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Explorations with Polycarbocyclic Cage Compounds

Description: A variety of novel cage-functionalized pyridyl containing crown ethers have been prepared for use in selective alkali metal complexation studies. A highly preorganized, cage-functionalized cryptand also has been designed and has been synthesized for use as a selective Li+ complexant. The alkali metal picrate extraction profiles of these cage-functionalized crown ethers also have been studied. Novel cage-functionalized diazacrown ethers have been prepared for selective alkali metal complexation studies. Alkali metal picrate extraction experiments have been performed by using this new class of synthetic ionophores to investigate the effects of cage-annulation and the influence of N-pivot lariat sidearms upon their resulting complexation properties. Novel pyridyl containing calix[4]arene receptors were prepared. Analysis of their respective 1H NMR and 13C NMR spectra suggests that calix[4]arene moieties in the ligand occupy the cone conformation. The complexation properties of these host molecules were estimated by performing a series of alkali metal picrate extraction experiments. An optically active cage-functionalized crown ether which contains a binaphthyl moiety as the chiral unit was prepared. The ability of the resulting optically active crown ether to distinguish between enantiomers of guest ammonium ions (i.e., phenylethylamonium and phenylglycinate salts) in transport experiments was investigated. Hexacyclo[11.2.1.02,12.05,10.05,15.010,14]hexadeca-6,8-diene-4,11-dione was prepared from hexacyclo[7.4.2.01,9.03,7.04,14.06,15] pentadeca-10,12-diene-2,8-dione. Unanticipated but remarkable acid and base promoted rearrangements of this new cage dione to novel polycyclic systems were observed and subsequently were investigated. The structures of the new systems thereby obtained were determined unequivocally by application of X-ray crystallographic methods. It is noteworthy that the reactions reported herein each provide the corresponding rearranged product in high yield in a single synthetic step. Pi-facial and regioselectivity in the thermal Diels-Alder cycloaddition between hexacyclo[11.2.1.02,12.05,10.05,15.010,14]hexadeca-6,8-diene- 4,11-dione and ethyl propiolate have been explored. This reaction proceeds via stereospecific approach of the dienophile toward the syn face of the diene p -system. However, [4+2]cycloaddition proceeds with ...
Date: August 1999
Creator: Chong, Hyun-Soon

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

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 Ta significantly degrade the strength of Cu/Ta chemical interactions, and affect the kinetics of Cu diffusion into bulk Ta. On clean Ta, monolayer coverages of Cu will de-wet only above 600 K. A partial monolayer of adsorbed oxygen (3L O2 at 300 K) results in a lowering of the de-wetting temperature to 500 K, while saturation oxygen coverage (10 L O2, 300 K) results in de-wetting at 300 K. Carbide formation also lowers the de-wetting temperature to 300 K. Diffusion of Cu into the Ta substrate at 1100 K occurs only after a 5-minute induction period. This induction period increases ...
Date: December 1999
Creator: Chen, Li

A Quenchofluorometric Study of Polycyclic Aromatic Hydrocarbons in Molecularly Organized Media

Description: Detection, identification and separation of polycyclic aromatic compounds in environmental samples are of extreme importance since many of these compounds are well known for their potential carcinogenic and/or mutagenic activities. Selective quenching of molecular fluorescence can be utilized effectively to analyze mixtures containing different polycyclic aromatic hydrocarbons. Molecularly organized assemblies are used widely in detection and separation of these compounds mainly because of less toxicity and enhanced solubilization capabilities associated with these media. Feasibility of using nitromethane and the alkylpyridinium cation as selective fluorescence quenching agents for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is critically examined in several molecularly organized micellar solvent media. Fluorescence quenching is used to probe the structural features in mixed micelles containing the various combinations of anionic, cationic, nonionic and zwitterionic surfactants. Experimental results provide valuable information regarding molecular interactions between the dissimilar surfactants.
Date: May 1998
Creator: Pandey, Siddharth

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)

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 constructed in order to understand the surface catalyzed oxidative degradation of polyperfluoroethers. The activation of oxygen molecules can be explained. The Lewis acid character of the iron fluoride surface can be predicted. Based on these results, mechanisms of the degradation processes are discussed.
Date: May 1995
Creator: Wang, Yanbin

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. The detection of Ag+ content in KODAK waste water was carried out successfully by this novel sensor. Trace levels of organic impurities in the hydrofluoric acid solutions and in the cleanroom air were characterized by multiple internal reflection infrared spectroscopy (MIRIS) using an organics probe prepared directly from a regular silicon wafer.
Date: May 1997
Creator: Xu, Fei, 1971-

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 features of this rearrangement are discussed. II. 4,7,1 l-trimethylpentacyclo[6.3.0.0.^2,6.0^3,l0.0^5,9]undecane-exo-4,exo-7-diol (23a) was successfully synthesized. This diol crystallizes in a helical tubuland lattice although its molecular structure does not possess C2 rotational symmetry.
Date: May 1995
Creator: Liu, Zenghui

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

New Adventures in the Chemistry of Polycarboncyclic Ring Systems

Description: I. Diels-Alder reactions of 1,2,3,4,9,9-hexachloro-1,4,4a,8a-tetrahydro-1,4-metha- nonaphthalene (16) and 1,2,3,4,9,9-hexachloro-1,4,6,7-tetrahydro-1,4-methanonaphthalene (17) toward dienophiles N-methyl-1,2,4-triazoline-3,5-dione (MTAD), N-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and/or N-methylmaleimide (NMM) have been examined. II. Epoxides derived from functionalized 1,4,4a,9a-tetrahydro-9,10-dioxo-1,4-methanoanthracenes (1a and 1b) undergo acid- and base-promoted intramolecular nucleophilic ring-opening to form new polycyclic alcohols. III. The title cycloalkylidenecarbene has been generated via reaction of 8-methylenepentacyclo[5.4.0.0^{2,6}.0^{3,10}. 0^{5.9}]undecan-11-one (44) with diethyl diazomethyl-phosphonate (DAMP). This species could be trapped in situ by cyclohexene, thereby affording the corresponding cycloadduct 46a and 46b.
Date: December 1997
Creator: Dong, Zhiming (Eric)

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 titanium nitride (TiN) substrates during Cu MOCVD, under ultra-high vacuum (UHV) conditions and low substrate temperatures (T < 500 K). The results obtained from X-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Temperature Programmed Desorption (TPD) measurements indicate substantial differences in the chemical reaction pathways of metallic Cu formation from Cu(hfac)2 on TiN versus Ta surfaces.
Date: December 1997
Creator: Nuesca, Guillermo M.

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 states were assigned from either 13C-6Li coupling or a new technique based on the relative intensity of NMR peaks using different nuclei. The compounds formed depend upon the method of formation and the alkoxide. The unique properties of the lithium hydride/lithium alkoxide mixed aggregates are their high solubility in hydrocarbon solutions, very reactive bases, showing 6Li-1H couplings, and having only one hydride ion per aggregate. Their formation, reactivity, solubility, and aggregation states were found to depend on the size of lithium alkoxides. X-ray crystal structures of lithium tert-butoxide and lithium menthoxide were also studied and found to be hexameric.
Date: December 1997
Creator: Nguyen, Hanh D.

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 of the solid-state properties of two of the larger calixarenes, and in comparison to other reported structures reveals patterns to the observed conformations both in the solid state and in solution. The formation of metal complexes has also been investigated and has focused extensively upon the metals as guests. Thus, the ability of the calixarenes to act as ligands in inorganic complexes has been virtually untapped, despite the polyoxo binding site they can easily provide, and very few metallocalixarenes have been reported. The second part of this study goes beyond the simple solid-state properties of such compounds, and involves the synthesis of several metallocalixarenes as part of a project directed at the functionalization of calixarenes with the components of a class of catalysts known to polymerize various olefins. These catalysts, commonly referred to as Ziegler-Natta catalysts, are introduced in Chapter 4. The new compounds presented here--three new aluminocalixarenes in Chapter 5 and a new titanocalixarene in Chapter 6--were synthesized so as to contain some of the same components observed in several of the other catalysts. These new compounds have been characterized crystallographically as well as through proton and multinuclear NMR, and observed conformational patterns are discussed.
Date: May 1998
Creator: Smith, Janna Marie

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-

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 have been no structural data presented concerning the complexes between the simple unsubstituted calix[6]arenes and the metal ions of groups 1 and 2. The structures of four complexes, containing cesium, rubidium, and calcium are reported as determined by X-ray crystallography. The solution behavior of the complexes for both representative groups is also discussed, in particular with regard to conformational stabilization of the calix[6]arenes and the role of solvent upon this stabilization. These complexes are also investigated as starting materials for the selective functionalization of the calix[6]arenes.
Date: December 1997
Creator: Wolfgong, William J.

The Synthesis and Chemistry of Polyciclic Cage Compounds

Description: Chapter I describes the synthesis of a trishomocubyl helical tubuland diol and some aspects of its inclusion chemistry. Thus, all three isomers of 4,7-dimethylpentacyclo[6.3.0.0^2,6.0^3,10.0^5,9]undecane-4,7-diol have been prepared and their X-ray structures have been determined. The syn,syn-isomer crystallizes in a double-stranded hydrogen-bonded lattice, while anti,syn-isomer forms a hydrogen-bonded layer lattice. In contrast, the anti,anti-isomer is a new member of the helical tubuland diol host family; its crystal lattice consists of parallel canals with a trefoil-shaped cross-section of area 25.4 Å^2. Chapter II describes the synthesis of new molecular clefts. These molecular clefts have been synthesized via base-promoted reactions of 3,6-diaryl-l,2,4,5-tetrazines with tetracyclo[6.3.0.0^4,11.0^5,9]undecane-3,6-dione and with tricyclo[6.3.0.0^2,6]undecane-3,11-dione, respectively. Compounds of this type are of interest as a potential new class of host molecules for use in host-guest complexation studies. Chapter III reports the synthesis of stereospecifically deuterated spiro(oxetane-3,8'-pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecanes) and their acid-promoted ring opening and concomitant rearrangements. The deuterium-containing reaction products have been characterized via analysis of their NMR and mass spectra. The results strongly suggest that intramolecular 1,5-hydride shifts provide an important pathway through which the acid promoted rearrangements occur. Chapter IV reports the oxidation of heptacyclo-[6.6.0.0^2,6.0^3,13.0^4,11.0^5,9.0^10,14] tetradecane (HCTD) via application of Barton's "GoAgg" systems. The products have been characterized by NMR and mass spectral analysis. Under GoAgg^v conditions, oxidation of HCTD proceeds to afford heptacyclo [6.6.0.0^2,6.0^3,13.0^4,11.0^5,9.0^10,14]tetradecan-7-one in 1% yield.
Date: December 1994
Creator: Wang, Yanjun

Thermophysical and Mechanical Properties of Polymer Liquid Crystals and Their Blends

Description: Tensile properties, namely the elastic modulus, tensile strength, percent of elongation at yield and at the break were determined for the pure components and blends. The results are connected to the respective phase diagrams and demonstrate that blending makes property manipulation possible. Blends for which the mechanical properties are better than those of pure EPs can be obtained.
Date: May 1994
Creator: López, Betty Lucy

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 obtained. However, I and II reacted rapidly with methanol at room temperature to give the ring-opened products (E)-2- methoxy-2,5,5-trimethyl-2-silahex-3-ene, III, 1,1- diphenyldimethylamine, IV, and 2-methoxy-2,5,5-trimethyl-3- (N-methylaminodiphenyl) methyl-2-silahexane, V.
Date: December 1991
Creator: Uang, Shinian

Sulfur-induced Corrosion at Metal and Oxide Surfaces and Interfaces

Description: Sulfur adsorbed on metallic and oxide surfaces, whether originating from gaseous environments or segregating as an impurity to metallic interfaces, is linked to the deterioration of alloy performance. This research dealt with investigations on the interactions between sulfur and iron or iron alloy metallic and oxide surfaces under ultrahigh vacuum conditions. Sulfur was either intentionally dosed from a H2S source on an atomically clean metal surface, or segregated out as an impurity from the bulk to the metal surface by annealing at elevated temperatures.
Date: August 1997
Creator: Cabibil, Hyacinth (Hyacinth Liesl)

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

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 hexafluorobenzene/benzene mixtures.
Date: December 1993
Creator: Wang, Kuen-Shian

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 (Scheme 9 in Chapter 2). E-1,2-di(1'-adamantyl)ethene (15) was synthesized by iodine promoted isomerization of 14. Both structures were established unequivocally via single-crystal X-ray structural analysis. E-1-(exo-8'-Pentacyclo[5.4.0.0²,⁶.0³,¹⁰,0⁵,⁹]undecyl)-2-phenylethylene (16a) was synthesized, and its structure was established via analysis of its 1H, 13C, and 2D COSY NMR spectra. Part III. Reactions of electrophiles, i.e.,:CCl_2, PhSCl, and Br_2, to Z- and E-1,2-di(1'-adamantyl)ethenes (14 and 15, respectively) are described (Scheme 5, 8, 10, and 13 in Chapter 3). Structures of the corresponding products were established unequivocally via analysis of their respective one- and two-dimensional NMR spectra and/or single-crystal X-ray structural analysis. Part IV. An improved asymmetric synthesis of optically active (S)-4-hydroxy-2-cyclohexenone 1 (64%ee, determined via Mosher's method) has been developed (Scheme 5 in Chapter 4). The key step in this synthesis involves the baker's yeast reduction of 13. The absolute configuration of the major product, (S)-1, was established unequivocally via single-crystal X-ray structural analysis of a precursor. The optical purity of the major product 14a (80%de, 67%ee) was established via careful integration of relevant gated-decoupled 13C NMR spectra.
Date: August 1995
Creator: Xing, Dongxia