Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. Justin Schwartz, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed June 17, 2004). Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 140-151).

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Yoder, Douglas; Committee Member: Graham, Samuel; Committee Member: Allen, Janet; Committee Member: Klein, Benjamin; Committee Member: Voss, Paul. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Tin oxide (SnO2) has been investigated and used as a gas sensing material for numerous applications from the very start of the sensor industry. Most of these sensors use semiconductors (mostly SnO2) as the sensing material. In this work, SnO2 was prepared using 2 techniques: firstly the MOCVD where we dope the sample with fluorine and secondly sputtering technique where samples are undoped in our case. These samples were tested at different conditions of temperature varying from room temperature to 150 degrees C, in ambient gas atmosphere of 200 CC Nitrogen (N2). The typical thickness of the sputtered samples was 1500 A with a sheet resistance of 300; and these sputtered samples were found to be more porous. These samples when tested in room temperature showed a change of -4 [mu]A change for 10% and -9 [mu]A for 90% of H2. While at higher temperatures (150 degrees C) the current change for 10% increased from -4 [mu[A to -2 mA showing that higher ambient temperatures increased the sensitivity of the samples. The repeatability of the samples after a period of 3 days were found to be well within 10%. The samples prepared by MOCVD were fluorine doped, the samples were conductive to 1 order of magnitude more than the sputtered ones. 3 different samples of approximate thicknesses 3000, 6000 and 9000 A were prepared and tested in this work, with typical resistivity of 6 /cm and the grains in this case are typically more compact. The conductive samples showed no response at room temperature, including the 6000 and 9000 A samples. While at higher temperatures (150degreesC) the 3000 A sample showed very sensitive response to H2. Also noticed was that the response was linear compared to the sputtered samples. The samples showed very good repeatability and sensitivity.

A couple of processes for electrosynthetic production of expendable reagents, namely acids, bases, and oxidants, from the native salt content of raw waters and industrial wastes were investigated, and the composition of mixed acids and bases made of sodium sulfate or sodium chloride salts were predicted using a model predicated on conservation principles, mass action relations, and Pitzer equations. Electrodialysis with bipolar membranes (BMED) was used to produce acids and bases in a single pass. Product concentration was limited only by the salt content of the feed water. The current efficiency for acid production was slightly higher than that for base, but neither dropped below 75%. Acid and base current utilization showed the same trends with respect to feed salt content and flow velocity, with higher efficiency at higher feed salt concentrations and flow velocities. Operating the BMED stack near the limiting current density of the bipolar membrane (BLCD) or above the limiting current density of the diluate compartment (LCD) decreased current efficiency and increased electrical power dissipation. Electrodialytic acid and base production was approximately10 times cheaper than the chemicals' f.o.b. unit costs as quoted on Alibaba.com. The mechanism and cost of on site peroxodisulfuric acid production by electrolysis of sulfuric acid solutions with boron doped diamond film anodes was investigated experimentally and with molecular dynamics (MD) and density functional theory (DFT) simulations. The cost of on site peroxodisulfate production was approximately 4 times less expensive than purchasing a 25 lb bag. It was shown that direct discharge of sulfate species produces sulfate radicals, which subsequently combined to form peroxodisulfuric acid. The likely hood of these reactions was dependent on electrode surface condition. Sulfate radicals could also be produced in solution by reaction with hydroxyl radicals generated by water discharge.

This research investigated the mechanism, kinetics and feasibility of nitrate, arsenate, and trichloroethylene inactivation on zerovalent iron (ZVI), mixed-valent iron oxides, and boron doped diamond film electrode surfaces, respectively. Nitrate ( ) is a common co-contaminant at sites remediated using permeable reactive barriers (PRBs). Therefore, understanding nitrate reactions with ZVI is important for understanding the performance of PRBs. This study investigated the reaction mechanisms of with ZVI under conditions relevant to groundwater treatment. Tafel analysis and electrochemical impedance spectroscopy were used to probe the surface reactions. Batch experiments were used to study the reaction rate of with freely corroding and cathodically protected iron wires. The removal kinetics for the air formed oxide (AFO) were 2.5 times slower than that of water formed oxide (WFO).This research also investigated the use of slowly corroding magnetite (Fe3O4) and wustite (FeO) as reactive adsorbent media for removing As(V) from potable water. Observed corrosion rates for mixed valent iron oxides were found to be 15 times slower than that of zerovalent iron under similar conditions. Electrochemical and batch and column experiments were performed to study the corrosion behavior and gain a deeper understanding on the effects of water chemistry and operating parameters, such as, empty bed contact times, influent arsenic concentrations, dissolved oxygen levels and solution pH values and other competing ions. Reaction products were analyzed by X-Ray diffraction and XPS to determine the fate of the arsenic.This research also investigated use of boron doped diamond film electrodes for reductive dechlorination of trichloroethylene (TCE). TCE reduction resulted in nearly stoichiometric production of acetate. Rates of TCE reduction were found to be independent of the electrode potential at potentials below -1 V with respect to the standard hydrogen electrode (SHE). However, at smaller overpotentials, rates of TCE reduction were dependent on the electrode potential. Short lived species analysis and density functional simulations indicate that TCE reduction may occur by formation of a surface complex between TCE and carbonyl groups present on the surface.

In this thesis, I have developed a tunable two-color two-stage ultrafast Yb:fiber chirped pulse amplifier for the generation of short-pulse mid-infrared (MIR) radiation in the long-wavelength side of the "molecular fingerprint" (2.5-25 μm) using difference frequency generation (DFG) technique. The two colors called blue and red are in the wavelengths 1.03-1.11 μm and are amplified simultaneously in the same Yb-doped fiber amplifier (YDFA) stages in order to reduce the induced environmental noise on the phase difference of the pulses and to minimize the complexity and system cost. I will present numerical simulations on the two-stage YDFA system to amplify a two-color spectrum in the wavelengths 1.03-1.11 μm. The first and second YDFA called preamplifier and main amplifier are single-clad, single-mode and double-clad, single-mode YDFA respectively. From numerical simulations, the optimal length of the preamplifier to have equal power at two colors centered at 1043 nm and 1105 nm are in agreement with experimental results. It is well known that the power of MIR radiation generated by difference frequency mixing of two wavelengths scales up with the product of mixing powers in a fixed-field approximation. Furthermore, for the gain narrowing effect on the short-wavelength side of the YDFA gain profile, the spectral bandwidth of the blue color decreases resulting in pulse broadening. In addition, for the two colors separated largely, the amplified spontaneous emission is intensified. Considering the cited factors, I will present the modeling results on the two-color, two-stage YDFA system that the product of the power of the two colors is maximized for a maximized wavelength separation between the two mixing colors and a minimized gain narrowing on the blue color in order to build an as broadly tunable and powerful as possible ultrafast mid-infrared source by difference frequency mixing of the two colors. In this research, I achieved a wavelength separation as broad as 71 nm between pulses centered at 1038 nm and 1109 nm from the two-color ultrafast YDFA system. I achieved combined average powers of 2.7 W just after the main amplifier and 1.5 W after compressing the two-color pulses centered at 1041 nm and 1103 nm to nearly Fourier transform limited pulses. From autocorrelation measurements, the full width at half maximum (FWHM) of the compressed two-color pulses with the peak wavelengths of 1041 nm and 1103 nm was ~500 fs. By mixing the tunable two-color pulses in a 1-mm-thick GaSe crystal using DFG technique, I achieved tunable short-pulse MIR radiation. In this research, I achieved short-pulse MIR radiation tunable in the wavelengths 16-20 μm. The MIR tuning range from the lower side was limited to the 16 μm because of the 71-nm limitation on the two-color separation and from the upper side was limited to the 20 μm because of the 20-μm cutoff absorption wavelength of GaSe. Based on measured MIR spectra, the MIR pulses have a picosecond pulse duration in the wavelengths 16-20 μm. The FWHM of measured spectra of the MIR pulses increases from 0.3 μm to 0.8 μm as the MIR wavelength increases from 16 μm to 20 μm. According to Fourier transform theory, the FWHM of the MIR spectra corresponds to the bandwidth of picosecond MIR pulses assuming that the MIR pulses are perfectly Fourier-transform-limited Gaussian pulses. In this research, I achieved a maximum average power of 1.5 mW on short-pulse MIR radiation at the wavelength 18.5 μm corresponding to the difference frequency of the 500-fs two-color pulses with the peak wavelengths of 1041 nm and 1103 nm and average powers of 1350 mW and 80 mW respectively. Considering the gain bandwidth, Ti:sapphire is a main competitor to the YDFA to be used in the two-color ultrafast laser systems. In the past, the broad gain bandwidth of Ti:sapphire crystal has resulted in synchronized two-color pulses with a wavelength separation up to 120 nm. Apart from its bulkiness and high cost, Ti:sapphire laser system is limited to a watt-level output average power at room temperature mainly due to Kerr lensing problem that occurs at high pumping powers. In comparison, YDFA as a laser amplifier has a narrower gain bandwidth but it is superior in terms of average power. Optical parametric generation (OPG) and optical parametric amplification (OPA) techniques are two competitors to DFG technique for the generation of short-pulse long-wavelength MIR radiation. Although OPG offers a tunability range as broad as DFG, the MIR output power is lower because of the absence of input signal pulses. From the OPA technique, the tunability range is not as broad as the DFG technique due to limitations with the spectral bandwidth of the optical elements. Currently, quantum cascade lasers (QCLs) are the state-of-art MIR laser sources. At the present time, the tunability range of a single MIR QCL is not as abroad as that achieved from the DFG technique. More, mode-locked MIR QCLs are not abundant mainly because of the fast gain recovery time. Thus, the generation of widely tunable short-pulse MIR radiation from DFG technique such as that developed in this thesis remains as a persistent technological solution. The application of the system developed in this thesis is twofold: on one hand, the tunable two-color ultrashort pulses will find applications for example in pump-probe ultrafast spectroscopy, short-pulse MIR generation, and optical frequency combs generation. On the other hand, the short-pulse MIR radiation will find applications for example in time-resolved MIR spectroscopy to study dynamical behavior of large molecules such as organic and biological molecules.

Diluted magnetic semiconductor oxides (DMSOs) have received great attention recently due to their outstanding applications in optoelectronic and spintronic devices. Ever since the initial observation of ferromagnetism at room temperature in cobalt-doped titania, extensive effort is concentrated on preparation of transition metal doped wide band gap semiconductors, especially Mn- doped ZnO. Compared to Mn-doped ZnO, magnetic interactions in SnO! and In!O! semiconductors have been underexplored. SnO! and In!O! semiconductors have many applications, owing to their high charge carrier density and mobility as well as high optical transparency. Investigation on electronic structure changes induced by dopants during the synthesis procedure can effectively influence magnetic interactions between charge carriers. In this work, a combination of structural and spectroscopic methods was used to probe as-synthesized SnO! and In!O! nanocrystals doped with Mn!! and Mn!! as precursors. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy are powerful techniques to explore formal oxidation state of manganese dopant, electronic environment, number of nearest neighbors around the absorbent, and bond lengths to the neighboring atoms. Analysis reveals the presence of multiple oxidation states in the doped nanocrystals, and establishes a relation between !"!! ratio and expansion or contraction of lattice parameters. !"!! Although doping semiconductors are crucial for manipulating the functional properties, the influence of dopants on nanocrystals structure is not well understood. Nanocrystalline films prepared from colloidal Mn-doped SnO! and In!O! nanocrystals through spin coating process exhibit ferromagnetic behavior in temperatures ranging from 5 K to 300 K. Magnetic transformation from paramagnetic in free-standing Mn-doped nanocrystals to strong ferromagnetic ordering in nanocrystalline films is attributed to the formation of extended structural defects, e.g., oxygen vacancies at the nanocrystals interface. Magnetic circular dichroism (MCD) studies clearly show that Mn!! occupies different symmetry sites in indium oxide, when bixbyite and rhombohedral In!O! nanocrystals (NCs) are compared.

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