vapour sensing properties of bio-inspired synthetic nanostructures

Vapour Sensing Proper/es of Bio-Inspired Synthe/c Nanostructures

Olivier Poncelet1, Guillaume Tallier1, Sébas/en Mouchet2, Jonathan Rasson1, Olivier Deparis2 and Laurent A. Francis1

1 ICTEAM Ins/tute - Université catholique de Louvain, Belgium 2 Department of Physics - Université de Namur, Belgium

Living Light Conference 2016, May 4th – 6th, San Diego

1

Fundamentals

Concepts

Real objects

Tools & Methods

Natural nano-structures

Artificial nano-structures (1D, 2D & 3D)

Characterization

Interpretation & Modelling

Nanoscale synthesis

Simulation

Bio-inspired nano-optics

2

Fundamentals

Concepts

Real objects

Tools & Methods

Natural nano-structures

Artificial nano-structures (1D, 2D & 3D)

Characterization

Interpretation & Modelling

Nanoscale synthesis

Simulation

Bio-inspired nano-optics

Bio-inspired applications

Inspira/ons from Morpho (godar,)

Applica/ons:!gazes!and!heat!sensors!Black plate (124,1)

REFLECTANCE SENSITIVITY TO VAPOURS

A principle of highly selective vapour response based onhierarchical photonic structures and demonstrated usingM. sulkowskyi iridescent scales is illustrated in Fig. 2. Measurementsof differential reflectance spectra DR provide informationabout the nature and concentration of the vapours:DR ¼ 100% ! (R/R0 2 1), where R is a spectrum collected fromscales upon vapour exposure and R0 is a spectrum collected fromscales upon exposure to a carrier gas (dry N2).

To examine the chemical selectivity of response of thesephotonic structures, we exposed a "5 ! 5 mm region of the wingto a variety of vapours, presented individually at differentconcentrations, and monitored the DR spectra with a fibre optic(1-mm diameter illumination spot). Figure 3a illustrates the DR

spectra of scales upon exposure to water, methanol and ethanolvapours with very similar solvent polarities (ET ¼ 63.1, 55.4 and51.9 kcal mol21, respectively) and refractive indices (n ¼ 1.333,1.328 and 1.361, respectively). Exposures to solvent vapourscaused reflectance increase, and immersion in a liquid solventcaused reflectance decrease (similar to earlier observations9,29) dueto the drop in the lamellae–external medium refractive indexcontrast. We have found strikingly different DR response patternsof the scales to these closely related vapours. The mostpronounced differences in DR were at 325–500 nm and inresponse magnitude at 500–600 nm. As reported artificialphotonic sensors do not have such spectral selectivity and thusrequire chemical modifications23, these spectral features inspiredus to investigate the responses further.

bal

cr

p mr

R

R

500 nm 500 nm

bl

Figure 1 Two views of the Morpho photonic structure. a, Longitudinal SEM view of a fractured photonic structure of a Morpho scale showing a side view of threeridges (R), with their lamellae (l) and associated microribs (mr). Also shown are parts of several crossribs (cr; here fractured) that join the ridges as well as thebottom layer (bl) of the scale and several pillars (p) that connect the bottom scale layer with the photonic structure. b, TEM view of a transverse section of the edge

of a Morpho scale, showing the closely packed ridges (R) and their associated lamellae. The section also catches some of the pillars that connect the photonicstructure with the relatively featureless bottom layer of the scale.

Morpho sulkowskyibutterfly wing

Hierarchicalphotonic structureof butterfly scale

Reflectedlight todetector

Vapour

DR (%

)

500 nm

l (nm)Distinct spectral response

to different vapours

Figure 2 New principle of highly selective vapour response based on hierarchical photonic structures and demonstrated using M. sulkowskyi iridescentscales. Measurements of differential reflectance spectra DR provide information about the nature and concentration of the vapours: DR ¼ 100% ! (R/R0 2 1),where R is a spectrum collected from scales upon vapour exposure and R0 is a spectrum collected from scales upon exposure to a carrier gas (dry N2).

ARTICLES

nature photonics | VOL 1 | FEBRUARY 2007 | www.nature.com/naturephotonics124

Our design was inspired by the photonic nanoarchitecture ofMorpho butterfly scales (Fig. 1) and suggests several avenues forthe development of future nanoengineered structures. Unlikemany other examples of nanostructures in nature that exhibit struc-tural colour17, the design of the Morpho butterfly scales makes use ofa photonic air-filled nanoarchitecture (Fig. 1a,b; SupplementaryFigs S1, S2) with a thermal mass of 2.2 × 10213 J K21, which issignificantly smaller than that of other detectors (SupplementaryTable S2). Surface functionalization of Morpho scales withsingle-walled carbon nanotubes (SWNTs) (Fig. 1c,d) leads to anincrease in the MWIR absorption cross-section of the Morphobutterfly nanostructure.

The thermal response of Morpho butterfly scales originates fromthe thermal expansion of this hierarchical structure, which causes anincrease in spacing between the ridges, expansion of the lamellarstructure and a thermally induced reduction in the refractiveindex of the structure following periodic MWIR illumination.This leads to modulation in the multilayer interference and diffrac-tion pattern by a ‘wavelength conversion’ process to visible radiation(Fig. 1e). We took advantage of the extremely low thermal mass ofthe air-filled nanoarchitectures of Morpho butterfly scale structuresand the infrared absorption properties of natural insect cuticle andSWNTs (used as a dopant in the scale structures) to explore aninnovative design of bio-inspired MWIR detector. We have demon-strated experimentally and theoretically that absorption of MWIRphotons by the Morpho scale nanostructure modulates visible-light iridescence upon illumination with white light.

Spectral responseWe decorated the scales of Morpho butterflies with SWNTs toenhance the efficiency of the thermal coupling of MWIR photonsto the cuticle-based reflective structures. Doping of the Morpho

scales with SWNTs produced a slight decrease ("15%) in the reflec-tion spectra (Fig. 2) without altering the position of the character-istic main reflection peak ("498 nm) of the scale.

The desired improved thermal coupling between the Morphobutterfly chitin-based wing structure and SWNTs was achieved byleveraging several well-known beneficial characteristics of SWNTssuch as high MWIR absorption, rapid thermal conversion ofMWIR photons and exceptional thermal conductivity (seeSupplementary Information for details and references). These prop-erties are advantageous for infrared imaging because all thermal/bolometric infrared detectors must not only complete an effectivethermal conversion, but must also efficiently disperse the heat

Visiblereflected light

readout

MWIRradiation

Suspended low-thermal-massphotonic nanostructure

e

ModulatedMWIR radiation

Modulatedvisible radiation

b

400 nm

a

500 nm

500 nm

c

d

R

L R L R

CR

L

Figure 1 | New principle of uncooled thermal detection based on the air-filled photonic architecture of iridescent scales of a Morpho butterfly. a,Transmission electron microscope image of a cross-section of the Morpho nanostructure. Inset: Morpho sulkowskyi butterfly, as used in this study. b, Designparameters of a Morpho reflective scale. c,d, Scanning electron microscope images of a portion of a Morpho scale before (c) and after (d) modification withSWNTs. e, Experimental schematic with a free-standing Morpho nanostructure, its excitation with MWIR radiation and readout of the visible response.R, ridge; L, lamella; CR, crossrib.

300 400 500 600 700 800

Bare

With SWNTs

Sign

al in

tens

ity (a

.u.)

Wavelength (nm)

Figure 2 | Reflectance spectra of scale reflectors of Morpho butterflies.Spectra are for before and after decoration with SWNTs.

ARTICLES NATURE PHOTONICS DOI: 10.1038/NPHOTON.2011.355

NATURE PHOTONICS | VOL 6 | MARCH 2012 | www.nature.com/naturephotonics196

[Radislav!A.!Potyrailo!et.$Al.,$2007]!$$ [Andrew!D.!Prise!et.$Al.,$2012]!$$

Vapor!and!solvent!

H2O'''''CH3OH'''''C2H5OH'

Infrared!

[Potyrailo R. A. et. al. – 2012] Towards high-speed imaging of infrared photons with bioinspired nanoarchitectures

Nature Photonics

Heat sensing

Applica/ons:!gazes!and!heat!sensors!Black plate (124,1)

REFLECTANCE SENSITIVITY TO VAPOURS

A principle of highly selective vapour response based onhierarchical photonic structures and demonstrated usingM. sulkowskyi iridescent scales is illustrated in Fig. 2. Measurementsof differential reflectance spectra DR provide informationabout the nature and concentration of the vapours:DR ¼ 100% ! (R/R0 2 1), where R is a spectrum collected fromscales upon vapour exposure and R0 is a spectrum collected fromscales upon exposure to a carrier gas (dry N2).

To examine the chemical selectivity of response of thesephotonic structures, we exposed a "5 ! 5 mm region of the wingto a variety of vapours, presented individually at differentconcentrations, and monitored the DR spectra with a fibre optic(1-mm diameter illumination spot). Figure 3a illustrates the DR

spectra of scales upon exposure to water, methanol and ethanolvapours with very similar solvent polarities (ET ¼ 63.1, 55.4 and51.9 kcal mol21, respectively) and refractive indices (n ¼ 1.333,1.328 and 1.361, respectively). Exposures to solvent vapourscaused reflectance increase, and immersion in a liquid solventcaused reflectance decrease (similar to earlier observations9,29) dueto the drop in the lamellae–external medium refractive indexcontrast. We have found strikingly different DR response patternsof the scales to these closely related vapours. The mostpronounced differences in DR were at 325–500 nm and inresponse magnitude at 500–600 nm. As reported artificialphotonic sensors do not have such spectral selectivity and thusrequire chemical modifications23, these spectral features inspiredus to investigate the responses further.

bal

cr

p mr

R

R

500 nm 500 nm

bl

Figure 1 Two views of the Morpho photonic structure. a, Longitudinal SEM view of a fractured photonic structure of a Morpho scale showing a side view of threeridges (R), with their lamellae (l) and associated microribs (mr). Also shown are parts of several crossribs (cr; here fractured) that join the ridges as well as thebottom layer (bl) of the scale and several pillars (p) that connect the bottom scale layer with the photonic structure. b, TEM view of a transverse section of the edge

of a Morpho scale, showing the closely packed ridges (R) and their associated lamellae. The section also catches some of the pillars that connect the photonicstructure with the relatively featureless bottom layer of the scale.

Morpho sulkowskyibutterfly wing

Hierarchicalphotonic structureof butterfly scale

Reflectedlight todetector

Vapour

DR (%

)

500 nm

l (nm)Distinct spectral response

to different vapours

Figure 2 New principle of highly selective vapour response based on hierarchical photonic structures and demonstrated using M. sulkowskyi iridescentscales. Measurements of differential reflectance spectra DR provide information about the nature and concentration of the vapours: DR ¼ 100% ! (R/R0 2 1),where R is a spectrum collected from scales upon vapour exposure and R0 is a spectrum collected from scales upon exposure to a carrier gas (dry N2).

ARTICLES

nature photonics | VOL 1 | FEBRUARY 2007 | www.nature.com/naturephotonics124

Our design was inspired by the photonic nanoarchitecture ofMorpho butterfly scales (Fig. 1) and suggests several avenues forthe development of future nanoengineered structures. Unlikemany other examples of nanostructures in nature that exhibit struc-tural colour17, the design of the Morpho butterfly scales makes use ofa photonic air-filled nanoarchitecture (Fig. 1a,b; SupplementaryFigs S1, S2) with a thermal mass of 2.2 × 10213 J K21, which issignificantly smaller than that of other detectors (SupplementaryTable S2). Surface functionalization of Morpho scales withsingle-walled carbon nanotubes (SWNTs) (Fig. 1c,d) leads to anincrease in the MWIR absorption cross-section of the Morphobutterfly nanostructure.

The thermal response of Morpho butterfly scales originates fromthe thermal expansion of this hierarchical structure, which causes anincrease in spacing between the ridges, expansion of the lamellarstructure and a thermally induced reduction in the refractiveindex of the structure following periodic MWIR illumination.This leads to modulation in the multilayer interference and diffrac-tion pattern by a ‘wavelength conversion’ process to visible radiation(Fig. 1e). We took advantage of the extremely low thermal mass ofthe air-filled nanoarchitectures of Morpho butterfly scale structuresand the infrared absorption properties of natural insect cuticle andSWNTs (used as a dopant in the scale structures) to explore aninnovative design of bio-inspired MWIR detector. We have demon-strated experimentally and theoretically that absorption of MWIRphotons by the Morpho scale nanostructure modulates visible-light iridescence upon illumination with white light.

Spectral responseWe decorated the scales of Morpho butterflies with SWNTs toenhance the efficiency of the thermal coupling of MWIR photonsto the cuticle-based reflective structures. Doping of the Morpho

scales with SWNTs produced a slight decrease ("15%) in the reflec-tion spectra (Fig. 2) without altering the position of the character-istic main reflection peak ("498 nm) of the scale.

The desired improved thermal coupling between the Morphobutterfly chitin-based wing structure and SWNTs was achieved byleveraging several well-known beneficial characteristics of SWNTssuch as high MWIR absorption, rapid thermal conversion ofMWIR photons and exceptional thermal conductivity (seeSupplementary Information for details and references). These prop-erties are advantageous for infrared imaging because all thermal/bolometric infrared detectors must not only complete an effectivethermal conversion, but must also efficiently disperse the heat

Visiblereflected light

readout

MWIRradiation

Suspended low-thermal-massphotonic nanostructure

e

ModulatedMWIR radiation

Modulatedvisible radiation

b

400 nm

a

500 nm

500 nm

c

d

R

L R L R

CR

L

Figure 1 | New principle of uncooled thermal detection based on the air-filled photonic architecture of iridescent scales of a Morpho butterfly. a,Transmission electron microscope image of a cross-section of the Morpho nanostructure. Inset: Morpho sulkowskyi butterfly, as used in this study. b, Designparameters of a Morpho reflective scale. c,d, Scanning electron microscope images of a portion of a Morpho scale before (c) and after (d) modification withSWNTs. e, Experimental schematic with a free-standing Morpho nanostructure, its excitation with MWIR radiation and readout of the visible response.R, ridge; L, lamella; CR, crossrib.

300 400 500 600 700 800

Bare

With SWNTs

Sign

al in

tens

ity (a

.u.)

Wavelength (nm)

Figure 2 | Reflectance spectra of scale reflectors of Morpho butterflies.Spectra are for before and after decoration with SWNTs.

ARTICLES NATURE PHOTONICS DOI: 10.1038/NPHOTON.2011.355

NATURE PHOTONICS | VOL 6 | MARCH 2012 | www.nature.com/naturephotonics196

[Radislav!A.!Potyrailo!et.$Al.,$2007]!$$ [Andrew!D.!Prise!et.$Al.,$2012]!$$

Vapor!and!solvent!

H2O'''''CH3OH'''''C2H5OH'

Infrared!

[Potyrailo R. A. et. al. – 2007] Morpho buCerfly wing scales demonstrate highly selec,ve vapour response.

Nature Photonics

Vapour sensi/vity

Iridescence Fluid sensing

3

Inspira/ons from Papilio blumei 400 450 500 550 600 650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength [nm]

Ref

lect

ance

Papilio blumei

Papilio!blumei!

400 450 500 550 600 650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength [nm]

Ref

lect

ance

Papilio blumei

Papilio!blumei!

4.6. Caractérisations des structures polarisantes bio-inspirées 111

Figure 4.48: Effets de polarisations observés macroscopiquement, par M1.

calculés par simulations (Figure 4.52).

Cavités triangulairesPour les cavités triangulaires, la mesure est plus facile puisque, en théorie, toutela lumière est réfléchie dans la direction incidente. Ici on mesure bien ce que lasimulation calcule. Le spectre mesuré à l’aide du spectromètre correspond auspectre calculé par RT + MT en lumière non polarisée.

[Poncelet et. al. – 2015] Synthesis of bio-inspired mul,layer polarizers and

their applica,on to an,-counterfei,ng Bioinspira,on & Biomime,cs

[Wang W. et. al. – 2014] Demonstra/on of higher colour response with ambient refrac/ve index in Papilio

blumei as compared to Morpho rhetenor Scien/fic Reports

more vigorous than that of the tree-like structure. Thus, in the fol-lowing sections we discuss the model of the concave structure inorder to determine the cause of this heightened colour response.

Sensitivity of the reflection intensity to ambient RI. Reflectancespectra for different field angles (h) of the concave structure are

shown in Figure 5. To understand the relationship between thecolour response, field angle, and the ambient RI, followingobservational characteristics. (1) The reflectance decreased withincreasing of RI. (2) The drop rate of the reflectance (betweenRI51 and RI51.3) decreased as field angle (h) increased. (3) Thehighest drop rate (between RI51 and RI51.3) was located from 90u

Figure 2 | The contour plot of reflectance spectra of P.B. and M.R. versus wavelengths and viewing angles in ethanol and in air. (a)(b) P.B. in ethanoland in air; (c)(d) M.R. in ethanol and in air.

Figure 3 | The models of P.B. and M.R. and the boundary conditions. (a) the 2D and 3D models of tree-like structure evolved from multilayer(b) the 2D and 3D models of concave structure evolved from multilayer. The parameters y1, y2, d and h is shown. The 3-D model is shown in right. (c) theboundary conditions in vertical direction is absorbing (perfectly matched layer, PML) and in horizontal direction is periodic (periodic boundarycondition, PBC). The blue colour is chitin and the green colour is air or ethanol.

www.nature.com/scientificreports

SCIENTIFIC REPORTS | 4 : 5591 | DOI: 10.1038/srep05591 3

Gas sensi/vity

Applica/ons:!An/ccounterfei/ng!surface!BERTHIER et al. Multiscaled polarization effects in insects 127

FIGURE 8 (a) SEM view of a cross section ofa cover scale of Suneve coronata dorsal wingsurface, showing the multilayered structure ofthe membrane and a front view of the scale, (b)showing the regular disposition of the right an-gles

FIGURE 9 The electric fields of a non-polarized wave falling on a diop-tre. According to Snell’s law, the angle of incident θi is equal to the angle ofreflection. The electric field of s wave Es, perpendicular to the plane of inci-dence P.I. remains in the dioptre plane, whatever the incidence – contrary tothe field Ep

the incident medium and refracted at an angle θr in the secondmedium. Two components can then be defined with the elec-tric field parallel to the plane of incidence (p-component) orperpendicular to this plane (s-component) (Fig. 9).

According to the classical boundaries conditions for theelectric field E and the displacement field D, the reflectivity

FIGURE 10 Variations in the reflection factors of s and p waves with the incident angle at the surface of an absorbing material characterized by a complexindex n = n1–ik1, where k1 is the extinction coefficient. (a) For a given angle of incidence θB, known as Brewster angle, the reflection factor of the p wave ona non-absorbing material is equal to zero: the reflected wave is totally s-polarized. (b,c) When the extinction coefficient increases, both Rp and Rs increaseand the minimum of Rp is not equal to 0.

of the s-component, whose electric field always stays in theplane of the dioptre, is monotonously growing with the angleof incidence from R0 at normal incidence to 1 at grazing in-cidence. The reflectivity of the p-component, on the contrary,goes through a minimum for a particular angle θB – the Brew-ster angle – given by:

tgθB = n1

n0, (2)

for non-absorbing materials (Fig. 10a). For θi = θB, the re-flected light is totally p-polarized. Note that θB is alwaysgreater than 45 for a non-absorbing surface in air (n0 = 1).

For absorbing medium, the refractive index n1 should bereplaced by n = n1–ik1 and the minimum of reflection for thep-wave is no more equal to 0 so that the reflected light isstrongly but not totally polarized. We can define a polarizationcontrast P as:

P = Rs − Rp

Rs + Rp, (3)

running from −1 for a p-polarized wave to +1 for an s-polarized one.

Reflection and transmission by a single film

Biophotonic structures considered here are generally consti-tuted by a stack of films. Anyway, one can define an equivalent

[Serge!Berthier!et.$Al.,$2007]!$$Suneve$coronata$

[Poncelet!Olivier]!Cicindella$chinensis$

[Poncelet!Olivier]!Papilio$blumei$

Under!crosscpolarizer$

Blue!is!polarized!Yellow!is!unpolarized!

BERTHIER et al. Multiscaled polarization effects in insects 129

FIGURE 14 Calculated reflectivity of a succession of multilayered planesand grooves of the same width and for the two polarization states

FIGURE 15 When one uses ridged areas only, the surfaces present the samecolour under natural light and it is impossible to distinguish any pattern. Theridges areas can become apparent by using a polarizer letting the reflectedcomponent penetrate. TE and TM are relative to the central motif structures

cumbersome equipment and therefore only concerns centralbodies.

Once their symmetry broken, the effects produced by Pa-pilio and Cicincedela structures can ensure the two first levelsof protection. They can on the one hand generate bright irides-cent colours fulfilling the first level of protection requirementsand on the other hand, create chromatic effects depending onpolarization that correspond to the second level of protection.

In Suneve coronata, no colorimetric effects appear be-cause two opposite polarizing structures are intimately com-bined. But this original arrangement can be advantageouslyused if these structures are spatially separated.

In the following, the calculations are made under normalincidence so that the subscripts s and p are no more appro-priate. They are replaced by TE (transverse electric) and TM(transverse magnetic), relative to the axe of the grooves.

FIGURE 16 Changes in colouration with the polarization of the two sys-tems: plane/grooves and perpendicular grooves. In the first one, the colourchanges but not the luminosity, in contrast with the perpendicular groovessystem

CIE coordinates (x’, y’) Luminosity (Lab)

TE 0.23, 0.52 16.9TM 0.16, 0.36 −6.5

TABLE 1 Chromaticity coordinates of a motif composed of multilayeredplanes and grooves


TE 0.09, 0.23 13TM 0.12, 0.24 33

TABLE 2 Chromaticity coordinates of a motif composed of multilayeredperpendicular grooves. The colour stays unchanged but the contrast of lumi-nosity is important

Change of colour

Many different processes can be imagined based on the twomain effects. The one directly inspired from the phenom-ena produced by structures found in Papilio and Cincidela isbased on succession of grooves and alternated planes of thesame width. This results in a compound colour, one of thecomponents of which can be suppressed to modify the colourby using a polarizer. The motif colour can, thus, vary fromgreen to yellow for example by either suppressing or lettingenter the blue component reflected by multilayer grooves thatreflect yellow under normal incidence (Fig. 12).

The spectra of these different elements, calculated bythe transfer matrix method (Abeles, 1967) are presented onFig. 13. The system is a multilayer of alternatively high (nh =1.94) and low (nl = 1.51) index and thicknesses such that theproduced green colour under normal incidence is very simi-lar to that of the butterfly Suneve coronata: eh = 185 nm andel = 117 nm.










TE 0.23, 0.52 16.9TM 0.16, 0.36 −6.5



TE 0.09, 0.23 13TM 0.12, 0.24 33


Change of colour



[Berthier!et.$Al.,!2007!]!










TE 0.23, 0.52 16.9TM 0.16, 0.36 −6.5



TE 0.09, 0.23 13TM 0.12, 0.24 33


Change of colour



[Berthier et. al. – 2007] Mul/scaled polariza/on effects in Suneve coronata (Lepidoptera) and other insects:

applica/on to an/-counterfei/ng of banknotes Applied physics A

Polariza/on

4

Part I

Morpho-like nanostructures

8 Photonique des insectes

verture d’un band-gap photonique dans un matériau implique l’impossibilité dese propager pour une onde d’une certaine fréquence tout comme son homonymeélectronique empêche les électrons ayant un certain vecteur d’onde de se propa-ger dans la matière. Le plus commun des cristaux photoniques présent sur lesinsectes est un empilement périodique 1D de deux matériaux d’indices optiquesdifférents, appelé miroir de Bragg (Figure 1.3.a). Les propriétés réfléchissantesde ce types de structures sont discutées au chapitre 2. Un aperçu des types decristaux photoniques observables chez les papillons et les scarabées est abor-dées dans les sections suivantes. Un état-de-l’art des intérêts technologiques detelles structures ainsi que de leurs fabrications clôturera ce chapitre.

1.2.1 Cristaux photoniques sur les lépidoptères

Les cristaux photoniques présents sur les papillons font partie intégrantede leurs écailles (Figure 1.4). Ces écailles font en moyenne une centaine demicrons en longueur pour 50 microns en largeur et grandissent à la surface del’aile à l’image des tuiles d’un toit de maison. Il existe deux types principauxd’écailles, les écailles dites de recouvrement et les écailles de fond. Les écaillesde recouvrement sont directement en contact avec l’air. Elles sont souvent ditesstructurelles car elles sont formées de cristaux photoniques donnant la couleuraux papillons.

Figure 1.4: Zoom sur une aile bleue d’un Morpho godarti, laissant apparaitreles écailles et à chacune sa microstructure.

166 Structures bio-inspirées : Morpho

Figure 5.33: Echantillon de 7,5 mm de côté avec un réseau 2000x1000 enAl2O3/TiO2 sous-gravé pendant 15 min à 75 ˝C. (a) Photo de l’échantillon enl’abscence d’illumination directe, (b) image SEM du réseau et (c) diffractionde la lumière par le même échantillon sous différents angles d’observation.

5.6.2 SpectrométrieLa Figure 5.34 présente les spectres spéculaires mesurés à l’aide d’une fibre

bifurquée. Les inserts montrent une photo sous microscope des échantillonsanalysés. Le modèle de simulation utilisé a dû être modifié légèrement afin deprendre en compte plusieurs paramètres expérimentaux, soit l’angle d’ouver-ture de la fibre optique et la taille croissante du tronc des lamelles. Malgréde nombreuses différences, la forme générale des spectres est relativement bienrespectée. L’échantillon Al2O3/TiO2 possède une teinte tirant vers le vert carles troncs ont été légèrement moins sous gravés.

Figure 5.34: Mesure au spectromètre d’un échantillon (a) Al2O3/TiO2 sousgravé et (b) Al2O3/HfO2 sous gravé. Taille des réseaux : 1200 nm x 600 nm.

5.6.3 Spectrométrie en milieu gazeuxEn raison de l’absence de dispositif de caractérisation pour ce genre de

mesure, un système expérimental a été élaboré (Figure 5.35). Celui-ci consiste

Ar/ficial Natural

5

[Potyrailo R. A. et. al. – 2007] Morpho buCerfly wing scales demonstrate highly selec,ve vapour response.

Nature Photonics 6

Principal component analysis (PCA)

Theore/cal gas sensi/vity by FDTD simula/ons

−0.2 0 0.2 0.4 0.6 0.8 1−0.2

0

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1

0.24 0.26 0.28 0.3 0.32 0.34

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0.4v

Physisorp/on or condensa/on around the structures 5 bi-layers

v

TiO2 (n=2.5)

Al2O3(n=2.5)

IPA (n=1.377)

400 500 600 7000.2

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Longueur d’onde [nm]

Réf

lect

ance

Rref

400 500 600 700−0.6−0.4−0.2

00.20.4

Longueur d onde [nm]

300 400 500 600 700 8000.2

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6R

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Réf

lect

ance

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lect

ance

With IPA

Wavelength [nm]

Refle

ctan

ce

IPA thickness

R =Rref R

Rref

7

Computa/on of Σ ΔR for sensi/vity

8

Impact of the design on the sensi/vity (sim.ed)

9

v v

TiO2 (n=2.5)

Al2O3(n=2.5)

IPA (n=1.377)

No selec/vity between different vapours!

−30

−20

−10

0

10

20

−15−10

−50

510

15−10

−5

0

5

PC 1PC 2

PC 3

IPA

Methanol

Water

FDTD simula/on - PCA analysis on ΔR

10

How to make them (according to literature)?


Figure 5.1: Images MEB des structures reproduitent et inspirées du Mor-pho, adaptées de (a) [79] réplique en alumine ALD, (b) [78] réplique en résine(PDMS), (c) [158] réplique en Fe3O4, (d) [161] structure en SiO2 et Si3N4,(e) [162] structure gravée dans la résine, (f) [163] motifs interférentiels inscrisdans une photo-résine, (g) [91] structure réalisée par FIB-CVD, (h) [166] Braggsur substrat de quartz et (i) [168] Bragg sur une monocouche de colloïdes desilice.

Toutes ces techniques présentées ici ont chacune leur avantage et leur incon-vénient, résumés dans le Tableau 5.1. Certaines permettent un contrôle excep-tionnel des dimensions de la structure, nécessaire dans un but d’optimisationde celle-ci, mais sont lourdes à mettre en place et extrêmement lentes (litho-graphie électronique, FIB-CVD). L’utilisation des échantillons naturels permet

[Watanabe et. al., 2004]

FIB-CVD




[Radwanul et. al., 2013]

e-beam lithography

[Radwanul et. al., 2014]

3URFRI63,(9RO(

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/12/2014 Terms of Use: http://spiedl.org/terms

Interferen/al lithography




Deep-UV + standard techniques

[Aryal et. al., 2012]

www.nature.com/scientificreports/

5Scientific RepoRtsȁͻǣͷͼͼͽȁǣͷͶǤͷͶ;Ȁͷͼͼͽ

contribution to green color apart from a very weak peak at 630 nm, which is consistent to the optical image in Fig. 5g.

Ǧ Ǥ To demonstrate angle relevant coloration of the fabricated wing scales, reflectance spectra were scanned from various viewing angles by an angle-resolved microspectroscope (ARM-51M; Ideaoptics Instruments Co. Ltd., China). As schematically shown in Fig. 7, the incident

Figure 3. The FDTD simulations of spatial distributions of the electric field, E2 for the three wavelengths in Figure 3b. (a,b) correspond to the wavelengths at 493 and 524 nm, respectively, in Green_3. The strongest travelling mode seen in the PMMA/LOR pillar in (a) is responsible for the reflection dip at 493 nm in the spectra (both the red and the blue line) in figure 3b. The relatively weak E2 in the multilayer in (b) (524 nm) and (c) (532 nm) explains the high reflection in the spectra. The dash lines highlight the lamellae structures.

Figure 4. The micrographs of scanning electron microscope (SEM) for fabricated wing scales with aligned lamellae multilayers. (a) An overview of the mimicked scale with low magnification. (b) A close-up view of the cross-section of the 11-layer lamellae structure. (c) The cross-sectional view of the 15 layers structure. The top PMMA layer was bent up in the cleaving of the sample. (d) The ridge grating as highlighted by dash-lines.

[Zhang Sichao et. al., 2015]

PMMA/LOR + e-beam

[Potyrailo et. al., 2015]

PMMA/MMA-MAA + e-beam

11

How we did it

Litho opt. + RIE

Plasma CCl4

Removing Cr

Wet etching by H3PO4/IPA

Chrome Hard mask

(a)

(c)

(b)

(d)

(d)

(c) (b)

(a)

12

TiO2/Al2O3 HfO2/Al2O3

1 µm 200 nm

TiO2

Al2O3 Al2O3

HfO2

13

Different sizes

14

Different geometries

15

S/c/on issue is solved by IPA rinsing

16

Some other pictures ...

17

Failed cleaving

18

Colors exhibited by the samples

1 mm

200 nm

0,5 cm

3 mm

19

Thesis of Sébas/en Mouchet – Université de Namur Fundamental Mechanisms of structural colora/on: addi/ve and induced colours

Sept. 2015

Test set-up: measurement chamber

Establishing /me before recording the spectrum: 5 min

20

Ethanol sensi/vity

Wavelength [nm] Wavelength [nm]

Refle

ctan

ce

Refle

ctan

ce

IPA sensi/vity

Wavelength [nm] Wavelength [nm]

Refle

ctan

ce

Refle

ctan

ce

Measurements comparison

Ethanol

IPA

HfO2

TiO2

23

Perspec/ves

Full coa/ng

Al2O3

TiO2

HfO2

Polymer cas/ng

Fabrica/on of the Bragg structure using porous silicon

SiO2

24

Part II

Blumei-like porous structures

1.2. Cristaux photoniques naturels 11

Figure 1.7: Zoom sur la partie verte d’une aile d’un Urania leilus. Les écaillessont convexes et formées d’un multicouche.

Figure 1.8: Zoom sur la partie verte de l’aile d’un Papilio blumei. Les écaillessont légèrement convexes et présentent des micro-cavités concaves.




Ar/ficial Natural

26

Fabrica/on techniques of the nanostructure

Literature

[Kolle et. al., 2010]

Colloïds + ALD

No porosity

+ ALD

Porosifica/on

Macro-curvature + porous Bragg mirror







Natural structure from Papilio species

Papilio blumei

28 [Poncelet et. al., 2015]

HNA wet etching

31

Mul/ple paths interac/ons

Fabrica/on step-by-step

32

The substrate doping increases anisotropy

•  p++ silicon is needed to get a smoothly etched surface

•  But, it reduces the isotropicity of the wet etching

•  We produced a flat Bragg mirror in porous silicon for comparison to figure out the impact of the curvature 33

Measurements with ethanol vapour

The sensi/vity is increased by using cavi/es Flat surface Bragg mirror Porous cavi/es Bragg mirror

34

Measurements comparison

Increased sensi/vity is observed for both ethanol and 2-propanol

Higher response for ethanol

Ethanol

IPA

35

Morpho (best result)

36

How to get an improved bio-inspired vapour sensor?

A sharp filter func/on à  Bragg mirror needed

But … not too good.

λ

R

Porous/selec/ve material(s)

λ

R

Mul/ple paths à Curved surfaces

Conclusions

ü  Vapour sensi/vity is exhibited by Morpho and Blumei-inspired

synthe/c nanostructures

ü  Large-scale fabrica/on schemes have been proposed that are based

on standard op/cal lithography, ALD mul/layers or porous silicon, and

a combina/on of wet and dry etching

ü  The sensi/vity is increased for a mul/ple paths porous nanostructure

ü  The selec/vity is material dependant (unlike theore,cally predicted …)

37

Acknowledgements

Jean-Pol Vigneron† and Serge Berthier for inspira/on UCL WINFAB technical team for help with microfabrica/on Ac/ons de Recherches Concertées (BIOSTRUCT project) of the Académie universitaire Louvain, and the F.R.S.-FNRS for funding

38

Thank you! Ques/ons?

[email protected]

vapour sensing properties of bio-inspired synthetic nanostructures

Science