The behavior of cemented sands is examined experimentally and theoretically in this study. The first segment of the investigation involves an extensive laboratory program to examine the effects of slenderness ratio, effects of cementation, and effects of confining pressure on the stress-strain curves of cemented sands. Results show that specimens with slenderness ratio of 1.5 or greater exhibit lower strength, higher dilatation rates, and relatively brittle behavior when compared to samples with slenderness ratio of 1. Furthermore, cemented sands have an essentially straight line Mohr-Coulomb failure envelope, whose cohesion intercept increases with the degree of cementation of the soil. The effective friction angles measured for cemented sands with various cementation levels are in the same ranges as the effective friction angle evaluated for uncemented sands. Moreover, failure modes of the material varies from brittle to ductile depending upon the level of cementation and the degree of confinement. In general, as cementation increases, cemented sand exhibits a brittle failure behavior; while increasing the confining pressure causes a ductile failure response. The second portion of the project includes development of a constitutive model for cemented sands. Cemented sand is viewed as a multi-phase material comprising three phases: sand, cement, and pore water. The elastoplastic behavior of cemented sands is the consequence of the behavior of the individual phases plus the interaction of the phases. The individual phases (sand and cement) are modeled using the theory of plasticity. Mixtures theory is used to assemble the individual phases to simulate the overall behavior of cemented sands. The gradual damage of the internal structure of cemented sands is also incorporated within the model. The agreement between experimental data and model predictions is very good. In summary, mixtures theory using simple plasticity models for the individual phases is capable of capturing the complex behavior of cemented sands.

The magnitude and temperature dependence of both the nucleation and crystal growth rates in lithium diborate glass were determined in the temperature range, 490 to 520°C. Comparison of the nucleation rates predicted by Classical Nucleation Theory and those found experimentally shows that the predicted classical nucleation rates are about 95 orders of magnitude smaller than the experimentally determined values. In addition, Classical Nucleation Theory does not predict the temperature dependence found experimentally. Comparison is also made with silicate glass systems which have been shown to exhibit homogeneous nucleation. Crystal nucleation in the lithium diborate glass almost certainly proceeds by a homogeneous mechanism. Comparisons are made between experimentally obtained values of the crystal growth rate in lithium diborate glass and those computed using surface nucleated crystal growth theory. Although the temperature dependence of the experimental growth rates at large undercoolings appears to be described well by the latter model, the computed values of the growth rates are about 60 orders of magnitude too small. Using a temperature dependent surface tension (obtained from fitting crystal nucleation data) in the surface nucleated crystal growth model partially reduces the discrepancy between the experimental and calculated magnitudes of the growth rate, but produces an incorrect prediction for the temperature dependence of the growth rate.

Alkaline solutions based on ammonium hydroxide and quaternary ammonium hydroxides such as choline (hydroxyethyl trimethyl ammonium hydroxide) and TMAH (tetramethyl ammonium hydroxide) are used widely in the wet processing of silicon wafers for the control of ionic and particulate impurities. The Wilhelmy plate technique was used in characterizing the ability of alkaline solutions to alter the wettability of wafers. Choline improved the water wettability of wafers, and at concentrations greater than 1000 ppm, rendered the wafers very hydrophilic. Ellipsometric and XPS analyses showed that the exposure of choline-treated surfaces to air resulted in the oxidation of Si to SiO₂. The increase of wettability of wafers in TMAH solutions was due to the roughness introduced by the high etch rate of TMAH solutions. Ammonia solutions without the addition of H₂O₂ did not increase wettability. The addition of H₂O₂ and a non-ionic surfactant to alkaline solutions significantly increased the wettability of wafers, decreased the etch rate, and resulted in smoother surfaces. The use of isopropyl alcohol (IPA) in the drying of wafers has been considered by the semiconductor industry. The addition of IPA to water resulted in a decrease in surface tension at the solution/vapor interface. The surface excess of IPA molecules at the solution/air interface was calculated to have a maximum value of 8.5 x 10⁻¹⁰ moles/cm² at a solution composition of 25% IPA and 75% water. IPA solutions with less than 25% IPA were very effective in removing PSL particles on hydrophilic wafers. Hydrophilic particles such as alumina and glass were difficult to remove from wafers in DI water and IPA solutions, however, hydrophobic particles such as silicon were slightly removable in DI water and IPA solutions. The wettability of particles (θ) and substrate (α) in solutions played important roles in removing particles on substrates. Leenaars' equation for the calculation of magnitude of surface tension force which balance adhesion force, F(A), did not seem to hold for solutions containing less than 25% IPA. Modification to this equation by adding a surface pressure term, π*, was considered in explaining the experimental results.

A uniform coating of precursors of various metal oxides on individual alumina particles was achieved by controlled hydrolysis of metal alkoxides in a slurry of alumina. Heterogeneous deposition of the precursors on the surface of the alumina particles was attributed to the electronegative character of alkoxy groups of the metal alkoxides. The powder coating techniques provided superior microstructures with homogeneous size and spatial distribution of secondary phases. It also lowered the sintering temperature of alumina in certain systems. In order to characterize microstructure development of the coated alumina during heating, powder compacts were rapidly quenched from elevated temperatures into liquid nitrogen and their interfaces and microstructures were examined by analytical TEM and FE-SEM. The EM studies revealed that the alumina particle surfaces act as sites for heterogeneous nucleation. The final structure of the alumina simultaneously doped with precursors of cupric oxide and titania was reached in the presence of a liquid phase but a large shrinkage occurred before the liquid formed. This phenomenon was explained from the viewpoints of superplasticity of the precursors and of a solid state reaction during heating. This speculation was supported by the similar accelerated sintering behavior with an addition of bismuth oxide and titania. The sintering behavior of alumina coated with a precursor of titania or zirconia, oxides of group 4 elements, was very different. The solid solution between alumina and titania after the nucleation of rutile on the surface of alumina resulted in sintering rate enhancement, while the slow self-diffusion characteristics of zirconia resulted in "droplets" on the surface of alumina particles which impeded the grain boundary migration.

The deposition and characterization of HfO2 films for potential application as a high-k gate dielectric in MOS devices has been investigated. DC magnetron reactive sputtering was utilized to prepare the HfO2 films. Structural, chemical, and electrical analyses were performed to characterize the various physical, chemical and electrical properties of the sputtered HfO2 films. The sputtered HfO2 films were annealed to simulate the dopant activation process used in semiconductor processing, and to study the thermal stability of the high-k films. The changes in the film properties due to the annealing are also discussed in this work.Glancing angle XRD was used to analyse the atomic scale structure of the films. The as deposit films are amorphous, regardless of the film thickness. During postdeposition annealing, the thicker films crystallized at lower temperature 600 C, and ultra-Thin (5.8 nm) film crystallized at higher temperature (600 - 720 C). The crystalline phase which formed depended on the thickness of the films. The low temperature phase (monoclinic) formed in the $10-20$ nm annealed films, and high temperature phase (tetragonal) formed in the ultra--thin annealed HfO2 film. The TEM cross-section studies of as deposited samples show the interfacial layer (< 1nm) exists between HfO2/Si for all film thicknesses. The interfacial layer grows thicker during heat treatment, and grows more rapidly when grain boundaries are present. XPS surface analysis shows the as deposited films are fully oxidized with an excess of oxygen. Interfacial chemistry analysis indicated that the interfacial layer is a silicon-rich silicate layer, which tends to transform to silica-like layer during heat treatment.I-V measurements show the leakage current density of the Al/as deposit-HfO2/Si MOS diode is of the order of 10^{-3} A/cm^2, which is two orders of magnitude lower than that of ZrO2 film with similar physical thickness. Carrier transport is dominated by Schottky emission at lower electric fields, and by Frenkel-Poole emission in the higher electric field region. After annealing, the leakage current density decreases significantly as the structure remains amorphous structure. It is suggested that this decrease is assorted with the densification and defect healing which accures when the porous as-deposited amorphous structure is annealed. The leakage current density increases of the HfO2 layer crystallizes on annealing, which is attributed to the presence of grain boundaries. C-V measurements of the as deposited film shows typical C-V characteristics, with negligible hystersis, a small flat band voltage shift, but great frequency dispersion. The relative permittivity of HfO2/interfacial layer stack obtained from the capacitance at accumulation is 15, which corresponds to EOT (equivalent oxide thickness)= 1.66 nm. After annealing, the frequency dispersion is greatly enhanced, and the C-V curve is shifted toward negative voltage. Reliability tests show that the HfO2* 0films which remain amorphous after annealing possess superior resistance to constant voltage stress and ambient aging.This study concluded that the sputtered HfO2 films are amorphous as deposited. The postdeposition annealing alters the crystallinity, interfacial properties, and electrical characteristics. The HfO2 films which remain amorphous structure after annealing possess the best electrical properties.

Ammonia-peroxide mixture (APM) is a widely used wet chemical system for particle removal from silicon surfaces. The conventional APM solution in a volume ratio of 1:1:5 (NH4OH:H2O2:H2O) is employed at elevated temperatures of 70-80 °C. At these temperatures, APM solution etches silicon at a rate of ~3 Å/min, which is unacceptable for current technology node. Additionally, APM solutions are unstable due to the decomposition of hydrogen peroxide and evaporative loss of ammonium hydroxide resulting in the change in APM solution composition. This has generated interest in the use of dilute APM solutions. However, dilution ratios are chosen without any established fundamental relationship between particle-wafer interactions and APM solutions.Atomic force microscopy has been used to measure interaction forces between H-terminated Si surface and Si tip in APM solutions of different compositions. The approach force curves results show attractive forces in DI-water, NH4OH:H2O (1:100) and H2O2:H2O (1:100) solutions at separation distances of less than 10 nm for all immersion times (2, 10 and 60 min) investigated. In the case of dilute APM solutions, the forces are purely repulsive within 2 min of immersion time. During retraction, the adhesion force between Si surface and Si tip was in the range of 0.8 nN to 10.0 nN. In dilute APM solutions, no adhesion force is measured between Si surfaces and repulsive forces dominated at all distances. These results show that even in very dilute APM solutions, repulsive forces exist between Si surface and particle re-deposition can be prevented.The stability of APM solutions has been investigated as a function of temperature (24 - 65 °C), dilution ratio (1:1:5 - 1:2:100), solution pH (8.0 - 9.7) and Fe2+ concentration (0 - 10 ppb) using an optical concentration monitor. The results show that the rate of H2O2 decomposition increased with an increase in temperature, solution pH and Fe2+ concentration. The kinetic analysis showed that the H2O2 decomposition follows a first order kinetics with respect to both H2O2 and OH- concentrations. In the presence of Fe2+, hydrogen peroxide decomposition follows a first order reaction kinetics with respect to H2O2 concentration.

Fabrication and synthesis of nanostructured materials are essential aspects of nanoscience and nanotechnology. Although researchers are now able to create and tailor different nanostructured materials, the ability to precisely control the materials' sizes, shapes, and properties at the nanoscale level remains challenging. The aim of this dissertation was to develop new methods to aid researchers in overcoming these challenges. The study investigated two different methods used to create one-dimensional carbon nanostructures, i.e. carbon nanotubes and carbon nanopillars.In the first section, chemical vapor deposition method was used to grow carbon nanotubes (CNTs). Studies examining the effects of methane and hydrogen flow rates on the growth of CNTs were conducted. Results indicated that multi-walled CNTs with metallic properties could be obtained at a methane flow rates as low as 300 cc/min. At higher methane flow rates, i.e. 600-700 cc/min, semiconducting single-walled CNTs and double-walled CNTs were produced. Another phase of this section developed a new and simple CNT growth method using a solid carbon source and indicated polyacrylonitrile and nanosized SiO₂ were effective in producing MWCNTs. In the second part, a new nanoimprint technique was developed to enable printing of nanostructures at sub-100nm level using various polymers. This technique inherited its high-resolution feature from traditional nanoimprint lithography, but without the use of pressure. To demonstrate, PAN nanopillar structures were printed and converted to carbon. In another phase of the part, the use of our imprint technique resulted in the creation and conversion of polysilazane nanostructures to ceramic for the first time.The final section of this dissertation is devoted to study the impact of porosity in gas diffusion layers (GDLs) on the performance of fuel cells. In one study, a new technique using SEM images to determine GDL porosity was developed. The difference between SEM calculated porosities and mercury intrusion porosimetry measurements were less than 2%. The second study characterized fuel cell performances using GDLs constructed with additional micro porous layers (MPLs) and treated with different wet proofing treatments (WPT). Results showed that when MPL is added, cell performance decreases. However, the increase in WPT in the MPL improved cell performance.

The first part of this dissertation focuses on self-assembled composites. Self-assembled composites composed of vertically aligned multiwalled carbon nanofibers (VA-MWCNF) combined with a graphitic layer (GL) arranged perpendicular to MWCNF axes‘ have been produced at low temperature (445 °C) using low pressure thermal chemical vapor deposition (LPCVD). Electron microscopy and Raman spectroscopy were used to analyze composite morphology, structure and quality. It is found that different composite morphologies and modification of the GL structure can be obtained by varying the nickel (Ni) catalyst underlayer materials, the catalyst pre-treatment method, the gas recipe, the gas flow rates and the pressure conditions of the LPCVD process. Pre-treatment of the catalyst with H2 plasma or NH₃ gas was also investigated. It is found that even a short, one minute H2 plasma pre-treatment of the catalyst results in a significant break-down of the VA-MWCNF/GL composite structure. On the other hand, a one or ten minute catalyst pre-treatment with NH₃ gas results in a structural modification of the GL but retains the VA-MWCNF/GL composite structure. An increase in time of NH₃ gas pre-treatment leads to reduced VA-MWCNF/GL composite height. A growth mechanism for VA-MWCNF/GL composites was proposed. The focus, of the second part of this dissertation, is on the analysis of natural chalks used in traditional old master drawings. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis were performed on bulk samples of natural black chalk, steatite and calcite natural white chalks and on samples of these chalks applied to paper using various techniques. Critical information was obtained about the morphology and sub-micron features of the chalk particles, the chalk/paper interaction of each application technique and elemental composition of the bulk chalk samples. It was found that the particle size and morphology of the natural white chalks reduced their ability to hold to the paper. This information provides insight as to why black chalk is more resistant to abrasion than the natural white chalks which is important for the conservation of extant chalk drawings.

Pollucite (CsAlSi₂O₆) is a refractory phase within the Cs₂O-Al₂O₃-SiO₂. It melts at >1900°C and also has a reported thermal expansion value of 15 x 10⁻⁷/°C. These qualities make it suitable for study as a high temperature structural ceramic. Amorphous powders were synthesized by a novel sol-gel process in the Cs₂O-Al₂O₃-SiO₂ system. Gels were produced from tetraethoxysilane (TEOS), Aluminum chelate, and Cs-acetate. Powders were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), chemical, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The glass transition and crystallization temperatures were determined to be 945°C and 1026°C, respectively, for the amorphous powders. Pollucite and mullite phases were observed by XRD of bulk glass-ceramics. A density of 3.02 gm/cm³ was observed for the hot pressed material. Dielectric constants in the frequency range 1kHz-1MHz were found to be in the range of 5.23 to 5.78 for the as hot pressed and heat treated samples. Thermal expansion coefficients were also determined.

A method for the preparation of submicron, monodispersed, spherical particles of aluminum hydrous oxide has been developed. The method consists of the hydrolysis of aluminum acetylacetonate in alcoholic solution by the direct addition of a base at room temperature. The effects of the process parameters including temperature, solvent, type and concentration of base, aluminum acetylacetonate concentration, and stirring time are examined as well as the process reproducibility, particle composition and particle stability. Results obtained have shown that monodispersed particles can be formed with a mean particle diameter of eighty five to two hundred and fifteen nanometers and the mean size is reproducible to within ten percent of the mean diameter. Particles that are redispersed in fresh solvent are stable for at least thirty days. A model is proposed which explains the kinetics of particle growth and the influence of experimental parameters such as temperature, pH, concentration and the solvent on the formation of particles.