Silicon carbide has been preferred over other wide band-gap semiconductors for high power applications because of its unique ability to grow a thermal oxide, challenges lie in the quality of the dielectric and of the SiO2/SiC interface. This thesis focuses on the electrical properties and the reliability of the oxide and its interface with silicon carbide. In particular, the effects of processing parameters, such as implant activation, oxidation conditions (partial pressure), and post-oxidation anneal (nitridation), are considered. Tests are performed on metal-oxide-semiconductor (MOS) capacitors probed by capacitance-voltage measurements (CV), carrier injection (tunneling, photo-emission, irradiation), and time-dependent dielectric breakdown (TDDB). The most important new finding is that nitrogen, required for passivating the complex SiO2/SiC interface, can be detrimental to its reliability. Indeed, nitridation leads to the formation of hole traps, yielding large voltage instabilities.

To support the world's insatiable desire for energy in the coming century without risking environmental catastrophe, paradigm-shifting research into next-generation photovoltaics and solid-state white lighting is necessary. The Rosenthal group has been pursuing a fully solid-state, inorganic nanostructured photovoltaic featuring pyrolytically synthesized semiconductor nanocrystals deposited within a mesoporous nanocrystalline anatase (meso-nc-TiO2) framework. The synthesis and characterization of meso-nc-TiO2 pores and nanotubes with deposited nanocrystals represents a significant milestone in the fabrication of our next-generation photovoltaic devices. Additionally, a variety of nanocrystal systems were imaged using aberration-corrected atomic number contrast scanning transmission electron microscopes (Z-STEM). Most significantly, the first ever Z-STEM images of ultra-small white-light emitting CdSe nanocrystals were collected, which will aid in the development of a solid-state white-light source.

A new deposition technique for high performance polymer films, resonant infrared laser ablation (RIR-LA) is presented. Ultraviolet laser deposition techniques have been shown to cause decomposition and depolymerization of the deposited polymer films. We hypothesized that the infrared radiation would be a gentler technique compared to ultraviolet radiation and should leave the polymer structure intact. We proposed a technique where a solution-based polymeric precursor is frozen in liquid nitrogen, placed in vacuum chamber, and ablated by a rastered infrared laser beam. Then the ejected material is collected on a substrate forming a thin polymeric film. First we tested the technique on a 15 weight % pyromellitic dianhydride-co-4,4-oxidianiline (PMDA-ODA) in N-methylpyrrolidinone (NMP), the polymeric precursor to polyimide. PMDA-ODA is converted to polyimide by a thermal cure near 250 °C. Fourier transform infrared spectroscopy results confirmed that the PMDA-ODA was transferred intact and without curing by RIR-LA. Molecular weight studies show that only a small portion of the original molecular weight is lost, allowing for the preservation of strength and structural properties. The technique was then tested with other polymers including polyamide imide and polyether imide. Both polymers were successfully transferred intact with no signs of curing. Polyamide imide boasts an even lower cure temperature than polyimide at only 150°C, illustrating how effective RIR-LA is at avoiding thermal transformations.

This dissertation reports the study of defects in Cadmium Zinc Telluride (CZT) and Cadmium Manganese Telluride (CMT) nuclear detectors. In this dissertation I studied the defects associated with surface processing of detectors as well as the extended defects present in the crystals. Synchrotron radiation, Infrared microscopy and Atomic Force Microscopy were employed to identify and study the defects. Detector response and performance from x-ray mapping and external sources was correlated with the observed defects. The Pockels electro-optic effect was used to observe non-uniformities of the internal electric field caused by defects. This collection of data was employed to produce a counting algorithm to show the expected performance of detectors based on sizes, concentration and distribution of inclusions. An optimal surface processing method combining polishing and chemical etching was established. Finally the first response of a CMT detector to high energy gamma radiation was demonstrated.

Electro-osmotic (EO) pumps directly convert electrical energy into fluids kinetic energy, which have many advantages such as a simple and compact structure, no mechanical moving parts, and easy integration. In general, it is easy for EO pumps to generate enough pressure but it has been a challenge for EO pumps to produce a high flowrate. EO pumps have found applications in various micro-/nano-electro-mechanical systems (MEMS/NEMS) and have the potential to impact a variety of engineering fields including microelectronics cooling and bio-analytical systems. This dissertation focuses on the design, fabrication and characterization of EO pumps based on two novel porous membrane materials: SiO2-coated anodic porous alumina and SiNx-coated porous silicon. High quality porous alumina membranes of controllable pore diameters in the range of 30-100 nm and pore lengths of 60-100 &181;m were fabricated by electrochemical anodization. The pores are straight, uniform and hexagonally close-packed with a high porosity of up to 50%. The inner surface of the pore was coated with a thin layer (~5 nm) of SiO2 conformally to achieve a high zeta potential. The EO pumping flowrate of the fabricated anodic alumina membranes, coated and uncoated, was experimentally measured. Results indicate that the high zeta potential of the SiO2 coating increases the pumping flowrate even though the coating reduces the porosity of the membrane. The nanostructured SiO2-coated porous anodic alumina membranes can provide a normalized flowrate of 0.125 ml/min/V/sq. cm. under a low effective applied voltage of 3 V, which sets a record high normalized flowrate under low applied voltage. To realize field effect control of EO pumping, we designed and fabricated SiNx-coated porous silicon membranes with the silicon core as the electrode to apply a transverse gate potential. The gate potential will modulate the zeta potential of the pore wall and thereby provide control over the EO flowrate. The membranes were fabricated out of heavily doped silicon wafers using microfabrication techniques. The pores have a 15 &181;m &215; 40 &181;m cross sectional area with a thin layer of SiNx coated conformally over the pores by low-pressure chemical vapor deposition (LPCVD). The range of gate voltages applied was from -45 V to +40 V. For Vg < 0, current leakage through the SiNx film was observed whereas negligible leaking current was detected for Vg > 0. This current rectification effect is known as electrolytic rectification, as a result of which a greater EO flow control, nearly 70% reduction in flow velocity, was observed for positive gate bias and 15% flow velocity enhancement under negative gate bias of similar magnitude. Ionic current is closely related to EO flow and the last part of the dissertation is devoted to ionic current measurements through commercially made nanoporous glass membranes (4 nm average pore diameter). This study was motivated by a molecular dynamics (MD) simulation highlighting an unusual ionic current trend in a 3 nm diameter pore having high surface charge density at high electrolyte concentrations. The ionic current was measured with two kinds of electrolytes NaCl and KCl. The experimental results, however, indicated an expected linear trend of ionic current for electrolyte concentrations beyond 1 M, contrary to the results of the MD simulation study, which was attributed to a low surface charge density measured for the porous glass membranes.

White light-emitting diodes (LEDs) have attracted great interest recently due to their capability for higher efficiency and longer lifetimes compared to other current lighting technologies. In pursuit of a white LED that has improved characteristics over commercial white LEDs, the focus of this dissertation is on the optical properties of white-light emitting cadmium selenide (CdSe) nanocrystals. Phosphor-based LEDs typically require an encapsulant to protect the phosphor from heating and photo-oxidation, as well as to inhibit particle aggregation. In this dissertation, a number of encapsulant materials were tested to determine which material would mix well with the nanocrystals in solution before deposition, cure properly as a film, and maintain the optical properties of the CdSe nanocrystals. A biphenylperfluorocylcobutyl (BP-PFCB) polymer performed the best of the encapsulants tested, with over twice the emission intensity of the next best encapsulant as well as a much higher percentage of UV excitation light absorbed at a certain thickness. In addition, several methods to improve the device efficiency of these LEDs were investigated, including experimentally optimizing the LED excitation wavelength, film thickness, and nanocrystal concentration in the film. The optimum device parameters were found to be a 365 nm or 385 nm LED exciting a film of 60-140 μm in thickness with a nanocrystal weight concentration in BP-PFCB of 10%, resulting in a luminous efficacy of 1 lm/W, CIE coordinates of (0.35, 0.37), and a color rendering index (CRI) of 86. Furthermore, while scattering from micron-sized phosphors used in LEDs can cause significant losses, the scattering cross section for ultrasmall CdSe nanocrystals was found to be five orders of magnitude lower than the absorption cross section, thus scattering from nanocrystals can be neglected. Finally, a more accurate approach to determining the nanocrystal concentration of a solution and extinction coefficient was investigated. These results represent the initial steps towards building an ultrasmall CdSe nanocrystal-based, photoluminescent LED, and with further improvements could result in higher quality lighting products.

The oxides of rare-earth elements (rare-earth sesquioxide: RE2O3) are known for their optical and dielectric properties. Europium oxide is known for characteristic red luminescence and gadolinium oxide has excellent insulating properties (band gap: 5.5 eV). Development of ultra-small nanocrystals (sub-3 nm diameter) of these rare-earth oxides and investigation of their optical and dielectric properties are explored in this dissertation. A new synthesis process was developed successfully to produce ultra-small colloidal nanocrystals, which were capped with oleic acid. Europium oxide nanocrystals exhibited a new luminescence peak because of the occupation of Eu3+ ions in a surface site. The nanocrystals were assembled into films from their suspensions in hexane by electrophoretic deposition. Films of europium oxide were highly transparent in visible spectral region because of minimal scattering losses within the films and exhibited characteristic red luminescence. Gadolinium oxide nanocrystals exhibited charge-storage properties when integrated in a metal-insulator-semiconductor structure. Layered heterostructures of carbon nanotubes and nanocrystals were fabricated and their charge-storage properties were studied.

The operation and properties of semiconductor devices depends critically on a materials electronic structure. Point defects, such as vacancy and interstitial defects that arise from operation in radiative atmospheres or during less-than-ideal growth processes, have a significant influence on electronic material properties and tend to degrade device operation. Here we show that a novel ultrafast time-resolved pump-probe technique, known as coherent acoustic phonon spectroscopy, is capable of non-destructive, quantitative, depth-dependent measurement of point defect profiles arising from ion irradiation in gallium arsenide. In the CAP response, defects are observable through reduction of the CAP oscillation amplitude, which is demonstrated to be connected to a decrease in the photoelastic constant at the 1.42 eV GaAs band-edge caused by defect-induced lattice strain. Finally, we present theoretical calculations that support our proposed model and agree well with experimental observations

The goal of this work was to determine the luminescent lifetime of these phosphor materials as a function of temperature. Cerium-doped yttrium aluminum garnet and europium-doped pyrochlores were synthesized using combustion synthesis. The phosphors were characterized using X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Lifetime measurements were taken over a range of temperatures. The garnet materials exhibited thermal quenching between 30-125 ◦ C . In contrast, the pyrochlore materials did not exhibit thermal quenching until well past 300 ◦ C . The results presented in this work have shown that high energy states, such as the charge transfer state or the d -orbitals, play a key role in the thermal quenching properties of materials. For Ce-doped materials, our results indicate that materials which cause the splitting of the d -orbitals to increase will cause the emission from the d1 → 4 f transition to thermally quench at higher temperatures. The lifetime of the 5 D0 → 4 f emission line of Eu3+ is dependent on the location of the charge transfer state. We suggest that the reason higher quenching temperature are observed in materials such as YBO3 : Eu and the other pyrochlores is because these materials have high-energy charge transfer states. Tuning Eu3+ materials to maximize the energy of the charge transfer state may improve thermal quenching properties of thermographic phosphors.

This dissertation investigates the incorporation of Photosystem I (PSI), a supramolecular protein complex that participates in the light reactions of photosynthesis, into electrochemical systems intended for the conversion of photonic energy into chemical energy and electricity. First, I describe the fabrication of nanoporous gold leaf electrode films and detail the process by which they are decorated with PSI complexes. I further explain how the feature size of the substrate must be tuned such that the pores may accommodate multiple PSI complexes in order to produce enhanced photocurrent with respect to a planar electrode. Second, I develop a kinetic model for the photocatalytic effect produced by a monolayer of PSI on a planar electrode. I solve the resulting system of partial differential equations numerically and use the simulation to extract kinetic parameters from experimental data. Third, I describe the construction of stand-alone PSI-based photoelectrochemical cells, demonstrate their light transduction capabilities, and show that the devices continue to produce photocurrent for at least 9 months after their fabrication. Fourth, I present a method to deposit multilayer films of PSI by vacuum-assisted assembly. I characterize the resulting films optically and electrochemically and show that photocurrent production increases with thickness of the films. Furthermore, I demonstrate the largest photocurrent responses of the films are produced in response to irradiation by light of wavelengths that correspond to peaks in the films absorbance spectra. Finally, I offer general perspectives conclusions about the results presented herein and outline future directions in which this project may progress.