Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xi, 110 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 85-89).

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains x, 114 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 112-114).

Thesis (Ph. D.)--Carleton University, 2000. / Also available in electronic format on the Internet.

Ti: sapphire femtosecond laser ablation of dielectrics (fused silica and BK7 glass) and metals (Cu, Fe, Al) is presented. Results of laser -induced breakdown experiments in fused silica and BK7 glass employing 130 fs -1.7 ps, 790 nm laser pulses are reported. The fluence ablation threshold does not follow the scaling of ~ when pulses are shorter than 1 ps. Single-shot and multi-shot (130 fs pulse) ablation of selected materials are investigated with laser wavelengths of 395 nm, 790 nm, and 1300 nm. The ablation threshold is almost independent of the laser wavelength. The surface morphologies in metals after ultrashort pulse ablation are very different from dielectrics and semiconductors. The roughness of the ablated surface depends on the thermal properties of the metal target. The preliminary TEM result from Cu single crystal that was irradiated by single laser pulses shows few defects in the center region of the ablated crater. Single-shot ablation of single-crystal Fe induces much different surface features than on selected samples of poly-crystal Fe metal. / Thesis / Master of Engineering (ME)

No description available.

No description available.

Environmental response as determined by the cell-polymer interaction stands as the greatest restriction to the implementation of new polymeric materials. Cell-polymer interactions are most influenced by substrate surface free energy, surface chemistry, topography, and rigidity[1]. Alteration of these properties through surface treatment has become a common approach to attain the desired cellular interaction. This study investigates Kr-F excimer laser(248 nm) surface modification of poly(methyl methacrylate), glycol-modified poly(ethylene terephthalate), and polytetrafluoroethylene and its effect on the adhesion of Escherichia Coli K-12 bacteria. These three polymers were chosen for their very different mechanisms of ablation as well as their range of surface free energies and bacterial responses[2-4]. Polymers were ablated using a pulsed Kr-F excimer laser with a dose of 3.3x 10-9 W/cm2 per pulse. This high level of UV radiation was sufficient to cause significant surface damage on both PMMA and PTFE. PETG showed some signs of wavering in the surface and material removal was confirmed through optical microscopy. Due to the extensive damage associated with ablation, a much lower-powered, continuous beam Kr-F laser was used for contact angle samples. It delivered a dose of 1.27 W/cm2. Contact angle measurements were then taken which showed dose-dependent surface free energy in all three polymers. Following ablation, bacterial adhesion to PETG was improved two-fold, while it decreased in both PTFE and PMMA. Surface chemistry analysis supported the idea that the ablation occurred through chain scission, since there were no new surface groups created. There were significan texture modifications observed in PTFE and PMMA whicle PETG demonstrated the rolling structure characteristic of polyesters following laser ablation described in Wefers et al [4] and Hopp et al [5]. Contact angle measurements showed a correlation between radiation dose and surface free energy of all three polymers. / Master of Science

published_or_final_version / Chemistry / Master / Master of Philosophy

Microwave spectroscopy is a gas phase technique typically geared toward measuring the rotational transitions of Molecules. The information contained in this type of spectroscopy pertains to a molecules structure, both geometric and electronic, which give insight into a molecule's chemistry. Typically this type of spectroscopy is high resolution, but narrowband ≤1 MHz in frequency. This is achieved by tuning a cavity, exciting a molecule with electromagnetic radiation in the microwave region, turning the electromagnetic radiation o, and measuring a signal from the molecular relaxation in the form of a free induction decay (FID). The FID is then Fourier transformed to give a frequency of the transition. "Fast passage" is defined as a sweeping of frequencies through a transition at a time much shorter (≤10 s) than the molecular relaxation (≈100 s). Recent advancements in technology have allowed for the creation of these fast frequency sweeps, known as "chirps", which allow for broadband capabilities. This work presents the design, construction, and implementation of one such novel, high-resolution microwave spectrometer with broadband capabilities. The manuscript also provides the theory, technique, and motivations behind building of such an instrument. In this manuscript it is demonstrated that, although a gas phase technique, solids, liquids, and transient species may be studied with the spectrometer with high sensitivity, making it a viable option for many molecules wanting to be rotationally studied. The spectrometer has a relative correct intensity feature that, when coupled with theory, may ease the difficulty in transition assignment and facilitate dynamic chemical studies of the experiment. Molecules studied on this spectrometer have, in turn, been analyzed and assigned using common rotational spectroscopic analysis. Detailed theory on the analysis of these molecules has been provided. Structural parameters such as rotational constants and centrifugal distortion constants have been determined and reported for most molecules in the document. Where possible, comparisons have been made amongst groups of similar molecules to try and get insight into the nature of the bonds those molecules are forming. This has been achieved the the comparisons of nuclear electric quadrupole and nuclear magnetic coupling constants, and the results therein have been determined and reported.

Modification of nanostructures via laser processing is of great interest for a wide range of applications such as aerospace and the storage of nuclear waste. The primary goal of this dissertation is to improve the understanding of nanostructures through two primary routes: the modification of aerogels and pulsed laser ablation in ethanol. A new class of materials, patterned aerogels, was fabricated by photopolymerizing selected regions of homogeneous aerogel monoliths using visible light. The characterization and fabrication of functionally graded, cellular and compositionally anisotropic aerogels and ceramics is discussed. Visible light was utilized due to it’s minimal absorption and scattering by organic molecules and oxide nanoparticles within wet gels. This allowed for the fabrication of deeply penetrating, well resolved patterns. Similarly, nanoporous monoliths with a typical aerogel core and a mechanically robust exterior ceramic layer were synthesized from silica aerogels cross-linked with polyacrylonitrile. Simple variations of the exposure geometry allowed fabrication of a wide variety of anisotropic materials without requiring layering or bonding. Nanoparticle solutions were prepared by laser ablation of metal foils (Fe and Mo) in ethanol. Ablation of Fe generated Fe3O4 and Fe3C nanoparticles which were superparamagnetic with a saturation magnetization Ms = 124 emu/g. Zero field cooled (ZFC) measurements collected at an applied field of 50 Oe displayed a maximum magnetic susceptibility at 120 K with a broad distribution. Field cooled (FC) measurements showed a thermal hysteresis indicative of temperature dependent magnetic viscosity. Pulsed laser ablation of a Mo foil in ethanol generated inhomogeneous nanoparticles where Mo and MoC coexisted within the same aggregate. Formation of these unique nanoparticles is likely due to phase separation that occurs when a high temperature carbide phase cools after the laser pulse terminates. Similarly, magnetic nanoparticle suspensions were generated by pulsed laser ablation of Fe and Mo in ethanol. The formation of several carbide phases with no discernable alloy formation was seen. A decrease in magnetization with a decrease in Fe concentration was seen which was reconciled with the decreased Fe content in the system. However, at Fe concentrations below ~ 40%, an increase in Ms and Hc was observed which was reconciled with the disappearance of the ε–Fe3C. TEM analysis showed the formation of core-shell nanoparticles and Energy Filtered TEM showed the distribution of Fe-based nanoparticles in the suspensions.