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R. Bachelot , H. Ibn-El-Ahrach 1 , O. Soppera 2 , A. Vial 1 ,A.-S. Grimault 1 , G. Lérondel 1 , J. Plain 1 and P. Ro

Spectral degeneracy breaking in plasmon resonance of single metal nanoparticles by nanoscale near-field photopolymerization. R. Bachelot , H. Ibn-El-Ahrach 1 , O. Soppera 2 , A. Vial 1 ,A.-S. Grimault 1 , G. Lérondel 1 , J. Plain 1 and P. Royer 1

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R. Bachelot , H. Ibn-El-Ahrach 1 , O. Soppera 2 , A. Vial 1 ,A.-S. Grimault 1 , G. Lérondel 1 , J. Plain 1 and P. Ro

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  1. Spectral degeneracy breaking in plasmon resonance of single metal nanoparticles by nanoscale near-field photopolymerization R. Bachelot, H. Ibn-El-Ahrach1, O. Soppera2 , A. Vial1 ,A.-S. Grimault1, G. Lérondel1, J. Plain1 and P. Royer1 1 Laboratoire de Nanotechnologie et d’Instrumentation Optique, Institut Charles Delaunay. FRE CNRS 2848. Université de Technologie de Troyes, France 2 Département de Photochimie Générale ,Université de Haute-Alsace Mulhouse, France

  2. Tuning plasmon resonance of metallic nanoparticles (MRS bulletin May 2005, Vol. 30, N°5) • Geometry : shape and size • Rods, stars, triangles… • Chemical synthesis / e-beam lithography • Single particle coupling (dimers, trimers,chains,..) • Core/shell approach • Ex: «Nanorice» (Rice University) • Effective refractive index (polymer coating, surrounding medium) • Nanosensors • But so far only isotropic modification (symmetry was kept) What about anisotropic modification of the surrounding index ?

  3. A new approach: local photopolymerization Triggered by local enhanced fields of metal nanostructures Based on local isomerization

  4. hn The Photopolymer formulation Eosin absorption spectrum composition: Initiator ( Eosin Y) Co-initiator (MDEA) Monomer (PETIA) Radical polymerization

  5. The photopolymer formulation • Formulation properties • Polymerization threshold energy • Refractive index • 1.48 for 0% reticulation • (liquid formulation) • 1.52 for 100% reticulation • (Crosslinked polymer)

  6. Experimental set-up Interference area Diaphragm Lens Optical fiber Polarizer Mirror Beam splitter A key parameter : the threshold energy.Far field characterization of this parameter Ar laser 515nm

  7. Far field characterization of the Photopolymerization Experimental characterization of the threshold energy of polymerization Threshold polymerization energy (a)AFM image of a polymer grating obtained after 12mJ/cm² (b)AFM image of a polymer grating obtained after 20mJ/cm² Threshold energy value = 10 mJ/cm²

  8. FDTD P Dose Confined optical source Dose Threshold energy Dpolymérisation Incident energy Dincidente x x Near field photopolymerization • Principle • Incident energy Ei< Ethreshold Overcoming the threshold energy by local enhancement of the optical near field

  9. Experimental approach 1) E-beam lithography 4) Monomer removal (Rinsing) 5) Characterization: - AFM -Spectroscopy 2) Coating (drop) 3) Illumination Near field illumination Array of Ag particles Diameter ~ 70nm height = 50nm D=2,5mW/cm2 four time weaker than the threshold polymerization value Argon Laser (514 nm) linear Polarization 500 nm

  10. Results : AFM images p p p AFM Images after irradiation E intensity ( FDTD) • 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

  11. P (d) (c) (b) (a) Results : polarized extinction spectroscopy Spectral degeneracy breaking of the SPR in the hybrid nanoparticle • New induced symmetry CC2 • Two artificial plasmon eigenmodes (508nm and 528nm) (a), (b) : isotropic response

  12. Polarized extinction spectroscopy E FWHM () θ FWHM maximum for 45 degrees / axis of the hybrid particle Linear combination of the two eigenmodes Dipolar diagram resonance() Continuous tunable SPR mode ? Quasi Continuous tunable SPR mode

  13. Polarized extinction spectroscopy  distribution of nanoscale effective refractive index neff() Dipolar diagram Spatial extension of the two polymer lobes Nanoscale effective index distribution neff() Reference : particle surrounded by an “homogeneous” medium: glass substrate + liquid formulation before exposure ( nm~1.5)

  14. P Conclusion • Controlled Nanoscale photopolymerization around a single metallic particles excited close to their dipolar plasmon resonance • Breaking of symmetry of the dielectric environment of the nanoparticles • Spectral degeneracy breaking of the SPR • Nanoscale effective index distribution • Tunability of the plasmon resonance • First step towards new hybrid metal-organic particles with new functionalities (polymer engineering) • Refractive index, photoluminescence (absorption), • Nonlinearity • Exciting higher SP modes • Multiple exposures

  15. Thank you for your attention • Thanks to J.J. Greffet, R. Carminati and A. Bouhelier

  16. 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

  17. P P Case of the photo-izomerization (C. Hubert et al. Nanoletters 5, 615) Case of the photo-polymerization Radical aminyle E:eosin, AH:amine +propagation+termination

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