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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    ELECTROCHEMICAL SYNTHESIS, TRANSFORMATION, AND CHARACTERIZATION OF MnO2 NANOWIRE ARRAYS FOR SUPERCAPACITOR ELECTRODES
    (2013) Duay, Jonathon William; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The utilization of MnO2 nanowire arrays for future light weight energy storage devices is investigated here. One of the more specific questions this work looks to answer is: Can ultra high density arrays of MnO2 nanowires really be used to create future flexible micro-supercapacitors with high energy density, high power density, and long cycle lives? This research investigates the energy storage properties of dense arrays of solely MnO2 nanowires and synergistic MnO2 nanowire composites consisting of two or more materials/architectures, where the composite materials are able to offset some of the detrimental intrinsic properties of the MnO2 nanowires. Accordingly, a complete flexible supercapacitor device was prepared utilizing a coaxial MnO2/poly (3, 4-ethylenedioxythiophene) (PEDOT) core/shell nanowire array cathode with a PEDOT nanowire array anode. This material demonstrated metrics considerably better than current devices even while being flexed. In addition, a hierarchical MnO2 nanofibril/nanowire array was synthesized by transformation of a bare MnO2 nanowire array. This material was investigated for its supercapacitor properties while altering the parameters of its nanowire and nanofibril architectures. Finally, MnO2 nanowires were investigated for their charge storage mechanism using ICP-AES to detect Li ion to Mn ion ratios during the charging and discharging process. Their charge storage process was found to differ depending on whether the electrolyte solvent used was aqueous or organic. These projects all help advance energy storage devices well beyond their current status as bulky, heavy energy sources toward their prospective use as light weight, flexible, micro- power sources.
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    A Physics of Failure Based Qualification Process for Flexible Display Interconnect Materials
    (2011) Martin, Thomas; Christou, Aris; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The next paradigm shift in display technology involves making them flexible, bringing with it many challenges with respect to product reliability. To compound the problem, industry is continuously introducing novel materials and experimenting with device geometries to improve flexibility and optical performance. Hence, a method to rapidly qualify these new designs for high reliability applications is imperative. This dissertation involves the development of a qualification process for gate line interconnects used in flexible displays. The process starts with the observed failure mode of permanent horizontal lines in the displays, followed by the identification of the underlying failure mechanism. Finite element analyses are developed to determine the relationship between the physical flexing and the mechanical stress imposed on the traces. The design of an accelerated life test is performed based on the known agent of failure being cyclic bending that induces a tensile strain. A versatile dedicated test system is designed and integrated in order to rapidly capture changes in resistance of multiple traces during test. Dedicated test structures are also designed and fabricated to facilitate in-situ electrical measurements and direct observations. Since the test structures were consumed during the integration of the test system, random failure times are used in the process of determining a life-stress model. Different models are compared with respect to their applicability to the underlying failure mechanism as well as parameter estimation techniques. This methodology may be applied towards the rapid qualification of other novel materials, process conditions, and device geometries prior to their widespread use in future display systems.
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    Some mechanics challenges and solutions in flexible electronics
    (2009) Tucker, Matthew Brody; Li, Teng; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flexible electronics is an emerging field with potential applications such as large area flexible displays, thin film solar panels, and smart prosthesis, to name a few. Promising future aside, there are challenges associated with flexible electronics including high deformability requirements, needs for new manufacturing techniques and high performance permeation barriers. This thesis aims to explore possible solutions to address these challenges. First, a thin stiff film patterned with circular holes is proposed as a deformable platform to be used in flexible electronics in either component and circuit level. Second, we explore possible pathways to improve the quality of transfer printing, a nanofabrication technique that can potentially enable roll-to-roll printing of flexible devices. Third, we investigate the failure mechanism of multilayer permeation barriers for flexible electronics and offer an improved design to achieve better mechanical reliability.