Now showing items 8006-8025 of 20306

    • FUNCTIONS UNDERLYING PERFORMANCE OF LEARNING-DISABLED CHILDREN IN INTELLIGENCE AND NEUROPSYCHOLOGICAL TESTS.

      GAMBLE, CONSTANCE MARIA. (The University of Arizona., 1987)
      This study was designed to determine the factorial validity of specific components of the Reitan-Indiana Neuropsychological Battery with a learning disabled population. Scores of 42 children, 38 males, 4 females, ages 6.2 to 8.8 years were compiled on specific tests of the Reitan-Indiana. Principal component factoring of the original correlation matrix was followed by principal factoring, using a 4 factor solution; varimax rotation with six iterations produced the desired reduction of the correlation matrix; four factors emerged for the learning disabled population, which accounted for 53% of the variance: verbal intelligence, psychomotor speed, achievement, and memory. The factor structure that emerged was not consistent with the surface factors of the battery as conceptualized by its author suggesting that this battery may lack construct validity when used with a learning disabled population.
    • Fund Development and Donor Race: How Colorblindness and a ‘Sales Mentality’ Delimits Expanding the Donor Base

      Rhoades, Gary D.; Jensen-Ives, Johanne Kirsten; Kraus, Amanda; Cabrera, Nolan L.; Deil-Amen, Regina J. (The University of Arizona., 2019)
      This qualitative case study examined the practices used by higher education development professionals and institutions to better understand how a donor’s race is considered as part of the fundraising process. It employed a Critical Race Theory (CRT) framework (Delgado, 2001) designed to combine the scholarship on fund development and race. The central frames of color-blind racism (Bonilla-Silva, 2006) were key organizing concepts for the analysis of findings in this study. Additionally, this research used concepts of White savior ideology (Cammarota, 2011) and poverty porn (Collin, 2009) to interpret the messages and language used in the higher education development field. To provide context for this study, the concept of academic capitalism (Slaughter & Rhoades, 2004) is engaged relative to the pressure higher education development professionals may experience connected to their fundraising efforts. This study employed several qualitative methods for gathering data which consisted of interviews, document analysis, and observation. Findings revealed that development officers utilized a colorblind approach or a one size fits all method for their fundraising, which maps on to several of the four central frames of color-blind racism (Bonilla- Silva, 2006). The findings from this study also suggest that the growing ‘sales mentality’ and pressure to generate more revenue for big campaigns is fueling a development environment where fundraisers are being conditioned to desire a donor who is White and familiar with the philanthropic process; therefore not taking up too much of their time. Institutional, practical, and research-oriented recommendations and implications are presented to inform the work of higher education advancement professionals. This research contributes to the scholarship in CRT, but also provides new empirical based scholarship on a topic that was previously unexplored between higher education fundraising and race.
    • Fundamental Aspects of Emersion and Electrowetting Interfaces

      Pemberton, Jeanne E.; Mudalige, Akmeemana Kosduwa (Anoma); Pemberton, Jeanne E.; Pemberton, Jeanne E.; Brown, Michael; Monti, Oliver; Armstrong, Neal R.; Wysocki, Vicki (The University of Arizona., 2006)
      The process of immersing a solid substrate into a solution and removing it so as to leave a thin layer of solution on the surface is referred to as emersion. The interfacial structure and properties of thin liquid films at bare, organically modified Ag substrates and Ag electrodes are investigated using emersion approach. The effect of viscosity on emersed layer thickness of glycerol/water solutions at Ag is studied and found that the emersed layer thicknesses were sensitive to the viscosity. The molecular basis of the behavior was investigated by elucidating the interfacial structures using emersion PM-IRRAS spectroscopy and found that the composition is not uniform throughout the emersed layer. The behavior of these solutions with shear rate was investigated by measuring the emersed layer thickness as a function of shear rate and found that the emersed layer thickness is sensitive to the shear rate at low viscosities while insensitive at high viscosities. The emersed layer thickness values of a series of NaF solutions were measured in the double layer region encompassing the PZC using ellipsometry at a given velocity. No systematic dependence of emersed layer thickness on potential was observed and were not adequately described by GCS theory. However, dependence of emersed layer thickness on concentration was observed. The average emersed layer thickness for 0.1 M, 0.01 M and 0.05 M NaF solutions are ~1.6 nm and for 0.005 M and 0.001 M NaF are ~ 0.5 nm. This behavior was interpreted using the effective viscosity at the electrode surface.Model electrowetting systems based on Ag surfaces modified with -COOH-terminated alkanethiol SAMs were emersed from solutions of different pH and the thickness of emersed layers using ellipsometry, wetting properties using contact angle measurements, composition and % deprotonation using XPS and interfacial structure using emersion spectroscopies were investigated. This study shows that the subtle change in molecular structure gives very small but observable differences in macroscopic contact angle.
    • Fundamental aspects of particulate contamination of tungsten and thermal oxide wafers during chemical-mechanical polishing

      Raghavan, Srini; Chilkunda, Raghunath, 1965- (The University of Arizona., 1997)
      Chemical-mechanical polishing (CMP) has emerged as a new processing technique for achieving a high degree of planarity (< 10 μm) for submicron devices in very large scale integrated (VLSI) process technology. Metal as well dielectic films can be planarized using CMP. Polishing of tungsten (W) and interlayer dielectric (SiO₂) films is carried out using alumina (Al₂O₃) based slurries which typically contain acids, complexing and oxidizing agents. One of the challenges of CMP is the effective removal of slurry particles (e.g., Al₂O₃) that are deposited on the wafer (e.g., W) surface during polishing. Control of particulate deposition during CMP as well as the development of post CMP cleaning techniques to remove deposited particles require an understanding of the surface and solution chemistry of the wafers and particles under polishing conditions. In this research, an attempt is made to develop an understanding of the importance of the electrostatic interactions in particle deposition using electrokinetic potential data, particle deposition results from small scale polishing experiments and calculated interaction energies between a particle and wafer surface. The electrokinetic potential of tungsten, thermal oxide (SiO₂) wafers and alumina particles were measured as a function of solution chemistry. The measured electrokinetic potential data was used to calculate the interaction energy between an alumina particle and a wafer (e.g., W) surface using the well known DLVO (Derjaguin-Landau-Verwey-Overbeek) theory.
    • Fundamental Characterization of Chemical Mechanical Planarization Relating to Slurry Dispensing and Conditioning Method

      Philipossian, Ara; Han, Ruochen; Philipossian, Ara; Shadman, Farhang; Raghavan, Srini (The University of Arizona., 2017)
      The first part of our study introduces a new method for rapidly generating an "improved" Stribeck curve (i.e. Stribeck+ curve) that, compared to traditional Stribeck curves, shows a more complete tribological picture of the chemical mechanical planarization (CMP) process. The method significantly reduces the consumables and time required to obtain the curve compared to traditional means. Results of the Stribeck+ curve are consistent with individual tests using several different consumables combinations. All copper CMP Stribeck+ examples clearly indicate the lubrication mechanism and transitions thereof between different polishing conditions. Variability in COF as well as a much wider range in U/P are also explored. In the second part of our study, the Stribeck+ curve is successfully applied to silicon dioxide CMP processes to characterize the tribology of such processes under different process conditions and consumables. Results show our Stribeck+ curve methodology to be capable of rapidly determining and differentiating the tribological mechanism among all cases studied. The Stribeck+ curve helps indicate process stability as shown by the spread of the COF vertical clusters. The Stribeck+ curve also confirms a previously known effect that the greater the ratio of pad’s up-features to the total pad area, the greater the probability of wafer hydroplaning. As the third part of our study, we investigate the effect of different pad surface micro-textures on the tribological, thermal and kinetic attributes during copper CMP. Different micro-textures are generated by two different chemical vapor deposited (CVD) diamond-coated conditioner discs (i.e. Disc A and Disc B). Results show that while pad temperature and removal rate increase with polishing pressure and sliding velocity on both discs, Disc B generates consistently lower removal rates and COF than Disc A. To fundamentally elucidate the cause(s) of such differences, pad surface contact area and topography are analyzed using laser confocal microscopy. The comparison of the pad surface micro-texture analysis indicates that Disc A causes a pad surface with a smaller abruptness (λ) and much more solid contact area which results in a higher removal rate. In contrast, Disc B generates less contact areas and COF. A two-step modified Langmuir–Hinshelwood model is employed to simulate copper removal rates as well as chemical and mechanical rate constants. The simulated chemical to mechanical constant ratios indicate that Disc A produces a more mechanically limited process under all conditions tested. In the fourth part of our study, the position of a slurry injection system (SIS) is optimized to achieve a more cost-effective and environmentally benign CMP process using a widely-adopted ceria-based "reverse slurry". Here, SIS is configured with different angles in order to investigate slurry dilution characteristics caused by residual pad rinsing with ultrapure water (UPW) that is known to affect silicon dioxide removal. UPW dilution effect on removal rate, coefficient of friction and pad surface temperature is explained by maintaining a constant dilution ratio for each of the SIS configuration tests. Results indicate that SIS negative rotation angles increase the actual slurry dilution ratio on top of the polishing pad. This generates more Ce3+ which boosts removal rates. Application of negatively rotated SIS allows significantly lower slurry flow rates and/or shorter polishing times leading to more environmental friendly semiconductor manufacturing processes. Finally, it is confirmed that variations in SIS configuration has no impact on silicon dioxide to silicon nitride removal rate selectivity. In the fifth and final part of our study, the silicon dioxide removal rate using a "reverse" ceria-based slurry is investigated under four different combinations of conditioning modes and slurry application methods. In a “reverse” slurry, addition of water acts to promote material removal. Overall, the process using ex-situ conditioning with the SIS results in the highest removal rate, while the process using in-situ conditioning with the conventional point application (PA) generates the lowest removal rate. This study explains the differences in silicon dioxide removal rate based on the variations of the actual slurry dilution ratio on the pad associated with conditioning and slurry application methods. Frictional analysis and Stribeck+ curves are employed to elucidate the tribological characteristics. Results show that the conditioning modes and the slurry application methods vary the extent of the polishing vibrations. Silicon dioxide removal rate is found to linearly correlate with the extent of COF fluctuation. The work underscores the importance of optimum slurry flow dynamics and injection geometry to obtain a more cost-effective and environmentally benign CMP process.
    • FUNDAMENTAL CHARACTERIZATION OF TRIBOLOGICAL, THERMAL, FLUID DYNAMIC AND WEAR ATTRIBUTES OF CONSUMABLES IN CHEMICAL MECHANICAL PLANARIZATION

      Wei, Xiaomin; Philipossian, Ara; Saez, A. Eduardo; Muscat, Anthony (The University of Arizona., 2010)
      This dissertation presents several studies relating to fundamental characterization of CMP consumables in planarization processes. These are also evaluated with the purposes of minimizing environmental impact and reducing cost of ownership (COO).The first study is conducted to obtain the retaining ring wear rate in a typical ILD CMP process and is specifically intended to investigate the effect of retaining ring materials and slot designs during the CMP process. The results show that retaining ring materials have effect on the COF, pad temperature and retaining ring wear rate, while retaining ring slot designs affect the pad surface abruptness. The second study is performed to compare the effect of different retaining ring slot designs on the slurry film thickness within the pad-wafer interface. A novel non-intrusive optical technique, dual emission UV-enhanced fluorescence (DEUVEF), was applied to accurately measure the film thickness of the slurry underneath the wafer during polishing. It is indicated that the optimized retaining ring slot design can significantly reduce the COO of CMP processes by increasing slurry utilization.A COF method is applied to measure the slurry mean residence time (MRT) during CMP. This technique uses transient COF data induced by a shift in slurry concentration to determine MRT. Variations in consumables as well as sliding velocity, pressure and slurry flow rate can affect the slurry MRT. One study in this dissertation focus on the effect of retaining ring slot designs on the slurry MRT. Another study compares the slurry MRT under same polishing conditions using pads with different groove width. Both studies are conducted on multiple sliding velocity, pressure and slurry flow rate variations to understand the characteristics of consumable designs. The method of measuring MRT during polishing presented in this dissertation can be easily applied in general CMP processes.The subsequent studies focus in the diamond conditioner discs characterization techniques. A newly developed method for determining active diamonds and aggressive diamonds on a diamond conditioner disc under a certain vertical load is elaborated in this dissertation. Later, this technique together with scanning electron microscopy (SEM) imaging is implemented to analyze diamond pullout and fracture in CMP. Five different types of diamond conditioner discs are subjected to a novel accelerated wear test respectively to compare the extent of diamond pullout and fracture under the same conditioning condition
    • Fundamental Consumables Characterization of Advanced Dielectric and Metal Chemical Mechanical Planarization Processes

      Sampurno, Yasa; Philipossian, Ara; Shadman, Farhang; Blowers, Paul; Lynch, David (The University of Arizona., 2008)
      This dissertation presents a series of studies relating to kinetics and kinematics of inter-layer dielectric and metal chemical mechanical planarization processes. These are also evaluated with the purposes of minimizing environmental and cost of ownership impact.The first study is performed to obtain the real-time substrate temperature during the polishing process and is specifically intended to understand the temperature distribution across the polishing wafer during the chemical mechanical planarization process. Later, this technique is implemented to study the effect of slurry injection position for optimum slurry usage. It is known that the performance of chemical mechanical planarization depends significantly on the polishing pad and the kinematics involved in the process. Variations in pad material and pad grooving type as well as pressure and sliding velocity can affect polishing performance. One study in this dissertation investigates thermoset and thermoplastic pad materials with different grooving methods and patterns. The study is conducted on multiple pressure and sliding velocity variations to understand the characteristic of each pad. The analysis method elaborated in this study can be applied generically.A subsequent study focuses in a slurry characterization technique. Slurry, a critical component in chemical mechanical planarization, is typically a water-based dispersion of fine abrasive particles with various additives to control material removal rate and microscratches. Simultaneous turbidity and low angle light scattering methods under well-defined mixing conditions are shown to quantify the stability of abrasive particle from aggregations. Further contribution of this dissertation involves studies related to the spectral analysis of raw shear force and down force data obtained during chemical mechanical planarization. These studies implemented Fast Fourier Transforms to convert force data from time to frequency domain. A study is performed to detect the presence of larger, defect-causing particles during polishing. In a further application on diamond disc conditioning work is performed to achieve optimum break-in time and an optimum conditioning duty cycle. Studies on spectral analysis are also extended to planarization of shallow trench isolation pattern wafers to monitor the polishing progress in real-time.
    • Fundamental electrochemical aspects of chemical mechanical planarization of aluminum thin films

      Farrell, James; Fang, Yan (The University of Arizona., 2000)
      The chemical mechanical planarization (CMP) process is critical in fabricating ultra large scale integrated (ULSI) circuit devices in semiconductor industry. In a typical aluminum damascene interconnect scheme, Al is usually blanket deposited over a liner layer to fill contact holes and vias. After deposition, the excess of Al is removed by CMP, leaving Al only in the holes and vias to form interconnects. Since the slurries used for aluminum CMP typically contain an oxidant and other chemical additives, the electrochemical behavior of Al and the liner may be expected to affect the polishing rates. In addition, when the excess of Al is removed, a surface transition from Al to liner occurs. Since Al and the liner may exhibit different electrochemical behaviors in the slurry, galvanic coupling between Al and the underlayer is a possibility. Such a coupling may lead to localized corrosion or rate control problems. The objective of this research was to characterize the fundamental electrochemical behavior of thin aluminum-0.5%copper, titanium and aluminum/titanium stack films before, during and after abrasion in a commercially available alumina based slurry containing iodate as an oxidant. A special apparatus in which electrochemical tests can be carried out during polishing was fabricated and used for this research. It was found that the electrochemical corrosion rates during abrasion were much smaller than the actual polishing rates obtained with the simulated CMP apparatus, indicating that the mechanism of Al removal by the iodate based slurry may not be dominated by electrochemical factors. A sharp rise in corrosion potential (Ecorr) during the transition from Al to Ti film was measured during polishing of the Al/Ti film stack. This potential change during transition was of the order of 1V on the Al film deposited at room temperature. The transition was much sharper with the low-temperature (25°C) Al film than the high-temperature (475°C) Al thin film. The slower transition in OCP in high-temperature films is most likely due to a Ti-Al intermetallic compound formed at the Al/Ti interface. The galvanic corrosion between Al and Ti during polishing and Al post-polishing corrosion issues were also investigated. It was found that the galvanic corrosion rate between Al and Ti is 6*10⁻⁴ A/cm² and the corrosion potential is -0.24 V. Also, the corrosion current density for Al after abrasion and immersion in de-ionized water is lower than that in the slurry. In addition, the post polishing corrosion of Al in after abrasion in the iodate based alumina slurry was also investigated. It was found that the corrosion of Al in DI water after abrasion was insignificant.
    • Fundamental Information-Theoretic Limits of Distributed Information Retrieval and Processing

      Tandon, Ravi; Attia, Mohamed Adel; Lazos, Loukas; Vasic, Bane; Glickenstein, David (The University of Arizona., 2020)
      We consider an information theoretic study of the challenges facing distributed information processing and retrieval systems, in which the data is partitioned, stored, and processed across distributed machines/workers. In our research, we propose practical solutions leveraging tools from information and coding theory. In large-scale systems, there are several challenges in moving towards distributed algorithms compared to other centralized approaches. These challenges include communication bottlenecks due to data movement across machines, latency due to heterogeneity among working nodes, and privacy concerns from untrustworthy service providers. In this dissertation, we address the above challenges by a) devising novel coding schemes and optimal storage design to minimize the communication overhead needed to shuffle the data among distributed nodes; b) minimizing the impact of heterogeneity via novel iterative work exchange and balancing among nodes, and c) characterizing the fundamental limits of privately retrieving information from distributed databases under the following practical constraints: limited storage at databases, tolerable privacy leakage, and privacy for hidden latent variables.Data shuffling between a distributed cluster of nodes is one of the critical steps in implementing large-scale learning algorithms. Randomly shuffling the data-set among a cluster of workers allows different nodes to obtain fresh data assignments at each learning epoch. This process has been shown to provide statistical improvements in the learning process (via testing and training error). However, the statistical benefits of distributed data shuffling come at the cost of extra communication overhead from the master node to worker nodes, and can act as one of the major bottlenecks in the overall time for computation. Another major bottleneck that adversely impacts the time efficiency is the computational heterogeneity of distributed nodes, often limiting the task completion time due to the slowest worker. In our first contribution, we propose new approaches to increase the time efficiency in distributed computing systems. First, we study how to use codes and exploit excess storage at workers in a principled manner in order to reduce communication overhead for distributed data shuffling. Then, we present our approach of work exchange to combat the latency problem, in which faster workers can be reassigned additional leftover computations that were originally assigned to slower workers. In distributed retrieval systems, assuring privacy while retrieving information from public databases has become a crucial need for users. Private information retrieval (PIR) allows a user to retrieve a desired message from a set of databases without revealing the identity of the desired message. The replicated database scenario, where N databases store each of the K messages was considered by Sun and Jafar, and the optimal download cost was characterized. In our second objective, we consider a practical scenario where the databases are not replicated and have storage limitations. In particular, we study the problem of PIR from uncoded storage constrained databases, where each database has a limited storage capacity and is only allowed to store uncoded data. The novel aspect of this work is to characterize the optimum download cost of PIR from uncoded storage constrained databases for any storage value. In our third and final objective, we consider other practical scenarios for the PIR model where perfect privacy is not necessarily required. These scenarios arise in applications where some leakage in the privacy is tolerable with the goal of enhancing the PIR capacity. We focus on two models for privacy leakage. In the first model, we assume asymmetric bounded leakage for both user privacy, i.e., message identity and database privacy, i.e, information user obtains about unwanted messages. We refer to this model as Asymmetric Leaky PIR (AL-SPIR). We study the three-way tradeoff between user privacy, database privacy, and communication efficiency of PIR. In the second model, we propose a novel relaxed privacy definition for PIR. Instead of hiding the message index queried by the user, we focus on providing information-theoretic privacy for latent traits. We model the user profile with a latent variable model captured by a latent random variable S. Using this new privacy notion, also refereed to as Latent Variable PIR (LV-PIR), we show how the PIR download cost from a single database can be reduced.
    • FUNDAMENTAL INVESTIGATIONS OF A 148 MEGAHERTZ INDUCTIVELY COUPLED PLASMA DISCHARGE.

      WEBB, BRYAN DOUGLAS. (The University of Arizona., 1985)
      Fundamental investigations have been carried out on an Inductively Coupled Plasma (ICP) operated at 148 MHz, a frequency which is nearly three times higher than any previously reported for analytical ICPs used in spectrochemical analysis. High frequency operation is expected to provide easier sample introduction into the discharge, with a consequence of less energetic conditions in the central channel. Several plasma diagnostic techniques were employed in order to determine the conditions experienced by the analyte species in this source for spectrochemical analysis. Three different torch systems were investigated at 148 MHz and compared to the "standard" 27 MHz configuration. The highest excitation temperatures and electron densities were obtained in the 27 MHz configuration, and the lowest values in the largest torch at 148 MHz. Intermediate values were obtained in the intermediate-size torches at 148 MHz. These observations correlate reasonably well with the ratio of the plasma radius to the skin depth (r/s). The skin depth defines the region in which the majority of the electrical energy is deposited into the discharge, and is smaller at 148 MHz than at 27 MHz. The measurement of electron densities also allows the estimation of how closely a particular discharge approaches Local Thermal Equilibrium (LTE). As may be expected, LTE is most closely approached in the 27 MHz arrangement. The less energetic conditions characterized by lower temperatures and electron densities result in less intense analyte emission from the high frequency ICPs. Signal-to-Background ratios and detection limits reflect this trend, but the linearity of the calibration curves and freedom from vaporization interferences are not degraded. Finally, the introduction of organic solvents is much easier, and better detection limits in an organic matrix are obtained at 148 MHz. These investigations have shown the utility of classifying the effects of changing torch sizes and operating frequencies by means of the r/s ratio. This provides the analyst with a means of selecting the general range of conditions to be employed in a particular analysis.
    • Fundamental investigations of double-negative (DNG) metamaterials including applications for antenna systems

      Ziolkowski, Richard W.; Kipple, Allison Denise (The University of Arizona., 2004)
      The postulated characteristics of double-negative (DNG) materials--i.e., materials with simultaneously negative permittivity and negative permeability (ε < 0, μ < 0)--and recent attempts to realize those characteristics with synthetic metamaterials are briefly reviewed. Investigations into the causality of signal propagation in a DNG medium are then presented. Previous research in this topic is examined, and it is verified that a DNG medium must be dispersive in order to be causal. An accurate time-domain description of propagation in a DNG medium is shown to be elusive due to the presence of dispersion, though approximate solutions and recommendations for future analytical research are provided. The results of numerical investigations into this topic are then discussed, and the anticipated combination of causal signal transmission and a negative phase shift are observed in the numerical data. Potential applications of DNG metamaterials to antenna systems are then presented. A DNG shell is observed to reduce the intrinsic reactance sensed by an infinitesimal electric dipole, thereby increasing the dipole's radiated power. Analytical expressions for the fields in the dipole--DNG shell system are derived, and numerical results for a variety of DNG shell configurations are discussed. The presence of a DNG shell is shown to increase the dipole's radiated power by orders of magnitude in some cases. A circuit model of the dipole--DNG shell system is additionally presented and used to interpret the system's physical behavior. The scattering properties of nested metamaterial shells are then analyzed. Various layering combinations of DNG, double-positive (DPS) and single-negative (SNG) shells are observed to produce resonant scattering of an incident, fundamental radial transverse-magnetic (TMᵣ) wave. Reciprocity between the metamaterial configurations that exhibit TMᵣ scattering resonances and those shown to maximize the power radiated by the infinitesimal electric dipole is demonstrated. Several additional metamaterial configurations are shown to produce both resonant TMᵣ scattering and resonant dipole radiation. A resonant configuration with one epsilon-negative (ENG) shell is especially appealing due to its manufacturability. The effects of a DNG layer on the creeping waves scattered by a small metal sphere are also discussed as a minor yet curious offshoot to the scattering analyses.
    • FUNDAMENTAL LIMITATIONS ON THE OPERATION OF OPTICAL BISTABLE DEVICES IN A RING CAVITY AND IN GALLIUM-ARSENIDE ETALONS.

      Gibbs, Hyatt M.; OVADIA, SHLOMO.; Dror, Sarid (The University of Arizona., 1984)
      The fundamental limitations on the operation of optical bistable devices in a ring cavity and in GaAs etalons are investigated. Experimental results of spontaneous transitions due to shot noise fluctuations are found in good agreement with various "ladder" models, if one allows the counting rates to vary accordingly. Stability analysis for two-photon homogeneously broadened media reveals single-wavelength instabilities for the laser but not for absorptive optical bistability. Appreciable regions of sidemode gain exist for both problems allowing for multiwavelength instabilities to occur. GaAs bistable devices show attractive features such as low power and high speed at room temperature for optical processing. However, experimental evidence in GaAs confirm the computer simulations of bistability that cavity losses, due to unsaturable background absorption, limit the switching power at room temperature. Methods to overcome the different limitations in GaAs devices toward parallel computation are then addressed from a system approach.
    • Fundamental studies in the solid-phase extraction of organic cations and neutral compounds: The role of hydrophobic and ionic interactions

      Burke, Michael F.; Gonzalez, Ricardo Rene (The University of Arizona., 2001)
      The work presented is a systematic investigation of silica-based sorbents using solid-phase extraction (SPE). Properties of various cation exchangers and mixed beds comprised of strong cation exchange particles and alkyl-modified silica particles were explored. The role of ionic and nonpolar interactions was examined in terms of retention and elution of analytes. A series of displacement experiments was used to characterize the interactions and energy-minimized, three-dimensional models were used to illustrate these interactions. Selectivity of cation exchangers was probed by introducing cations differing in size, hydrophobic nature and charge before and after introduction of the analytes. The ionic strength, the solvent composition and the pH of the liquid phase were parameters that were varied in order to define the type of interaction that was responsible for retention, lack of retention, or elution during the SPE procedure. Application of mixed sorbents toward the extraction of basic drugs of abuse, as well as the use of reversed-phase silica and a resin for the extraction of a neutral organonitrogen species were also investigated. With propylene-linked cation exchangers (under appropriate pH conditions), it was shown that the primary mode of interaction is through ionic forces. As a consequence, there is no selectivity of these sorbents for cations based on hydrophobic nature. With ethylbenzene and octylene-linked exchangers, there is an increase in selectivity for cations with increasing hydrophobic nature. The linker chain is adequately long enough to allow for nonpolar interactions with the aliphatic side groups, just as a resin-based exchanger allows. With short and long chain exchangers, there is selectivity proportional to the charge of the ion. The proposed reason for this is a combination of multiplesite attachment of polyprotic species to the surface and increased probability of single-site interaction proportional to the number of charged nitrogen atoms on the molecule. It was shown that mixed sorbent beds offer advantages in operator control over the retention of organic bases in a high ionic strength sample matrix. The retention mechanism was elucidated, demonstrating a clear contribution of nonpolar forces to retention with the mixed sorbents as was observed with the long-chain cation exchangers.
    • Fundamental studies of micromechanics, fracturing progression, and flow properties in tuffaceous rocks for the application of nuclear waste repository in Yucca Mountain.

      Wang, Runqi.; Kemeny, John M.; Poulton, Mary M.; Labrecque, Douglas J.; Harpalani, Satya; Lever, Paul J.A. (The University of Arizona., 1994)
      Yucca Mountain, Nevada is the proposed site for the underground storage of high-level civilian nuclear waste in the United States. The repository must be isolated from the general environment for at least 10,000 years. Ground water and gases are potential carriers of radioactive materials. Fractures and connected pores in the host rock are the major pathways for ground water and gases. Therefore, the mechanical and flow properties of the host rock should be understood and utilized in the design of the underground repository. Samples of Topopah Spring tuff from Yucca Mountain were used in this study. Cylindrical specimens were prepared to perform uniaxial and triaxial "damage" tests where specimens are loaded to a particular stress level to induce damage and fracturing and then unloaded. Mechanisms of microcracking at different fracturing levels have been studied by using both an optical microscope and a Scanning Electron Microscope (SEM). The original rock sample without loading was also observed under the microscopes. Many kinds of defects including pores, preexisting fractures, and soft inclusions were found in the undamaged Apache Leap tuff samples. Pores were determined to be the main microstructures in Topopah Spring tuff that could influence the mechanical and hydrologic properties. Under compressive stresses, microcracking initiates from some of the pores. These microcracks will interact and coalescence to form large microcracks or macroscopic cracks as the load is increased. Crack propagation phenomena, such as pore cracking, pore linking, pore collapse and the formation of en echelon arrays were all found in specimens unloaded prior to complete failure. The failure of tuff specimens is often through a process of shear localization. In summary, the deformation and failure of both tuffs occurred by progressive fracturing, starting from microcracking on the small scale, and ending as fractures coalesced to form macroscopic fractures and shear localization. On the basis of the experimental studies, micromechanical models such as the pore collapse model and the pore linking model have been developed based on fracture mechanics theory. These models are used to predict the constitutive behavior for tuff and the predicted stress-strain curves match well with the experimental curves.
    • Fundamental studies of the deformability and strength of jointed rock masses at three dimensional level.

      Wang, Shuxin.; Kulatilake, Pinnaduwa H.S.W.; Kemeny, John M.; Glass, Charles E.; Contractor, Dinshaw N. (The University of Arizona., 1992)
      The deformability and strength properties of jointed rock masses are two of the fundamental parameters needed for the design and performance estimation of rock structures. Due to the presence of complicated minor discontinuity patterns (joints, bedding planes etc.), jointed rock masses show anisotropic and scale (size) dependent mechanical properties. At present, satisfactory procedures are not available to estimate anisotropic, scale dependent mechanical properties of jointed rock. Because of the statistical nature of joint geometry networks in rock masses, the joint patterns should be characterized statistically. The available joint geometry modeling schemes are reviewed. One of these schemes is used in this dissertation to generate actual joints in rock blocks. Three dimensional distinct element code (3DEC), which is used to perform stress analyses on jointed rock blocks in this study, is introduced and its shortcoming is identified. To overcome the shortcoming of 3DEC, a new technique is developed by introducing fictitious joints into rock blocks. Concerning the introduced fictitious joints, their geometry positions are mathematically determined; the representative mechanical properties for them found at 2D level are reviewed and verified at 3D level. By using the new technique, the deformation and strength properties of the rock blocks with many different joint configurations are found. Then effects of joint geometry parameters on the mechanical properties of jointed rock blocks are investigated. It is found that the joint geometry patterns have significant influences on the mechanical properties of rock blocks. All the joint geometry parameters are then integrated into fracture tensor. The relationships between the mechanical properties of jointed rock blocks and the fracture tensor parameters (its first invariant and directional component) are investigated. The possibility of obtaining the equivalent continuum behavior (REV properties) of jointed rock blocks is explored by using the aforementioned relationships. Finally, based on the research results, a new 3D constitutive model for jointed rock masses is developed to describe their pre-failure behavior. The constitutive model includes the effects of joints in terms of fracture tensor components and it shows the anisotropic and scale dependent natures of jointed rock masses.
    • Fundamental studies on the removal of copper in hydroxylamine based chemistries of interest to copper chemical-mechanical planarization

      Raghavan, Srini; Huang, Wayne Hai-Wei (The University of Arizona., 2003)
      The advancement of IC technology has led to an increasing demand for faster and cheaper microelectronic devices. One of the key processing steps in fabricating ultra-large scale integration devices is copper chemical-mechanical planarization (CMP). Traditional copper CMP slurries use hydrogen peroxide as an oxidant. A novel copper CMP slurry based on hydroxylamine chemistry is being considered as an alternative to hydrogen peroxide based slurries. The main goal of the research reported in this dissertation is to understand the removal of copper in hydroxylamine based chemistries. Copper removal experiments were performed on a regular CMP tool and a specially designed electrochemical abrasion cell (EC-AC). The effects of applied pressure and abrasion speed were investigated on both tools. The electrochemistry of copper in hydroxylamine based chemistry was investigated using electrochemical techniques on the EC-AC tool. The techniques include electrochemical polarization and voltammetry. The effects of solution pH and hydroxylamine concentration on the polarization of copper were systematically investigated. The fate of hydroxylamine and other nitrogen-based species were studied using capillary electrophoresis chromatography. The removal rates of copper obtained from a regular CMP tool were twice as much as the rates obtained from the EC-AC tool. However, the removal rates from both tools showed the same trend with respect to pH. Interestingly, a maximum peak in copper removal rates occurs at a pH value of 6, and a significant decrease in rates occur at pH values deviating from 6. The copper removal results obtained from the EC-AC tool with and without abrasion showed that the high removal rate at pH 6 is largely due to chemical attack. The reactions involved in the oxidation of copper are dependent on the decomposition and complexation behaviors of hydroxylamine. Electrochemical analysis showed the removal of copper may be dependent on the reduction of nitric oxide (NO) to hyponitrous specie (H₂N₂O₂). Capillary electrophoresis chromatography analyses showed the consumption of hydroxylamine and species generated from the autooxidation/reduction of hydroxylamine. In slightly alkaline pH conditions, the removal of copper was predominantly due to mechanical abrasion of the surface oxide. This was supported by the potential-pH diagrams and the analysis of applied pressure and relative velocity. At pH values ranging from 3 to 5, the removal of copper was due to oxidation of Cu to Cu²⁺.
    • The Fundamentality of Fit

      Timmons, Mark; Howard, Christopher; Timmons, Mark; Cohen, Stewart; Horgan, Terence; Rosati, Connie (The University of Arizona., 2017)
      Normative reasons for attitudes are facts that count in favor of those attitudes, but a fact can favor an attitude in two very different ways. One way in which a fact can favor an attitude is by making the attitude fitting (apt, merited, correct). For example, the fact that Sharon spends much of her time doing charity work is a fact that favors admiring Sharon, since it’s a fact that makes her admirable, and so fit to admire. Call any fact that favors an attitude by making it fitting a "fit-related reason." A second way in which a fact can favor an attitude is by making the attitude somehow valuable, or good to have. For example, the fact that an evil dictator will order my execution unless I admire him is a fact that favors my admiring the dictator, since it's a fact that makes my admiring him good. Call any fact that favors an attitude by making it somehow good to have a "value-related reason." This dissertation has two main goals. The first is to develop an ontology of normativity that can accommodate a view on which both fit- and value-related reasons are genuine reasons. Many authors, including Derek Parfit, T.M. Scanlon, and Mark Schroeder, favor a "reasons-first" ontology of normativity: they take reasons to be normatively basic, and claim that all other normative facts, properties, and relations can be analyzed or accounted for in terms of the reason relation. A central alternative, famously defended by G.E. Moore in Principia Ethica, is the "value-first" ontology—an ontology that takes value or goodness to be normatively basic and claims that the rest of the normative can be accounted for in terms of the property of being good. In the opening chapter of my dissertation, "The Fundamentality of Fit," I advance an ontology of normativity, originally suggested by Franz Brentano and A.C. Ewing, according to which fittingness is the basic normative relation, in terms of which the rest of the normative can be explained. I argue that neither the reasons- nor the value-first ontology can accommodate a view on which both fit- and value-related reasons are genuine reasons. Then I explain how my "fittingness-first" ontology can. Of course, any threat to the plausibility of the view that both fit- and value-related reasons are genuine reasons would undermine the case for my ontology of normativity. And so a full defense of my fittingness-first ontology will require a systematic defense of the substantive normative view it's designed to accommodate. The second goal of my dissertation is to provide this defense. A normative view that says that both fit- and value-related reasons are genuine reasons consists in three component claims: (1) that fit-related reasons are genuine reasons; (2) that value-related reasons are genuine reasons; and (3) that fit- and value-related reasons can be compared against one another to yield univocal verdicts concerning what attitudes one ought, all-things-considered, to have. The first of these claims—that fit-related reasons are genuine reasons—is among the most widely shared in contemporary normative theory. The latter two, however, are more controversial. In the second and third chapters of this dissertation, I defend each of these claims in turn. One way to showcase the plausibility of a normative view that says that both fit- and value-related reasons are genuine reasons is to show that it explains our intuitions in a variety of substantive normative debates. This would, in turn, provide support for my fittingness-first ontology, since, relative to its main competitors, my ontology uniquely accommodates and predicts such a view. In the final chapter, I put this methodological observation into practice by testing the substantive normative predictions of my fittingness-first view against our intuitions in the debate concerning what kinds of considerations can provide reasons for love. I argue that acknowledging the existence of both fit- and value-related reasons for love solves a number of persistent problems in this debate.
    • Fundamentals and Application of Porous Media Filtration for the Removal of Nanoparticles from Industrial Wastewater

      Shadman, Farhang; Rottman, Jeffrey J.; Sierra-Alvarez, Reyes; Aspinwall, Craig A.; Shadman, Farhang (The University of Arizona., 2012)
      Increasing use of engineered nanomaterials presents concerns as some nanoparticles appear to be harmful to both human health and the environment. Effective treatment methods are required to remove problematic nanoparticles from (waste)water streams. Porous media filtration, commonly used for the removal of particulate matter, shows promise for nanoparticle treatment. The goal of this work is to investigate the potential of porous media filtration for the abatement of nanoparticles from aqueous waste streams. To this end, an automated method was developed that allows real-time and in-situ monitoring of nanoparticle transport and retention in porous media using online measurement of UV-visible absorbance or fluorescence. Development of fluorescent-core nano-silica (n-SiO₂) in controllable sizes provided an excellent tracer for nanoparticle transport in porous media. Measurement of n-SiO₂ by destructive techniques is complicated by high natural Si background levels. Fluorescence monitoring enables real-time measurement, facilitating rapid evaluation of n-SiO₂ transport. Synthesized n-SiO₂ remain in their primary sizes making an evaluation of the behavioral change of particles due to transition into the "nano" range possible. A comparison of the role of particle size on transport in porous media displayed the importance of particle number concentration as the dominance of site-specific adsorption may be obscured by simple mass concentration evaluation.T he effectiveness of different bed materials, namely, sand, activated carbon (AC), and diatomaceous earth (DE), for the removal of TiO₂ nanoparticles (n-TiO₂) from aqueous streams was investigated. DE proved promising for n-TiO₂ capture shown by its high bed capacity (33.8 mg TiO₂ g⁻¹(medium)) compared to AC (0.23 mg TiO₂ g⁻¹(medium)) or sand (0.004 mg TiO₂ g⁻¹(medium)). The presence of organic and synthetic contaminants produced varying effects on n-TiO₂ retention, mostly due to either enhanced electrostatic or steric interactions. Application of a process simulator combining physical straining with site-specific interactions, delineating physisorption from chemisorption and diffusion limited interactions, enabled the accurate fit of n-TiO₂ transport in sand, AC and DE. The fitting process revealed the advantage of DE due to increased physisorption and physical straining of n-TiO₂. Modeling of this system afforded the elucidation of controlling retention mechanisms and provides a basis for future scaling and system design.
    • Fundamentals and Applications of Organic Electrochemical Transistors for Biosensing

      Ratcliff, Erin; Harris, Jonathan; Savagatrup, Suchol; Printz, Adam; Guzman, Roberto (The University of Arizona., 2021)
      Sensors that interface with biological environments such as human sweat, foods, and biofuels have garnered significant interest in recent years. The primary need in these complex fields is for a sensor device that can provide a real-time data stream in chemically unforgiving environments while also being portable or wearable and consume low power. Electronic devices that include organic semiconductors can begin to address these issues, as they are flexible, biocompatible and scalable materials. Yet, organic semiconductors are still being actively understood. They have relatively complex microstructural transformations when a voltage is applied to them in an electrochemical environment. Further, their unique ability to conduct both electronic charges and ions offer competing design principles when using them in a device. Understanding these processes occurring during device use is crucial for their application. This work first utilizes a model organic semiconductor, poly(3-hexylthiophene), to examine the microstructural changes occurring during electrochemical oxidation, and possible alternatives to improve ion conduction. Then, P3HT is used as the semiconductor channel in a floating gate organic electrochemical transistor modified with an ion gel to prevent degradation. The final device with modifications to each interface is used for sensing of a yeast used in the biofuel process, Yarrowia lipolytica. The critical interfacial factors that contribute to the overall performance of this device are examined, with a particular focus on reproducibility and manufacturability. It’s found that the final device can provide simplicity and amplification above traditional impedance-based sensors.