1. 1 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 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 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 Spectral degeneracy breaking in plasmon resonance of single metal nanoparticles by nanoscale near- field photopolymerization

2. 2 n Geometry : shape and size –Rods, stars, triangles… –Chemical synthesis / e-beam lithography n Single particle coupling (dimers, trimers,chains,..) n Core/shell approach –Ex: «Nanorice» (Rice University) n 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 ? Tuning plasmon resonance of metallic nanoparticles (MRS bulletin May 2005, Vol. 30, N°5)

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

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

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

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

7. 7 Far field characterization of the Photopolymerization 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 Threshold polymerization energy Threshold energy value = 10 mJ/cm²

8. 8 n Principle ã Incident energy E i < E threshold Near field photopolymerization Dose x D incidente D polymérisation Dose x Incident energy Threshold energy Confined optical source Overcoming the threshold energy by local enhancement of the optical near field P FDTD

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

10. 10 Results : AFM images AFM Images after irradiation p p ãTwo symmetric polymer lobes built up near the metal particles and oriented along the direction of polarization of the incident light ãPolymer lobes describe the spatial distribution of the optical near field of the metallic nanoparticle excited close to its dipolar plasmon resonance p E intensity ( FDTD)

11. 11 (a) (b) Results : polarized extinction spectroscopy ã New induced symmetry C   C 2 Spectral degeneracy breaking of the SPR in the hybrid nanoparticle (c) (d) ã Two artificial plasmon eigenmodes (508nm and 528nm) P (a), (b) : isotropic response

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

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

14. 14 Conclusion n Controlled Nanoscale photopolymerization around a single metallic particles excited close to their dipolar plasmon resonance n 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 n First step towards new hybrid metal-organic particles with new functionalities (polymer engineering) –Refractive index, photoluminescence (absorption), –Nonlinearity –Exciting higher SP modes –Multiple exposures P

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

16. 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. 17 E:eosin, AH:amine Case of the photo-polymerization Case of the photo-izomerization (C. Hubert et al. Nanoletters 5, 615) PP Radical aminyle +propagation+termination

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