published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

No description available.

The dramatic expansion of the electronics industry over the past 40 years has been based on the progressive reduction in size of the silicon-based semiconductor components of integrated circuits. The miniaturisation of semi-conductor circuits cannot, however, continue indefinitely, and we are rapidly approaching the stage where quantum effects will prevent further dramatic improvements in computer performance using existing technology. As a result, the field of molecular electronics, which seeks to identify and develop much smaller molecular analogues of the transistors that make up integrated circuits, has expanded rapidly over the past few years. Recent studies suggested that extended metal atom chains (EMAC) may have many potential applications in molecular electronics, but it is clear that this potential can only be realised if we establish a link between the fundamental electronic properties of these systems and the transport of electrons. For this reason the ultimate goal of this thesis is to relate the electronic structure of extended metal chains to their electron transport properties. We address the problem using non-equilibrium Green’s function, in conjugation with density functional theory. In the results sections of this thesis we present calculations on tricobalt, trichromium and trinickel chains. Our data suggested that in the trimetal chains, the dominant electron transport channel is the σ manifold, while the π systems establish the contact with the electrodes. The implication of this is that even when the highly polarized π channels are strongly rehybridised by the applied electric field, current flow is not affected. In the trichromium systems we find that the distortion of the chain away from the symmetric equilibrium structure does not perturb the current flow but rather enhances it. Our rather counter intuitive conclusion is therefore that ‘broken wires’ (highly unsymmetric) are more efficient conductors than their symmetric counterparts. We have performed calculation on longer penta- and heptacobalt structures chains to establish the extent to which longer structures attenuate the conductance. Our calculations show significant oscillations of the conductance due to development of a one-dimensional band structure about the Fermi level. The evolution of the electron transport properties in cobalt chains with different length is a complex one, but it is clear that narrowing the band gap in longer chains makes it increasingly likely that the Fermi level will be in resonance with one or more of the orbitals of the extended metal atom chain.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--Oregon Graduate Center, 1980.

Ph.D. / Inorganic Chemistry / Copper (I) forms π complexes with olefin-containing metal complexes in aqueous solution. Reduction of a series of pyridinepentaammineruthenium (III) ions, where L is a pyridine or 4-substituted pyridines, was studied. For the (NH[subscript 3]) [subscript 5] Ru (III)-4-viny1pyridine ion it is possible to measure separately preequilibrium binuclear ion formation and electron transfer. The electron transfer pathway is determined to be intramolecular from comparison with rate behavior of (NH[subscript 3]) [subscript 5] (III)-4-ethylpyridine, Cu (I) and (NH[subscript 3]) [subscript 5] (III)-pyridine, Cu (I) redox pairs. Rate parameters are also determined for the reverse reaction. Cu (II) catalyzed autoxidation of the (NH[subscript 3]) [subscript 5] (II) - 4-vinylpyridine ion. The redox equilibrium constant determined from the kinetic data agrees reasonably with that calculated from the redox potentials of the reactants. Qualitative models have been advanced from which it is suggested that the entropy of activation gives a measure of the probability for electron transfer in the activated complex, values near zero indicating that electron-tunneling is not rate-limiting. Cu(I)-olefin containing binuclear ions of (NH[subscript 3])[subscript 5]Co(III)L, where L is an alkylpyridine or alkylamine, undergo efficient intramolecular electron transfer when irradiated in the Cu(I)-olefin(n*) absorption band. The results of photoredox studies of a series of alkylamine and alkylpyridine containing binuclear ions are reported. The quantum yields for Co (II) production is shown to falloff monotonically for increasing number of methylene carbons in the chain. Binuclear ions containing polyisoprenyl bridging ligands were also investigated. Mixed solvent studies show decreased quantum yield with increasing ethanol content of the aqueous media. Medium and chain configuration effects are discussed.

Structural determinations and electrochemical properties in the series of multinuclear ferrocenyl¡Vethynyl complexes with formula [(£b5-C5H5)(P2)MII-C¡ÝC-(fc)n-C¡ÝC-MII(P2)(£b5-C5H5)] (fc = ferrocenyl; M = Fe(II), Os(II); P2 = Ph2PCH2CH2PPh2 (dppe)) are reported. These complexes undergo sequential reversible oxidation events from 0.0 to 1.0 V referred to the Ag/AgCl electrode in anhydrous CH2Cl2 solution and the low-potential waves have been assigned to the two end-capped metallic centers. The magnitude of the electronic coupling between the two terminal metallic centers in the series of complexes was estimated by the electrochemical technique. Based on the correlation between the ¡µE1/2 values and the second redox potentials of the end-capping metallic centers in the series of complexes, a qualitative explanation for the difference of the electronic coupling is given. Furthermore, we attempt to fabricate the SAMs of ferrocenyl-ethynyl molecules on gold surface and confirmed by XPS spectrum and the RAIR spectrum. CV and CA electrochemistry technique was employed in studied electron transfer rate (k).

Thesis (Ph.D.)--University of Central Florida, 2009. / Adviser: Michael N. Leuenberger. Includes bibliographical references (p. 104-115).