In this work we examine Ag-Au and Ni-Cu nanoclusters: their structural,compositional, and morphological characteristics are investigated in detail. The clusters are produced by the inert gas aggregation (IGA) method from magnetron sputtered alloy targets, in an UHV compatible system. The design of the system is optimized for production and deposition of the clusters with size in the range 5 nm < D < 10 nm. In order to increase the flux of sub-5 nm clusters in the system, we conducted modeling and experimental studies of cluster motion: the simulations showed that skimmers with wider internal angles might significantly improve the flux of smaller nanoclusters; however, the experimental study revealed a major influence of the background gas on scattering of such nanoclusters which consequently led to the loss of their flux. A comprehensive study of Ag0:85Au0:15 nanoclusters was conducted over a period of more than 2 years. Nanoclusters with sizes in the range 3 nm < D < 10 nm were deposited onto a-C films at various surface coverages and systematically investigated by transmission electron microscopy. We found that Ag-Au nanoclusters initially exhibited icosahedral and decahedral structural motifs, with a very small fraction of face centered cubic nanoclusters present. This may suggest that the source conditions used in the experiments (primarily Ar flow) left Ag-Au nanoclusters kinetically trapped in structures which correspond to local thermodynamic minima, rather than global energetically favoured atomic configurations. When left exposed to ambient conditions, over time Ag-Au nanoclusters exhibited structural, morphological, and compositional changes: core-shell and Janus nanoclusters were observed in aged samples, as well as fragmentation of bigger particles. We attribute these changes to oxidation of the Ag component and increased diffusion of Ag₂O over the substrates. The final morphology of aged nanocluster-based thin films is governed by a combination of diffusion, Ostwald ripening, and the Plateau-Rayleigh instability. High resolution transmission electron microscopy confirmed the presence of fivefold symmetric structures in Ni-Cu nanoclusters; however, their higher oxidation rate may have influenced the structures from the outset. In addition, when these nanoclusters were exposed to the electron beam, crystalline artifacts (nanochimneys)started to grown on them, with a structure corresponding to the NiO structure. Ni-Cu nanoclusters are subsequently used as catalysts in a pilot study of carbon nanotube synthesis which confirmed that such alloy nanoclusters are catalytically active for single-wall and multi-wall carbon nanotube growth.

Carbon nanotubes (CNTs) have been successfully grafted onto the surfaces of spherical silica gels via a floating-catalyst chemical vapour deposition method. Two types of silica gels were used as substrates; SG6 (6 – 8 nm pore size) and SG26 (26 – 34 nm pore size). The optimum growth conditions were found to be 760 °C growth temperature, 3 hours growth time, and 5 wt .% of ferrocene catalyst (dissolved in toluene) injected into the furnace at a rate of 0.04 ml/min. Under these conditions, CNTs coated the exterior surface of the gels with growth occurring from both the pores and from the surface. The geometry and porosity of the silica gel were also found to influence the alignment and density of the grafted CNTs, with SG6 producing the best quality hybrid particle under the above conditions (labelled SG6_3). Thermal Gravimetric Analysis showed the yield of CNTs grown under these optimum condition was 33.6 + 0.37 wt. %. As the CNTs remained strongly attached to the surface of the gel, the grafting process produced excellent dispersion of the CNTs within polymer matrices as CNT bundle formation was prevented. The inclusion of micron size silica introduced a large excluded volume within polymer matrices, with the dispersion of CNTs restricted to a region along the silica surface. This arrangement aided the formation of an electrically conductive network in a poly (vinyl) alcohol matrix, where the critical percolation threshold (pc) was calculated as 0.62 wt. % of SG6_3, equivalent to a CNT content of 0.2 wt. %.The inclusion of SG6_3 into an epoxy resin suspension did not alter the rheological behaviour of the resin up to the highest loading employed (5 wt. %, ≈1.65 wt. % of CNTs). Within the linear viscoelastic region the viscoelastic moduli of the neat resin remained within the same magnitude, whilst the addition of 1.65 wt. % of commercially available CNTs into the same resin increased the storage and loss moduli by up to seven and three orders of magnitude, respectively. The complex viscosity of the suspension remained unchanged regardless of the amount of SG6_3 added; whereas an increase in viscosity of up to five orders of magnitude resulted from the addition of 1.65 wt. % non – grafted CNTs.Grafting of CNTs onto the surface of micron size spherical silica gel has been shown to provide a means of incorporating CNTs into a polymer without increasing viscosity. In addition, the SG6_3 also formed an electrically-conductive percolated network in an epoxy resin composite at low levels of addition, with pc = 0.16 wt. % of CNTs (i.e. 0.5 wt. % SG6_3).

Carbon nanotubes (CNTs) possess exceptional mechanical, thermal and electrical properties along their main axis, superior to those of most materials. These can be exploited on a macroscopic scale by assembling the CNTs into a fibre with the nanotubes preferentially oriented parallel to each other and to the fibre axis. CNT fibres can be produced continuously, directly from the gas phase during CNT synthesis by chemical vapour deposition (CVD), and spun at rates of up to 70 m/min. Their combination of outstanding mechanical, electrical and thermal properties and low density (1 g/cm3) makes CNT fibres a potential candidate for high-performance applications. The fibre specific strength and stiffness are typically 1 GPa/SG and 50 GPa/SG, respectively; however, at small gauge lengths (> 2mm) they also show values of 6-9 GPa/SG strength and 180-390 GPa/SG stiffness. The electrical conductivity of the CNT fibres is approximately 8 x 10 5 S/m and their thermal conductivity of the order of 50 W/mK. These properties derive from the long length, high alignment and efficient packing of the nanotubes in the fibre. Further improvements to the fibre structure and properties at long gauge lengths are possible through removal of impurities from the fibre by annealing.

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Electrochemical Supercapacitors (ES), also known as Supercapacitor or Ultracapacitor, has been regarded as an advanced electrical energy storage device for decades. Fabrication of advanced electrode materials is of critical importance for advanced ES. Among various materials used for ES electrode, polypyrrole (PPy) is found to be a promising material due to high specific capacitance, good electrical conductivity, low cost and ease of processing. The use of advanced anionic dopants and addition of multiwall carbon nanotube (MWCNT) have been proved an .effective approach towards advanced PPy based ES with improved electrochemical behaviors. In this research, chemical polymerization of PPy powders and PPy/MWCNT composite materials have been successfully accomplished in presence of advanced anionic dopants, including chromotrope families, amaranth, pyrocatechol violet, eriochrome cyanine R and acid fuchsin. The influence of polyaromatic dopants with different molecular size, charges and charge to mass ratios on the microstructure and electrochemical characteristics has been discussed. PPy coated MWCNT with uniform microstructures was successfully achieved in simple chemical methods. The results showed PPy powders with enhanced microstructures and electrochemical behaviors can be obtained by using such advanced anionic dopants. Multi-charged polyaromatic dopants with larger molecular size benefitted PPy powders with smaller particle size, improved specific capacitance, and enhanced cycling stability, at high electrode mass loadings. Moreover, advanced aromatic dispersant and chemical synthesis was proved a simple and effective method for fabrication of PPy/MWCNT composite materials at different PPy/MWCNT mass ratio, among which the powder with PPy/MWCNT mass ratio of 7:3 showed optimum electrochemical performance. Last but not the least, the use of advanced high porosity current collector (Ni foam) allowed high electrode mass loading and good electric conductivity. As a result, advanced PPy/MWCNT composite materials which allows improved electrochemical behaviors, especially at high mass loading, are promising electrode materials for ES. / Thesis / Master of Applied Science (MASc)

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Interest in nanoscale heat and mass transport has been augmented through current trends in nanotechnology research. The theme of this dissertation is to characterize electric charge, mass and thermal transport at the nanoscale using a fundamental molecular simulation method, namely molecular dynamics. This dissertation reports simulations of (1) ion intake by carbon nanotubes, (2) hydrogen storage in carbon nanotubes, (3) carbon nanotube growth and (4) nanoscale heat transfer. Ion transport is investigated in the context of desalination of a polar solution using charged carbon nanotubes. Simulations demonstrate that when either a spatially or temporally alternating charge distribution is applied, ion intake into the nanotubes is minimal. Thus, the charge distribution can either be maintained constant (for ion encapsulation) or varied (for water intake) in order to achieve different effects. Next, as an application of mass transport, the hydrogen storage characteristics of carbon nanotubes under modified conditions is reported. The findings presented in this dissertation suggest a significant increment in storage in the presence of alkali metals. The dependence of storage on the external thermodynamic conditions is analyzed and the optimal range of operating conditions is identified. Another application of mass transport is the growth mode of carbon nanostructures (viz. tip growth and base growth). A correct prediction of the dominant growth mode depends on the energy gain due to the addition of C-atoms from the carbon-metal catalyst solution to the graphene sheets forming the carbon nanostructures. This energy gain is evaluated through molecular dynamics simulations. The results suggest tip growth for Ni and base growth for Fe catalysts. Finally, unsteady nanoscale thermal transport at solid-fluid interfaces is simulated using non-equilibrium molecular dynamics simulations. It is found that the simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity. Temperature discontinuities are observed between the solid-like interfaces and their neighboring fluid molecules. With an increase in the temperature of the solid wall the interfacial thermal resistance decreases. / Ph. D.