Junctions are the key component for 3D carbon nanotube (CNT)-graphene seamless hybrid nanostructures. Growth mechanism of junctions of vertical CNTs growing from graphene in the presence of iron catalysts was simulated via quantum mechanical molecular dynamics (QM/MD) methods. CNTs growth from graphene with iron catalysts is based on a ‘‘base-growth’’ mechanism, and the junctions were the mixture of C-C and Fe-C covalent bonds. Pure C-C bonded junctions could be obtained by moving the catalyst during CNT growth or etching and annealing after growth. The growth process of 3D CNT-graphene junctions on copper templates with nanoholes was simulated with molecular dynamic (MD) simulation. There are two mechanisms of junction formation: (i) CNT growth over the holes that are smaller than 3 nm, and (ii) CNT growth inside the holes that are larger than 3 nm. The growth process of multi-layer filleted CNT-graphene junctions on the Al2O3 template was also simulated with MD simulation. A simple analytical model is developed to explain that the fillet takes the particular angle (135°). MD calculations show that 135° filleted junction has the largest fracture strength and thermal conductivity at room temperature compared to junctions with 90°,120°, 150°, and 180° fillets. The tensile strengths of the as-grown C–C junctions, as well as the junctions embedded with metal nanoparticles (catalysts), were determined by a QM/MD method. Metal catalysts remaining in the junctions significantly reduce the fracture strength and fracture energy. Moreover, the thermal conductivities of the junctions were also calculated by MD method. Metal catalysts remaining in the junctions considerably lower the thermal conductivity of the 3D junctions.

Cette thèse s’inscrit dans le cadre du développement de nouveaux matériaux permettant de se substituer aux métaux pour les applications de transport de l’électricité. L’excellente conductivité électriques des nanotubes de carbone (NTC) ainsi que le fait qu’ils peuvent être assemblés sous forme de fil en font une alternative prometteuse. Cependant, la conductivité électrique des fils en NTC n’est pas encore suffisante pour directement concurrencer les métaux. Ce travail de thèse cherche à identifier et comprendre les points bloquants pour les dépasser et ainsi améliorer la conductivité des fils en NTC. Les nanotubes de carbones sont fabriqués par la technique de Chemical Vapour Deposition sous forme de tapis. Ces tapis dit "filable" permettent d'extraire une nappe de NTC que l’on densifie ensuite pour former un fil. Tous les travaux de la littérature sur ce type de fil rapportent des résistivités supérieures à 1 mΩ.cm. Afin de comprendre cette limite apparente, une étude approfondie du transport électronique de ces fils est présentée en étudiant le comportement de la résistance du matériau entre 3 K et 300 K. Cette analyse met en évidence que le transport dans les fils de NTC est dominé par les contacts entre NTC en dessous de 70 K et qu’il est dominé par le transport intrinsèque des NTC au-dessus de 70 K. L'amélioration de la conductivité des fils en NTC à température ambiante passe par l’amélioration de la conductivité intrinsèque des NTC. Pour ce faire, deux techniques sont présentées dans ce travail, l’amélioration de la qualité structurale des NTC obtenue par un recuit à plus de 2000 °C et le dopage. L'amélioration linéaire de la conductivité du fil de NTC avec la qualité structurale des NTC nous a permis d’atteindre un record de résistivité à 0.76 mΩ.cm. Le dopant présenté dans ce travail (PtCl4) est pour la première fois utilisé pour des fils en NTC. Ce dopant possède une excellente efficacité (résistivité diminuées par 3) et une très grande stabilité dans le temps. L’amélioration de la qualité structurale des NTC augmente fortement l’efficacité de dopage. La qualité structurale est indispensable pour atteindre d’excellentes conductivités électriques. Un schéma récapitule l’influence des différents paramètres expérimentaux sur le transport électronique des fils en NTC. Enfin, l’étude du transport électronique dans les matériaux en NTC a permis de développer un nouveau modèle de transport s’ajustant à la fois à nos travaux ainsi qu’à tous ceux de la littérature. Ce modèle consiste en deux résistances en série. La première résistance décrit le transport dans les matériaux en NTC en dessous de 70 K et est très bien décrite par la théorie d’un Liquide de Luttinger. La deuxième résistance dépend à la fois du transport intrinsèque des parois métalliques et semi-conductrices des NTC ainsi que de l’arrangement des NTC entre eux (faisceaux ou individualisés). Ce modèle permet de tirer les informations intrinsèques aux fils comme la façon dont les électrons sont injectés dans les NTC, l’influence des NTC semi-conducteurs par rapport aux métalliques et les libres parcours moyen des électrons dans la structure. L’ensemble de ces résultats indique que les paramètres indispensables pour obtenir des fils très conducteurs sont pour des NTC: d’une excellente qualité structurale, fabriqué sous forme individualisée et avec une forte proportion de parois métalliques. / The overall framework of this PhD. work is to develop new materials to replace metals in electrical wiring. Carbon nanotubes (CNT) are a good alternative as they show a high electrical conductivity as well as they can be assembled into yarns. However, CNT yarns have not yet reached the electrical conductivity of individual CNTs preventing them from competing with metals. The aim of this work is to identify the factors limiting the CNT yarn conductivity, increase the CNT yarn conductivity and model their electrical transport. In this work, carbon nanotubes are grown in array by Chemical Vapour Deposition. Our CNT arrays are spinnable meaning that, CNT webs can be drawn from it and then densified into yarns. All the published works on this type of CNT yarns reveal that their resistivities are limited above 1 mΩ.cm. In order to understand this apparent limitation, we present an extensive study of the CNT yarn electrical transport by measuring the yarn resistance behavior from 3 K to 300 K. We show that the CNT yarn electrical transport is dominated by the contact resistance between CNTs below 70 K and by the intrinsic CNT resistance above. In order to improve the CNT yarn electrical conductivity at room temperature, it is essential to improve the intrinsic CNT conductivity. Two ways are investigated, the first one is to increase the CNT structural quality by annealing above 2000 °C, and the second one is doping. Annealing treatment drastically improves the CNT structural quality, revealing that the CNT yarn resistivity linearly decreases with the CNT quality improvement. This treatment allows reaching a resistivity record of 0.76 mΩ.cm for undoped yarn made from CNT array. In addition, we present a new dopant for CNT yarn (PtCl4) that shows both high doping efficiency (CNT resistivity decreased by almost a factor of 3) and a very long term stability. By combining successively annealing and doping treatments, we found out that the doping efficiency is drastically increased by the CNT structural quality improvement. From all our experimental studies and the literature data analysis, we present a scheme showing the influence of many parameters on the CNT yarn electrical transport. After bringing to light that existing electrical transport models do not correctly explain the CNT yarn electrical transport, we developed a new model that perfectly fits both our data and those of the literature. Our model consists in two resistances in series. The first resistance represents the CNT material electrical transport below 70 K and is very well explained by the Luttinger Liquid theory. The second resistance depends on both the intrinsic CNT wall electrical transport (metallic or semi-conducting) and the CNT arrangement (bundled or individualized). Our model allows extracting CNT yarn physical parameters such as the way electrons tunnel from one CNT to another, the role of semi-conducting walls versus metallic ones and the electron mean free paths in the structure. All these results highlight that the main ways to make CNT yarns with high electrical conductivities involve individualized CNTs, with an excellent structural quality and also a high metallic CNT wall content.

Carbon-infiltrated carbon nanotube (CICNT) forests are carbon nanotube (CNT) forests infiltrated with pyrolytic carbon to increase durability by becoming a solid material. This material can be tuned to maintain the nanotube geometry of a CNT forest and can also be fabricated on a variety of materials and geometries. Additionally, the present work has indicated that CICNT forests may resist bacterial proliferation and biofilm formation. This phenomenon is not due to the CICNT chemistry; it is presumably due to the CICNT nanostructure morphology. Thus, both silicon and stainless steel substrates were used to investigate CICNT's structural resistance to Methicillin-resistant Staphylococcus aureus (MRSA) biofilm. From in vitro experimental testing, CICNT on both these substrates resisted MRSA cell attachment and biofilm proliferation. The discovery of this non-pharmaceutical biofilm resistance expands the potential applications of CICNT to include medical devices that are prone to infection and/or devices that contribute to infection. Two representative applications were investigated: external fixator pins and scalpel blades. CICNT-coated versions of these applications underwent additional MRSA biofilm resistance testing as well as mechanical testing. In particular, external fixator pins were identified as a high potential application of CICNT surface coating technology. Previous work on both CNT and CICNT forests has largely been performed on planar structures. However, any potential medical device applications involve curved substrates. In particular, concave curvatures are challenging due to the potential for stress-related CICNT forest defects. Thus, the present work also included a study of the incidence rates and determining factors of these defects. SEM images of the cross-sections revealed different types of microscale forest defects while the top surface showed morphologies that are largely consistent with flat substrates. CICNT forest height and substrate curvature were identified as contributing factors to CICNT forest defect incidence rates. Thus, the present work advances the understanding of bacterial resistance and microstructure-related properties of CICNT surface coatings, with applications in medical devices.

Le but principal de ces travaux de thèse fut la conception et la réalisation de biocapteurs par utilisation de méthodes de transduction sans marquage, comme la spectroscopie d’impédance électrochimique (EIS), pour la détection de cible d’intérêts. Pour cela, différentes architectures moléculaires, spécifiques à la molécule d’intérêt ciblée, ont été développées afin de permettre la transduction du signal issu de la reconnaissance entre le biorécepteur et son substrat, et conduire ainsi à la détection de la cible.Les systèmes mis au point reposent sur l’intégration de nanomatériaux, tels que les nanotubes de carbones ou le disulfure de tungstène, pour assurer l'immobilisation de l'entité biospécifique à la surface du capteur. L’intérêt de ces matériaux est multiple puisqu’ils permettent une très forte augmentation de la surface spécifique du système et sont également mis à contribution lors de la fonctionnalisation de la surface de l’électrode. Un des grands défis rencontré dans le développement des biocapteurs étant la stratégie d'immobilisation de l'entité biospécifique sur la surface du capteur.Ces travaux se sont donc dans un premier temps intéressés à la réalisation et à la caractérisation de films minces de ces nanomatériaux ainsi qu’à leur transfert à la surface d’une électrode. Dans ce contexte, le but est de concevoir des bioarchitectures poreuses à base de polymères fonctionnels électrogénérés autour des nanostructures de carbone permettant la pénétration de grandes biomolécules comme des anticorps pour développer des immunocapteurs de haute performance.La seconde partie de ce travail s’est donc orientée vers la conception de biocapteurs par utilisation de ces différents matériaux. La fiabilité du procédé de la construction de ces nanostructures poreuses a été validée par la conception de systèmes immunologiques pour la détection de l’anticorps de l’antitoxine du choléra et l’anticorps de la toxine de la dengue.Enfin, un dernier biocapteur enzymatique, s’appuyant sur l’utilisation de nano-bâtonnets de disulfure de tungstène, a été développé. Ce dernier permet la détection de deux molécules d’intérêts, à savoir le catéchol et la dopamine, par utilisation de la polyphénol oxydase. / The main purpose of this work was the design and the development of biosensors by using non-marking transduction methods, such as electrochemical impedance spectroscopy (EIS), for the detection of targets of interests. To this end, various molecular architectures have been developed to allow the transduction of the signal resulting from the recognition between the bioreceptor and its substrate, and thus lead to the detection of the target.The systems developed are based on the integration of nanomaterials, such as carbon nanotubes or tungsten disulfide, to ensure the immobilization of the biospecific entity at the surface of the sensor. The advantages of these materials are multiples, since they allow a very large increase in the specific surface area and are also used in the functionalization of the surface of the electrode. Indeed, one of the major challenges encountered in the development of biosensors is the strategy involved in the immobilization of the biospecific entity on the surface of the sensor.This work was initially interested in the realization and characterization of thin films of these nanomaterials as well as their transfer to the surface of an electrode. In this context, the aim is to design porous bioarchitectures based on electrogenerated functional polymers around carbon nanostructures allowing the penetration of large biomolecules such as antibodies to develop high-performance immunosensors.The second part of the work was oriented towards the design of biosensors using these different materials. The reliability of the process has been validated by the design of immunological systems for the detection of the anti-cholera toxin antibody and dengue toxin antibody.Finally, a last enzymatic biosensor, based on the use of tungsten disulfide nano-sticks, has been developed. The latter allows the detection of two molecules of interest, catechol and dopamin, by the use of polyphenol oxidase.

Pillared-graphene structure (PGS) is a novel three-dimensional structure consists of parallel graphene sheets that are separated by carbon nanotube (CNT) pillars that is proposed for efficient thermal management of electronics. For microscale simulations, finite element analyses were carried out by imposing a heat flux on several PGS configurations using a Gaussian pulse. The temperature gradient and distribution in the structures was evaluated to determine the optimum design for heat transfer. The microscale simulations also included conducting a mesh-independent study to determine the optimal mesh element size and shape. For nanoscale simulations, Scienomics MAPS software (Materials And Processes Simulator) along with LAMMPS (Large-scale Atomic/ Molecular Massively Parallel Simulator) were used to calculate the thermal conductivity of different configurations and sizes of PGS. The first part of this research included investigating PGS when purely made of carbon atoms using non-equilibrium molecular dynamics (NEMD). The second part included investigating the structure when supported by a copper foil (or substrate); mimicking production of PGS on copper. The micro- and nano-scale simulations show that PGS has a great potential to manage heat in micro and nanoelectronics. The fact that PGS is highly tunable makes it a great candidate for thermal management applications. The simulations were successfully conducted and the thermal behavior of PGS at the nanoscale was characterized while accounting for phonon scattering the graphene/CNT junction as well as when PGS is supported by a copper substrate.

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Organic field-effect transistors (OFETs) have attracted tremendous attention due to their flexibility, transparency, easy processiblity and low cost of fabrication. High-performance OFETs are required for their potential applications in the organic electronic devices such as flexible display, integrated circuit, and radiofrequency identification tags. One of the major limiting factors in fabricating high-performance OFET is the large interfacial barrier between metal electrodes and OSC which results in low charge injection from the metal electrodes to OSC. In order to overcome the challenge of low charge injection, carbon nanotubes (CNTs) have been suggested as a promising electrode material for organic electronic devices. In this dissertation, we study the effect of carbon nanotube (CNT) density in CNT electrodes on the performance of organic field effect transistor (OFETs). The devices were fabricated by thermal evaporation of pentacene on the Pd/single walled CNT (SWCNT) electrodes where SWCNTs of different density (0-30/um) were aligned on Pd using dielectrophoresis (DEP) and cut via oxygen plasma etching to keep the length of nanotube short compared to the channel length. From the electronic transport measurements of 40 devices, we show that the average saturation mobility of the devices increased from 0.02 for zero SWCNT to 0.06, 0.13 and 0.19 cm2/Vs for low (1-5 /µm), medium (10-15 /µm) and high (25-30 /µm) SWCNT density in the electrodes, respectively. The increase is three, six and nine times for low, medium and high density SWCNTs in the electrode compared to the devices that did not contain any SWCNT. In addition, the current on-off ratio and on-current of the devices are increased up v to 40 times and 20 times with increasing SWCNT density in the electrodes. Our study shows that although a few nanotubes in the electrode can improve the OFET device performance, significant improvement can be achieved by maximizing SWCNT/OSC interfacial area. The improved OFET performance can be explained due to a reduced barrier height of SWCNT/pentacene interface compared to metal/pentacene interface which provides more efficient charge injection pathways with increased SWCNT/pentacene interfacial area.