The ESR g-value and susceptibility measurements for DMTM(TCNQ)₂ have been studied as a function of angle made by crystal with magnetic field and temperature. The angular dependence of g-value is fitted to g² = α+βcos2θ - γsin2θ for three orthogonal directions of crystal rotation. The principal g-values are close to those expected for TCNQ compounds: g₁ = 2.0034, g₂ = 2.0030, g₃ = 2.0024. The susceptibility as a function of temperature agrees with bulk susceptibility measurements except that the maximum position occurs at about 30 K. The results of Oostra et al. for bulk susceptibility showed a maximum at around 50 K. The phase transition reported by Visser et al. at 272 K is observed in the ESR data as a 15% decrease in susceptibility. The linewidth is remarkably anisotropic typical of TCNQ salts. The phase transition study is done for two orientations of the crystal with the magnet field. In one of the orientations the linewidth narrows from 0.15 to 0.11 gauss and in the other it narrows from 0.24 to 0.18 gauss. In the former case there is a growth of a second line due to the twinned stack; transformation twinning takes place at the phase transition. A small level-crossing interaction is inferred from the change in relative intensities of the lines near the crossover. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Understanding the radiation chemistry of water is important in many disciplines including the nuclear industry, astrochemistry, and medicine. In recent years, low-energy electrons have been paid much greater attention, due to their abundance and reactivity in irradiated materials. Electrons with energies < 20 eV may interact via the dissociative electron attachment (DEA) mechanism, which has been found to cause single-strand breaks in DNA.DEA in water involves the capture of a low energy electron by a neutral water molecule into an outer orbital and is generally accompanied by excitation of the H2O molecule, causing it to dissociate. The aim of this work is to study the OH radical produced in DEA to H2O using laser-induced fluorescence (LIF).A high-vacuum chamber equipped with low energy electron gun, molecular beam and laser system was built for gas-phase studies of DEA in water. LIF spectra were recorded from OH formed by dissociation of gas-phase H2O, for determination of the rotational and vibrational state distributions. In addition to the gas-phase studies, low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices were investigated using a combination of temperature-programmed desorption (TPD) and infrared reflection-absorption spectroscopy (IRAS).For CO trapped within approximately 50 mono-layers of the vacuum interface both reduction and oxidation products were observed including HCO, H2CO, H3CO and CH3OH, and CO2. Concentration profiles of CO versus film thickness showed two zones in the film: a near-surface zone of preferential oxidation, and a zone of preferential reduction deeper in the film. A Monte Carlo model was developed based on diffusion of H atoms through the ice lattice, which supported the experimental results.

The studies presented in this thesis are in two areas. An investigation of aromatic nitrene molecules using EPR spectroscopy was undertaken. This revealed a general tendency for these molecules to exhibit two forms when trapped in a crystalline lattice. This is qualitatively interpreted as a perturbing effect of nitrogen evolved during generation from the azide. Single crystal experiments were made on 2,4,6-tribromophenyl nitrene, which exhibited an unusually large anisotropy in the zero field splitting, implying a bent structure. Temperature variation of several aromatic nitrene zero field splittings were made. The variation was interpreted as thermal averaging amongst states possessing different zero field parameters. The nature of these states however, could not be inferred. The variation is compared with similar studies. A computer program to least squares fit EPR angular data to a spin Hamiltonian has been written. This programme was used to obtain a description of the angularly dependent EPR data from an aromatic nitrene, and also for a radical species with a large hyperfine interaction. / Science, Faculty of / Chemistry, Department of / Graduate

Two phase transitions have been found in DEM(TCNQ)₂ at 400(3) K and at 442(6) K to 453(6) K using ESR and measurements of the microwave conductivity. These temperatures are less than the values of 415 K and 483 K previously obtained from temperature dependent Guinier measurements. Below 400(3) K two ESR lines, I and II are observed corresponding to the two stacks, B and A, in DEM(TCNQ)₂. Above 400(3) K and below 453(6) K only one line remains with the same g value as line I. The angular dependence of the g value was fitted to g[sub=‖]² = g[sub=⊥] ²cos2θ + g²sinθ and values of g[sub=⊥] = 2.003551(14) and g[sub=‖] = 2.00273015) were obtained. Between 298 K and 442(6) K the conductivity was that of a semiconductor with an exitation energy E[sub=0] = 0.385(52) e.v. The -4k[sub=⌐] phase transition is postulated at 447(9) K. The phase transition at 400(3) K is due to a transfer of spin density from stack A to stack B, and has no effect on the total spin susceptibility or on the conductivity to within the experimental error. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

M.Sc. / Donor-acceptor (D-A) systems consist of a donor covalently or non-covalently linked to an acceptor. The simplest D–A system consists of a donor linked to an acceptor and is called a dyad system. Photoactive dyad systems are molecular devices designed to perform through the separation of charge separation states and the conversion of solar energy to chemical energy in analogy to photosynthesis.1 These dyad systems consist of a donor which is usually a chromophore and an acceptor. The design of these systems is guided to mimic photo-induced electron transfer (PET) and charge separation (CS), which are fundamental processes of photosynthesis. In nature, photosynthetic units are often built from dyads consisting of pigments like chlorophyll (donors), non–covalently linked to quinones, (acceptors). The donor harvests light energy and transfers the energy to the nearby pigment molecules until it eventually reaches a special region of the chlorophyll macrocycle called the reaction centre where this light energy is then converted to electrochemical energy. Photoactive dyad systems act as artificial photosynthetic models as they reproduce photo–induced electron transfer and charge separation of natural photosynthesis. In this project, dyad systems were made by covalently linking zinc pheophorbide, a modified chlorophyll derivative to double–walled carbon nanotubes (DWCNTs). Zinc pheophorbide acts as the donor and DWCNTs as the acceptors. Chlorophyll was modified by cutting the phytol chain and inserting zinc as the central metal to yield zinc pheophorbide. This derivative is stable against irradiation, has a good range of acceptor wavelength and is also a good light harvester. DWCNTs are one dimensional nanowires with two concentric tubes. They readily accept electrons because they have an extended π electron system. These electrons are then transported efficiently under ballistic conditions. DWCNTs were synthesised by catalytic chemical vapour deposition (CCVD) of methane over Mg0.99Co0.075Mo0.025O catalyst. In dyad system 1, amidated zinc pheophorbide molecules were covalently attached to oxidised DWCNTs in the presence of N–ethyl–N’–(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) \ and N–hydroxysuccinnimide (NHS) as a catalysts. Dyad system 2 was synthesized by attaching zinc pheophorbide molecules to amidated DWCNTs using the same catalysts.

Electronic processes, such as electronic breakdown and electron emission, in gases and liquids have implications in microplasmas, laser applications, water purification, biomedical applications, geographical mapping, and radiation detection. Electron emission and breakdown mechanisms are heavily researched and characterized in gases. Much of the current research into these mechanisms is focused on unifying breakdown and emission mechanisms. For electron emission, these mechanisms include field emission (FE), space-charge-limited emission (SCLE), thermionic emission (TE), and photoemission (PE), while gas breakdown emission mechanisms include Paschen’s law (PL) and Townsend breakdown (TB)with ion-enhanced FE becoming important at microscale. This research first unified SCLE and FE in vacuum and has been extended to include SCLE with collisions (for a gas at non-vacuum) and TE. This thesis extends this approach in electron emission unification, referred to as “nexus” theory, in two directions. First, we will apply this theory to liquids to examine the transition from FE to SCLE and hypothesize about the implications should there be a phase change. Second, we will incorporate PE, which becomes important with increasing interest in ultrafast laser phenomena at nanoscale and development of solar cells, with SCLE, TE, and FE.<div><br></div><div>Initial nexus theory studies included gas at non-vacuum pressures by including electron mobility in the electron force law. In principle, this behavior should be the same whether the medium is air or liquid. Electron emission and breakdown, which can arise from field emission, are increasingly important in plasma water treatment, pulsed power systems, radiation detection, and even understanding the physics of high electric fields applied to liquid helium for the Spallation Neutron Source. To demonstrate the applicability of nexus theory to liquids, we fit experimental data for electron emission in hydrocarbons to the full theory unifying FE to SCLE with and without collisions. The measured current followed Fowler-Nordheim scaling for FE at lower voltages with space charge beginning to contribute at higher voltages; none of the hydrocarbons study fully transitioned to Mott-Gurney (SCLE with collisions) scaling within the experimentally studied parameter range. Considering a higher mobility representative of a vapor in the theory demonstrates the feasibility of achieving Child-Langmuir (SCLE in vacuum)scaling for the gaps of the size considered experimentally. Thus, this approach may ultimately be applied to model electron emission during both phases changes and transitions between the mechanisms.<br></div><div><br></div><div>We next extended the gas nexus theory to analyze the transitions between PE and the other emission mechanisms. We modified the previous theory that used the generalized thermal-field emission (GTF) theory for electron current to instead use the generalized thermal-field photoemission (GTFP) theory. Using this, we obtained exact solutions for current as a function of applied voltage and demonstrated the asymptotic behavior with regard to the modified Fowler DuBridge (MFD) equation, which models PE. We combined the MFD equation with the other asymptotic solutions to develop state diagrams unifying the various emission mechanisms to provide guidance to the mechanisms and transitions relevant under various conditions of mobility, gap distance, temperature, and laser energy/wavelength/frequency. These diagrams provide guidance on which asymptotic solution or more detailed theory would be necessary to accurately relate current and voltage under various operating conditions.<br></div>

This thesis is a systematic description of normal and abnormal dog spermatozoa by means of bright field light and transmission electron microscopy, and an investigation into the effect that abnormal sperm have on canine fertility. A total of 101 ejaculates were collected from 88 dogs, of 34 different breeds. Sperm samples were examined macroscopically for volume, colour, consistency, and pH. Microscopic evaluation of sperm motility was conducted on all samples. Morphological evaluation using light microscopy was conducted on 71 of the samples. Samples from 10 of the dogs were examined ultrastructurally. A novel classification for abnormal dog sperm is presented. Abnormal sperm were classified into one of the following groups: Acrosomal defects, head defects, midpiece defects, tail defects and other abnormalities. Abnormalities were further sub-divided into major and minor defects. The most common abnormalities encountered were major sperm head defects. The abnormalities are compared with those described for other species, in particular the bull and man. The association between the percentage abnormal sperm in the ejaculate and the fertility of the dog was statistically evaluated. On this basis, the dogs were divided into normal and sub-normal groups. The percentage normal morphology below which fertility was adversely affected was found to be sixty percent. The fertility of dogs with greater than or equal to 60 percent normal morphology was 61 percent, while the fertility of dogs with · less than 60 percent normal morphology was 13 percent. There was no statistical difference between the ages of the dogs in the two groups; from this it was concluded that sub-fertility may affect a dog at any age. A means of evaluating dogs for reproductive potential is discussed.

Recently the theoretical discovery of single channel quantum dragons has been reported. Quantum dragons are a class of nanodevices that may have strong disorder but still permit energy-independent total quantum transmission of electrons. This thesis illustrates that multi-channel quantum dragons also exit in rectangular nanotubes and provide an approach to construct multi-channel quantum dragons in rectangular nanotubes. Rectangular nanotube multi-channel quantum dragons have been validated by matrix method based quantum transmission calculation. This work could pave the way for constructing multi-channel quantum dragons from more complex nanostructures such as single-walled zigzag carbon nanotubes and single-walled armchair carbon nanotubes.

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