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Ce travail de thèse consiste en une étude des mécanismes de croissance des nanotubes de carbone monofeuillets par spectroscopie Raman in situ. La première partie de ce travail est consacrée à la mise en évidence des limites en température et en pression partielle de précurseur carboné du domaine de croissance des nanotubes de carbone monofeuillets. L’atout principal de la spectroscopie Raman in situ étant de pouvoir corréler informations structurales et cinétiques, cette approche a aussi permis d'étudier l'influence des principaux paramètres de synthèse (T, P, nature du précurseur carboné et du catalyseur) sur les cinétiques de croissance et de désactivation, ainsi que sur la nature et la quantité des espèces carbonées désordonnées produites. Enfin, l’influence de la température et de la pression partielle de précurseur sur le diamètre des nanotubes formés a également été étudiée. Ce travail a finalement conduit à la mise en évidence de plusieurs processus élémentaires impliqués dans : l’activation, la croissance, la désactivation, la qualité structurale, la pureté et la sélectivité en diamètre des nanotubes. / This work presents a study of the Single-Walled Carbon Nanotubes growth mechanisms by in situ Raman measurements. The first part of the manuscript is devoted to the determination of the temperature and precursor partial pressure limits of the Single-Walled Carbon Nanotubes growth domain. Furthermore, in situ Raman spectroscopy allows to correlate structural information and kinetics: this approach permits to study the influence of the main synthesis parameters (T, P, nature of the carbon precursor and of the catalyst) on the growth and deactivation kinetics, and on the nature and the quantity of disordered carbon species synthesized. Lastly, a study on the temperature and precursor partial pressure effects on the nanotubes diameters is reported. All the data collected have finally led to a discussion about the elementary processes involved in: activation, growth, deactivation, structural quality, purity and diameter selectivity of Single-Walled Carbon Nanotubes.

Les nanotubes de carbone (NTC) n'ont eu de cesse, depuis leur (re)-découverte par Sumio Iijima en 1991, de passionner la communauté scientifique. Leurs propriétés électroniques, optiques et mécaniques exceptionnelles en font l'un des matériaux les plus prometteurs dans le domaine des nanotechnologies. Néanmoins, l'utilisation des NTC en microélectronique se heurte à de nombreux problèmes. En particulier, les propriétés électroniques de ces nanotubes sont dépendantes de plusieurs paramètres : leur diamètre, leur organisation et le nombre de feuillets qui le composent. Ainsi, l’obtention de nanotubes exclusivement semiconducteurs (recherchées pour réaliser un dispositif microélectronique tel qu’un transistor) ne peut être garantie par les techniques de synthèse actuelles. Ces techniques (CVD, ablation laser, etc…) ne conduisent en général qu’à un mélange de nanotubes semiconducteurs et métalliques, difficiles à trier.Dans le cas spécifique des nanotubes de carbone « zig-zag », leur comportement électronique n’est défini que par le diamètre. Une synthèse de nanotubes exclusivement « zig-zag » et de diamètres contrôlés apporterait donc une solution définitive à ce problème.La chimie des calixarènes peut apporter des réponses à cette problématique. On utiliserait alors la chimie moléculaire pour former le NTC de façon séquentielle. L’objectif du travail réalisé est d'obtenir une structure de type « zig-zag » avec un diamètre strictement contrôlé par la taille du calixarène de départ.Nous avons abordé plusieurs méthodes de synthèse en fonction du motif de répétition envisagé pour la croissance séquentielle du nanotube de carbone. Dans un premier temps, une stratégie basée sur le motif cyclacène a été utilisée. Les résultats de ces travaux seront présentés dans le chapitre II. Au cours de ce chapitre nous présenterons la synthèse et la fonctionnalisation des calixarènes de départ, en vue de leur utilisation pour des réactions de types Wittig Horner ou Oléfination de Julia.Enfin, au cours du chapitre III, nous présenterons les résultats obtenus par utilisation d’une autre stratégie, basée sur la répétition d’un motif métacyclopolyphénylène. Cette stratégie est basée sur une succession de réactions de couplage de Suzuki, catalysés par des complexes de palladium. / Since their re-discovery in 1991 by Sumio Ijima, carbon nanotubes (CNT’s) have not stopped fascinating the scientific community. Their electronic, optical, and mechanical properties render them one of the most promising materials in the field of nanotechnology. Nevertheless, the use of CNT’s is has been hampered by a number of problems due to the fact that the electronic properties of CNT’s are dependent on several parameters such as diameter, organization and number of sheets that make them up. Because of these factors, obtaining nanotubes that function exclusively as semiconductors (such as those used for fabricating microelectronic devices such as transistors) cannot be guaranteed with the synthetic methods used today. These techniques (CVD, laser ablation, etc) are only capable of yielding a mixture of semiconducting and metallic nanotubes difficult to separate.In the particular case of « zig-zag » nanotubes, their electronic behavior is defined by their diameter. Thus, a synthetic method capable of rendering exclusively « zig-zag » nanotubes with discrete diameters would yield a solution to the problem.Calixarene chemistry can give answers to this problem. Using molecular chemistry in order to form CNT’s in a sequential fashion, the objective of this work will be to obtain exclusively « zig-zag » nanotubes with discrete diameters that are imposed by the size of the calixarene used as a starting block. We have tried several methods for the synthesis of CNT’s depending on the repetition motif used for the sequential growth of the desired carbon nanotube. Firstly, a strategy based on the acene functionality was used. The results of this work are presented in chapter II, where we will describe the synthesis and functionalization of the starting calixarenes used in reaction types such as Wittig Horner and Julia Olefination.Chapter III shows the results obtained using a different strategy based on the repetition of the metacyclopolyphenylene unit. This strategy is based on the reiteration of successive Suzuki coupling reactions catalyzed by palladium complexes.

This thesis presents models and simulations of dielectrophoretic separation of micro and nano particles. The fluid dynamics involved and the dielectric properties of water inside single-walled carbon nanotube are studied as well. Based on the effective dipole moment method, the particle dynamic model focuses on the translational motions of micro particles. The hydrodynamic force between the particles and the particle-particle electrostatic interactions are considered as well. By comparing the dimensionless parameters, the dominating force can be determined. Based on a simplified version of the particle dynamic model, two numerical simulations are carried out to predict the efficiency of dielectrophoretic separation of micro size particles. The first calculation suggests a strategy to improve the trapping efficiency of E.coli bacteria by applying superimposed AC electric fields. The second calculation discusses the concept of mobility and improves the separation rate of particles by a multi-step trapping-releasing dielectrophoresis strategy. The model is extended down scale to calculate the separation of metallic and semiconducting single-walled carbon nanotubes by the modified effective dipole moment method for prolate ellipsoids. The steeply changed gradient of electric field results in the local joule heating therefore creates gradient of dielectric properties in the solution. As a result, certain pattern of fluid flow with a considerable strength is created and affects the motion of carbon nanotubes especially close to the electrode gap, which indicates that the so-called electrothermal flow should be considered in designing the experiment to separate single-walled carbon canotubes. When the length scale of particles is comparable to that of the electrodes, the calculation of dielectrophoretic force by the effective dipole moment is considered not to be accurate since only the electric field in the center point is taken into account. Hence in the thesis a new method based on distributed induced charge is suggested. By approximating a straight slender body as a prolate ellipsoid, the electric field of multiple points along the centerline are all considered in the calculation and the interaction between particles could be concurrently taken care. This method is expected to be an improved method to calculate the dielectrophoretic force of rod-like virus, DNA, nanowires and carbon nanotubes. The dielectric property of water confined in carbon nanotubes is expected to be dramatically different from that of bulk water. The thesis also contains a molecular dynamics study to reveal the difference also a dependence on the diameter of carbon nanotubes. The results show that along the axial direction, both the static permittivity and the relaxation time are larger than the isotropic bulk water, and in the cross-section plane it is opposite. When the radius of the carbon nanotubes increases, the properties of water inside become closer to the bulk water. / QC 20100820

Existing growth methods produce single-walled carbon nanotubes (SWCNTs) with a range of structures and electronic properties, but many potential applications require pure nanotube samples. Density gradient ultracentrifugation (DGU) has recently emerged as a technique for sorting as-grown mixtures of single-walled nanotubes into their distinct ( n,m ) structural forms, but this approach has been limited to samples containing only a small number of nanotube structures, and has often required repeated DGU processing. For the first time, it has been shown that the use of tailored nonlinear density gradient ultracentrifugation (NDGU) can significantly improve DGU separations. This new sorting process readily separated highly polydisperse samples of SWCNTs grown by the HiPco method in a single step to give fractions enriched in any of ten different ( n,m ) species. In addition, minor variants of the method allowed separation of the minor-image isomers (enantiomers) of seven ( n,m ) species. Optimization of this new approach was aided by the development of instrumentation that spectroscopically mapped nanotube contents inside undisturbed centrifuge tubes. Besides, sorted nanotube samples enabled the discovery of novel oxygen-doped SWCNTs with remarkable photophysical properties. Modified nanotube samples were produced using mild oxidation of SWCNTs with ozone followed by a photochemical conversion step that induced well-defined changes in emissive properties. As demonstrated for a set of ten separated SWCNT ( n,m ) structures, chemically altered nanotubes possess slightly lower band gap energies with correspondingly longer photoluminescence wavelengths. Treated samples showed distinct, structure-specific near-infrared fluorescence at wavelengths 10 to 15% longer than the pristine semiconducting SWCNTs. Quantum chemical modeling suggests that dopant sites harvest light energy absorbed in undoped nanotube regions by trapping mobile excitons. The oxygen-doped SWCNTs are much easier to detect and image in biological specimen than pristine SWCNTs because they give stronger near-IR emission and do not absorb at the shifted emission wavelength. This novel modification of SWCNT properties may lead to new optical and electronic applications, as it provides a way to change optical band gaps in whole nanotubes or in selected sections.

Ce travail de thèse expérimental porte sur l'élaboration et l'étude de systèmes hybrides 1D de nanotubes de carbone mono-feuillets, fonctionnalisés de manière non covalente, sous deux aspects. La première étude s'intéresse à l'intercalation de rubidium dans les faisceaux de nanotubes. L'objectif est de faire le lien entre les propriétés structurales des nanotubes dopés et leurs propriétés électroniques au cours du dopage. Un dispositif original dédié, adapté à l'utilisation sur grands instruments et permettant le suivi « in-situ » de l'intercalation par une approche multi-techniques, a été développé dans ce but. Nous mettons en évidence par EXAFS que l'arrangement local autour des ions rubidium est dépendant de la stœchiométrie des composés étudiés. Il apparaît alors qu'à faible taux de dopage, les sites de défauts oxygénés sont privilégiés. Le changement de structure est également relié à une transition semi-conducteur/métal des nanotubes, observée par mesure de résistance électrique et spectroscopie Raman, et induite par le dopage des nanotubes par le rubidium.La seconde partie expérimentale est consacrée à l'étude du confinement d'oligothiophènes à l'intérieur de nanotubes de carbone mono-feuillets. Des mesures de diffraction des rayons X et de microscopie électronique en transmission haute résolution démontrent l'efficacité de notre protocole d'encapsulation. D'autre part, différentes spectroscopies, absorptions UV-Visible et infrarouge et diffusion Raman, indiquent un transfert de charge relativement faible entre les molécules encapsulées et les nanotubes de carbone. Ce résultat est très bien mis en évidence par les modifications de profil, d'intensité et de fréquence des modes Raman hautes fréquences. On notera le bon accord entre les résultats obtenus ici et les effets de renormalisation de l'énergie de phonon discutés dans la littérature. En complément, des effets de confinement liés au diamètre des nanotubes ont été mis en évidence par l'étude des modes Raman basses fréquences. Deux modèles structuraux sont proposés pour expliquer les tendances observées. Le premier suggère un comportement indépendant de la nature de l'espèce insérée. Dans le second, le nombre de chaines d'oligothiophènes encapsulées en fonction du diamètre des tubes est pris en compte. De plus, nous montrons également une influence significative des défauts structuraux sur les systèmes hybrides. / This experimental work concerns the development and the study of 1D hybrid systems of single-walled carbon nanotubes non-covalently fonctionnalized. Two different approaches are discussed. The first experimental study deals with the intercalation of rubidium in carbon nanotubes bundles. The aim is to link structural and electronic properties along the doping process. To do, we developed an original and dedicated home-made set adapted to the use on synchrotron facilities. It permits the following of the intercalation by means of an in-situ multi-techniques approach. In this part, we pointed out that the local environnement of rubidium is dependant of the compound stœchiometries. It appears that oxygenated surface defects are first occupied for low doping rates. The structure modification is also linked to a semiconducting/metal transition of carbon nanotubes observed by resistance measurements and Raman spectroscopy. The second experimental study is devoted to the confinement of oligothiophenes inside single-walled carbon nanotubes. X-Ray diffraction and high resolution transmission electronic microscopy measurements demonstrate the efficiency of our encapsulation process. Several spectroscopic techniques such as UV-Visible and infrared absorptions and Raman diffusion indicate a weak charge transfer between both systems. This result is well evidenced by the profile, intensity and frequency modifications of the high frequency Raman modes. We note the good agreement of these results with the energy renormalisation of phonons discussed in the literature. In addition, some confinement effects depending on carbon nanotubes diameter are pointed out by the study of low frequency Raman modes. Two models are proposed to explain the observed trend. The first one suggests a behavior independent of the nature of the inserted element. In the second one, the number of oligothiophene chains encapsulated in function of carbon nanotubes diameter is considered. We also show a significative influence of carbon nanotube defects on hybrid systems.

Utilizing density functional theory (DFT) the Vienna Ab initio Simulation Package (VASP) was used to calculate the Raman spectra for five single-walled carbon nanotubes (SWCNTs) with chiralities (4,4), (6,6), (8,0), (12,0) and (7,1). The radial breathing mode (RBM), when compared with experimental frequencies, shows good correlation. When compared to RBM:s calculated with tight binding the frequencies calculated with DFT displayed higher accuracy. The precision of G-band frequencies were inconclusive due to lack of experimental data. The frequencies did not agree well with the results from tight-binding theory. The correctness of the Raman activity estimations using results from DFT calculations was found to be questionable. An unknown mode, which was found to be highly Raman active in the calculated spectra of (4,4), (6,6), and possibly (8,0), and (12,0), is also discussed. It was concluded that further calculations on larger tubes, especially armchair tubes are relevant for future studies. Further verification of the determination of Raman activity is also needed. / F7042T - Project in Engineering Physics

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