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 Degree Discipline: Materials Science
Characterizaton of Triethoxyfluorosilane and Tetraethoxysilane Based Aerogels

Characterizaton of Triethoxyfluorosilane and Tetraethoxysilane Based Aerogels

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Date: December 2001
Creator: Roepsch, Jodi Ann
Description: Aerogels are highly porous, low dielectric constant (low k) materials being considered by the semiconductor industry as an interlayer dielectric. Low k materials are needed to overcome capacitance problems that limit device feature sizes. Precursors triethoxyfluorosilane (TEFS) and tetraethoxysilane (TEOS) were used to prepare bulk aerogels. Samples were prepared by sol-gel methods, and then carbon dioxide supercritically-dried. Effects of varying the water to precursor ratio were studied with respect to aerogel properties and microstructure. Methods of analysis for this study include FTIR-ATR, TEM, RBS, EDS, SEM, dielectric constant determination by impedance and surface area by gas adsorption. Si-F bonds were determined to be present in both acid- and base-catalyzed TEFS as well as HF-catalyzed TEOS. Fluorine promotes a fractal network microstructure as opposed to a particle-like microstructure. Surface area and dielectric constant were determined to increase slightly with increases in the water to precursor ratio.
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The Electron Emission Characteristics of Aluminum, Molybdenum and Carbon Nanotubes Studied by Field Emission and Photoemission.

The Electron Emission Characteristics of Aluminum, Molybdenum and Carbon Nanotubes Studied by Field Emission and Photoemission.

Date: December 2002
Creator: Sosa, Edward Delarosa
Description: The electron emission characteristics of aluminum, molybdenum and carbon nanotubes were studied. The experiments were setup to study the emission behavior as a function of temperature and exposure to oxygen. Changes in the surface work function as a result of thermal annealing were monitored with low energy ultra-violet photoelectron spectroscopy for flat samples while field emission energy distributions were used on tip samples. The change in the field emission from fabricated single tips exposed to oxygen while in operation was measured using simultaneous Fowler-Nordheim plots and electron energy distributions. From the results a mechanism for the degradation in the emission was concluded. Thermal experiments on molybdenum and aluminum showed that these two materials can be reduced at elevated temperatures, while carbon nanotubes on the other hand show effects of oxidation. To purely reduce molybdenum a temperature in excess of 750 ºC is required. This temperature exceeds that allowed by current display device technology. Aluminum on the other hand shows reduction at a much lower temperature of at least 125 ºC; however, its extreme reactivity towards oxygen containing species produces re-oxidation. It is believed that this reduction is due to the outward diffusion of aluminum atoms through the oxide. Carbon nanotubes ...
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Temperature dependent rheology of surfactant-hydroxypropyl cellulose solutions.

Temperature dependent rheology of surfactant-hydroxypropyl cellulose solutions.

Date: December 2002
Creator: Snively, C. Todd
Description: The rheology of 1-8% hydroxypropyl cellulose (HPC) solutions has been studied in the temperature range of 20-45 degrees Celsius. The results showed that the relative viscosity at each HPC concentration decreases with increasing temperature. The relative viscosity decreases drastically at about 43 degrees Celsius due to a phase transition. The influence of anionic surfactant, sodium dodecylsulfate (SDS), induced gelation of a 2% HPC solution. The HPC solutions gelled at surfactant SDS concentrations ranging from 0.4 to 1.0 critical micelle concentration (CMC). The gelation of the HPC/SDS hydrogel is explained in the surfactant SDD - bridged HPC linear polymer chains. The complex viscosity - concentration profile was determined below the CMC of the SDS - water pair. The peak itself was a function of frequency indicating the presence of two relaxation times within the gelled network.
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Stability of Field Emitter Arrays to Oxygen Exposures

Stability of Field Emitter Arrays to Oxygen Exposures

Date: December 2002
Creator: Godbole, Soumitra Kumar
Description: The purpose of these experiments was to determine the degradation mechanisms of molybdenum based field emitter arrays to oxygen exposures and to improve the overall reliability. In addition, we also evaluated the emission current stability of gold-coated field emitter arrays to oxygen exposures. oxygen at 1x10-6 torr was introduced into the chamber through a leak valve for different lengths of time and duty cycles. To ensure identical oxygen exposure and experimental measurement conditions, tips on half the area of the FEA were fully coated with gold and the other half were left uncoated. The emission current from the gold coated half was found to degrade much less than that from the uncoated half, in the presence of oxygen. Also in the absence of oxygen, the emission current recovery for the gold-coated side was much quicker than that for the uncoated side.
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Fabrication of MOS capacitor and transitor structure using contact photolithography.

Fabrication of MOS capacitor and transitor structure using contact photolithography.

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Date: August 2002
Creator: Su, Danni
Description: This problem in lieu of thesis report describes a practical photolithographic method to produce micro patterns on metal-oxide-semiconductor or metal-oxide-semiconductor-metal layers for electrical measurements. The desired patterns are then transferred from the photo mask to the photoresist-coated metal film by exposure, followed by wet etching. In the procedure described in this report, it was observed that microstructures as small as 27 mm with an edge roughness of ~ 2 mm can be reproducibly generated with this process. MOS capacitors and transistors structures can be fabricated by using this technique. The method described in this report requires access to only simple facilities so that it is relatively inexpensive, and the overall time required for the whole process is short.
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Mechanical Properties of Polymer Modified Mortar

Mechanical Properties of Polymer Modified Mortar

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Date: August 2002
Creator: Palos, Artemio
Description: The mechanical properties of the polymer-modified mortar are markedly improved over conventional cement mortar. We utilized recycled ABS in powder form and a polymer latex emulsion, polymer percentage ranges from 0 to 25 percent by polymer/cement ratio were investigated. The mechanical properties investigated were compression strength and adhesion strength. Compression strength effects did not have an impact on adhesion strength. Adhesion strength was calculated with pullout testing apparatus designed by the author. Results indicate that recycled ABS had a lower adhesive strength than the acrylic latex emulsion and the base mortar, but did increase in adhesive strength when mixed with maleic-anhydride. The adhesive strength was investigated for a Fiber Reinforced Polymer (FRP) made of an "E" glass fiber that is a continuous strand roving oriented and pre-tensioned longitudinally in an isopthalic polyester matrix material. The FRP rebar was compared to standard steel rebars, and found that the standard steel corrugated rebar had a higher adhesive strength, due to mechanical interlocking. This was clarified by measurements using a smooth steel rebar. Characterization of the polymer-modified mortar was conducted by pore analysis and scanning electron microscopy. Scanning Electron Microscopy was implemented to view the polymer particles, the cement fibrils formed by the ...
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Hypotheses for Scratch Behavior of Polymer Systems that Recover

Hypotheses for Scratch Behavior of Polymer Systems that Recover

Date: May 2002
Creator: Bujard, Bernard
Description: Scratch recovery is a desirable property of many polymer systems. The reason why some materials have demonstrated excellent scratch recovery while others do not has been a mystery. Explaining the scratch resistance based upon the hardness of a material or its crosslink density is incorrect. In this thesis, novel polymers were tested in an attempt to discover materials that show excellent scratch recovery - one of the most important parameters in determining the wear of a material. Several hypotheses were developed in an attempt to give an accurate picture of how the chemical structure of a polymer affects its scratch recovery. The results show that high scratch recovery is a complex phenomenon not solely dependent upon the presence of electronegative atoms such as fluorine.
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Cure kinetics and processing parameters of neat and reinforced high performance epoxy resins : evaluation of techniques

Cure kinetics and processing parameters of neat and reinforced high performance epoxy resins : evaluation of techniques

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Date: December 1999
Creator: Bilyeu, Bryan
Description: Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4’-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Conditions
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Mineral-filled polypropylene: Improvement of scratch resistance

Mineral-filled polypropylene: Improvement of scratch resistance

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Date: December 2001
Creator: Khatib, Jamal F.
Description: A potential alternative to acrylonitrile-butadiene-styrene (ABS) and polycarbonate+ABS (PC+ABS), pigmented mineral-filled polypropylene (PP) finds an opening in automotive interior components such as instrument panels, knee bolsters, consoles, etc. Because of the lack of surface aesthetics, pigmented mineral-filled PP is experiencing a limitation to its acceptance in many applications. This study focuses on exploring various mineral fillers and additives in polypropylene to provide a material with enhanced scratch resistance. Several physical properties including Rockwell and Shore D hardness are investigated, and it is determined that Filler W improves scratch resistance. It is also determined that Filler T-filled-PP has poor scratch resistance even with the addition of a lubricant.
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Characterization of methyltrimethoxysilane sol-gel polymerization and the resulting aerogels.

Characterization of methyltrimethoxysilane sol-gel polymerization and the resulting aerogels.

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Date: August 2003
Creator: Dong, Hanjiang
Description: Methyl-functionalized porous silica is of considerable interest as a low dielectric constant film for semiconductor devices. The structural development of these materials appears to affect their gelation behaviors and impact their mechanical properties and shrinkage during processing. 29Si solution NMR was used to follow the structural evolution of MTMS (methyltrimethoxysilane) polymerization to gelation or precipitation, and thus to better understand the species that affect these properties and gelation behaviors. The effects of pH, water concentration, type of solvents, and synthesis procedures (single step acid catalysis and two-step acid/base catalysis) on MTMS polymerization were discussed. The reactivity of silicon species with different connectivity and the extent of cyclization were found to depend appreciably on the pH value of the sol. A kinetic model is presented to treat the reactivity of both silicon species involved in condensations separately based on the inductive and steric effects of these silicon species. Extensive cyclization in the presence of acid, which was attributed to the steric effects among numerous reaction pathways for the first time, prevents MTMS gelation, whereas gels were obtained from the two-step method with nearly random condensations. The experimental degree of condensation (DC) at the gel point using the two-step procedure was determined ...
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