As electronic and optical devices shrink to the nanoscale, accurate methods for characterizing electromagnetic fields generated by sub-wavelength structures become increasingly important. Absorption in poly(methyl methacrylate) (PMMA) via 4th harmonic generation in metallic nanostructures is a way to characterize complex resonance modes. When exposed with a femptosecond Ti:sapphire oscillator, the damaged PMMA surrounding the nanoparticles can be imaged with an scanning electron microscope, creating an electric near-field intensity profile. This occurs without absorbing the fundamental frequency, and provides an accurate visualization of the resonant fields. Localized surface plasmonic near-fields generated by metallic nanorods have been mapped previously with this technique. In this document, nanorods and bowtie antennas are fabricated and the electric near-field intensity imaged with PMMA mapping. We then analyzed this data to determine more about the technique and about what drives the resonance of plasmonic nanoantennas.

An important aspect of engineering systems for use in extreme environments is understanding the performance of electronic components in radiation environments (e.g., space environments, nuclear reactors, particle accelerators). To accomplish this, experimental and computational modeling approaches are used to understand physical mechanisms that lead to system level failures. When experimentally investigating displacement damage, a common radiation effect, the most important parameter to measure is the particle fluence. An approach that offers benefits over traditional measurement techniques uses the degradation of current gain in silicon bipolar junction transistors as a direct metric for displacement damage in silicon. This thesis covers the bipolar device physics and particle/crystal interactions necessary to understand how displacement damage leads to gain degradation and describes how bipolar devices can be applied as displacement damage sensors to measure particle fluence. The use of bipolar junction transistors as displacement damage sensors in neutron irradiations is demonstrated at lower fluences than previously achieved and first-of-a-kind displacement damage sensor measurements for proton irradiations are provided. The non-ionizing energy loss (NIEL) of each particle is shown to adequately correlate the two particle types, neutrons and protons, across five orders of magnitude of particle fluence using three bipolar junction transistors (2N1486, 2N2484, 2N2222).

Colloidal semiconductor nanocrystals have become one of the most versatile systems for studying the fundamental properties of nanoscale materials and their applications. The ternary I-III-VI2 semiconductors hold particular promise for applications due to their flexible stoichiometry, low toxicity constituent elements, and range of desirable band gap energies (0.5 â 3.5 eV). Furthermore, I-III-VI2 nanocrystals can be isolated in metastable, anisotropic crystal structures not seen in the bulk. This structural anisotropy can be exploited to produce nanostructures with asymmetric morphology and electronic structure, which can enhance their performance in optoelectronic applications. In this dissertation, metastable, anisotropic crystal structures of I-III-VI2 materials are synthesized and their optoelectronic properties are investigated. CuInS2 has been widely explored for use in solar energy capture due to its band gap near the visible spectral region. Here, a direct synthesis to luminescent CuInS2 nanocrystals with the anisotropic wurtzite phase is developed and the mechanism of their formation is identified. A combined experimental and theoretical approach is then used to identify the radiative defect responsible for the luminescence observed. Furthermore, hybrid wurtzite CuInS2-Pt nanocrystals are prepared and their photoelectrical properties characterized to determine the efficacy of this system in photocatalytic applications. The knowledge obtained from the CuInS2 system is then applied to additional I-III-VI2 materials, CuFeS2 and AgFeS2. Wurtzite CuFeS2 is prepared using three distinct synthetic routes and the resultant nanocrystals are compared to each other and the In-containing analogues. Anisotropic, orthorhombic nanocrystals of AgFeS2 are also synthesized and characterized for the first time. The presence of Fe in both these systems leads to the observation of broad multimodal absorbance features at low energy, which can be utilized in thermoelectric and photothermal applications. Experimental measurements and density functional theory calculations indicate that this unique absorbance originates from changes in the composition of the nanocrystals.

Researchers discovered the existence of non-coding RNA while unraveling the secrets of the human genome. Non-coding RNA molecules are never translated into proteins, yet they are highly abundant and serve critical functions within all cells. Imbalances in one class of regulatory non-coding RNA, known as microRNA (miRNA), lead to diseases such as cancer and cardiovascular disease. MiRNA inhibition is a potent therapeutic strategy because single miRNAs can regulate hundreds of different disease-associated genes. Peptide nucleic acids (PNA) are excellent miRNA inhibitors, yet they have no innate ability to reach miRNA targets in the body. This worksâ central hypothesis is that therapeutic anti-miRNA activity can be improved by engineering nanoparticles to increase PNA blood circulation half-life, cellular uptake, and targeted delivery to the cytoplasm of diseased cells. In this thesis, two highly tunable biomaterials (porous silicon and âsmartâ polymers) are combined to form composite nanoparticles that improve the PNA therapeutic delivery. These nanocomposites are shown to be non-toxic, increase PNA blood-circulation half-life from <1 min to 70 min, and improve PNA delivery to its site of action in target cells. This thesis demonstrates how nanotechnology can aid the clinical translation of a promising new class of therapeutics.

Porous silicon, a nanostructured material formed by electrochemical etching of a silicon substrate, is an ideal candidate for constructing optical biosensors due to its large internal surface area, straightforward fabrication, and tunable optical properties that can be exploited to form numerous photonic structures. A major challenge for porous silicon biosensors is its reactive surface that is highly susceptible to oxidation and corrosion in an aqueous environment. In DNA sensing applications, porous silicon corrosion can mask the DNA binding signal as the dissolution of porous silicon is accelerated by the negative charges on the phosphate backbone of the DNA molecules. This corrosion process can be mitigated through surface passivation of porous silicon and the use of charge neutral peptide nucleic acid molecules as capturing probes for DNA targets. Complete mitigation can be achieved by additionally introducing Mg2+ ions to shield the negative charges on the DNA targets. Another key challenge facing porous silicon biosensors is the inefficient analyte transport through nanopores, which can be as slow as a few molecules per pore per second for molecules whose size approaches that of the pore opening. An open-ended porous silicon membrane is demonstrated to overcome the mass transport challenge by allowing analytes to flow through the pores in microfluidic-based assays. The flow-through approach for biosensing using porous silicon membranes enables a 6-fold improvement in sensor response time compared to closed-ended, flow-over porous silicon sensors when detecting high molecular weight analytes (e.g., streptavidin). For small analytes, little to no sensor performance improvement is observed as the closed-ended porous silicon films do not suffer significant mass transport challenges with these molecules. Experimental results and finite element method simulations also indicate that the flow-through scheme enables more reasonable response times for the detection of dilute analytes and reduces the volume of solution required for analysis. Overall, the improvement of surface stabilization and analyte transport efficiency in porous silicon photonic structures opens the door to a fast and reliable optical biosensing platform.

This research is focused on developing a new type of gamma-ray scintillator and is motivated by the need for more accurate positron emission tomography (PET) imaging. PET scans are used to display regions of high-metabolic activity within the body and can indicate the presence of tumors, so clear images are essential for accurate diagnoses and treatment options. Scintillation detectors currently used for PET scans typically have a time resolution of hundreds of ps that yields images with poorly defined and blurred boundaries. Conversely, ZnO nanowires have a response time that is an order of magnitude faster with the potential for an analogous improvement to spatial resolution. Moreover, initial experiments show ZnO nanowires are radiation hardened with highly transient lattice defects. To optimize overall scintillator efficiency, the emission can be enhanced through a combination of optical-cavity effects (15x enhancement) and plasmon-exciton coupling (3x enhancement), while the low interaction volume of the nanowires can be addressed by adding a high-Z backing layer to attenuate incoming gamma rays. The ability to decouple, and address separately, emission efficiency and gamma-ray interaction provides a unique materials workbench and establishes ZnO nanowires as a highly promising PET scan scintillator material.

Gallium arsenide and other III-V materials are well known for their excellent optical and electronic properties and have led to the development of high-performance optoelectronics. Several combinations of III-V semiconductors are now being considered as potentially attractive alternatives to silicon for these applications. However, further development requires fundamental understanding of processes that govern light-matter interactions. Specifically, surface strain and ultrafast dynamics are of great interest to the optoelectronic industry. The research of this dissertation represents an initial exploration of the factors influencing nonlinear optical responses on semiconductor surfaces. The results of this research have the potential to inform the field of nonlinear optics about which lattice behaviors are most likely to contribute to static and transient second harmonic generation (SHG). This information allows for future work to focus on the connection between SHG, dipole contributions, and interatomic potentials in semiconductors under different conditions. This research also provides information about whether strain, resonances, and subpicosecond lattice behaviors can be fit with a simple analytical solution. The results of this research reveal that an analytical fit of polarization-resolved SHG is sensitive to interatomic potential and dipole variations in all three dimensions simultaneously.

Corrosion is a major issue in applications involving materials in normal and severe environments, especially when it involves corrosive fluids, high temperatures, and radiation. Left unaddressed, corrosion can lead to catastrophic failures, resulting in economic and environmental liabilities. In nuclear applications, where metals and alloys, such as steel and zirconium, are extensively em- ployed inside and outside of the nuclear reactor, corrosion accelerated by high temperatures, neu- tron radiation, and corrosive atmospheres, corrosion becomes even more concerning. The objec- tives of this research are to study and develop surface modification techniques to protect zirconium cladding by the incorporation of a specific barrier coating, and to understand the issues related to the compatibility of the coatings examined in this work. The final goal of this study is to recommend a coating and process that can be scaled-up for the consideration of manufacturing and economic limits. This dissertation study builds on previous accident tolerant fuel cladding research, but is unique in that advanced corrosion methods are tested and considerations for implementation by industry are practiced and discussed. This work will introduce unique studies involving the materials and methods for accident tolerant fuel cladding research by developing, demonstrating, and consid- ering materials and processes for modifying the surface of zircaloy fuel cladding. This innova- tive research suggests that improvements in the technique to modify the surface of zirconium fuel cladding are likely. Three elements selected for the investigation of their compatibility on zircaloy fuel cladding are aluminum, silicon, and chromium. These materials are also currently being investigated at other labs as alternate alloys and coatings for accident tolerant fuel cladding. This dissertation also investigates the compatibility of these three elements as surface modifiers, by comparing their mi- crostructural and mechanical properties. To test their application for use in corrosive atmospheres, the corrosion behaviors are also compared in steam, water, and boric-acid environments. Various methods of surface modification were attempted in this investigation, including dip coating, diffu- sion bonding, casting, sputtering, and evaporation. The benefits and drawbacks of each method are discussed with respect to manufacturing and economic limits. Characterization techniques utilized in this work include optical microscopy, scanning electron microscopy, energy-dispersive spec- troscopy, X-ray diffraction, nanoindentation, adhesion testing, and atomic force microscopy. The composition, microstructure, hardness, modulus, and coating adhesion were studied to provide en- compassing properties to determine suitable comparisons and to choose an ideal method to scale to industrial applications. The experiments, results, and detailed discussions are presented in the following chapters of this dissertation research.

The chemical vapour transport reactions of some Group III-V semiconductors with hydrogen halides have been studied hy a modified entrainment method. Enthalpies and entropies for the transport reactions in the systems: indium arsenide-hydrogen bromide, indium arsenide-hydrogen chloride and gallium arsenide-hydrogen bromide were calculated. The effect of surface kinetics on the rate of transport of gallium arsenide by hydrogen bromide gas was investigated. Binary diffusion coefficients for hydrogen bromide and hydrogen chloride gases in hydrogen have been obtained by a study of the transport of indium in hydrogen bromide or hydrogen chloride under limiting equilibrium conditions. Using literature results for the temperature dependence of the vapour pressure of zinc, the binary diffusion coefficients of zinc atoms in helium and in argon over the temperature range 850 - 1120 K were determined. A modified entrainment method apparatus was used to monitor the evaporation of zinc in the inert gas.

<p> The progressive advancements in communication and transportation has changed human daily life to a great extent. While important advancements in battery technology has come since its first demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. One considerable bottleneck is the cathode energy density, the Li-rich layered oxide compounds xLi₂MnO₃.(1-x)LiMO₂ (M= Ni, Mn, Co) (0.5= Co) (0.5=discharge capacities greater than 280 mAh g^-1 (almost twice the practical capacity of LiCoO₂).</p><p> In this work, neutron diffraction under <i>operando</i> battery cycling is developed to study the lithium and oxygen dynamics of Li-rich compounds that exhibits oxygen activation at high voltage. The measured lattice parameter changes and oxygen position show movement of oxygen and lattice contractions during the high voltage plateau until the end of charge. Lithium migration kinetics for the Li-rich material is observed under operando conditions for the first time to reveal the rate of lithium extraction from the lithium layer and transition metal layer are related to the different charge and discharge characteristics.</p><p> In the second part, a combination of multi-modality surface sensitive tools was applied in an attempt to obtain a complete picture to understand the role of NH4F and Al₂O₃ surface co-modification on Li-rich. The enhanced discharge capacity of the modified material can be primary assigned to three aspects: decreased irreversible oxygen loss, the activation of cathode material was facilitated with pre-activated Mn³⁺ on the surface, and stabilization of the Ni redox pair. These insights will provide guidance for the surface modification in high voltage cathode battery materials of the future.</p><p> In the last part, the idea of Li-rich has transferred to the Na-ion battery cathode. A new O3 - Na_0.78Li_0.18Ni_0.25Mn_0.583O_w is prepared as the cathode material for Na-ion batteries, delivering exceptionally high energy density and superior rate performance. The single-slope voltage profile and ex situ synchrotron X-ray diffraction data demonstrate that no phase transformation happens through a wide range of sodium concentrations (0.8 Na removed). Further optimization could be realized by tuning the combination and ratio of transition metals.</p>