Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item 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.Item WAVELENGTH DEPENDENCE IN OPTICAL TWEEZERS(2010) Hester, Brooke Cranswick; Losert, Wolfgang; Rolston, Steven; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optical trapping forces are dependent upon the difference between the trap wavelength and the extinction (scattering plus absorption) resonances of a trapped particle. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given experiment. Although optical forces due to a near-resonant laser beam have been extensively studied for atoms, the situation for larger particles has not been explored experimentally. The ability to selectively trap certain particles with a given extinction peak may have many practical applications. Here, resonance-based trapping is investigated using nanoshells, particles with a dielectric core and metallic coating that exhibit tunable plasmon resonances, and with silica and polystyrene beads. A measure of the trap strength was realized for single particles trapped in three dimensions, and near-resonant trapping was investigated by measuring the trap strength as a function of trap wavelength. Since the resulting trapping is highly temperature dependent, this necessitated temperature measurements of single optically trapped particles. To make these measurements a new optical tweezer apparatus was designed and constructed; the apparatus has wavelength tunability and was used to study these resonance effects. Optical trap stiffness, which is analogous to the spring constant of a stable trap, is measured for trapped particles that exhibit either single or multiple extinction resonances. The applications of this apparatus are not limited to force spectroscopy. Other measurement systems and techniques could be easily implemented into the custom-built apparatus, allowing for the measurement of various properties of single optically trapped particles as a function of wavelength.