UNT Theses and Dissertations - 609 Matching Results

Search Results

prev Results: 301 - 324 next
open access

Molecular Modeling Study of Oxidative Degradation of Polyperfluoroethers Catalyzed by Iron Fluoride Surfaces : An Extended Hückel Theory Approach

Description: Extended Hückel methods are known to be a useful tool in understanding surface phenomena. Important quantities about atoms and chemical bonds can be obtained from this computationally simple method, although caution must be exercised in interpreting the results. Application of Extended Hückel calculations to large metal clusters reveals the role of d orbitals in solids. Basic ideas of constructing model compounds have been developed. Several model systems for surface chemisorption processes are… more
Date: May 1995
Creator: Wang, Yanbin
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Investigation of Copper Out-Plating Mechanism on Silicon Wafer Surface

Description: As the miniaturization keeps decreasing in semiconductor device fabrication, metal contamination on silicon surfaces becomes critical. An investigation of the fundamental mechanism of metal contamination process on silicon surface is therefore important. Kinetics and thermodynamics of the copper out-plating process on silicon surfaces in diluted HF solutions are both evaluated by several analytical methods.
Date: August 1995
Creator: Chien, Hsu-Yueh
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Stereoselective Solid-State NaBH₄ Reduction of 1-Methylpentacyclo[5.4.0.0²,⁶.0³,¹⁰,0⁵,⁹]undecane-8, 11-Dione, Synthesis and Chemistry of Strained Alkenes, and Chemical and Microbial Synthesis of Racemic and Optically Active (S)-4-Hydroxy-2-Cyclohexenone

Description: Part I. Reduction of the 1-methylpentacyclo [5.4.0.0²,⁶.0³,¹⁰,0⁵,⁹]undecane-8, 11-dione (9) with solid NaBH₄ resulted in highly stereoselective reduction of both C=O groups in the substrate, thereby affording the corresponding endo-8, endo-11-diol (11a). The configuration of 11a was established unequivocally by converting 11a into the corresponding cyclic thiocarbonate ester, 12. Part II. Z-1,2-Di(1'-adamantyl)ethene (14) was synthesized with a high degree of stereoselectively in four steps (Sc… more
Date: August 1995
Creator: Xing, Dongxia
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Structural Elucidation of tert-Butyllithium/Lithium Alkoxide and Lithium Hydride/Lithium Alkoxide Mixed Aggregates

Description: The effects of lithium alkoxides on the rates of reactions and on the structures of a series of tert-butyllithium/lithium alkoxide mixed aggregates were studied, where the alkoxides were iso-butoxide, tert-butoxide and menthoxide. It was found that their effects depend not only on their amount present, but also on their steric bulk. The tert-butyllithium/lithium alkoxide mixed aggregates were exposed to UV light or heat to form lithium hydride/lithium alkoxide mixed aggregates. The aggregation… more
Date: December 1997
Creator: Nguyen, Hanh D.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

I. On the Mechanism of Acid Promoted Rearrangement of PCU-Derived Pinacols II. Synthesis of a Trimethyltrishomocubyl Helical Tubuland Diol

Description: I. Reductive dimerization of pentacyclo[5.4.0.0.^2,6.0^3,10.0^5'9]undecane-8-one-(PCU-8-one, 53) affords a mixture of meso and d,l pinacols (55a and 55b respectively). Acid promoted rearrangement of 55a and 55b conceivably can proceed with migration of C(7)-C(8) and/or C(8)-C(9) to form the corresponding pinacolone(s). In our hands, acid promoted rearrangement of 55a and 55b each proceeds with exclusive migration of C(7)- C(8) bond, thereby affording 58a and 59a respectively. Mechanistic featur… more
Date: May 1995
Creator: Liu, Zenghui
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Spectrofluorometric Probe Methods for Examining Preferential Solvation in Binary Mixtures

Description: Spectrofluorometric probe methods are developed and examined regarding their ability to model preferential solvation around probe molecules in binary solvents. The first method assumes that each fluorophore is solvated by only one type of solvent molecule and that each fluorophore contributes to the emission intensity. Expressions for this model are illustrated using fluorescence behavior of pyrene, benzo[e]pyrene, benzo[ghi]perylene, and coronene dissolved in binary n-heptane + 1,4-dioxane and… more
Date: August 1994
Creator: Wilkins, Denise C.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Surface and Interfacial Studies of Metal-Organic Chemical Vapor Deposition of Copper

Description: The nucleation and successful growth of copper (Cu) thin films on diffusion barrier/adhesion promoter substrates during metal-organic chemical vapor deposition (MOCVD) are strongly dependent on the initial Cu precursor-substrate chemistry and surface conditions such as organic contamination and oxidation. This research focuses on the interactions of bis(1,1,1,5,5,5-hexafluoroacetylacetonato)copper(II), [Cu(hfac)2], with polycrystalline tantalum (Ta) and polycrystalline as well as epitaxial tita… more
Date: December 1997
Creator: Nuesca, Guillermo M.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

FT-NMR and Raman Spectroscopic Studies of Molecular Dynamics in Liquids

Description: NMR relaxation and Raman lineshape analysis are well known methods for the study of molecular reorientational dynamics in liquids. The combination of these two methods provides another approach to tackle the characterization of molecular dynamics in liquids. Investigations presented here include (1) NMR relaxation study of polycyclic compounds in solution, (2) the study of nitromethane reorientational dynamics using the NMR and Raman methods, and (3) Raman lineshape analysis of reorientation he… more
Date: December 1993
Creator: Wang, Kuen-Shian
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Kinetic Studies of the Reactions of Alkyl and Silyl Hydrides

Description: The Kinetics of the reactions involving alkyl and silyl hydrides were studied by the flash photolysis / resonance fluorescence technique. The reactions of alkyl radicals (R = C₂H₅, i-C₃H₇, t-C₄H₉) with HBr have been studied at room temperature and the rate constants obtained (units are in cm³ s^-1 ) are: k₃.₃ = (7.01 ± 0.15) x 10^-12, k₃.₂ = (1.25 ± 0.06) x 10^-11, k₃.₁ = (2.67 ± 0.13) x 10^-11 These results, combined with previously determined reverse rate constants and other kinetic informati… more
Date: August 1996
Creator: Yuan, Jessie (Jessie Win-Jae)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Substituent Effects on Diazeniumdiolate Anions: an AB Initio and DFT Study

Description: Nitroglycerin and isoamyl nitrate have been used as nitrovasodilators since the nineteeth century. However, not until recently has it been known that these compounds were useful since they promoted the release of NO in the body. More recently, a new class of drugs, NO donors, has been developed. These include S-nitrosothiols (RSNO), sydnonimines, and nucleophilic NO adducts.
Date: December 1997
Creator: García, Samuel A. (Samuel Anthony)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Investigation of Ultratrace Metallic and Organic Contaminants in Semiconductor Processing Environments

Description: Detection of ultratrace levels of metallic ion impurities in hydrofluoric acid solutions and alkaline hydrogen peroxide solution was demonstrated using a silicon-based sensing electrode. The sensor's operation principle is based on direct measurements of the silicon open-circuit potential shift generated by the interaction between metallic ions and the silicon-based sensing surface. The new sensor can have practical applications in the on-line monitoring of microelectronic chemical processing. … more
Date: May 1997
Creator: Xu, Fei, 1971-
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Part 1. Investigation of Aluminum Amino Acid Complexes; Part 2. Structural Studies of Aluminum Chalcogen Bonds

Description: Five different complexes of aluminum and amino acids have been synthesized and characterized. Reaction between aluminum halides and amino acids that do not contain either a carboxylate or a hydroxy group in the side chain produce complexes of the general formula, [Al(amino acid)_n(halide)_3-n]_m. The most prevalent form of this form of complex is where n = 2, and an example of this in which the halide is replaced by hydroxide ligand has been structurally characterized. The complex for which n =… more
Date: May 1996
Creator: Gravelle, Philip W. (Philip Wyn)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Regioselective Coupling Reactions of Diiodophenol Derivatives

Description: Palladium catalyzed reactions of derivatives of 2,4-diiodophenol are explored. Coupling reactions with a series of terminal alkynes and formylation are found to be efficient and regioselective. Coupling with stananne reagents and alkenes do not work. The nature of the oxygen protecting group is critical. The phytotoxic natural product, Eutypine, is synthesized by using regioselective formylation and alkyne coupling. An approach to the plant antimicrobial compound Plicatin B is examined.
Date: December 1994
Creator: Ji, Jianhua
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Preparation and Stereochemistry of Reactive Intermediates Containing a Silicon-Carbon Double Bond

Description: 1,1-Dimethyl-2-neopentylsilene reacted with the N-methylimine of benzophenone to give 1,2,2-trimethyl-3- neopentyl-4,4-diphenyl-l-aza-2-silacyclobutane, I, and 2,3,4,4a-tetrahydro-2,3,3-trimethyl-1-phenyl-4-neopentyl-2- aza-3-silanephthalene, II, in 35% and 20% yields, respectively. Compounds I and II did not serve as thermal silene precursors. Heating I and II to over 280°C did not yield 1,3-disilacyclobutanes. In the presence of 2,3- dimethyl-1,3-butadiene typical silene products were not obt… more
Date: December 1991
Creator: Uang, Shinian
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Solvent and Ionic Complexes of the Calix[6]arenes

Description: One of the more attractive attributes of calixarenes is their wide variety of possible conformations and hence cavity shapes. However, the flexibility that allows this long-range benefit gives rise to major synthetic challenges when working with the larger members of the family. O-alkylations have proven to be the most widely employed synthetic routes to "functionalization" of the calixarenes, and these have shown a dependence upon both solvent and the metal ions present. Surprisingly, there ha… more
Date: December 1997
Creator: Wolfgong, William J.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Mixed Alkyllithim/Lithium Alkoxide Aggregates with Less Sterically Crowded Alkyl Groups

Description: Mixed alkyllithium / lithium alkoxide aggregates in the form (RLi)n(ROLi)m were formed by addition of corresponding alcohol compounds at different Li/O ratios. Variable temperature 13C and 6Li NMR spectroscopy were used to verify the formation of the mixed aggregates and to study their behavior in hydrocarbon solution. Spectra for the lithium n-propoxide / n-propyllithium and iso-butyllithium / lithium iso-butoxide systems each indicated at least one mixed aggregate.
Date: December 1997
Creator: Thornton, Terry L. (Terry Lee), 1962-
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Part I: Solid State Studies of Larger Calixarenes : Part II: Synthesis and Characterization of Metallocalixarenes

Description: Calixarenes are a class of macrocyclic compounds that have garnered interest in large part because of their ability to form host-guest complexes with various types of molecules. For all of the studies of complex formation by calixarenes, most of the work to date has concentrated upon the smaller calixarenes, and little is understood about the relationship between the complexes formed when in solution and that observed in the solid state. The first part of the study, presented in Chapter 3, is o… more
Date: May 1998
Creator: Smith, Janna Marie
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

NMR Study of the Reorientational and Exchange Dynamics of Organometallic Complexes

Description: Investigations presented here are (a) the study of reorientational dynamics and internal rotation in transition metal complexes by NMR relaxation experiments, and (b) the study of ligand exchange dynamics in transition metal complexes by exchange NMR experiments. The phenyl ring rotation in Ru3(CO)9(μ3-CO)(μ3-NPh) and Re(Co)2(CO)10(μ3- CPh) was monitored by 13C NMR relaxation experiments to probe intramolecular electronic and/or steric interactions. It was found that the rotation is relatively … more
Date: May 1996
Creator: Wang, Dongqing
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

A Study of the Processing Properties of Hard-Particle Reinforced Composite Solders

Description: The microstructural, mechanical and thermal properties of various composite solder formulations were investigated. Special interest was given in observing the processing properties, microstructural characteristics, fatigue behavior, tensile strength, and the effect of environmental ageing on the composite solder formulations. The solderability parameters wetting and speed of soldering, reflow temperature, and the thermal stability of the resulting composite solder were also examined.
Date: May 1994
Creator: Calderon, Jose Guadalupe
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

The Analysis of Volatile Impurities in Air by Gas Chromatography/Mass Spectrometry

Description: The determination of carbon monoxide is also possible by trapping CO on preconditioned molecular sieve and thermal desorption. Analysis in this case is performed by gas chromatography/mass spectroscopy, although the trapping technique is applicable to other suitable GC techniques.
Date: May 1993
Creator: Talasek, Robert Thomas
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

A Materials Approach to Silicon Wafer Level Contamination Issues from the Wet Clean Process

Description: Semiconductor devices are built using hyperpure silicon and very controlled levels of doping to create desired electrical properties. Contamination can alter these precisely controlled electrical properties that can render the device non-functional or unreliable. It is desirable to determine what impurities impact the device and control them. This study consists of four parts: a) determination of acceptable SCI (Standard Clean 1) bath contamination levels using VPD-DSE-GFAAS (Vapor Phase Decomp… more
Date: December 1996
Creator: Hall, Lindsey H. (Lindsey Harrison)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Rational Design of Metal-organic Electronic Devices: a Computational Perspective

Description: Organic and organometallic electronic materials continue to attract considerable attention among researchers due to their cost effectiveness, high flexibility, low temperature processing conditions and the continuous emergence of new semiconducting materials with tailored electronic properties. In addition, organic semiconductors can be used in a variety of important technological devices such as solar cells, field-effect transistors (FETs), flash memory, radio frequency identification (RFID) t… more
Date: December 2012
Creator: Chilukuri, Bhaskar
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
Back to Top of Screen