Thesis (Ph. D.)--University of Oregon, 2001. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 198-209). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: chromophore -- N-ethyl-3-carbazolylalanine -- 9-anthrylalanine -- chiral amino acids -- cyclic peptide -- solid-phase peptide synthesis -- enzymatic resolution -- cyclization. Includes bibliographical references (p. 92-95).

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vi, 70 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 57-61).

Using the vapor-liquid-solid (VLS) growth method, silicon nanowires and germanium nanowires are grown. We find the high growth rate is responsible for the silicon nanowires with less growth defects when they are grown by use of silicon tetrachloride as a precursor and hydrogen as a carrier gas. Based on this funding, large area, high aspect ratio, h111i oriented silicon nanowires are successfully grown on Si (111) and Si (100). Novel growth mechanisms of VLS growth method were discovered in SiOx nanoflowers and silicon nanocones. In SiOx nanoflowers grown at the tip of silicon nanowires, it is found that they are produced via the enhanced oxidation of silicon at the gold-silicon interface. Furthermore, the analysis of the flower pattern reveals that it is the observation of the dense branching morphology on nanoscale and on spherical geometry. For the silicon nanocones, they are grown by the in situ etching of the catalysts of Ga/Al by HCl during the growth. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) reveal that the nanocones are composed of amorphous silicon oxides and crystalline Si. Based on the similar chemistry of hydrogen reduction of SiCl₄ for the growth of silicon nanowires, single crystalline germanium nanowires are grown by use of GeCl4 as a precursor and H₂ as a carrier gas. As one of important application of one dimensional nanostructures, the field emission properties of 1-D nanostructures are explored. The field emission properties of a single graphite nanocone are measured in SEM. The inter-electrode separation is controlled using scanning tunneling microscopy (STM) approach method, allowing the precise and ne determination of the separation. Its Fowler-Nordheim plot shows it emits currents in accordance with the Fowler-Nordheim field emission. Its onset voltage, field enhancement factor show that its basic field emission parameters are comparable to those of a single carbon nanotube. It is observed that single nanocone is damaged after emitting a current of about 100 nA, which seems to be due to its hollow interior structure. / text

Within the exact framework established recently, which is a successful marriage between the time dependent density functional theory for open electronic system and quantum dissipation theory formulated in the hierarchical equations of motion, an entirely new scheme is proposed in this thesis to simulate the time-dependent quantum transport in nano-devices at both zero and finite temperature equally without relying on the pole structure of the Fermi distribution function. Neither does it depend on any non-unique parametrization of the line-width matrix, hence, this new practical approach can be integrated with the first principles simulations seamlessly. Beyond the exact framework, a reliable method which works under the Wide- Band-Limit approximation at zero temperature is also developed. At the price of loss of some non-Markovian memory effects on the dynamics, a set of equations of motion which terminates at the first tier instead of the second tier is obtained. Benefiting from the latest advancement of numerical analysis, a hybrid fourth-order Runge-Kutta algorithm is proposed to solve this set of equations of motion which comprises stiff ones. Based on this result, an alternative scheme is considered to deal with the same approximation at finite temperature. As an illustration of these new approaches, the transient current of the one dimensional tight-binding periodical chain with and without a single impurity, driven by some time alternating and/or static bias voltages, are investigated. The influence of temperature and switch-on rate of bias voltage is exemplified. Particularly, in the one dimensional tight-binding chain with a single impurity which breaks its perfect periodicity, an asymmetry between the left and right transient current is found. Comparison between the results under the Wide-Band-Limit approximation and those with the exact description is carried out. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

In this thesis, various micro- and nano-structures, fabricated by micro- and nanosphere lithography (NSL), were applied onto gallium nitride (GaN) based direct-bandgap semiconductors to develop optical micro-cavities supporting whispering gallery mode (WGM) lasing action. This work includes three major sections. The first section introduces the novel nanostructures patterned by NSL and discusses their characterization. The second section elaborates the free-standing microdisk (FSD) cavities supporting WGM lasing. Last section provides an effective approach for optimizing FSD system by replacing the interface layer. Novel nanostructures for various applications are fabricated by NSL. First we developed and demonstrated a drop-on-demand method for fabricating twodimensional (2D) photonic crystal (PhC) arrays. Different geometries, such as nano-pillar and nano-cone, were obtained with variant etching parameters. The GaN PhCs comprising nano-pillar array with diameter of 200 nm were fabricated by different nano-patterning methods, NSL, focused ion beam lithography (FIB), and E-beam lithography (EBL). The surface morphologies and optical properties of fabricated structures were evaluated by various characterization techniques, including scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, and transmission measurement. The NSL technique is regarded as a preferable approach in fabricating nanostructures. The FSD systems with diverse diameters of 1, 2, and 7 μm were prepared by laser lift-off (LLO) and microsphere lithography (MSL). The FSDs showed vertical and smooth sidewalls as confirmed by SEM images and served as an outstanding microcavities supporting WGM lasing. Optically pumped WGM lasing was obtained at room temperature for FSD systems. The lasing characteristics were fully studies. The thresholds were determined from the plots of PL peak intensity versus pumping energy density and the values were 5.01, 8.54, and 9.06 mJ/cm2 for FSDs with diameter of 1, 2, and 7 μm respectively. The remarkable quality (Q) factor of 2576 was achieved from 1 μm FSD. Anlysis for different thresholds and Q-factors were also discussed. By decreasing the FSD size, the number of lasing peaks is reduced to achieve single mode lasing due to the shrinkage of microdisk providing relatively large mode spacing. An elegant approach was conducted to improve the optical confinement in FSD system in the last section. The beneath layer, originally ITO, was replaced by a reflecting metallic Ni/Ag layer. The SEM images revealed that a thin FSD standing on metallic supporting layer was successfully fabricated. The WGM lasing was also obtained through optical pumping. Lasing mode centered at 430.0 nm has a threshold of 8.82 mJ/cm2 and a Q-factor of 1673. The free space range (FSR) was determined to be 3 nm. A comparison between FSD system with ITO layer and the one with NiAg layer indicated that the metallic layer can server as a reflecting layer and improved the optical confinement of the system. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Nanoparticles/nanocrystals have been recognized by their remarkable and technologically attractive properties which are different from those of bulk materials due to their ultra large surface area and extremely fine nanostructure. Highly sophisticated properties such as optical, magnetic, electronic, catalytic, mechanical, chemical and tribological properties can be obtained by advanced nanostructured coatings, making them desirable for industrial applications. This thesis encompasses the fabrication of nano/micro-structures of cuprous oxide (Cu2O) including nanocrystals, nanowires, nanocrystalline coatings and co-deposition of Cu2O/Cu by electrodeposition. The investigation in this thesis involved a systematic study by using a simple two-electrode system with copper sulphate as the electrolyte at pH 4.0 at room temperature and without the aids of any additive. The substrates under investigation included silicon wafer, stainless steel plate, highly oriented pyrolytic graphite (HOPG) and silver wire. By changing the kinds of the substrates, deposition modes, and deposition potentials, different types of nano/micro-structures of Cu2O were yielded. Nanometer-to-micron sized Cu2O single crystals were fabricated on an Au/Pd sputter-coated silicon wafer and stainless steel cathode. Different morphologies of the crystals were studied and their structural characterization was performed. The Cu2O crystals were generally of an octahedral shape. A growth mechanism was proposed to explain the morphologies of the observed nano/micro-structures. The effect of the electrodeposition parameters such as deposition voltage and deposition time, on the size of the crystals and their coverage on the substrates was examined. Highly aligned Cu2O nano/microwires were fabricated on the step edges of the HOPG substrate. With the same deposition potentials, longer deposition time would increase the diameter of the wires. Various crystal morphologies including flower-like and butterfly-like structures, and dendrites and truncated octahedra were observed on the working electrode of HOPG. Some of the morphologies were revealed for the first time by the one-step electrodeposition. To investigate the differences between yield by DC and pulsed electrodeposition respectively, the sizes and coverages of the deposited crystals on the substrate by DC and pulsed electrodeposition were compared. Two completely different forms of Cu2O, namely uniform nanocrystalline coatings and isolated single crystals, were fabricated on Ag microwires by pulsed and DC electrodeposition respectively. The results illustrated a very different effect on crystal nucleation between DC and pulsed electrodeposition, and suggested the possibility of using different voltage waveforms for electrodeposition in order to fabricate coatings with different nano/micro-structures on substrates. Gradual transition in the deposition products from pure Cu2O to pure Cu during electrodeposition with various DC potential was investigated. The percentage of Cu content was studied in depth for a full picture of the relationship between the depositing potentials and the compositions of the deposits. This thesis provides a method to fabricate nanocrystalline Cu2O, Cu and Cu/Cu2O on substrates in a single step without the use of additives. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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The effect of dispersing discreet periclase (magnesium oxide) or brookite (titanium oxide) nanoparticles into poly(1-trimethylsilyl-1-propyne) (i.e., a super glassy polymer) and 1,2-polybutadiene (i.e., a rubbery polymer) has been examined. Particle dispersion has been investigated using atomic force microscopy and transmission electron microscopy to determine particle/aggregate size and distribution. Titanium dioxide nanoparticles dispersed into aggregates on the order of nanometers, as did magnesium oxide in 1,2-polybutadiene. However, the magnesium oxide filled poly(1-trimethylsilyl-1-propyne) did not exhibit nanoparticle aggregates below approximately one micron in characteristic dimensions. Nanocomposite transport properties were studied, where permeability and solubility coefficients were determined for light gases with increasing pressure, and diffusion coefficients were calculated from the solution-diffusion model. The permeability of light gases in the heterogeneous films increased with increasing particle loading. Depending on particle loading, brookite filled nanocomposite light gas permeability increased to over four times that of the unfilled polymer, whereas at high periclase loadings the nanocomposites exhibited light gas permeabilities in excess of an order of magnitude higher than the unfilled materials. Even at these high loadings the light gas selectivities were higher than predicted for films containing transmembrane defects. Solubility was relatively unaffected by the void volume concentration, although it did increase to some extent depending on the nanoparticle concentration. Wide angle X-ray diffraction, nuclear magnetic resonance, and Fourier transform infra-red experiments were used to determine if the nanoparticles remained stable during film preparation. TiO₂ nanoparticles did not appear to react with water, the polymer matrixes or test gases used in this research. However, under certain circumstances, periclase reacted with adventitious water to form brucite. A desilylation reaction occurred when brucite was exposed to polymers or small molecule compounds that contained a trimethylsilyl group attached to a conjugated organic backbone. This reaction caused certain disubstituted polyacetylenes to become insoluble in common organic solvents.