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KeywordsMaterials Science & Engineering
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PublisherThe University of Arizona.
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EmbargoEmbargo: Release after 12/05/2012
AbstractFabrication and synthesis of nanostructured materials are essential aspects of nanoscience and nanotechnology. Although researchers are now able to create and tailor different nanostructured materials, the ability to precisely control the materials' sizes, shapes, and properties at the nanoscale level remains challenging. The aim of this dissertation was to develop new methods to aid researchers in overcoming these challenges. The study investigated two different methods used to create one-dimensional carbon nanostructures, i.e. carbon nanotubes and carbon nanopillars.In the first section, chemical vapor deposition method was used to grow carbon nanotubes (CNTs). Studies examining the effects of methane and hydrogen flow rates on the growth of CNTs were conducted. Results indicated that multi-walled CNTs with metallic properties could be obtained at a methane flow rates as low as 300 cc/min. At higher methane flow rates, i.e. 600-700 cc/min, semiconducting single-walled CNTs and double-walled CNTs were produced. Another phase of this section developed a new and simple CNT growth method using a solid carbon source and indicated polyacrylonitrile and nanosized SiO₂ were effective in producing MWCNTs. In the second part, a new nanoimprint technique was developed to enable printing of nanostructures at sub-100nm level using various polymers. This technique inherited its high-resolution feature from traditional nanoimprint lithography, but without the use of pressure. To demonstrate, PAN nanopillar structures were printed and converted to carbon. In another phase of the part, the use of our imprint technique resulted in the creation and conversion of polysilazane nanostructures to ceramic for the first time.The final section of this dissertation is devoted to study the impact of porosity in gas diffusion layers (GDLs) on the performance of fuel cells. In one study, a new technique using SEM images to determine GDL porosity was developed. The difference between SEM calculated porosities and mercury intrusion porosimetry measurements were less than 2%. The second study characterized fuel cell performances using GDLs constructed with additional micro porous layers (MPLs) and treated with different wet proofing treatments (WPT). Results showed that when MPL is added, cell performance decreases. However, the increase in WPT in the MPL improved cell performance.
Degree ProgramGraduate College
Materials Science & Engineering