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An Analysis of the Effectiveness of Computer Assisted Instruction in General Chemistry at an Urban University.

Description: The science-major General Chemistry sequence offered at the University of Houston has been investigated with respect to the effectiveness of recent incorporation of various levels of computer technology. As part of this investigation, questionnaire responses, student evaluations and grade averages and distributions from up to the last ten years have been analyzed and compared. Increased use of web-based material is both popular and effective, particularly with respect to providing extra information and supplemental questions. Instructor contact via e-mail is also well-received. Both uses of technology should be encouraged. In contrast, electronic classroom presentation is less popular. While initial use may lead to improved grades and retention, these levels decrease quickly, possibly due to a reduction in instructor spontaneity.
Date: May 2002
Creator: McGuffey, Angela

Applications of Nanomanipulation Coupled to Nanospray Mass Spectrometry in Trace Fiber Analysis and Cellular Lipid Analysis.

Description: The novel instrumentation of nanomanipulation coupled to nanospray mass spectrometry and its applications are presented. The nanomanipulator has the resolution of 10nm step sizes allowing for specific fine movement used to probe and characterize objects of interest. Nanospray mass spectrometry only needs a minimum sample volume of 300nl and a minimum sample size of 300attograms to analyze an analyte making it the ideal instrument to couple to nanomanipulation. The nanomanipulator is mounted to an inverted microscope and consists of 4 nano-positioners; these nano-positioners hold end-effectors and other tools used for manipulation. This original coupling has been used to enhance the current abilities of cellular probing and trace fiber analysis. Experiments have been performed to demonstrate the functionality of this instrument and its capabilities. Histidine and caffeine have been sampled directly from single fibers and analyzed. Lipid bodies from cotton seeds have been sampled indirectly and analyzed. The few applications demonstrated are only the beginning of nanomanipulation coupled to nanospray mass spectrometry and the possible applications are numerous especially with the ability to design and fabricate new end-effectors with unique abilities. Future study will be done to further the applications in direct cellular probing including toxicology studies and organelle analysis of single cells. Further studies will be directed in forensic applications of this instrument including gunshot residue sampled from fibers.
Date: December 2008
Creator: Ledbetter, Nicole

Comparison of Homework Systems (Four Web-Based) used in First-Semester General Chemistry

Description: Web-based homework systems are becoming more common in general chemistry as instructors face ever-increasing enrollment. Yet providing meaningful feedback on assignments remains of the utmost importance. Chemistry instructors consider completion of homework integral to students' success in chemistry, yet only a few studies have compared the use of Web-based systems to the traditional paper-and-pencil homework within general chemistry. This study compares the traditional homework system to four different Web-based systems. Data from eight, semester classes consisting of a diagnostic pre-test, final semester grades, and the number of successful and unsuccessful students are analyzed. Statistically significant results suggest a chemistry instructor should carefully consider options when selecting a homework system.
Date: May 2009
Creator: Belland, Joshua

Computational Studies of Bonding and Phosphorescent Properties of Group 12 Oligomers and Extended Excimers.

Description: Density functional (ca, BLYP, BPW91, B3LYP and B3PW91), MP2 and CCSD(T) methods in combination with LANL2DZ or cc-pVxZ-PP (where x=D(double), T(triple) Q(quadruple), and 5(quintuple)) basis sets have been employed in computing electronic transition energies of zinc and cadmium monomers. CCSD(T)/aug-cc-pV5Z-PP combination finds values that are 150 cm-1 from the experimental value for the zinc monomer and 240 cm-1 remove from the cadmium monomer excitation experimental value. These method/basis set combinations are also used to find spectroscopic values (re, De, we, wexe, Be , and Te) that rival experimental values for dimers and excimers. Examples of this can be seen with the CCSD(T)/aug-cc-pV5Z-PP combination phosphorescent emission results. The values found are within 120 cm-1 of the zinc emission energy and 290 cm-1 of the cadmium emission energy. While this combination rigorously models spectroscopic constants for monomers, dimers, and excimers, it does not efficiently model these constants for larger clusters with available modern computational resources. It is important to show spectroscopic trends (bonding, phosphorescent excitation and emissions) as clusters increase as the monomer and dimer emission energies do not model solid state metallophilic interactions and phosphorescence. The MP2/LANL2DZ combinations show qualitative cooperative bonding trends in group oligomers and extended excimers as size increases and shape change. Changes in excitation and emission energies are also shown as a function of size and shape of the clusters.
Date: August 2008
Creator: Determan, John J.

Computational Studies of Selected Ruthenium Catalysis Reactions.

Description: Computational techniques were employed to investigate pathways that would improve the properties and characteristics of transition metal (i.e., ruthenium) catalysts, and to explore their mechanisms. The studied catalytic pathways are particularly relevant to catalytic hydroarylation of olefins. These processes involved the +2 to +3 oxidation of ruthenium and its effect on ruthenium-carbon bond strengths, carbon-hydrogen bond activation by 1,2-addition/reductive elimination pathways appropriate to catalytic hydrogen/deuterium exchange, and the possible intermediacy of highly coordinatively unsaturated (e.g., 14-electron) ruthenium complexes in catalysis. The calculations indicate a significant decrease in the Ru-CH3 homolytic bond dissociation enthalpy for the oxidation of TpRu(CO)(NCMe)(Me) to its RuIII cation through both reactant destabilization and product stabilization. This oxidation can thus lead to the olefin polymerization observed by Gunnoe and coworkers, since weak RuIII-C bonds would afford quick access to alkyl radical species. Calculations support the experimental proposal of a mechanism for catalytic hydrogen/deuterium exchange by a RuII-OH catalyst. Furthermore, calculational investigations reveal a probable pathway for the activation of C-H bonds that involves phosphine loss, 1,2-addition to the Ru-OH bond and then reversal of these steps with deuterium to incorporate it into the substrate. The presented results offer the indication for the net addition of aromatic C-H bonds across a RuII-OH bond in a process that although thermodynamically unfavorable is kinetically accessible. Calculations support experimental proposals as to the possibility of binding of weakly coordinating ligands such as dinitrogen, methylene chloride and fluorobenzene to the "14-electron" complex [(PCP)Ru(CO)]+ in preference to the formation of agostic Ru-H-C interactions. Reactions of [(PCP)Ru(CO)(1-ClCH2Cl)][BAr'4] with N2CHPh or phenylacetylene yielded conversions that are exothermic to both terminal carbenes and vinylidenes, respectively, and then bridging isomers of these by C-C bond formation resulting from insertion into the Ru-Cipso bond of the phenyl ring of PCP. The QM/MM and DFT calculations on full complexes ...
Date: December 2007
Creator: Barakat, Khaldoon A.

A Computational Study on 18+δ Organometallics

Description: The B3LYP density functional has been used to calculate properties of organometallic complexes of Co(CO)3 and ReBr(CO)3, with the chelating ligand 2,3-bisphosphinomaleic anhydride, in 19- and 18-electron forms. The SBKJC-21G effective core potential and associated basis set was used for metals (Co/Re) and the 6-31G* basis set was used for all other elements. The differences of bond angles, bond distances, natural atomic charges and IR vibrational frequencies were compared with the available experimental parameters. The differences between the 19- and 18-electron systems have been analyzed. The results reveal that the 19th electron is mostly distributed over the ligand of 2,3-bisphosphinomaleic anhydride, although partially localized onto the metal fragment in 1 and 2*. Two different methods, IR-frequencies and natural atomic charges, were used to determine the value of δ. Present computed values of δ are compared with available experimental values, and predictions are made for unknown complexes.
Date: May 2002
Creator: Yu, Liwen

Diffusion Barriers/Adhesion Promoters. Surface and Interfacial Studies of Copper and Copper-Aluminum Alloys

Description: The focus of this research is to study the interaction between copper and the diffusion barrier/adhesion promoter. The behavior of copper sputter-deposited onto sputter-cleaned tantalum nitride is investigated. The data show that copper growth on tantalum nitride proceeds with the formation of 3-D islands, indicating poor adhesion characteristics between copper and Ta0.4N. Post-annealing experiments indicate that copper will diffuse into Ta0.4N at 800 K. Although the data suggests that Ta0.4N is effective in preventing copper diffusion, copper's inability to wet Ta0.4N will render this barrier ineffective. The interaction of copper with oxidized tantalum silicon nitride (O/TaSiN) is characterized. The data indicate that initial copper depositions result in the formation a conformal ionic layer followed by Cu(0) formation in subsequent depositions. Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 800 K, copper "de-wetting" occurs for temperatures above 500 K. These results indicate that in conditions where the substrate has been oxidized facile de-wetting of copper may occur. The behavior of a sputter-deposited Cu0.6Al0.4 film with SiO2 (Cu0.6Al0.4/SiO2) is investigated. The data indicate that aluminum segregates to the SiO2 interface and becomes oxidized. For copper coverages less than ~ 0.31 ML (based on a Cu/O atomic ratio), only Cu(I) formation is observed. At higher coverages, Cu(0) is observed. These data are in contrast with the observed behavior of copper metal deposited onto SiO2 (Cu/SiO2). The data for Cu/SiO2 show that copper does not wet SiO2 and forms 3-D nuclei. Furthermore, post-annealing experiments performed on Cu0.6Al0.4/SiO2 show that neither de-wetting nor diffusion of copper occurs for temperatures up to 800 K, while Cu diffusion into SiO2 occurs ~ 600 K. These data indicate that aluminum alloyed with copper at the SiO2 interface serves as an effective adhesion promoter and thermal diffusion barrier.
Date: August 2000
Creator: Shepherd, Krupanand Solomon

Electrochemical Deposition of Zinc-Nickel Alloys in Alkaline Solution for Increased Corrosion Resistance.

Description: The optimal conditions for deposition of zinc-nickel alloys onto stainless steel discs in alkaline solutions have been examined. In the past cadmium has been used because it shows good corrosion protection, but other methods are being examined due to the high toxicity and environmental threats posed by its use. Zinc has been found to provide good corrosion resistance, but the corrosion resistance is greatly increased when alloyed with nickel. The concentration of nickel in the deposit has long been a debated issue, but for basic solutions a nickel concentration of 8-15% appears optimal. However, deposition of zinc-nickel alloys from acidic solutions has average nickel concentrations of 12-15%. Alkaline conditions give a more uniform deposition layer, or better metal distribution, thereby a better corrosion resistance. Although TEA (triethanolamine) is most commonly used to complex the metals in solution, in this work I examined TEA along with other complexing agents. Although alkaline solutions have been examined, most research has been done in pH ≥ 12 solutions. However, there has been some work performed in the pH 9.3-9.5 range. This work examines different ligands in a pH 9.3-9.4 range. Direct potential plating and pulse potential plating methods are examined for optimal platings. The deposits were examined and characterized by XRD.
Date: December 2009
Creator: Conrad, Heidi A.

Electrochemical Study of Under-Potential Deposition Processes on Transition Metal Surfaces

Description: Copper under-potential deposition (UPD) on iridium was studied due to important implications it presents to the semiconductor industry. Copper UPD allows controlled superfilling on sub-micrometer trenches; iridium has characteristics to prevent copper interconnect penetration into the surrounding dielectric. Copper UPD is not favored on iridium oxides but data shows copper over-potential deposition when lower oxidation state Ir oxide is formed. Effect of anions in solution on silver UPD at platinum (Pt) electrodes was studied with the electrochemical quartz crystal microbalance. Silver UPD forms about one monolayer in the three different electrolytes employed. When phosphoric acid is used, silver oxide growth is identified due to presence of low coverage hydrous oxide species at potentials prior to the monolayer oxide region oxide region.
Date: August 2006
Creator: Flores Araujo, Sarah Cecilia

Electrochemical synthesis of CeO2 and CeO2/montmorillonite nanocomposites.

Description: Nanocrystalline cerium oxide thin films on metal and semiconductor substrates have been fabricated with a novel electrodeposition approach - anodic oxidation. X-ray diffraction analysis indicated that as-produced cerium oxide films are characteristic face-centered cubic fluorite structure with 5 ~ 20 nm crystal sizes. X-ray photoelectron spectroscopy study probes the non-stoichiometry property of as-produced films. Raman spectroscopy and Scanning Electron Microscopy have been applied to analyze the films as well. Deposition mode, current density, reaction temperature and pH have also been investigated and the deposition condition has been optimized for preferred oriented film formation: galvanostatic deposition with current density of -0.06 mA/cm2, T > 50oC and 7 < pH < 10. Generally, potentiostatic deposition results in random structured cerium oxide films. Sintering of potentiostatic deposited cerium oxide films leads to crystal growth and reach nearly full density at 1100oC. It is demonstrated that in-air heating favors the 1:2 stoichiometry of CeO2. Nanocrystalline cerium oxide powders (4 ~ 10 nm) have been produced with anodic electrochemical synthesis. X-ray diffraction and Raman spectroscopy were employed to investigate lattice expansion phenomenon related to the nanoscale cerium oxide particles. The pH of reaction solution plays an important role in electrochemical synthesis of cerium oxide films and powder. Cyclic voltammetry and rotation disk electrode voltammetry have been used to study the reaction mechanisms. The results indicate that the film deposition and powder formation follow different reaction schemes. Ce(III)-L complexation is a reversible process, Ce3+ at medium basic pH region (7~10) is electrochemically oxidized to and then CeO2 film is deposited on the substrate. CE mechanism is suggested to be involved in the formation of films, free Ce3+ species is coordinated with OH- at high basic pH region (>10) to Ce2O3 immediately prior to electrochemically oxidation Ce2O3 to CeO2. CeO2 / montmorillonite nanocomposites were electrochemically produced. X-ray ...
Date: December 2003
Creator: Wang, Qi

Fluorination Effect on the Conformational Properties of Alkanes

Description: A Series of fluorophores of the general formular P(CF2)nP and P(CF2)n-1CF3 has been synthesized. Copper catalyzed coupling of 1-bromopyrene and the corresponding mono and di-iodoperfluoroalkanes were used in most cases. For the n=3 dimer, a novel 1,w-perfluoroalkylation of pyrene via bis-decarboxylation of hexafluorogultaric acid was utilized. These compounds, along with suitable hydrocarbon analogs, are being used to study the flexibility of fluorocarbon chains using emission. We have found that the excimer formation for the fluorinated pyrene monomers is highly dependent on concentration and is less efficient than for pyene. Excimer formation for the fluorinated pyrene dimers is much more efficient than for the fluorocarbon monomers and is only slightly concentraion dependent. Steady-state emission spectra indicate hydrocarbon dimers-models form excimers more efficiently than the fluorinated dimers suggesting the fluorinated chains are stiffer than the hydrocarbons. We conducted the temperature-dependent studies and quantified the conformational difference.
Date: May 2002
Creator: Xu, Wenjian

General Chemistry Topic Coverage (GCTC) comparison between community colleges and universities in the United States.

Description: This study is based on survey responses of 224 general chemistry instructors at United States (U.S.) community colleges and universities representing 46 states. The mean values of General Chemistry Topic Coverage (GCTC) score, developed by this researcher specifically for this dissertation study as a measure of course content, were statistically analyzed. The aim of this study is to answer five research questions: (a) Is there a difference in mean GCTC scores between U.S. community colleges and four-year colleges and universities? (b) If there is a difference in mean GCTC score between the two study groups, what are the observed differences in subtopics covered between community colleges and four-year colleges and universities? (c) Considering both community colleges and universities, is there a difference in mean GCTC score between the different designated U.S. regions? (d) Considering both community college and university professors, is there a difference in GCTC score for professors with a master's degree compared to those with a doctorate?, and (e) Is there a correlation between GCTC score and the percentage of students that major in science? Results indicate that there is a statistically significant difference in course content between community colleges and universities, there is a statistically significant difference between different U.S. regions, there is no statistically significant difference between professors with an earned master's versus those with an earned doctorate degree, and there is no statistically significant correlation between general chemistry course content and the percentage of a professor's students majoring in science. Details of the observed differences between community college and university course content are discussed, and recommendations for future research are presented.
Date: December 2006
Creator: El-Ashmawy, Amina Khalifa

Improvement of Homogeneity and Adhesion of Diamond-Like Carbon Films on Copper Substrates

Description: Electrodeposition method is used to deposit diamond-like carbon (DLC) films on copper substrates via anodic oxidation at low temperature. These films are characterized using Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Homogeneity of these films is studied using Raman spectroscopy and scanning electron microscopy. Scotch tape peel tests indicate adherent film on copper substrate. Carbon phase transformation is studied using thermal annealing experiments in conjunction with Raman spectroscopy and scanning electron microscopy. A cathodic electrochemical method is also studied to deposit diamond-like carbon films on copper substrates. However, films deposited by the cathodic route have poor adhesion and quality compared to anodically deposited films. It is also possible to grow diamond phase on copper substrates using acetylene in liquid ammonia via electrodeposition route. An electrochemical method is proposed for boron doping into DLC films.
Date: August 2004
Creator: Vavilala, Suma

Interaction of learning approach with concept integration and achievement in a large guided inquiry organic class.

Description: A study was conducted to investigate the relationship of students' concept integration and achievement with time spent within a topic and across related topics in a large first semester guided inquiry organic chemistry class. Achievement was based on evidence of algorithmic problem solving; and concept integration was based on demonstrated performance explaining, applying, and relating concepts to each other. Twelve individual assessments were made of both variables over three related topics - acid/base, nucleophilic substitution and electrophilic addition reactions. Measurements included written, free response and ordered multiple answer questions using a classroom response system. Results demonstrated that students can solve problems without conceptual understanding. A second study was conducted to compare the students' learning approach at the beginning and end of the course. Students were scored on their preferences for a deep, strategic, or surface approach to learning based on their responses to a pre and post survey. Results suggest that students significantly decreased their preference for a surface approach during the semester. Analysis of the data collected was performed to determine the relationship between students' learning approach and their concept integration and achievement in this class. Results show a correlation between a deep approach and concept integration and a strong negative correlation between a surface approach and concept integration.
Date: August 2009
Creator: Mewhinney, Christina

Investigation of Structure and Properties of Low Temperature Deposited Diamond-Like Carbon Films

Description: Electrodeposition is a novel method for fabrication of diamond-like carbon (DLC) films on metal substrates. In this work, DLC was electrochemically deposited on different substrates based on an anodic oxidation cyclization of acetylene in liquid ammonia. Successfully anodic deposition was carried out for DLC onto nickel substrate at temperatures below -40°C. Comparative studies were performed on a series of different carbon sources (acetylene, sodium acetylide, and a mixture of acetylene and sodium acetylide). The films were characterized using a variety of methods including Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), XPS valence band spectra, and/or scanning electron microscopy (SEM). Raman spectroscopy is used as a bench mark technique to verify the presence of deposited DLC films, to access the films homogeneities, and to provide the ratio of the different carbon phases, mainly disordered graphite (D) and graphite (G) phases in the films. A combination of the Raman with FTIR and valence band spectra analysis allowed the distinction between hydrogenated DLC and unhydrogenated DLC films. Three different kinds of DLC [(1) hydrogenated DLC (a-C:H); (2) tetrahedral hydrogenated DLC (ta-C:H); and (3) graphitic-like DLC] were deposited depending upon the deposition conditions and substrates. Temperature and current density are the most important parameters to govern the quality of the deposited films, where adding of acetylide into the electrolyte led to films with a higher degree of graphitic phases. The proposed mechanism for acetylene anodic oxidation does not involve direct electron transfer but electrochemical cyclization of acetylene radical cations and hydrogen abstraction at the termination steps. Sodium acetylide, however, dissociates to an acetylenic ion, C2H-, in liquid ammonia. The electrochemistry heterogeneity also leads to island and two-dimensional (2D) nucleation growth of DLC films. Different bond formations of metal to carbon and different chemisorptions of acetylene on metal play important roles ...
Date: August 2004
Creator: Pingsuthiwong, Charoendee

Investigation of the Pressure Dependence of SO3 Formation

Description: The kinetics of the pressure dependent O + SO2 + Ar reaction have been investigated using laser photolysis resonance fluorescence at temperatures of 289 K, 399 K, 581 K, 699 K, 842 K and 1040 K and at pressures from 30-665 torr. Falloff was observed for the first time in the pressure dependence. Application of Lindemann theory yielded an Arrhenius expression of k(T) = 3.3 x 10-32exp(-992/T) cm6 molecule-1 s-1 for the low pressure limit and k(T) = 8.47 x 10-14exp(-468/T) cm3 molecule-1 s-1 for the high pressure limit at temperatures between 289 and 842 K. The reaction is unusual as it possesses a positive activation energy at low temperature, yet at higher temperatures the activation energy is negative, illustrating a reaction barrier.
Date: December 2003
Creator: Naidoo, Jacinth

Kinetic studies and computational modeling of atomic chlorine reactions in the gas phase.

Description: The gas phase reactions of atomic chlorine with hydrogen sulfide, ammonia, benzene, and ethylene are investigated using the laser flash photolysis / resonance fluorescence experimental technique. In addition, the kinetics of the reverse processes for the latter two elementary reactions are also studied experimentally. The absolute rate constants for these processes are measured over a wide range of conditions, and the results offer new accurate information about the reactivity and thermochemistry of these systems. The temperature dependences of these reactions are interpreted via the Arrhenius equation, which yields significantly negative activation energies for the reaction of the chlorine atom and hydrogen sulfide as well as for that between the phenyl radical and hydrogen chloride. Positive activation energies which are smaller than the overall endothermicity are measured for the reactions between atomic chlorine with ammonia and ethylene, which suggests that the reverse processes for these reactions also possess negative activation energies. The enthalpies of formation of the phenyl and &#946;-chlorovinyl are assessed via the third-law method. The stability and reactivity of each reaction system is further rationalized based on potential energy surfaces, computed with high-level ab initio quantum mechanical methods and refined through the inclusion of effects which arise from the special theory of relativity. Large amounts of spin-contamination are found to result in inaccurate computed thermochemistry for the phenyl and ethyl radicals. A reformulation of the computational approach to incorporate spin-restricted reference wavefunctions yields computed thermochemistry in good accord with experiment. The computed potential energy surfaces rationalize the observed negative temperature dependences in terms of a chemical activation mechanism, and the possibility that an energized adduct may contribute to product formation is investigated via RRKM theory.
Date: August 2009
Creator: Alecu, Ionut M.

Kinetic Studies of Hydroxyl and Hydrogen Atom Reactions

Description: Gas phase kinetics of the reactions involving hydroxyl radical and hydrogen atom were studied using experimental and ab initio theoretical techniques. The rate constant for the H + H2S reaction has been measured from 298 to 598 K by the laser photolysis/resonance fluorescence (LP-RF) technique. The transition state theory (TST) analysis coupled with the measurements support the suggestion that the reaction shows significant curvature in the Arrhenius plot. The LP-RF technique was also used to measure the rate constant of the H + CH3Br reaction over the temperature range 400-813 K. TST and density functional theory (DFT) calculations show that the dominant reaction channel is Br-abstraction. The reaction H + CF2=CF-CF=CF2 was first studied by flash photolysis/resonance fluorescence (FP-RF) method. The experiments of this work revealed distinctly non-Arrhenius behavior, which was interpreted in terms of a change in mechanism. DFT calculations suggest that the adduct is CF2H-CF•-CF=CF2. At lower temperatures a mixture of this molecule and CF2•-CFH-CF=CF2 is likely. The theoretical calculations show that H atom migrates in the fluoroethyl radicals through a bridging intermediate, and the barrier height for this process is lower in the less fluorinated ethyl radical. High level computations were also employed in studies of the rate constants of OH + chloroethylenes reactions. VTST calculations indicate that, except the reaction of OH + C2Cl4, these reactions present a complex behavior. For OH + C2Cl4, conventional TST calculation shows a simple positive temperature-dependence behavior.
Date: May 2002
Creator: Hu, Xiaohua

Metal-Aluminum Oxide Interactions: Effects of Surface Hydroxylation and High Electric Field

Description: Metal and oxide interactions are of broad scientific and technological interest in areas such as heterogeneous catalysis, microelectronics, composite materials, and corrosion. In the real world, such interactions are often complicated by the presence of interfacial impurities and/or high electric fields that may change the thermodynamic and kinetic behaviors of the metal/oxide interfaces. This research includes: (1) the surface hydroxylation effects on the aluminum oxide interactions with copper adlayers, and (2) effects of high electric fields on the interface of thin aluminum oxide films and Ni3Al substrate. X-ray photoelectron spectroscopy (XPS) studies and first principles calculations have been carried out to compare copper adsorption on heavily hydroxylated a- Al2O3(0001) with dehydroxylated surfaces produced by Argon ion sputtering followed by annealing in oxygen. For a heavily hydroxylated surface with OH coverage of 0.47 monolayer (ML), sputter deposition of copper at 300 K results in a maximum Cu(I) coverage of ~0.35 ML, in agreement with theoretical predictions. Maximum Cu(I) coverage at 300 K decreases with decreasing surface hydroxylation. Exposure of a partially dehydroxylated a-Al2O3(0001) surface to either air or 2 Torr water vapor results in recovery of surface hydroxylation, which in turn increases the maximum Cu(I) coverage. The ability of surface hydroxyl groups to enhance copper binding suggests a reason for contradictory experimental results reported in the literature for copper wetting of aluminum oxide. Scanning tunneling microscopy (STM) was used to study the high electric field effects on thermally grown ultrathin Al2O3 and the interface of Al2O3 and Ni3Al substrate. Under STM induced high electric fields, dielectric breakdown of thin Al2O3 occurs at 12.3 } 1.0 MV/cm. At lower electric fields, small voids that are 2-8 A deep are initiated at the oxide/metal interface and grow wider and deeper into the metal substrate, which eventually leads to either physical collapse or dielectric ...
Date: December 2001
Creator: Niu, Chengyu

Metallization and Modification of Low-k Dielectric Materials

Description: Aluminum was deposited onto both Teflon AF and Parylene AF surfaces by chemical vapor deposition of trimethylaluminum. This work shows that similar thin film (100 Angstroms) aluminum oxide adlayers form on both polymers at the low temperature dosing conditions used in the studies. Upon anneal to room temperature and above, defluorination of the polymer surfaces increased and resulted in fluorinated aluminum oxide adlayers; the adlayers were thermally stable to the highest temperatures tested (600 K). Angle-resolved spectra showed higher levels of fluorination toward the polymer/adlayer interface region. Copper films were also deposited at low temperature onto Teflon AF using a copper hexafluoroacetylacetonate-cyclooctadiene precursor. Annealing up to 600 K resulted in the loss of precursor ligands and a shift to metallic copper. As with aluminum adlayers, some polymer defluorination and resulting metal (copper) fluoride was detected. Parylene AF and polystyrene films surfaces were modified by directly dosing with water vapor passed across a hot tungsten filament. Oxygen incorporation into polystyrene occurred exclusively at aromatic carbon sites, whereas oxygen incorporation into parylene occurred in both aromatic and aliphatic sites. Oxygen x-ray photoelectron spectra of the modified polymers were comparable, indicating that similar reactions occurred. The surface oxygenation of parylene allowed enhanced reactivity toward aluminum chemical vapor deposition. Silicon-carbon (Si-Cx) films were formed by electron beam bombardment of trimethylvinylsilane films which were adsorbed onto metal substrates at low temperatures in ultra-high vacuum. Oxygen was also added to the films by coadsorbing water before electron beam bombardment; the films were stable to more than 700 K, with increasing silicon-oxygen bond formation at elevated temperatures. Copper metal was sputter deposited in small increments onto non-oxygenated films. X-ray photoelectric spectra show three-dimensional copper growth (rather than layer-by-layer growth), indicating only weak interaction between the copper and underlying films. Annealing at elevated temperatures caused coalescence or growth ...
Date: December 2008
Creator: Martini, David M.

An NMR study of 2-ethyl-1-butyllithium and of 2-ethyl-1-butyllithium/lithium 2-ethyl-1-butoxide mixed aggregates

Description: A 1H, 13C, and 6Li NMR study of 2-ethyl-1-butyllithium indicated that 2-ethyl-1-butyllithium exists only as a hexameric aggregate over the entire temperature range of 25 to - 92.1 ° C in cyclopentane. Reacting 2-ethyl-1-butyllithium with 2-ethyl-1-butanol resulted in alkyllithium/lithium alkoxide mixed aggregates, apparently of the form Ra(RO)bLia+b. A multinuclear, variable temperature NMR study of samples with O:Li ratios of 0.2 and 0.4 showed, in addition to the alkyllithium, the formation of four mixed aggregates, one of them probably an octamer. Higher O:Li ratio samples showed the formation of several other mixed aggregates. Mixing 2-ethyl-1-butyllithium with independently prepared lithium 2-ethyl-1-butoxide formed the same mixed aggregates formed by in situ synthesis of lithium alkoxide. Lithium 2-ethyl-1-butoxide also exists as aggregates in cyclopentane.
Date: May 2001
Creator: Ferreira, Aluisio V. C.

NMR study of 2-ethylhexyllithium aggregate and 2- ethylhexyllithium/lithium 2-ethyl-1-hexoxide mixed aggregates.

Description: A 1H, 13C, and 6Li NMR study of 2-ethylhexyllithium showed that 2- ethylhexyllithium exists solely as a hexamer in cyclopentane solution over the temperature range from 25 to -65 °C. Furthermore, 2-ethylhexyllithium and lithium 2- ethyl-1-hexoxide were shown to form mixed aggregates when the alkoxide was formed in situ by reacting 2-ethylhexyllithium with 2-ethyl-1-hexanol. A multinuclear, variable temperature NMR study of a sample with an O:Li ratio of 0.2 led to the identification of at least four such aggregates, one of which was found to be a hexamer with the composition R5(RO)Li6. Studies of samples with higher O:Li ratios, up to 0.8, showed additional mixed aggregates present. All solutions containing mixed aggregates were also shown to contain hydrocarbon soluble lithium hydride. A study of lithium 2-ethyl-1- hexoxide indicated that it aggregates in solution as well.
Date: December 2001
Creator: Petros, Robby A.

NMR Study of n-Propyllithium Aggregates

Description: A variable temperature 1H, 13C, and 6Li NMR study of n-propyl-6Li-lithium showed five different aggregates, similar to that in the literature as (RLi)n, n= 6, 8, 9, 9, 9. There were also a number of additional new species, identified as lithium hydride containing aggregates. Unexpectedly, a series of 13C{1H} 1-D NMR experiments with selective 6Li decoupling showed evidence for 13C-6Li spin-spin coupling between the previously reported (RLi)n aggregates and various hydride species.
Date: December 2002
Creator: Davis, James W.

The performance of density functional theory with the correlation consistent basis sets.

Description: Density functional theory has been used in combination with the correlation consistent and polarization consistent basis sets to investigate the structures and energetics for a series of first-row closed shell and several second-row molecules of potential importance in atmospheric chemistry. The impact of basis set choice upon molecular description has been examined, and irregular convergence of molecular properties with respect to increasing basis set size for several functionals and molecules has been observed. The possible reasons and solutions for this unexpected behavior including the effect of contraction and uncontraction, of the basis set diffuse sp basis functions, basis set superposition error (BSSE) and core-valence sets also have been examined.
Date: August 2005
Creator: Wang, Xuelin