Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-04T15:25:57Z No. of bitstreams: 1 patriciabarrossantos.pdf: 5111164 bytes, checksum: a7268529a7643972391f0dd226a987a3 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-17T13:32:29Z (GMT) No. of bitstreams: 1 patriciabarrossantos.pdf: 5111164 bytes, checksum: a7268529a7643972391f0dd226a987a3 (MD5) / Made available in DSpace on 2017-05-17T13:32:29Z (GMT). No. of bitstreams: 1 patriciabarrossantos.pdf: 5111164 bytes, checksum: a7268529a7643972391f0dd226a987a3 (MD5) Previous issue date: 2016-07-28 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho consistiu na síntese e caracterização de catalisadores plasmônicos nanoestruturados híbridos metal∕semicondutor, para aplicação na fotodegradação do corante têxtil Reactive Black 5 (RB5), utilizando irradiação no visível. Foram sintetizadas nanopartículas de óxido de zinco, cobre (CuNPs) e prata (AgNPs), bem como catalisadores plasmônicos híbridos do tipo Cu∕ZnO e Ag∕ZnO que foram submetidos a diversas técnicas de caracterização como, espectroscopia Raman, UV-VIS, DRX de policristais, MEV e MET. Os processos de fotodegradação foram realizados em um reator labmade, no qual a solução de corante (1×10-5mol L-1) foi irradiada utilizando lâmpada fluorescente (11W) e∕ou incandescente (100W) como fontes de irradiação no visível. A fotodegradação do corante RB5 foi monitorada através de espectroscopia eletrônica no UV-VIS, espectroscopia vibracional Raman ressonante (RR) e intensificada por superfície (SERS), sendo possível observar mudanças relacionadas ao processo de fotodegradação. A espectroscopia no UV-VIS mostrou a queda na intensidade da banda de absorção do grupo cromóforo com o tempo de irradiação; por outro lado, RR e SERS permitiram observar a formação de espécies fluorescentes e mudanças no perfil espectral vibracional. Não ocorreu a fotólise do corante por nenhuma das duas fontes de irradiação utilizadas. AgNPs não promoveram a fotodegradação do RB5, porém nanopartículas de ZnO degradaram cerca de 66% das moléculas de corante, sob irradiação no visível (lâmpada incandescente). Fotocatalisadores plasmônicos do tipo Ag∕ZnO foram utilizados nos processos de degradação do RB5 utilizando ambas as fontes de irradiação no visível, sendo adicionados ao meio do corante de formas diferentes. Quando utilizado diretamente em suspensão e sob irradiação da lâmpada fluorescente o percentual de fotodegradação foi de 97%. Já com a adição do catalisador no estado sólido à solução de corante e sob irradiação da lâmpada fluorescente 72% das moléculas de RB5 foram degradadas. Esse último resultado pode ser comparado ao obtido utilizando ZnO como catalisador, e mostra um ganho de 22% na eficiência catalítica no visível na presença do material plasmônico AgNP/ZnO. / The present work consisted in the synthesis and characterization of plasmonic nanostructured hybrids metal∕semiconductor catalysts, for application on photodegradation of the Reactive Black 5 (RB5) textile dye using visible irradiation. Nanoparticles consisting of zinc oxide, copper (CuNPs) and silver (AgNPs) were synthesized, as well as plasmonics catalysts of Cu∕ZnO and Ag∕ZnO types. The materials underwent several characterizations using techniques such as Raman Spectroscopy, UV-VIS, polycrystal DRX, SEM and TEM. Photodegradation processes were carried out in a labmade reactor, in which a dye solution (1×10-5mol L-1) was irradiated using fluorescent (11W) and∕or glowing (100W) lamp bulb as sources of radiation in the visible range. The photodegradation of the RB5 dye was monitored through electronic spectroscopy UV-VIS, and vibrational spectroscopies resonant Raman (RR) and surface enhanced Raman spectroscopy (SERS). UV-VIS allowed observing changes related to the photodegradation process, as a drop in intensity of the absorption band of the chromophoric group. RR and SERS techniques results presented the formation of fluorescent species and changes in the vibrational spectral profile. The photolysis of the dye didn’t occur under any of the sources of irradiation used. AgNPs didn’t promote the photodegradation of the RB5, but nanoparticles of ZnO degraded about 66% of the dye molecules, under the visible radiation (incandescent lamp). Plasmonics photocatalysts Ag∕ZnO were used in the processes of degradation of the RB5 using both sources of irradiation in the visible range, but it was added to the dye solution in different ways. When used directly in suspension and under fluorescent lamp irradiation the photodegradation percentage was 97%. With the addition of the catalyst in the solid state to the dye solution and under fluorescent lamp irradiation 72% of the RB5 molecules were degraded. This last result can be compared to that achieved using ZnO as catalyst and shows a 22% gain in catalytic efficiency under visible light in the presence of the plasmonic material AgNP/ZnO.

Les signaux non linéaires provenant de nanostructures métalliques et cristallines sont connus pour être fortement dépendants vis à vis de la polarisation. Ceci est dû à leur propriété de symétrie locale, reliée à leur réponse volumique ou surfacique. Les signaux de polarisation venant de nanostructures de taille inférieure à la limite de diffraction sont généralement mesurés avec un spot limité par la diffraction (300 nm) ce qui représente la moyenne du signal. Cette technique a pour défaut de perdre l'information spatiale du signal de polarisation. Nous avons développé une nouvelle méthode de microscopie à polarisation non-linéaire qui exploite l'information en dessous de la limite de diffraction.Une analyse de Fourier d'un signal non linéaire a été faite en dessous de la limite de diffraction sur une image sur-échantillonnée et corrigée (taille du pixel=50 nm). Le gain en résolution est du à la sensibilité spatiale de la polarisation. Pour ce faire, nous avons mesuré un signal polarisé de seconde harmonique de nanostructures plasmoniques de différentes formes (150 nm). Nous avons montré que la nature vectorielle du champs local confiné peut être retrouvé avec une résolution de 40 nm en utilisant la nanoscopie polarisée non linéaire. Nous avons par ailleurs montré que nous pouvons imager l'hétérogénéité spatiale de nanoparticules ferroélétriques cristallines (BaTiO3) de taille allant de 100 nm à 500 nm. Ceci prouve l'existence d'une coque centrosymétrique dans des petites structures. Enfin, les nanocristaux de KTP nanostructures sont les candidats idéaux pour la générations de signaux non linéaires bien maîtrisée. / In this work, we develop a novel polarized nonlinear microscopy method that exploits sub-diffraction resolution information. Fourier analysis of the polarization modulated nonlinear signal is performed on over-sampled, drift-corrected images (50nm pixel size). The information gained by polarization-induced modulation signals provides a higher level of spatial selectivity that is directly related to the local optical response of the investigated system, at a scale below the diffraction limit. The gain in spatial scale is due to the additional spatial sensitivity brought by polarization. This approach is applied to polarized second harmonic generation imaging in plasmonic nanostructures (150nm size) of multi-branched shapes, in which the vectorial nature of the local field confinement can be retrieved with a resolution of 40 nm. We also demonstrate the possibility to image spatial heterogeneities within crystalline ferroelectric BaTiO3 nanoparticles of 70nm to 500nm size, emphasizing in particular the existence of a centrosymmetric shell in small size structures. These nanostructures will be used as starting models for coherent optical probes in biological media (cells, tissue slices or in vivo) with two objectives. First, the nonlinear nature of their emission will make them stable and tunable nanosources, able to report their localization with high accuracy in 3D, potentially sensing local environment changes, and actively inducing perturbations such as controlled temperature increase at the nanoscale. Second, the coherent nature of their emission will make them useful as local nanoprobes for wavefront and polarization correction through scattering media.

No description available.

Cette thèse présente une étude exploratoire de plusieurs aspects du couplage fort lumière-matière dans des matériaux moléculaires. Différentes propriétés héritées d’un tel couplage sont démontrées, ouvrant de nombreuses possibilités d’applications, allant du transfert d’énergie à la génération de signaux optiques non-linéaires et à l’élaboration de réseaux polaritoniques chiraux. Au travers des thématiques abordées, l’idée d’un couplage lumière-matière entrant en compétition avec les différentes fréquences de dissipation des molécules se révèle être cruciale. Ainsi, la prédominance du couplage cohérent au champ électromagnétique apparaît comme un moyen de modifier les propriétés quantiques des états moléculaires, ouvrant la voie à une nouvelle chimie des matériaux en cavité. / This thesis presents an exploratory study of several aspects of strong light-matter coupling in molecular materials. Different properties inherited from such a coupling are demonstrated, opening the way to numerous applications, ranging from energy transfer to the generation of non-linear optical signals and to the development of chiral polaritonic networks. Through the topics covered, the idea of a light-matter coupling strength competing with the different frequencies of relaxation of the molecules proves to be crucial. Thus, the predominance of the coherent coupling to the electromagnetic field appears as a new mean of modifying the quantum properties of molecular systems, opening the way to a new chemistry of materials in optical cavities.

Recent advances in nanofabrication techniques have opened up new avenues and numerous possible applications in both nanoscale electrochemistry and analytical nanoscience by enabling the fabrication of reproducible nanoelectrodes with different new geometries. Nanoelectrodes exhibit advantages including enhanced mass transport, higher current densities, improved signal-to-noise ratios, and lower ohmic drop. In this dissertation, the use of nanoelectrodes in the electrochemical response properties investigations or in the spectroelectrochemical studies is the unifying factor among all the chapters. First (in Chapter 4), we presented a direct comparison between the electrochemical characteristics of two finite nanoelectrodes arrays with different geometries: 6 × 6 recessed nanodiscs and nanorings microarrays. Using computational methods, it was demonstrated that the electrode geometry’s parameters have a drastic influence on the mass transport properties of the nanoelectrodes. The results presented here are the first combination of experimental and numerical studies that elucidate the transport on nanoring electrode arrays. The comparison of the electrochemical behavior between nanostructures using full 3D simulations is also unique. Second, we have provided a comprehensive numerical study on the redox cycling performance properties of a 6 × 6 recessed nanorings-ring electrode array configuration. The simulation results were in good agreement with the experimental data. After validating the model against experiments, a comprehensive computational investigation revealed avenues to optimize the performance of the structure in terms of geometric parameters and scan rates. The second half of this dissertation is comprised of the spectroelectrochemical studies. The combination of surface plasmon resonance with electrochemistry presents new paths to investigateredox reaction events at the electrode surface since it brings an additional dimension to the classical electrochemical approaches. Third, we have reported a novel active plasmonic device based on a new switching mechanism for the nanohole electrodes array to bridge between photonics and electronics at nanoscales. The inner surfaces of the nanohole electrodes in the array were coated with an electroconductive polymer, polypyrrole, (PPy). Then, it was shown that light transmitted through the PPy- modified nanohole electrodes can be easily tuned and controled by applying an external potential. We were also able to switch on and off the transmitted light intensity through the modified nanohole arrays by potential steps, demonstrating the potential of this platform to be incorporated into optoelectronic devices. Finally, we have fabricated larger area plasmonic periodic nanopillar 3D electrodes using a rapid, high-throughput, and cost-effective approach: the laser interference lithography. Then, the electrochemical behavior of these electrodes was investigated both experimentally and computationally. The properties were ‘compared with a flat electrode with an equivalent geometric area. Afterward, we have successfully probed the changes in the concentration of a reversible redox pair near the electrode surface induced by various applied potentials, in an in-situ EC-SPR experiment. / Graduate

Im Bereich opto-elektronischer Sensortechnik ist ein eindeutiger Trend hin zu immer kleineren Bauelementen und immer spezifischeren Messanwendungen zu erkennen. Plasmonische Materialien auf der Basis von Nanostrukturen bieten sich hierbei hervorragend für dieses Aufgabenfeld an. Deren optische Absorbanzpeaks lassen sich über die geometrischen Parameter der Nanostrukturen einfach und präzise steuern und reagieren äußerst empfindlich auf Brechungsindexänderungen im Umgebungsmedium. Die Herstellung von aufrecht stehenden, teppichartig angeordneten Nanorods auf Basis von anodisierten Aluminiumoxidmatrizen bietet als skalierbares Bottom-up-Verfahren eine einzigartige Kombination aus Prozessgeschwindigkeit, Steuerbarkeit und Kosteneffizienz. In der vorliegenden Dissertation wurde untersucht, wie sich verschiedene Sputterparameter während der Herstellung von Aluminiumdünnschichten auf deren Anodisierungseigenschaften, sowie die anschließende Porenbefüllung und die plasmonischen Eigenschaften des so erzeugten Materials auswirken. Hierzu wurde reines Aluminium bei verschiedenen Sputterleistungen und -raten abgeschieden und hinsichtlich seiner Oberflächenkonfiguration und Prozessierbarkeit im bereits etablierten Nanorodproduktionsverfahren untersucht. Gleichwohl fanden Versuche statt, Aluminiumschichten mit einer schwachen Siliziumlegierung sowie durch reaktives Sputtern mit Sauerstoff voroxidiertes Aluminium zu anodisieren und für die Nanorodherstellung zu nutzen. Als typisches Ergebnis dieser Versuche zeigt sich eine deutliche Verbesserung des Anodisierungs- und Abscheideverhaltens, wenn die Sputterparameter so gewählt werden, dass eine möglichst feinkristalline Schicht abgeschieden wird. Während die Variation der Sputterleistung nur in einer mäßigen Verbesserung und die Siliziumlegierung sogar in einer Verschlechterung der optischen Eigenschaften resultieren, zeigt sich die Sauerstoffzugabe als äußerst vorteilhaft für den Herstellungsprozess sowie die plasmonischen Eigenschaften der fertigen Strukturen. Hierbei weisen Aluminiumschichten mit einem Sauerstoffanteil von 10 22 at.% die gleichmäßigste Anodisierung sowie die schmalsten Plasmonenresonanzpeaks auf, bei gleichzeitig hoher Reproduzierbarkeit. Für derartige Proben konnte eine annähernd vollständige Porenbefüllung erreicht werden. Weiterhin ist die Breite der Plasmonenresonanz hier vergleichbar mit der eines simulierten, defektfreien Nanorodarrays mit perfekt hexagonaler Nanorodanordnung, sodass von einer deutlichen Optimierung gesprochen werden kann, welche nun weitere Untersuchungen an diesem System oder sogar eine großtechnische Produktion ermöglicht Letztendlich offenbart eine quantitative Analyse der Strom-Zeit-Kurve der Anodisierung, dass diese in Form und Ausprägung mit der Güte der plasmonischen Eigenschaften der so produzierten Strukturen korreliert. Somit bietet sich diese als schnelles und günstiges Verfahren zur Qualitätskontrolle in einem sehr frühen Prozessstadium an. / Optical sensing witnesses an increasing trend towards smaller components and more specific applications. Nanostructure-based materials excellently fulfil these kinds of task. Their optical absorbance peaks are easily and precisely controllable by changing the structures‘ geometrical parameters, and have shown to be highly sensitive to refractive index changes of the surrounding medium. The fabrication of free-standing arrays of metallic nanorods based on anodised aluminium oxide matrices as a scalable bottom-up process offers a unique combination of throughput in production, process control and cost efficiency. The scope of the present dissertation thesis is the exploration of different sputtering parameters and techniques for the fabrication of aluminium thin-films, their influence on the anodisation properties as well as subsequent pore filling, and of course the optical properties of the final plasmonic structure. For this, pure aluminium was deposited at different sputtering powers and rates, and was investigated regarding its surface configuration as well as its usability within the well-established nanorod fabrication process. Similarly, attempts were made to anodise aluminium alloyed with small quantities of silicon as well as substoichiometric aluminium oxide, which was prepared by reactive sputtering under partial oxygen pressure. As a typical result of these studies, it was found that a considerable improvement of anodisation and electroplating behaviour could be achieved, provided the sputtering conditions were chosen such that the deposited films\' crystal size becomes as small as possible. While the variation of the sputtering power lead only to a marginal improvement and the silicon admixture even deteriorated the sample quality, the use of partially oxidised aluminium layers proved to be highly advantageous for the fabrication process as well as the plasmonic properties of the final structures. The optimal oxygen content was found to be 10 22 at.%, with these samples showing the most regular anodisation behaviour, the smallest absorbance peak width, and at the same time a high reproducibility. Furthermore, the peak width of these samples is comparable to that of simulated, defect-free nanorod arrays in a perfect hexagonal arrangement. These fabrication parameters can therefore be viewed as highly optimised and well-suited for further investigations of this material or even a large-scale production process. Finally, a quantitative analysis of the current-time-curve of an anodisation process reveals a correlation between its characteristics and the samples’ plasmonic qualities. Hence, the analysis of this curve may be used as a fast and cheap method of quality control at the early stages of the fabrication process.

Le développement des nouvelles technologies de l'information et de la communication nécessite la miniaturisation et l'intégration des dispositifs optiques. La plasmonique, qui utilise des nanostructures métalliques pour manipuler la lumière à l'échelle nanométrique, permet la réalisation de dispositifs optiques jusqu'à des limites ultimes. Le but de la présente étude est de concevoir et de fabriquer des nanoarchitectures complexes qui peuvent être incorporées dans différents dispositifs plasmoniques capables de guider la lumière de manière active. Diverses nanostructures d'or, telles que des nanotriangles d'or creux ou des nanotripodes enrobés d'or, ont été synthétisés et assemblés en utilisant des liens moléculaires ou un origami d'ADN. Les propriétés optiques des nanodispositifs fabriqués ont été étudiées afin de démontrer leur capacité à guider la lumière. / The development of new information and communication technologies requires the miniaturization and integration of optical devices. Plasmonics, a field of optics that utilizes metallic nanostructures to manipulate light at the nanoscale, enables the scaling of optical devices down to ultimate limits. The purpose of the present study is to design and fabricate complex nanoarchitectures that can be incorporated into different plasmonic devices able to guide light in an active way. Various gold nanostructures, such as hollow gold nanotriangles or gold coated nanotripods, were synthesized and assembled using molecular linkers or a DNA origami template. The optical properties of the fabricated nanodevices were investigated in order to evidence their ability to guide light.

Le but de cette thèse est d’étudier le processus de la génération d’harmoniques d’ordre élevé (HHG, de l’anglais high-order harmonic generation) dans des solides et la possibilité d’augmenter l’efficacité de la génération en exploitant l’exaltation locale du champ incident dans des nanostructures. La HHG dans les gaz est connue depuis plusieurs décennies et a été étudiée en détails, par contre la HHG dans les solides a été démontrée pour la première fois en 2011. Différents processus comme les oscillations interbandes et intrabandes y jouent un rôle fondamental. Le processus exact est toujours en cours d’investigation et est discuté dans la communauté. Dans ce manuscrit, nous étudions la génération d’harmoniques dans différents cristaux, comme ZnO, CaCO₃ et CdWO₄. Nous confirmons que la HHG dépend de la longueur d’onde génératrice et de l’orientation cristalline. Outre les cristaux 3D nous étudions la HHG dans des matériaux 2D comme le graphène. Grâce à sa grande mobilité électronique et sa structure de bande spécifique la HHG dans graphène est plus efficaces que dans des cristaux 3D.Typiquement des intensités de 10¹² TW/cm² ou plus sont nécessaires pour susciter la HHG. Ces intensités élevées sont généralement atteintes par des méthodes comme l’amplification par dérive de fréquence qui génère des impulsions femtosecondes à des énergies µJ ou mJ. Grâce aux progrès récents des techniques de nanofabrication, il est possible d’exalter un champ électrique laser de plusieurs ordres de grandeurs dans des nanostructures. Alors que la HHG dans les gaz assistée par la plasmonique a été démontrée comme n’étant pas réalisable, des travaux récents démontrent l’amplification de la HHG dans des solides. Dans ce travail, nous étudions l’amplification de la HHG dans différentes configurations. D’abord, nous analysons différents types de nanostructures, à savoir des bow ties, des nano-trous, des réseaux et des résonateurs. Nous comparons ces structures suivant plusieurs critères tels que le volume d’exaltation et l’exaltation crête. Différentes longueurs d’onde et cristaux sont utilisés. Une large amplification de plusieurs ordres de grandeur est démontrée pour la troisième harmonique. En plus, nous discutons l’endommagement des nanostructures causé par l’irradiation laser. Des nanostructures semiconductrices confinant la lumière par guidage sub-longueur d’onde ont plusieurs avantages par rapport aux nanostructures métalliques. Des nanocones semiconducteurs, par exemple, présentent un grand volume d’amplification, supérieur de plusieurs ordres de grandeur à ce qui a été démontré récemment, et évitent la fusion observée dans des nanostructures métalliques. Nous présentons plusieurs itérations de l’expérience avec des nanocones de ZnO en améliorant le système de détection et la géométrie des nanocones entre chaque étape. Nous utilisons différents lasers et différentes géométries de nanocones. Nous avons observé les harmoniques d’un laser à 3.1 µm dans des nanocones de ZnO jusqu’à l’ordre 15. L’amplification de plusieurs ordres de grandeur d’harmoniques perturbatives et non perturbatives, générées à partir des impulsions d’un oscillateur nanojoule à une cadence MHz et une longueur d’onde de 2.1 µm, est démontrée pour la première fois jusqu’à H9. Le facteur d’amplification dépend de l’éclairement du faisceau pompe. Nous étudions également la forte amplification de la luminescence et proposons des méthodes pour séparer sa contribution de la contribution cohérente. En outre, nous démontrons plusieurs applications de la HHG dans les solides. Premièrement, nous proposons une nouvelle méthode pour déduire la distribution spatiale du champ électrique dans des nanostructures en analysant les dommages induits par laser. Deuxièmement, nous utilisons l’émission du nanocone, qui est cohérente spatialement, pour imager des objets avec une résolution à l’échelle nanométrique. Enfin, nous générons des harmoniques portant un moment orbital angulaire contrôlé. / The aim of this dissertation is to study the process of high-order harmonic generation (HHG) in solids and the possibility to amplify solid HHG by exploiting local field enhancements in nanostructures. While HHG in gases has been known for several decades and has been extensively studied, HHG in solids was first reported in 2011. Different processes such as interband and intraband oscillations were identified to play an important role in solid HHG. However, the process is still under investigation and debated in the community. Here, we study the generation of high harmonics in different crystals, such as ZnO, CaCO₃ and CdWO₄. We confirm that HHG depends on the driving wavelengths and on crystalline orientation. Beside 3D bulk crystals, we investigate HHG in 2D materials such as graphene. Due to its high electron mobility and its special band structure HHG in graphene is more efficient than in bulk crystals. Typically, intensities of 10¹² TW/cm² or more are needed to trigger HHG. The high intensity is reached by employing schemes like chirped pulse amplification which generates femtosecond pulses with µJ- or mJ-energies. Thanks to recent advances in nanofabrication techniques, nanostructures can enhance a laser electric field by several orders of magnitude. While plasmonically enhanced HHG in gases was shown not to be feasible, recent works reported on the amplification of HHG in solids. In this work, we explore the amplification of crystal HHG under various configurations. We first study different types of plasmonic nanostructures, namely bow ties, nanoholes, gratings and resonators. We compare them with respect to different parameters such as enhancement volume and peak enhancement. Different driving wavelengths and crystals are used. Strong amplification by several orders of magnitude is demonstrated for the third harmonic. Furthermore, we discuss radiation-induced damage of plasmonic nanostructures. Semiconductor nanostructures which confine light by subwavelength waveguiding have several advantages with respect to metallic nanostructures. Semiconductor nanocones for example exhibit a large amplification volume, several orders of magnitudes larger than previously reported and avoid melting observed in metallic nanostructures. We carry out several iterations of experiments with ZnO nanocones where the detection system and the nanocone geometry are improved in each cycle. We use different driving lasers and different optimized nanocone geometries. HHG in ZnO nanocones up to 15th order from a 3.1 µm driving laser is demonstrated. Amplification by several orders of magnitude of both perturbative and non-perturbative harmonics from nanojoule-oscillator pulses at MHz repetition rate and 2.1 µm wavelength is demonstrated, for the first time up to H9. The amplification factor depends on the pump intensity. We also explore the strong amplification of luminescence and propose ways to disentangle its contribution from the coherent one. Furthermore, we explore several applications of crystal HHG. First, we propose a new way to deduce the electric field spatial distribution in nanostructures by analyzing the radiation-induced damage. Secondly, we use the spatially coherent emission from the nanocone to image nanoscale objects with nanometer scale resolution. In addition, we generate solid harmonics that carry an orbital angular momentum.

Les propriétés optiques des nanoparticules métalliques, caractérisées par l'existence d'une résonance plasmon de surface (SPR) dans le domaine visible, sont aujourd'hui couramment utilisées afin de détecter et de caractériser des espèces chimiques, en solution ou déposées sur des substrats (dans les capteurs par exemple). Dans ce travail, j'ai optimisé la réalisation puis la caractérisation physico-chimique et optique d'interfaces composées de nanoparticules d'or d'environ 15 nm de diamètre sur des substrats de silicium et de verre fonctionnalisés par des silanes, à l'aide de méthodes d'optique linéaire et non linéaire. La spectroscopie UV-visible en réflexion et transmission, couplée aux microscopies électronique et à force atomique, et aidée par la modélisation, m'a permis de corréler les propriétés optiques des particules à leur densité locale sur la surface. La spectroscopie optique non linéaire par génération de fréquence somme (SFG) permet de sonder la chimie de surface des particules et du substrat ainsi que de tirer parti de l'amplification locale des processus optiques par excitation de la SPR. Après avoir montré qu'elle amplifie effectivement des signaux SFG moléculaires peu intenses de la couche de silanes, j'ai révélé la présence dans la couche organique de greffage de groupements méthyles résultant d'une réaction de silanisation incomplète, démontré le lien entre la stabilité temporelle chimique et plasmonique des interfaces et l'irradiation laser, caractérisé finement la qualité de fonctionnalisation des particules par des thiols et montré la relation de proportionnalité entre réponses optiques linéaire et non linéaire en surface. Finalement, j'ai étudié directement le processus d'amplification de la SFG par le couplage à la SPR en réalisant une spectroscopie à deux dimensions infrarouge et visible. J'ai montré que ce couplage est mesurable même sur de petites particules déposées, et qu'il se produit dans la zone spectrale d'existence du plasmon de surface (du vert au rouge). La comparaison avec une surface plane de platine et d'or m'a permis d'extraire de façon fine des facteurs d'amplification, qui correspondent à ce que prédit une modélisation simple de la plasmonique en jeu dans ces interfaces. / Optical properties of metallic nanoparticles, exhibiting a surface plasmon resonance (SPR) in the visible range, are nowadays extensively used to detect and characterize chemical entities, either in solution or deposited on substrates (e.g. sensors). In this work, I have optimized the creation of interfaces composed of 15nm in diameter gold nanoparticles on silicon and glass substrates after functionnalization by silanes, and their chemical and optical characterization by linear and nonlinear optical methods. I have used UV-visible spectroscopy in reflexion and transmission geometries, coupled to electronic and atomic force microscopies, with the help of optical simulations, to correlate the optical properties of the particles to their local density at the surface. Nonlinear sum frequency generation spectroscopy is able to probe the surface chemistry of both the particles and the substrate, through a local amplification of optical processes due to the excitation of the SPR. After showing that the latter does indeed amplify the low intensity molecular SFG signals from the silane layer, I have revealed the presence, in the organic layer, of unreacted methyl groups arising from an incomplete silanization, evidenced the link between plasmonic and chemical stability in time and laser irradiation, finely assessed the quality of surface functionnalization of the particles by thiols, and established the linear relationship between linear and nonlinear optical responses at the surface. Finally, I have directly studied the amplification process itself by coupling to the SPR through two dimension spectroscopic studies in the visible and infrared ranges. I have shown that the coupling is indeed measurable, even on small deposited particles, and that it happens in the spectral zone where the surface plasmon exists (from green to red). A comparison to flat platinum and gold surfaces leads to a fine estimation of amplification factors, which correspond to the predictions of a simple model for the plasmonic processes at stake at such interfaces.

When an electromagnetic wave illuminates metal nanostructure under right circumstances, it can couple to the motion of electrons and thus give rise to so-called LSPR. When these collective oscillations non-radiatively decay, they excite charge carriers that can have, for a short moment of time, highly non-thermal energy distribution. These so-called "hot" electrons and holes can then take part in photochemical applications, e.g. in reactions on photoactive electrodes where hot electrons act as catalysts. Gold nanoparticles seem to be a good candidate for fabrication of such electrodes because they exhibit resonantly enhanced absorption due to plasmon excitation in the visible and near infrared spectral range, which could make the solar energy harvesting more efficient. In this work we present electrohemical experiments that should help to clarify the underlying principles of photochemical reactions involving hot electrons. Our model system consists of indium tin oxide electrodes covered with tungsten disulphide nanotubes that were previously decorated by gold nanoparticles. By comparing the results of chronoamperometric measurements on individual components of this system it was shown that excitation of plasmonic nanoparticles indeed leads to photocurrents and that electrochemical methods can serve as a valuable tool for analysis of photochemical reactions catalyzed by hot electrons.