This thesis describes the growth of Sp2 carbon materials - namely graphene and carbon nanotube (CNT) materials using a chemical vapour deposition (CVD) process. A novel CVD process tool based on a photothermal process (PT-CVD) that differs from standard thermal CVD has been developed. This thesis reports the investigations into the properties of the deposited carbon nanomaterials and applications that exploit their electronic properties. The first investigation is into the growth of vertically aligned MWCNT forests. Growth of CNTs at 370°C by a one-step PT-CVD method was demonstrated. The growth rate can reach ~ 1.3 um/min, which is faster than most other reported thermal CVD methods. The use of bimetallic catalyst (Fe/Ti) and the use of rapid thermal process are the keys to this process. AFM topography studies showed that the fast top-down heating mode of the PT-CVD leads to the formation of a Fe/Ti uniform solid solution, which is believed to improve the CNT growth. These CNTs are composed of a few layer crystalline graphene sheets with a 5-6 nm diameter. Raman scattering provides supporting evidence that the as-grown CNTs are of high quality, better than some CNTs grown at higher temperatures by traditional CVD methods. CVD growth of graphene was investigated using Cu foils as substrate, with the field- effect in the graphene subsequently demonstrated by transferring it to a back-gate bottom contact transistor arrangement using poly-4-vinyl-phenol gate dielectric as an alternative to oxide based insulators. This graphene transistor showed a simple, inexpensive fabrication method that is completely compatible to large scale fabrication of organic devices, to demonstrate a field effect hole mobility of 37 cm2/ Vs. Despite the mobility being lower than that found in exfoliated graphene, it demonstrates the potential of a graphene based all carbon transistor for large area electronics. The fabrication and electrical performance of a 3 terminal graphene device is further reported. This device displayed characteristics similar to a p-type graphene FET. While past investigations of distortion and saturation in transfer characteristics of graphene FET indicated that metal-graphene interaction may be the controlling mechanism, this device operation is based on the design of transferring graphene onto a Diamond-like- carbon DLC/p-Si heterostructure with Si as the back contact and with the DLC acting as the dielectric support in contact to graphene. Thus, this provided a mechanism for the DLC/p-Si heterojunction to moderate the I-V characteristics of this device, resulting in a p-type only conduction process in graphene that is also saturable. Following the work on using conventional thermal CVD (T-CVD) for graphene growth, we demonstrated the possibility of using the PT-CVD to develop a graphene growth process. It is found that the non-thermal equilibrium nature of PT -CVD process resulted in a much shorter duration in both heating up and cooling down, thus allows the reduction of the overall growth time for graphene. The choice of performing growth on Ni also allows for the alleviation of hydrogen blister damage that is commonly encountered during growth on Cu substrates. To characterize the film's electrical and optical properties, pristine PT -CVD grown graphene was used as the transparent electrode material in an organic photovoltaic devices (OPV) and is found to be comparable to that reported using pristine graphene prepared by conventional CVD.

Carbon is one of the most versatile materials available to man, for hundreds of years the 3D forms of carbon (diamond and graphite) have been exploited for their electrical and physical properties, however only in recent decades have the OD (fullerenes), 1D (nanotubes) and 2D (graphene) forms of carbon been available to study and use for new technologies. The experimental realisation of single layer (SLG) and few layer (FLG) graphene has led to an explosion of interest in the properties and capabilities of this material. Although single layer graphene had been considered theoretically a number of years earlier, it had long been the consensus that a single atom thick material would not be stable in the free state.

Au cours des prochaines années, neuf centrales nucléaires de type UNGG (Uranium Naturel Graphite Gaz) devront être démantelées en France. Ces centrales utilisent le graphite comme modérateur et réflecteur de neutrons. Pendant leur exploitation, celui-ci est activé. Leur démantèlement conduira à 23000 tonnes de déchets de graphite irradiés à gérer. Ce travail focalise sur deux radionucléides contenus dans ces déchets : le 36Cl et le 3H. Le 36Cl a l'une des demi-vies les plus longues (301 000 ans). Par contre, le 3H a une demi-vie plus courte (12 ans), mais contribue beaucoup à l'activité initiale des déchets. Différentes données expérimentales suggèrent que le 36Cl et le 3H sont piégés à différents endroits du graphite, comme les boucles de dislocation, les surfaces ou les joints de grains. Le seul mécanisme de migration des radionucléides est le relâchement. Pour cette raison, il est important de comprendre quels sont les pièges et les différentes conditions du relâchement.Le graphite UNGG a une structure complexe, hétérogène et multi-échelle qui diffère du monocristal idéal du graphite. Cependant, pour comprendre les données macroscopiques, les études théoriques à l'échelle nanoscopique et microscopique sont des outils importants, même si elles reposent sur des modèles plus simples. Dans cette thèse, une approche multi-échelle a été utilisée afin d’étudier les interactions des radionucléides avec le graphite ainsi que les mécanismes de diffusion et de piégeage à l'échelle du nm-μm.Les interactions du 3H et du 36Cl avec différents défauts du graphite ont été étudiées dans le cadre de la théorie fonctionnelle de la densité (DFT). L'hydrogène forme une liaison covalente avec le graphite massique ainsi qu'avec ses surfaces (001), (100) et (110). Plusieurs reconstructions de surface ont été explorées. Les résultats montrent que les hypothèses existantes sur le piégeage de l'hydrogène doivent être affinées. Le comportement du Cl est plus complexe. Sa chimisorption est observée sur les surfaces (100) et (110). Cependant, sur la surface (001), le Cl interagit par transfert de charge. Le Cl2 n'interagit que par interactions de van der Waals avec celle-ci. Le Cl2 se dissocie dans le graphite massique.Les diffusions du H et du Cl dans le graphite irradié ont été étudiées en effectuant des simulations de dynamique moléculaire. Les résultats ab initio ont été utilisés pour développer des potentiels de type « bond order » afin de modéliser l'interaction des radionucléides avec la matrice de graphite, qui possède des contributions à court et à long portée. Pour le Cl, un nouveau potentiel a été paramétré qui reproduit toutes les données obtenues au niveau DFT. Pour les interactions 3H-graphite, les potentiels AIREBO/M, pour les interactions C-H, et LCBOP, pour les interactions C-C, ont été utilisés.Pour évaluer l'influence de la structure complexe du graphite UNGG sur le comportement des radionucléides, plusieurs modèles atomiques ont été utilisés pour rendre compte de cette diversité, tels que les surfaces, les joints de grains et les nanopores.Pour le Cl, des simulations d'irradiation ont été réalisées pour une gamme d’énergie allant de 1 à 10 keV et une gamme de température de 200 à 500ºC. Les dépendances à la température et à la direction d'irradiation ont été étudiées. D’une façon générale, les dommages causés par l'irradiation perpendiculaire aux surfaces augmentent avec la température. L'irradiation à des angles d’incidence <90º aux surfaces peut causer plus ou moins de dommages par rapport à l'irradiation perpendiculaire selon le type de surface.Les diffusions du H et du Cl montrent que tous les bords de cristallites avec des liaisons pendantes sont des pièges. Pour le Cl, la diffusion dans le graphite nanoporeux a révélé deux emplacements préférés: les bords des cristallites où le Cl forme une liaison covalente et les coins des microfissures où le Cl interagit par transfert de charge. / In the upcoming years, nine nuclear UNGG (Uranium Naturel Graphite Gaz) power plants will have to be dismantled in France. In these power plants, nuclear graphite was used as a neutron moderator and reflector, and was activated during operation. The dismantlement will lead to 23000 tons of irradiated graphite waste, which will have to be managed. The graphite is classified as a nuclear waste containing radionuclides with low activity and long half-life. Two radionuclides are the focus of this work: 36Cl and 3H. 36Cl has one of the longest half-lives (about 301000 years) among the waste's radionuclides. 3H has a shorter half-life (12 years), but contributes significantly to the waste’s initial activity. Previous experiments suggest that both, 36Cl and 3H, are mainly fixed at different traps in graphite, which are defective structures, such as dislocation loops, surfaces, or grain boundaries. Since the only significant migration mechanism of these radionuclides is release, it is important to understand where the traps are located and the conditions of the release.UNGG graphite has a complex heterogeneous multi-scale structure which differs substantially from an ideal monocrystal of graphite. However, in order to understand macroscopic data, theoretical studies at the nano- and microscopic scale are an important tool to explain underlying phenomena even though they rely on simpler models due to the limitations of computation power. A multi-scale approach was therefore applied to study the local interactions of the radionuclides with graphite as well as diffusion and trapping mechanisms on the nm-μm length scale.First, the interaction of 3H and 36Cl with defects in graphite was studied with density functional theory (DFT). Hydrogen interacts covalently with bulk graphite as well as with the studied surfaces (001), (100), and (110). Several surface reconstructions were investigated: arch-type reconstructions and in-plane reconstructions. The results show that the existing hypothesis on the trapping of hydrogen needs to be refined. The behavior of Cl is more complex. On the (100) and (110) surface chemisorption is observed. However, on the (001) surface a strong charge transfer interaction is observed for Cl. In contrast to that, Cl2 only interacts via weak van der Waals interactions with this surface. In bulk graphite Cl2 dissociates.The diffusion of H and Cl in irradiated graphite has been investigated by performing molecuar dynamics simulations. The ab initio results were used to develop bond order potentials to model the interaction of radionuclides and the graphite matrix, which attributes for short and long range interactions. For Cl, a new potential has been parameterized which is able to describe all aspects obtained with DFT. For the 3H-graphite interactions, the bond order potential AIREBO/M was used for C-H interactions. For C-C interactions the LCBOP potential was used.To evaluate the influence of the complex heterogeneous structure of the UNGG graphite on the radionuclide's behavior, several different atomic models were studied to account for this diversity such as surfaces, grain boundaries and nanopores.For Cl, irradiation simulations of different systems were performed up to an energy of 10 keV for the primary knock-on atom (PKA), and in a temperature range of 200 to 500ºC. The dependence on temperature and irradiation direction was investigated. In general, direct irradiation damage increases with temperature. Irradiation at incident angles <90º can create more or less damage compared to the perpendicular one depending on the surface type.Diffusion of H and Cl along surfaces shows that all crystallite edges with dangling bonds can serve as traps. For Cl, diffusion in nanoporous graphite revealed two preferred locations : First, the crystallite edges where Cl forms strong covalent; second, the corners of microcracks where Cl interacts via charge transfer.