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Carbon nanotubes (CNTs) and graphene have shown promising potential as next-generation transparent conducting materials due to their high electrical and thermal conductance, flexibility and transparency in both visible and infrared spectral regions. In this study transparent and conductive thin films with a novel hemicellulose and double-walled carbon nanotube (HC-DWCNT) hybrid material were produced with spray-coating, droplet casting and vacuum filtration deposition methods. HC-DWCNT material is easily dispersed in water and usable for mass-production. These films showed good conductivity, stability at ambient air, very good transparency in the visible and excellent transparency in the infrared spectral regions while having few percent haze. The best sample had sheet resistance of 115 ± 9 ohm/sq and direct transmittance of 81.6 % at 550 nm wavelength. The properties of the prepared films were compared to CNT, graphene and their hybrid films reported by research groups by reviewing their fabrication methods and film performances. While many of these other films have shown higher shortterm quality, it was found that the performances of HC-DWCNT films were quite promising for future development considering the stability of the films and the fact that dopants or post-treatments were not used for enhancing the performance of the best samples.

Current thesis presents computational studies of the torsional twist in single walled carbon nanotubes (SWCNTs). Since SWCNTs can be viewed as rolled up graphene sheets, our aim is to explain their torsion constants via shear mod- ulus of graphene in pristine, and single- and double vacancy cases. In addition, fundamental energy gap response to torsion is investigated. Calculations of defected structures is computationally expensive as it requires larger simula- tion cell with large number of atoms. To reduce the cost of computations we take the advantage of chiral symmetry of nanotubes instead of translational one, and faster performance of density-functional tight-binding method compared to other computational methods. Shear modulus calculations show that its value approaches that of graphene for large diameter tubes and is most sensitive to size in case of armchair tubes. Vacancies diminish shear modulus for most of the nanotubes and concentration-induced decrease has linear character regardless of chirality. Studies on direction-dependent shearing of graphene reveals that in the presence of double vacancy shear modulus has the biggest fluctuations from its average value compared to pristine and single vacancy instances. Torsion significantly modifies electronic structure as well - metallic tubes undergo tran- sition to semiconducting state, during which band gap change is linear, peaking and decreasing to zero again for most of the tubes. Results give the ground for assumption that for large diameter tubes the peak values, reached during torsion, converge.

The interaction of light with carbon nanomaterials is the main focus of this thesis. I explore several nanostructured systems involving different allotropes of carbon, and characterize them both electrically, if applicable, and optically. Special attention is paid to search for plasmon-like excitations on the systems, or utilizing surface plasmons on characterization. The first objective is to achieve control of carbon nanotube (CNT) conductivity with surface plasmon polaritons (SPPs), which resulted in the first CNT field-effect transistor (FET) that can be gated definitively with SPPs. The second objective is the investigation of optical properties of various thin carbon-based molecular networks. Recently developed methods allow separation of different types of CNTs. Inspired by that, films consisting of only metallic-type single-walled (SW)CNTs were studied, which led to the discovery of a dispersive collective optical resonance in these thin films.With similar methods, conductive polymer films were also measured. To pursue the first goal, a FET was fabricated using a semiconducting-type SWCNT and a thin silver film as a backgate, on which SPPs were excited close to the CNT via the Kretschmann total internal reflection (TIR) configuration. As a result, the CNT FET could be gated at a low optical excitation power using SPPs, which most likely trigger desorption on the device, alter the Schottky barriers on CNT contacts and modulate the current. A scanning near-field optical microscope was also used to measure the local photosensitivity of the CNT FETs. Thin films of chirality-selected SWCNTs were measured with optical spectroscopy in TIR conditions, and a new collective excitation was discovered in metallictype SWCNTs. This dispersive phenomenon appeared only with a polarization not able to excite regular SPPs, and was linked to the excitonic transitions of the tubes. It shared features with SPPs such as the dependence on both the film thickness and the properties of the surrounding medium. Transparent conductive polymer films, some with graphene flakes, were also characterized, and their optical properties evaluated with TIR spectroscopy. No plasmonic or other peculiar resonances were detected, but the study led to a method to evaluate the optical anisotropy in thin polymer films. Using this method, it was possible to measure thick and uneven films, that are unsuitable for ellipsometry.