Gaëlle Gassin-Martin

1. 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 interfacesLaboratoire de Spectrométrie Ionique et Moléculaire (LASIM) – Lyon -

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

3. Overview • Molecular film • Langmuir film formation • Importance of optical measurement • Properties upon compression • Polarisation resolved Second Harmonic Generation (SHG) • Metallic nanoparticles film • Evolution of interactions upon compression • Linear reflectance • SHG • Film dynamics at the air/water interface • Intensity correlation analysis

4. air water Molecule :DiA hydrophobic tail hydrophilic head • Amphiphilic molecule • Large nonlinear response (electrons p delocalised, « push-pull » structure) • Excellent surface SHG probe

5. Molecular films Langmuir trough • Control the densityin situ Densification

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

7. Filter Photon counter Laser femto Mirrors Chopper Langmuir trough 70° Langmuir trough Polarisation resolved SHG of a film- Experimental set up - • Polarisation measurement • A l/2 wave plate permits the variation of the incident light polarisation • An analyser to select the emergent light polarisation • Experimental curves interpretation, exit S polarised l/2 Lens Analyser Pressure Measurement Above Langmuir trough profile

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

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

10. Microscopic dimension Induced dipole defined by : Hyperpolarisabilty 1st order polarisability • Hyperpolarisabilty tensor βmicroscopic parameter which characterises the molecule. • Susceptibility tensor χmacroscopic parameter which characterises the surface.

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

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

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

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

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

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

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

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

19. Overview • Molecular Film • Langmuir films • Importance of optical measurement • Proprieties under compression • SHG resolved in polarisation • Film of metallic nanoparticles • Evolution of interactions upon compression • linear reflectance • SHG • Film dynamic at the air/water interface • Intensity correlation analysis

20. Thioalkanes C12 Nanoparticles Synthesis Metallic Nanoparticles Gold and Sliver Ø 7 nm Brust Method • Surface capped thioalkanes hydrophobic particles adapted to 2D film formation Silver Nanoparticles in chloroform Chain length variation: Nano Particle • Chains C18 limited interactions • Chains C12 , C6 … allowed interactions Collaboration LPCML ( Olivier Tillement, Stéphane Roux)

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

22. Beam splitter Objective Pressure Measurement Langmuir trough Detection Detection Filter Lampe HaDe femto Laser Dichroïc mirror Beam splitter Filter Objective Objective Langmuir trough Langmuir trough Linear reflectance and SHG of a film-experimental set up- Reflected Spectrum at 90° incidence on the surface Sources : Linear measurements : HaDe lamp Nonlinear measurements : femtosecond laser Metallic Nanoparticles capped C18

23. Linear reflectance -Silver nanoparticles film- Surface density : 3, 4 and 7x1014 particles /m² • Strong fluctuations of reflectance • Disappearance 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

24. Linear reflectance -Silver nanoparticles film- Surface density: 3, 4 et 7x1014 particles /m² The behaviour is easily observed after normalised of the reflectance spectra • Maximum reflectance Amplitude increases at 660 nm with compression

25. 50 nm Linear reflectance modelling -Silver nanoparticles film- Simulations with hypothesis of particles aggregate Simulations with hypothesis of non aggregated particles Surface density : 9x1014 particles /m² Broaden = Effective film theory for spherical particles heterogeneous set of ellipsoid Isolated particles (weak surface fraction ) Particles in strong interaction equivalent to an ellipsoid (model) High surface fraction Effective film theory for ellipsoidal particles • 2nd resonance shows the beginning of interactions

26. Conclusions -Silver nanoparticles film- Diluted system (surface filling factor = 3%) Long alcane Chains C18 Expect : No aggregation No interaction • Strong fluctuations at weak compression which disappear at high density • Prove :Inhomogeneous surface, existence of domains Domains movements frozen • 2nd plasmon resonance increases • Prove :Interactions appear upon compression Modification of for the particles SHG Compression

27. 420 nm Measured noise 400 nm Measured SHG SHG of particles films -Gold nanoparticles film- • Continuous compression • Density: 2 to 11x1014 particles/m² Compression Few sharp picks

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

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

30. Conclusion -Silver nanoparticles film- Diluted system (surface filling factor = 3%) Long alkane Chains C18 Expect: No aggregation No interaction • 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 Recurrence of these fluctuations phenomenon • Reflectance • SHG

31. SignalFluctuations To extract quantitative information from this systematic observation • Analysis using autocorrelation calculation Autocorrelationfunction SHG signal intensity 2 distinct characteristic times hydrophilic silver Nanoparticles Ø 7 nm

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

33. Density : 1.7x1014 part/m² Density : 3.2x1014 part/m² Density : 4.4x1014 part/m² = 1 second = 2 seconds = 6 seconds = 40 seconds Density : 5.3x1014 part/m² Density : 8x1014 part/m² >> 100 seconds Reflectance fluctuation all along compression -Silver nanoparticles film- Signal intensity Autocorrelation function Linear signal study • Characteristic fluctuation time increases • g(0) value decreases Silver nanoparticles Ø 7 nm capped C12

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

35. Evolution of the parameter t Characteristic time increases • Frozen movements on the surface for high density Agreggate size evolution from nm to µm Compression

36. Spot light Domain Autocorrelation function from a silver nanoparticles film density 2x1014 part/m² vi Autocorrelation curve fitting -Silver nanoparticles film- Checked : No disregard waves Autocorrelation function Brownian diffusion Lateral flow

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

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

39. 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