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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    THE APPLICATIONS OF MULTIPHOTON ABSORPTION POLYMERIZATION
    (2013) Qin, Sijia; Fourkas, John T.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Among various nano/micro-fabrication techniques, multiphoton absorption polymerization (MAP) stands out for its high resolution and its capability of creating arbitrary three-dimensional micro-structures. This thesis will focus on the applications of, and improvements to, MAP. MAP was used to fabricate polymer double-ring resonators (DRRs) because MAP's high resolution allows for precise control of the coupling gap sizes. Pedestal acrylic DRRs with 33 nm free spectral range and -15 dB isolation were fabricated, and their properties showed qualitative agreement with simulation results. Single-mode, acrylic microring resonator devices were fabricated on a low-index substrate using MAP and were coupled to side-polished fibers as in-line devices. High-finesse spectral notches with low insertion loss were observed at the fiber output. Surface mapping of the polished face of the fiber was accomplished by moving a microring resonator device across and along the fiber core. The optimal coupling region on the polished face of the fiber could be identified through the change of modulation depth. Spectral modulation induced by varying the pressure on a microring resonator device coupled to a side-polished fiber was also investigated. Efficient multiphoton radical generation chemistry has been developed for use in aqueous media and has been applied to the fabrication, manipulation, and assembly of 3-D polymeric and biomolecular structures through a combination of MAP and optical tweezers. The combination of MAP and optical tweezers allows for the realization of structures such as tape-like and rope-like microthreads that can be used in complex microfabrication techniques such as microbraiding and microweaving. These capabilities enhance the toolbox of methods available for the creation of functional microstructures in aqueous media. MAP-fabricated and UV-cured acrylic patterns were treated with reactive ion etching (RIE) to create high-roughness "nanograsses." The nanograss patterns have shown the potential to be used as superhydrophobic materials. The density and dimension of the nanograss depends on the total exposure dose. Different etch angles gave different etch structures.
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    MULTIPHOTON ABSORPTION: FABRICATION, FUNCTIONALIZATION AND APPLICATIONS
    (2009) Li, Linjie; Fourkas, John T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Despite the remarkable progress in micro/nano-scale fabrication that has occurred over the last decades, feature sizes are still restricted by the diffraction limit. The resolution in conventional photolithography is generally constrained to approximately one quarter of a wavelength (lamda) of the light used. Multiphoton absorption polymerization (MAP) offers another option for high-resolution fabrication. Using nonlinear optical and chemical effects, MAP can generate features with a transverse dimension as small as 80 nm using 800-nm laser excitation. MAP has the additional capability of fabricating arbitrary 3D structures, which is essential in many applications. Details of MAP fabrication setup and process are described in this thesis. Novel optical devices have been fabricated with MAP. One drawback of MAP is that the resolution in axial direction remains about three to five times poorer because of the shape of the laser focal point. A novel technique called Resolution Augmentation through Photo-Induced Deactivation (RAPID) lithography has been developed to overcome this issue. With RAPID, resolution of 40 nm in axial direction has been achieved. The aspect ratio of the volume element of MAP has been reduced from about 3 to 0.5. Selective functionalization of polymeric microstructure has been performed in two ways. In the first approach, microstructures are fabricated with hybrid resists that permits the chemical functionality only applies to one material. The second method is able to pattern both binary and gray-scale functionalities onto polymer surface. The density of the surface functional groups is determined by the intensity of the exposed light. The nonlinear novelty of multiphoton absorption has not only been realized in MAP, it also shows promise for multiphoton absorption based microscopy. Photoluminescence from noble metal nanostructures has been used for two-photon imaging of living cells. Multiphoton Absorption Induced Luminescence (MAIL) has been used to monitor the targeting and endocytosis of goldnanoparticles to human umbilical vein endothelial cells. Field-enhanced phenomena have been studied with MAIL and MAP.
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    Benzocyclobutene Microring Resonators
    (2007-11-26) Chen, Wei-Yen; Ho, Ping-Tong; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Wavelength division multiplexing (WDM) at optical carrier frequencies offers more capacity and flexibility of fiber networks and upgrades conventional point-to-point fiber-optic transmission links to multiuser networks for the demand of high-speed network systems. The microring resonator, which has been seen in action in many photonic devices, is ideal for WDM applications in realization of narrow bandwidth with a wide free spectral range. In this research, microring resonators are fabricated in benzocyclobutene (BCB), a popular polymer in photonics and electronics applications. First, the single-mode BCB undercut-cladding waveguides were designed to reduce bending loss. BCB microring resonators were fabricated based on those principles. BCB single-microring devices were demonstrated as add-drop filters and notch filters with a negative coupling gap. Not only are the microring resonators compact (as small as 5 µm in radius) for photonic VLSI, they also exhibit a high out-of-band rejection (~ 30 dB), high extinction as well as a high finesse (~ 285). In addition, BCB lattices consisting of over one hundred microring resonators were fabricated and demonstrated as bandstop filters. The lattices, despite the large number of resonators, exhibit an extremely low propagation loss. Finally, optical bistability and the field-enhanced all-optical nonlinear switching were demonstrated in BCB microring devices.