Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Controlled Nucleation and Growth of Carbon Nanotubes(2024) Alibrahim, Ayman; Wang, YuHuang; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Single-walled carbon nanotubes (SWCNTs) exhibit exceptional electrical, mechanical, and optical properties, making them potential game changers for diverse applications. However, the synthesis of SWCNTs faces significant challenges, including low yield, inadequate control over catalyst particle size, and prevalent impurities. This dissertation focuses on elucidating SWCNTs' nucleation and growth mechanisms to address these challenging issues. First, I applied in-situ absorption spectroscopy to monitor the SWCNT production by chemical vapor deposition. Second, I investigated the factors affecting metal catalyst nucleation and introduced a confinement strategy that enabled a record-breaking growth rate of 4500 meters per hour for SWCNTs. Furthermore, I developed a novel “seed doping” technique to control the nucleation of metal catalysts, significantly reducing catalyst particle size and producing purer, smaller-diameter SWCNTs continuously. Finally, I explored the role of ethanol in enabling the controlled growth of double-walled carbon nanotubes by building on SWCNTs as templates.Item NANOPOROUS AAO: A PLATFORM FOR REGULAR HETEROGENEOUS NANOSTRUCTURES AND ENERGY STORAGE DEVICES(2009) Perez, Israel; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoporous anodic aluminum oxide (AAO) has vast implications as a tool for nanoscience research and as a nanostructure in which nanoscale devices can be fabricated because of its regular and ordered nanopores. Self-assembly plays a critical role in pore ordering, causing nanopores to grow parallel with one another in high density. The mild electrochemical conditions in which porous AAO grows along with its relatively cheap starting materials makes this nanomaterial a cost effective alternative to advanced photolithography techniques for forming high surface area nanostructures over large areas. In this research, atomic layer deposition (ALD) was used to deposit conformal films within in nanoporous AAO with hopes to 1) develop methodologies to characterize ALD depositions within its high aspect ratio nanopores and 2) to better understand how to use nanoporous AAO templates as a scaffold for energy devices, specifically Metal-Insulator-Metal (MIM) capacitors. Using the nanotube template synthesis method, ALD films were deposited onto nanoporous AAO, later removing the films deposited within the templates nanopores for characterization in TEM. This nanotube metrology characterization involves first obtaining images of full length ALD-AAO nanotubes, and then measuring wall thickness as a function of depth within the nanopore. MIM nanocapacitors were also constructed in vertical AAO nanopores by deposition of multilayer ALD films. MIM stacks were patterned into micro-scale capacitors for electrical characterization.Item TEMPLATE SYNTHESIZED NANOTUBES, NANOWIRES AND HETEROGENEOUS COAXIAL NANOWIRES FOR ELECTROCHEMICAL ENERGY STORAGE(2009) Liu, Ran; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Template synthesized nanomaterials have been successfully applied in electrochemical energy storage systems such as supercapacitors and lithium ion batteries. The first part of present study will list examples of applying various nanomaterials such as nanowires, nanotubes and heterostructured nanowires in different electrochemical energy storage systems for enhancing their charge/discharge rates, energy densities and power densities, etc. The following of the thesis will describe the template synthesis of nanomaterials in details. The experimental part of this thesis will concentrate on the fabrication of alumina template and the detailed experimental setups for aluminum anodization and template synthesis of nanomaterials. The rest of the thesis analyzes four cases of using template synthesized nanomaterials in electrochemical energy storage, which include my major work during my PhD studies. The first one is utilizing poly(3,4- ethylenedioxythiophene) (PEDOT) nanotubes as electrode materials for highpowered supercapacitor. The thin-walled nanotubes allow fast charge/discharge of the PEDOT to achieve high power. The second one is related to synthesis and characterization of RuO2/PEDOT composite nanotubes for supercapacitors. Loading appropriate amount of RuO2 can effectively enhance the specific capacitance of PEDOT nanotube. The third case illustrates the synthesis of MnO2/PEDOT coaxial nanowires by one step coelectrodeposition for electrochemical energy storage. The combined properties of MnO2 and PEDOT enable the coaxial nanowires to have very high specific capacitances at high current densities. Their formation mechanism will be explored and their nanostructures are tuned for optimized electrochemical properties. The final case reports the MnO2-Nanoparticles enriched PEDOT nanowires for enhanced electrochemical energy storage capacity. Large amount of the MnO2 nanoparticles can be loaded into PEDOT nanowires after they are soaked in KMnO4 solution. Thus loaded MnO2 nanoparticles effective enhance the energy densities of PEDOT nanowires without causing too much volume expansion to them.Item Barcoded Silica Nanotubes for Bioanalysis(2007-09-25) He, Bo; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Analysis of the chemical/biological species involved in health care is the most important step for diseases diagnosis and new drug screening. Barcoded nano/microparticles are attracting more and more interest for detection and identification of multiplexed chemical/biological species simultaneously. However, the development of barcoded particles is still in an early stage. To solve problems existing in current barcoded particles, such as spectral overlap and degradation of materials, our group has invented barcoded silica nanotubes (SNTs) and applied them to multiplexed immunoassays and cancer marker detection as coding materials. Barcode SNTs are fabricated by a multistep anodization template synthesis method. Each barcoded SNT has several segments with different reflectance values depending on their diameters and wall thicknesses. Therefore, the barcode of each SNT can be "read-out" with a conventional optical microscope. Barcoded SNTs have shown high stability and dispersibility in aqueous buffer media. Suspension arrays with barcoded SNTs have shown high sensitivity and high selectivity for the detection of multianalytes in the multiplexed immunoassays. Magnetic field separation is one promising technique to replace tedious filtration or centrifugation separation for rapid, gentle, and reliable isolation of target analytes. Barcoded SNTs have been coupled with magnetic bead (MB) separation for protein detection and analysis. The species and number of final collected SNTs represent the types and amount of analyte proteins, respectively. By using barcoded SNTs instead of fluorescence as signals, these suspension arrays overcome the problems existing in current MB suspension arrays, such as fluorescence quenching and interference of MBs' autofluorescence. Barcoded magnetic nanotubes (BMNTs) have also been successfully fabricated as dual-functional microcarriers for multiplexed immunoassays and cancer biomarker detection with magnetic separation. BMNTs combine the shape variety of barcoded SNTs and superparamagnetic properties of magnetic nanotubes. BMNTs overcome the problems in the existing dual-functional particles. The iron oxide nanocrystals are evenly dispersed in the inner void of the tubular structures without interference with the optical barcoded patterns. BMNTs have shown high selectivity when applied in multiplexed assays and cancer biomarker detection. The identification of BMNTs with software shows promising results for rapid data analysis. The dual-functional BMNTs provide a promising way for ultrafast, gentle, efficient, and automated detection of target chemical/biochemical molecules for diagnosis and drug screening.