Radiation effects studies performed on electronics typically consist of electrical characterization of device performance to analyze the impact of radiation damage. Very few studies have focused on surface characterization of materials under high energy radiation, particularly those materials widely used in electronics such as silicon. This study addresses this gap in knowledge by first studying the influence of radiation on the surface of bare silicon, and then evaluating the high-energy radiation response of two silicon-based devices: a silicon photonic ring resonator and an amorphous silicon (a-Si:H) solar cell with a novel, metal covered, porous a-Si:H grating functioning as a back reflector. Irradiation of unpassivated bare silicon with 10-keV x-rays and 662-keV gamma rays, resulted in an enhanced rate of native oxide growth, which saturated at the typical native oxide thickness of ~ 2 nm. The oxidation rate was correlated to x-ray dose rate via an empirical thin oxide growth model. The transmission response of a silicon photonic ring resonator was then evaluated upon exposure to 10-keV x-rays and 662-keV gamma rays. Radiation exposure of the unpassivated ring resulted in a blue shift in resonance wavelength proportional to the incident total dose, while the transmission spectrum of a ring passivated with native oxide or a polymer coating remained immune to ionizing radiation. Next, an amorphous silicon n-i-p solar cell with a silver covered porous a-Si:H grating was fabricated and its performance was evaluated before and after irradiation with 4-MeV protons. The porous a-Si:H grating, fabricated by metal assisted chemical etching and a simple imprinting technique, led to a 30% increase in solar cell efficiency for thin active layers in comparison to identical solar cells with flat metal back reflectors. The enhancement was primarily attributed to increased photon absorption due to light scattering from the roughened metal grating. No degradation in solar cell performance was observed upon irradiation with 4-MeV protons for a fluence of 10^13 cm^(-2).

Electromagnetic metamaterials are artificially fabricated structures that exhibit properties unattainable in naturally occurring materials, such as negative index, epsilon-near-zero, ultra-high index, perfect lensing, and cloaking. Since their inception, metallic unit cells have dominated the field of metamaterials. However, metallic unit cells suffer from conduction loss, magnetic saturation at high frequencies, often exhibit an anisotropic optical response, and require expensive lithography methods for fabrication. Recently, there has been burgeoning interest in exploiting the Mie resonances in high index dielectric particles to design all-dielectric metamaterials, which not only have much less absorption losses at optical frequencies than their metallic counterparts but also provide the potential for achieving isotropic optical responses due to their simple unit cell geometry. The main motivation of this dissertation is two fold - first, to understand how electric and magnetic Mie resonances in dielectric particles can be used to design metamaterials exhibiting novel and unique optical properties; and second, to experimentally realize metamaterials using nanofabrication techniques, with a strong motivation towards achieving three dimensional and large scale metamaterials .

Three previously unreported photo-carrier relaxation pathways are presented and discussed in GaAs-based systems. In bulk GaAs, a transient bleach of the spin-split exciton transition 1s->2p is reported following photo-excitation at low temperatures and is likely caused by final state blocking of the 2p_1 exciton level. The bleach of the 1s->2p_-1 transition is delayed with respect to that of the free carriers and 1s->2p_+1, suggesting electronic relaxation occurs through two simultaneous mechanisms: elastic scattering between quantized conduction band states and spin-dependent relaxation through the 2p_1 exciton states. For ErAs:GaAs composites, the response at short time delays is completely dependent on the occupation of the interface trap state between the ErAs nanoparticles and the GaAs matrix. Occupation of the interface state depends on the photo-carrier energy, carrier density, and trap density. Carrier scattering from the interface state plays a large role in the response as it prevents full relaxation of the system on ultrashort timescales. The composite ErAs:GaAs systems also exhibit an oscillatory response highly suggestive of surface plasmon polaritons at the interface between the semi-metallic ErAs and semiconducting GaAs, which couple to the GaAs phonon modes. The oscillation frequencies are observed to follow the same trend with volume fraction as the static absorption resonance peaks, suggesting different nanoparticle size distributions exist with different ErAs incorporation.

Current generation infrared (IR) photodetection requires a tradeoff between sensitivity and practicality. For applications requiring high sensitivity, the available options require varying levels of expensive and bulky cryocooling to reduce noise or to enable detection. Cheaper, more portable devices suffer from low quantum efficiencies or relatively slow recovery speeds. Computational and experimental studies have been performed to investigate the possibility of realizing a highly efficient, room temperature IR photodetector through plasmonic enhancement of a vanadium dioxide (VO2) bolometer. By incorporating metamaterial and plasmonic antenna geometries exhibiting near unity absorption and high field confinement, the photon flux requirement for a detection event can be significantly reduced. Several geometries were explored with promising theoretical performance, and improvements to these designs are suggested based on initial experimental results.

How social media and Kickstarter are saving cult television shows like Arrested Development and Veronica Mars.

The favorable conductive properties of carbon nanotubes (CNTs) offer opportunities for constructing CNT-based nanocomposites with improved thermal conduction for a range of potential applications. Such lightweight composite materials are expected to have thermal properties that depend on their CNT volume fraction and operating temperature. The construction of CNT-based nanocomposites is challenged by the available processing methods for CNTs that are compatible with the construction of multi-laminated composite structures. The overall goal of this effort is to develop enhanced thermal properties in carbon nanotube-polymer composites that can replace traditional aerospace metallic materials to reduce the weight in space structures. The key innovation of this dissertation is in dispersing the carbon nanotubes onto a prepreg composite structure that sustains thermal storage and increase the thermal transport to support scientific instrumentation to more effectively radiate heat from a composite structure while increasing the thermal properties. The employed structures consisted of individual plies of IM7 prepreg composite with an embedded 8552 epoxy that were each coated with a CNT layer and then combined into the final composite structure using a vacuum-based hand layup technique for curing the 8552 epoxy. The composites were investigated by Raman spectroscopy, thermogravimetric analysis, thermal diffusivity, and differential scanning calorimetry. With varying the concentration of SWCNT up to 30 wt% to the IM7 prepreg composite, its heat capacity sustained over the tested temperature range and its through-thickness thermal diffusivity increased by 30% vs. the virgin composite material. By modeling, such additions of randomly oriented SWCNTs are suggested to increase the in-plane thermal conductivity by 120 to 150% over the temperature range of 120 to 470 K and by 30% in the through-thickness direction. A possible explanation of these improvements in the thermal conductivities are the reductions of the interfacial resistances between the SWCNTs, the 8552 epoxy, and the IM7 composite. The developed methods provide the opportunity for enhancing the thermal properties of a composite through the use of CNTs as additives. Such improvements would be particularly useful in aerospace applications for solar arrays, fairings, and thermal radiators.

The 2013 Report Card for the Nations Infrastructure, published by the American Society of Civil Engineers, estimates that more than 10% of the over 607,000 bridges in the United States are structurally deficient. Engendering a further sense of urgency for addressing bridge integrity is the impact of projected climate change and associated weather events. The most recent assessment report published by the IPCC concludes that the frequency of heavy precipitation events is increasing along with a concomitant increase in severe flooding. Several software applications are available that perform flood modeling and, in some instances, damage analysis resulting from the flood. Of the software identified, FEMAs HAZUS-MH, or Hazus, offers a balance between affordability, simplicity and accuracy. Hazus does demonstrate limitations when modeling floods in sub-county areas but at the county-level scale, predicted floods approximate observed floods. Using the US DOTs HEC-18 guide for bridge scour, a methodology was developed for estimating the monetary damage of bridge scour from a future flood event using flood parameters supplied by Hazus and other readily available resources. Results of the methodology indicated predicted and observed damage values did not exhibit a statistically significant difference (p=0.22, tá=0.05). Additionally, a Pearsons correlation coefficient of approximately 0.94 was observed. A demonstration of the methodology application was performed in which several bridges in Little Rock, Arkansas were assessed for adaptation planning prioritization.

Thesis (Ph. D.)--University of Technology Sydney, 2007.

Thesis (Ph. D.)--Texas A&M University, 2004. / "Major Subject: Interdisciplinary Engineering" Title from author supplied metadata (automated record created on Feb. 17, 2005.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A&M University, 2004. / "Major Subject: Interdisciplinary Engineering" Title from author supplied metadata (automated record created on Feb. 17, 2005.) Vita. Abstract. Includes bibliographical references.