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Transient photocapacitance (TPC) and transient photocurrent (TPI) spectroscopy have been used to examine the defect structure in the upper-half of the bandgap of CdTe solar cells, with an emphasis on understanding the effect of copper. TPC spectra reveal two defects in the CdTe devices at optical energies of 1.2eV and 0.9eV with respect to the valence band. The origin of the 1.2eV defect could not be associated with a particular element, although copper and zinc were ruled out as sources. TPI spectra were used to observe that the density of the 1.2eV defect was dramatically reduced by thermally annealing the devices, suggesting that the defect itself is annealed during the treatment. The set of CdTe samples examined used a rapid thermal processing treatment to control the amount of copper that diffused into the CdTe layer from the Cu:ZnTe interfacial layer at the back of the device. Comparison of devices with varying amounts of copper in the CdTe layer revealed that the 0.9eV defect seen in TPC was associated with the presence of copper in the absorber layer. TPI spectra confirmed the association of the 0.9eV with copper and showed that the magnitude of the 0.9eV defect signal increased as more copper was diffused into the CdTe layer. A proportional link between the density of the 0.9eV defect observed in TPI spectra and the amount of copper in the absorber layer observed via ToF-SIMS further established that copper is responsible for the existence of the defect. Numerical modeling of the CdTe devices was used to confirm that the spatial distribution of copper observed in ToF-SIMS was consistent with the relative variation of defect magnitudes observed in TPI. The fact that the copper-associated 0.9eV defect lies close to mid-gap suggests that it will act as an efficient recombination center in CdTe. Therefore, it is suggested that this work has detected the deep defect that is responsible for the decreased minority carrier lifetime that has been previously associated with the amount of copper in the CdTe layer

"The development and clinical adoption of more effective fixation devices for re-approximating and immobilizing the sternum after open-heart surgery to enable bony healing has been limited, in part, by the lack of in vitro test methods used to evaluate these devices which precisely emulate in vivo loading of the sternum. The present study is an initial effort to determine the loading parameters necessary to improve current in vitro and numerical test methods by characterizing the direction, magnitude, and distribution of loading along the sternotomy midline in vivo using a porcine model. Changes in forces incurred by death and embalming were also investigated to estimate the applicability of cadavers as chest models for sternal fixation. Two instrumented plating systems were used to measure the magnitude, direction, and distribution of forces across the bisected sternum in four pigs during spontaneous breathing, ventilated breathing, and coughing for four treatments; live, dead, embalmed, and refrigerated. Forces were highest in the lateral direction and highest at the xiphoid. An important finding was that the magnitude of the respiratory forces in all directions was smaller than anticipated from previous estimations, ranging from 0.37 N to 43.8 N. No significant differences in force were found between the four treatments, most likely due to the very small magnitude of the forces and high variability between animals. These results provide a first approximation of in vivo sternal forces and indicate that small cyclic fatigue loads should be applied for long periods of time, rather than large quasistatic loads, to best evaluate the next generation of sternal fixation devices. "

The purpose of this study is to evaluate the endothelialization, exclusion of the aneurysm from circulation and intra-aneurysmal thrombus formation induced by the implantation of endovascular flow divertors for the purpose of bridging aneurysms. The design of the flow divertors was based on previous in vitro hemodynamic experiments in aneurysm models. The significance of this work is manifested in the development of a minimally invasive technology that may be employed for aneurysm treatment. Divertors with two different filament sizes and three different porosities were implanted in the rabbit elastase-induced aneurysm model and their effectiveness evaluated both angiographically and histologically. Preliminary results demonstrated that it is possible to achieve substantial reduction in intraaneurysmal flow immediately after device deployment. Angiographically, the aneurysms were excluded from the circulation with the medium and low porosity devices. In addition, the device performed as expected: smooth deployment, no intralumenal clot formation, and exclusion of aneurysm from the circulation without occluding other arterial branches. Additional data is needed to make definitive conclusions regarding endothelialization and the formation of a neointima.

Isoelectric trapping (IET), has proven to be one of the most successful electrophoretic techniques used for separations of ampholytic compounds. IET is carried out in multicompartment electrolyzers (MCEs) in which adjacent compartments are joined through buffering membranes whose pH values bracket the pI of the ampholytic component to be trapped in the compartment. The present small-scale instruments use plastics as their structural materials, which causes poor Joule heat dissipation. The separation compartments have cylindrical or pear-shaped interiors with large internal diameters, which create long heat transfer paths. The long electrode distances yield low field strengths that lead to low electrophoretic velocities for the analytes. These factors interrelatedly limit the electric power that can be applied to the system, contributing to long separation times. Furthermore, these devices do not offer a realistic solution to the problems associated with the detection of low abundance proteins. To address these problems, two novel IET devices have been developed for small-scale IET separations. The first device, named MSWIFT, was constructed using thermally conductive, high-purity alumina as the structural material of the separation compartments. By creating narrow, 0.1- or 0.2-mL channels in thin alumina blocks, the heat transfer path from the center of the compartment to the wall was significantly decreased; and the distance between electrodes was greatly shortened. MSWIFT achieved 6 to 50 times faster IET separations compared to other MCEs. The second device, named ConFrac, was developed to simultaneously fractionate and concentrate ampholytic components from a complex sample into 0.1-mL collection compartments. By designing a system with a 2-dimensional pH gradient and allowing recirculation of the sample feed, the ConFrac demonstrated enrichment of analytes by a factor of 100 and greater.

A wearable cooling system was developed in this study for use in elevated temperature environments by military, fire-fighting, chemical-response, and other hazardous duty personnel. Such a system is expected to reduce heat-related stresses, increasing productivity and allowable mission duration, reduce fatigue, and lead to a safer working environment. The cooling system consists of an engine-driven vapor-compression system assembled in a backpack configuration, coupled with a cooling garment containing refrigerant lines worn in close proximity to the skin. A 2.0 L fuel tank in the backpack powers a small-scale engine that runs a compressor modified from the original air compression application to the refrigerant compression application here. A centrifugal clutch and reduction gear train system was designed and fabricated to couple the engine output to the refrigerant compressor and heat rejection fan. The overall cooling system, including the wearable evaporator, had a total mass of 5.31 kg (11.7 lb) and measured 0.318 נ0.273 נ0.152 m (12.5 נ10.75 נ6 inches). Testing was conducted in a controlled environment to determine system performance over a wide range of expected ambient temperatures (37.7-47.5㩬 evaporator refrigerant temperatures (22.2-26.1㩬 and engine speeds (10,500-13,300 RPM). Heat removal rates of up to 300 W, which is the cooling rate established in the literature as being required for maintaining comfort at an activity level comparable to calisthenics or moderate exercise, were demonstrated at a nominal ambient temperature of 43.3㠨110橮 Modeling the fuel as 88 percent methanol (LHV ~ 1.992ױ07 J/kg) and 12 percent oil, the system consumed 1750 W at an average fuel mass flow rate of 0.316 kg/hr to provide a nominal cooling rate of 178 W for 5.7 hrs between refueling.

Scanning Probe Lithography (SPL) is a versatile nanofabrication platform that leverages microfluidic “ink” delivery systems with Scanning Probe Microscopy (SPM) for generating surface-patterned chemical functionality on the sub-100 nm length scale. One of the prolific SPL techniques is Dip Pen Nanolithography™ (DPN™). High resolution, multiplexed registration and parallel direct-write capabilities make DPN (and other SPL techniques) a power tool for applications that are envisioned in micro/nano-electronics, molecular electronics, catalysis, cryptography (brand protection), combinatorial synthesis (nano-materials discovery and characterization), biological recognition, genomics, and proteomics. One of the greatest challenges for the successful performance of the DPN process is the delivery of multiple inks to the scanning probe tips for nano-patterning. The purpose of the present work is to fabricate a microfluidic ink delivery device (called “Centiwell”) for DPN (and other SPL) applications. The device described in this study maximizes the number of chemical species (inks) for nanofabrication that can be patterned simultaneously by DPN to conform the industrial standards for fluid handling for biochemical assays (e.g., genomic and proteomic). Alternate applications of Centiwell are also feasible for the various envisioned applications of DPN (and other SPL techniques) that were listed above. The Centiwell consists of a two-dimensional array of 96 microwells that are bulk micromachined on a silicon substrate. A thermoelectric module is attached to the back side of the silicon substrate and is used to cool the silicon substrate to temperatures below the dew point. By reducing the temperature of the substrate to below the dew point, water droplets are condensed in the microwell array. Microbeads of a hygroscopic material (e.g., poly-ethylene glycol) are dispensed into the microwells to prevent evaporation of the condensed water. Furthermore, since poly-ethylene glycol (PEG) is water soluble, it forms a solution inside the microwells which is subsequently used as the ink for the DPN process. The delivery of the ink to the scanning probe tip is performed by dipping the tip (or multiple tips in an array) into the microwells containing the PEG solution. This thesis describes the various development steps for the Centiwell. These steps include the mask design, the bulk micromachining processes explored for the micro-fabrication of the microwell array, the thermal design calculations performed for the selection of the commercially available thermoelectric coolers, the techniques explored for the synthesis of the PEG microbeads, and the assembly of all the components for integration into a functional Centiwell. Finally, the successful implementation of the Centiwell for nanolithography of PEG solutions is also demonstrated.

Isoelectric trapping (IET), has proven to be one of the most successful electrophoretic techniques used for separations of ampholytic compounds. IET is carried out in multicompartment electrolyzers (MCEs) in which adjacent compartments are joined through buffering membranes whose pH values bracket the pI of the ampholytic component to be trapped in the compartment. The present small-scale instruments use plastics as their structural materials, which causes poor Joule heat dissipation. The separation compartments have cylindrical or pear-shaped interiors with large internal diameters, which create long heat transfer paths. The long electrode distances yield low field strengths that lead to low electrophoretic velocities for the analytes. These factors interrelatedly limit the electric power that can be applied to the system, contributing to long separation times. Furthermore, these devices do not offer a realistic solution to the problems associated with the detection of low abundance proteins. To address these problems, two novel IET devices have been developed for small-scale IET separations. The first device, named MSWIFT, was constructed using thermally conductive, high-purity alumina as the structural material of the separation compartments. By creating narrow, 0.1- or 0.2-mL channels in thin alumina blocks, the heat transfer path from the center of the compartment to the wall was significantly decreased; and the distance between electrodes was greatly shortened. MSWIFT achieved 6 to 50 times faster IET separations compared to other MCEs. The second device, named ConFrac, was developed to simultaneously fractionate and concentrate ampholytic components from a complex sample into 0.1-mL collection compartments. By designing a system with a 2-dimensional pH gradient and allowing recirculation of the sample feed, the ConFrac demonstrated enrichment of analytes by a factor of 100 and greater.

Photonic crystals have the capability to control electromagnetic waves due to the existence of photonic bandgap. The devices based on photonic crystal structures usually have the advantage of substantial size reduction compared to their conventional counterparts, which may lead to miniaturization and large-scale integration of optical and optoelectronic devices.In this dissertation, several novel optical devices based on photonic crystals are designed and analyzed, including a compact power splitter, a compact polarizing beam splitter, an optical intersection of nonidentical optical waveguides, and a single mode coupled resonator optical waveguide. The simulation results show superior advantages compared to their conventional counterparts. In addition, a new fabrication method based on combining a custom-built blue laser writer and the technique of optical holography is developed for the purpose of mass production of useful photonic crystal devices.