Search

The sensing performance of a micro-sensor based on a thick film of nitrogen-doped single-walled carbon nanotube (SWCNTs) is compared to a pristine SWCNTs film. Transfer length method analysis is used to extract the film sheet resistance from electrical measurements and reveals that the gas sensing mechanism is mainly attributed to the charge transfer between gas molecules and SWCNTs. We demonstrate that the sensitivity to NH3 can be improved by using a sensor based N-doped SWCNTs films while the sensitivity to NO2 and water vapour is unmodified. These unique gas-sensing properties can be used to develop a new NH3-selective differential gas sensor.

A comparative study was made of sorted semi-conducting single walled carbon nanotube (SWCNT) films and unsorted SWCNT films for gas sensing applications. The transmission line method is used to monitor separately the SWCNTs film resistance and the contact resistance between electrodes and the SWCNTs, thus revealing that the sensing mechanism mainly relies on a modification of the tube conductivity during gas exposure. The fabricated sensors demonstrate a detection limit of 20 ppb NO2 and 600 ppb NH3 mainly attributed to experimental setup limitations. Moreover, semi-conducting nanotubes happened to be 2.5 times more sensitive to NH3 than unsorted ones, thus proving that selectivity can be improved by sorting the SWCNTs. The temperature dependence of the sensor sensitivity was studied, and a good agreement was found between experimental results and the Langmuir adsorption model.

A variety of fabrication methods for single-walled carbon nanotubes (SWCNTs) has been developed, but none of them has been proven to generate tubes of only one chirality. Hence, a sample of as-produced SWCNTs always consists of a mixture of metallic and semiconducting tubes. By this, the application of SWCNTs in electronics, optics and sensing is limited today. Recently, the sorting of carbon nanotubes using density gradient ultracentrifugation (DGU) has been demonstrated. We report on an improved sorting according to electronic type by applying a two-step procedure: In the first step, we enriched semiconducting SWCNTs via DGU. In the second step, the sorted fractions have been reinserted and a second DGU was performed, winnowing metallic SWCNTs. Employing this procedure, we were able to reduce the content of metallic SWCNTs from 38 to 11%. Furthermore, we assembled carbon nanotube field-effect transistors with a high ON/OFF ratio from the sorted fraction in a single st ep by dielectrophoresis.

This work focuses on the elaboration of sorted semi-conducting single walled carbon nanotube films (SC-SWCNT films), and the evaluation of a gas microsensor based on these films. First, we show that semi-conducting carbon nanotubes could be sorted from solutions containing both metallic and semi-conducting nanotubes by ultracentrifugation in a density gradient. SC-SWCNT films were then obtained by filtration through a nitrocellulose membrane, then transferred on TLM (transmission line method) electrodes to separately measure the resistivity and the contact resistance. We finally show characterization results obtained using NO2 and NH3 as a target gas.

The growth of silver nanoparticles in mesostructured hybrid silica films under laser illumination is investigated by optical absorption spectroscopy and transmission electron microscopy. At low laser doses in the UV range, a blue-shift of the plasmon resonance is observed for increasing particle size. This size dependence is interpreted on the basis of the Mie theory assuming a two-layer core−shell model resulting from the localization of the nanoparticles in the block copolymer part of the film. At higher laser doses, the observed red-shift of the resonance wavelength and decrease of the absorbance level at resonance are attributed to the formation of a high refractive index shell around the nanoparticles that thickens slowly with the dose. The growth kinetics of silver nanoparticles is also studied for different illumination wavelengths in the UV and visible ranges. Surprisingly, the nanoparticles also grow under visible illumination. This is partly attributed to the release of electrons by the degradin...

International audience; Mesostructured organic–inorganic silica films containing AgNO3 are used as template to form ordered and dense layers of silver nanoparticles embedded in a dielectric matrix. The hybrid silica films are mesostructured by a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide ((PEO)106(PPO)70(PEO)106, F127) and contain the silver precursor (AgNO3) which is dissolved directly in the silica sol prior to deposition. The films are reacted with a sodium borohydride solution (NaBH4), which leads to the formation of a plane ordered network of silver oblate nanoparticles with a narrow size distribution located just below the film surface, and observed by Transmission Electron Microscopy (TEM). The minor and major axis lengths are equal to 5.3 ± 0.5 and 7.2 ± 0.6 nm, respectively. The characterization of the mesostructured film before and after the reductive treatment evidences that silver particles grow in place of copolymer micelles in the upper layer of the mesostructured thin film. Rutherford Backscattering Spectrometry (RBS) measurements support the hypothesis that silver ions initially dispersed in the film volume migrate toward the film surface to form the monolayer of silver nanoparticles, organized and stabilized by the copolymer micelles in the film. IR and ellipsometric measurements are used to characterize the changes in the hybrid copolymer-silica matrix.

International audience; The optical properties of gold and silver nanoparticles (NPs) dispersed in water and distributed in shape are investigated by introducing a shape distributed effective medium theory (SDEMT). This model takes into account the variation of depolarization parameter induced by a NP shape distribution. Simulations show that the shape distribution induces an inhomogeneous broadening and a decrease of the amplitude of the plasmon band. The number of plasmon bands and their positions depend on both the mean value of depolarization parameter and the NP material. By fitting the measured absorption spectra with the SDEMT, we unambiguously demonstrate that the depolarization parameter distribution, i.e., the shape distribution of nanoparticles can be deduced from absorption spectra.

International audience; We report ellipsometric measurement on single walled carbon nanotube (SWCNT) films performed in a large spectral range from 0.07eV to 4.97eV. The complex dielectric functions of SWCNTs are correlated to their diameter distribution extracted from transmission electron microscopy. Here we show that the transition energies between Van Hove singularities are directly related to the strong one dimensional confinement. In the infrared spectral range, the real part of the dielectric function becomes negative. The electronic properties of SWCNTs are extracted from ellipsometry by using a Drude model. The mobility and the mean free path of charge carriers are limited by the high number of SWCNT contacts. In accordance with tight binding simulation, the conductivity and the charge carrier concentration increase with the SWCNT diameter. Finally, we demonstrate that the S-plasmon energy depends on the charge carrier concentration. 2

International audience; Silver nanoparticles were produced by nanosecond pulsed-laser ablation at 1064 nm of Ag in pure water. These experiments were performed using an alternative ablation cell design where a cylindrical shaped Ag target was horizontally irradiated, while the liquid was stirred by a stir rod coaxially arranged to the target. The repeatability of the generated colloids properties (extinction and size distribution) is assessed by statistical tools. The colloids properties prepared under stationary liquid are found to be unpredictable, while they are highly repeatable at high stirring speed. At the same time, electronic microscopy examinations of the irradiated Ag targets revealed that the width of the laser-machined grooves exponentially decays in stationary liquid and almost linearly under high stirring speed as the ablation proceeds. In the latter case, the decay rate was found to be constant from one experiment to the other, while it was not repeatable stationary liquid. We show that the decay of the groove width is due to an attenuation of the laser energy reaching the target surface due to the formation of a more or less dense NPs layer in front of the target as the ablation proceeds. Using the ablation time-dependence of the groove width, we can quantify the attenuation factor of the laser energy with exposure time. Finally, the relationship between the laser energy attenuation, stirring speed, and repeatability of the colloids properties is interpreted and discussed in terms of mass transfer.

International audience; A modified effective medium theory (MEMT) is introduced to determine morphological characteristics and the volume fraction of colloidal metallic nanoparticles. By analyzing the optical absorption spectra of gold nanoparticles (NPs), this model is used to determine the distribution of prolate and oblate NPs and to demonstrate the presence of spherical NPs. In addition to interband transition, the model takes into account the longitudinal and transversal surface plasmon resonances. The results predicted by the MEMT theory were found to be in very good agreement with the shape distributions obtained by transmission electron microscopy. We found that fitting optical absorption spectra using MEMT provides a robust tool for measuring the shape and concentration of metallic NPs.

International audience; Thick films of single walled carbon nanotubes (SWCNTs) with different diameter and chirality distributions are characterized by combining transmission electron microscopy and spectroscopic ellipsometry. The dependence of the dielectric function with the increase of the SWCNT diameter occurs with a drastic redshift of the S11, S22 and M11 transition energies. The transfer integral parameter γ0 of SWCNT is also evaluated and analyzed. We demonstrate that parts of the optical properties of SWCNTs are attributed to a one dimensional confinement effect.

International audience; We report on a comparative study between dielectric functions of Si nanoparticles (Si-NPs) obtained from Bruggeman effective medium approximation (BEMA), Maxwell-Garnett (MG), and a modified Maxwell-Garnett (MMG) models. Unlike BEMA and MG, a size-distribution dependent dielectric function of Si-NPs is considered in the introduced MMG model. We show that the standard deviation sigma of a size distribution can be evaluated by analyzing the imaginary part of the dielectric functions of Si-NPs extracted from BEMA and MMG. In order to demonstrate this, several samples composed of Si-NPs embedded in silicon-rich silicon nitride are investigated by spectroscopic ellipsometry over the photon energy range varying between 2 and 4 eV. Assuming a lognormal size distribution of the Si nanoparticles, it is evidenced that the parameter sigma ranges between 1.15 and 1.35. The values of size dispersion deduced by this methodology are in good agreement with TEM observations.

International audience; The optical properties of metallic spherical nanoparticles embedded in host liquid matrix are studied. Extended Maxwell-Garnett-Mie formulation which accounts for size dispersion, the intrinsic confinement, and extrinsic size effect, is proposed for the calculation of the effective dielectric function and absorption coefficient of size dispersion of colloidal solution of Au and Ag nanoparticles in water. We demonstrate that the size distribution induces an inhomogeneous broadening and an increase of the amplitude of the plasmon band. A large redshift of the plasmon band is also observed for silver nanoparticles. Compared to the conventional Maxwell Garnett theory, we demonstrated that this model gives better description of the measured absorption spectra of colloidal gold solutions.

Among direct-bandgap semiconducting nanomaterials, single-walled carbon nanotubes (SWCNT) exhibit strong quasi-one-dimensional excitonic optical properties, which confer them a great potential for their integration in future photonics devices as an alternative solution to conventional inorganic semiconductors. In this paper, we will highlight SWCNT optical properties for passive as well as active applications in future optical networking. For passive applications, we directly compare the efficiency and power consumption of saturable absorbers (SAs) based on SWCNT with SA based on conventional multiple quantum wells. For active applications, exceptional photoluminescence properties of SWCNT, such as excellent light-emission stabilities with temperature and excitation power, hold these nanometer-scale materials as prime candidates for future active photonics devices with superior performances.

Équipe 104 : Nanomatériaux; International audience; Silicon nanocrystals (Si-NC) with different sizes (2-6 nm) are synthesized by evaporation. The system is composed of a single Si-NC layer that is well controlled in size. The numerical modeling of such system, without a large size distribution, is suitable to perform easily the optical calculations. The nanocrystal size and confinement effects on the optical properties are determined by photoluminescence (PL) measurements, absorption in the UV visible range, and spectroscopic ellipsometry (SE). The optical constants and the bandgap energies are then extracted and analyzed. The dependence of the optical responses with the decrease of the size of the Si-NC occurs not only with a drastic reduction of the amplitudes of dielectric function but also by a significant expansion of the optical gap. This study supports the idea of a presence of a critical size of Si-NC for which the confinement effect becomes weak. The evolution of those bandgap energies are discussed in comparison with values reported in literature.

International audience; We studied the nanosecond laser-induced shape modifications of Ag colloids exposed to a converging laser beam during the ablation of a Ag target in water. To this end, we performed a series of laser ablation experiments in which the laser energy was varied while all other parameters were kept constant. In addition to transmission electron microscopy (TEM), the shape distribution of the Ag nanoparticles was determined by modelling the extinction spectra of the final colloidal solutions using theoretical calculations based on shape distributed effective medium theory (SDEMT). From these calculations, two physical parameters named sphericity and dispersity were introduced and used to gauge the evolution of the shape distribution of the particles. As the laser energy on the target was increased from 5 to 20 mJ/pulse, an apparently abrupt modification of the shape distribution of the particles was evidenced by both TEM and SDEMT calculations. This change is explained in terms of competitive fragmentation, growth and reshaping processes. On the basis the heating-melting-vaporization model, we demonstrate how the competition between these processes, occurring at different locations of the converging beam, determines the shape distribution of the final product. We highlight the relevance of the fluence gradient along the beam path and the laser interaction volume on the laser-induced modifications of the suspended particles during the ablation process.

This paper quantifies the migration of silver contained within mesostructured hybrid silica films and mesoporous titania films under exposure to modulated light. This quantization allows to demonstrate that all of the initial silver salt can be concentrated and reduced in domains accumulating the higher photonic energy. Entirely reduced in the form of nanoparticles of few nanometers size embedded in the silica matrix, silver is then quite stable even under subsequent homogeneous exposures. It is also shown that thanks to the relatively slow nanoparticle growth, successive multiple exposures can be used to create complex 3D microstructures within silica films using a simple dual beam interferometer. In mesoporous titania films, the UV photo-growth of silver nanoparticles remains limited to the vicinity of the film interface because of the matrix absorption and cannot provide deep 3D patterns of silver nanoparticles. However, 2D refractive index patterns can be obtained under UV exposure, erased with visible light and updated thanks to a reversible photochromic behavior. In such films, opposite migration flows of silver species are proven under UV intensity gradient and homogeneous visible exposure.

International audience; Vapour sensors based on single walled carbon nanotubes (SWCNT) networks offer a high sensitivity but poor selectivity. Different works were undertaken, with varying degrees of success, to overcome this drawback. In this context, we develop a new selective sensor architecture based on a SWCNT network covered with a mesoporous silica film elaborated by sol–gel process. The topological and chemical characteristics of this sensor are obtained by TEM, SEM, EDX, contact angle and electrical measurements. We demonstrate that highly polarised molecules are stopped by the silica layer while other molecules like NO2 can diffuse easily in the mesoporous silica layer to reach the SWCNT network without increasing the response time.

The composition, the structure and the optical properties of mesostructured hybrid silica films elaborated by sol-gel routine are studied versus the temperature of the post treatment by comparing ellipsometric measurements, atomic force microscopy and electronic microscopy characterizations, X-ray diffraction and thermal analysis. This paper shows that the refractive index variation is a combination between the structure contraction, the solvent evaporation, the silica wall condensation and the pyrolysis of the copolymer. We also investigate the optical properties of thermally grown silver nanoparticles in the mesotructured films and we demonstrate that these properties depend on the optical properties of the host matrix and on the silver concentration profile in the film.

In this paper we report a soft route leading to spherical or rod nanoparticles confined in SBA-15 thin films exhibiting a hexagonal mesostructure. For that purpose, these transparent mesoporous silica thin films are elaborated in the presence of a non ionic triblock copolymer P123 as structure directing agent. After soaking in a silver salt solution, they are heat treated to grow silver structures. In function of several experimental parameters as the immersion time in the silver salt solution, the solvent of the silver salt solution or the heat treatment temperature, nanorods and/or nano spherical particles can be obtained. These coloured samples are characterized by X-ray diffraction (XRD), ultraviolet–visible (UV–vis) absorption and Fourier transformed infrared (FTIR) spectroscopies, atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The presence of the nanorods has been showed by using polarized UV–vis spectroscopy. The results show that most of silver nanoparticles grow inside the film thickness.

Silver nanoparticles and silver nanowires have been grown inside mesostructured silica films obtained from block copolymers using two successive reduction steps: the first one involves a sodium borohydride reduction or a photoreduction of silver nitrate contained in the film, and the second one consists of a silver deposit on the primary nanoparticles, carried out by silver ion solution reduction with hydroxylamine chloride. We have demonstrated that the F127 block copolymer ((PEO)(106)(PPO)(70)(PEO)(106)), "F type", mesostructured silica film is a suitable "soft" template for the fabrication of spherical silver nanoparticles arrays. Silver spheres grow from 7 to 11 nm upon the second reduction step. As a consequence, a red shift of the surface plasmon resonance associated with metallic silver has been observed and attributed to plasmonic coupling between particles. Using a P123 block copolymer ((PEO)(20)(PPO)(70)(PEO)(20)), "P type", mesostructured silica film, we have obtained silver nanowires with typical dimension of 10 nm x 100 nm. The corresponding surface plasmon resonance is blue-shifted. The hydroxylamine chloride treatment appears to be efficient only when a previous chemical reduction is performed, assuming that the first sodium borohydride reduction induces a high concentration of silver nuclei in the first layer of the porous silica (film/air interface), which explains their reactivity for further growth.

International audience; Elaboration of mesoporous titanium oxide film supporting silver nanoparticles is described. Mesoporous titanium oxide films are characterized by TEM analysis. Titania films are infiltrated with a silver salt solution and chemical reduction treatments are performed using either a NaBH4 or a formaldehyde solution. Infiltrated films are then characterized by TEM, SEM, AFM, UV-visible spectroscopy, X-ray diffraction and Rutherford Backscattering Spectrometry (RBS). The utilization of a mesoporous titania substrate allows to control the nanoparticle size and the interparticle distance. RBS experiments provide the evidence that NaBH4 treatment induces a strong accumulation of silver nanoparticles in the sub-surface of the layer, while formaldehyde treatment induces the formation of silver nanoparticles embedded into almost the whole depth of the titania film. Large silver nanocrystals are also formed at the film surface whatever the reducer used. A broad visible absorption band related to the surface plasmon resonance (SPR) is obtained in both cases which is strongly red-shifted compared to the SPR obtained for silver nanoparticles inside a silica matrix. Moreover, irradiation with visible light causes the photooxidation of silver nanoparticles by titania and a complete discoloration of the material. The photooxidation is related to a drastic decrease in the silver nanoparticle size and is found to be reversible, particularly, in the case of the material obtained by the formaldehyde reduction.

International audience; Ellipsometry is an optical technique that is widely used for determining optical and geometrical properties of optical thin films. These properties are in general extracted from the ellipsometric measurement by solving an inverse problem. Classical methods like the Levenberg–Marquardt algorithm are generally too long, depending on direct calculation and are very sensitive to local minima. In this way, the neural network has proved to be an efficient tool for solving these kinds of problems in a very short time. Indeed, it is rapid and less sensitive to local minima than the classical inversion method. We suggest a complete neural ellipsometric characterization method for determining the index dispersion law and the thickness of a simple SiO2 or photoresist thin layer on Si, SiO2, and BK7 substrates. The influence of the training couples on the artificial neural network performance is also discussed.

International audience; Elaboration of mesostructured silica films with a triblock copolymer polyethylene oxide–polypropylene oxide–polyethylene oxide, (PEO–PPO–PEO) and controlled growth of silver nanoparticles in the mesostructure are described. The films are characterized using UV–visible optical absorption spectroscopy, TEM, AFM, SEM, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Organized arrays of spherical silver nanoparticles with diameter between 5 and 8nm have been obtained by NaBH4 reduction. The size and the repartition of silver nanoparticles are controlled by the film mesostructure. The localization of silver nanoparticles exclusively in the upper-side part of the silica-block copolymer film is evidenced by RBS experiment. On the other hand, by using a thermal method, 40nm long silver sticks can be obtained, by diffusion and coalescence of spherical particles in the silica-block copolymer layer. In this case, migration of silver particles toward the glass substratefilm interface is shown by the RBS experiment

Optimal performances of integrated optical devices are obtained by the use of an accurate and reliable characterization method. The parameters of interest, i.e., optical indices and thickness of the waveguide structure, are calculated from effective indices by means of an inversion procedure. We demonstrate how an artificial neural network can achieve such a process. The artificial neural network used is a multilayer perceptron. The first result concerns a simulated anisotropic waveguide. The accuracy in the determination of optical indices and waveguide thickness is 5 x 10(-5) and 4 nm, respectively. Then an experimental application on a silica-titania thin film is performed. In addition, effective indices are measured by m-lines spectroscopy. Finally, a comparison with a classical optimization algorithm demonstrates the robustness of the neural method.

International audience; We report an experimental technique that determines the chirality distribution in single wall carbonnanotube (SWCNT) films. Films of CoMoCat SWCNTs and SWCNTs enriched in (6,5) chiralityare considered. Classical methods like photoluminescence spectroscopy frequently give incompletedistribution. In this way, spectroscopic ellipsometry is used to determine the dielectric function ofSWCNT film. The chirality abundance obtained by analysing the ellipsometric data with a tightbinding model is compared with that deduced from photoluminescence excitation spectroscopy.We demonstrate that ellipsometry is an efficient tool for a complete and quantitative determinationof the chirality distribution and the metallic/semiconducting ratio.

In this work, methods are introduced to the determination of optical properties of thin silver films and nanostructures. We present an optical resonant system consisting of a mirror, a transparent layer and a thin silver film. The layer sequences and the nanostructure of the thin films are investigated by optical methods consist of reflectance measurements. The structures are analyzed by atomic force microscopy and scanning electron microscopy. The optical properties are determined by modeling the reflectance data. We have found that the growth mechanisms of the silver layer are correlated to its optical properties. It also found that temperature treatments produce isolated particles with a narrow plasmon resonance.

Single walled carbon nanotube (SWCNT) networks present outstanding potential for the development of SWCNT-based gas sensors. Due to the complexity of the transport properties of this material, the physical mechanisms at stake during exposure to gas are still under debate. Previously suggested mechanisms are charge transfer between gas molecules and SWCNT and Schottky barrier modulation. By comparing electrical measurements with an analytical model based on Schottky barrier modulation, we demonstrate that one mechanism or the other is predominant depending on the percolation of metallic carbon nanotubes. Below the metallic SWCNT percolation threshold, sensing is dominated by the modulation of the Schottky barrier, while above this threshold, it is only attributed to a charge transfer between SWCNT and gas molecules. Both mechanisms are discussed in terms of sensitivity and resolution leading to routes for the optimization of a gas sensor architecture based on highly enriched semiconducting carbon nanotube films.

A method dedicated to authentication of products submitted to a data inscription during their manufacturing process is suggested. It includes a management of the origin of the machine providing the reference product signature. The strength of the method is based on some links established by turns at the registration stage between all the elements to protect. Specific variations coming from product data photo-inscription physically induce a fundamental link between material and immaterial product components. This link is exploited via a specific signature extraction.

International audience; The elaboration of mesoporous silica films supporting silver nanoparticles is described. Mesoporous silica films were infiltrated with silver salt solutions of different concentrations and chemical reduction treatment was performed in situ by NaBH4. The films have been characterized by TEM, AFM, XRD, and UV–vis spectroscopy. Homogeneous distributions of silver nanoparticles have been obtained by this method.

Noble metal nanoparticles (NPs) are the site of a surface plasmon resonance phenomenon resulting from the collective oscillation of their conduction electrons under the effect of an electromagnetic wave. In the case of gold and silver NPs, the resonant frequency is in the visible range, which gives these plasmonic NPs unique optical properties. In particular, the position and intensity of the plasmon resonance depend on their size, shape (aspect ratio) and the index of the host medium. The possible applications require pure samples and mono-dispersed distribution. The chemical synthesis of NPs allows the shape and size of NPs to be controlled. However, it requires the use of stabilizing agents, which lead to surface contamination by synthetic residues. To limit this disadvantage, the physical technique of laser ablation in a liquid medium is a promising alternative, which, however, suffers from a lack of control over the shape and size of the NPs produced. The shape and size of NPs produced by liquid laser ablation (ALML) are closely related to the three essential steps of the process: Target / laser interaction; Mass transport; Laser / NPs interaction suspended in the liquid. In order to understand the mechanisms governing each of these stages, it is necessary to study them separately. In this work, we focused on the mechanisms of interaction between the laser beam and the NPs suspended in the liquid. Depending on the energy density absorbed by the suspended NPs, they undergo fragmentation or remodeling. We then studied the mechanisms behind the phenomenon of fragmentation. The evolution of the shape distribution of NPs during NP fragmentation was studied by developing an original and quantitative technique of in-situ optical spectroscopy. And, the evolution of the volume fraction of NPs during their preparation by ALML by in-situ optical spectroscopy is obtained and analyzed. In parallel with the experimental work, we have developed theoretical models for understanding the mechanisms of formation of metallic nanoparticles by laser ablation in a liquid medium. A modest study on the modeling of optical and thermal properties of the Laser-Nanoparticle interaction is discussed in this thesis., Spécialité doctorale "Physique de la matière condensée" présentée par MANSOUR Yehia Soutenue le le 16 Décembre 2020 Études théorique et expérimentale de la formation des nanoparticules métalliques par ablation laser en milieu liquide. Modélisations des propriétés optiques et thermiques de l'interaction Laser-Nanoparticules.Les nanoparticules (NPs) de métaux nobles sont le siège d’un phénomène de résonance plasmon de surface résultant de l’oscillation collective de leurs électrons de conduction sous l’effet d’une onde électromagnétique. Dans le cas de NPs d’or et l’argent, la fréquence de résonance est située dans visible ce qui confère à ces NPs plasmoniques des propriétés optiques uniques. En particulier, la position et l’intensité de la bande de résonance plasmon peuvent varier en fonction de leur taille, leur forme (rapport d'aspect) et de l'indice du milieu hôte. Les possibilités d’applications nécessitent des échantillons purs et de distribution mono disperse. La synthèse des NPs par voie chimique permet de contrôler dans une certaine mesure la forme et la taille des NPs. Elle nécessite cependant l’utilisation d’agents stabilisants qui mènent à une contamination de surface par les résidus de synthèse. Pour limiter cet inconvénient, la technique physique d’ablation laser en milieu liquide est une alternative prometteuse qui souffre cependant d’un manque de contrôle de la forme et de la taille des NPs produites. La forme et la taille des NPs élaborées par ablation laser en milieu liquide (ALML) sont étroitement liées aux trois étapes essentielles du processus : Interaction cible/laser ; Transport de masse ; Interaction laser/NPs en suspension dans le liquide. Afin d’appréhender les mécanismes régissant chacune de ces étapes, il est nécessaire de les étudier séparément. Dans ce travail, nous nous sommes focalisés sur les mécanismes d’interaction entre le faisceau laser et les NPs en suspension dans le liquide. Suivant la densité d’énergie absorbée par les NPs en suspension, celles-ci subissent la fragmentation ou le remodelage. Par la suite nous avons étudié les mécanismes à l’origine du phénomène de la fragmentation. L’évolution de la distribution de forme des NPs lors de la fragmentation des NPs a été étudiée en développant une technique originale et quantitative de spectroscopie optique in-situ. De même, l’évolution de la fraction volumique des NPs au cours de leur élaboration par ALML par spectroscopie optique in-situ est obtenue et analysée. En parallèle aux travaux expérimentaux, nous avons développé des modèles théoriques pour la compréhension des mécanismes de formation des nanoparticules métalliques par ablation laser en un milieu liquide. Une autre étude approfondie sur la modélisation des propriétés optiques et thermiques de l'interaction Laser-Nanoparticules est discutée dans cette thèse. Un modèle thermique de Takami modifié nommé MTM (Modified Takami Model) a été également introduit. Son utilité importante a été démontrée pour l’interprétation des mécanismes de l’interaction laser-NPs.