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Browsing by Author "Parkinson, Bruce, advisor"

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    Combinatorial discovery and optimization of novel metal oxide materials for photoelectrolysis using visible light
    (Colorado State University. Libraries, 2008) Woodhouse, Michael, author; Parkinson, Bruce, advisor
    Efficient and inexpensive production of hydrogen from water and sunlight has been the "holy grail" of photoelectrochemistry since Fujishima and Honda first demonstrated the feasibility of the process by illuminating TO2 single crystals with UV light. While it was a great proof of concept, a more suitable material will most likely be an oxide semiconductor containing multiple metals that will each contribute to the required properties of stability, light absorption, and being catalytic for hydrogen or oxygen evolution. Therefore we developed a high throughput combinatorial approach to prepare overlapping patterns of metal oxide precursors onto conducting glass substrates that can be screened for photolectrolysis activity by measuring the photocurrent generated by rasterng a laser over the materials while they are immersed in an electrolyte. A ternary oxide containing cobalt, aluminum and iron, and not previously known to be active for the photoelectrolysis of water, was identified using the combinatorial technique. The optimal composition and thickness for photoelectrochemical response of the newly identified material has been further refined using quantitative ink jet printing. Chemical analysis of bulk and thin film samples revealed that the material contains cobalt, aluminum and iron in a Co3O 4 spinel structure with Fe and Al substituted into Co sites with a nominal stoichiometry of Co3-x-yAlxFeyO4 where x and y are about 0.18 and 0.30 respectively. The material is a p-type semiconductor with an indirect band gap of around 1.5 eV, a value that is nearly ideal for the efficient single photoelectrode photoelectroylsis of water. Photoelectrochemical measurements indicate that the material has a respectable photovoltage but the photocurrent is limited by the slow kinetics for hydrogen evolution. This new cobalt iron aluminum oxide is most likely not the "holy grail" of photoelectrochemistry that we seek, but our methodology gives a rational approach for future materials discovery and optimization.
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    Synthesis and characterization of metal chalcogenide and metal oxide nanostructures
    (Colorado State University. Libraries, 2008) Chick, Ka Yee (Anna), author; Parkinson, Bruce, advisor
    Metal chalcogenide and metal oxide materials are of interest for sensing and energy conversion applications due to their semiconducting properties. Nanostructures made from such materials, therefore, have potential to work as building blocks for nanoelectronics. Various synthetic methods have been developed for the preparation of different nanostructures. In this dissertation, three different synthetic methods are presented in the preparation of different metal chalcogenide and metal oxide nanostructures. The as-produced nanostructures were characterized by transmission electron microscopy (TEM), high-resolution (HR-) TEM, scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), and x-ray diffraction (XRD).
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    Synthesis and electrical property measurements of individual layered transition metal dichalcogenide nanotubes and nanowires
    (Colorado State University. Libraries, 2008) Seley, David B., author; Parkinson, Bruce, advisor
    Nanotubes of the layered transition metal dichalcogenides (LTMDs) including MoS2, WS2, ReS2, and ReSe 2 have been synthesized. Additionally, nanowires of WS2 have been synthesized. All of the 1-dimensional structures synthesized used some form of a template to structurally direct 1-dimensional growth. The synthesis of the nanotubes of MoS2, WS2, and ReS2 utilized the pores of anodic aluminum oxide membranes to direct nanotube growth. WS 2 nanowires were grown with the assistance of the surfactant cetyltrimethylammonium bromide. ReSe2 nanotubes were synthesized by using Se nanotubes as a sacrificial template. The nanotubes and nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Information about the shape, identity, and nanostructure was gained utilizing these techniques. Electron beam lithography was used to make electrical contacts to the nanowires. Once the contacts were made, two point room temperature current voltage curves were recorded for MoS2, ReS2, and ReSe 2 nanotubes. The current voltage characteristics displayed I-V curves that were nearly linear, nearly symmetric, and nearly rectifying for these systems. The currents passed through these nanotubes ranged from nanoamperes to microamperes. Additional experiments on ReSe2 nanotubes indicated a change in resistance with exposure to ammonia and photocurrent generation when exposed to light.