This thesis presents the preparation of vertically aligned carbon nanotubes using porous anodic alumina templates via thermal chemical vapour deposition. The characteristics of prepared carbon nanotubes in terms of tube diameter, length, density, uniformity and alignment were investigated. The formation of porous anodic alumina membranes was studied. In order to prepare well-ordered porous anodic alumina templates, three approaches towards anodization of aluminium were examined. Effects of Al surface morphology and anodization conditions on the formation of the porous anodic alumina membrane were investigated. Co catalyst was electrochemically deposited at the bottom of the pores of porous anodic alumina templates by applying an alternating current. Prior to the AC electrodeposition, the barrier layer at the base of the pores was thinned in order to facilitate the deposition process. The thinning effect of three barrier layer thinning approaches was examined. The effect of electrodeposition duration on the pore filling was investigated. Carbon nanotubes were grown using Co-loaded porous anodic alumina templates via thermal chemical vapour deposition of C₂H₄. Effects of the presence of the Co catalyst, the amount of Co deposited at the bottom of the pores and the presence of water vapour on the carbon nanotube growth were examined. The characteristics of the grown carbon nanotubes in terms of tube diameter, length, density, uniformity and alignment were investigated. Moreover, a post-treatment after the carbon nanotube growth was proposed in order to obtain vertically aligned carbon nanotubes. In addition, vertically aligned carbon nanotubes were grown on Si chips. Two methods were used to prepare a catalytic layer on the Si chips for carbon nanotube growth.

It has been known that a significant part of the thermal budget of an electronic package is occupied by the thermal interface material which is used to join different materials. Research in reducing this resistance through the use of vertically aligned multiwall carbon nanotube based thermal interface materials is presented. Transferred arrays anchored to substrates using thermal conductive adhesive and solder was analyzed through a steady-state infrared measurement technique. The thermal performance of the arrays as characterized through the measurement system is shown to be comparable and better than currently available interface material alternatives. Furthermore, a developed parametric model of the thermal conductive adhesive anchoring scheme demonstrates even greater potential for improved thermal resistances. Additionally, a developed transient infrared measurement system based on single point high speed temperature measurements and full temperature mappings is shown to give increased information into the thermophysical properties of a multilayer sample than other steady-state techniques.

This study sought to improve the performance of Si-based anodes through the use of hierarchically structured electrodes to provide the nanoscale framework needed to accommodate large volume changes while controlling the interfacial area – which affects solid-electrolyte interphase (SEI) formation. To accomplish this, electrodes were fabricated from vertically aligned carbon nanotubes (VACNT) infiltrated with silicon. On the nanoscale, these electrodes allowed us to adjust the surface area, tube diameter, and silicon layer thickness. On the micro-scale, we have the ability to control the electrode thickness and the incorporation of micro-sized features. Treatment of the interfacial area between the electrolyte and the electrode by encapsulating the electrode controls the stabilization and reduction of unstable SEI. Si-VACNT composite electrodes were prepared by first synthesizing VACNTs on Si wafers using photolithography for catalyst patterning, followed by aligned CNT growth. Nano-layers of silicon were then deposited on the aligned carbon nanotubes via LPCVD at 200mTorr and 535°C. A thin copper film was used as the current collector. Electrochemical testing was performed on the electrodes assembled in a CR2025 coin cell with a metallic Li foil as the counter electrode. The impact of the electrode structure on the capacity at various current densities was investigated. Experimental results demonstrated the importance of control over the superficial area between the electrolyte and the electrode on the performance of silicon-based electrodes for next generation lithium ion batteries. In addition, the results show that Si-VACNT height does not limit Li transport for the range of the conditions tested.

Carbon nanotube (CNT) forests have outstanding thermal, electrical, and mechanical properties, which have generated significant interest as thermal interface materials (TIMs). Some drawbacks to using CNTs as TIMs include poor substrate adhesion, high interface resistances inhibiting thermal transport, and lack of electrical insulation in electronic component applications. It is thus useful to be able to modify CNTs to reduce their electrical conductivity while maintaining high thermal conductivity and interface conductance, and high mechanical compliance. A recent report suggests that nanoscale oxide coatings could be applied to CNTs in forests without changing the mechanical deformation behavior of the forests. Oxide coatings could also provide environmental stability as well as better adhesion to the substrate compared to pristine CNT forests. In this study, we investigated thermal and electrical resistance of CNT forests with an oxide coating. Low-pressure chemical vapor deposition (LPCVD) was used to produce CNTs on high-conductivity Si substrates. Plasma-enhanced atomic layer deposition (PALD) was used to deposit Al2O3 on individual CNTs in forests. This process was facilitated by O2 plasma pretreatment to functionalize the surface of the CNTs and nucleate oxide growth. Several analytical techniques were used to characterize the CNT-oxide composites, including scanning electron microscopy, Raman and X-ray photoelectron spectroscopy. Thermal conductivity and thermal interface resistance were measured using a modified photoacoustic technique. The oxide coating had no significant effect on the effective thermal conductivity of the forests, in contrast to expectations of increased phonon scattering. Electrical resistivity measurements were made and a threefold increase was observed for the oxide-coated forests. This approach could emerge as a promising route to create a viable TIM for thermally conductive and electrically insulating applications.

Les supercondensateurs, basés sur des cycles rapides de charge/décharge d’ions, sont une solution intéressante pour répondre à la problématique du stockage d’énergie. Les nanomatériaux carbonés, couplés ou non à des matériaux actifs, présentent des potentialités en tant qu’électrode comparativement au carbone activé couramment utilisé. Dans le cadre d’un laboratoire commun, le CEA, Nawatechnologies et les universités de Tours et Cergy, cherchent à développer des électrodes plus efficaces mettant en œuvre des tapis de nanotubes de carbone verticalement alignés (VACNT) sur collecteur d’aluminium. C’est dans ce contexte que se situe ma thèse CIFRE avec comme objectif le développement et la compréhension de la croissance de nanotubes alignés sur feuille d’aluminium par une méthode de dépôt chimique en phase vapeur (Chemical Vapor Deposition (CVD)) assistée par aérosol. Au démarrage de ma thèse, cette technique était maîtrisée par le LEDNA (UMR-NIMBE), mais seulement pour des températures relativement élevées (>800°C). L’enjeu était donc d’étendre cette méthode pour répondre à l’utilisation de l’aluminium comme substrat, ce qui nécessité un abaissement de la température de croissance des VACNT au-dessous du point de fusion de l’Al (660°C). Dans ce cas, les précurseurs catalytiques et carbonés utilisés à plus haute température ne se décompose pas efficacement, c’est pourquoi il a été nécessaire d’ajouter deux composés : l’hydrogène qui favorise la décomposition du précurseur catalytique et l’acétylène dont la décomposition thermique et catalytique est plus favorable à basse température. La thèse est structurée autour de trois axes : l’optimisation du procédé de synthèse, la compréhension des mécanismes de croissances et une étude visant à remplacer l’acétylène par des précurseurs biosourcés. / Supercapacitors, with fast charge / discharge cycles, represent an interest for energy storage. Carbon nanomaterial have a great potential as electrode as compared to common activated carbon based electrodes. CEA, Nawatechnologies, university Tours and Cergy develop electrodes based on vertically aligned carbon nanotubes (VACNT) on aluminium substrate in a joint laboratory. In this context, the aim of my thesis is to develop and understand the growth of VACNT on aluminum foil by aerosol assisted Chemical Vapor Deposition (CVD). At the beginning of my thesis, this technique was mastered by the LEDNA (UMR-NIMBE), but only for relatively high temperatures (>800°C). The challenge was therefore to extend this method to respond to the use of aluminium as a substrate, which necessitated a lowering of the growth temperature of VACNT below the melting point of Al (660°C). In this case, the catalytic and carbonaceous precursors used at higher temperatures do not decompose effectively, so it was necessary to add two compounds : hydrogen which increases decomposition of the catalyst precursor [3] and acetylene with a catalytic and thermal decomposition more favorable around 600° C [5]. Therefore, the approach in this work is first to identify the most relevant synthesis parameters to reach VACNT growth at such a low temperature by varying them and analyzing subsequently the products obtained. Moreover, attention is paid on study of Al surface before growth or during the initial steps of VACNT growth, and of CNT / Al interface to understand VACNT formation mechanisms at lower temperatures.

By structural health monitoring (SHM) of composite structures, their sustainability, safety and economics can be improved. On one hand, it enables using components to their full life or having them replaced early before otherwise unforeseen failure. On the other hand, it may make structures lighter as designs with smaller safety margins would be possible. Cryogenic liquid hydrogen tanks for aircraft would need to become lighter to enable such fossil-free aviation, which could require SHM. Vertically aligned carbon nanotubes (VACNT) have been used as embedded sensors in composites for temperature and strain sensing while other architectures of nanotubes have been used to detect fatigue damage. In this work, VACNT embedded in carbon fibre/epoxy composites are cycled both thermally and mechanically to investigate their suitability to detect damage in composite cryogenic tanks. It was found VACNT retain their strain sensing ability after cycling to cryogenic temperatures and that a relationship of increasing electrical resistance to increased cycling and damage is possible. That indicates VACNT are suitable for SHM of cryogenic tanks, but more testing and better electrical insulation of the VACNT is needed to confirm this. / Genom att övervaka kompositstrukturers livslängd med structural health monitoring (SHM), kan miljöhållbarheten, säkerheten och ekonomin i att använda dem förbättras. Å ena sidan möjliggör det att komponenter används sin fulla livslängd eller ersätts innan annars oförutsedda skador leder till kollaps. Å andra sidan kan det göra strukturer lättare eftersom designer med mindre säkerhetsmarginaler vore möjliga. Kryotankar för flytande väte i flygplan behöver bli lättare för att möjliggöra sådant fossilfritt flygande, vilket skulle kunna kräva SHM. Vertikalt riktade kolnanorör (vertically aligned carbon nanotubes, VACNT) har använts som inbäddade temperatur- och töjningssensorer i kompositer och andra kolnanorörsmaterial har använts för att detektera utmattningsskador. I detta arbetet har VACNT inbäddat i kolfiber och epoxi cyklats både termiskt och mekaniskt för att undersöka dess lämplighet som sensorer för skadedetektering i kryotankar. Det konstaterades att VACNT behåller sin töjningsdetekteringsförmåga efter termisk cykling till kryotemperatur och att det är möjligt att ett förhållande om ökande resistans med ökande cykling och skada kan finnas. Det indikerar att VACNT vore lämpliga för SHM i kryotankar, men mer provning och bättre elektrisk isolering av VACNT behövs för att bekräfta det.

Les travaux de cette thèse ont porté sur l'élaboration, l'optimisation et l'étude d'électrodes composites de nanotubes de carbone verticalement alignés (VACNT) sur un collecteur d'aluminium et modifiés par l'oxyde de manganèse (MnO₂). Les VACNT synthétisés par voir CVD à basse température (580°C:) directement sur le collecteur ont permis d'obtenir des tapis de NTC parfaitement alignés d'une épaisseur allant de 20 à 80 µm et possédant des densités de 10¹¹ NTC.cm² et dont le taux de catalyseur (Fe) est inférieur à 1%. Leur modification par du MnO2 permet d’accroître leur capacité de stockage électrochimique. Afin de réaliser un enrobage optimal des VACNT par le MnO₂, différents précurseurs de l'oxyde ainsi que diverses méthodes(dépôts électrochimiques, chimiques, CVD) ont été utilisées et optimisées. Les composites élaborés ont ensuite été étudiées en tant que matériau d'électrode pour la réalisation de supercondensateurs asymétriques eu milieux aqueux. / This thesis was focused on the development, optimization and study of composite electrodes of vertically aligned carbon nanotubes (VACNT) on an aluminum collector and modified with manganese oxide (MnO₂).VACNT were synthesized by a CVD process at low temperature (580° C) directly on the collector. Perfectly aligned CNT forest with a thickness of 20 to 80 μm were obtained with high densities of 10¹¹ NTC.cm² and whose catalyst (Fe) content is less than 1%. Their modification with MnO₂ increase their electrochemical storage capacity. In order to achiew optimal coating of VACNT by MnO₂, different precursors of the oxide and various methods ( electrochemical, chemical, CVD) were used and optimized. Composites were studied as electrode material for the realization of asymmetric supercapacitors in aqueous media. In addition, structurals, morphologicals and electrochemicals analyzes carried out on the different materials allowed a better understanding of the role of the elaboration's conditions on the properties of the VACNT/MnO₂ composites obtained.

Exploring new technologies that can meet the world’s energy demands in an efficient and clean manner is critically important due to the depletion of natural resources and environmental concerns. Dye-sensitized solar cells (DSSCs) are low-cost and clean technology options that use solar energy efficiently and are being intensively studied. How to further reduce the cost of this technology while enhancing device performance is one of the demanding issues for large scale application and commercialization of DSSCs. In this research dissertation, four main contributions are made in this regard with the motivation to reduce further cost of DSSC technology. Firstly, ~10% efficiencies were achieved after developing understanding of key concepts and procedures involved in DSSCs fabrication. These efficiencies were achieved after step-by-step modifications in the DSSC design. Secondly, carbon nanotubes (CNTs) were successfully employed as an alternative to Pt in the counter electrodes of DSSCs. DSSCs fabricated with CNTs were ~86% as efficient as Pt-based cells. Non-aligned CNTs were successfully grown using four different CVD methods and finally, multi-walled vertically aligned CNTs (MW-VACNTs) were synthesized using water-assisted chemical vapor deposition (WA-CVD). Thirdly, carbon derived from pyrolysis of nanocrystalline cellulose (NCC) was successfully employed in counter electrodes of DSSCs instead of Pt. DSSCs with NCC were ~58% as efficient as Pt-based DSSCs. Fourthly, novel organic metal-free dyes were designed and employed instead of commonly used Ru-based dyes. DSSCs with these novel sensitizers were ~62% as efficient as those using the conventional Ru-based dyes. Characterization techniques including current-voltage measurements, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetery (CV), thermogravimetric analysis (TGA), small angle x-ray scattering (SAXS), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) were used.