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  Partner: UNT Libraries
 Department: Department of Chemistry
 Language: English
 Degree Level: Doctoral
 Collection: UNT Theses and Dissertations
Acceptor-sensitizers for Nanostructured Oxide Semiconductor in Excitonic Solar Cells

Acceptor-sensitizers for Nanostructured Oxide Semiconductor in Excitonic Solar Cells

Date: August 2014
Creator: Berhe, Seare Ahferom
Description: Organic dyes are examined in photoelectrochemical systems wherein they engage in thermal (rather than photoexcited) electron donation into metal oxide semiconductors. These studies are intended to elucidate fundamental parameters of electron transfer in photoelectrochemical cells. Development of novel methods for the structure/property tuning of electroactive dyes and the preparation of nanostructured semiconductors have also been discovered in the course of the presented work. Acceptor sensitized polymer oxide solar cell devices were assembled and the impact of the acceptor dyes were studied. The optoelectronic tuning of boron-chelated azadipyrromethene dyes has been explored by the substitution of carbon substituents in place of fluoride atoms at boron. Stability of singlet exited state and level of reduction potential of these series of aza-BODIPY coumpounds were studied in order to employ them as electron-accepting sensitizers in solid state dye sensitized solar cells.
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Accuracy and Efficiency in Computational Chemistry: The Correlation Consistent Composite Approach

Accuracy and Efficiency in Computational Chemistry: The Correlation Consistent Composite Approach

Date: August 2011
Creator: Wilson, Brent R.
Description: One of the central concerns of computational chemistry is that of efficiency (i.e. the development of methodologies which will yield increased accuracy of prediction without requiring additional computational resources – RAM, disk space, computing time). Though the equations of quantum mechanics are known, the solutions to these equations often require a great deal of computing power. This dissertation primarily concerns the theme of improved computational efficiency (i.e. the achievement of greater accuracy with reduced computational cost). Improvements in the efficiency of computational chemistry are explored first in terms of the correlation consistent composite approach (ccCA). The ccCA methodology was modified and this enhanced ccCA methodology was tested against the diverse G3/05 set of 454 energetic properties. As computational efficiency improves, molecules of increasing size may be studied and this dissertation explored the issues (differential correlation and size extensivity effects) associated with obtaining chemically accurate (within 1 kcal mol-1) enthalpies of formation for hydrocarbon molecules of escalating size. Two applied projects are also described; these projects concerned the theoretical prediction of a novel rare gas compound, FKrOH, and the mechanism of human glutathione synthetase’s (hGS) negative cooperativity. The final work examined the prospect for the parameterization of the modified embedded atom ...
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Accurate and Reliable Prediction of Energetic and Spectroscopic Properties Via Electronic Structure Methods

Accurate and Reliable Prediction of Energetic and Spectroscopic Properties Via Electronic Structure Methods

Date: August 2013
Creator: Laury, Marie L.
Description: Computational chemistry has led to the greater understanding of the molecular world, from the interaction of molecules, to the composition of molecular species and materials. Of the families of computational chemistry approaches available, the main families of electronic structure methods that are capable of accurate and/or reliable predictions of energetic, structural, and spectroscopic properties are ab initio methods and density functional theory (DFT). The focus of this dissertation is to improve the accuracy of predictions and computational efficiency (with respect to memory, disk space, and computer processing time) of some computational chemistry methods, which, in turn, can extend the size of molecule that can be addressed, and, for other methods, DFT, in particular, gain greater insight into which DFT methods are more reliable than others. Much, though not all, of the focus of this dissertation is upon transition metal species – species for which much less method development has been targeted or insight about method performance has been well established. The ab initio approach that has been targeted in this work is the correlation consistent composite approach (ccCA), which has proven to be a robust, ab initio computational method for main group and first row transition metal-containing molecules yielding, on ...
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Accurate Energetics Across the Periodic Table Via Quantum Chemistry

Accurate Energetics Across the Periodic Table Via Quantum Chemistry

Date: December 2015
Creator: Peterson, Charles Campbell
Description: Greater understanding and accurate predictions of structural, thermochemical, and spectroscopic properties of chemical compounds is critical for the advancements of not only basic science, but also in applications needed for the growth and health of the U.S. economy. This dissertation includes new ab initio composite approaches to predict accurate energetics of lanthanide-containing compounds including relativistic effects, and optimization of parameters for semi-empirical methods for transition metals. Studies of properties and energetics of chemical compounds through various computational methods are also the focus of this research, including the C-O bond cleavage of dimethyl ether by transition metal ions, the study of thermochemical and structural properties of small silicon containing compounds with the Multi-Reference correlation consistent Composite Approach, the development of a composite method for heavy element systems, spectroscopic of compounds containing noble gases and metals (ArxZn and ArxAg+ where x = 1, 2), and the effects due to Basis Set Superposition Error (BSSE) on these van der Waals complexes.
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Adherence/Diffusion Barrier Layers for Copper Metallization: Amorphous Carbon:Silicon Polymerized Films

Adherence/Diffusion Barrier Layers for Copper Metallization: Amorphous Carbon:Silicon Polymerized Films

Date: May 2004
Creator: Pritchett, Merry
Description: Semiconductor circuitry feature miniaturization continues in response to Moore 's Law pushing the limits of aluminum and forcing the transition to Cu due to its lower resistivity and electromigration. Copper diffuses into silicon dioxide under thermal and electrical stresses, requiring the use of barriers to inhibit diffusion, adding to the insulator thickness and delay time, or replacement of SiO2 with new insulator materials that can inhibit diffusion while enabling Cu wetting. This study proposes modified amorphous silicon carbon hydrogen (a-Si:C:H) films as possible diffusion barriers and replacements for SiO2 between metal levels, interlevel dielectric (ILD), or between metal lines (IMD), based upon the diffusion inhibition of previous a-Si:C:H species expected lower dielectric constants, acceptable thermal conductivity. Vinyltrimethylsilane (VTMS) precursor was condensed on a titanium substrate at 90 K and bombarded with electron beams to induce crosslinking and form polymerized a-Si:C:H films. Modifications of the films with hydroxyl and nitrogen was accomplished by dosing the condensed VTMS with water or ammonia before electron bombardment producing a-Si:C:H/OH and a-Si:C:H/N and a-Si:C:H/OH/N polymerized films in expectation of developing films that would inhibit copper diffusion and promote Cu adherence, wetting, on the film surface. X-ray Photoelectron Spectroscopy was used to characterize Cu metallization of ...
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Adhesion/Diffusion Barrier Layers for Copper Integration: Carbon-Silicon Polymer Films and Tantalum Substrates

Adhesion/Diffusion Barrier Layers for Copper Integration: Carbon-Silicon Polymer Films and Tantalum Substrates

Date: December 1999
Creator: Chen, Li
Description: The Semiconductor Industry Association (SIA) has identified the integration of copper (Cu) with low-dielectric-constant (low-k) materials as a critical goal for future interconnect architectures. A fundamental understanding of the chemical interaction of Cu with various substrates, including diffusion barriers and adhesion promoters, is essential to achieve this goal. The objective of this research is to develop novel organic polymers as Cu/low-k interfacial layers and to investigate popular barrier candidates, such as clean and modified tantalum (Ta) substrates. Carbon-silicon (C-Si) polymeric films have been formed by electron beam bombardment or ultraviolet (UV) radiation of molecularly adsorbed vinyl silane precursors on metal substrates under ultra-high vacuum (UHV) conditions. Temperature programmed desorption (TPD) studies show that polymerization is via the vinyl groups, while Auger electron spectroscopy (AES) results show that the polymerized films have compositions similar to the precursors. Films derived from vinyltrimethyl silane (VTMS) are adherent and stable on Ta substrates until 1100 K. Diffusion of deposited Cu overlayers is not observed below 800 K, with dewetting occurred only above 400 K. Hexafluorobenzene moieties can also be incorporated into the growing film with good thermal stability. Studies on the Ta substrates demonstrate that even sub-monolayer coverages of oxygen or carbide on polycrystalline ...
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Adsorbate-enhanced Corrosion Processes at Iron and Iron Oxide Surfaces

Adsorbate-enhanced Corrosion Processes at Iron and Iron Oxide Surfaces

Date: December 1994
Creator: Murray, Eric
Description: This study was intended to provide a fuller understanding of the surface chemical processes which result in the corrosion of ferrous materials.
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Advancements in Instrumentation for Fourier Transform Microwave Spectroscopy

Advancements in Instrumentation for Fourier Transform Microwave Spectroscopy

Date: August 2011
Creator: Dewberry, Christopher Thomas
Description: The efforts of my research have led to the successful construction of several instruments that have helped expand the field of microwave spectroscopy. The classic Balle-Flygare spectrometer has been modified to include two different sets of antenna to operate in the frequency ranges 6-18 GHz and 18-26 GHz, allowing it to function for a large range without having to break vacuum. This modified FTMW instrument houses two low noise amplifiers in the vacuum chamber to allow for the LNAs to be as close to the antenna as physically possible, improving sensitivity. A new innovative Balle-Flygare type spectrometer, the efficient low frequency FTMW, was conceived and built to operate at frequencies as low as 500 MHz through the use of highly curved mirrors. This is new for FTMW techniques that normally operate at 4 GHz or higher with only a few exceptions around 2 GHz. The chirped pulse FTMW spectrometer uses horn antennas to observe spectra that span 2 GHz versus the standard 1 MHz of a cavity technique. This instrument decreases the amount of time to obtain a large spectral region of relative correct intensity molecular transitions. A Nd:YAG laser ablation apparatus was attached to the classic Balle-Flygare and chirped ...
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Affordances of Instrumentation in General Chemistry Laboratories

Affordances of Instrumentation in General Chemistry Laboratories

Date: August 2010
Creator: Sherman, Kristin Mary Daniels
Description: The purpose of this study is to find out what students in the first chemistry course at the undergraduate level (general chemistry for science majors) know about the affordances of instrumentation used in the general chemistry laboratory and how their knowledge develops over time. Overall, students see the PASCO™ system as a useful and accurate measuring tool for general chemistry labs. They see the probeware as easy to use, portable, and able to interact with computers. Students find that the PASCO™ probeware system is useful in their general chemistry labs, more advanced chemistry labs, and in other science classes, and can be used in a variety of labs done in general chemistry. Students learn the affordances of the probeware through the lab manual, the laboratory teaching assistant, by trial and error, and from each other. The use of probeware systems provides lab instructors the opportunity to focus on the concepts illustrated by experiments and the opportunity to spend time discussing the results. In order to teach effectively, the instructor must know the correct name of the components involved, how to assemble and disassemble it correctly, how to troubleshoot the software, and must be able to replace broken or missing components ...
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Aldohaloketenes and the Stereochemistry of Aldohaloketene Cycloadditions

Aldohaloketenes and the Stereochemistry of Aldohaloketene Cycloadditions

Date: May 1970
Creator: Hoff, Edwin Frank
Description: The objective of this research problem was to synthesize aldohaloketenes and investigate the chemistry of this new class of ketenes.
Contributing Partner: UNT Libraries
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