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Static and dynamic studies using linear reflectance and second harmonic generation of molecular and metallic nanoparticles films at the air/water interface. Gaëlle Gassin-Martin Nonlinear Optics and interfaces Laboratoire de Spectrométrie Ionique et Moléculaire (LASIM) – Lyon -

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General idea: Nanometric studies using nonlinear optics oBi-dimensional films upon compression Control of the average distance between nano- objects Control of the average distance between nano- objects Vary the amplitude of the interactions Vary the amplitude of the interactions oOptical measurement of the electronic delocalisation Molecular systems (molecular aggregates) Molecular systems (molecular aggregates) Metallic systems (nanoparticles) Metallic systems (nanoparticles) Aims

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oMolecular film oLangmuir film formation oImportance of optical measurement oProperties upon compression Polarisation resolved Second Harmonic Generation (SHG) Polarisation resolved Second Harmonic Generation (SHG) oMetallic nanoparticles film oEvolution of interactions upon compression Linear reflectance Linear reflectance SHG SHG oFilm dynamics at the air/water interface Intensity correlation analysis Intensity correlation analysis Overview

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Molecule : DiA hydrophilic head hydrophilic head hydrophobic tail air water oAmphiphilic molecule oLarge nonlinear response (electrons delocalised, « push-pull » structure) Excellent surface SHG probe Excellent surface SHG probe

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Molecular films Control the density in situ Control the density in situ Langmuir trough Langmuir trough Densification

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Film isotherms Knowledge of certain macroscopic states (S, P, T, pH…) all along the film formation Knowledge of certain macroscopic states (S, P, T, pH…) all along the film formation Control of interactions in the system Control of interactions in the system compression Condensed liquid Expanded liquid Compression

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Polarisation resolved SHG of a film - Experimental set up - Experimental curves interpretation, exit S polarised Experimental curves interpretation, exit S polarised 70° Langmuir trough Mirrors Laser femto Filter Chopper Langmuir trough Photon counter profile Above Analyser Polarisation measurement Polarisation measurement oA wave plate permits the variation of the incident light polarisation oAn analyser to select the emergent light polarisation Pressure Measurement Langmuir trough Lens

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Second harmonic generation SHG process : brings into play the second order polarisation SHG 2 nd order susceptibility tensor SHGmeasurement Excitation at 800 nm at 800 nm

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Centrosymmetric property The symmetry is very important for this process The symmetry is very important for this process SHG is always null in centrosymmetric medium SHG is always null in centrosymmetric medium Wide interest with the surface which represents a symmetry break exclusive measurement of surface properties ( ) exclusive measurement of surface properties ( ) Centrosymmetric medium

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Microscopic dimension Microscopic dimension Induced dipole defined by : oHyperpolarisabilty tensor β microscopic parameter which characterises the molecule. oSusceptibility tensor χ macroscopic parameter which characterises the surface. polarisability Hyperpolarisabilty 1 st order

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Surface pressure : continuous growing Surface pressure : continuous growing Molecular film collapse -DiA molecular film - oHigh monolayer compression oSimultaneous measurements : Molecular Density : 0.4 to 3 nmoles/cm² Some information remain inaccessible by surface pressure measurement. SHG technique convincing DiA : 2 carbon chains liquid film with a lot of defects liquid film with a lot of defects SHG signal falls related to multilayer formation SHG: Signal falls at high density SHG: Signal falls at high density centrosymmetry Non centrosymmetry Micelle Contre-ions

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Polarisation analysis -DiA molecular film - Molecular Density : 0.43 nmoles/cm² Isotropic surface ED Approximation (electric dipolar) High degree of symmetry High degree of symmetry incident polarisation angle

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Isotropic chiral Surface -DiA molecular film - Molecular Density : 0.8 nmoles/cm² Monolayer compression Monolayer compression isotropic surface ED Approximation Chirality with ED approximation not sufficient Chirality with ED approximation not sufficient (Chiral) Chiral Unique possible origin for 90° angle deformation is chirality's phenomenon

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Introduction of magnetic components -DiA molecular film - MD Approximation MD Approximation Molecular Density : 0.8 nmoles/cm² Isotropic chiral Surface ED Approximation Chirality with MD approximation adapted Chirality with MD approximation adapted (Chiral) (Chiral)

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Fitting curves Tensor elements which translate surface state all along compression A B C D E F G A B C D E F G Evolution of S-polarised curves all along compression -DiA molecular film - Progressive symmetry breaking all along the compression Progressive symmetry breaking all along the compression Molecular Density : 0.2 to 1.4 nmoles/cm² threshold : 0.5 nmoles/cm² A B C D E F G

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Increase chiral tensor element Increase chiral tensor element Becomes comparable to Becomes comparable to Uncertainty about the origin of chiral tensor evolution Uncertainty about the origin of chiral tensor evolution Chiral tensor element -DiA molecular film- Compression Sign change

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oMicroscopic models of chiral aggregates Helix aggregates Helix aggregates Microscopic Interpretation -DiA Molecular film - Even if we lack some information we know : DiA non chiral molecule attest an isotropic chiral surface attest an isotropic chiral surface Progressive formation of chiral structures upon compression Progressive formation of chiral structures upon compression Model: an electron along an helix It drives us to think about:

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Conclusions -DiA molecular film- Langmuir technique : squeeze the molecules to form a 2D film Chiral aggregates formation Chiral aggregates formation SHG technique : sensible to surface phenomenon Measure electronic delocalisation effects in these chiral aggregates upon compression Measure electronic delocalisation effects in these chiral aggregates upon compression Molecular Films Nanoparticles Films

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oMolecular Film oLangmuir films oImportance of optical measurement oProprieties under compression SHG resolved in polarisation SHG resolved in polarisation oFilm of metallic nanoparticles oEvolution of interactions upon compression linear reflectance linear reflectance SHG SHG oFilm dynamic at the air/water interface Intensity correlation analysis Intensity correlation analysis Overview

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Thioalkanes C 12 Metallic Nanoparticles Gold and Sliver Ø 7 nm Nanoparticles Synthesis hydrophobic particles adapted to 2D film formation Silver Nanoparticles in chloroform Nano Particle Surface capped thioalkanes Surface capped thioalkanes BrustMethod Chain length variation: Chains C 18 limited interactionsChains C 18 limited interactions Chains C 12, C 6 … allowed interactionsChains C 12, C 6 … allowed interactions Collaboration LPCML ( Olivier Tillement, Stéphane Roux)

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Consequences on optical response (new resonances, field enhancement…) Consequences on optical response (new resonances, field enhancement…) Aggregates formation Aggregates formation Emergence of interactions upon compression Emergence of interactions upon compression Nanoparticles Films -Aims- Nanoparticles deposit thanks to a microlitric syringe Film compression

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Lampe HaDe Beam splitter Objective Langmuir trough Detection Langmuir trough Pressure Measurement Objective Beam splitter Linear reflectance and SHG of a film -experimental set up- Reflected Spectrum at 90° incidence on the surface Sources : Sources : Linear measurements : HaDe lamp Metallic Nanoparticles capped C 18 femto Laser Filter Dichroïc mirror Objective Langmuir trough Detection Nonlinear measurements : femtosecond laser

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Surface density : 3, 4 and 7x10 14 particles /m² 3, 4 and 7x10 14 particles /m² Linear reflectance -Silver nanoparticles film- oStrong fluctuations of reflectance oDisappearance of fluctuations for high density Reflectance is the ratio between reflection spectrum of the film to the reference reflection spectrum 2 consecutive measurements for each compression

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oMaximum reflectance Amplitude increases at 660 nm with compression Surface density: 3, 4 et 7x10 14 particles /m² 3, 4 et 7x10 14 particles /m² Linear reflectance -Silver nanoparticles film- The behaviour is easily observed after normalised of the reflectance spectra

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Particles in strong interaction equivalent to an ellipsoid (model) High surface fraction Surface density : 9x10 14 particles /m² Linear reflectance modelling -Silver nanoparticles film- Simulations with hypothesis of non aggregated particles Simulations with hypothesis of particles aggregate Isolated particles (weak surface fraction ) Effective film theory for spherical particles Effective film theory for ellipsoidal particles 50 nm 2 nd resonance shows the beginning of interactions 2 nd resonance shows the beginning of interactions heterogeneous set of ellipsoid Broaden =

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Conclusions -Silver nanoparticles film- Strong fluctuations at weak compression which disappear at high density Strong fluctuations at weak compression which disappear at high density Prove : Inhomogeneous surface, existence of domains Domains movements frozen Domains movements frozen 2 nd plasmon resonance increases 2 nd plasmon resonance increases Prove : Interactions appear upon compression Prove : Interactions appear upon compression Diluted system (surface filling factor = 3%) Long alcane Chains C 18 Expect : No aggregation No interaction No interaction Compression Modification of for the particles SHG

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Measured noise oContinuous compression oDensity: 2 to 11x10 14 particles/m² SHG of particles films -Gold nanoparticles film- 400 nm 420 nm Measured SHG Compression Few sharp picks

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Non linear signal -Gold nanoparticles film- For each average density: o o Log normal fit Intensity histograms 6 temporal domains

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Necessity to introduce the tensor. It proves the presence of interactions between particles Necessity to introduce the tensor. It proves the presence of interactions between particles Density variation Density variation N But do not decrease Nonlinear signal -Gold nanoparticles film-

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Conclusion -Silver nanoparticles film- Necessity to introduce the element at high compression Necessity to introduce the element at high compression Prove: Existence of interactions in compressed film Link with the increase of the second resonance plasmon concerning reflectance measurements Link with the increase of the second resonance plasmon concerning reflectance measurements Recurrence of these fluctuations phenomenon Reflectance Reflectance SHG SHG Diluted system (surface filling factor = 3%) Long alkane Chains C 18 Expect: No aggregation No interaction No interaction

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Signal Fluctuations To extract quantitative information from this systematic observation Analysis using autocorrelation calculation Analysis using autocorrelation calculation Autocorrelation function 2 distinct characteristic times hydrophilic silver Nanoparticles Ø 7 nm SHG signal intensity

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Autocorrelation calculation Signal memory measurement between t et t + Two characteristic values: Function at the origin Function at the origin g(0) Decorrelation characteristic time Decorrelation characteristic time

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Reflectance fluctuation all along compression -Silver nanoparticles film- Density : 1.7x10 14 part/m²Density : 3.2x10 14 part/m² Density : 4.4x10 14 part/m² Density : 5.3x10 14 part/m² Density : 8x10 14 part/m² = 1 second = 2 seconds = 6 seconds = 40 seconds >> 100 seconds Characteristic fluctuation time increases Characteristic fluctuation time increases g(0) value decreases g(0) value decreases Signal intensity Autocorrelation function Linear signal study Silver nanoparticles Ø 7 nm capped C 12

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Evolution of the parameter g(0) g(0) decreases g(0) Compression Density of particles aggregates increases under the laser spot Density of particles aggregates increases under the laser spot g(0)

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Evolution of the parameter Evolution of the parameter Characteristic time increases Compression Frozen movements on the surface for high density Frozen movements on the surface for high density Agreggate size evolution fromnm to µm

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Autocorrelation curve fitting -Silver nanoparticles film- Autocorrelation function Autocorrelation function from a silver nanoparticles film density 2x10 14 part/m² Spot light Domain vivi Brownian diffusion Lateral flow Checked : No disregard waves

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Conclusions -Nanoparticles films- Conclusions -Nanoparticles films- Some interactions between particles appear when the surface is compressed : Linear reflectance Linear reflectance SHG SHG Possibility to measure the dynamics of the film : Presence of moving nanoparticules domains Presence of moving nanoparticules domains Dynamic evolution during compression Dynamic evolution during compression Compression

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General Conclusions oMolecular films upon compression: Molecular aggregates arrangement Molecular aggregates arrangement Presence of chirality in aggregates Presence of chirality in aggregates Evidence of electronic delocalisation in aggregates Evidence of electronic delocalisation in aggregates oBi-dimensional Langmuir films studies: Control the distance between nano-objects Control the distance between nano-objects Modulate the interactions between nano- objects Modulate the interactions between nano- objects oMetallic nanoparticles films: Beginning of interactions upon compression Beginning of interactions upon compression Observation of the film dynamics Observation of the film dynamics nano-objects without interaction 2D system with interaction

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Have a look to my PhD group … Thank you every one ! ! Pierre-François Brevet, Emmanuel Benichou, Guillaume Bachelier, Isabelle Russier-Antoine, Christian Jonin, Guillaume Revillod, Chawki Awada, Yara El Harfouch, Julien Duboisset, Lin Pu

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