Parmi tous les polymères conducteurs, le polypyrrole est l’un des plus utilisés notamment à cause de ses propriétés telles que la facilité de préparation, la stabilité environnementale et la biocompatibilité qui permettent son utilisation dans de très nombreuses applications. Le polypyrrole peut être préparé par polymérisation chimique ou électrochimique, cette dernière méthode étant la plus appropriée si on souhaite entre autre contrôler l’épaisseur du film de polypyrrole déposé. Les nanostructures de polypyrrole sont généralement synthétisées en présence de gabarits (« soft-template » ou « hard-template »).Le but de cette thèse est orienté suivant deux axes. Il s’agit dans un premier temps de synthétiser des (nano)structures de polymère conducteur par voie électrochimique et sans emploi d’une matrice support. Puis dans un second temps, d’utiliser ces (nano)structures dans des applications de type (bio)capteurs.Le premier chapitre de cette thèse établit une revue de l’état de l’art concernant la synthèse, les propriétés et les applications des polymères conducteurs. Dans le deuxième chapitre de ce manuscrit, nous décrivons le matériel et les différentes techniques de caractérisation utilisées au cours de ce travail. Le troisième chapitre s’articule autour de la synthèse par voie électrochimique de films de polypyrrole suroxydé et de nanostructures de polypyrrole, alors que le quatrième chapitre présente les résultats de l’étude de l’influence de différents paramètres expérimentaux à savoir le potentiel appliqué, la durée de polarisation, le pH de la solution de pyrrole et la concentration en pyrrole et en anions d’acide faible. Dans le cinquième chapitre nous discutons les différents mécanismes de formation de (nano)structures de polypyrrole décrits dans la littérature en nous basant notamment sur les expériences de suivi du pH interfacial au cours de la polymérisation. Nous proposons également un mécanisme en accord avec les résultats obtenus avec des monomères de pyrrole ou d’EDOT. Le sixième et dernier chapitre est consacré aux applications étudiées à savoir les (bio)capteurs de glucose et de pH et la synthèse de polypyrrole sur des électrodes de titane et sur des fibres de carbone. / Polypyrrole is one of the most widely investigated conducting polymer notably due to its high conductivity under its doped oxidized form, its biocompatibility and good stability in air and aqueous media allowing its use for various applications. Polypyrrole can be synthesized either by a chemical oxidation (powder) or electrochemical oxidation (film coating). To control over the location and the thickness of the deposit, the electropolymerization can be considered as the main method. Polypyrrole nanostructures are usually synthesized in the presence of templates (hard-templates or soft-templates).The aim of this PhD thesis is oriented towards two directions. In the first one, we synthesized polypyrrole nanostructures by electropolymerization and without using a template. Then we used these nanostructures as a material for various applications including (bio)chemical sensors.The first chapter of this thesis establishes a review of the state of the art concerning the synthesis, properties and applications of conducting polymers. In the second chapter of this manuscript, we describe the equipment and various characterization techniques used in this work. The third chapter focuses on the electrochemical synthesis of overoxydized polypyrrole and polypyrrole (nano)structures, while the fourth chapter presents the results of the study of the influence of various experimental parameters. In the fifth chapter we discuss the different formation mechanisms of polypyrrole (nano)structures described in the literature based in particular on the experiences of interfacial pH monitoring during the polymerization. We also propose a mechanism in accordance with the results obtained with pyrrole or EDOT monomers. The sixth and final chapter is devoted to the applications studied namely the glucose and pH (bio)sensors and synthesis of polypyrrole on titanium electrodes and carbon nanofibers.

Philosophiae Doctor - PhD / The first report of a functioning photo-electrochemical solar cell in 1991 attracted a lot of interest from scientists and industrial groups. From an industrial point of view these so-called dye-sensitised solar cells (DSCs) offered the promise of moderate efficiency devices at ultra-low costs, owing to simple processing methods and the use of inexpensive materials. From an academic viewpoint, DSCs raised important scientific questions around the fundamental processes governing their operation and how these processes influence the photon-to-electron conversion efficiency of the cell. Major successes have since been achieved in understanding these processes, however the conversion efficiency of the best manufactured DSCs remains around 11%, significantly lower than that of their silicon photovoltaic counterparts. In traditional DSCs, charge generation is achieved by ultrafast electron injection from a photo-excited ruthenium-based dye molecule into the conduction band of a film of TiO₂ nanoparticles, subsequent dye regeneration by an I⁻ /I⁻₃ containing redox electrolyte and finally hole transportation to a platinum-coated counter electrode. The low DSC efficiencies are attributed to scattering of electrons at the interface between two TiO₂ nanoparticles leading to recombination with holes present in the redox electrolyte. Recent studies have shown that the application of films of highly ordered TiO₂ nanotubes instead of nanoparticles has the potential to improve the overall conversion efficiency of the cell. This is ascribed to the one-dimensional nature of nanotubes, which provides a linear transportation route for electrons generated during operation of the DSC. As a result the recombination probability of the electrons with nearby holes in the device is decreased. This work investigated the synthesis of Al₂O₃-coated TiO₂ nanotubes via the anodisation technique for application in DSCs. TiO₂ nanotube arrays with an average length of 15 μm, diameter of 50 nm and wall thickness of 15 nm were synthesised via anodisation using an organic neutral electrolyte consisting of 2 M H₂O + 0.15 M NH₄F + ethylene glycol (EG) at an applied voltage of 60 V for 6 hours. In addition, scanning electron microscope (SEM) micrographs showed that anodisation at these conditions yields nanotubes with smooth walls and hexagonally shaped, closed bottoms. X-ray diffraction (XRD) patterns revealed that the as-anodised nanotubes were amorphous and as such were annealed at 450 °C for 2 hours in air at atmospheric pressure, which yielded crystalline anatase TiO₂ nanotubes. Highresolution transmission electron microscope (TEM) images revealed that the nanotube walls comprised of individual nano-sized TiO₂ crystallites. Photoluminescence (PL) spectroscopy showed that the optical properties, especially the bandgap of the TiO₂ nanotubes are dependent on the crystallinity, which in turn was dependent on the structural characteristics, such as the wall thickness, diameter and length. The PL measurements were supplemented by Raman spectra, which revealed an increased in the quantum confinement of the optical phonon modes of the nanotubes synthesised at low anodisation voltages, consequently yielding a larger bandgap The annealed nanotubes were then coated with a thin layer of alumina (Al₂O₃) using a simple sol-gel dip coating method, effectively used to coat films of nanoparticles. Atomic force microscopy (AFM) showed that the average nanotube diameter increased post sol-gel deposition, which suggests that the nanotubes are coated with a layer of Al₂O₃. This was confirmed with HR-TEM, in conjunction with selected area electron diffraction (SAED) and XRD analyses, which showed the coating of the nanotube walls with a thin layer of amorphous Al₂O₃ with a thickness between 4 and 7 nm. Ultraviolet-visible (UVvis) absorbance spectra showed that the dye-adsorption ability of the nanotubes are enhanced by the Al₂O₃ coating and hence is a viable material for solar cell application. Upon application in the DSC, it was found by means of photo-current density – voltage (I – V) measurements that a DSC fabricated with a 15 μm thick layer of bare TiO₂ nanotubes has a photon-to-light conversion efficiency of 4.56%, which increased to 4.88% after coating the nanotubes with a layer of alumina. However, these devices had poorer conversion efficiencies than bare and Al₂O₃-coated TiO₂ nanoparticle based DSCs, which boasted with efficiencies of 6.54 and 7.26%, respectively. The low efficiencies of the TiO₂ nanotube based DSCs are ascribed to the low surface area of the layer of nanotubes, which yielded low photocurrent densities. Electrochemical impedance spectroscopy (EIS) showed that the electron lifetime in the alumina coated nanotubes are almost 20 times greater than in a bare layer of nanoparticles. In addition, it was also found that the charge transfer resistance at the interface of the TiO₂/dye/electrolyte is the lowest for an Al₂O₃-coated TiO₂ layer.

Les nanostructures de polymères suscitent un grand intérêt grâce à leurs propriétés uniques comme le facteur de forme important. Cette propriété est essentielle pour l’utilisation dans des domaines où les interactions de surface sont mises en jeu. Un exemple d’une telle application est la détection de gaz. La polyaniline (PANi) s’est montrée prometteuse pour l’utilisation dans les capteurs d’ammoniac. La synthèse conventionnelle (chimique ou électrochimique) de nanofibres de PANi a été largement décrite dans la littérature mais cette voie possède de nombreux inconvénients. Parmi eux, figurent plusieurs étapes de synthèse (la synthèse, la purification, le dépôt sur le substrat) et l’utilisation de produits chimiques (oxydants, acides) peu respectueux de l’environnement. La polymérisation assistée par plasma froid (PECVD) permet de s’en affranchir car seul le monomère est utilisé qui se polymérise directement sur le substrat. Ainsi, ce travail de thèse a pour objectif d’élaborer des nanostructures de polyaniline plasma tout en conservant au mieux l’unité monomère dans le polymère. Le paramètre essentiel qui détermine le processus de nanostructuration est la puissance de décharge. A forte puissance, des films fortement structurés sont obtenus mais les molécules de monomère sont totalement fragmentées. En revanche, une faible puissance conduit à des films avec conservation de l’entité monomère mais sans structure morphologique particulière. Nous avons développé une méthode permettant de combiner les avantages de chaque régime : ce procédé dit « bottom-up » est réalisé en variant la puissance au cours du dépôt selon deux ou trois étapes. Les paramètres qui influencent les structures chimique et morphologique sont déterminés et les procédés à deux et trois étapes sont comparés. Par ailleurs, la synthèse « top-down » de nanostructures par gravure de la couche mince de PANi est également étudiée en fonction des paramètres du plasma (puissance et temps de décharge, débit du gaz de gravure et polarisation du substrat). Finalement, nous avons synthétisé, en phase plasma, des nanocomposites associant les nanostructures de PANi et des particules métalliques de Pd déposées par pulvérisation. La structure chimique des films de PANi est caractérisée par les spectroscopies UV-Vis, IR-TF et XPS. Pour mettre en évidence la nanostructuration des couches minces, les microscopies MEB et AFM sont utilisées. Cette dernière permet également de calculer la valeur de rugosité ainsi que la surface spécifique de la PANi. La spectroscopie EDX est utilisée pour mettre en évidence et pour quantifier le palladium dans les films synthétisés. Les couches obtenues sont finalement caractérisées sous gaz par mesures de variation d’absorbance afin de déterminer leur sensibilité et leur temps de réponse à l’ammoniac. / Polymer nanostructures are of great interest due to their unique properties such as high shape factor. This property is essential for applications where surface interactions are involved. One example of such an application is the gas detection. Polyaniline (PANi) has been shown as a promising material for ammonia detection. Conventional synthesis (chemical orelectrochemical) of PANi nanofibers has been widely described in the literature but this way has many drawbacks. They include several steps (synthesis, purification, deposition on the substrate) and the use of chemicals (oxidants, acids) which are not environmentally friendly. The polymerization assisted by cold plasma (PECVD) allows overcoming it, as only themonomer is used and is directly polymerized on the substrate. This thesis work aims to develop plasma polyanilinenanostructures while retaining the monomer unit in the polymer. The key parameter that determines thenanostructuring process is the discharge power. At high power, highly structured films are obtained but the monomer molecules are totally fragmented. On the contrary, low power allows conservation of the monomer unit but no surface structuring is observed. We developed a method which combines the advantages of each regime. This "bottom-up" process consists to vary the input power during deposition in two or three stages. Parameters influencing the chemical and morphological structures are determined and the two and three steps methods are compared. Furthermore, the "top-down" synthesis of nanostructures by etching the PANi layer is also studied according to the plasma parameters (power and discharge time, etching gas flow rate and substrate bias). Finally, in plasma phase, we synthesized nanocomposite by combining PANi nanostructures and sputtered Pd particles. The chemical structure of the PANi films is characterized by UV-Vis spectroscopy, FT-IR and XPS. In order to highlight the nanostructuring of thin films, SEM and AFM microscopy areused. The latter one allows also the calculation of the roughness and specific surface of the PANi. EDX spectroscopyis used to bring out the presence of palladium and to quantify it. Finally, the obtained layers are characterized under gas byabsorbance variation measurements in order to determine their sensitivity and response time to ammonia.

This thesis explores a novel methodology to fabricate three dimensional (3D) metal-dielectric structures, and two dimensional (2D) graphite layers for emerging metamaterials and graphene applications. The investigations we report here go beyond the limitations of conventional fabrication techniques that require multiple post-processing steps and/or are restricted to fabrication in two dimensions. Our method combines photoreduction mechanism with an ultrafast laser direct writing process in innovative ways. This study aims to open the doors to new ways of manufacturing nanoelectronic and nanophotonic devices. With an introductory analysis on how the various laser and chemical components affect the fabrication mechanism, this dissertation is divided into three sections. / Engineering and Applied Sciences

Multifunctional nanocomposites are promising for a variety of applications ranging from microwave devices to biomedicine. High demand exists for magnetically tunable nanocomposite materials. My thesis focuses on synthesis and characterization of novel nanomaterials such as polymer nanocomposites (PNCs) and multi-walled carbon nanotubes (MWCNTs) with magnetic nanoparticle (NP) fillers. Magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) NPs with controlled shape, size, and crystallinity were successfully synthesized and used as PNC fillers in a commercial polymer provided by the Rogers Corporation and poly(vinylidene fluoride). Magnetic and microwave experiments were conducted under frequencies of 1-6 GHz in the presence of transverse external magnetic fields of up to 4.5 kOe. Experiments confirm strong magnetic field dependence across all samples. When incorporated in to a cavity resonator device, tangent losses were reduced, quality factor increased by 5.6 times, and tunability of the resonance frequency was demonstrated, regardless of NP-loading. Work on PNC materials revealed the importance of NP interactions in confined spaces and motivated the study of confinement effects of magnetic NPs in more controlled environments, such as MWCNTs with varying diameters. MWCNTs were synthesized with diameters of 60 nm, 100 nm, 250 nm, and 450 nm to contain magnetic NP fillers (~10 nm) consisting of ferrites of the form MFe2O4, where M = Co2+, Ni2+, or Fe2+. All confined samples exhibit superparamagnetic-like behavior with stronger magnetic response with respect to increasing MWCNT diameter up to 250 nm due to the enhancement of interparticle interactions. This thesis provides the first systematic study of this class of nanocomposites, which paves the way to inclusion of novel nanostructured materials in real-world applications.

Natural gas is stored as compressed natural gas (CNG) in heavy steel cylinders under pressures of 200-250 atm. However, such a method of storage has certain disadvantages which include multistage compression costs, limited driving range and safety aspects. Hence, alternative methods of storage such as adsorbed natural gas (ANG) which involve adsorbing natural gas at moderate pressures and room temperatures in a suitable nanoporous material are currently being explored. In this thesis, we have isolated model carbon nanostructures and defect geometries most likely to be found in these materials and investigated their specific interactions with methane. The thesis is concerned with ab-initio density functional theory calculations on these various model carbon nanostructures in order to identify the potential candidates that enhance methane adsorption. The adsorption energies of methane on graphite and graphene sheets were similar, with a value of 12.3 kJ/mol for graphene. The Stone-Wales defect in graphene was found to increase the methane adsorption energy to 37.2 kJ/mol, and small surface undulations on the graphene sheet resulted in a smaller increase (16 kJ/mol) in the adsorption energy relative to graphene. The presence of an interstitial carbon was found to significantly reduce the adsorption energy to 5.2 kJ/mol. The enhanced adsorption energy in the case of the Stone-Wales defect was attributed to the significant charge redistribution in the vicinity of the defect. A variety of functional groups such as carboxylic acid (COOH), carbonyl (CO), phenol (OH), pyran (-O-), phenone (=O), peroxide (OOH) and amine (NH2) groups have been observed on carbon surfaces. Extensive density functional calculations of methane adsorbed on various chemically functionalized graphene nanoribbons were carried out to evaluate their methane adsorption energies. A significant finding in this study, is the increased adsorption energies (relative to graphene) that occur for the functional groups containing the OH moiety. The adsorption energies for edge functionalized graphene nanoribbons are 27.6 and 69.7 kJ/mol for COOH and OOH functionalization. Additional computations reveal a strong correlation between the induced dipole moment on methane and the strength of the adsorption energies obtained for the extended nanoribbons. Adsorption isotherms for methane were obtained using grand canonical Monte Carlo simulations for slit-like graphitic pores with and without functional groups. For both OH and COOH functionalized graphite, we observe more than a 40 % increase in the volumetric loading over bare graphite for the highest weight % of the functional group and smallest pore width considered. The maximum volumetric loading decreases with a decrease in the wt% of the functional groups and with an increase in the pore width.

In situ Raman spectroscopy was used to explore etching of carbon nanotubes as well as their growth from C60. The thesis is in three parts: (1) C60 seed particles were partially oxidized in air and were used to grow carbon nanotubes and other nanocarbon structures. Seed oxidization was characterized by monitoring the evolution of the Raman Ag(2) peak and the D band, and oxidation temperature was found to be critical to nanotube growth. (2) To further explore oxidation, carbon nanotubes were thermally oxidized in air at different temperatures, while the evolution of different Raman bands was tracked. Etching dynamics and band intensity evolution were tracked in situ. Notably, metallic species were found to etch much more rapidly than semiconducting species of similar diameter. (3) To confirm and expand on this, a novel, simultaneous two-laser Raman spectroscopy setup was used to track the thermal oxidation of carbon nanotubes in O2 and CO2 gases at different temperatures. Metallic species were resonant with one laser line, while semiconducting species were resonant with the other, so changes to sample metallicity could be tracked unambiguously in two separate spectra. Again, metals were found to etch more rapidly. In situ Raman spectroscopy can track the evolution of nanotubes in real time and provide insight into processing. In general, detailed process monitoring like this can help in the development of selective synthesis and processing.

Cette thèse traite de comportements non-linéaires dans deux types de systèmes bidimensionnels différents: les hétérostructures semiconductrices ainsi qu'un matériau monocouche, le graphène. Elle comporte deux axes principaux: l'étude de la quantification de Wannier-Stark dans les super-réseaux de puits quantiques biaisés électriquement, et la modélisation d'effets nouveaux pour la génération de rayonnement électromagnétique dans le domaine Terahertz. Dans les super-réseaux de puits quantiques soumis à une tension externe, le champ électrique induit un confinement bidimensionnel des porteurs de charge nommé quantification de Wannier-Stark. On modélise deux conséquences originales de cette quantification: d'une part, les fortes non-linéarités de photocourant dans un super-réseau placé entre deux barrières tunnel épaisses, et d'autre part, la possibilité de contrôler électriquement le couplage lumière-matière et le gain dans la gamme Terahertz dans un super-réseau biaisé couplé à une microcavité planaire. Dans un second temps, on étudie quantitativement deux effets non-linéaires nouveaux pour la génération Terahertz. Le premier est l'exaltation de l'émission Terahertz dans un système polaritonique en régime de laser à polaritons. On modélise précisément cet effet et on propose un nouveau dispositif utilisant une microcavité double et permettant de réduire très significativement les pertes par diffusion. Le second effet étudié est le transfert d'impulsion photonique dans le graphène sous excitation impulsionnelle. On construit un modèle microscopique prédictif de ce phénomène qui permet de déterminer les paramètres importants pour l'optimisation de l'impulsion Terahertz générée. Ce travail théorique a été mené en étroite collaboration avec plusieurs équipes expérimentales. / This thesis treats of nonlinear behaviors in two different types of bidimensional systems: semiconductor heterostructures as well as a monolayer material, graphene. It consists into two main parts: the study Wannier-Stark quantification in electrically biased quantum well superlattices, and the modelling of new effects for electromagnetic wave generation in the Terahertz range. In quantum well superlattices under an external voltage, the electric field induces bidimensional confinement of the charge carriers, this effect is known as Wannier-Stark quantification. We examine two interesting consequences of this confinement: the strong photocurrent nonlinearities induced when the superlattice is placed between thick tunnel barriers, and the possibility to control light-matter coupling as well as Terahertz gain in superlattices coupled to a semiconductor microcavity. In a second part of this work, we study quantitatively two new nonlinear effects for Terahertz generation. The first one is Terahertz emission exaltation in a polaritonic system reaching the polariton lasing regime. We model precisely this effect and suggest a new scheme using a double microcavity and providing very significant reduction of the diffusion losses. The second effect is photon drag in graphene under pulsed excitation. We build a microscopic and predictive model for this phenomenon which provides a comprehensive insight on the relevant parameters for the optimisation of the Terahertz generation. This theoretical work was done in tight collaboration with several experimental groups.

Opto-electronic semiconductor technology continues to grow at an accelerated pace, as the industry seeks to perfect devices such as light emitting diodes for purposes of optical processing and communication. A strive for greater efficiency with shrinking device dimensions, continually pushes the technology from both a design and materials aspect. Nanosystems such a quantum dots, also face new material engineering challenges as they enter the realm of quantum mechanics, with each system and material having markedly different electronic properties. Traditionally, the semiconductor industry has focused on materials such Group II-VI and III-V compounds as the basis material for future opto-electronic needs. Unfortunately, these material systems can be expensive and have difficulties integrating into current Si-based technology. The industry is reluctant to leave silicon due in part to silicon's high quality oxide, and the enormous amount of research invested into silicon based circuit fabrication. Although recently materials such as GaN are starting to dominate the electro-optical industry since a Si-based substitute has not been found. The purpose of the dissertation was to examine several promising systems that could be easily integrated into current Si-based technology and also be produced using simple inexpensive fabrication techniques such ion implantation. The development of optically active nano-sized precipitates in silica to form the active layer of an opto-electronic device was achieved with ion implantation and thermal annealing. Three material systems were investigated. These systems consisted of carbon, silicon and metal silicide based nanocrystals. The physical morphology and electronic properties were monitored using a variety of material characterization techniques. Rutherford backscattering/channeling were used to monitor elemental concentrations, photoluminescence was used to monitor the opto-electronic properties and transmission electron microscopy was used to study the intricate morphology of individual precipitates. The electronic properties and the morphology were studied as a function of implant dose, anneal times and anneal temperatures.

In this work, I studied the hybrid system based on self-assembled guanosine crystal (SAGC) conjugated to wide-bandgap semiconductor gallium nitride (GaN). Guanosine is one of the four bases of DNA and has the lowest oxidation energy, which favors carrier transport. It also has large dipole moment. Guanosine molecules self-assemble to ribbon-like structure in confined space. GaN surface can have positive or negative polarity depending on whether the surface is Ga- or N-terminated. I studied SAGC in confined space between two electrodes. The current-voltage characteristics can be explained very well with the theory of metal-semiconductor-metal (MSM) structure. I-V curves also show strong rectification effect, which can be explained by the intrinsic polarization along the axis of ribbon-like structure of SAGC. GaN substrate property influences the properties of SAGC. So SAGC has semiconductor properties within the confined space up to 458nm. When the gap distance gets up to 484nm, the structure with guanosine shows resistance characteristics. The photocurrent measurements show that the bandgap of SAGC is about 3.3-3.4eV and affected by substrate properties. The MSM structure based on SAGC can be used as photodetector in UV region. Then I show that the periodic structure based on GaN and SAGC can have photonic bandgaps. The bandgap size and the band edges can be tuned by tuning lattice parameters. Light propagation and emission can be tuned by photonic crystals. So the hybrid photonic crystal can be potentially used to detect guanosine molecules. If guanosine molecules are used as functional linker to other biomolecules which usually absorb or emit light in blue to UV region, the hybrid photonic crystal can also be used to tune the coupling of light source to guanosine molecules, then to other biomolecules.