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Carbon nanotubes show a wide range of transport behavior that varies from ballistic to hopping regime, depending on the nature of disorder in the system. Minute variations in disorder can lead from weak to strong localization, and this yields complex and intriguing features in the analysis of transport data. This dissertation reports an experimental study of charge transport in optically transparent single-wall carbon nanotube (SWNT) networks and field-effect devices. The SWNT network comprises randomly aligned (bundles of) tubes that have both high optical transparency in visible, near-infrared (IR) wavelength range and high electrical conductivity. Various aspects of charge transport in this material including magnetotransport, high electric-field transport and gate induced field-effect are investigated and presented within a consistent framework. The temperature dependence of resistance suggests hopping transport in the network. Since strong localization is observed for the disordered network, the disorder is further characterized by a magnetotransport study and a pulsed electric-field dependence study down to low temperatures (1.3 K). The magnetoresistance (MR) has contributions from two quantum effects -a forward interference mechanism leading to a negative MR and a wavefunction shrinkage mechanism leading to positive MR. The temperature dependence of the coefficient of this negative MR is shown to follow inverse power-law dependence, in accordance with theoretical predictions. The intrinsic parameters obtained from this analysis suggest a transverse localization of charge on the bundle boundaries. The electric-field dependence, measured to high fields, follows the predictions of hopping transport in high electric-field regime. A scaling analysis indicates that electric-field and temperature play similar roles in the transport. The calculated dependence of ‘threshold electric-field’ is also suggestive of this competing process between phonons and electric-field. The applicability of the concept of ‘effective temperature’ is explored for this system; the electric-field induced suppression of MR is studied. The network resistance as well as the optical transparency of the network is modulated with gate voltage using an electrolyte gate dielectric. The gating can tune the absorptions associated with the van Hove singularities in the SWNT DOS and a time response study for this ‘smart window’ is done for the modulation. A novel technique is used to characterize organic and nanotube field-effect transistors and this allows estimation of device parameters such as transconductance and channel impedance. The ac impedance of the SWNT network is also investigated as a possible tool to probe network connectivity. To summarize, the role of disorder in charge transport is investigated for these novel transparent SWNT networks using magnetic-field, electric-field, temperature and field-effect dependent transport measurements.

Ce manuscrit présente une étude expérimentale autour de la synthèse des nanotubes de carbone et de leurs possibles intégrations dans des dispositifs. Les remarquables propriétés électroniques et optiques des nanotubes en font un matériau de choix pour entre autres, la nanoélectronique. Néanmoins, l’intégration des nanotubes dans des dispositifs performants est encore aujourd’hui un défi. Cela repose principalement sur la difficulté d’obtenir de grandes quantités de nanotubes mono-paroi avec des propriétés uniformes, propriétés qui sont définies par la structure du nanotube (i.e. leur angle chiral et leur diamètre). Ainsi, réaliser des synthèses de nanotube de carbone avec un contrôle de leur structure représente un point clé pour le progrès dans ce domaine.Nous avons donc mis en place une nouvelle méthode de synthèse de nanotubes de carbone basée sur la chimie de coordination et le dépôt chimique en phase vapeur activé par filament chaud. Cette synthèse permet la conception de nombreux nouveaux catalyseurs bimétalliques pour la croissance des nanotubes de carbone. Comme le procédé mis en place est très générique, des études paramétriques peuvent être réalisées de manière à mieux comprendre l’influence des différents paramètres de la croissance sur la structure des nanotubes obtenue. Nous discuterons ici du rôle de la température et de la composition chimique du catalyseur. Les nanotubes obtenus sont principalement caractérisés par spectroscopie Raman et par microscopies électroniques.Afin de valider les observations obtenues par spectroscopie Raman, les nanotubes synthétisés ont aussi été intégrés dans des dispositifs de type transistor à effet de champ. Une analyse des performances des transistors en fonction des différents nanotubes utilisés dans le canal est présentée.Enfin, les nanotubes intégrés dans ces transistors ont été fonctionnalisés avec un chromophore de ruthénium. Nous avons montré que cette fonctionnalisation nous permet de moduler, grâce à une impulsion lumineuse, la conductivité du dispositif sur trois ordres de grandeur. / This manuscript presents an experimental study around the single wall carbon nanotubes (SWCNT) synthesis and their possible integration in nanodevices. The unique electronic and optical properties of carbon nanotubes make them a choice material for various applications, particularly in nano-electronics.Nevertheless, their integration in effective devices is still a challenge. This is mainly due to the difficulty to obtain large quantity of SWCNT with uniform properties, defined by their structure (i.e. chiral angle and diameter). Therefore, structure controlled growth of SWCNTs is a key point for progress in this field.Here, we established a new synthesis approach based on coordination chemistry and hot-filament chemical vapor deposition. This approach allows the design of various bimetallic catalyst nanoparticles for the SWCNT growth. As the synthesis process is generic, parametric study can be performed in order to better understand the influence of the various parameters on the structure of the as-grown SWCNTs. In particular, we will discuss the role of the growth temperature and the chemical composition of the catalyst on the final SWCNTs structure. The obtained SWCNTs are mainly characterized by Raman spectroscopy and electronic microscopy.In order to validate the observations performed by Raman measurement, the synthesized SWCNTs have been also integrated in field effect transistors (FET) devices. An analysis of the performance of the FET-device as a function of the SWCNTs used in its channel will be presented.Finally, SWCNTs integrated in these transistors have been functionalized with an inorganic chromophore of ruthenium.We demonstrate that the functionalization of the SWCNTs leads to a three order of magnitude reversible switch of the device conductivity triggered by visible light.

Since many years, carbon nanotubes (CNTs) have been considered for a wide range of applications due to their outstanding mechanical properties. CNTs are tubular structures, showing a graphene like hexagonal lattice. Our interest in the calculation of the mechanical properties is motivated by several applications which demand the knowledge of the material behavior. One application in which the knowledge of the material behavior is vital is the CNT based fiber. Due to the excellent stiffness and strength of the individual CNTs, these fibers are expected to be a promising successor for state of the art carbon fibers. However, the mechanical properties of the fibers fall back behind the properties of individual CNTs. It is assumed that this gap in the properties is a result of the van-der-Waals interactions of the individual CNTs within the fiber. In order to understand the mechanical behavior of the fibers we apply a molecular mechanics approach. The mechanical properties of the individual CNTs are investigated by using a modified structural molecular mechanics approach. This is done by calculating the properties of a truss-beam element framework representing the CNT with the help of a chemical force field. Furthermore, we also investigate the interactions of CNTs arranged in basic CNT assemblies, mimicking the ones in a simple CNT fiber. We consider the van-der-Waals interactions in the structure and calculate the potential surface of the CNT assemblies.