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Carbon nanotubes have become one of the most important building blocks critical to nanotechnology. Carbon nanotubes have attracted the interests of many scientists since their discovery due to their remarkable properties and have been widely used for various applications. However, the bottle neck in nanotube research has been the lack of a cheap, continuous and fast nanotube production method. This study concerns a reactor where nanotubes are continuously deposited on a carbon substrate using arc discharge at atmospheric pressure. This process appears to be the first to employ an arc discharge as the method for continuous mass deposition of nanotubes on a substrate. This nanotube deposition method eliminates the generic multistep process of nanotube deposition on substrates for its use in many applications. The effect of various parameters influencing growth and morphology of nanotubes on the substrate in the arc reactor (inter-electrode gap, atmosphere composition, current density, flushing, substrate type and speed and catalyst) have been systematically explored to optimise nanotube growth. The field emission properties of the nanotube laden substrate are studied for use and applicability as electron emitters. The nanotube samples demonstrated superior emission properties, low turn-on field and excellent current stability when put into applications such as a luminescent tube and an ionisation sensor. Theoretical modelling of the behaviour of a single nanotube during field emission was performed using finite element analysis software (COMSOL 3.2) to understand the effect of nanotube length, diameter, and vacuum gap on an individual nanotube. The results reveal that resistive heating (temperature) limits the maximum current carried by an individual nanotube. Furthermore, a new growth model is introduced to explain the formation of nanotubes from graphene fragments and nanocrystallites, due to polarisation of carbon species near the electrode surface suggesting that carbon vapour is unlikely to be responsible for nanotube growth.

Multi-walled carbon nanotubes (MWNTs) are a relatively new allotrope of carbon that have potentially useful properties that may improve polymer composites. The work of this thesis explores the interactions between MWNTs and functionalized MWNTs within epoxy matrix and the properties of the MWNT/epoxy composite. These interactions were characterized with an emphasis on finding how well the MWNT/epoxy composite flows and how conductive it is after curing.

Carbon nanotubes have been studied for nearly two decades and their amazing properties continue to spur intense investigation in the area of polymer composites. In terms of potential commercialization, mutiwall carbon nanotubes (MWCNTs) are currently the most prevalent and economically viable form of nanotubes. Uncovering innovative means to take full advantage of their properties remains a fundamental issue. In this thesis, viability of their use to reinforce polymeric systems is reported. Acrylonitrilebutadiene- styrene (ABS) was used as the host matrix. MWCNTs were introduced to the ABS matrix via melt compounding. The resulting composite was thoroughly rheologically, thermally, and mechanically characterized. Several applications were also experimentally studied. The composites fatigue performance is measured and compared to a typical micron sized carbon fiber. These results indicate that both the nano and micron scale carbon fibers reduce the resistance to fatigue failure. The mechanism of failure in both cases appears to be different and is discussed. The use of microwave energy is investigated for the use of heating purposes. Results show a distinct advantage over conventional heating methods. Microwaves allow for volumetric, fast, selective, and controllable heating of the ABS system.

A cathode structure was demonstrated that utilizes aligned carbon nanotubes (CNTs) to improve the thermionic electron emission by increasing the field enhancement of the cathode surface. Aligned CNTs were grown on the surface of a tungsten substrate by plasma enhanced chemical vapor deposition. The tungsten-CNT structure was further coated with a thin film of low work function emissive materials by magnetron sputtering. Numerous cathodes with varying CNT morphology and oxide layer thickness were created. The field and thermionic emission of the cathodes were tested in order to study the effects of the surface properties on the emission characteristics. It was observed that the introduction of CNTs into an oxide cathode structure improves both the thermionic and field emission, even in cathodes with relatively low field enhancement factors. Because of the high field enhancement factors that are available for CNTs, there remains a potential for dramatically improved electron emission. / Department of Physics and Astronomy

Conductive polymers are promising pseudo capacitive materials as they feature both good conductivity and high capacitance. Formation of composite between conductive polymers and carbon nanotubes is a proven technique in enhancing the material electroactivity. In-situ polymerization of conductive polymers includes polyaniline, polypyrrole and PEDOT: PSS and composite with MWCNT has been successfully achieved. Composites fabricated by using different dopants and their performance were studied. Excellent achieved capacitive performance is due to the combination of pseudo capacitance and double layer capacitance. The MWCNTs content has significant influence on the morphology and structure of the polymerized ECP in the composite. And therefore affects the material conductivity and the charge storage performance. Two electrodes cell performance shows that Ppy/MWCNT composite shows a more promising performance as electrode materials for EC applications in contrast to PANI/MWCNT and PEDOT: PSS/MWCNT composites.

Conductive polymers are promising pseudo capacitive materials as they feature both good conductivity and high capacitance. Formation of composite between conductive polymers and carbon nanotubes is a proven technique in enhancing the material electroactivity. In-situ polymerization of conductive polymers includes polyaniline, polypyrrole and PEDOT: PSS and composite with MWCNT has been successfully achieved. Composites fabricated by using different dopants and their performance were studied. Excellent achieved capacitive performance is due to the combination of pseudo capacitance and double layer capacitance. The MWCNTs content has significant influence on the morphology and structure of the polymerized ECP in the composite. And therefore affects the material conductivity and the charge storage performance. Two electrodes cell performance shows that Ppy/MWCNT composite shows a more promising performance as electrode materials for EC applications in contrast to PANI/MWCNT and PEDOT: PSS/MWCNT composites.

Nowadays, cancer treatment and tissue regeneration have attracted large amount of attention. Single Wall Carbon Nanotubes (SWNT) possess large surface area and outstanding optical and electrical performance, making it a promising component in cancer therapy and tissue reengineering systems. In this study, four disease treating systems based on SWNT are developed. They are pH-sensitive poly(ethylene glycol)-doxorubicin(PEG-DOX)@SWNT drug release system, temperature sensitive SWNT hydrogel, SWNT based biocompatible magnetic hydrogel and biocompatible SWNT-gelatin-F127-cysteamine hydrogel for tissue engineering. The successfully synthesized target compounds are characterized by FTIR. The in vitro release of drugs from the drug release systems is evaluated upon changes of pH values and the laser scanning. The effect of cancer treatment systems on specific kind of cells are examined by confocal laser scanning microscopy (CLSM). The results indicate that all of the four systems show great potential in the biomedical applications especially in disease therapy applications.

Single-walled carbon nanotubes (SWNTs), with their superior combination of electrical and mechanical properties, have drawn attention from many researchers for potential applications in electronics. Many SWNT-based electronic device prototypes have been developed including transistors, interconnects and flexible electronics. In this thesis, a fabrication method for patterned SWNT networks and devices based on colloidal lithography is presented. Patterned SWNT networks are for the first time formed via solution deposition on a heterogeneous surface. This method demonstrates a simple and straight-forward way to fabricate SWNT networks in a controllable manner. Colloidal sphere monolayers were obtained by drop-casting from solution onto clean substrates. The colloidal monolayer was utilized as a mask for the fabrication of patterned SWNT networks. SWNT networks were shown to be patterned either by depositing SWNT solutions on top of a colloidal monolayer or by depositing a mixed SWNT-colloidal sphere aqueous suspension on the substrates. Colloidal monolayers were examined by optical microscopy and it was found that the monolayer quality can be affected by the concentration of colloids in solution. Polystyrene colloidal solution with concentration of 0.02 wt% ~ 0.04 wt % was found optimal for maximum coverage of colloidal monolayers on SiO2 substrates. After removing the colloidal spheres, the topology of the patterned SWNT networks was characterized by atomic force microscopy and scanning electron v microscopy. Two-dimensional ordered arrays of SWNT rings and SWNTs interconnecting the SWNT rings were observed in the resulting network structure. The height of the rings was about 4-10 nm and the diameter was about 400 nm. In some samples, mesh-like patterned SWNT networks are also observed. It is hypothesized that the capillary forces induced by Van der Waals interaction at liquid/air/solid interfaces play an important role during the formation of the patterned SWNT networks. Raman spectroscopy was also employed to identify the chirality and diameter of the SWNTs in the networks. Both metallic and semiconducting SWNTs were found in the networks and the diameter of the SWNTs was about 1 to 2 nm. The electrical properties of SWNT networks, including random SWNT networks, partially patterned SWNT networks and fully patterned SWNT networks were characterized by a probe station and a Keithley 4200 semiconductor measurement system. The random SWNT networks had two-terminal resistance varying between several MΩ to several hundred MΩ. Field effect behavior was observed in some devices with relatively high resistance and nonlinear I-V curves. Those devices had on/off ratio of less than 100. There was significant leakage current in the ―off‖ state likely due to metallic tube pathways in the networks. The partially patterned SWNT networks had resistance that varied from 20 KΩ to 10 MΩ, but did not display field effect behavior in our studies. The resistance of the patterned SWNT networks was about 10 MΩ - 100 MΩ. The electrical characteristics of the patterned SWNT networks as thin film transistors were investigated, and the on/off ratio of the devices varied from 3 to 105. The upper limit of mobility in the devices was about ~ 0.71 – 5 cm2/V·s. The subthreshold slope of patterned SWNT network FETs can be as low as 210 meV/dec. / Graduate / 0544

The mounting concern for renewable energies from ecologically conscious alternatives is growing in parallel with the demand for portable energy storage devices, fuelling research in the fields of electrochemical energy storage technologies. The supercapacitor, also known as electrochemical capacitor, is an energy storage device possessing a near infinite life-cycle and high power density recognized to store energy in an electrostatic double-layer, or through a pseudocapacitance mechanism as a result of an applied potential. The power density of supercapacitors far exceeds that of batteries with an ability to charge and discharge stored energy within seconds. Supercapacitors compliment this characteristic very well with a cycle life in excess of 106 cycles of deep discharge within a wide operational temperature range, and generally require no further maintenance upon integration. Conscientious of environmental standards, these devices are also recyclable. Electrochemical capacitors are currently a promising candidate to assist in addressing energy storage concerns, particularly in hybridized energy storage systems where batteries and supercapacitors compliment each other’s strengths; however specific challenges must be addressed to realize their potential. In order to further build upon the range of supercapacitors for future market applications, advancements made in nanomaterial research and design are expected to continue the materials development trend with a goal to improve the energy density through the development of a cost-efficient and correspondingly plentiful material. However, it is important to note that the characteristic power performance and exceptional life-cycle should be preserved alongside these efforts to maintain their niche as a power device, and not simply develop an alternative to the average battery. It is with this clear objective that this thesis presents research on an emerging carbon material derived from an abundant precursor, where the investigations focus on its potential to achieve high energy and power density, stability and integration with other electroactive materials. Activated carbons have been the dominant carbon material used in electric double-layer capacitors since their inception in the early 1970s. Despite a wide range of carbon precursors and activation methods available for the generation of high surface area carbons, difficulties remain in controlling the pore size distribution, pore shape and an interconnected pore structure to achieve a high energy density. These factors have restricted the market growth for supercapacitors in terms of the price per unit of energy storage. Activation procedures and subsequent processes for these materials can also be energy intensive (i.e. high temperatures) or environmentally unfriendly, thus the challenge remains in fabricating an inexpensive high surface-area electroactive material with favourable physical properties from a source available in abundance. Double-layer capacitive materials researched to replace active carbons generally require properties that include: high, accessible surface-area; good electrical conductivity; a pore size distribution that includes mesopore and micropore; structural stability; and possibly functional groups that lend to energy storage through pseudocapacitive mechanisms. Templated, fibrous and aerogel carbons offer an alternative to activated carbons; however the drawbacks to these materials can include difficult preparation procedures or deficient physical properties with respect to those listed above. In recent years nanostructured carbon materials possessing favourable properties have also contributed to the field. Graphene nanoplatelet (GNP) and carbon nanotube (CNT) are nanostructured materials that are being progressively explored for suitable development as supercapacitor electrodes. As carbon lattice structured materials either in the form of a 2-dimensional sheet or rolled into a cylinder both of these materials possess unique properties desirable in for electrode development. In the proceeding report, GNPs are investigated as a primary material for the synthesis of electrodes in both a pure and composite form. Three projects are presented herein that emphasize the suitability of GNP as a singular carbon electrode material as well as a structural substrate for additional electroactive materials. Investigation in these projects focuses on the electrochemical activity of the materials for supercapacitor devices, and elucidation of the physical factors which contribute towards the observed capacitance. An initial study of the GNPs investigates their distinct capacitive ability as an electric double-layer material for thin-film applications. The high electrically conductivity and sheet-like structure of GNPs supported the fabrication of flexible and transparent films with a thickness ranging from 25 to 100 nm. The thinnest film fabricated (25 nm) yielded a high specific capacitance from preliminary evaluation with a notable high energy and power density. Furthermore, fast charging capabilities were observed from the GNP thin film electrodes. The second study examines the use of CNT entanglements dispersed between GNP to increase the active surface area and reduce contact resistances with thin-film electrodes. Through the use MWNT/GNP and SWNT/GNP composites it was determined that tube aspect ratio influences the resulting capacitive performance, with the formation of micropores in SWNT/GNP yielding favourable results as a composite EDLC. The third study utilizes electrically conducting polypyrrole (PPy) deposited onto a GNP film through pulse electrodeposition for use as a supercapacitor electrode. Total pulse deposition times were evaluated in terms of their corresponding improvements to the specific capacitance, where an optimal deposition time was discovered. A significant increase to the total specific capacitance was observed through the integration PPy, with the majority charge storage being developed via psuedocapacitive redox mechanisms. A summary of the studies presented here centers on the development of GNP electrodes for application in high power supercapacitor devices. The potential use for GNP in both pure and composite electrode films is explored for electrochemical activity and capacitive capabilities, with corresponding physical characterization techniques performed to examine influential factors which contribute to the final results. The work emphasizes the suitability of GNP material for future investigations into their application as carbon or carbon composite electrodes in supercapacitor devices.