ber-
optic devices for telecommu-
nications. Currently, he is the
Director of the Harvard-MIT
Summer Institute for Biomedical Optics. His research
areas include optical imaging, photomedicine, biomaterials
photonics, and biological lasers.
The FEM simulations solve Maxwell’s equations using a com-
mercial software package (e.g., Comsol Multiphysics), which
is less time consuming as a result of its fl exible triangular
mesh while maintaining accuracy. Using the FEM, the effects
of different structural properties such as alternating lamella,
a “Christmas tree”-like shape, and offsets between neigh-
boring ridges, and their infl uence on wide angle defl ection
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were investigated.
[ 15 ]
Additionally, Morpho scale architectures
can also be simulated by the rigorous coupled-wave analysis
(RCWA).
[ 8,24 ]
It utilizes the software module DiffractMOD that
implements various algorithms, including a fast converging of
Maxwell’s equations. Table 1 shows the list of analytical tech-
niques associated with Morpho butterfl y models.
3. Replication of Morpho Scale Nanostructures
Through advances in nanotechnology, several attempts have
been made to mimic the photonic structure and the iridescent
features of the Morpho butterfl y scales.
[ 15,27 ]
Biotemplating (or
biomineralization) has been utilized to deposit a compatible
oxide onto an organic Morpho wing template to preserve the
exact features of the structure. Lithography was also used for
fabricating Morpho nanostructures, focusing on the reproduc-
tion of the bright blue color instead of replicating the exact
structure. Recently, dual-beam laser interference lithography
(LIL) was utilized for Morpho replication.
3.1. Deposition-Directed Replication of Morpho Butterfl y Scales
Biotemplating wing scales is a commonly used method to
produce accurate replicas. A scale structure was replicated
using atomic layer deposition (ALD) by coating a butterfl y
wing sample with an alumina (Al
2
O
3
) layer at 100 °C.
[ 27 ]
The
thickness of each layer was controlled by varying the cycle
of deposition. After the cycles were completed, the original
butterfl y wing was burned out in the presence of oxygen by
annealing the sample at 800 °C for 3 h to produce a wing shell.
The sample was further crystallized into a robust structure.
This method preserved the complex structure of the Morpho
wing, due to the uniformity of the Al
2
O
3
coating ( Figure 3 a).
In complex nanostructures, achieving uniform and conformal
features by ALD is limited by the degree of saturation and
surface diffusion behavior.
[ 28,29 ]
The ALD method is low cost
and is reproducible while providing accurate control over the
nanostructure geometry. However, obtaining large numbers of
natural wing samples is obviously a challenge for the mass pro-
duction of butterfl y structures.
Another replication of a Morpho nanostructure through ALD
consisted of a “Christmas tree”-resembling structure.
[ 29 ]
This
method was similar to the previously reported approach except
that the deposition temperature of Al
2
O
3
was 80 °C. Addition-
ally, silica replication was reported, which involved copying the
wing of the Morpho rhetanor . The fabrication was performed
through physical vapor deposition (PVD) under pretested con-
ditions that preserved the multilayers of the butterfl y ridges and
scales (Figure 3 a).
[ 30 ]
The same study also contained a titania-
based replication of the Morpho menelaus by chemical solution
deposition (CSD; see Figure 3 b). The fabrication involved a sol–
gel process for replicating the lepidopteran wings.
[ 18 ]
Other pro-
cedures combined with this technique were solution evapora-
tion and dip coating.
[ 30 ]
Although the conditions of this method
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Figure 1. Nanostructure of the Morpho butterfl y. a) A photograph of the Morpho didius butterfl y showing blue iridescence. Scale bar = 1 cm, Reproduced
with permission.
[ 8 ]
Copyright 2011, Elsevier. b) A magnifi ed image of an M. rhetanor wing showing the ordered arrangement of its single layer of ground
scales. Scale bar = 100 µm. c) A magnifi ed image of an M. didius wing illustrating the two distinct types of scales, with the glass scales overlying the
ground scales, scale bar = 100 µm. Panels (b) and (c) reproduced with permission.
[ 9 ]
Copyright 1999, The Royal Society. d) Scanning electron micro-
scope (SEM) images of an oblique view of the male butterfl y M. didius. Scale bar = 1 µm. e) A cross-section of a ground scale of the male butterfl y
Morpho didius . Scale bar = 1 µm. Panels (d) and (e) reproduced with permission.
[ 10 ]
Copyright 2012, The Royal Society.
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were more desirable than those for PVD (ambient pressure and
room temperature), the replicas produced were fragile due to
cracking. Recently, PVD was utilized to selectively modify the
lamella layer of Morpho sulkowskyi .
[ 32 ]
The edges of lamella were
exposed to an incoming fl ux of gold to form a layer of 50 nm.
The gold-modifi ed wing structures had IR absorbance that
allowed tuning of the lamella nanostructure.
Experimentation with sol–gels has enabled the formation of
an intricate, continuous, and conformal nanocrystalline Morpho
scale structures. A foundation of titanium
dioxide was used to produce distortion-free
3D nanostructures. The basis of this method
relied on the chitin content found in the
wing scales, providing the hydroxyl groups
required to initiate the sol–gel process.
[ 31 ]
Thin layers of oxide were coated onto the
Morpho wing through layer-by-layer (LBL)
deposition using a computer-controlled sol–
gel process (Figure 3 d).
[ 18 ]
The wings were
then annealed at 900 °C. Finally, conversion
of the structure into rutile titania replicas
was executed by using a surface sol–gel
process with tin(IV) isopropoxide as a rutile-
promoting dopant.
[ 31 ]
This method has the
same limitation as the ALD proposition, that
is, the fabrication requires an organic (or
synthetic) template. Using a synthetic tem-
plate requires an additional step, which is
time consuming and costly. However, there
are many benefi ts of a sol–gel-controlled
process, such as facile shape control, mild
reaction conditions, and compatibility with a
wide variety of chemicals.
[ 33 ]
Additionally, the
structure of the material can be controlled
down to a sub-micrometer level from the ear-
liest stage of processing.
Focused ion beam-assisted chemical vapor
deposition (FIB-CVD) was also utilized for
replications (Figure 3 e). Initially a 3D mold
was fabricated by producing 3D computer-
aided design (CAD) data, which was con-
verted to a scanning signal, as an FIB scan-
ning apparatus to form the fi nal mold.
[ 13 ]
The FIB system
formed the Morpho quasi-structure by deposition of C
14
H
10
(phenanthrene), which was selected as the source due to its
high deposition rate as compared to previously tested speci-
mens of C
8
H
8
(styrene) and C
16
H
10
(pyrene) (Figure 3 d). The
drawbacks of this method are its high cost and limited scala-
bility, despite being able to produce accurate Morpho nanostruc-
tures of the same shape and size while maintaining comparable
optical characteristics of the original wing scale.
[ 18 ]
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Table 1. Analytical and numerical analysis methods in Morpho butterfl y models.
Method Description Features and Limitations Ref.
Analytical Multilayer
theory
Based on multilayer
grating equations
Allows fast calculation of
transmission and refl ection spectra
[5,9]
Lamellar grating
electromagnetic theory
Converting refl ection coeffi cients of any
structure into colours
Allows obtaining color maps to have a global insight
of refl ection properties of the modelled structure.
The tilted ridges are not taken into account.
[20,25]
Numerical FDTD Quasi-periodic arrangement
of tree-like structures
Computes scattered fi eld intensities due to infi nite cylinders.
The method is slower compared to others.
[4,21–23,26]
FEM Solves Maxwell’s equation using COMSOL
Multiphysics and related softwares
Utilizes fl exible triangle-shaped mesh
with high accuracy and speed.
[15]
RCWA Models constructed by DiffractMOD,
which is a general design tool for optically
diffractive structures
Implements algorithms including a fast converging
formulation of Maxwell equations and
a numerical stabilization scheme
[8,24]
Figure 2. Principles of the blue coloration in the Morpho butterfl y. a) Multilayer interference,
b) diffraction, and c) incoherence. d) Pigment layer. e) Angle-resolved measurements of the
back scattered light from M. rhetenor . Reproduced with permission.
[ 16 ]
Copyright 2014, Nature
Publishing Group.
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3.2. Lithographic Replication of Morpho Butterfl y Scales
The earliest replications through lithography involved the fab-
rication of multilayer structures to mimic the Morpho scales by
depositing layers of SiO
2
and TiO
2
onto a nanopatterned sur-
face ( Figure 4 a). The initial nanopattern was engraved onto a
quartz substrate, by a combination of electron beam lithography
(EBL) and dry etching, which is a crucial stage in the process
to achieve the accurate dimensions of the pattern. This method
does not produce a structure emulating the exact features of
the Morpho nanostructure, instead it focuses on reproducing
the optical characteristics of the blue iridescence by controlling
the size of the lattice spacing and width engraved onto the sub-
strate. Finally, seven pairs of SiO
2
and TiO
2
layers (40 nm thick)
were LBL coated onto the fabricated nanopattern using electron
beam deposition. The thickness of oxides could be controlled
more accurately over other materials during deposition which
infl uenced their usage in this process. Although EBL can pro-
duce nanoscale patterns with high resolution, the fabrication is
time consuming, and high cost.
Nanocasting lithography (NCL) was also utilized to pro-
duce a multilayer structure by modifying the original lithog-
raphy method. A master substrate featuring the initial ridges
was produced by conventional nanoimprint lithography (NIL).
This master substrate acted as a template to directly nanopat-
tern UV curable resin using the NCL ( Figure 5 a–d).
[ 35 ]
To form
the multilayer structures within the ridges, the same deposi-
tion technique was used (Figure 5 e). This method was advanta-
geous as costs are signifi cantly reduced since it only required a
conventional mask aligner and a spin coater. These approaches
allowed mass production by eliminating two high-cost and mul-
tistep processes: EBL and dry etching.
[ 36 ]
The accuracy of replica nanostructures was further devel-
oped by having an homogeneous and scalable template mold.
This process featured a fs laser to form the initial mold con-
taining ridges (replacing NIL), combined with electroforming
(replacing EBL) to create irregular multilayers within the
structure.
[ 37 ]
This method provided a faster production time
while keeping the structures anisotropic and random. A soft
lithography technique was also investigated to create a mul-
tilayered structure of the upper Morpho scales.
[ 34 ]
The fab-
rication consisted of a four step process that transformed
polydimethylsiloxane (PDMS) into the proposed nanostruc-
ture (Figure 4 c). LIL was also explored to replicate the pho-
tonic structure of the Morpho butterfl y scale.
[ 38 ]
Initially,
a glass substrate was spin coated with a photoresist, which
was then exposed to a two laser beams ( Figure 6 ). The sub-
strate was coated with a refl ective coating
to induce a vertical secondary interference.
The beams were kept homogenous by the
use of pinholes to eliminate high-frequency
distortions and a quartz plate moder-
ated transmitted power through one beam
path. Figure 6 also shows the resulting
“Christmas tree” nanostructure.
Titania was also utilized to form a hier-
archical structure featuring mesopores
to improve light absorption. The method
involved two pretreated Morpho wings, which
were ultra-sonicated at room temperature
with a high intensity probe.
[ 39 ]
Finally, calcina-
tion was performed, and wing remnants were
removed to form titania-based structures.
[ 39 ]
Table 2 shows the fabrication methods for
replicating Morpho scales.
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Figure 3. Morpho replication. a) SEM images of an alumina-templated
scale, where the replica exhibits fi ne structures, scale bar = 1 µm. Repro-
duced with permission.
[ 27 ]
Copyright 2006, American Chemical Society.
b) SEM image of M. rhetenor scales after physical deposition of SiO
2
,
scale bar = 100 µm. c) SEM image of M. menelaus scales after sol–gel
deposition of TiO
2
. Scale bar = 100 µm. Panels (b) and (c) reproduced
with permission.
[ 30 ]
Copyright 2014, Elsevier. d) SEM image of scales
exposed to 40 surface sol–gel deposition cycles involving a mixed
2-propanol solution of titanium(IV) isopropoxide and Sn(IV) isopropoxide,
scale bar = 1 µm. Reproduced with permission.
[ 31 ]
Copyright 2008, John
Wiley & Sons, Inc. e) Inclined-view SEM image of Morpho butterfl y scale
quasi-structure fabricated by FIB-CVD, scale bar = 1 µm. Reproduced with
permission.
[ 13 ]
Copyright 2005, Japan Society of Applied Physics.
Figure 4. Lithographic replication of butterfl y scales. A) Image of discrete multilayers formed
on the nanopatterned plate by nanocasting lithography. Reproduced with permission.
Copyright 2009, Society of Photo Optical Instrumentation Engineers. b) SEM image of the
ripple (nanogroove) pattern made by fs-laser fabrication (after electroforming on Ni plate).
Pitch = 300 nm. Reproduced with permission. Copyright 2012, Society of Photo Optical
Instrumentation Engineers. c) Characteristics of a butterfl y wing: ridge-like structures on repli-
cated scale surface via soft lithography. Reproduced with permission.
[ 34 ]
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4. Applications of Morpho Butterfl y Scale Replicas
The Morpho butterfl y demonstrates unique optical properties
that can be applied to the developments in photonic devices.
General Electric Global Research Center (GEGRC) has
studied the scales of the Morpho sulkowskyi for gas sensing.
The refl ectance spectra of the structure within the scales vary
with exposure to different vapors. A group of organic vapors:
methanol, ethanol, and dichloroethylene were distinguished
by analyzing refl ectance as a function of time.
[ 25,40 ]
By experi-
menting with different concentrations of each vapor, highly
sensitive properties of the scales were discovered. This behavior
was attributed to the ridge-lamella structure within the scales.
Existing nanofabricated structures may identify closely related
vapors, and thus require layers of chemicals to enhance selec-
tivity. Another Morpho butterfl y-inspired sensor was utilized to
detect different vapors.
[ 41 ]
After the nanostructures were fabri-
cated by e-beam lithography, they were coated with monolayers
of a fl uorine-terminated silane. To test the selectivity, they were
exposed to benzene, methyl ethyl ketone, acetonitrile, methanol
and water. The sensors selectively detected separate vapors in
pristine conditions and quantifi ed these vapors in mixtures in
the presence of moisture background.
Further development by GEGRC has led to the production
of a biomimetic chitin-based thermal sensor inspired by
the Morpho nanostructure. The sensor was designed to detect
mid-wave infrared light, since chitin has infrared absorp-
tion properties, and the optical properties of the sensor were
similar to the vapor sensor. The Morpho wing structure was
temperature sensitive: when the surrounding temperature
increased, the hierarchical structure was thermally expanded.
This increased the spacing between ridges, resulting in a ther-
mally induced reduction in the effective refractive index of the
structure.
[ 42 ]
Hence, the shift in the intensity of the diffracted
light at a fi xed wavelength was converted into a measurable
temperature change. Additionally, the wing scales were doped
with single-walled carbon nanotubes (SWCNTs) to enhance the
structure’s infrared absorption properties.
[ 42 ]
Not only does this
technique increased the sensitivity of the device, it improved
thermal conductivity and thermal conversion of NIR photons.
The improved thermal coupling between the chitin wing struc-
ture and the SWCNTs enabled the scales to effi ciently convert
incident radiation into visible iridescence changes, which has
application in thermal imaging devices.
5. Future Directions
The nanoarchitecture of replicated Morpho butterfl y scales can
be potentially functionalized to be specifi c to a wide range of
analytes. Recently, multilayer diffraction grating constructed
via silver halide and laser ablation holography in hydrogel
matrices enabled analyte-specifi c recognition.
[ 43 ]
Such multi-
layer structures have been functionalized with acrylic acid, por-
phyrin derivatives, 8-hydroxyquinoline, and boronic acid to be
sensitive to pH, metal ions, and carbohydrates.
[ 44 ]
The applica-
tions of these materials to Morpho -inspired nanoarchitectures
can expand the existing selectivity and sensing capabilities
for application in medical diagnostics, environmental moni-
toring, and food testing. Such devices may also be patterned
using laser writing to form optical devices such
as lenses and diffusers, or printed on fl exible
substrates.
[ 45 ]
Morpho nanarchitectures may also
be combined with emerging materials such as
graphene and carbon nanotubes to introduce
new functionalities such as high mechanical
strength, electrical conductivity, and transpar-
ency.
[ 46 ]
These devices may be multiplexed by
using microfl uidic devices, integrated into con-
tact lenses, or quantifi ed by smartphone cam-
eras.
[ 47 ]
Additionally, Morpho inspired solar cells
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Figure 5. Reproduction of the Morpho blue structures via NCL. The master plate is replicated by NCL using UV curable resin, and the SiO
2
and TiO
2
layers are deposited on the cured resin pattern. a) Deposition of UV resin on the substrate. b) Spin coating. c) A glass slide is placed on top and UV
is exposed to the resin. d) Release of the master plate. e) Deposition of multilayered thin fi lms on the replicated resin plate.
Figure 6. Fabrication process of horizontal structures by dual beam LIL. A photoresist is
spin coated on a clean glass substrate and exposed by two interfering laser beams. The
development of the photoresist results in a “Christmas tree”-like photonic structure on the
glass substrate.
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has been proposed, but they have not been experimentally dem-
onstrated yet.
[ 2,48 ]
The Morpho butterfl y wings contain rare 3D geometrical
structures, which are effectively responsible for their bright
blue irradiance colors. We have presented an overview of com-
putational methods which have been used to optimize the
optical properties and effects displayed by Morpho nanostruc-
tures. A range of nanofabrication methods that accurately pro-
duce replicas of these 3D nanostructures has been described.
We anticipate that the replicas of Morpho butterfl y wings will
fi nd myriad applications in highly sensitive optical sensing,
imaging, and effi cient photovoltaics.
Acknowledgements
H. Butt, A. K. Yetisen, and D. Mistry wrote the article. D. Mistry, S. A.
Khan, M. U. Hassan, and S. H. Yun edited the manuscript. H. Butt and
A. K. Yetisen contributed equally to this work. The authors declare no
competing fi nancial interests. H. Butt thanks the Leverhulme Trust for
the research funding.
Received: November 6, 2015
Revised: December 17, 2015
Published online: January 11, 2016
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Replication/Method Feature Dimension Sample Size Ref.
ALD Inversed 2D biotemplated
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NCL Multilayer structure 900 nm high N/A [35]
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LIL “Christmas tree”
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Soft lithography Multilayer 3D
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N/A [34]
Ultra-sonication Multilayer structures
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Inter-lamella spacing of 1.05–1.01 µm
and grain sizes of 14.3–11.1 nm
N/A [39]
504
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