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R. BachelotR. Bachelot, H. Ibn-El-AhrachH. Ibn-El-Ahrach11, O. Soppera, O. Soppera22 , A. Vial , A. Vial11 ,A.-S. ,A.-S. GrimaultGrimault11, G. Lérondel, G. Lérondel11, J. Plain, J. Plain11 and P. Royer and P. Royer1 1

1 Laboratoire de Nanotechnologie et d’Instrumentation Optique, Institut Charles Delaunay. FRE CNRS 1 Laboratoire de Nanotechnologie et d’Instrumentation Optique, Institut Charles Delaunay. FRE CNRS 2848. Université de Technologie de Troyes, France2848. Université de Technologie de Troyes, France

2 Département de Photochimie Générale ,Université de Haute-Alsace Mulhouse, France2 Département de Photochimie Générale ,Université de Haute-Alsace Mulhouse, France

Spectral degeneracy breaking in plasmon resonance of single metalnanoparticles by nanoscale near-field photopolymerization

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Geometry : shape and size Geometry : shape and size – Rods, stars, triangles…Rods, stars, triangles…– Chemical synthesis / e-beam lithographyChemical synthesis / e-beam lithography

Single particle coupling (dimers, trimers,chains,..)Single particle coupling (dimers, trimers,chains,..)

Core/shell approachCore/shell approach– Ex: «Nanorice»Ex: «Nanorice»

(Rice University)(Rice University)

Effective refractive index (polymer coating, surrounding medium) Effective refractive index (polymer coating, surrounding medium) – Nanosensors Nanosensors – But so far only isotropic modification (symmetry was kept)But so far only isotropic modification (symmetry was kept)

What about anisotropic modification of the surrounding index ?What about anisotropic modification of the surrounding index ?

Tuning plasmon resonance of metallic Tuning plasmon resonance of metallic nanoparticles (MRS bulletin May 2005, Vol. 30, nanoparticles (MRS bulletin May 2005, Vol. 30,

N°5)N°5)

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Based on local isomerization

A new approach: local photopolymerization

Triggered by local enhanced fields of metal nanostructures

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The Photopolymer The Photopolymer formulationformulation

composition:

Initiator ( Eosin Y)

Co-initiator (MDEA)

Monomer (PETIA)

Radical polymerization

Eosin absorption spectrum

h

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The photopolymer formulationThe photopolymer formulation

Formulation propertiesFormulation properties– Polymerization threshold Polymerization threshold

energyenergy– Refractive indexRefractive index

1.48 for 0% reticulation

(liquid formulation)

1.52 for 100% reticulation

(Crosslinked polymer)

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A key parameter : the threshold A key parameter : the threshold energy.energy.

Far field characterization of this Far field characterization of this parameterparameter

Optical fiberLens

Diaphragm

Beam splitter

Mirror

Polarizer

Experimental set-up

Interference area

Ar laser 515nm

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Far field characterization of the Far field characterization of the PhotopolymerizationPhotopolymerization

Experimental characterization of the threshold energy of polymerization

(a)AFM image of a polymer grating obtained after 12mJ/cm²

(b)AFM image of a polymer grating obtained after 20mJ/cm²

4 6 8 10 12 14 16 18 20 22 24-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Gra

tin

g d

ep

th

m)

Dose (mJ/cm2)

Threshold polymerization

energy

Threshold energy value = 10 mJ/cm²

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PrinciplePrinciple

Incident energy EIncident energy Eii< E< Ethresholdthreshold

Near field Near field photopolymerizationphotopolymerization

Dose

x

Dincidente

Dpolymérisation

Dose

x

Incident energy

Threshold energy

Confined optical source

Overcoming the threshold energy by local enhancement of the optical near field

P

FDTD

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Experimental approachExperimental approach

1) E-beam lithography1) E-beam lithography

4) Monomer removal (Rinsing)4) Monomer removal (Rinsing)5) Characterization: - AFM5) Characterization: - AFM

-Spectroscopy-Spectroscopy

2) 2) CoatingCoating (drop) (drop)

3) 3) IlluminationIllumination

Near field illuminationNear field illumination

Array of Ag particles

Argon Laser (514 nm)

linear Polarization

D=2,5mW/cm2

four time weaker than the

threshold polymerization value500 nm

Diameter ~ 70nmDiameter ~ 70nmheight = 50nmheight = 50nm

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Results : AFM imagesResults : AFM images

97nm260nm

AFM Images after irradiationAFM Images after irradiation

pp

Two symmetric polymer lobes built up near the metal particles and oriented along the direction of polarization of the incident light

Polymer lobes describe the spatial distribution of the optical near field of the metallic nanoparticle excited close to its dipolar plasmon resonance

p

E intensity E intensity ( FDTD)( FDTD)

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500 600

1,00

1,05

1,10

1,15

1,20

1,25

1,30

1,35

1,40

1,45

1,50

Inte

nsi

ty (

a.u

.)

Wavelenth (nm)

(a)

500 600

1,00

1,05

1,10

1,15

1,20

1,25

1,30

1,35

1,40

1,45

1,50

Inte

nsi

ty (

a.u

.)

Wavelenth (nm)

(b)

Results : polarized extinction Results : polarized extinction spectroscopyspectroscopy

New induced symmetry CC2

Spectral degeneracy breaking of the SPR in the hybrid nanoparticle

500 600

1,00

1,05

1,10

1,15

1,20

1,25

1,30

1,35

1,40

1,45

1,50

Inte

nsi

ty (

a.u

.)

Wavelenth (nm)

(c)

500 600

1,00

1,05

1,10

1,15

1,20

1,25

1,30

1,35

1,40

1,45

1,50

Inte

nsi

ty (

a.u

.)

Wavelenth (nm)

(d)

Two artificial plasmon eigenmodes (508nm and 528nm)

97nm

P

(a), (b) : isotropic response

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Polarized extinction spectroscopyPolarized extinction spectroscopyDipolar diagram

Eθ0

30

60

90

120

150

180

210

240270

300

330

508

512

516

520

524

508

512

516

520

524

Re

so

na

nc

e W

av

ele

ng

ht

(nm

)

Continuous tunable SPR mode ?

resonance()

0

30

60

90

120

150

180

210

240270

300

330

95

100

105

110

95

100

105

110

FW

HM

(

nm

)Linear combination of the two eigenmodes

FWHM maximum for 45 degrees / axis of the hybrid particle

FWHM ()

Quasi Continuous tunable SPR mode

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0

30

60

90

120

150

180

210

240270

300

330

1,12

1,16

1,20

1,24

1,28

1,12

1,16

1,20

1,24

1,28

ne

ff

d

dnn

nnn

Ag

mres

resmeff

/4

)(

Nanoscale effective index distribution neff()

Minor axis Major axis

Effective index 1,06 1,14 1,28

Hybrid particlesOriginal sample

Spatial extension of the two polymer lobes

neff()Dipolar diagram

Polarized extinction spectroscopy Polarized extinction spectroscopy distribution of nanoscale effective distribution of nanoscale effective

refractive indexrefractive index

Reference : particle surrounded by an “homogeneous” medium: glass substrate + liquid formulation before exposure ( nm~1.5)

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ConclusionConclusion

Controlled Nanoscale photopolymerization around a single Controlled Nanoscale photopolymerization around a single metallic particles excited close to their dipolar plasmon metallic particles excited close to their dipolar plasmon resonanceresonance

Breaking of symmetry of the dielectric environment of the Breaking of symmetry of the dielectric environment of the nanoparticlesnanoparticles– Spectral degeneracy breaking of the SPRSpectral degeneracy breaking of the SPR– Nanoscale effective index distribution Nanoscale effective index distribution – Tunability of the plasmon resonance Tunability of the plasmon resonance

First step towards new hybrid metal-organic particles with First step towards new hybrid metal-organic particles with new functionalities (polymer engineering) new functionalities (polymer engineering) – Refractive index, photoluminescence (absorption), Refractive index, photoluminescence (absorption), – NonlinearityNonlinearity– Exciting higher SP modesExciting higher SP modes– Multiple exposuresMultiple exposures

97nm

P

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Thank you for your Thank you for your attentionattention

Thanks to J.J. Greffet, R. Carminati Thanks to J.J. Greffet, R. Carminati and A. Bouhelierand A. Bouhelier

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which kind of energy conversion ?

In NSOM : energy transfer between evanescent waves and the nanoprobe conversion of inhomogeneous surfaces waves into homogeneous propagating waves

In our cases : near-field optical energy is locally transferred into chemical energy new method of near-field imaging + new functionalities

E:eosin, A:amine

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E *Eh AH ** AHE

** AEH *AM

E:eosin,

AH:amine

Case of the photo-polymerization

Case of the photo-izomerization (C. Hubert et al. Nanoletters 5, 615)

P

P Radical aminyle

+propagation+termination

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