published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Not available / text

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Molecular assemblies are promising candidates for nano-scale electronics due to their chemical and structural versatility. The successful fabrication of assembly-based nano-scale electronics, where molecular assemblies comprise the electrically-active components, requires the ability to reliably form molecular assemblies and the ability to 'wire them into electrical junctions. This dissertation focuses on the processing-structure relationships of model conjugated dithiols, the formation of electrical junctions with these molecular assemblies, and the characterization of these junctions. Biphenyldithiol (BPDT), terphenyldithiol (TPDT), and quaterphenyldithiol (QPDT) are assembled in solution from their thioacetyl precursors which are converted in-situ to thiolates using NH4OH. We elucidated how the type of substrate, the solvent quality, and the concentrations of NH4OH and the thioacetyl precursors affect the final structures of these assemblies. BPDT molecular assemblies are disordered on both gold (Au) and gallium arsenide (GaAs) at all conditions explored. TPDT and QPDT adopt the most upright molecular orientations on both Au and GaAs when the assembly is carried out from EtOH-rich solutions at low NH4OH and high precursor concentrations. At these conditions, the assembly formation process is dominated by the adsorption of thioacetylterminated molecules. When the assembly is carried with high NH4OH and low precursor concentrations, adsorption is dominated by thiolates; TPDT and QPDT are disordered on Au and GaAs. None of the molecules adsorb significantly on GaAs from THF. The presence of S-Au bonds at the molecular assembly -- top Au contact interface was directly probed by x-ray photoelectron spectroscopy. Depositing Au electrodes on QPDT assemblies by nTP in dichloroethane results in the reproducible formation of S-Au bonds at the molecule-Au interface. Finally, we measured the electrical response of the model conjugated molecular assemblies on GaAs through direct contact with galinstan. The current densities scale inversely with the tunneling distance, which is determined by factors including the length of the conjugated molecule and the molecular orientation of the assembly. We also examined the electrical response of GaAs--QPDT--Au junctions in which the Au electrodes were transferred using an elastomeric stamps. The electrical characteristics of these junctions were independent of orientation of the molecules and the presence of SAu bonds at the charge transfer nterface. Hydrocarbon contamination on the Au electrodes left by the elastomeric stamp during transfer masked any electrical response from QPDT. It is therefore crucial to ensure the pristine quality of the electrical contact in order to reliably measure the electrical response of the molecular assembly. The fabrication and testing of assembly-based electrical junctions is challenging in terms of both controlling the assembly structures and measuring their electrical response. Careful attention must therefore be paid to each aspect of molecular assemblybased junction formation and characterization. / text

Within the field of optics, one of the topics being currently investigated with considerable interest is that of plasmonics, which refers to the use of surface plasmons on metallic nanostructures to manipulate light. It can be argued that this has been largely driven by two reasons. First, surface plasmons enable light to be concentrated into deep sub-wavelength regions, and therefore provide a means for overcoming the diffraction limit, which states that light can be focused to dimensions no smaller than roughly half the wavelength. Second, recent years have seen rapid development in nanofabrication methods - largely driven by applications in silicon microelectronics - that permit the realization of the metallic nanostructures needed for plasmonics. The goal of this thesis has been to harness these recent dramatic advances in plasmonics to address a long-standing problem in optics: the fact that Raman scattering cross sections are very small. / Engineering and Applied Sciences

published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

<p> Since its discovery in 1985, buckminsterfullerene (C₆₀) has been extensively studied due to its unique properties and it's now being produced in multi-ton quantities. The ability to form stable aqueous C₆₀ colloids (known as nano-C₆₀ or <i>n</i>C₆₀) and the availability of these in natural systems at environmentally-relevant concentrations led to significant interest concerning the environmental health and safety of these colloidal aggregates. Addressing two issues with regard to this material's environmental health and safety concerns we have looked at the oxidative mechanism of these <i>n</i>C₆₀ colloidal aggregates and their thermal stability. For making accurate kinetics and measurements on oxidation caused by aqueous-<i>n</i>C₆₀ colloidal dispersions, we have developed experimental methods utilizing dihydrorhodamine 123 (DHR123) as a sacrificial probe molecule to monitor oxidation by fluorescence spectroscopy and kinetic models to explain observed oxidation. Evaluation of the oxidative behavior of fullerene colloids has been determined using the oxidation rate as a function of <i>n</i>C₆₀ concentration, <i> n</i>C₆₀ surface area, number of colloidal particles and C₆₀O content, operating where necessary under inert atmosphere and oxygen rich conditions. The effect of temperature on these colloids plays a significant role in both their synthesis and reactivity. Given that the colloids are mainly composed of C₆₀ and C₆₀O, C₆₀O might play a significant role in stabilizing the colloid, hence increasing the temperature might cause thermally-activated reactions with C₆₀O. Thermal stability of these colloids prepared by all four primary <i>n</i>C₆₀ synthesis methods has been investigated. Incorporation of C₆₀ into polymers is of potential interest for applications, for sequestration to address potential environmental health and safety issues, and as a component in novel architectures. A new composite material was developed by encapsulating C₆₀ into cross-linked polymer network formed by &gamma;-cyclodextrin. A simple synthesis route to achieve composite membranes of intercalated C₆₀ in the polymer network is presented.</p>

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