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Title: HIGH QUALITY GATE DIELECTRIC/MoS2 INTERFACES PROBED BY THE CONDUCTANCE METHOD.
Creator: Krishnaprasad Sharada, Adithi Pandrahal, Roy, Tania, Abdolvand, Reza, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description: Two-dimensional materials provide a versatile platform for various electronic and optoelectronic devices, due to their uniform thickness and pristine surfaces. We probe the superior quality of 2D/2D and 2D/3D interfaces by fabricating molybdenum disulfide (MoS2)-based field effect transistors having hexagonal boron nitride (h-BN) and Al2O3 as the top gate dielectrics. An extremely low trap density of ~7x10^10 states/cm2-eV is extracted at the 2D/2D interfaces with h-BN as the top gate...
Show moreTwo-dimensional materials provide a versatile platform for various electronic and optoelectronic devices, due to their uniform thickness and pristine surfaces. We probe the superior quality of 2D/2D and 2D/3D interfaces by fabricating molybdenum disulfide (MoS2)-based field effect transistors having hexagonal boron nitride (h-BN) and Al2O3 as the top gate dielectrics. An extremely low trap density of ~7x10^10 states/cm2-eV is extracted at the 2D/2D interfaces with h-BN as the top gate dielectric on the MoS2 channel. 2D/3D interfaces with Al2O3 as the top gate dielectric and SiOx as the nucleation layer exhibit trap densities between 7x10^10 and 10^11 states/cm2-eV, which is lower than previously reported 2D-channel/high-k-dielectric interface trap densities. The comparable values of trap time constants for both interfaces imply that similar types of defects contribute to the interface traps. This work establishes the case for van der Waals systems where the superior quality of 2D/2D and 2D/high-k dielectric interfaces can produce high performance electronic and optoelectronic devices.
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Date Issued: 2018
Identifier: CFE0007214, ucf:52209
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007214

Title: Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials.
Creator: Jennings, Jeffrey, Vaidyanathan, Raj, Kar, Aravinda, Coffey, Kevin, Challapalli, Suryanarayana, Brisbois, Elizabeth, Yu, Xiaoming, University of Central Florida
Abstract / Description: Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive...
Show moreInduction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities.An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop.An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.
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Date Issued: 2018
Identifier: CFE0007756, ucf:52378
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007756

Title: Consumer Tradeoffs in Material and Experiential Purchases.
Creator: Urumutta Hewage, Ganga, He, Xin, Rugar, Yael Zemack -, Wang, Ze, Sivo, Stephen, University of Central Florida
Abstract / Description: Material and experiential purchases have gained much attention in psychology and consumer behavior alike (Carter and Gilovich 2010; Nicolao, Irwin, and Goodman 2009; Rosenzweig and Gilovich 2012; Tully, Hershfield, and Meyvis 2015). In three essays, I examine the theoretical and practical implications of consumer tradeoffs in this domain. In the first essay, I explore how regulatory focus influences the tradeoffs between material and experiential purchases. Results of five laboratory studies...
Show moreMaterial and experiential purchases have gained much attention in psychology and consumer behavior alike (Carter and Gilovich 2010; Nicolao, Irwin, and Goodman 2009; Rosenzweig and Gilovich 2012; Tully, Hershfield, and Meyvis 2015). In three essays, I examine the theoretical and practical implications of consumer tradeoffs in this domain. In the first essay, I explore how regulatory focus influences the tradeoffs between material and experiential purchases. Results of five laboratory studies and two field studies (using Instagram and Google Trends data) suggest that, as the regulatory focus shifts from prevention to promotion, there is a higher likelihood of choosing experiential purchases and such an effect is driven by focus of attention. The second essay examines how self-construal may shape material-experiential tradeoffs. Results show that independent self-view develops a higher preference towards experiential purchases than interdependent self-view(-)an effect driven by individual's uniqueness consideration. I demonstrate this effect across seven experimental studies and a field study (using United Nations data). I also show that type of decision moderates the results. The third essay investigates how purchase type influences consumers' preference for mystery options. Five lab studies and a field study (using Groupon data) provide evidence that, when making experiential purchases consumers favor mystery options than when making material purchases. Such an effect is driven by the need for excitement. Additionally, moderated by priming of excitement and target of the decision (self vs. other). Together, these three essays contribute to a better understanding of tradeoffs in these two types of purchases. My findings add to the work on regulatory focus, self-construal, and consumer judgements and decision making. I also offer managerial insights to develop effective marketing strategy.
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Date Issued: 2019
Identifier: CFE0007547, ucf:52605
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007547

Title: Photochemistry and Applications of Diels-Alder Adducts and Photoacids in Materials Science.
Creator: Johns, Valentine, Liao, Yi, Miles, Delbert, Zou, Shengli, Gesquiere, Andre, Su, Ming, University of Central Florida
Abstract / Description: Utilizing light as an energy source for reactions has intrigued many chemists. This has led to the development of the principles of photochemistry. The Photo retro Diels Alder (PrDA) reaction is one such system that has potential for use in materials science as well as in the life sciences. However, there was no guide to predict whether a compound could undergo the PrDA reaction, which limits the widespread use of this reaction. Another system is that of photoacids (molecules that release...
Show moreUtilizing light as an energy source for reactions has intrigued many chemists. This has led to the development of the principles of photochemistry. The Photo retro Diels Alder (PrDA) reaction is one such system that has potential for use in materials science as well as in the life sciences. However, there was no guide to predict whether a compound could undergo the PrDA reaction, which limits the widespread use of this reaction. Another system is that of photoacids (molecules that release protons upon irradiation reversibly). Since most fundamental processes involve proton transfer, these types of photoacids have great potential which is yet to be explored. This thesis describes the design and synthesis of various aromatic DA adducts. These adducts were made to undergo the rDA reaction using UV (Ultra-Violet) light. Experimental results showed that the photoreactivity of these adducts depends on the electron-donating ability of the diene component and the electron-withdrawing ability of the dienophile component. In addition, mechanistic study of this reaction revealed the formation of a charge separated intermediate with a singlet excited state. The potential of the PrDA reaction was also explored in two ways. One was by designing isomeric DA adducts from pentacene and TCNE (tetracyanoethylene) which are capable of switching from one isomer to another via a PrDA process. The other way was the design and synthesis of a polymer with an anthracene diketone moeity which could undergo a PrDA reaction to change from an insulator to a semiconductor. Finally, the syntheses of a number of photoacids which not only become acidic upon irradiation but also respond to visible light reversibly have been explored. A rationale has been developed for the design of photoacids with desired photo-induced response. While electron donating and accepting groups in strategic positions help tune the pH; using different combinations of ethanol and water affect the rate of the forward and the backward processes. A photoacid monomer was also incorporated into three photoacid polymers which respond to visible light reversibly, hence promising widespread applications of these photoacids.
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Date Issued: 2012
Identifier: CFE0004556, ucf:49235
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004556

Title: Vision-Based Testbeds for Control System Applicaitons.
Creator: Sivilli, Robert, Xu, Yunjun, Gou, Jihua, Cho, Hyoung, Pham, Khanh, University of Central Florida
Abstract / Description: In the field of control systems, testbeds are a pivotal step in the validation and improvement of new algorithms for different applications. They provide a safe, controlled environment typically having a significantly lower cost of failure than the final application. Vision systems provide nonintrusive methods of measurement that can be easily implemented for various setups and applications. This work presents methods for modeling, removing distortion, calibrating, and rectifying single and...
Show moreIn the field of control systems, testbeds are a pivotal step in the validation and improvement of new algorithms for different applications. They provide a safe, controlled environment typically having a significantly lower cost of failure than the final application. Vision systems provide nonintrusive methods of measurement that can be easily implemented for various setups and applications. This work presents methods for modeling, removing distortion, calibrating, and rectifying single and two camera systems, as well as, two very different applications of vision-based control system testbeds: deflection control of shape memory polymers and trajectory planning for mobile robots. First, a testbed for the modeling and control of shape memory polymers (SMP) is designed. Red-green-blue (RGB) thresholding is used to assist in the webcam-based, 3D reconstruction of points of interest. A PID based controller is designed and shown to work with SMP samples, while state space models were identified from step input responses. Models were used to develop a linear quadratic regulator that is shown to work in simulation. Also, a simple to use graphical interface is designed for fast and simple testing of a series of samples. Second, a robot testbed is designed to test new trajectory planning algorithms. A template-based predictive search algorithm is investigated to process the images obtained through a low-cost webcam vision system, which is used to monitor the testbed environment. Also a user-friendly graphical interface is developed such that the functionalities of the webcam, robots, and optimizations are automated. The testbeds are used to demonstrate a wavefront-enhanced, B-spline augmented virtual motion camouflage algorithm for single or multiple robots to navigate through an obstacle dense and changing environment, while considering inter-vehicle conflicts, obstacle avoidance, nonlinear dynamics, and different constraints. In addition, it is expected that this testbed can be used to test different vehicle motion planning and control algorithms.
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Date Issued: 2012
Identifier: CFE0004601, ucf:49187
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004601

Title: INVESTIGATION OF REACTIVELY SPUTTERED BORON CARBON NITRIDE THIN FILMS.
Creator: Todi, Vinit, Sundaram, Kalpathy, University of Central Florida
Abstract / Description: Research efforts have been focused in the development of hard and wear resistant coatings over the last few decades. These protective coatings find applications in the industry such as cutting tools, automobile and machine part etc. Various ceramic thin films like TiN, TiAlN, TiC, SiC and diamond-like carbon (DLC) are examples of the films used in above applications. However, increasing technological and industrial demands request thin films with more complicated and advanced properties. For...
Show moreResearch efforts have been focused in the development of hard and wear resistant coatings over the last few decades. These protective coatings find applications in the industry such as cutting tools, automobile and machine part etc. Various ceramic thin films like TiN, TiAlN, TiC, SiC and diamond-like carbon (DLC) are examples of the films used in above applications. However, increasing technological and industrial demands request thin films with more complicated and advanced properties. For this purpose, B-C-N ternary system which is based on carbon, boron and nitrogen which exhibit exceptional properties and attract much attention from mechanical, optical and electronic perspectives. Also, boron carbonitride (BCN) thin films contains interesting phases such as diamond, cubic BN (c-BN), hexagonal boron nitride (h-BN), B4C, [two]-C3N4. Attempts have been made to form a material with semiconducting properties between the semi metallic graphite and the insulating h-BN, or to combine the cubic phases of diamond and c-BN (BC2N heterodiamond) in order to merge the higher hardness of the diamond with the advantages of c-BN, in particular with its better chemical resistance to iron and oxygen at elevated temperatures. New microprocessor CMOS technologies require interlayer dielectric materials with lower dielectric constant than those used in current technologies to meet RC delay goals and to minimize cross-talk. Silicon oxide or fluorinated silicon oxide (SiOF) materials having dielectric constant in the range of 3.6 to 4 have been used for many technology nodes. In order to meet the aggressive RC delay goals, new technologies require dielectric materials with K<3. BCN shows promise as a low dielectric constant material with good mechanical strength suitable to be used in newer CMOS technologies. For optical applications, the deposition of BCN coatings on polymers is a promising method for protecting the polymer surface against wear and scratching. BCN films have high optical transparency and thus can be used as mask substrates for X-ray lithography. Most of the efforts from different researchers were focused to deposit cubic boron nitride and boron carbide films. Several methods of preparing boron carbon nitride films have been reported, such as chemical vapor deposition (CVD), plasma assisted CVD, pulsed laser ablation and ion beam deposition. Very limited studies could be found focusing on the effect of nitrogen incorporation into boron carbide structure by sputtering. In this work, the deposition and characterization of amorphous thin films of boron carbon nitride (BCN) is reported. The BCN thin films were deposited by radio frequency (rf) magnetron sputtering system. The BCN films were deposited by sputtering from a high purity B4C target with the incorporation of nitrogen gas in the sputtering ambient. Films of different compositions were deposited by varying the ratios of argon and nitrogen gas in the sputtering ambient. Investigation of the oxidation kinetics of these materials was performed to study high temperature compatibility of the material. Surface characterization of the deposited films was performed using X-ray photoelectron spectroscopy and optical profilometry. Studies reveal that the chemical state of the films is highly sensitive to nitrogen flow ratios during sputtering. Surface analysis shows that smooth and uniform BCN films can be produced using this technique. Carbon and nitrogen content in the films seem to be sensitive to annealing temperatures. However depth profile studies reveal certain stoichiometric compositions to be stable after high temperature anneal up to 700[degrees]C. Electrical and optical characteristics are also investigated with interesting results. The optical band gap of the films ranged from 2.0 eV - 3.1 eV and increased with N2/Ar gas flow ratio except at the highest ratio. The optical band gap showed an increasing trend when annealed at higher temperatures. The effect of deposition temperature on the optical and chemical compositions of the BCN films was also studied. The band gap increased with the deposition temperature and the films deposited at 500oC had the highest band gap. Dielectric constant was calculated from the Capacitance-Voltage curves obtained for the MOS structures with BCN as the insulating material. Aluminum was used as the top electrode and the substrate was p-type Si. Effect of N2/Ar gas flow ratio and annealing on the values of dielectric constant was studied and the dielectric constant of 2.5 was obtained for the annealed BCN films. This by far is the lowest value of dielectric constant reported for BCN film deposited by sputtering. Lastly, the future research work on the BCN films that will be carried out as a part of the dissertation is proposed.
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Date Issued: 2011
Identifier: CFE0004033, ucf:49181
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004033

Title: First Principles Studies of Pattern Formations and Reactions on Catalyst Surfaces.
Creator: Le, Duy, Rahman, Talat, Roldan Cuenya, Beatriz, Schelling, Patrick, Sohn, Yongho, University of Central Florida
Abstract / Description: This dissertation undertakes theoretical research into the adsorption, pattern formation, and reactions of atoms, molecules, and layered materials on catalyst surfaces. These investigations are carried out from first-principles calculations of electronic and geometric structures using density functional theory (DFT) for predictions and simulations at the atomic scale. The results should be useful for further study of the catalytic activities of materials and for engineering functional...
Show moreThis dissertation undertakes theoretical research into the adsorption, pattern formation, and reactions of atoms, molecules, and layered materials on catalyst surfaces. These investigations are carried out from first-principles calculations of electronic and geometric structures using density functional theory (DFT) for predictions and simulations at the atomic scale. The results should be useful for further study of the catalytic activities of materials and for engineering functional nanostructures.The first part of the dissertation focuses on systematic first-principles simulations of the energetic pathways of CO oxidation on the Cu2O(100) surface. These simulations show CO to oxidize spontaneously on the O-terminated Cu2O(100) surface by consuming surface oxygen atoms. The O-vacancy on Cu2O(100) then is subsequently healed by dissociative adsorption of atmospheric O2 molecules.The second part discusses the pattern formation of hydrogen on two and three layers of Co film grown on the Cu(111) surface. It is found that increasing the pressure of H2 changes the hydrogen structure from 2H-(2 x 2) to H-p(1 x 1) through an intermediate structure of 6H-(3 x 3).The third part compares the results of different ways of introducing van der Waals (vdW) interactions into DFT simulations of the adsorption and pattern formation of various molecules on certain substrates. Examinations of the physisorption of five nucleobases on graphene and of n-alkane on Pt(111) demonstrate the importance of taking vdW interactions into account, and of doing so in a way that is best suited to the particular system in question. More importantly, as the adsorption of 1,4 diaminebenzene molecules on Au(111) shows inclusion of vdW interactions is crucial for accurate simulation of the pattern formation.The final part carries out first-principles calculations of the geometric and electronic structure of the Moire pattern of a single layer of Molybdenum disulfide (MoS2) on Cu(111). The results reveal three possible stacking types. They also demonstrate that the MoS2 layer to be chemisorbed, albeit weakly, and that, while Cu surface atoms are vertically disordered, the layer itself is not strongly buckled.
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Date Issued: 2012
Identifier: CFE0004224, ucf:48991
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004224

Title: Electrochemical Studies of Nanoscale Composite Materials as Electrodes in PEM Fuel Cells.
Creator: Anderson, Jordan, Zhai, Lei, Blair, Richard, Hampton, Michael, Zou, Shengli, Seal, Sudipta, University of Central Florida
Abstract / Description: Polymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels....
Show morePolymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels. Small organic molecules such as alcohols and formic acid have shown promise as alternatives to hydrogen in PEMFCs due to their higher stability at ambient conditions. The drawbacks for using these fuels in PEMFCs are related to their incomplete oxidation mechanisms, which lead to the production of carbon monoxide (CO). When carbon monoxide is released in fuel cells it binds strongly to the platinum anode thus limiting the adsorption and subsequent oxidation of more fuel. In order to promote the complete oxidation of fuels and limit poisoning due to CO, various metal and metal oxide catalysts have been used.Motivated by promising results seen in fuel cell catalysis, this research project is focused on the design and fabrication of novel platinum-composite catalysts for the electrooxidation of methanol, ethanol and formic acid. Various Pt-composites were fabricated including Pt-Au, Pt-Ru, Pt-Pd and Pt-CeO2 catalysts. Electrochemical techniques were used to determine the catalytic ability of each novel composite toward the electrooxidation of methanol, ethanol and formic acid. This study indicates that the novel composites all have higher catalytic ability than bare Pt electrodes. The increase in catalytic ability is mostly attributed to the increase in CO poison tolerance and promotion of the complete oxidation mechanism of methanol, ethanol and formic acid. Formulations including bi- and tri-composite catalysts were fabricated and in many cases show the highest catalytic oxidation, suggesting tertiary catalytic effects. The combination of bi-metallic composites with ceria also showed highly increased catalytic oxidation ability. The following dissertation expounds on the relationship between composite material and the electrooxidation of methanol, ethanol and formic acid. The full electrochemical and material characterization of each composite electrode is provided.
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Date Issued: 2012
Identifier: CFE0004510, ucf:49264
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004510

Title: Vibration Reduction of Mistuned Bladed Disks via Piezoelectric-Based Resonance Frequency Detuning.
Creator: Lopp, Garrett, Kauffman, Jeffrey L., Das, Tuhin, Xu, Yunjun, University of Central Florida
Abstract / Description: Recent trends in turbomachinery blade technology have led to increased use of monolithically constructed bladed disks (blisks). Although offering a wealth of performance benefits, this construction removes the blade-attachment interface present in the conventional design, thus unintentionally removing a source of friction-based damping needed to counteract large vibrations during resonance passages. This issue is further exacerbated in the presence of blade mistuning that arises from small...
Show moreRecent trends in turbomachinery blade technology have led to increased use of monolithically constructed bladed disks (blisks). Although offering a wealth of performance benefits, this construction removes the blade-attachment interface present in the conventional design, thus unintentionally removing a source of friction-based damping needed to counteract large vibrations during resonance passages. This issue is further exacerbated in the presence of blade mistuning that arises from small imperfections from otherwise identical blades and are unavoidable as they originate from manufacturing tolerances and operational wear over the lifespan of the engine. Mistuning is known to induce vibration localization with large vibration amplitudes that render blades susceptible to failure induced by high-cycle fatigue. The resonance frequency detuning (RFD) method reduces vibration associated with resonance crossings by selectively altering the blades' structural response. This method utilizes the variable stiffness properties of piezoelectric materials to switch between available stiffness states at some optimal time as the excitation frequency sweeps through a resonance. For a single-degree-of-freedom (SDOF) system, RFD performance is well defined. This research provides the framework to extend RFD to more realistic applications when the SDOF assumption breaks down, such as in cases of blade mistuning. Mistuning is inherently random; thus, a Monte Carlo analysis performed on a computationally cheap lumped-parameter model provides insight into RFD performance for various test parameters. Application of a genetic algorithm reduces the computational expense required to identify the optimal set of stiffness-state switches. This research also develops a low-order blisk model with blade-mounted piezoelectric patches as a tractable first step to apply RFD to more realistic systems. Application of a multi-objective optimization algorithm produces Pareto fronts that aid in the selection of the optimized patch parameters. Experimental tests utilizing the academic blisk with the optimized patches provides validation.
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Date Issued: 2018
Identifier: CFE0007488, ucf:52639
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007488

Title: Evaporative Vapor Deposition for Depositing 2D Materials.
Creator: Gleason, Kevin, Putnam, Shawn, Zhai, Lei, Deng, Weiwei, University of Central Florida
Abstract / Description: The development of a new deposition technique called evaporative vapor deposition (EVD) is reported, allowing deposition and formation of atomically-thin, large area materials on arbitrary substrates. This work focuses on the highly popular monolayer material (-) graphene oxide (GO). A droplet of a GO solution is formed on a heated polymer substrate, and maintained at steady-state evaporation (all droplet parameters are held constant over time). The polymer substrate is laser patterned to...
Show moreThe development of a new deposition technique called evaporative vapor deposition (EVD) is reported, allowing deposition and formation of atomically-thin, large area materials on arbitrary substrates. This work focuses on the highly popular monolayer material (-) graphene oxide (GO). A droplet of a GO solution is formed on a heated polymer substrate, and maintained at steady-state evaporation (all droplet parameters are held constant over time). The polymer substrate is laser patterned to control the droplet's contact line dynamics and the droplet's contact angle is maintained using a computer controlled syringe pump. A room temperature silicon wafer is translated through the vapor field of the evaporating GO droplet using a computer controlled translation stage. Dropwise condensation formed on the silicon wafer is monitored using both optical and infrared cameras. The condensation rate is measured to be ~50pL/mm2?s (-) 500 pL/mm2?s and dependent on the substrate translation speed and height difference between the droplet's apex and substrate surface. Nano-sized GO flakes carried through the vapor phase are captured in the condensate, depositing on the translating wafer. Deposition rate is dependent on the stability of the solution and droplet condensate size. Characterization with Raman spectroscopy show expected shifts for graphene/graphite. The presented EVD technique is promising toward formation of large scale 2D materials with applications to developing new technologies.
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Date Issued: 2015
Identifier: CFE0006035, ucf:50969
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006035

Title: Phase Transformations and Microstructural Evolution in the U-10 wt.% Mo Alloy with Various Zr Additions at 900C and 650C.
Creator: Eriksson, Nicholas, Sohn, Yongho, Challapalli, Suryanarayana, Coffey, Kevin, University of Central Florida
Abstract / Description: The Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising...
Show moreThe Reduced Enrichment for Research and Test Reactor (RERTR) now known as the Material Minimization and Management Reactor Control program (MMMRC) seeks to replace the use of highly enriched uranium (HEU) fuels used in research and test nuclear reactors around the world. The low enriched uranium (LEU) fuels must have fissionable uranium densities comparable to the HEU fuels. After extensive investigation by various researchers around the world, the U-Mo alloys were selected as a promising candidate. The Mo alloyed with U allows for the stabilization of the face-centered cubic ?-U phase, which demonstrated favorable irradiation behavior. However, deleterious diffusional interaction between the fuel and the cladding, typically Al-base alloy, remain a challenge to overcome for application of U-Mo alloys as the LEU fuel. Zr has been identified as a potential diffusion barrier between monolithic U-10 wt.% Mo (U10Mo) metallic fuel and AA6061 cladding alloys for the development of a LEU fuel system. However, interdiffusion and reaction between the Zr barrier and U10Mo fuel can produce phases such as Mo2Zr, and promote the destabilization of ?-U phase into ?'-U (U2Mo) and ?-U. In order to better understand this phenomenon, this study examined the phases that are present in the U10Mo alloys with varying Zr concentration, 0, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0 wt.% at room temperature after heat treatment at 900(&)deg;C for 168 hours and 650(&)deg;C for 3 hours. These two temperatures are relevant to fuel plate fabrication process of homogenization and hot-rolling, respectively. Scanning electron microscopy and X-ray diffraction were employed to identify and quantitatively document the constituent phases and microstructure to elucidate the nature of phase transformations. For U10Mo alloys containing less than 1.0 wt.% Zr, there was no significant formation of Mo2Zr after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. The ?-U phase also remained stable correspondingly for these alloys containing less than 1.0 wt.% Zr. For U10Mo alloys containing 2 wt.% or more Zr, a significant amount of Mo2Zr formation was observed after 900?C homogenization and subsequent heat treatment at 650?C for 3 hours. For these alloys, destabilization of ?-U into ?'-U (U2Mo), UZr2 and ?-U was observed. The alloy containing 20 wt.% Zr, however, did not demonstrate ?-U decomposition even though Mo2Zr was observed after heat treatments. The formation of Mo2Zr effectively reduced the stability of the metastable ?-U phase by depleting the ?-stabilizing Mo. The destabilization of ?-U phase into the ?-U phase is not favorable due to anisotropic and poor irradiation behavior of ?-U phase. Therefore the formation of Mo2Zr at the interface between U10Mo fuel and Zr diffusion barrier must be carefully controlled during the fabrication of monolithic LEU fuel system for successful implementation.
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Date Issued: 2015
Identifier: CFE0005943, ucf:50812
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005943

Title: Optimal Switch Timing for Piezoelectric-Based Semi-Active Vibration Reduction Techniques.
Creator: Kelley, Christopher, Kauffman, Jeffrey, Das, Tuhin, Xu, Yunjun, University of Central Florida
Abstract / Description: Semi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every...
Show moreSemi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every displacement extrema. Due to the complexity of analyzing a system with discrete switches, these control laws were developed based on intuition. The few analyses that attempt to determine an optimal switching law mathematically only evaluate the system at resonance. This thesis investigates the effects of switch timing on vibration reduction and the frequency dependence of the optimal switch timing control law. Regardless of the switch timing, sensing uncertainties, noise, and modeling errors can cause the switches to occur away from the designed moment. Thus, this work also quantifies the expected degradation in vibration reduction performance due to variations in the designed switch time. Experimental, numerical, and analytical solutions agree that the optimal switch timing of these semi-active techniques depends on frequency. A closed-form solution for the optimal switch timing is derived in terms of well-known, non-dimensional parameters.
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Date Issued: 2016
Identifier: CFE0006336, ucf:51555
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006336

Title: Synthesis and Characterization of Core-Shell Zinc Silica Nanoparticles and Zinc Silica Nanogels for Agricultural Applications.
Creator: Berroth, Megan, Santra, Swadeshmukul, Moore, Sean, Jewett, Travis, University of Central Florida
Abstract / Description: Plant pathogens are a serious problem facing the agricultural industry today. Current methodologies use copper based biocides as the main form of defense. Unfortunately this can lead to damaging environmental effects and increased rates of antimicrobial resistance. In this study, antimicrobial activity of multiple alternative zinc-based nanoformulations were tested against three important plant pathogens: Xanthomonas alfalfae, Pseudomonas syringae, and Clavobacter michiganensis. Xanthomonas...
Show morePlant pathogens are a serious problem facing the agricultural industry today. Current methodologies use copper based biocides as the main form of defense. Unfortunately this can lead to damaging environmental effects and increased rates of antimicrobial resistance. In this study, antimicrobial activity of multiple alternative zinc-based nanoformulations were tested against three important plant pathogens: Xanthomonas alfalfae, Pseudomonas syringae, and Clavobacter michiganensis. Xanthomonas sub species cause Citrus canker, a devastating disease that affects millions of citrus trees worldwide while the latter two affect tomato crops. Materials synthesis was completed and the resulting nanoformulations were characterized by Atomic Absorption Spectroscopy, Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy, and X-Ray Photoelectron Spectroscopy. The antimicrobial efficacy of the newly synthesized formulas and two commercially available products, Kocide 3000 (DuPont) and Nordox (Brandt), were determined by Minimum Inhibitory Concentration Assays followed by Bacterial Viability Assays. The subsequent data demonstrated a marketed difference in the way the antimicrobial agents acted upon the bacterial species. The core-shell zinc silica nanoparticles (C-SZnSiNP) proved to be ineffective, while the zinc silica nanogel (ZnSiNG) was as successful at killing the bacteria as the commercial products. This shows promise for a new alternative material with zinc at the forefront of the fight against plant pathogens.
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Date Issued: 2015
Identifier: CFE0006209, ucf:51099
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006209

Title: Development and Implementation of a Streamlined Process for the Creation and Mechanization of Negative Poisson's Ratio Meso-Scale Patterns.
Creator: Shuler, Matthew, Gordon, Ali, Kauffman, Jeffrey L., Ghosh, Ranajay, University of Central Florida
Abstract / Description: This thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be...
Show moreThis thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be developed in order to confer transformative thermomechanical responses to structures where transverse expansion is more desirable than contraction. For example, materials at high temperature. Additionally, patterns that take into account manufacturing limitations, while maintaining the properties characteristically attached to negative Poisson's Ratio materials, are ideal in order to utilize the potential of NPR structures. A novel NPR pattern is developed, numerically analyzed, and optimized via design of experiments. The parameters of the meso-structure are varied, and the bulk response is studied using finite element analysis (FEA). The candidate material for the study is Medium-Density Fiberboard (MDF). This material is relevant to a variety of applications where multiaxial stresses, particularly compressive, lead to mechanical fatigue. Samples are fabricated through a laser cutting process, and a comparison is drawn through the use of experimental means, including traditional tensile loading tests and digital image correlation (DIC). Various attributes of the elasto-plasticity responses of the bulk structure are used as objectives to guide the optimization process.
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Date Issued: 2017
Identifier: CFE0006795, ucf:51830
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006795

Title: Hidden Narrative: A Family of Objects.
Creator: Hassard, Alesha, Price, Mark, Cooper, Larry, Watson, Keri, University of Central Florida
Abstract / Description: My artwork aims to create an ephemeral world filled with metaphorical materials. I examine and use my own experiences and perspectives, presenting fluctuations between childhood and adulthood. The personal objects that represent these times frame an implied sentience. The objects, gathered and installed in specific groupings, connote familial relationships.
Date Issued: 2016
Identifier: CFE0006114, ucf:51190
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006114

Title: Mechanical Properties and Thermal Residual Stresses of ZrB2-SiC Ceramic Composites for Hypersonic Vehicle Applications.
Creator: Stadelmann, Richard, Orlovskaya, Nina, Kumar, Ranganathan, Raghavan, Seetha, University of Central Florida
Abstract / Description: Ultra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young's, shear, and bulk moduli, along with Poisson's ratio, 4-point bending strength, and single edge V-notched beam (SEVNB)...
Show moreUltra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young's, shear, and bulk moduli, along with Poisson's ratio, 4-point bending strength, and single edge V-notched beam (SEVNB) fracture toughness were measured. In addition, in-situ bending experiments under a Raman microscope were performed to determine the piezo-spectroscopic coefficients of SiC Raman active peaks for calculation of thermal residual stresses. The results show that these materials are possible candidates for hypersonic air-breathing vehicles due to their high Young's modulus, ability to withstand high temperatures, and relatively low densities.
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Date Issued: 2013
Identifier: CFE0005060, ucf:49945
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005060

Title: Chemical Differentiation of Human Osseous, Non-human Osseous, and Non-osseous Materials Using Scanning Electron Microscopy - Energy Dispersive X-ray Spectrometry (SEM/EDX) and Multivariate Statistical Analysis.
Creator: Meizel-Lambert, Cayli, Schultz, John, Sigman, Michael, Toyne, J. Marla, University of Central Florida
Abstract / Description: Identification of osseous materials is generally established on gross anatomical factors; however, highly fragmented or taphonomically altered materials are often problematic and alternative methods, such as biological, histological, or chemical analysis, must be utilized. Recently, chemical methods have been proposed to sort unknown materials according to their Ca/P ratios. Ubelaker and colleagues (2002) proposed using SEM/EDX to achieve this distinction and Christensen and colleagues (2012)...
Show moreIdentification of osseous materials is generally established on gross anatomical factors; however, highly fragmented or taphonomically altered materials are often problematic and alternative methods, such as biological, histological, or chemical analysis, must be utilized. Recently, chemical methods have been proposed to sort unknown materials according to their Ca/P ratios. Ubelaker and colleagues (2002) proposed using SEM/EDX to achieve this distinction and Christensen and colleagues (2012) have validated X-ray Fluorescence Spectrometry (XRF) for this application. An alternative method of analysis involves performing principal component analysis (PCA) on element spectra to classify unknown materials based on their trace element composition. Zimmerman (2013) proposed the validity of this method with data obtained using hand held XRF. Subsequently, performing PCA on elemental data obtained using SEM/EDX demonstrates potential for material differentiation. Elemental weight percent data were collected using SEM/EDX then processed in R, version 3.0.1, by the R Foundation for Statistical Computing using PCA and Fisher Linear Discriminant Analysis. A two-tiered analysis was undertaken to improve discrimination between sample groups. The first tier involved distinguishing between osseous and non-osseous materials. After outliers were removed overall correct classification was 98.02% with one of 1504 osseous and 39 of 520 non-osseous spectra misclassifying. Since forty spectra were collected for each sample, the single misclassifying spectra would not affect the overall classification of the sample, resulting in 100% correct classification with a 0% error rate for the osseous samples. The second tier assessed differentiation of human and non-human osseous materials but demonstrated a poor correct classification rate of 72.41%. Finally, a blind study was conducted using 20 samples to assess the applicability for using this method to classify unknown materials as osseous or non-osseous. All of the samples were correctly classified resulting in 100% correct classification, further demonstrating the efficiency of SEM/EDX and statistical analysis for differentiation of osseous and non-osseous materials. Due to its high specificity, small sample requirements, and relative non-destructive testing protocol, as well as its presence in most modern crime laboratories, SEM/EDX has been proposed as a laboratory method for chemical differentiation of osseous and non-osseous materials. Additionally, the proposed method does not require advanced training or knowledge of analytical chemistry as the SEM/EDX provides clear results that can be processed using publically available statistical analysis software. By assessing and improving chemical analysis methodologies used for material differentiation, forensic anthropologists might be able to identify osseous and non-osseous samples as a preemptive step in forensic investigations involving fragmentary and taphonomically modified materials, reducing time and cost investments spent on forensically insignificant samples.
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Date Issued: 2014
Identifier: CFE0005665, ucf:50185
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005665

Title: Atmospheric Pressure Chemical Vapor Deposition of Functional Oxide Materials for Crystalline Silicon Solar Cells.
Creator: Davis, Kristopher, Schoenfeld, Winston, Likamwa, Patrick, Moharam, Jim, Habermann, Dirk, University of Central Florida
Abstract / Description: Functional oxides are versatile materials that can simultaneously enable efficiency gains and cost reductions in crystalline silicon (c-Si) solar cells. In this work, the deposition of functional oxide materials using atmospheric pressure chemical vapor deposition (APCVD) and the integration of these materials into c-Si solar cells are explored. Specifically, thin oxide films and multi-layer film stacks are utilized for the following purposes: (1) to minimize front surface reflectance without...
Show moreFunctional oxides are versatile materials that can simultaneously enable efficiency gains and cost reductions in crystalline silicon (c-Si) solar cells. In this work, the deposition of functional oxide materials using atmospheric pressure chemical vapor deposition (APCVD) and the integration of these materials into c-Si solar cells are explored. Specifically, thin oxide films and multi-layer film stacks are utilized for the following purposes: (1) to minimize front surface reflectance without increasing parasitic absorption within the anti-reflection coating(s); (2) to maximize internal back reflectance of rear passivated cells, thereby increasing optical absorption of weakly absorbed long wavelength photons (? (>) 900 nm); (3) to minimize recombination losses by providing excellent surface passivation; and (4) to improve doping processes during cell manufacturing (e.g., emitter and surface field formation) by functioning as highly controllable dopant sources compatible with in-line diffusion processes. The oxide materials deposited by APCVD include amorphous and polycrystalline titanium oxide, aluminum oxide, boron-doped aluminum oxide, silicon oxide, phosphosilicate glass, and borosilicate glass. The microstructure, optical properties, and electronic properties of these films are characterized for different deposition conditions. Additionally, the impact of these materials on the performance of different types of c-Si solar cells is presented using both simulated and experimental current-voltage curves.
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Date Issued: 2015
Identifier: CFE0005599, ucf:50267
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005599

Title: Multifunctional, Multimaterial Particle Fabrication Via an In-Fiber Fluid Instability.
Creator: Kaufman, Joshua, Abouraddy, Ayman, Schoenfeld, Winston, Christodoulides, Demetrios, Seal, Sudipta, University of Central Florida
Abstract / Description: Spherical micro- and nano-particles have found widespread use in many various applications from paint to cosmetics to medicine. Due to the multiplicity of desired particle material(s), structure, size range, and functionality, many approaches exist for generating such particles. Bottom-up methods such as chemical synthesis have a high yield and work with a wide range of materials; however, these processes typically lead to large polydispersity and cannot produce structured particles. Top-down...
Show moreSpherical micro- and nano-particles have found widespread use in many various applications from paint to cosmetics to medicine. Due to the multiplicity of desired particle material(s), structure, size range, and functionality, many approaches exist for generating such particles. Bottom-up methods such as chemical synthesis have a high yield and work with a wide range of materials; however, these processes typically lead to large polydispersity and cannot produce structured particles. Top-down approaches such as microfluidics overcome the polydispersity issue and may produce a few different structures in particles, but at lower rates and only at the micro-scale. A method that can efficiently produce uniformly-sized, structured particles out of a variety of materials and at both the micro- and nano-scales does not yet exist.Over the past few years, I have developed an in-fiber particle fabrication method that relies on a surface tension-driven fluid instability, the Plateau-Rayleigh capillary instability (PRI). Thermal treatment of a multimaterial core/cladding fiber induces the PRI, causing the initially intact core to break up into a periodic array of uniformly-sized spherical particles. During this time, I have demonstrated that this method can produce particles from both polymers and glasses, in a multiplicity of structures, and from diameters of over 1 mm down to 20 nm. Furthermore, by using a stack-and-draw method, a high density of cores may be incorporated into a single fiber, making the in-fiber PRI approach a highly scalable process. Finally, I have shown that it is possible to add dopants to the particles to give them functionality. By structuring the particles, it is thus possible to fabricate multi-functional particles whose functionalities may be allocated arbitrarily throughout the volume of the particles.
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Date Issued: 2014
Identifier: CFE0005357, ucf:50479
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005357

Title: Novel properties of ferromagnetic p-wave superconductors.
Creator: Lorscher, Christopher, Klemm, Richard, Leuenberger, Michael, Rahman, Talat, Schoenfeld, Winston, University of Central Florida
Abstract / Description: This thesis investigates the many extraordinary physical properties of the candidate p-wave ferromagnetic superconductors UCoGe and URhGe, and proposes theoretical predictions for p-wave superconductors yet to be discovered. In particular, we carry out angular dependent quantum field theoretical calculations of the thermodynamic H - T phase diagram known as the upper critical field, or more appropriately for ferromagnetic superconductors the upper critical induction, for various p-wave...
Show moreThis thesis investigates the many extraordinary physical properties of the candidate p-wave ferromagnetic superconductors UCoGe and URhGe, and proposes theoretical predictions for p-wave superconductors yet to be discovered. In particular, we carry out angular dependent quantum field theoretical calculations of the thermodynamic H - T phase diagram known as the upper critical field, or more appropriately for ferromagnetic superconductors the upper critical induction, for various p-wave superconducting order parameter symmetries including: The axial Anderson-Brinkman-Morel(ABM) state, the chiral Scharnberg-Klemm (SK) state, and the completely broken symmetry polar state (CBS), as well as for some other states with partially broken symmetry (PBS) superconducting order parameter symmetries. The most notable contribution of the work presented in this thesis is the application of the Klemm-Clem transformations to analytically calculate the full angular and temperature dependencies of the upper critical field for orthorhombic materials, which may prove to be useful to experimentalists in identifying these exotic states of matter experimentally. Second, this work formulates a double spin-split ellipsoidal Fermi surface (FS) model for ferromagnetic superconductors in the normal state, which introduces a field dependence to the effective mass in one crystallographic direction on the dominant Fermi surface and to the chemical potential, and is subsequently applied to the normal state of URhGe to explain theoretically the anomalous specific heat data of Aoki and Flouquet. Extension of this work to understanding the still elusive reentrant high-field superconducting phase of URhGe and the S-shaped upper critical field curve for external magnetic field parallel to the b-axis direction inUCoGe is discussed. Third, this work also presents theoretical fits to the upper critical field data of Kittika et al. for Sr2RuO4 using the helical p-wave states and including Pauli limiting effects of the three components of the triplet pair-spin fixed to the highly conducting layers by strong spin-orbit coupling.
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Date Issued: 2014
Identifier: CFE0005371, ucf:50451
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005371

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