Physical Sciences and Mathematics Commons^™

The Effect Of Ionization Density In Applications Of Radiation Detection, Dosimetry, And Therapy, Daniel Mulrow

Arts & Sciences Electronic Theses and Dissertations

This dissertation covers a wide range of topics but is linked by the common theme of radiation interacting with materials and studying the result of those interactions. The introduction describes the fundamentals of how radiation interacts with material and how we are able to detect that radiation and the application of how we use those interactions in radiation oncology. The thesis starts with a chapter detailing the temperature dependence of the photophysics in two organic scintillators. This chapter is the foundation for a future study that will look the degree to which these scintillators can distinguish between gammas and neutrons …

Method Development For Enhancing Sensitivity Of Dynamic Nuclear Polarization Nuclear Magnetic Resonance Spectroscopy For Structural Studies Of Pkc-Drug Interactions, Patrick Terrence Judge

Arts & Sciences Electronic Theses and Dissertations

To perform the most relevant structural studies on biological systems, experiments need to be carried out when the target proteins are in their endogenous cellular environment. Nuclear magnetic resonance (NMR) is well-suited to probe the structure and dynamics of a wide variety of systems, including biologically relevant proteins. However, NMR suffers from an inherent lack of sensitivity. Dynamic nuclear polarization (DNP) NMR is a powerful technique that is used to enhance NMR sensitivity by transferring the greater polarization of exogenously doped electron spins to nuclear spins of interest though the use of a high-power microwave source. Solid effect radicals offer …

In-Situ Imaging Of Surface Heterogeneity In Semiconductor Photocatalysts Using Singlemolecule Fluorescence Microscopy, Meikun Shen

Arts & Sciences Electronic Theses and Dissertations

Metal oxide semiconductors have been used as promising photocatalysts to convert solar energy into useful fuels, such as water splitting, carbon dioxide reduction, and nitrogen fixation reactions. However, the typical metal oxide photocatalysts' efficiency often suffers from their weak visible light absorption and low charge carrier mobilities. One common strategy to mitigate these limitations is to introduce oxygen vacancies into the lattice of the semiconductor photocatalysts. This strategy has been applied to many metal oxide photocatalysts, such as titanium oxide, tungsten oxide, and zinc oxide, and oxygen vacancies indeed enhance their catalytic activities. Various roles of oxygen vacancies have all …

Spectroscopic Investigations Of Excited Charge Carriers In Ii-Vi Nanoparticles, William Matthew Sanderson

Arts & Sciences Electronic Theses and Dissertations

The large absorption cross sections and the tunability of the energetic spacings between the states in the conduction (CB) and valence band (VB) within a semiconductor nanoparticle (NP) make them promising media for capturing electromagnetic radiation and converting it into charge carriers, or electricity. In photovoltaic devices that incorporate semiconductor NPs, it would be ideal if every photon could be absorbed by a NP and the carriers could be collected with perfect efficiency and without loss of energy. The relaxation pathways of the carriers within the NPs down to the band edge and their fate at the band edge contribute …

Instrumentation For Dynamic Nuclear Polarization And Application Of Electron Decoupling For Electron Relaxation Measurement, Nicholas Howard Alaniva

Arts & Sciences Electronic Theses and Dissertations

Dynamic nuclear polarization nuclear magnetic resonance (DNP NMR) exploits internal electron spin and nuclear spin interactions to increase sensitivity and uncover valuable information regarding structure and dynamics of a system. To manipulate these interactions, instrumentation is developed to combine high-power microwave and radiofrequency irradiation with the ability to spin samples at the magic angle (MAS) at temperatures from 90 K to 4.2 K. Electron decoupling uses frequency-modulated microwaves to mitigate the electron-nuclear dipolar interaction, improving signal intensity and resolution in DNP NMR experiments. Electron decoupling is combined with short DNP periods to encode electron spin information in polarized nuclear signal. …

Magic Angle Spinning Spheres And Improved Microwave Coupling For Magnetic Resonance, Pin-Hui Chen

Arts & Sciences Electronic Theses and Dissertations

Nuclear magnetic resonance (NMR) is a nondestructive technique used to characterize molecular structure and dynamics with atomic resolution. In solid-state NMR, magic angle spinning (MAS) is commonly implemented to improve spectral resolution by partially averaging anisotropic interactions. To further improve NMR sensitivity, dynamic nuclear polarization (DNP) is utilized to transfer the polarization from electron spins to nuclei of interest using microwaves. Advanced MAS DNP NMR instrumentation, such as spherical rotors for stable and fast spinning, dielectric lenses to effectively couple the microwaves into the sample, and the separation of receiving and transmitting circuits to decrease measurement noise, are developed to …

Solid-State Nmr Of Co2 Mineralization And Nmr Crystallography, Jinlei Cui

Arts & Sciences Electronic Theses and Dissertations

The work described in this dissertation has been accomplished by using solid-state nuclear magnetic resonance (SSNMR) spectroscopy to investigate CO2 mineralization and to refine the positions of protons in the crystalline system. The reaction of forsterite (Mg2SiO4) and 13CO2 is presented here, which is measured using in-situ 13C NMR spectroscopy without removing the sample from the reactor. 29Si SSNMR is used to investigate the reaction of forsterite with 13CO2 in the presence of water or NaCl brine as a function of depth in the sample. Additionally, we also show that NMR crystallography can significantly improve structure refinement of hydrogens’ positions …

Solid-State Nmr Of Co2 Mineralization And Nmr Crystallography, Jinlei Cui

Arts & Sciences Electronic Theses and Dissertations

The work described in this dissertation has been accomplished by using solid-state nuclear magnetic resonance (SSNMR) spectroscopy to investigate CO2 mineralization and to refine the positions of protons in the crystalline system. The reaction of forsterite (Mg2SiO4) and 13CO2 is presented here, which is measured using in-situ 13C NMR spectroscopy without removing the sample from the reactor. 29Si SSNMR is used to investigate the reaction of forsterite with 13CO2 in the presence of water or NaCl brine as a function of depth in the sample. Additionally, we also show that NMR crystallography can significantly improve structure refinement of hydrogens’ positions …

Electron Decoupling With Chirped Microwave Pulses For Magic Angle Spinning Dynamic Nuclear Polarization Nuclear Magnetic Resonance Spectroscopy, Edward Paul Saliba

Arts & Sciences Electronic Theses and Dissertations

Dynamic nuclear polarization (DNP) is a method of generating hyperpolarization of nuclear spins for nuclear magnetic resonance (NMR) spectroscopy. Coherent, time domain techniques make the possibility of DNP directly to spins of interest at room temperature and higher feasible in magic angle spinning (MAS) NMR, allowing for optimal experimental repetition times to be limited by the T_1 of the electron, rather than a much longer T_1DNP, with excellent resolution. The strong hyperfine couplings that make such direct DNP transfers possible, however, can lead to short nuclear relaxation times that result in broadening of nuclear resonances and reduce sensitivity. This dissertation …

Wave Function Engineering In Cdse/Pbs Core/Shell Nanocrystal Heterostructures, Brian Matthew Wieliczka

Arts & Sciences Electronic Theses and Dissertations

Colloidal semiconducting nanocrystals hold significant potential for third generation photovoltaics as solution processable materials that can surpass the Shockley-Queisser limit through multiexciton generation. In pursuit of this goal, the synthesis and optical characterization of CdSe/PbS core/shell quantum dots is reported. The spectroscopic behavior of these particles demonstrates their potential for use in optoelectronic devices, taking advantage of wave function engineering of the electron and hole. The rock salt PbS shell grows on all sides of the underlying zinc blende CdSe quantum dot, creating a core/shell structure. With increasing shell thickness, the band edge absorption and photoluminescence transitions decrease in energy …

Photophysical Characterization And Wavelength Tuning Of Natural And Synthetic Oxobacteriochlorins And Biohybrids, Don Hood

Arts & Sciences Electronic Theses and Dissertations

ABSTRACT OF THE DISSERTATION

Photophysical Characterization and Wavelength Tuning of Natural and Synthetic Oxobacteriochlorins and Biohybrids

By

Donald L. Hood

Doctor of Philosophy in Chemistry

Washington University in St. Louis, 2018

Dr. Dewey Holten, Chairperson

Herein is discussed the theoretical and practical unpinnings of photophysical behaviors and kinetic constants for tetrapyrrole macrocycles, to wit, porphyrins, chlorins, and bacteriochlorins. Understanding the characteristic photophysical response of tetrapyrroles to changes in environment or substituents is important to designing synthetic chromophores with tunable absorption wavelengths and for preparing useful biohybrids of natural photosynthetic light antennas combined with unnatural chromophores attached to the light antenna …

Building On Nature: Spectroscopic Studies Of Photosynthesis-Inspired Pigments, Fused Light Harvesting Proteins, And Bacterial Reaction Center Mutants, Kaitlyn Faries

Arts & Sciences Electronic Theses and Dissertations

Photosynthesis is the dominant form of solar energy conversion on the planet, making it critical to understand the fundamentals of the process in order to effectively mimic and improve upon it for human energy needs. The initial stages of photosynthesis include light harvesting and chemical conversion of that harvested energy via electron transport, with both of these stages relying on pigments (or chromophores) such as chlorophyll and specific protein architectures for the processes. In this work, the fundamental underpinnings of photosynthetic light harvesting and electron transport are explored via spectroscopy of various photosynthetic systems with altered natural pigments and proteins. …

Instrumentation For Cryogenic Dynamic Nuclear Polarization And Electron Decoupling In Rotating Solids, Faith Joellen Scott

Arts & Sciences Electronic Theses and Dissertations

Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) using the higher polarization of electron radical spins compared to nuclear spins. The addition of electron radicals for DNP to the sample can cause hyperfine broadening, which decreases the resolution of the NMR resonances due to hyperfine interactions between electron and nuclear spins. Electron decoupling has been shown to attenuate the effects of hyperfine coupling in rotating solids. Magic angle spinning (MAS) DNP with electron decoupling requires a high electron Rabi frequency provided by a high-power microwave source such as a frequency-agile gyrotron. This dissertation describes the development …

Nuclear Spin Alignment In Optically Pumped Semiconductors, Matthew M. Willmering

Arts & Sciences Electronic Theses and Dissertations

Nuclear magnetic resonance (NMR) has shown its ability to be a very informative analytical technique due to the ability to measure very small changes in the energy splittings due to the nuclei’s local environment. However, this ability is hindered by the low sensitivity of the experiment. Many methods have been postulated and implemented to enhance the sensitivity of NMR experiments; one of which is optically pumped NMR (OPNMR). In this dissertation, the usefulness and potential applications of OPNMR are presented. First, a doubly resonant OPNMR probe was fabricated in order to complete more advanced NMR techniques while optically pumping the …