Thesis (Ph. D.)--University of Sydney, 2007. / Title from title screen (viewed may 17, 2007). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Biomedical Sciences, Faculty of Health Sciences. Degree awarded 2007; thesis submitted 2006. Includes bibliographical references. Also issued in print.

Thesis (M.F.A.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaf 36).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xii, 286 p.; also includes graphics (some col.). Includes bibliographical references (p. 273-286). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xviii, 178 p.; also includes graphics (some col.) Includes bibliographical references (p. 173-178). Available online via OhioLINK's ETD Center

The physics of two-phase systems is explored here, particularly magneto-transport and low temperature d.c. conductivity in thin films. The extraordinary magnetoresistance (EMR) effect was analysed in the context of previous experimental and theoretical considerations. The magnetoresistance (MR) may be enhanced by up to two orders of magnitude by changing the geometry. This was investigated using finite element analysis. Thin film samples consisting of a layered structure of Germanium-Tin-Germanium (Ge-Sn-Ge) were created in collaboration with Shandong University in China. Ge layers were kept at a constant thickness across all samples, with variable Sn thickness. Regions of Sn form island-like shapes ten times larger than the average film thickness, as is seen in scanning electron microscope (SEM) images. Raman spectroscopy was conducted on these samples, from which it is concluded that the Ge layers are amorphous in nature. It was seen that there is a relationship between the electrical resistance and the film thickness which is indicative of a metal-insulator transition (MIT). The temperature dependence of resistivity was subsequently investigated. The temperature coefficient of resistivity (TCR) of the samples is seen to become negative as the thickness of the Sn layer is reduced below a certain critical thickness. Depending on their thickness, samples were designated as metallic or insulator, and various models associated with metals and insulators fitted to the data. While it is impossible to be absolutely certain of the validity of each of the models, some are a better fit than others. The same temperature dependence of resistivity was measured with an applied magnetic field. This is compared with the previous EMR investigation, however the MR of the samples is only of the order of a few percent which corresponds to ordinary MR, seen in most metals. The magnetic field measurements suppress a resistivity down-turn at very low temperatures (T < 10K) which suggests the presence of superconductivity. Analysis of dr=dT shows that the onset of superconductivity is lower for samples with a lower Sn thickness. Additionally, the deposition rate of the Sn layer affects the resistivity significantly; a higher deposition rate causes a decrease in resistivity. It is supposed that this is due to a change in the microstructure of the film. Finally, piezo-resistivity was considered by applying mechanical compression to the samples. The added pressure causes a drop in resistivity.

Issues with the dissolution and diffusion of polysulfides in liquid organic electrolytes hinder the advance of lithium–sulfur (Li-S) batteries for next generation energy storage. To trap and re-utilize the polysulfides, brush-like, zinc oxide (ZnO) nanowires based interlayers were prepared ex-situ using a wet chemistry method and were coupled with a sulfur/multi-walled carbon nanotube (S/MWCNT) composite cathode. The cell with this configuration showed a good cycle life at a high current rate ascribed to (a) a strong interaction between the polysulfides and ZnO nanowires grown on conductive substrates; (b) fast electron transfer and (c) an optimized ion diffusion path from a well-organized nanoarchitecture. A praline-like flexible interlayer consisting of titanium oxide (TiO2) nanoparticles and carbon (C) nanofiber was further prepared in-situ using an electrospinning method, which allows the chemical adsorption of polysulfides throughout a robust conductive film. A significant enhancement in cycle stability and rate capability was achieved by incorporating this interlayer with a composite cathode of S/MWCNT. These results herald a new approach to building functional interlayers by integrating metal oxides with conductive frameworks. The derivatives of the TiO2/C interlayer was synthesized by changing the precursor concentration and carbonization temperature. Finally, a dual-interlayer was fabricated by simply coating titanium nitride (TiN) nanoparticles onto an electro-spun carbon nanofiber mat, which was then sandwiched with a sulfur/assembled Ketjen Black (KB) composite cathode with an ultra-high sulfur loading. The conductive polar TiN nanoparticles not only have a strong chemical affinity to polysulfides through a specific sulfur-nitrogen bond but also improve the reaction kinetics of the cell by catalyzing the conversion of the long-chain polysulfides to lithium sulfide. Besides, carbon nanofiber mat ensures mechanical robustness to TiN layer and acts as a physical barrier to block polysulfides diffusion. The incorporation of dual interlayers with sulfur cathodes offers a commercially feasible approach to improving the performance of Li-S batteries.

The introductory Chapter to this thesis outlines fundamental aspects of 4f lanthanide(III) coordination chemistry, in particular compounds that possess the intriguing properties of slow relaxation of magnetisation, (or the ability to behave as single-molecule magnets, SMMs). The recent renaissance into the study of the magnetic behaviour of 4f-coordination complexes has led to the consideration of utilising organometallic precursors for the development of novel lanthanide containing compounds, which may possess interesting magnetic properties, subsequently forming the basis of Chapter Two. In Chapter Two, the syntheses and structures of the novel lithiated thiolate ligand, lithium triphenylsilylthiolate, (Ph3SiS-Li) (2.1), and the sulfur-bridged, dimetallic dysprosium(III) and gadolinium(III) complexes [(MeCp)2Dy(µ-SSiPh3)]2 (2.2) and [(MeCp)2Gd(µ-SSiPh3)]2 (2.3), are described in detail. The structural and physical properties of these compounds are analysed through NMR, elemental analysis and SQUID magnetometry, alongside supporting theoretical calculations to reveal that compound 2.2 is the first dimetallic, sulfur-bridged SMM reported, giving an energy barrier to the reversal of magnetisation of Ueff = 192 ± 5 K.56bChapter Three reports on the structural development of a series of lanthanide monomers, exhibiting the general motif [Ln(OSiPh3)3(THF)3] (where Ln = Dy(3.4), Er(3.5), Ho(3.6), Gd(3.7), Tb(3.8)), exploiting the siloxide ligand Ph3SiOH through two novel synthetic routes. This Chapter also provides new analytical insight to these complexes by exploring their magnetic properties through a series of SQUID measurements and through the analysis of their electronic properties using air sensitive, variable temperature optical absorption spectroscopy. Compounds 3.4 and 3.5 were revealed to be SMMs, with 3.5 having a much higher thermal barrier to the reversal of magnetisation, Ueff = ~ 28 K, than 3.4, which are supported by theoretical analysis. Chapter Four describes the utility of ligand 2.1 and Ph3SiOH in the context of 3d transition metal cyclopentadienyl chemistry, outlining the syntheses and structures of three distinct compounds; the trimetallic, [Cp2Mn3(µ-OSiPh3)4](4.7), the hetero-cubane tetramer [CpMn(µ-SSiPh3)]4 (4.8) and the dimetallic thiolate-bridged [CpCr(µ-SSiPh3)]2 (4.9) compound. These compounds were formed in reactions exploiting organometallic manganocene and chromocene precursors. Magnetic susceptibility measurements were conducted on these compounds to gain further insight into their structural properties. The magnetic exchange coupling constants for Mn(II) compounds 4.7 and 4.8 were J = - 4.4 cm-1 and J = - 3.0 cm-1 respectively. Furthermore, having demonstrated the use of metal-cyclopentadienyl building blocks in the synthesis of novel SMMs, Chapter Five discusses the possibility of further advancement on the development of this class of magnetic molecules.

No description available.

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Um estudo da interação entre desordem e polarização de spin no GaMnAs ajuda a compreender a natureza dos estados, estendidos ou localizados, bem como as consequências para as transições observadas sobre as propriedades de transporte e às mudanças na ordem magnética de momentos magnéticos localizados em sítios de Mn. Este estudo pressupõe a ocorrência de uma banda impureza com baixas concentrações de Mn, que merge na banda valência no caso de concentrações mais elevadas. A abordagem teórica, baseada em um formalismo de espalhamento múltiplo auto-consistente, através do cálculo da função de Green para buracos determina-se a função densidade espectral no nível de Fermi. A escolha de uma figura de mérito, com base na largura e sobre a posição do máximo da função densidade espectral no espaço recíproco, leva a um diagrama de fase que determina o caráter metálicos ou não metálicos da amostra. Também é possível identificar a mobility edge, e como consequência, a densidade efetiva de portadores livre. Uma amostra é definida pelo par de parâmetros independentes, a concentração de Mn e a densidade buraco. As melhores amostras, aquelas com os maiores valores de mérito, tem uma relação entre a densidade de buracos estendidos e a concentração de Mn aproximadamente de 0.3, muito próximo do raio de 10-25% observada entre as amostras reais produzidos com a mais alta temperatura de transição. Além disso, a relação entre essas concentrações de Mn correspondente as transições metal-não-metal e não-metal-metal que é de aproximadamente 2.4, muito próximo do valor 2.1 da amostras reais. Uma interpretação da ocorrência de ferromagnetismo com alta temperatura de transição em GaMnAs é dada como uma consequência da interação entre o mecanismo de interação assistido por estados localizados e interações indiretas assistida pelo estdos buraco estendidos. Portadores mediando magnetismo em semicondutores mostram diferenças importantes e potencialmente úteis a diferenças de magnetismo em metais tais como o luz- ou voltagem elétrica -controlando ferromagnetismo. Motivado por experiências reportadas em poços quânticos de GaAs com uma dopagem delta de Mn com altas temperaturas Currier (temperatura de transição) mais elevadas do que em bulk de (Ga, Mn)As, nós exploramos teoricamente a viabilidade do campo elétrico controlar ferromagnetismo em poços quânticos. Nós calculamos auto-consistentemente a interação de troca indireta em Mn-Mn íons e aplicamos a simulação Monte Carlo para encontrar transição temperatura Tc. A nossa abordagem permite-nos estudar sistematicamente os efeitos de confinamento quântico e da posição da camada magnética de Mn e Tc, que vai além da aproximação do campo médio. Nós comparamos nossos resultados com os resultados experimentais e sugerimos caminho para o melhor controle do ferromagnetismo. / A study of the interplay between disorder and spin polarization in the diluted magnetic semiconductor GaMnAs helps to understand the character of states, extended or localized. This study assumes the occurrence of an impurity band which merges into the valence band at higher concentrations. The theoretical approach, based on a self-consistent multiple scattering formalism, determines the spectral density function at the Fermi level from the calculation of the hole's Green's functions. A choice of a figure of merit, based on the width and on the position of the maximum of the spectral density function in the reciprocal space, leads to a phase diagram determining the metallic or non-metallic character of the sample. It is also possible to identify mobility edges and, in consequence, the density of effectively free carriers. A model sample is defined by the pair of independent parameters, Mn concentration and hole density. The best samples, those with the highest figures of merit, have a ratio between the extended hole density and the Mn concentration near 0.3, very close to ratio of 10-30% observed among the real samples produced with the highest transition temperatures. Also, the ratio between those Mn concentrations corresponding to the metal-to-non-metal and non-metal-to-metal transitions is approximately 2.4, very close to the value 2.1 inferred from the real samples. An interpretation of the occurrence of high transition temperature ferromagnetism in GaM-nAs is given as a consequence of the interplay between interaction mechanism assisted by localized states and indirect interactions assisted by extended hole states. Carrier mediated magnetism in semiconductors show important and potentially useful differences from magnetism in metals,such as light- or bias-controlled ferromagnetism. Motivated by experiments reporting higher Currier temperatures in GaAs quantum wells with Mn-delta doping than the ones observed in bulk (Ga,Mn)As, we explore theoretically the feasibility of bias-controlled ferromagnetism these systems. We calculate self-consistently indirect Mn-Mn exchange interaction, and apply Monte Carlo approach to find transition temperature Tc. Our approach allows us to systematically study the eects of quantum confinement and the position of Mn layer on magnetic ordering and Tc, beyond mean field approximation. We compare our findings with the experimental results and suggest paths toward improving the control of ferromagnetism.