The objective of this research is to build a prototype of a carbon nanotube (CNT)-based micro X-ray tube array, which can be used in a real-time cone-beam computed tomography (CT) scanner for cancer research. The X-ray tube array consists of an electron source, control grids, focusing electrodes, and an anode plate. All the experiments have been executed in an ultra high vacuum environment at a pressure of 10⁻⁷ Torr. A thin film consisting of multi-wall carbon nanotubes (MWNTs) was used as the electron source. A diode configuration was employed to test the field emission performance of the CNT thin film. The current density achieved was 1mA/cm² at 10V/µm. After the initial burn-in process, a relatively steady emission current was obtained for duration of 170 hours. The control grid was made of 25% opening space stainless steels mesh. Meshes with different wire diameters were tested in a triode structure, and some differences were observed. Multi-anode field emission tests and multi-tube electric field simulations were executed. Experiments and simulations have revealed crosstalk between pixels during field emission. Based on the above experiments and simulations, a signal pixel prototype has been fabricated and is being tested. Moreover, some potential optimizations that will be used in the second prototype are also discussed

The main objectives of the present Ph.D. thesis are comprehensive studies on activity, selectivity and stability of iron catalysts supported on carbon nanotubes (CNTs) for Fischer-Tropsch (FT) reactions. In order to prepare iron catalyst supported on CNTs, it was necessary to study CNT synthesis in bulk scale. Therefore, a part of this research was devoted to the production and characterization of CNTs. High purity, aligned films of multi-walled carbon nanotubes were grown on quartz substrates by feeding a solution of ferrocene in toluene, in a carrier gas of Ar/H2, into a horizontal chemical vapour deposition (CVD) reactor. Results for CNTs synthesized using a wide range of toluene concentrations indicated that, for carbon concentrations higher than ~9.6 mol/m3, catalyst deactivation occurs due to encapsulation of iron metal particles.<p> As the first step of catalyst development for FT reactions a fixed bed micro-reactor system was built and the effects of acid treatment on the activity, product selectivity and stability of iron Fischer-Tropsch catalysts supported on carbon nanotubes were studied. The results of Raman analysis showed that the acid treatment increased the number of functional groups as anchoring sites for metal particles. Fe catalysts supported on CNTs which were pre-treated with nitric acid at 110°C were more stable and active compared to the un-treated catalysts. In order to study the effects of catalytic metal site position on FT reactions, a method was developed to control the position of the deposited metal clusters on either the inner or outer surfaces of the CNTs. According to the results of the FT experiments, the catalyst with catalytic metal sites inside the pores exhibited higher selectivity (C₅⁺ = 36 wt%) to heavier hydrocarbons compared to one with sites on the outer surfaces (C₅⁺ = 24 wt%) . In addition, deposition of catalytic sites on the interior surfaces of the nanotubes resulted in a more stable catalyst.<p> The effects of pore diameter and structure of iron catalysts supported on CNTs on Fischer-Tropsch reaction rates and selectivities were also studied. In order to examine the effects of pore diameter, two types of CNTs with similar surface areas and different average pore sizes (12 and 63 nm) were prepared. It was found that the deposition of metal particles on the CNT with narrow pore size (in the range of larger than 10-15 nm) resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.<p> Promotion of the iron catalyst supported on CNTs with Molybdinium in the range of 0.5-1 wt % resulted in a more stable catalyst. Mo improves the stability of the iron catalyst by preventing the metal site agglomeration. Promotion of the iron catalysts with potassium increased the activity of FT and water-gas-shift reactions and the average molecular weight of the hydrocarbon products. Promotion of the iron catalyst supported on CNTs with 0.5% Cu and 1wt% K resulted in an active (5.6 mg HC/g-Fe.h), stable and selective catalyst (C₅⁺ selectivity of 76%) which exhibited higher activity and better selectivity compared to the similar catalysts reported in the literature. Kinetic studies were conducted to evaluate reaction rate parameters using the developed potassium and copper promoted catalyst. It was found that the CO₂ inhibition is not significant for FT reactions. On the other hand, water effects and presence of vacant sites should be considered in the kinetic models. A first-order reaction model verified that the iron catalyst supported on CNTs is more active than precipitated and commercial catalysts. The results of the present Ph.D. thesis research provide a map for designing catalysts using carbon nanotubes as a support. The key messages of the present thesis are as follows:<p> 1- If the interaction of the metal site and support is strong, which poses negative effects on the catalytic performance, carbon nanotubes can be one solution.<p> 2- Acid pre-treatments are required prior to impregnating nanotubes with metal salt solution. Also, the strong acid treatment should be used for deposition of catalytic sites inside the pores of nanotubes.<p> 3- The structure and pore size of nanotubes have significant influence on the stability, activity and selectivity of the target catalyst.<p> 4- The position of the catalytic sites has to be selected based on the type of reaction. In the case of Fischer-Tropsch reactions, the deposition of catalytic sites inside the pores of nanotubes results in higher activity, longer life span.<p> The outcome of this Ph.D. thesis has been published/submitted in the form of 13 journal papers, one patent, one technical report and presented at 11 conferences.

The objective of this research is to build a prototype of a carbon nanotube (CNT)-based micro X-ray tube array, which can be used in a real-time cone-beam computed tomography (CT) scanner for cancer research. The X-ray tube array consists of an electron source, control grids, focusing electrodes, and an anode plate. All the experiments have been executed in an ultra high vacuum environment at a pressure of 10⁻⁷ Torr. A thin film consisting of multi-wall carbon nanotubes (MWNTs) was used as the electron source. A diode configuration was employed to test the field emission performance of the CNT thin film. The current density achieved was 1mA/cm² at 10V/µm. After the initial burn-in process, a relatively steady emission current was obtained for duration of 170 hours. The control grid was made of 25% opening space stainless steels mesh. Meshes with different wire diameters were tested in a triode structure, and some differences were observed. Multi-anode field emission tests and multi-tube electric field simulations were executed. Experiments and simulations have revealed crosstalk between pixels during field emission. Based on the above experiments and simulations, a signal pixel prototype has been fabricated and is being tested. Moreover, some potential optimizations that will be used in the second prototype are also discussed

<p>Nanostructures are being intensely studied due to unusual material properties and simple scaling concerns in the microelectronics industry. Fabricating useful nano-scale structures and devices, either by arranging existing nanoparticles such as carbon nanotubes or by manipulating bulk materials into nanometer-scale geometries, is a challenging prospect. One promising approach is to generate a nanometer-scale pattern and transfer that geometry into another material. The research described in this dissertation concerns the fabrication of nanometer-scale patterns, by Atomic Force Microscope-based methods and Electron Beam Lithography, on planar surfaces and the transfer of those patterns into functional materials. Differences in surface energy were used to guide the growth of bulk conducting polymer along predefined nano-scale patterns. Carbon nanotubes were assembled into an ordered and continuous material with no guidance and used to lithographically write silicon oxide nanopatterns on a silicon surface. Finally, the two previous projects were combined, and surface energy patterns were used to guide the deposition of dense carbon nanotube bundles along a planar substrate.</p> / Dissertation

This work is mainly focused upon the preparation, processing and evaluation of mechanical and material properties of epoxy/single walled carbon nanotube (SWCNT) nanocomposite thin films. B-staged epoxy/SWCNT nanocomposite thin films at 50% of cure have been prepared for improving conductivity and mechanical performance of laminated composites. The SWCNTs were functionalized by oxidation and subsequent grafting using polyamidoamine generation 0 dendrimers (PAMAM-G0). The epoxy nanocomposites containing SWCNTs were successfully cast into thin films by manipulating degree of cure and viscosity of epoxy. The first section of this study focuses on the covalent oxidation and functionalization of single-walled carbon nanotubes (SWCNTs), which is necessary in order to obtain the full benefit of the SWCNTs inherent properties for reinforcement. In the second section of this work the preparation of B-staged epoxy/SWCNT nanocomposite thin films is discussed and what the purposes of thin films are. Additionally, the morphology as well as mechanical properties is evaluated by numerous means to obtain a clear picture as to the mechanisms of the epoxy/SWCNT nanocomposites. Furthermore, the effects of using sulfanilamide as a more attractive surface modifier for improved dispersion and adhesion and the effects of nylon particles for improved toughening on epoxy/SWCNT nanocomposites are discussed which displays improvements in numerous areas. Finally, based on these findings and previous studies, the B-staged epoxy/SWCNT nanocomposite thin films can be seamlessly integrated into laminated composite systems upon heating, and can serve as interleaves for improving conductivity and mechanical strengths of laminated fiber composite systems.

Transport Properties of Nanocomposites were studied in this work. A Monte Carlo technique was used to model the percolation behavior of fibers in a nanocomposite. Once the percolation threshold was found, the effect of fiber dimensions on the percolation threshold in the presence and absence of polymer particles was found. The number of fibers at the percolation threshold in the presence of identically shaped polymer particles was found to be considerably lower than the case without particles. Next, the polymer particles were made to be of different shapes. The shapes and sizes of the fibers, as well as the polymers, were made the same as those used to obtain experimental data in literature. The simulation results were compared to experimental results, and vital information regarding the electrical properties of the fibers and fiberfiber junctions was obtained for the case of two stabilizers used during composite preparation ? Gum Arabic (GA) and Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). In particular, the fiber-fiber connection resistances, in the case of these 2 stabilizers, were obtained. A ratio between the fiber path resistance and the total connection resistance, giving the relative magnitude of these resistances in a composite, was defined. This ratio was found through simulations for different fiber dimensions, fiber types and stabilizers. Trends of the ratio with respect to composite parameters were observed and analyzed, and parameters to be varied to get desired composite properties were discussed. This study can serve as a useful guide to choose design parameters for composite preparation in the future. It can also be used to predict the properties of composites having known fiber dimensions, fiber quality and stabilizing agents.

Development of nanoscience and nanotechnology requires rapid and robust nanomanufacturing processes to produce nanoscale materials, structures and devices. The dissertation aims to contribute to two major challenging and attractive topics in nanomanufacturing. Firstly, this research develops fabrication techniques for three dimensional (3D) structures and integrates them into functional devices and systems. Secondly, a novel process is proposed and studied for rapid and efficient manipulation of nanomaterials using a directed self-assembly process. The study begins with the development of nanoimprint lithography for nanopatterning and fabrication of 3D multilayer polymeric structures in the micro- and nano-scale, by optimizing the layer-transfer and transfer-bonding techniques. These techniques allow the integration of microfluidic and photonic systems in a single chip for achieving ultracompact lab-on-a-chip concept. To exemplify the integration capability, a monolithic fluorescence detection system is proposed and the approaches to design and fabricate the components, such as a tunable optical filter and optical antennas are addressed. The nanoimprint lithography can also be employed to prepare nanopatterned polymer structures as a template to guide the self-assembly process of nanomaterials, such as single-walled carbon nanotubes (SWNTs). By introducing the surface functionalization, electric field and ultrasonic agitation into the process, we develop a rapid and robust approach for effective placement and alignment of SWNTs. These nanomanufacturing processes are successfully developed and will provide a pathway to the full realization of the lab-on-a-chip concept and significantly contribute to the applications of nanomaterials.

A recently developed chemical vapor deposition (CVD) synthesis process called CoMoCAT yields single-wall carbon nanotubes (SWCNT)s of controlled diameter and chirality, making them extremely attractive for technological applications. In this dissertation, we use molecular dynamics simulations and density functional theory to study the selective growth mechanisms. In the CoMoCAT process, growth of SWCNTs happens on Co clusters with diameters of about 1 �. Effective force fields for Ni-C interactions developed by Yamaguchi and Maruyama for the formation of metallofullerenes and the reactive empirical bond order Brenner potential for C-C interactions are modified to describe interactions in such system. Classical molecular dynamics (MD) simulations using this force field are carried out to study the growth of SWCNT on floating and supported metal clusters. The effect of metal-cluster interactions on the growth process is discussed. The energy of forming one more ring at the open end of one-end-closed nanotubes with different chiralities, which is believed to be the basic step of nanotube elongation, are studied as a function of tube length. The energy and shape of the frontier highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of armchair nanotubes are studied and used to explain the change of reaction energy with tube length. Another property, the aromaticity of the rings forming a tube is also studied using Nucleus Independent Chemical Shift (NICS) as probe. NICS of rings in one-end-closed nanotubes with different chirality are studied as a function of tube length. NICS behavior of one-end-closed nanotube is compared with that of two-ends-open nanotube with the same chirality for nanotubes (6, 5) and (9, 1). Also (8, 3) nanotubes with one end open and the other end bonded to three different kinds of cap structures are compared. Since from both experimental observation and from our MD simulation results, the growth process of SWCNT can be affected by the interaction between Co clusters and their substrate, the performance of a series of CoN Clusters (N=1-4, 7, 10, 14, 15) adsorbed on MoC surface are studied with density functional theory.

The shielding effectiveness (SE) of the novel multiwall carbon nanotube (MWCNT) plastic composites is studied for the purpose of the electromagnetic interference (EMI) protection and the electromagnetic susceptibility (EMS) improvement in the application of the optical transmitter and receiver modules. The experimental results showed that the liquid crystal polymer (LCP) based MWCNT composites can exhibit a high SE of 38 dB ~ 45 dB within the frequency range of 1 GHz ~ 3 GHz. The shielding capability was demonstrated by examining the electromagnetic susceptibility performance of the optical transmitter and receiver modules, which were packaged by the MWCNT-LCP composites. The EMS performance was evaluated by eye diagram and bit-error-rate test in a 2.5 Gbps lightwave transmission system. The results showed that the MWCNT-LCP composite packaged modules with more weight percentage of the MWCNTs can exhibit a higher SE, and hence showed effective EMS performance, a better mask margin, and a lower power penalty. A novel polyimide (PI) plastic consisting of finely ionic liquid (IL) dispersed MWCNTs was also demonstrated to have high SE under a lower MWCNT loading. The experimental results showed that the IL dispersed MWCNT-PI composite can exhibit a high SE of 40 dB ~ 46 dB within the frequency range of 1 GHz ~ 3 GHz. By comparison, the composite fabricated by non-dispersed process required a higher loading of MWCNTs than the dispersed one. To understand the detailed intermolecular forces among MWCNTs, the dispersion mechanism of the MWCNTs is studied qualitatively. The aggregation of MWCNTs is from van der Waals forces among MWCNTs, and it can be dispersed by using IL dispersant. This is due to the predominant cation-

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