K-space functionalities in 2-D phononic crystals (PCs) were studied through the use of the finite difference time domain method (FDTD) as well as the plane wave expansion method (PWE) to solve for the propagation behavior of acoustic waves in these periodic structures. Each of these methods are fully explained in sections 2 and 3 in Appendix A. Characteristics of the various structures were found which aid in the design of the PC to obtain very specific and controlled propagation behavior.Various refractive behaviors were studied which included positive, negative, or zero-angle refraction depending on the angle of the incident wave. For all three cases of refraction, the transmitted beam underwent splitting upon exiting the crystal. These properties are analyzed theoretically as well as demonstrated experimentally. Band structures and equifrequency surfaces (EFSs) show that the observed properties result from the unique geometry of the PC's EFSs as compared to that of the incident media. These properties were extended to the applications of multiplexing and demultiplexing in which the separation of information carried by acoustic waves was attributed entirely to their differences in wave vector. To the best of our knowledge, this is the first report of a k-space multiplexing/demultiplexing device.Subwavelength resolution imaging capabilities of a flat lens composed of a phononic crystal (PC) were also studied. It was found that the image resolution of the PC flat lens beats the Rayleigh diffraction limit because bound modes in the lens can be excited by evanescent waves emitted by the source. These are modes that propagate only in the direction parallel to the lens surface. These modes resonantly amplify evanescent waves that contribute to the reconstruction of an image. The effect on the image resolution and focal point on various structural and operational parameters were studied. These parameters included source frequency, geometry of the lens, source position, and time. The mechanisms by which these factors affect resolution are discussed in terms of the competition between the contribution of propagative modes to focusing and the ability of the source to excite bound modes of the PC lens.

Lithium-ion batteries (LIBs) are receiving significant attention from both academia and industry as one of the most promising energy storage and conservation devices due to their high energy density and excellent safety. Graphite, the most widely used anode material, with limitations on energy density, can no longer satisfy the requirements proposed by new applications. Therefore, further improvement on the electrochemical performance of anodes has been long pursued, along with the development of new anode materials. Among potential candidates, Si and Sn based anodes are believed to be the most promising. However, the dramatic volume expansion upon Li-intercalation and contraction upon Li de-intercalation cause mechanical instability, and thus cracking of the electrodes. To overcome this issue, many strategies have been explored. Among them the most efficient strategies include introduction of a nanostructure, coupled with a buffering matrix and coating with a protective film. However, although cycling life has been significantly increased using these three strategies, the capacity retention still needs improvement, especially over extensive charge-discharge cycles. In addition, more efforts are still needed to develop new fabrication methods with low costs and high efficiency. To further improve mechanical stability of electrodes, understanding of the failure mechanisms, particularly, the failure mechanisms of Si and Sn nanomaterials is essential. Therefore, some of the key factors including materials fabrication and microstructural changes during cycling are studied in this work. Hollow Si nanospheres have proved to be have a superior electrochemical performance when applied as anode materials. However, most of fabrication methods either involve use of processing methods with low throughput, or expensive temporary templates, which severely prohibits large-scale use of hollow Si spheres. This work designed a new template-free chemical synthesis method with high throughput and simple procedures to fabricate Si hollow spheres with a nanoporous surface. The characterization results showed good crystallinity and a uniform hollow sphere structure. The substructure of pores on the surface provides pathways for electrolyte diffusion and can alleviate the damage by the volume expansion during lithiation. The success of this synthesis method provides valuable inspiration for developing industrial manufacturing method of hollow Si spheres.3D graphene is the most promising matrix that can provide the necessary mechanical support to Sn and Si nanoparticles during lithiation. 2D graphene, however, results in Sn/graphene nanocomposites with a continuous capacity fade during cycling. It is anticipated that this is due to microstructural changes of Sn, however, no studies have been performed to examine the morphology of such cycled anodes. Hence, a new Sn/2D graphene nanocomposite was fabricated via a simple chemical synthesis, in which Sn nanoparticles (20-200 nm) were attached onto the graphene surface. The content of Sn was 10 wt.% and 20 wt.%. These nanopowders were cycled against pure Li-metal and, as in previous studies, a significant capacity decrease occurred during the first several cycles. Transmission and scanning electron microscopy revealed that during long term cycling electrochemical coarsening took place, which resulted in an increased Sn particle size of over 200 nm, which could form clusters that were 1 m. Such clusters result in a poor electrochemical performance since it is difficult for complete lithiation of the Sn to occur. It is hence concluded that the inability of Sn/2D graphene anodes to retain high capacities is due to coarsening that occurs during cycling. In addition to using forms of carbon to buffer the Sn expansion, it has been proposed to alloy Sn with S, which has a low redox potential vs Li⁰/Li⁺. Therefore, another new anode proposed here is that of SnS attached to graphite. The as prepared powders had a flower-like structure of the SnS alloy. Electrochemical cycling and subsequent microstructural analysis showed that after electrochemical cycling this pattern was destroyed and replaced by Sn and SnS nanoparticles. Based on the electron microscopy and XRD analysis, it was concluded that selective leaching of S occurs during lithiation of SnS particles, which results into nano SnS and Sn particles to be distributed throughout the electrolyte or SEI layer, without being able to take part in the electrochemical reactions. This mechanism has not been noted before for SnS anodes and indicates that it may not be possible to retain the initial morphology of SnS alloy during cycling, or the ability of SnS to be active throughout long term cycling. To conclude it should be stated that the goal and novelty of this thesis was (i) the fabrication of new Si, Sn/graphene and SnS/C nanostructures that can be used as anodes in Li-ion batteries and (ii) the documentation of the mechanisms that disrupt the initial structural stability of Sn/2D graphene and SnS/C anodes and result in severe capacity loss during long term cycling (over 100 cycles). These systems are of high interest to the electrochemistry community and battery developers.

GeₓSe₍₁₋ₓ₎ and AsₓSe₍₁₋ₓ₎ glasses have found use in many technological applications due to their excellent rheological properties and their wide IR transparency window. However, the low glass transition temperatures of these glasses leads to large changes in their properties, due to structural relaxation, over the weeks and months subsequent to their fabrication. Thus, obtaining a more thorough understanding of structural relaxation and its relation to the structure, composition, and processing of these glasses is important in furthering their use. Structural investigations, using NMR and Raman spectroscopies, performed on the GeₓSe₍₁₋ₓ₎ family of glasses show that the structure of these glasses is composed of two distinct microdomains. One corresponds to a rigid GeSe₂-like domain and the other corresponds to a floppy Se domain. These results are compared to other existing structural models for GeₓSe₍₁₋ₓ₎ glasses. Enthalpy measurements on both GeSe₉ and GeSe₄ optical fibers which were aged up to five years demonstrate that both compositions undergo a large amount of enthalpy relaxation in this time period. Raman spectroscopy performed concurrently with enthalpy measurements on the same GeSe₉ and GeSe₄ fibers shows that one of the structural changes taking place within the glass network is the conversion of edgesharing to corner-sharing tetrahedra in the GeSe₂-like phase. Moreover, the rate at which this conversion takes place is shown to be similar to the rate of enthalpy relaxation, suggesting that this structural change is one of the main mechanisms for structural relaxation in GeₓSe₍₁₋ₓ₎ glasses. Implementation of the Tool-Narayanaswamy-Moynihan (TNM) model as a hybrid computer model allowing the prediction of the four relaxation parameters Δh*, log(A), x, and β via optimization of simulated and experimental data was accomplished. It was found that a multi-rate version of the TNM model, which obtains an average set of model parameters via optimization of multiple experimental thermal histories simultaneously, was able to predict relaxation parameters for AsₓSe₍₁₋ₓ₎ glasses within the 2.10 ≤ <r> ≤ 2.50 compositional domain, where <r> is the average bond coordination of the glass network as defined by the Phillips and Thorpe constraints model. Above <r> = 2.50, however, the model fails, due to a bimodal distribution of relaxation times within the glass structure contrary to the TNM model assumption of a unimodal distribution of relaxation times, thus rendering the model inapplicable. Muti-rate modeling of the GeₓSe₍₁₋ₓ₎ family of glasses was also attempted, however the TNM model also fails for this family of glasses due to the inherently bimodal distribution of relaxation times which arises from their bimodal structure.

Quantum-scale semiconductors embedded in an electrically-active matrix have the potential to improve photovoltaic (PV) device power conversion efficiencies by allowing the solar spectral absorption and photocarrier transport properties to be tuned through the control of short and long range structure. In the present work, the effects of phase assembly on quantum confinement effects and carrier transport were investigated in CdTe - ZnO nanocomposite thin films for use as a spectrally sensitized n-type heterojunction element. The nanocomposites were deposited via a dual-source, sequential radio-frequency (RF) sputter technique that offers the unique opportunity for in-situ control of the CdTe phase spatial distribution within the ZnO matrix. The manipulation of the spatial distribution of the CdTe nanophase allowed for variation in the electromagnetic coupling interactions between semiconductor domains and accompanying changes in the effective carrier confinement volume and associated spectral absorption properties. Deposition conditions favoring CdTe connectivity had a red shift in absorption energy onset in comparison to phase assemblies with a more isolated CdTe phase. While manipulating the absorption properties is of significant interest, the electronic behavior of the nanocomposite must also be considered. The continuity of both the matrix and the CdTe influenced the mobility pathways for carriers generated within their respective phases. Photoconductivity of the nanocomposite, dependent upon the combined influences of nanostructure-mediated optical absorption and carrier transport path, increased with an increased semiconductor nanoparticle number density along the applied field direction. Mobility of the carriers in the nanocomposite was further mediated by the interface between the ZnO and CdTe nanophases which acts as a source of carrier scattering centers. These effects were influenced by low temperature annealing of the nanocomposite which served to increase the crystallinity of the phases without modification of the as-deposited phase assembly and associated absorption properties. Integration of the nanocomposite as an n-type heterojunction element into a PV device demonstrated the ability to tune device response based on the spectral absorption of the nanocomposite sensitizer film as dictated by the phase assembly. Overall the various phase assemblies studied provided increased opportunity for optimization of the absorption and carrier transport properties of the nanocomposite thin films.

Researchers using Darcy's law to model flow in porous media must satisfy the requirement for sufficient scale separation between the pore scale and the model scale. This requirement is analogous to that for any continuum model, where application is restricted to scales larger than the underlying discrete structure. In the case of Darcy's law when the model scale becomes too small, the measurement of the permeability - the material property required to close the relationship - becomes polluted by the boundary conditions, either physical or numerical. The requirements for adequate scale separation to obtain permeability measurements (also known as satisfying the conditions for a representative elementary volume, or REV, for permeability) have not been previously reported. Likewise, the behavior of Darcy models when applied at sub-REV length scales has not been reported. Here, the results of Stokes simulations of transverse flow in 90,000 sequential random packings of monodisperse cylinders at a variety of liquid fractions and averaging-volume sizes show that approximately 200 cylinders must be present in an averaging volume before the effects of periodic boundary conditions on the Stokes simulations (the conventional choice for permeability measurements using Stokes flow) are no longer evident in the measured permeability. Direct comparisons between flow predictions from a two-dimensional, tensor-based Darcy model and a Stokes model for additional 10,000 domains show that the Darcy model is an unbiased predictor of the flow distribution in the system, even when the permeability is expected to contain boundary-condition artifacts. Though unbiased, the Darcy models do show considerable reduction in accuracy as the model scale shrinks toward the pore scale, with significant declines observed after the side length of a square averaging volume reaches 10 times the cylinder diameter. Finally, a novel approach for visualizing flows using the linear properties of the Stokes equations shows how the periodic boundary conditions affect the flow, and motivates the development of a generalized approach for obtaining permeability that does not require periodic boundary conditions. Modest improvements in the Darcy model relative to the actual Stokes flow result when the new approach is used to obtain permeability at small averaging volumes.

Calcium signal can be found in many types of cell. It has been treated as a life and death signal in cell-level for triggering life at fertilization, controlling the development and differentiation of cells into specialized types, mediating the subsequent activity, and finally affecting the cell death. In tissues, intercellular calcium wave is thought to serve as a long-range signaling, affected by the cell architecture. The aim of this thesis is to provide insight into the intercellular calcium waves in multicellular complex structures subjected to mechano- or chemical-stimuli. In the mechano-stimulated study, we combine the development of theoretical and experimental study of the propagation of calcium signals in multicellular structures composed of human endothelial cells. This analysis provides evidence for an effect of architecture on the propagation of calcium signals and the effect of single and dual stimulation on the multicellular structures. A simple model was established based on the calcium release/intake reaction and diffusion through gap junction from stimulated cell to the downstream cells. The simulation result shows similar results as what is shown in experiments. In the chemical-stimulated model, we studied computationally the interdependence between intracellular calcium and inositol-1,4,5-trisphosphate (IP₃) pathway and cell-cell communication via gap junction. We investigate the influence of the microenvironment of cells on the frequency of intracellular calcium oscillation. The simulation result shows that the oscillation frequency of an isolated cell is lower than that of a cell embedded in a cell-chain. This phenomenon is attributed to retrograde diffusion of calcium and IP₃ originating from a widening range of cells in the chain undergoing oscillations. It further demonstrates the important influence of microenvironment on the bio-signaling propagation.

This thesis entails a detailed microstructure analysis of directionally solidified (DS) Al-7Si alloys processed in microgravity aboard the International Space Station and similar duplicate ground based experiments at Cleveland State University. In recent years, the European Space Agency (ESA) has conducted experiments on alloy solidification in microgravity. NASA and ESA have collaborated for three DS experiments with Al- 7 wt. % Si alloy, aboard the International Space Station (ISS) denoted as MICAST6, MICAST7 and MICAST12. The first two experiments were processed on the ISS in 2009 and 2010. MICAST12 was processed aboard the ISS in the spring of 2014; the resulting experimental results of MICAST12 are not discussed in this thesis. The primary goal of the thesis was to understand the effect of convection in primary dendrite arm spacings (PDAS) and radial macrosegregation within DS aluminum alloys. The MICAST experiments were processed with various solidification speeds and thermal gradients to produce alloy with differences in microstructure features. PDAS and radial macrosegregation were measured in the solidified ingot that developed during the transition from one solidification speed to another. To represent PDAS in DS alloy in the presence of no convection, the Hunt-Lu model was used to represent diffusion-controlled growth. By sectioning cross-sections throughout the entire length of solidified samples, PDAS was measured and calculated. The ground-based (1-g) experiments done at Cleveland State University CSU were also analyzed for comparison to the ISS experiments (0-g). During steady state in the microgravity environment, there was a reasonable agreement between the measured and calculated PDAS. In ground-based experiments, transverse sections exhibited obvious radial macrosegregation caused by thermosolutal convection resulting in a non-agreement with the Hunt- Lu model. Using a combination of image processing techniques and Electron Microprobe Analysis, the extent of radial macrosegregation was found to be a function of processing conditions and PDAS.

Sol-gel processing has been demonstrated to produce supported inorganic and hybrid microporous membranes with controlled physical and chemical properties under mild conditions. In preparing asymmetric membranes on mesoporous ceramic supports using traditional sol-gel processes, however, infiltration of the final coating material from smaller nanoparticles into the porous support can lead to unpredictable membrane thicknesses, poor reproducibility and reduced flux for separations.Herein we describe a size exclusion approach to prepare membranes by depositing well-defined relatively monodisperse particles on a mesoporous ceramic support. Ensuring that the particles remain on the surface by size exclusion can reduce or even eliminate infiltration. But if the porosity of the membrane top-layer is going to be finer than that of the support, it must be possible to sinter the particles to eliminate the interstitial porosity. Low temperature sintering is accomplished by preparing relatively compliant polysilsesquioxane particles through the introduction of organic substituents into the network of particles.To prepare membranes by size exclusion, we developed a sol-gel route to synthesize bridged polysilsesquioxane particles by polymerizing a dilute solution of monomers below their gelation concentration. Dynamic light scattering was used to monitor the particle size and size distributions during polymerizations up to the formation of gels. A membrane top-layer was successfully coated on a mesoporous titania-zirconia support through size exclusion of octylene- bridged polysilsesquioxane particles. To assist in determining if infiltration into the support has occurred and if particles are size-excluded from penetrating the support, we have covalently modified polysilsesquioxane particles with a fluorescent dye to provide direct visual evidence of the location of particles in the ceramic membrane. This is the first report of fluorescent diagnostics being used to detect infiltration and verify size exclusion of particles in asymmetric membrane deposition. We further created supported membranes of poly(phenylsilsesquioxane) through size exclusion of particles deposited on the support and then cured to establish a glassy, defect-free membrane coating without infiltration upon thermal exposure. Infiltration was verified with fluorescent dyes covalently bound into the particles. The size exclusion approach combined with fluorescent diagnostics allowed for the simplification of membrane formation and elimination of infiltration.

This dissertation describes the finding that dissolved carbon dioxide is a potent inhibitor of sonoluminescence and describes the implications of the finding in the development of improved megasonic cleaning formulations. Megasonic cleaning, or the removal of contaminants particles from wafer surfaces using sound-irradiated cleaning fluids, has been traditionally used in the semiconductor industry for cleaning of wafers. Recently however, advancing technology and miniaturization has made wafer features increasingly susceptible to damage by megasonic energy. International Technology Roadmap for Semiconductors (ITRS) 2011 predicts the critical particle diameter, critical particle count and killer defect numbers to be 22 nm, 113 #/wafer and 4.3 #/mm², respectively, on a 300 mm wafer for 45 nm technology node. A critical challenge in the field, therefore, is to achieve removal of small particles (22 nm to 200 nm) without causing damage to fine wafer features. The work described here addresses this challenge by identifying sonoluminescence and solution pH as two key factors affecting damage and cleaning efficiency, respectively and establishing novel means to control them using CO₂(aq) release compounds in the presence of acids and bases. Sonoluminescence (SL) behavior of the major dissolved gases such as Ar, Air, N₂, O₂ and CO₂ was determined using a newly designed Cavitation Threshold Cell (CT Cell). SL, which is the phenomenon of release of light in sound-irradiated liquids, is a sensitive indicator of cavitation, primarily transient cavitation. It was found that all the tested dissolved gases such as Ar, Air, N₂ and O₂, generated SL signal efficiently. However, dissolved CO₂ was found to be completely incapable of generating SL signal. Based on this interesting result, gradual suppression of SL signal was demonstrated using CO₂(aq). It was further demonstrated that CO₂(aq) is not only incapable but is also a potent inhibitor of SL. The inhibitory role of CO₂(aq) was established using a novel method of controlled in-situ release of CO₂ from NH₄HCO₃. ~130 ppm CO₂(aq) was shown to be necessary and sufficient for complete suppression of SL generation in air saturated DI water. The method however required acidification of solution for significant release of CO₂, making it unsuitable for the design of cleaning solutions at high pH. Analysis of the underlying ionic equilibria revealed that the loss of released CO₂(aq) upon increase in pH can be compensated by moderate increase in added NH₄HCO₃. Using this method, simultaneous control of SL and solution pH was demonstrated in two systems, NH₄HCO₃/HCl and NH₄OH/CO₂, at two nominal pH values; 5.7 and 7.0. Damage studies were performed on wafer samples with line/space patterns donated by IMEC and FSI International bearing Si/metal/a-Si gate stacks of thickness ~36 nm and Si/Poly-Si gate stacks of thickness ~67 nm, respectively. A single wafer spin cleaning tool MegPie® was used for the generation of megasonic energy for inducing damage to the structures. It was demonstrated that CO₂ dissolution in DI water suppresses damage to the gate stacks in a dose-dependent manner. Together, these studies establish a systematic and strong correlation between CO₂(aq) concentration, SL suppression and damage suppression. Significant damage reduction (~50 % to ~90 %) was observed at [CO₂(aq)] > ~300 ppm. It was also demonstrated that CO₂(aq) suppresses damage under alkaline pH condition too. This demonstration was made possible by the successful design of two new cleaning systems NH₄HCO₃/NH₄OH and CO₂/NH4OH that could generate CO₂(aq) under alkaline conditions. Damage suppressing ability of the newly designed cleaning systems were compared to the standard cleaning system NH₄OH at pH 8.2 and it was found that NH₄HCO₃/NH₄OH and CO₂/NH₄OH systems were 80 % more efficient in suppressing damage compared to the standard NH₄OH cleaning system. Finally, megasonic cleaning studies were conducted in the same single wafer spin cleaning tool MegPie®, using SiO₂ particles (size 185 nm) deposited on 200 mm oxide Si wafers, as the contaminant. It was found that the standard cleaning chemical, NH₄OH, pH 8.2, was effective in achieving > 95 % particle removal for 2 min irradiation of megasonic energy at power densities > 0.7 W/cm². Based on these results, a new system, NH₄HCO₃/NH₄OH, was designed with an aim to release ~300 ppm CO₂ at pH 8.2. It was demonstrated that newly designed system NH₄HCO₃/NH₄OH, allowed significant suppression of damage in comparison to NH₄OH while maintaining > 90 % cleaning efficiency that was comparable to NH₄OH solution, at the same acoustic power densities. Taken together, these studies establish a potent and flexible means for the inhibition of SL generation over a wide pH range and acoustic power densities and demonstrate its use in suppression of wafer damage without compromising megasonic cleaning efficiency.

Chemical systems containing oxidants are widely used at various stages in semiconductor processing, particularly for wet cleaning and polishing applications. This dissertation presents a series of studies related to oxidative removal of materials in the Front-End-Of-Line (FEOL) and Chemical Mechanical Planarization (CMP) processes during IC fabrication. In the first part of this study, stripping of photoresists exposed to high dose of ions (1E16 As/cm²) was investigated in activated hydrogen peroxide systems. Stripping of photoresists (PR) exposed to high dose (>1E15/cm²) ion beams is one of the most challenging steps in FEOL processing. This is due to unreactive crust layer that forms on the resist surface during ion implantation. The use of hydrogen peroxide systems activated by metal ion or UV light, for disrupting crust formed on deep UV resist to enable complete removal of crust as well as underlying photoresist was investigated. A systematic evaluation of variables such as hydrogen peroxide and metal ion concentration, UV intensity, temperature and time was conducted and an optimal formulation capable of attacking the crust was developed. A two step process involving pretreatment with activated hydrogen peroxide solution, followed by treatment with sulfuric acid-hydrogen peroxide mixture (SPM) was developed for complete removal of crusted resist films. In the second part of this study, electrochemically enhanced abrasive removal of Ta/TaN films was investigated in solutions containing 2,5 dihydroxy benzene sulfonic acid (DBSA) and potassium iodate (KIO₃). This method known as Electrically-assisted Chemical Mechanical Planarization (ECMP) is generating a lot of interest in IC manufacturing. Ta/TaN films were abraded at low pressures (<0.5 psi) on a polyurethane pad under galvanostatic conditions. The effect of variables including pH, KIO3 concentration, and current density has been explored. In the optimized formulation, tantalum and tantalum nitride removal rates of ~170 A⁰/min and ~200 A⁰/min, respectively have been obtained at a current density of 1 mA/cm². The use of benzotriazole as a copper inhibitor was required to obtain Ta to Cu selectivity of 0.8:1. Additionally, the nature of the oxide film formed on tantalum during the electrochemical abrasion process was characterized.