Low frequency noise in giant magnetoresistive spin valves has been studied as a means of optimizing signal to noise ratios and characterizing device performance. The devices studied were sputter deposited NiFe/Cu/NiFe/FeMn spin valves with D R/R ∼ 4%. Static measurements demonstrated a strong dependence of the magnetic coupling and giant magnetoresistance (GMR) ratio on the thickness and quality of the Cu spacer layer and the bottom NiFe layer (free layer). These parameters were varied to determine how the noise in spin valve sensors would be affected. Noise power spectra were measured in patterned spin valves. The noise was observed to have a 1/f slope at low frequencies. The fluctuation-dissipation relation relating thermal fluctuations in magnetization to the resistance fluctuations was used to explain the origin of the 1/f noise. The noise was found to be sensitive to the anisotropy and defect density of the free layer. The noise was minimized for spin valves operating with parallel anisotropy axes and an applied field aligned along the hard axis of magnetization. Dynamic fields were used to measure the Barkhausen noise in the sense layer of the spin valve. The low frequency noise in the presence of dynamic fields was much greater than the 1/f noise background. Clustering of Barkhausen jumps was used to explain the observed dependence of the noise power on the magnitude and frequency of the applied field. Higher frequency signals resulted in lower Barkhausen noise. The noise was reduced when the applied field was aligned along the hard axis of magnetization.

Electromagnetic levitation, which can provide rapid heating and melting, homogeneity of melt and minimal specimen contamination, is an important branch of containerless processing. The longitudinal electromagnetic levitator is a new type of levitation device, which was invented recently and has a potential to become a containerless manufacturing processing tool. It has some unique advantages, such as good visual access to the sample, capability to support multiple samples, large loads and cylindrical shape sample availability. In this thesis, a brief review of the history and application of electromagnetic levitation is presented. Then the detailed theoretical analysis coupled with experimental work validating the theoretical models of the longitudinal electromagnetic levitator are presented. First, a new electric current model is introduced, which is more appropriate for the computation of the electromagnetic force field in the levitated specimen. Based on this new model, the essential equations for the electromagnetic field and the lifting force field for a cylindrical sample are derived, the current density distribution and the averaged power in the sample are analyzed. Additionally, both lifting force and lifting capacity for the longitudinal levitator are investigated analytically, and compared with experimental data with good agreement. These theoretical predictions can be used to design longitudinal levitators, to select suitable material for levitation, and to provide the framework for further investigation of materials processing using the longitudinal levitator. In addition, temperature distribution simulation for the sample levitated in the longitudinal electromagnetic levitator is implemented by analytical and numerical ways. Isothermal case, steady state and lumped system are discussed respectively as some special cases. The exact solution and numerical simulation of the temperature distribution for the levitated sample are compared with good agreement. The flow motion within the levitated sample and the numerical simulation of the temperature distribution with flow convection has also been investigated. The results provide important information of the levitation phenomena which are very useful for scientific and engineering applications, especially for materials processing.

The plasmon resonance in metallic nanoshells can be used to efficiently harvest solar energy and convert it into thermal or electronic form. Possible applications include improved optical coupling into silicon photodiodes, solar water heaters, and photocatalysis. We use standard optimization algorithms to theoretically determine the best mixture of different nanoshell species ([core, shell] sizes) for two practical scenarios. We show that a mixture of nanoshell species [r1, r2] = [47, 58] nm and [r1, r2] = [28, 42] run in a 6:5 volume ratio is optimal for absorbing AM 1.5 sunlight when deposited on a silicon surface. Surprisingly, we find that a single particle species is very good for scattering AM 1.5 light on a glass surface, and that very little benefit is gained by mixing different shells. Assumptions and approximations made in the analysis are discussed.

This thesis provides the first example of coordination of a 1,2,3-dithiazolyl (1,2,3-DTA) ligand through a N, O bidentate pocket that is reproducible in high purity and bulk quantities. More importantly, it reports the first magnetometry measurements on metal complexes of a 1,2,3-DTA ligand. The radical ligand 1,2,3-dithiazolyl-6,7-dimethyl-1,4-naphthoquinone (6,7-Me2DTANQ) has been prepared and fully characterized. Coordination complexes of 6,7-Me2DTANQ have also been prepared and the resulting species’ structural and magnetic properties are presented. The transition metal ions Ni2+ and Mn2+ produce volatile trinuclear M(hfac)2-Rad-M(hfac)2-Rad-M(hfac)2 complexes. The spin ground state of the trinuclear Mn complex ST = 13/2 results from antiferromagnetic (AFM) coupling. Short sulfur-sulfur contacts and sulfur-oxygen contacts between trinuclear complexes produce weak AFM coupling interactions between trimer units. The lanthanide ions Nd3+, Gd3+ and Dy3+ produce volatile [Ln(hfac)3-Rad]n complexes. The spin ground state of the Gd polymer is ST = 3 per monomeric unit due to Gd3+‒radical AFM coupling.

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The explosive growth in the information technology industry requires high-performance optical sources. In recent years, wavelength-tunable optical pulse sources are of interest for applications in optical instrumentation, communications, and sensing. This thesis demonstrates and analyzes the generation of wavelength tunable, picosecond pulses from mode-locked semiconductor fiber ring lasers. One structure using an intracavity electro-optic modulator and the other an injected optical control signal, are investigated and experimentally characterized. A single or superimposed linearly chirped fiber Bragg gratings are used to provide wavelength selectivity, tunability, and multi-wavelength operation. The semiconductor optical amplifier as the gain media makes it possible to obtain stable simultaneous oscillation of several wavelengths at any wavelength band with very small channel spacing. We have successfully generated picosecond pulses at one or two wavelengths over the reflection bandwidth(s) of the grating(s) by simply changing the modulation frequency.

A thorough investigation of a pulsed plasma x-ray source is presented with the intent of improving its design and maximizing its x-ray emission efficiency. In this approach a hollow gas column is puffed in the z-pinch diode by magnetically ionizing and compressing an inert gas in an annular plenum. This gas column is preionized by the radiation coming out from the plasma in the plenum and pinched by a fast electrical discharge. / It is shown that the system can be improved considerably by modifying the gas puff design. Three gas puffs developed in this work are optimized for x-ray emission from argon, krypton, and neon gases. In the optimized conditions the output x-ray energies of 0.5 J from Ar-K shell, 2 J from Kr-L shell, and more than 2 J from Ne-K shell are obtained. / The implosion dynamics is studied with different gases under varying conditions. The average implosion velocity, the final pinch diameter, the current waveform, and the emitted x-ray energy are measured. The pinched plasma parameters such as temperature, density, and the average ionic state are estimated using the corona model calculations, and the pinched current waveforms. The spectrum of the neon radiation clearly shows the characteristic H-like and He-like lines. The neon spectrum is used to estimate the plasma temperature. / The dynamic performance of the magnetically induced compression gas puff is studied carefully. A special ion probe was developed for studying the dynamic parameters of the gas puff. The ion measurements with the probe have led to the characterization of the gas puff performance under varying operating conditions. It is shown that ions are generated through photoionization of the injected gas by the UV light emitted from the inside of the gas puff plenum through the nozzle. It is found that the jet velocity and ion density can be in excess of $3 times10 sp3$ m/s and $2 times10 sp{14}$ cm$ sp{-3}$, respectively. / A theoretical model is developed to simulate the plasma evolution in the gas puff. This model uses the magneto hydrodynamic (MHD) equations solved by the finite difference method. The magnetic field in the vacuum is calculated using the Laplace equation and self consistent boundary conditions. The model predicts the evolution of plasma variables such as density, temperature, velocity, and magnetic field. It also calculates the variation of the total mass flow rate, optical output, and the ionic signal. The simulation results are shown to compare favourably with the experimental measurements.

As the demand for wireless communications increases, high speed and low cost electronics are desired. Traditionally, RF circuits are implemented using high performance technologies such as GaAs or SiGe in order to minimize noise and achieve high gain. However, those high performance processes are incompatible with mainstream digital circuitry, which are usually implemented in CMOS technologies. / In this thesis, an RF receiver frontend which consists of a differential low noise amplifier, active mixers, passive mixers, and a quadrature voltage-controlled oscillator, for 5 GHz applications are designed and manufactured in a digital CMOS process, in order to demonstrate the RF potential of CMOS processes. We explore the use of simple circuit topologies and common packaging to build CMOS receivers that can operate from IV supplies and lower, while providing reasonable image rejection without the use of any special image rejection filters. In addition, a high image rejection receiver is explored after designing it based on good and simple frequency planning. / Apart from inductors and capacitors, transformers are very useful passive components in RF applications. For example, transformers can act as on-chip single-ended to differential converters. In this thesis, a comprehensive study of transformer modeling is presented and discussed. A modeling program has been developed, and its accuracy verified through measurements of several transformer prototypes fabricated in a variety of state-of-the-art CMOS technologies. The program allows the generation of compact lumped transformer models to be used in circuit simulation.