Iron filled carbon nanotubes (FeCNT) can be described as carbon nanotubes which contain an iron nanowire of several micrometers length and a diameter of approximately 10-100 nm. The carbon shells protect the iron core from oxidation and mechanical damage thus enabling a wide range of applications that require a long-term stability. The magnetic properties of the enclosed nanowire are in part determined by its small size and elongated shape. Magnetic force microscopy (MFM) measurements show that the iron wire exhibits a single domain behavior. Due to the large shape anisotropy it is magnetized along the long wire axis in the remanent state. Two magnetic monopoles of opposing polarity are located at the wire extremities. Depending on the structure and geometry of the individual nanowire, switching fields in the range of 100-400 mT can be found when the external field is applied along the FeCNT’s easy axis. Cantilever magnetometry shows that the switching can be attributed to a thermally assisted magnetization reversal mechanism with the nucleation and propagation of a domain wall. The defined magnetic properties of individual FeCNT combined with their mechanical strength make them ideal candidates for an application as high resolution high stability MFM probes. The fabrication of such probes can be achieved with the help of a micromanipulation setup in a scanning electron microscope. FeCNT MFM probes achieve a sub 25 nm lateral magnetic resolution. MFM measurements with FeCNT MFM probes in external fields show that the magnetization of these probes is exceptionally stable compared to conventional coated MFM probes. This greatly simplifies the data evaluation of such applied field MFM measurements. The emphasis of this work was put on the calibration of FeCNT probes to enable straightforward quantitative MFM measurements. The defined shape of the magnetically active iron nanowire allows an application of a point monopole description. Microscale parallel current carrying lines that produce a defined magnetic field are used as calibration structures to determine the effective magnetic moment of different MFM probes. The line geometry is varied in order to produce multiple magnetic field decay lengths and investigate the influence on the effective probe moment. The results show that while the effective magnetic monopole moment of a conventional MFM probe increases with an increasing sample stray field decay length, the effective moment of a FeCNT MFM probe remains constant. This enables a MFM probe calibration that stays valid for a large variety of magnetic samples. Furthermore, the fitted monopole moment of a FeCNT probe (in the order of 10E-9 Am) is consistent with the moment calculated from the nanowire geometry and the saturation magnetization of iron.

L'étape clé pour intégrer des nanotubes de carbone à une échelle industrielle demeure un meilleur contrôle de leur croissance et notamment le contrôle sélectif de leurs chiralités en lien avec leurs propriétés électroniques. Ce travail a pour but de s'intéresser à la synthèse in-situ et à la caractérisation de nanotubes de carbone individuels par émission de champ pour mieux comprendre les mécanismes de nucléation et de croissance qui conditionnent sa chiralité. Nous avons développé un microscope à émission de champ couplé à un réacteur CVD (Chemical Vapor Deposition) pour observer directement la croissance catalytique de nanotubes de carbone individuels sur des pointes émettrices. Nous avons ainsi découvert que les nanotubes tournent souvent axialement pendant leur croissance, soutenant ainsi un modèle de « dislocation de vis ». L’analyse détaillée des résultats obtenus montre que nous observons directement la croissance atome par atome d'un nanotube monofeuillet individuel avec ajout d’un dimère de carbone à la fois à sa base. Parallèlement, des échantillons ont été caractérisés en détail sous émission de champ. Nous avons établi un protocole de collage de nanotubes individuels à l’apex d’une pointe métallique sous microscopies optique et électronique à balayage à l’aide d’un nanomanipulateur. Leur dépendance en température à très bas courant a été mise en évidence avec un compteur d’électrons afin d'identifier les différents domaines d'émission électronique. L'analyse des distributions énergétiques a fait apparaître un phénomène de chauffage induit qui peut mener à des températures de l’ordre de 2000 K à l’extrémité du nanotube lorsqu’il est soumis à un fort champ. / The key issue for realizing the potential of carbon nanotubes has always been, and still remains, a better control of their growth and in particular the selective control of their chirality related to their electronic properties. This work aims to address the in-situ synthesis and characterization of individual carbon nanotubes by field emission to better understand the mechanisms of nucleation and growth that determine their chirality. We have developed a field emission microscope coupled to a CVD reactor (Chemical Vapor Deposition) to observe directly the catalytic growth of individual carbon nanotubes on metallic tips. We found that nanotubes often turn axially during growth, thereby supporting a model of "screw dislocation". Detailed analysis of results shows that we directly observe the atom by atom growth of one individual single wall nanotube with addition of a carbon dimer to the base. In parallel, certain samples were characterized by in-depth field emission studies. For this we established a protocol of bonding individual nanotubes at the apexes of metal tips under optical and scanning electron microscopies using a nanomanipulator. Their temperature dependence at very low current has been demonstrated with an electron counter to identify the various fields of electron emission. Analysis of energy distributions revealed an induced heating phenomenon that can lead to temperatures of about 2000 K at the end of the nanotube subjected to strong fields that create high current emission.

Este estudo teve como objetivo principal desenvolver uma técnica para síntese de um nanocompósito de Y-TZP/MWCNT-COOH (Zircônia estabilizada por 3 mol% de ítria reforçada por nanotubos de carbono funcionalizado em -COOH) com propriedades mecânicas e ópticas que permitam a sua futura utilização como infraestrutura de próteses fixas dentárias e pilares protéticos para implantes. Assim, foram avaliados a microestrutura, resistência à flexão, tenacidade à fratura, limite de fadiga e propriedades ópticas do nanocompósito e comparada àquelas medidas para Y-TZP convencional (controle). O material Y-TZP/MWCNT-COOH foi desenvolvido pelo processo de co-precipitação de hidróxidos mistos associado ao tratamento hidrotérmico/solvotérmico e prensagem uniaxial em formato de blocos para sistemas CAD/CAM. O pó de MWCNT-COOH foi caracterizado por meio de MEV-FEG, TEM, TGA, DRX e FRX previamente a sua utilização para desenvolvimento do nanocompósito. Espécimes foram obtidos a partir do material Y-TZP/MWCNT-COOH para caracterização por meio de DRX, MEV-FEG e TEM, e comparação de suas propriedades estruturais (densidade e contração), ópticas, resistência à flexão, tenacidade à fratura e limite de fadiga com a Y-TZP convencional. O MWCNT-COOH apresentou-se em feixes de nanotubos de carbono recobertos por sílica tendo comprimento médio de 5,10 ± 1,34 ?m, com 90% dos comprimentos medidos (D90) estando abaixo de 6,9 ?m. Foi verificado a não possibilidade da utilização de líquidos orgânicos em nenhum passo da fabricação dos compósito Y-TZP/MWCNT-COOH por levar ao escurecimento do compósito, inviabilizando sua futura aplicação clínica. O tratamento hidrotérmico sem uso de líquidos orgânicos mostrou-se eficaz em proporcionar o revestimento do nanotubo de carbono por partículas de óxido de zircônio e ítrio. Entretanto, ocasionou a formação de aglomerados e partículas de Y-TZP com tamanho maiores que 5 ?m. Uma densidade relativa de 97,4% foi alcançada para o compósito experimental de Y-TZP contendo MWCNT-COOH, tendo uma razão de contraste de 0.9929 ± 0.0012 e um valor de diferença de cor da Y-TZP convencional de 6,1 ± 3,1 ( ?E). As propriedades mecânicas da Y-TZP/MWCNT-COOH, dureza Vickers (10,14 ± 1,27 GPa; p=0,25) e tenacidade à fratura (4,98 ± 0,30 MPa.m1/2; p=0,39), não apresentaram diferença significativa da Y-TZP convencional (dureza: 8,87 ± 0,89; tenacidade à fratura: 4,98 ± 0,30 MPa.m1/2). Entretanto, para a resistência à flexão (p=0,003) e limite de fadiga cíclica (LFC) foram obtidos valores inferiores para o material experimental Y-TZP/MWCNT-COOH (resistência à flexão: 299,4 ± 30,5 MPa; LFC: 179,4 ± 22,5 MPa) quando comparado à Y-TZP controle (resistência à flexão: 623,7 ± 108,8 MPa; LFC: 439,0 ± 56,4 MPa). Com base nos resultados apresentados, é possível concluir que a síntese de um nanocompósito de Y-TZP/MWCNT-COOH com propriedades ópticas adequadas para aplicação na odontologia restauradora foi possível por meio dos métodos descritos, entretanto algumas adequações nos métodos de síntese e processamento para criação do nanocompósito devem ser realizadas para se evitar a acentuada diminuição de importantes propriedades mecânicas do material. / This study aim was to develop a technique for synthetize nanocomposite of Y-TZP/MWCNT-COOH (3 mol% Yttria-Stabilized Tetragonal Zirconia reinforced with COOH functionalized carbon nanotubes) with mechanical and optical properties that allow their future use as fixed dental prosthesis infrastructure and implant abutments. Thus, the following properties of the nanocomposite were investigated and compared to those measured for conventional Y-TZP (control): microstructure, flexural strength, fracture toughness, fatigue limit and optical properties. Y-TZP/MWCNT-COOH material was developed by the co-precipitation of mixed hydroxides associated with the hydrothermal/solvothermal treatment and uniaxial pressing to form blocks for CAD/CAM systems. The MWCNT-COOH powder was characterized by SEM-FEG, TEM, TGA, XRD and XRF prior to its use for the development of nanocomposite. Specimens were obtained from the Y-TZP/MWCNT-COOH material and characterized by XRD, SEM-FEG and TEM. After characterization, the material had their structural properties (density and contraction), optical, flexural strength, fracture toughness and fatigue limit compared to a conventional Y-TZP. The MWCNT-COOH material was observed to be a bundle formation of carbon nanotube covered with silica with an average length of 5.10 ± 1.34 ?m, with 90% of the measured lengths (D90) being below 6.9 ?m. It has been found to be not possible to use organic liquids on any step of the Y-TZP/MWCNT-COOH manufacturing process due to darkening of the composite, making it unfeasible to future clinical application. The hydrothermal treatment without the use of organic liquids was effective in providing the carbon nanotube coating by zirconium and yttrium oxide particles. However, this treatment led to the formation of agglomerates and particles of Y-TZP with larger than 5 ?m. A relative density of 97.4% was achieved for the Y-TZP/MWCNT-COOH composite, having a contrast ratio of 0.9929 ± 0.0012, and a color difference value from the conventional Y-TZP of 6.1 ± 3.1 (?E). The mechanical properties of Y-TZP/MWCNT-COOH, Vickers hardness (10.14 ± 1.27 GPa; p = 0.25) and fracture toughness (4.98 ± 0.30 MPa.m1/2; p = 0.39), showed no significant difference from the conventional Y-TZP (hardness: 8.87 ± 0.89; fracture toughness: 4.98 ± 0.30 MPa.m1/2). However, flexural strength (p = 0.003) and cyclic fatigue limit (CFL) showed lower values for the experimental material Y-TZP/MWCNT-COOH (flexural strength: 299.4 ± 30.5 MPa; CFL: 179.4 ± 22.5 MPa) compared to Y-TZP control (flexural strength: 623.7 ± 108.8 MPa; CFL: 439.0 ± 56.4 MPa). Based on the results presented, it could be conclude that the synthesis of a nanocomposite of Y-TZP/MWCNT-COOH with optical properties suitable for application in restorative dentistry was made possible by the described methods, however some adjustments in synthesis and processing methods for the nanocomposite creation should be taken; to avoid the sharp decrease of important mechanical properties of the material.

Le nanotube de carbone double parois représente le cas idéal pour étudier la nature de l'interaction entre parois des tubes multiparois. En partant d'échantillons dispersés de DWNTs synthétisés par CVD, nous avons pu, grâce à la microscopie électronique en transmission haute résolution (METHR), établir une procédure robuste de détermination structurale des configurations. Il apparaît alors que certaines configurations structurales sont privilégiées alors que d'autres sont interdites, mettant en évidence les effets du couplage interparoi. À partir de simulations Monte Carlo réalisées sur des DWNTs de configurations interdites, nous avons montré que le tube interne modifie sa structure pour atteindre une stabilité énergétique, ce que nous avons pu rapprocher d'observations expérimentales. Pour étudier les propriétés électroniques des DWNTs observés expérimentalement, nous avons corrélé les techniques de METHR et d'absorption optique pour analyser des populations différenciées de tubes en nombre de parois, diamètre et nature électronique, grâce à la technique DGU (Ultracentrifugation de Gradient de Densité). À l'issue de trois tris successifs, nous avons pu isoler une population de tubes double parois pure à 95% et dont les tubes extérieurs sont de nature semi-conducteur à 90\%. / Double-walled carbon nanotube represents the ideal case to investigate the nature of the interaction between walls of multiwall tubes. Starting with scattered samples of DWNTs synthesized by CVD, we have established a robust procedure for structure determination of configurations based on high resolution electron microscopy transmission (HRTEM). After achieving a statistical study, it appears that some structural configurations have been favored while others are completely forbidden, highlighting the effects of inter-wall coupling. To go beyond, we have performed Monte Carlo simulations at atomic scale on DWNTs with forbidden configurations. As a result, we have shown that the inner tube changes its structure to achieve energy stability, in good agreement with experimental observations. To study the electronic properties of DWNTs observed experimentally, we correlated HRTEM and optical absorption techniques for analyzing differentiated tubes populations by number of walls, diameter and electronic nature, thanks to the technical DGU (Density Gradient Ultracentrifugation ). After three successive sorting, a pure population of double-walled tubes to 95% and of which 90% of the outer tubes are semiconductor has been isolated.

L’amortisseur thermique étudié dans le cadre de cette thèse a pour objectif de limiter les pics de température des composants électroniques fonctionnant en régime transitoire au moyen d’une structure composite consistant en un réseau de nanotubes de carbone (NTC) rempli de matériau à changement de phase (MCP) solide-liquide, le tout étant contenu dans un boîtier en silicium (Si). Ce système passif vise à augmenter l’inertie thermique volumique du composant grâce à la chaleur latente du MCP tout en maintenant une bonne conductance thermique grâce aux NTC. Un dispositif expérimental polyvalent a été développé spécifiquement pour caractériser les différentes générations d’échantillons fabriqués par les partenaires du projet THERMA3D. L’excitation thermique de l’échantillon est réalisée au moyen d’un laser en face amont et la réponse thermique est mesurée par caméra infrarouge simultanément sur les faces amont et aval. L’application d’une peinture sélectionnée sur l’échantillon permet d’accéder à sa température après un étalonnage dédié. Des méthodes d’estimation de paramètres ont été développées pour quantifier les deux caractéristiques essentielles de l’amortisseur thermique que sont sa capacité de stockage thermique et sa résistance thermique. Les sensibilités de la résistance thermique aux caractéristiques de la connexion Si/NTC et à la longueur des NTC ont été étudiées et les résistances thermiques d’interface Si/NTC ont été identifiées comme dominantes au sein du système. Des essais de cyclage thermique ont permis d’évaluer la fiabilité de l’ensemble de manière accélérée. Le comportement du MCP et la qualité du matériau de scellement ont été analysés par voie optique. Par ailleurs, la plus élevée des deux résistances thermiques d’interface Si/NTC a été localisée grâce à la visualisation infrarouge du réseau de NTC à travers le silicium semi-transparent. Enfin, une méthode de contrôle non destructif de la qualité de l’interface Si/NTC a été développée pour les amortisseurs thermiques de dernière génération. / The purpose of the studied thermal damper is to smooth the temperature peaks of transient electronic components via a composite structure consisting of an array of carbon nanotubes (CNT) filled with solid-liquid phase change material (PCM), the whole being embedded in a silicon (Si) casing. This passive system is intended to increase the thermal inertia per unit of volume of the electronic component thanks to the latent heat of the PCM while maintaining a high thermal conductance thanks to the CNT. A versatile test bench was specifically developed in order to characterize the different generations of samples fabricated by the partners of the THERMA3D project. The thermal excitation of the front side of the sample is generated by a laser and the thermal response is measured simultaneously on the front and back sides by an infrared camera. A selected paint can be deposited on the sample in order to access its temperature by means of a dedicated calibration. Parameter estimation methods were developed in order to quantify both main characteristics of the thermal damper: its heat storage capacity and its thermal resistance. The sensitivities of the thermal resistance to the features of the Si/CNT connection and to the length of the CNT were studied and it was found out that the interfacial thermal resistances Si/CNT are dominant in the system. Thermal cycling tests enabled to assess the reliability of the thermal damper in an accelerated manner. The behavior of the PCM and the quality of the sealing material were optically analyzed. Besides, the infrared visualization of the CNT array through the semi-transparent silicon enabled to identify the highest of both Si/CNT interfacial thermal resistances. Finally, a non-destructive testing method for the evaluation of the quality of Si/CNT interfaces was developed for the latest generation of thermal dampers.

Les circuits électroniques mesurés à des températures cryogéniques permettent d'étudier le comportement quantique des électrons. En particulier, les circuits de boites quantiques sont des systèmes accordables modèles pour l'étude des électrons fortement corrélés, symbolisée par l'effet Kondo. Dans cette thèse, des circuits de boîtes quantiques à base de nanotube de carbone sont intégrés à des cavités micro-onde coplanaires, avec lesquelles l'électrodynamique quantique en cavité (cQED) a atteint un degré de contrôle remarquable de l'interaction lumière-matière. Les photons de la cavité micro-onde sont ici utilisés pour sonder la dynamique de charge dans le circuit de boîtes quantiques. Plus précisément, la cavité micro-onde de grande finesse nous a permis de mesurer la compressibilité du gas d'électrons dans une boîte avec une sensibilité sans précédent. Des mesures simultanées de transport électronique et de la compressibilité montrent que la résonance Kondo observées dans la conductance est transparente aux photons micro-ondes. Cela révèle le gel de la dynamique de charge dans la boîte quantique pour ce mécanisme particulier de transport d'électrons et illustre que la résonance Kondo à N-corps dans la conductance est associée aux corrélations issues des fluctuations de spin d'une charge gelée. Nous étudions aussi dans cette thèse la possible émergence d'une nouvelle quasi-particule, appelée état lié de Majorana, et qui serait sa propre anti-particule. Dans ce but, une grille ferromagnétique a été placée sous le nanotube pour créer un couplage spin-orbit artificiel. L'observation d'états d'Andreev dans un tel dispositif est un premier pas prometteur vers la détection avec une architecture cQED d'états liés de Majorana dans les nanotubes de carbone. / On-chip electronic circuits at cryogenic temperature are instrumental to studying the quantum behavior of electrons. In particular, quantum dot circuits represent tunable model systems for the study of strong electronic correlations, epitomized by the Kondo effect. In this thesis, carbon nanotube based-quantum dot circuits are embedded in coplanar microwave cavities, with which circuit quantum electrodynamics (cQED) has reached a high degree of control of the light-matter interaction. Here, microwave cavity photons are used to probe the charge dynamics in the quantum dot circuit. More precisely, the high finesse cavity allows us to measure the compressibility of the electron gas in the dot with an unprecedented sensitivity. Simultaneous measurements of electronic transport and compressibility show that the Kondo resonance observed in the conductance is transparent to microwave photons. This reveals the predicted frozen charge dynamics in the quantum dot for this peculiar electron transport mechanism and illustrates that the many-body Kondo resonance in the conductance is associated to correlations arising from spin fluctuations of a frozen charge. A second quantum phenomenon addressed in this thesis is the possible emergence of a new quasi-particle in condensed matter, called Majorana bound state, which would be its own anti-particle. For that purpose, a ferromagnetic gate has been placed below a nanotube in order to generate a synthetic spin-orbit coupling. The observation of Andreev bound states in such a device is a first promising step towards the detection with a cQED architecture of Majorana bound states in a carbon nanotube.

One-dimensional (1D) nanostructures have gained tremendous attention over the last decade due to their wide range of potential applications. Particularly, ZnO 1D nanostructures have been investigated with great interest due to their versatility in synthesis with potential applications in electronics, optics, optoelectronics, sensors, photocatalysts and nanogenerators. The thesis deals with the challenges and the answer to grow ZnO 1D nanostructure by vapor phase transport (VPT) continuously without any length limitation. The conventional VPT technique has been modified for the non-catalytic growth of ultralong ZnO 1D nanostructures and branched structures in large area with controllable aspect ratio. It has been shown that the aspect ratio can be controlled both by thermodynamically (temperature) and kinetically (vapour flux). The thesis also deals with the fabrication of carbon nanotube (CNT) -ZnO based multifunctional devices and the field emission performance of ZnO nanowires by employing various strategies. The entire thesis has been organised as follows: Chapter 1 deals with Introduction. In this chapter, importance of ultralong nanowires and significance of ultralong ZnO nanowires has been discussed. Various efforts to grow ultralong ZnO nanowire with their advantages and disadvantages have been summarised. Lastly the significance of forming ZnO nanowires based nano hybrid structures and importance of doping in ZnO nanowires and has also been discussed. Chapter 2 deals with experimental procedure and characterization. In this chapter, a single step VPT method for the growth of ultralong ZnO nanowires that incorporates local oxidation barrier for the source has been described. The synthesized nanowires were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman & photoluminescence. Chapter 3 deals with growth of ZnO nanowires, controlling the aspect ratio of ZnO nanowires, and role of other experimental aspects. In this chapter, a way to grow nanowires continuously without any apparent length limitation, a way to control the diameter of the nanowires kinetically without catalyst particle or seed layer and obtaining smaller diameter of the nanowires by non-catalytic growth as compared to that set by the thermodynamic limit has been discussed. Furthermore, the significance and importance of local oxidation barrier on source for protecting them from degradation, ensuring the continuous supply of vapour and enabling the thermodynamically and kinetically controlled growth of nanowires has been discussed. Lastly, the scheme for large area deposition and a method to use same source material for several depositions has been presented. Chapter 4 deals with multifunctional device based on CNT -ZnO Nanowire Hybrid Architectures same device can be used as a rectifier, a transistor and a photodetector. In this chapter, the fabrication of CNT arrays-ZnO nanowires based hybrid architectures that exhibit excellent high current Schottky like behavior with p-type conductivity of ZnO has been discussed. CNT-ZnO hybrid structures that can be used as high current p-type field effect transistors (FETs) and deliver currents of the order of milliamperes has been presented. Furthermore, the p-type nature of ZnO and possible mechanism for the rectifying characteristics of CNT-ZnO has been discussed. Lastly, the use of hybrid structures as ultraviolet detectors where the current on-off ratio and the response time can be controlled by the gate voltage has been presented and also an explanation for photoresponse behaviour has been provided. Chapter 5 deals with the substrate-assisted doping of ZnO nanowires grown by this technique. In this chapter, the non-catalytic growth of ZnO nanowires on multiwalled carbon nanotubes (MWCNTs) and soda lime glass (SLG) with controlled aspect ratio has been presented. The elemental mapping to confirm the presence and distribution of carbon and sodium in ZnO nanowires and the transport studies on both carbon and sodium doped ZnO has also been presented. Furthermore the stability of carbon doped ZnO has also been presented. Lastly, the advantage of growing ZnO nanowires on MWCNTs and overall advantage associated with this technique has been discussed. Chapter 6 deals with formation of ZnO nanowire branched structures. In this chapter, a possibility to grow ZnO nanowires on already grown ZnO nanowires has been demonstrated. The formation of branched structure during multiple growth of ZnO nanowire on ZnO nanowire has been presented and evolution of aspect ratio in these branched structures has been discussed. Furthermore, the advantage of using ZnO branched structures and also the ZnO nanoneedles on MWCNT mat for field emission has been presented. Chapter 7 summarizes all the findings of the thesis.

Les travaux de cette thèse ont été consacrés à la synthèse de nanoparticules magnétiques d'oxyde de fer et d'oxyde de cobalt et de nanoparticules coeur-coquille constituées d'un coeur d'oxyde de fer recouvert d'oxyde de cobalt et à l'élaboration de nanomatériaux - composites nanostructures carbonées/nanoparticules d'oxyde métallique - pour des applications dans le domaine biomédical et celui de l'énergie. Pour la synthèse des NPs, la forme et la taille des NPs sont fortement dépendantes des conditions de réaction (nature des ligands, des solvants, température de réaction ... ) , ce qui affecte leurs propriétés magnétiques. De plus, des simulations ont montré que les chaînes de stéarate peuvent désorber plus facilement les atomes de fer que les atomes de cobalt et se libérer pour former des germes, ce qui pourrait expliquer le comportement distinctif entre les deux complexes. Ces nanoparticules magnétiques ont été synthétisées à l'intérieur de nanotubes de carbone en deux étapes aboutissant à des taux de remplissage très importants. Après fonctionnalisation, ces nanocomposites ont été introduits dans de cellules tumorales et ont été magnétiquement manipulées. Ils se sont révélés être très efficaces en tant qu'agents de contraste en IRM mais également dans le domaine de l'hyperthermie (activation sous éclairage dans le domaine de !'Infrarouge proche). Enfin, de nouveaux composites à partir de nanoparticules de Nb20 5 et de graphène (ou NTCs) ont été synthétisés et des résultat~prometteurs ont été obtenus dans des tests de batterie lithium-ion : leur utilisation en tant qu'anode a permis d'obtenir des capacités réversibles de 260 mAh/g. / This thesis was focused on the synthesis of magnetic nanoparticles of iron oxide and cobalt oxide and core-shell nanoparticles, consisting of a cobalt oxide coated iron oxide and on the development of composite nanomaterials - nanostructures carbon /metal oxide nanoparticles - for applications in the biomedical field and the energy. For the synthesis of NPs, the shape and size of NPs are dependent of the reaction conditions, which further affect their magnetic properties. Meanwhile, simulation showed that stearate chains can desorb more easily from iron atoms and release to form seeds than from cobalt atoms, which might explain distinctive behavior between the bath complexes. Regarding nanostructures carbon/metal oxide nanoparticles hybrid materials, the properties of the filled magnetic CNTs as heat mediator for photothermal ablation and as contrast agent for MRI were then evaluated and promising results have been obtained. Last, new composite materials (Nb205 nanoparticles/graphene or NTCs) were synthesized and promising results were obtaines in lithium battery tests : their use as anode allowed obtaining reversible capacities of 260 mAh/g.

Abstract The energy consumption around the globe is on the rise due to the exponential population growth and urbanization. There is a need for alternative and non-conventional energy sources, which are CO2-neutral, and a need to produce less or no environmental pollutants and to have high energy efficiency. One of the alternative approaches is hydrogen economy with the fuel cell (FC) technology which is forecasted to lead to a sustainable society. Hydrogen (H2) is recognized as a potential fuel and clean energy carrier being at the same time a carbon-free element. Moreover, H2 is utilized in many processes in chemical, food, metallurgical, and pharmaceutical industry and it is also a valuable chemical in many reactions (e.g. refineries). Non-renewable resources have been the major feedstock for H2 production for many years. At present, ~50% of H2 is produced via catalytic steam reforming of natural gas followed by various down-stream purification steps to produce ~99.99% H2, the process being highly energy intensive. Henceforth, bio-fuels like biomass derived alcohols (e.g. bio-ethanol and bio-glycerol), can be viable raw materials for the H2 production. In a membrane based reactor, the reaction and selective separation of H2 occur simultaneously in one unit, thus improving the overall reactor efficiency. The main motivation of this work is to produce H2 more efficiently and in an environmentally friendly way from bio-alcohols with a high H2 selectivity, purity and yield. In this thesis, the work was divided into two research areas, the first being the catalytic studies using metal decorated carbon nanotube (CNT) based catalysts in steam reforming of ethanol (SRE) at low temperatures (<450 °C). The second part was the study of steam reforming (SR) and the water-gas-shift (WGS) reactions in a membrane reactor (MR) using dense and composite Pd-based membranes to produce high purity H2. CNTs were found to be promising support materials for the low temperature reforming compared to conventional catalyst supports, e.g. Al2O3. The metal/metal oxide decorated CNTs presented active particles with narrow size distribution and small size (~2–5 nm). The ZnO promoted Ni/CNT based catalysts showed the highest H2 selectivity of ~76% with very low CO selectivity <1%. Ethanol was shown to be a more suitable and viable source for H2 than glycerol. The dense Pd-Ag membrane had higher selectivity but a lower permeating flux than the composite membrane. The MR performance is also dependent on the active catalyst materials and thus, both the catalyst and membrane play an important role. Overall, the membrane–assisted reformer outperforms the conventional reformer and it is a potential technology in pure H2 production. The high purity of H2 gas with a CO-free reformate for fuel cell applications can be gained using the MR system. / Tiivistelmä Maailman energiankulutus on kasvussa räjähdysmäisen väestönkasvun ja voimakkaan kaupungistumisen myötä. Tällä hetkellä energian tuottamisen aiheuttamat ympäristöongelmat ja taloudellinen epävarmuus ovat seikkoja, joiden ratkaisemiseksi tarvitaan vaihtoehtoisia ja ei-perinteisiä energialähteitä, joilla on korkea energiasisältö ja jotka tuottavat vähän hiilidioksidipäästöjä. Eräs vaihtoehtoisista lähestymistavoista on vetytalous yhdistettynä polttokennotekniikkaan, minkä on esitetty helpottavan siirtymistä kestävään yhteiskuntaan. Vety on puhdas ja hiilivapaa polttoaine ja energian kantaja. Lisäksi vetyä käytetään monissa prosesseissa kemian-, elintarvike-, metalli- ja lääketeollisuudessa ja se on arvokas kemikaali monissa prosesseissa (mm. öljynjalostamoissa). Uusiutumattomat luonnonvarat ovat olleet tähän saakka merkittävin vedyn tuotannon raaka-aine. Tällä hetkellä noin 50 % vedystä tuotetaan maakaasun katalyyttisellä höyryreformoinilla. Puhtaan (yli 99,99 %) vedyn tuotanto vaatii kuitenkin useita puhdistusvaiheita, jotka ovat erittäin energiaintensiivisiä. Integroimalla reaktio- ja puhdistusvaihe samaan yksikköön (membraanireaktori) saavutetaan huomattavia kustannussäästöjä. Biopolttoaineet, kuten biomassapohjaiset alkoholit (bioetanoli ja bioglyseroli), ovat vaihtoehtoisia lähtöaineita vedyn valmistuksessa. Tämän työn tavoitteena on tuottaa vetyä bioalkoholeista tehokkaasti (korkea selektiivisyys ja saanto) ja ympäristöystävällisesti. Tutkimus on jaettu kahteen osaan, joista ensimmäisessä tutkittiin etanolin katalyyttistä höyryreformointia matalissa lämpötiloissa (<450 °C) hyödyntämällä metallipinnoitettuja hiilinanoputkia. Työn toisessa osassa höyryreformointia ja vesikaasun siirtoreaktioa tutkittiin membraanireaktorissa käyttämällä vedyn tuotantoon tiheitä palladiumpohjaisia kalvoja sekä huokoisia palladiumkomposiittikalvoja. Hiilinanoputket (CNT) havaittiin lupaaviksi katalyyttien tukimateriaaleiksi verrattuna tavanomaisesti valmistettuihin tukiaineisiin, kuten Al2O3. CNT-tukiaineelle pinnoitetuilla aktiivisilla aineilla (metalli-/metallioksidit) todettiin olevan pieni partikkelikoko (~2–5 nm) ja kapea partikkelikokojakauma. Sinkkioksidin (ZnO) lisäyksellä Ni/CNT-katalyytteihin saavutettiin korkea vetyselektiivisyys (~76 %) ja erittäin alhainen hiilimoksidiselektiivisyys (<1 %). Etanolin todettiin olevan parempi vedyn raaka-aine kuin glyserolin. Tiheillä Pd-Ag-kalvoilla havaittiin olevan vedyn suhteen korkeampi selektiivisyys mutta matalampi vuo verrattuna palladiumkomposiittikalvoihin. Membraanireaktorin suorituskyky oli riippuvainen myös katalyytin aktiivisuudesta, joten sekä kalvolla että katalyyttimateriaalilla oli merkittävä rooli kyseisessä reaktorirakenteessa. Yhteenvetona voidaan todeta, että membraanierotukseen perustuva reformointiyksikkö on huomattavasti perinteistä reformeriyksikköä suorituskykyisempi mahdollistaen tehokkaan teknologian puhtaan vedyn tuottamiseksi. Membraanitekniikalla tuotettua puhdasta vetyä voidaan hyödyntää mm. polttokennojen polttoaineena.

Abstract The objective of this thesis is to demonstrate multi-dimensional carbon nanotube (CNT) structures in combination with various active materials in order to evaluate their performance in electrode applications such as cold emitters, electric double-layer capacitors (EDLC), and electrochemical sensor/catalyst devices. As the host materials for other active materials, the construction of multi-dimensional CNT nanostructures in this thesis is achieved by two different approaches. In the first, direct growth of 3-dimensional carbon nanostructures by catalytic chemical deposition to produce filamentary carbon as well as vertically aligned forests was applied. The second route that was utilized encompassed the immobilization of CNTs from dispersions to form 2-dimensional surface coatings as well as self-supporting porous buckypapers. Carbonaceous nanocomposites of the active materials are obtained by a number of different methods such as (i) growing nanotubes and filamentous structures on porous Ni catalyst structures, (ii) impregnating CNTs with organic receptor molecules or with Pd nanoparticles, (iii) plating and replacing Cu with Pd on the nanotubes by chemical and galvanic reactions, (iv) annealing W evaporated on CNTs to form CNT-WC composites in solid-solid reactions and (v) reacting S vapor with W coated on CNTs to synthesize CNT-WS2 edge-on lamellar structures of the dichalcogenide in the vertically aligned CNT forests. The 3-dimensional carbon-Raney®Ni composite electrodes show reasonable specific capacitance of ~12 F·g-1 in electric double-layer capacitors as well as a low turn-on field (<1.0 V·µm-1) in field emitter devices. CNT-Nafion®-trifluoroacetylazobenzene coatings on glassy carbon electrodes outperform their Nafion®-trifluoroacetylazobenzene counterparts in electrochemical sensing of different amine compounds (e.g. 10 mM cadaverine, putrescine or ammonia). Cu and CuPd/buckypaper composites display catalytic activity in electrocatalytic oxidation of methanol in alkaline media. On the other hand, nanocomposites of WC and WS2 with aligned CNT forest exhibit a promising performance in hydrogen evolution reactions with an overpotential between -0.5 and -0.7 V at pH~1. In addition, these respective CNT forest aligned nanocomposites also demonstrate a novel method to obtain macroscopic 3-dimensional catalytic electrode assemblies. The results in this thesis elucidate the combination of carbon based nanostructures with organic and inorganic materials as a feasible and versatile approach to produce electrodes for several applications. The following studies of each active carbonaceous composite are expected to boost the technological innovation in relevant fields and initiate further development for commercial exploitation. / Tiivistelmä Työn tavoitteena oli demonstroida moniulotteisia hiilinanoputkirakenteita (CNT), joihin yhdistetään erilaisia aktiivisia materiaaleja sekä arvioida niiden suorituskykyä elektrodisovelluksissa, kuten kenttäemitterissä, sähköisissä kaksoiskerroskondensaattoreissa ja sähkökemiallisissa anturi- ja katalyyttikomponenteissa. Moniulotteisten CNT-nanorakenteiden konstruoiminen muiden aktiivisten materiaalien isäntämateriaaliksi toteutettiin kahdella tavalla. Ensimmäisessä toteutuksessa sovellettiin katalyyttis-kemiallista pinnoitusta, jolla kasvatettiin suoraan kolmiulotteisia hiilinanorakenteita sekä kuitumaisena hiilenä että pystysuuntaan orientoituneina hiilinanoputkimetsinä. Toinen päämenetelmä oli hiilinanoputkien immobilisointi dispersioista kaksiulotteisiksi pinnoitteiksi ja itsetukeutuviksi huokoisiksi hiilinanoputkipapereiksi. Hiiltä sisältäviä aktiivisten materiaalien nanokomposiitteja valmistettiin useilla menetelmillä, kuten (i) kasvattamalla nanoputkia ja kuitumaisia rakenteita huokoisiin Ni-katalyyttirakenteisiin, (ii) kyllästämällä hiilinanoputkia orgaanisilla reseptorimolekyyleillä tai Pd-nanopartikkeleilla, (iii) pinnoittamalla ja korvaamalla nanoputkien päällä olevaa kuparia palladiumilla kemiallisten ja galvaanisten reaktioiden avulla, (iv) hehkuttamalla hiilinanoputkien pinnalle höyrystettyä wolframia (W) muodostamaan CNT-WC-komposiitteja kiinteä–kiinteä-reaktiolla sekä (v) antamalla rikkihöyryn reagoida W-pinnoitettujen hiilinanoputkien kanssa lamellaaristen CNT-WS2-kalkogenidirakenteiden syntetisoimiseksi pystysuuntaan orientoituneisiin CNT-metsiin. Kolmiulotteisilla hiili–Raney®Ni-komposiittielektrodeilla saavutetaan kohtuullinen ominaiskapasitanssi (~12 F·g-1) sähköisissä kaksoiskerroskondensaattoreissa ja pieni kytkeytymiskenttä (<1,0 V·μm-1) kenttäemitterikomponenteissa. CNT-Nafion®-trifluoroasetyyliatsobentseeni-pinnoitteet lasimaisilla hiilielektrodeilla ovat selvästi parempia erilaisten amiiniyhdisteiden (esimerkiksi 10 mM kadaveriini, putreskiini tai ammoniakki) sähkökemiallisessa havaitsemisessa kuin vastaavat Nafion®-trifluoroasetyyliatsobentseeni-pinnoitteet. Cu- ja CuPd-hiilinanoputkipaperikomposiitit osoittavat katalyyttistä aktiivisuutta metanolin sähkökatalyyttisessä hapettumisessa emäksisessä väliaineessa. Toisaalta WC- ja WS2-yhdisteiden ja orientoituneiden CNT-metsien muodostamat nanokomposiitit osoittavat lupaavaa suorituskykyä vedynmuodostamisreaktiossa -0,5…-0,7 V ylipotentiaalilla, ja nämä myös demonstroivat uutta menetelmää makroskooppisten kolmiulotteisten katalyyttisten elektrodirakenteiden toteuttamiseksi. Väitöskirjan tulokset osoittavat, että hiilipohjaisten nanorakenteiden ja orgaanisten/epäorgaanisten materiaalien yhdistäminen on toteuttamiskelpoinen ja monipuolinen lähestymistapa elektrodien valmistamiseksi useisiin sovelluksiin. Kunkin työssä esitetyn aktiivista hiiltä sisältävän komposiitin tutkimuksen odotetaan lisäävän kyseisen alan teknisiä innovaatioita ja synnyttävän lisää kehitystyötä tutkimuksen kaupalliseksi soveltamiseksi.