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 Bonjour à tous Aujourd’hui je vais vous presenté un bilan de mon travail de these dans l’equipe d’optique NLI Le titre de mon exposé est le suivant Nonlinear Optics and interfaces Laboratoire de Spectrométrie Ionique et Moléculaire (LASIM) – Lyon -

Aims Bi-dimensional films upon compression 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)

Overview Molecular film Metallic nanoparticles 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 L’ensemble du travail que nous avons effectuer durant ces 3 ans a debuter par la familiariser avec la technique de formation et d’etude de films langmuir à l’interface air eau . Nous avons debuter avec un molecule test permettre d’aprehender ce type de systeme les premiers resultats nous ont alors pousé approfondir nous

Molecule : DiA hydrophilic head hydrophobic tail Amphiphilic molecule air water hydrophilic head hydrophobic tail Amphiphilic molecule Large nonlinear response (electrons p delocalised, « push-pull » structure) Excellent surface SHG probe On commence donc par le concept assez neuf dans l’équipe il y a 3 ans de formation de films de langmuir Molecule test deja employée au sein de l’equipe notamment pour realiser des mesures HRS Tete hydrophile cationnique qui possede une forte affinité avec l’eau Chaine carbonnées Forment spontannéement des monocouches

Molecular films Langmuir trough Control the density in situ L’apect important de ce type de systeme est que Mesureur de pression « pointer «  correspond à la mesure de l’abaissement de la tension superficielle de la surface en presence de la monocouche Control the density in situ Densification

Film isotherms Expanded liquid Condensed liquid compression Compression Par etat solid on entend phase bidementionnelle figéeoù les interactions sont tres fortes Obtenir des informations sur l’organisation du système à l’échelle nanométrique on se tourne alors vers d’autres techniques Knowledge of certain macroscopic states (S, P, T, pH…) all along the film formation Control of interactions in the system

Polarisation resolved SHG of a film - Experimental set up - Laser femto Filter Chopper Langmuir trough Photon counter Polarisation measurement A l/2 wave plate permits the variation of the incident light polarisation An analyser to select the emergent light polarisation l/2 Lens Analyser Pressure Measurement Above 70° Langmuir trough Mirrors Focalise sur la surface Incidence oblique : valeur maxi de réflexion de Ishg Langmuir trough Experimental curves interpretation, exit S polarised profile

Second harmonic generation SHG process : brings into play the second order polarisation SHG Excitation at 800 nm SHG measurement Doublage de frequence = sgh processus nl dans lequel les photons interagissant avec le materiaux nl sont combiné pour former de nouveaux photons à 2 On mesure exxpremientalement un signal non linéaire à une fréquence: 2ωincidente, cohérent = notion de phase conservée 2 nd order susceptibility tensor

Centrosymmetric property Centrosymmetric medium The symmetry is very important for this process SHG is always null in centrosymmetric medium On considere la transformation de chaque vecteur par la symétrie centrale Surface = systeme bidimensionnel Penchons nous maintenant sur le lien microscopique que l’on peut faire du signal avec chacune des moelecules Wide interest with the surface which represents a symmetry break exclusive measurement of surface properties ( )

Microscopic dimension Induced dipole defined by : Hyperpolarisabilty 1st order polarisability Hyperpolarisabilty tensor β microscopic parameter which characterises the molecule. Susceptibility tensor χ macroscopic parameter which characterises the surface. Chaque molecules est decrite par un dipole induit En considerant une moyenne sur l’ensemble des molecules on lie chi et beta

Molecular film collapse -DiA molecular film - High monolayer compression Simultaneous measurements : Surface pressure : continuous growing Molecular Density : 0.4 to 3 nmoles/cm² Micelle Contre-ions SHG: Signal falls at high density Some information remain inaccessible by surface pressure measurement. SHG technique convincing Des les premières mesures nous avons pu mettre en evidence les interet de la technique shg % pression de surface Cassure rupture chute Notamment dans ce cas que j’utilise ici en particulier c’est la propriéte de symetrie de la surface qui est mise en jeux Non centrosymmetry DiA : 2 carbon chains liquid film with a lot of defects SHG signal falls related to multilayer formation centrosymmetry

Polarisation analysis -DiA molecular film - ED Approximation (electric dipolar) Isotropic surface Molecular Density : 0.43 nmoles/cm² On rentre dans la partie un peu + theorique Lobes sinusoidaux Approx de incident polarisation angle High degree of symmetry

Isotropic chiral Surface -DiA molecular film - Monolayer compression isotropic surface ED Approximation Chiral Molecular Density : 0.8 nmoles/cm² (Chiral) Un objet ne sse supperpose pas a son image dans un miroir (les mains en sont un tres bon exemple…) La prmeiere hyposthese faite est que la surface toujours isotrope devient chirale donc la notion de symétrie miroir est supprimée donc Cinf Toujours en de on introduit des chi avec melange de composantes Cos ne permet pas de moduler à 90° Chirality with ED approximation not sufficient Unique possible origin for 90° angle deformation is chirality's phenomenon

Introduction of magnetic components -DiA molecular film - Isotropic chiral Surface Molecular Density : 0.8 nmoles/cm² ED Approximation (Chiral) MD Approximation Affiner le modele pour introduire une evultion à 90° Approximation DE insuffisnte necessité d ’introduire termes dm (Chiral) Chirality with MD approximation adapted

Evolution of S-polarised curves all along compression -DiA molecular film - B C D E F G D B E A C G F C A B Progressive symmetry breaking all along the compression Si maintenant on voit l’evolution en fonction de la compresssion 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

Chiral tensor element -DiA molecular film- Increase chiral tensor element Becomes comparable to Anvancer un approchee microscopique precise me semble prematurere neammoins on peut donner qlq elements Takezoe = achiral mol = deracemisation= effet optique effet grand sur le chi xxz eem Glodmann=melange racemique compression donne formation de domaines riches en l’un ou autre enantioere Fujiwara = porphirin shg ld et cd formation de chiral aggregats a l’interface liquid liquid Sign change Uncertainty about the origin of chiral tensor evolution Compression

Microscopic Interpretation -DiA Molecular film - Even if we lack some information we know : DiA non chiral molecule attest an isotropic chiral surface Progressive formation of chiral structures upon compression Microscopic models of chiral aggregates It drives us to think about: Anvancer un approchee microscopique precise me semble prematurere neammoins on peut donner qlq elements Takezoe = achiral mol = deracemisation= effet optique effet grand sur le chi xxz eem Glodmann=melange racemique compression donne formation de domaines riches en l’un ou autre enantioere Fujiwara = porphirin shg ld et cd formation de chiral aggregats a l’interface liquid liquid Helix aggregates Model: an electron along an helix

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

Overview Molecular Film Film of metallic nanoparticles 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 L’ensemble du travail que nous avons effectuer durant ces 3 ans a debuter par la familiariser avec la technique de formation et d’etude de films langmuir à l’interface air eau . Nous avons debuter avec un molecule test permettre d’aprehender ce type de systeme les premiers resultats nous ont alors pousé approfondir nous

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 Thioalkanes C12 Chain length variation: Nano Particle Chains C18 limited interactions Chains C12 , C6 … allowed interactions Collaboration LPCML ( Olivier Tillement, Stéphane Roux)

Nanoparticles Films -Aims- Nanoparticles deposit thanks to a microlitric syringe Consequences on optical response (new resonances, field enhancement…) Aggregates formation Emergence of interactions upon compression Film compression Organistion proogressive plus ou moins reguliere On peut esperer aboutir a un reseau hexagonal compact dans les meilleur condition

Linear reflectance and SHG of a film -experimental set up- Langmuir trough Pressure Measurement Objective Beam splitter femto Laser Filter Dichroïc mirror Objective Langmuir trough Detection Lampe HaDe Beam splitter Objective Langmuir trough Detection Reflected Spectrum at 90° incidence on the surface Sources : Linear measurements : HaDe lamp Nonlinear measurements : femtosecond laser Reconnaît le spectre de la lampe blanche Spectre eau pure On etablit ensuite Metallic Nanoparticles capped C18

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 Valeur max pour un reseau hexagonal 2.6 10 16 part par m² …..les valeurs de densité en accord avec le fait que aggregats et grandes zones vides

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

Linear reflectance modelling -Silver nanoparticles film- Simulations with hypothesis of non aggregated particles Simulations with hypothesis of particles aggregate 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 Theorie de mileiu effectif attribue une constante dielectrique propre au film en fonction de sa densité mais ne modelise pas les interastion Theorie du film effectif n’est plus suffisante il, faut faire apparaître le siteractions grace en couplant 2 patrticules fortement la delcocalisation electronique s’opere Les premieres etapes consitent alors a former des elips pâr aggregationen petites chaines On a donc apparition d’une seconde resonnance plasmon lié a la geometrie de l’elipsoid petit axe et grand axe Effective film theory for ellipsoidal particles 50 nm 2nd resonance shows the beginning of interactions

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

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

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

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

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

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

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

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

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

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

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

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

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 Contrôle permanent de la densité Changement des paramètres (T, S, P …) en temps réel Mesures instantanées possibles Metallic nanoparticles films: Beginning of interactions upon compression Observation of the film dynamics

Have a look to my PhD group … Thank you every one ! ! Et merci à toute l’equipe de m’avoir soutenue et encadrer pendant ces années et merci à tous de m’avoir écouté ! Pierre-François Brevet, Emmanuel Benichou, Guillaume Bachelier, Isabelle Russier-Antoine, Christian Jonin, Guillaume Revillod, Chawki Awada, Yara El Harfouch, Julien Duboisset, Lin Pu