Raman spectroscopy involves change in the polarizability of the molecular system on excitation and is based on scattering process. Spontaneous Raman scattering is a two photon process, in which the input light initiates the excitation, which then leads to an emission of another photon due to scattering. It is extensively used to understand molecular properties. As spontaneous Raman scattering is a weak process, the detection of these weak Raman photons are rather difficult. Alternatively, resonance Raman (RR) scattering is another technique where the excitation wavelength is chosen according to the material under study. The excitation wavelength is chosen to be within the absorption spectrum of the material under study. RR spectroscopy not only provides considerable improvement in the intensity of the Raman signal, but also provides mode specific information i.e. the modes which are Franck-Condon active in that transition can be observed. There are reports on RR studies of many systems using pulsed light as an excitation source. It is necessary to use at least two pulsed laser sources for carrying out the time resolved RR spectroscopy. A single pulse source for excitation would lead to compromise either with temporal or spectral resolution which is due to the uncertainty principle. If an excitation pulse has pulse width of ~100 femtoseconds then the spectral resolution will be ~ 150 cm-1. It is clear now that for improving the temporal and spectral resolution simultaneously, usage of single pulse for Raman experiments (spontaneous scattering) is not adequate. The usage of multiple laser pulses may provide the way out to improve the resolutions. Nonlinear spectroscopy in a broad view helps in understanding the structural and dynamical properties of the molecular systems in a deeper manner. There are a number of techniques as a part of nonlinear spectroscopy that have emerged in due course to meet different requirements and to overcome some difficulties while understanding the molecular properties. Stimulated Raman (SRS) gain, coherent anti-Stokes Raman scattering (CARS) and the inverse Raman spectroscopy are a few to mention as third order nonlinear spectroscopic techniques which give the similar kind of information about the molecular systems. Stimulated Raman scattering is a more general process involved in nonlinear Raman processes. SRS involves at least two laser pulses and the difference in their frequencies should match with the vibrational frequency of the molecule. The polarization has to be matched between the Raman pump and the Raman probe pulses. We have developed a new nonlinear Raman technique in our laboratory named as ultrafast Raman loss spectroscopy (URLS) using the principles of nonlinear Raman scattering. It involves the Raman pump (~ 1 picosecond (ps) or ~ 15 cm-1spectral resolution) and Raman probe as a white light continuum (100 fs) whose frequency components ranges from 400-900 nm. The laser system consists of Tsunami which is pumped by a Millennia laser and Spitfire-Pro, a regenerative amplifier which is pumped by an Empower laser. Tsunami provides a 100 fs, 780 nm centered, 80 MHz and ~6 nJ energy laser pulses. The Tsunami output is fed into Spitfire to amplify its energy and change the repetition rate to 1 KHz. The pulse length of the input pulse is preserved in amplification. The output of amplifier is split into two equal parts; one part is used to pump the Optical Parametric Amplifier (OPA) in order to generate wavelengths in the range 480-800 nm. The output of the OPA is utilized to generate Raman pump which has to be in ps in order to get the best spectral resolution. A small portion of the other part of amplifier output is utilized to generate white light source for the Raman probe. The remaining part of the amplifier output is used to pump TOPAS to generate wavelengths in the ultraviolet region. URLS has been applied to many molecular systems which range from non-fluorescent to highly fluorescent. URLS has been demonstrated to be very sensitive and useful while dealing with highly fluorescent systems. URLS is a unique technique due to its high sensitivity and the Raman loss signal intensity is at least 1.5-2 times higher as compared to the Raman gain signal intensities. Cresyl violet perchlorate (CVP) is a highly fluorescent system. URLS has been applied to study CVP even at resonance excitation. Rhodamine B has also been studied using URLS. Spontaneous Raman scattering is very difficult to observe experimentally in such high quantum yield fluorescent systems. The variation in the lineshapes of the Raman bands for different RP excitation wavelengths in URLS spectra shows the mode dependent behavior of the absorption spectrum. The experimental observation of variation in the lineshape has been accounted using theoretical formalism. The thesis is focused on discussing the development of the new nonlinear Raman spectroscopic technique URLS in detail and its applicability to molecular systems for better understanding. A theoretical formalism for accounting the uniqueness of URLS among the other nonlinear Raman techniques is developed and discussed in various pictorial representations i.e. ladder, Feynman and closed loop diagrams. A brief overview of nonlinear spectroscopy and nonlinear Raman spectroscopy is presented for demonstrating the difference between the URLS and the other nonlinear Raman techniques.

In the past decade, great research effort was inspired by the need to realise active optical functionalities in silicon, in order to develop the full potential of silicon as a photonic platform. In this thesis we explore the possibility of achieving tunable delay and optical gain in silicon, taking advantage of the unique dispersion capabilities of photonic crystals. To achieve tunable optical delay, we adopt a wavelength conversion and group velocity dispersion approach in a miniaturised engineered slow light photonic crystal waveguide. Our scheme is equivalent to a two-step indirect photonic transition, involving an alteration of both the frequency and momentum of an optical pulse, where the former is modified by the adiabatic tuning possibilities enabled by slow light. We apply this concept in a demonstration of continuous tunability of the delay of pulses, and exploit the ultrafast nature of the tuning process to demonstrate manipulation of a single pulse in a train of two pulses. In order to address the propagation loss intrinsic to slow light structures, with a prospect for improving the performance of the tunable delay device, we also investigate the nonlinear effect of stimulated Raman scattering as a means of introducing optical gain in silicon. We study the influence of slowdown factors and pump-induced losses on the evolution of a signal beam along the waveguide, as well as the role of linear propagation loss and mode profile changes typical of realistic photonic crystal structures. We then describe the work conducted for the experimental demonstration of such effect and its enhancement due to slow light. Finally, as the Raman nonlinearity may become useful also in photonic crystal nanocavities, which confine light in very small volumes, we discuss the design and realisation of structures which satisfy the basic requirements on the resonant modes needed for improving Raman scattering.

Parmi les matériaux piézo-électriques, les pérovskites ferroélectriques à base de plomb sont connus pour avoir les meilleurs coefficients piézo-électriques et couplage électromécanique. Ils sont largement utilisés dans diverses applications industrielles et technologiques. Les "ferroélectrique relaxeurs" appartiennent à cette famille. Leur structure est caractérisée par la présence de nanorégions polaires orientées de façon aléatoire. Dans cette thèse, nous nous sommes intéressés à l'étude des propriétés structurales et dynamiques de matériaux ferroélectriques et relaxeurs tels que PbTiO3, PbZr0.52Ti0.48O3, PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3, et PbMg1/3Ta2/3O3 (PMT). La structure à longue et courte portée a été étudiée par diffraction de neutrons et spectroscopie d'absorption des rayons X (XAFS), alors que la spectroscopie hyper-Raman (HR) est utilisée pour sonder les vibrations. L'analyse de la structure locale de matériaux pérovskites complexes AB'B''O3 montre que la pression diminue le désordre statique des gros cations occupant le site B, tandis que le champ électrique appliqué a un effet opposé. Cette distortion induite sous champ pourrait être à l'origine des forts coefficient piézoélectrique dans ces matériaux. La diffusion HR dans PMN et PMT a permis d'observer pour la première fois le "mode mou" responsable de la dépendance en température de la constante diélectrique. L'analyse des règles de sélection et la description en modes propres des vibrations actives en HR, permet de rendre compte de l'implication de chaque atome dans le comportement structural en température des ferroélectriques relaxeurs. / Among piezoelectric materials, lead-based ferroelectric perovskites are known to have the largest piezoelectric coefficients and electromechanical coupling. They are widely used in dfferent industrial and technological applications. The so-called "relaxors" belong to this family. Their structure is characterized by the presence of randomly oriented polar nanoregions. In this thesis, we are interested in studying the structural and dynamical properties of prototypical ferroelectric materials and relaxors such as PbTiO3, PbZr0.52Ti0.48O3, PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3, and PbMg1/3Ta2/3O3 (PMT). The long and short range structure has been investigated by neutron diffraction and X-ray absorption fine structure (XAFS), while hyper-Raman scattering (HRS) is used to probe the vibrations. The local structure analysis of complex perovskite materials AB'B''O3 shows that pressure reduces the static disorder of the large cation occupying the B-site, while an applied electric field has an opposite effect. This field-induced distortion might relate to the large piezoelectric coefficient in such materials. HRS in PMN and PMT allows the first observation of the "primary" soft mode responsible for the temperature dependence of the dielectric constant. The selection rule analysis reveals the nature of the HRS active vibrational bands and enables us to get insights about the involvement of each atom in the structural modifications upon temperature.

Ce mémoire de thèse est consacré à l’étude d’une liaison tout-optique longue de 10 km dédiée à l’extension d’un observatoire câblé de fond de mer existant afin d’atteindre de nouvelles zones d’exploration. Les travaux de recherche qui y sont rapportés démontrent la faisabilité de cette liaison tout-optique entre un instrument déporté et une station terrestre avec une seule fibre optique longue de 10 km, qui transmet simultanément la puissance, nécessaire à l’alimentation de l’instrument (quelques centaines de milliwatts), et des données bidirectionnelles en temps réel.Le contexte de cette thèse est présenté au travers d’un état de l’art sur les observatoires câblés et sur la puissance sur fibre. Le choix de la fibre unique et la présence de fortes puissances optiques complexifient la mise en oeuvre de cette extension tout-optique, et sont à l’origine de l’apparition d'interactions entre l’énergie optique dédiée à l'alimentation (@1480 nm) et les données échangées (@1550 nm). Tout au long de ce document, les choix technologiques retenus sont argumentés et les effets optiques non linéaires tels que les diffusions Raman, Brillouin, Rayleigh, l’Émission Spontanée Amplifiée (ASE) sont décrits, modélisés et analysés expérimentalement. L’extension tout-optique proposée a été caractérisée à la fois en régimes statique et dynamique par des mesures du bilan de liaison, du rapport signal à bruit (SNR) et du taux d’erreur binaire (BER). Les résultats obtenus montrent la possibilité de fournir 160 mW électrique à l’instrument déporté en utilisant une source optique continue de 33 dBm sans dégrader excessivement les données bidirectionnelles transmises simultanément (BER<10-7). / This thesis is devoted to the study of a 10 km long all-optical network dedicated to extend a current cabled seafloor observatory, in order to reach new exploration areas. The research work described in this thesis demonstrates the feasibility of this all-optical link between a remote instrument and a shore station with a single 10 km long optical fiber, which simultaneously transmits the energy required to supply the instrument (several hundred milliwatts) and bidirectional data in real time.The thesis context is presented trough an analysis of the cabled seafloor observatories and of the power-over-fiber. The choice of a single optical fiber and the presence of high optical power complicate the implementation of this all-optical extension, and they cause the appearance of interactions between the optical energy dedicated to the power supply (@1480 nm) and the exchanged data (@1550 nm). Throughout this document, the technological choices are explained and the optical nonlinear effects are described, simulated and analyzed experimentally, such as Raman, Brillouin, and Rayleigh scattering and Amplified Spontaneous Emission (ASE). The proposed all-optical extension has been characterized in static and dynamic regimes with measures of the optical link budget, the Signal-to-Noise Ratio (SNR), and the Bit Error Ratio (BER). The results show the possibility to power the remote instrument with 160 mW, when using a continuous high optical laser source of 33 dBm without huge degradation of the bidirectional data transmitted simultaneously (BER<10-7).

Nesta tese de doutorado foram desenvolvidas metodologias para obter espectros Raman intensificados pela superficie de adsorbatos orgânicos em eletrodos de Fe, Co e Ni, que são metais que apresentam baixo fator de intensificação SERS. Foram desenvolvidos procedimentos de ativação eletroquímica para eletrodos puros dos três metais. Os protocolos de ativação eletroquímica foram utilizados para obter espectros SERS de piridina, 1,10-fenantrolina e 2- e 4-aminopiridina. O fator de intensificação determinado para o três metais, da ordem de 102-103 vezes, depende fortemente do modo vibracional do adsorbato. Os espectros SERS da piridina nos metais de transição, quando comparados com os cálculos de espectros vibracionais de cluster da piridina com átomos metálicos por DFT mostram que a formação do radical &#945;-piridil com a adsorção nos metais de transição, proposta na literatura, não ocorre. Os perfis de excitação SERS calculados pelo modelo de transferência de carga da piridina apresentaram boa correlação com os dados experimentais. Os resultados SERS para a 1,10-fenantrolina mostraram que a espécie que adsorve é a molécula livre, com a espécie adsorvida semelhante ao complexo sintetizado. A dependência das intensidades relativas com o potencial nos espectros SERS é diferente da observada para os espectros Raman ressonante dos complexos da phen com metais de transição, mostrando que o estado excitado monitorado pelas duas técnicas é diferente. O monitoramento da adsorção das 2-aminopiridinas nos metais de transição permitiu sugerir a adsorção pelo anel piridínico para potenciais menos negativos e através dos nitrogênios piridínico e amínico para potenciais mais negativos em eletrodos de Co e Ni, e para o Fe adsorve apenas pelo nitrogênio piridínico. Em solução eletrolítica 0,1 mol.L-1 KCl, a 4-aminopiridina passa de fracamente ligada para um complexo de superficie semelhante ao complexo sintetizado para potenciais mais negativos. Utilizando a solução eletrolítica 0,1 mol.L-1 KI, as duas espécies são observadas para um intervalo maior de potenciais. No eletrodo de Ni, observa-se 4-aminopiridina protonada para E = -0,7 V; para potenciais mais negativos um complexo de superficie semelhante ao complexo sintetizado é observado. Os filmes eletrodepositados de Co e Ni em eletrodos de Ag ativado eletroquimicamente permitiram a obtenção de espectros SERS da py com alto fator de intensificação. Os filmes com espessuras maiores que 2 monocamadas de Co ou Ni apresentaram bandas intensas da piridina adsorvida nestes metais, sem bandas da piridina adsorvida em Ag, indicando que os filmes não apresentam pinholes, com intensidade SERS 100 vezes maior do que os metais puros. As intensidades relativas dos espectros SERS são similares à obtidas nos espectros SERS da piridina nos metais puros para filmes finos mais espessos do que 7 monocamadas. Foram construídos substratos de Au SERS-ativos com alto desempenho e reprodutibilidade por eletrodeposição sobre uma máscara de microesferas de poliestireno. Os espectros SERS da 4-mercaptopiridina adsorvida nos substratos otimizados apresentaram intensidade 2 vezes maior do que o eletrodo de Au ativado eletroquimicamente. A reprodutibilidade do sinal SERS para estes substratos foi de &#177; 15 %, indicando que estes substratos podem ser utilizados como sensores para sistemas de interesse analítico. / Surface-enhanced Raman spectra of organic adsorbates on Fe, Co and Ni electrodes were acquired after the development of specific methodologies described in this PhD thesis. Electrochemical activation procedures were developed for the three bare metaIs electrodes. The electrochemical activation protocols were applied for the acquisition of SERS spectra of pyridine, 1,10-phenanthroline and 2- and 4-aminopyridine on Fe, Co e Ni electrodes. The total and relative intensities changes of SERS bands with the applied potentials were explained by the charge transfer mechanism, which had a large contribution in the SERS enhancement for these metaIs. The enhancement factor determined for the three metaIs, on the 102-103 times range, strongly depends on the adsorbate\' s vibrational modes. The SERS spectra of pyridine on the transition metals and vibrational spectra calculations of pyridine with metallic atoms showed that the formation of &#945;-pyridil in the adsorption on transition metaIs, suggested in the literature, didn\'t occur. The calculated pyridine SERS excitation profiles present reasonable correlaton with the experimental data. The SERS results for 1,10-phenanthroline showed that the free molecule was the adsorbing species. The potential dependence of the SERS relative intensities was different from those of the resonance Raman spectra of 1,10-phenanthroline complexes with transition metal ions, indicating that different excited states were probed by the two techniques. 2-aminopyridine adsorbed through the pyridinic ring at less negative potentials and through both pyridinic and aminic nitrogens at more negative potentials on Co and Ni electrodes, but for Fe electrode it adsorbed exclusively through the pyridinic nitrogen. 4-aminopyridine adsorbed perpendicularly to the electrode. In 0,1 mol.L-1 KCl electrolytic solution, 4-aminopyridine changed from weak1y bound to a surface complex similar to the synthesized complex at more negative potentials. In 0,1 mol.L-1 KI electrolytic solution, both species were observed in a larger potential interval. On the Ni electrode, protonated 4aminopyridine was observed for V = -0.7 V, and for more negative potentials a surface complex, similar to the synthesized one, was observed. The electrodeposition of ultrathin film of Co and Ni on electrochemically-activated Ag electrodes allowed obtaining SERS spectra of pyridine with high enhancement factors. The SERS spectra of py for films thickness higher than 2 monolayers of Co or Ni presented intense bands of pyridine adsorbed on these metals, and no bands of pyridine adsorbed on Ag were observed, indicanting the absence of pinholes in the films. The relative intensities of SERS spectra on the thin films were similar to those obtained for the SERS of pyridine on the bare metaIs electrodes for films thicker than 7 monolayers, but with SERS intensity 100 times higher. The SERS activity and signal strength reproducibility of Au nanostructured substrates obtained by electrodeposition on a polystyrene masking were evaluated. The SERS spectra of 4-mercaptopyridine adsorbed on optimized electrodes presented intensities 2 times greater than those of the electrochemically activated Au electrode. The SERS intensity reproducibility for these substrates was &#177; 15%, indicating the potential use of such substrates as sensors.

Recentemente, a dopagem de semicondutores (envolvendo compostos II-VI, IV-VI, III-V, e do grupo-IV) com espécies magnéticas tem sido extensivamente investigada em função do seu potencial em spintrônica. Neste contexto, semicondutores magnéticos baseados no Si e no Ge são atraentes devido à sua compatibilidade com a indústria de semicondutores existente. Entretanto, a solubilidade das espécies magnéticas nestes materiais em forma cristalina é muito baixa e, consequentemente, sua atividade magnética é limitada. Este não é o caso para o silício amorfo (a-Si) e o germânio amorfo (a-Ge), que podem conter elementos magnéticos além do limite de solubilidade de seus análogos cristalinos, e apresentar propriedades magnéticas notáveis. Motivado por estes fatos, este trabalho apresenta uma investigação abrangente de filmes finos de Si e Ge contendo diferentes quantidades de Mn e Co, trazendo informações úteis no entendimento das propriedades desta classe de materiais. As amostras foram preparadas por co-sputtering, e possuíram concentrações de Mn na faixa de ~ 0.1-24 at.%, e de Co na faixa de ~ 1-10 at.%. Após a deposição, os filmes foram submetidos a tratamentos térmicos cumulativos até 900 oC, e foram investigados por: espectroscopia de energia dispersiva de raios-x (EDS); espalhamento Raman; difração de raios-x; transmissão óptica; microscopias eletrônica de varredura (SEM), de força atômica (AFM) e de força magnética (MFM); magnetometria SQUID; método de van der Pauw; etc. Para fins comparativos, amostras puras também foram preparadas, tratadas e caracterizadas de forma similar. Os presentes resultados indicam que os átomos de Mn e Co foram incorporados de forma efetiva e homogênea nas matrizes amorfas. Além disso, os filmes sem tratamento (puros ou contendo impurezas) são essencialmente amorfos. Ao contrário, tratamentos em altas temperaturas induzem a cristalização das amostras, e alterações em suas demais características, dependentes da introdução de dopantes. Desta forma: suas propriedades estruturais, ópticas, morfológicas, elétricas, e magnéticas, são notadamente afetadas pela inserção de Mn e Co, e pela temperatura de tratamento térmico. Estas observações foram sistematicamente investigadas e serão apresentadas e discutidas em detalhe. / Along the last few years, the doping of semiconductors (either II-VI, IV-VI, III-V, and group-IV compounds) with magnetic species have been extensively studied due to their potential applications in spintronics. Among them, Si- and Ge-based magnetic semiconductors are very attractive because of their total compatibility with the well-established current semiconductor technology. In the crystalline form, however, these materials exhibit a low solubility limit to magnetic species and, consequently, limited magnetic activity. This is not the case for amorphous (a-)Si and a-Ge, which can contain magnetic elements beyond the solubility limit of their crystalline counterparts, and present improved magnetic properties. Motivated by these facts, this work contains a comprehensive investigation of Si and Ge thin films containing different amounts of Mn and Co, providing useful information concerning the properties of this class of materials. The samples were prepared by co-sputtering, rendering Mn concentrations in the ~ 0.1-24 at.% range, and Co contents in the ~ 1-10 at.% range. After deposition, the films were submitted to isochronal thermal annealing treatments up to 900 oC and investigated by: energy dispersive x-ray spectrometry (EDS); Raman scattering spectroscopy; x-ray diffraction; optical transmission measurements; scanning electron (SEM), atomic force (AFM) and magnetic force (MFM) microscopy techniques; SQUID magnetometry; van der Pauw technique; etc. For comparison purposes, pure samples were also prepared, annealed and characterized in a similar way. The present experimental results indicate that the Mn and Co atoms were effectively and homogenously incorporated into the amorphous hosts. Moreover, the as-deposited films (either pure or doped) are essentially amorphous. On the contrary, thermal annealing at increasing temperatures induces the crystallization of the samples, and changes in their further characteristics, that are dependent of the doping. In this way: their structural, optical, morphological, electrical, and magnetic properties, etc., are notably affected by the insertion of Mn and Co, and by the temperature of thermal annealing. These experimental observations were systematically studied and will be presented and discussed in detail.

In dieser Arbeit wurden nanostrukturierte Oberflächen durch Immobilisierung von Gold- und Silber¬nanopartikeln mit Organosilanen hergestellt und bezüglich ihrer Eigenschaften als Substrate für die oberflächenverstärkte Raman-Streuung (SERS) untersucht. In Experimenten zum Einfluss von Partikelgröße und -anordnung auf die plasmonischen Eigenschaften wurden wesentliche Erkenntnisse für die Optimierung SERS-aktiver Nanostrukturen gewonnen. Durch Kombination experimen¬teller Untersuchungen, unter Verwendung von spektroskopischen und bildgebenden Ver¬fahren, mit elektro¬dynamischen Simulationen der lokalen Felder, wurden Zusammen¬hänge zwischen den plasmo¬nischen und nanoskopischen Eigen¬schaften von Partikeln auf Oberflächen und ihren SERS-Eigenschaften hergestellt. Die nanostrukturierten Oberflächen weisen hohe und über einen weiten Analyt-konzentrations¬bereich stabile Verstärkungsfakoren bei hoher mikros¬kopischer Homo-genität der Verstärkung auf. Dies macht sie zu geeigneten Substraten für quantitative Anwendungen von SERS. Das Potenzial der nano-strukturierten Ober¬flächen für den Einsatz in analytischen Fragestellungen wurde anhand mehrerer Anwendungen gezeigt. Durch simultane Immobilisierung verschiedener Nano¬partikel unter Verwendung desselben Linker¬moleküls wurden erstmalig Ober¬flächen mit definierten plasmonischen und funktionellen Eigen¬schaften repro¬duzierbar erzeugt. Diese neuartigen Mischsubstrate wurden in der Verfolgung katalytischer Reaktionen eingesetzt, wodurch erstmals Reaktions-konstanten solcher Reaktionen mittels SERS bestimmt werden konnten. Die Ergebnisse der Arbeit legen einen breiten Einsatz der plasmonischen nano¬struk-turierten Ober¬flächen in der Zukunft nahe. Dieser reicht von Untersuchungen in der Kata-lyse¬forschung über mikroskopische Anwendungen von SERS bis zur Verwendung in der klinischen Diagnostik. / Within this work nanostructured surfaces were generated by immobilization of gold and silver nanoparticles with organosilanes and characterized regarding their suitability as substrates for Surface-enhanced Raman scattering (SERS). Essential knowledge for the optimization of SERS-active nanostructures could be found by experimental invest-igations on the influence of particle size and assembly on the plasmonic properties. Through combined experimental investigations, including spectroscopic and imaging techniques, and electrodynamic simulations of local fields, the plasmonic and nanoscopic properties of particles on surfaces were related to their SERS-properties. The nanostructured surfaces exhibit high and, over a wide range of analyte concentration, stable enhancement factors with high microscopic homogeneity. Therefore immobilized nanostructures are suitable substrates for quantitative SERS. The potential for the use of the nanostructured surfaces in analytical problems was shown in various applications. Signal fluctuations that can occur in the detection of complex analyte mixtures can be significantly reduced by immobilization of the nanoparticles. This offers the possibility to use multivariate statistical methods for automated classification and identification of molecule mixtures but also for multiplexing and imaging by SERS. Simultaneous immobilization of gold and silver nanoparticles and gold and platinum nanoparticles using the same linker molecule allowed for the first time to generate surfaces with defined plasmonic and functional properties with low cost and high reproducibility. These new mix and match-substrates were used to follow catalytic reactions and determine reaction constants of such reactions for the first time using SERS. The outcome of this work suggests a wide range of applications of plasmonic nanostructured surfaces in the future. This includes the investigation of catalysis, microscopic applications of SERS and clinical diagnosis.

Ce travail, qui concerne l’étude des nanotubes de carbone mono- et double parois, comporte deux volets distincts: (i) une compréhension des propriétés optiques et phononiques intrinsèques des nanotubes de carbone individuels, (ii) une approche expérimentale originale des propriétés des nanotubes de carbone double-parois fonctionnalisés de manières covalente et non-covalente. Concernant l’étude des propriétés intrinsèques des nanotubes de carbone individuels, des informations originales ont été obtenues en couplant des résultats de spectroscopie Raman, incluant la mesure des profils d’excitation des différents modes, avec des données d’absorption optique et de diffraction électronique. De manière générale, l’approche que nous avons développée a mis en avant la complémentarité de la spectroscopie Raman et de la diffraction électronique pour l’identification « la plus probable » de la structure de chaque tube. Parmi les résultats obtenus sur les tubes mono-paroi (SWNTs) individuels, on peut souligner la confirmation originale du caractère excitonique des transitions optiques obtenue en combinant des données d’absorption et de profils d’excitation Raman, ainsi que la mise en évidence d’un comportement inattendu des rapports d’intensité des composantes LO et TO des modes G. L’étude des nanotubes de carbone double-parois (DWNTs) individuels de structures clairement identifiées a permis de comprendre le rôle de la distance inter-tubes dans les déplacements en fréquence des modes Raman (modes de respiration (RBLM) et modes G), en associant à une distance inter-tube donnée une pression interne négative (positive) quand cette distance est supérieure (inférieure) à 0.34 nm. D’autre part, le rôle des effets d’interférences quantiques dans l’évolution avec l’énergie d’excitation des intensités des composantes LO et TO des modes G a été clairement identifié. Enfin, une attribution de l’origine des transitions optiques, mesurées par spectroscopie d’absorption, de différents DWNTs a été proposée.L’étude des propriétés de DWNTs fonctionnalisés a été réalisée en couplant des expériences de spectroscopie Raman, d’absorption UV-visible-NIR et de photoluminescence (PL), incluant les cartes d’excitation de la photoluminescence (PLE), sur des suspensions de DWNTs avant et après fonctionnalisation, (i) covalente via un groupement diazonium, (ii) covalente et non-covalente (pi-stacking) par un colorant. Ce travail présente une contribution au débat sur une question essentielle pour l’utilisation des DWNTs dans des dispositifs opto-électroniques, à savoir : « les DWNTs luminescent-ils ? Et si oui, quelle est l’origine de la luminescence ? ». La présence de photoluminescence dans nos échantillons de DWNTs est établie, et l’étude de son évolution avec différents types et degrés de fonctionnalisation démontre qu’elle ne peut provenir que des tubes internes des DWNTs (PL intrinsèque aux DWNTs), ou de SWNTs générés par l’extrusion des tubes internes de DWNTs durant la préparation des suspensions. D’autre part, on peut souligner la mise en évidence d’un transfert d’énergie du colorant vers le tube interne quand le colorant est greffé de manière covalente sur la tube externe. / This work concerns the study of mono- and double-walled carbon nanotubes. It contains two distinct parts: (i) the first part is devoted to the understanding of the intrinsic optical and phonon properties of individual carbon nanotubes; (ii) the second part reports an experimental investigation of the properties of covalently and non-covalently functionalized double-walled carbon nanotubes. Concerning the study of the intrinsic properties of the individual carbon nanotubes, new information was obtained by coupling Raman spectroscopy data, including the measurement of the excitation profiles of different Raman-active modes, with optical absorption and electronic diffraction data. From a general point of view, our approach put in evidence the complementarity of the Raman spectroscopy and electronic diffraction for “the most probable” assignment of the structure of the nanotubes.Among the results obtained on individual single-walled carbon nanotubes (SWNTs), one can underline the confirmation of the excitonic character of the optical transitions by combining optical absorption and Raman excitation profiles on the same nanotubes, and the evidence of an unexpected behavior of the relative intensities of the LO and TO components of the G-modes. The study of the index-identified individual double-walled carbon nanotubes has permitted to understand the role of the inter-walls distance in the frequency shifts of the radial breathing-like modes (RBLM) and G-modes, by associating a given inter-walls distance to a negative (positive) internal pressure when this distance is larger (smaller) than 0.34 nm. On the other hand, the role of quantum interferences in the evolution with the excitation energy of the intensities of the LO and TO components of the G-modes was clearly identified. Finally, the assignment of the optical transitions, measured by absorption spectroscopy, of index-identified DWNTs was proposed.The study of the properties of functionalized DWNTs was performed by combining Raman spectroscopy, UV-visible-NIR absorption and photoluminescence (PL), including maps of photoluminescence excitation (PLE), on suspensions of DWNTs before and after functionalization: (i) covalently by using diazonium, (ii) covalently and non-covalently (pi-stacking) by using dye molecules. This work is a contribution to the debate on an essential question for the use of the DWNTs in opto-electronic devices, namely: “Do the DWNTs they luminesce? And if yes, what is the origin of the luminescence?". The presence of photoluminescence in our samples of DWNTs was established, and the study of its evolution with various kinds and degrees of functionalization states that PL can only result from inner tubes (intrinsic PL of DWNTs), or from SWNTs generated by the extrusion of the internal tubes of DWNTs during the preparation of the suspensions. On the other hand, one must emphasize the evidence of an energy transfer from the dye molecules towards the internal tube when such molecules are covalently grafted on the outer tube.

Dans ce travail de thèse, nous avons étudié des effets d'optique non-linéaire d'ordre trois dans les cavités à cristaux photoniques en silicium. Le premier d'entre eux est un phénomène d'auto-oscillations à haute fréquence (GHz) dans ces cavités, qui a pour origine une modulation de la transmission de la cavité due à l'interaction entre la dispersion due aux porteurs libres et l’absorption à deux photons. Nous avons observé ces auto-oscillations, pour la première fois, dans les nanocavités à cristaux photoniques silicium avec une fréquence de l’ordre de 3 GHz et une grande pureté spectrale. Nous avons développé un modèle pour analyser les mécanismes qui régissent l'apparition de ces auto-oscillations, ainsi que les amplitudes des fréquences fondamentale et harmoniques de ces oscillations. Ce phénomène d'auto-oscillations permettrait de réaliser des sources micro-ondes en silicium très compactes. Le deuxième phénomène étudié est celui de la diffusion Raman, qui est le seul moyen d'obtenir des lasers entièrement en silicium démontré jusqu'à présent. Cette diffusion Raman a été mesurée tout d'abord dans des guides d'onde à cristaux photoniques étroits (W0.63) de longueur 100 microns, où nous avons pu obtenir un nombre de photons Stokes allant jusqu'à 9, montrant ainsi que la diffusion Raman stimulée prédominait dans ces guides d'onde, bien que nous n’ayons pas pu y obtenir un effet laser Raman franc. Nous avons ensuite mesuré la diffusion Raman dans des nanocavités doublement résonantes conçues spécifiquement à partir de ces guides d'ondes pour optimiser l'effet Raman, avec des facteurs de qualités allant jusqu'à 235000 pour la résonance Stokes. Bien que nous n'ayons pu mesurer que de la diffusion Raman spontanée dans ces cavités, avec un facteur de Purcell de 2.9, l'étude théorique que nous avons effectuée sur les lasers Raman, et qui s'accorde parfaitement avec les résultats expérimentaux, montre qu’il serait possible d'obtenir un laser Raman dans ces cavités avec un seuil en dessous du milliwatt à condition de diminuer ces pertes dues à l'absorption par porteurs libres. Ceci pourrait être accompli en diminuant le temps de vie des porteurs libres, par exemple en les retirant du silicium à l’aide d’une jonction MSM. / In this thesis, we studied third order nonlinear optical effects in photonic crystal cavities. The first of those effects is is the phenomenon of high frequency (GHz) self-pulsing in these cavities, which originates from a modulation of the transmission of the cavity due to the interaction between the free-carrier dispersion and the two-photon absorption. We have observed these self-induced oscillations for the first time in silicon photonic crystal nanocavities, with a frequency of about 3 GHz and a high spectral purity. We have developed a model to analyze the mechanisms that govern the onset of these oscillations, as well as the amplitudes of the fundamental and harmonic frequencies of these oscillations. This self-pulsing phenomenon would allow us to realize realize ultra-compact microwave sources made of silicon. The second phenomenon studied is that of Raman scattering, which is the only way to obtain lasers fully in silicon demonstrated so far. The Raman scattering was measured first in narrow photonic crystals waveguides (W0.63) of length 100 microns, where we could obtain a number of Stokes photons up to 9, showing that the stimulated Raman scattering predominated in these waveguides, although we have not been able to obtain a true Raman laser effect in them. We then measured the Raman scattering in doubly resonant nanocavities specifically designed from these waveguides to optimize the Raman effect, with quality factors up to 235000 for the Stokes resonance. Although we could only measure spontaneous Raman scattering in these cavities, with a Purcell factor of 2.9, the theoretical study that we conducted on the Raman lasers, which agrees perfectly with the experimental results, shows that it would be possible to obtain a Raman laser in these cavities with a threshold below the milliwatt, provided we reduce the losses due to the free-carrier absorption. This could be accomplished by decreasing the free-carrier lifetime, for example by removing the free carriers from the silicon using a MSM junction.

Ces travaux de thèse portent sur les phénomènes d’amplification du signal de diffusion Raman par effet de surface et par effet de pointe. Des réseaux de motifs métalliques de taille nanométrique arrangés spatialement ont été fabriqués par la méthode de transfert Langmuir-Blodgett et par lithographie à faisceau d’électrons. De telles structures de géométries contrôlées déposées à la surface de lamelles de microscope ont été développées afin d’amplifier le signal Raman de molécules adsorbées par effet SERS (Surface Enhanced Raman Spectroscopy). Ces nanostructures triangulaires en or de taille proche de la longueur d’onde ont des bandes de résonance plasmon dans le domaine spectral visible. En utilisant une source de laser appropriée dans ce domaine spectral, les facteurs d’amplification Raman d’une couche mono-moléculaire d’un dérivé azobenzène sont de plusieurs ordres de grandeur, et ce pour les deux techniques de nano-lithographie employées. Afin de compléter ces premiers résultats, des réseaux de fils d’or avec de grands facteurs de forme ont été fabriqués. Ces derniers montrent des résonances plasmons multipolaires et des facteurs d’amplification de l’ordre de 105. Les techniques de microscopie en champ proche ont également été développées afin de localiser précisément l’exaltation Raman et d’accroitre la résolution spatiale de mesures Raman. Des pointes métalliques en or de taille nanométrique ont ainsi permis d’amplifier localement le signal de diffusion de molécules placées à leur proximité par effet TERS (Tip Enhanced Raman Spectroscopy). Les développements logiciels et mécaniques entre un microscope confocal Raman et un microscope à force atomique ont été implémentés afin de contrôler simultanément les deux instruments. Ce montage expérimental a été appliqué à l’étude de nanofils semi-conducteurs de nitrure de gallium permettant de suivre leur signal vibrationnel avec une résolution spatiale inférieure à 200 nm. / This thesis work focuses on Raman scattering enhancements by metallic nanostructures. In the first part of this work, arrays of metallic patterns with nanometer dimensions were fabricated by the Langmuir-Blodgett deposition technique and electron-beam lithography. Such structures made of gold were fabricated onto microscope slides with the goal to enhance the Raman signal through SERS effect (Surface Enhanced Raman Spectroscopy). These patterns formed by an assembly of triangular nanostructures with sizes of hundreds of nanometers, exhibit plasmon resonance bands in the visible spectral region. By using an appropriate excitation laser source with respect to the plasmon frequency, Raman enhancement factors of a monolayer were found to be of several order of magnitude for both Langmuir-Blodgett and electron-beam lithography platforms. To further complement these results, gold wires arrays with large aspect ratio made by electron-beam lithography showed multipolar plasmon resonances with enhancement factors up to 105. In the second part of this thesis, near-field Raman microscopy has been developed with the aim to localize precisely the Raman enhancement and improve spatial resolution of Raman measurements. Atomic force microscopy gold tips have been used to locally enhance scattering signal of molecules in close proximity to the tip opening new opportunities. This approach known as TERS (Tip Enhanced Raman Spectroscopy) is of significant interest to probe nanomaterials, nanostructures or monolayers. Software and mechanical developments have been made between a confocal Raman microscope and an atomic force microscope to control simultaneously both instruments. This experimental setup was used to characterize gallium nitride semi-conductors nanowires with spatial resolution better than 200 nm.