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Title: Modeling and Spray Pyrolysis Processing of Mixed Metal Oxide Nano-Composite Gas Sensor Films.
Creator: Khatami, Seyed Mohammad Navid, Ilegbusi, Olusegun, Deng, Weiwei, Kassab, Alain, Coffey, Kevin, Divo, Eduardo, University of Central Florida
Abstract / Description: The role of sensor technology is obvious in improvement and optimization of many industrial processes. The sensor films, which are considered the core of chemical sensors, have the capability to detect the presence and concentration of a specific chemical substance. Such sensor films achieve selectivity by detecting the interaction of the specific chemical substance with the sensor material through selective binding, adsorption and permeation of analyte. This research focuses on development...
Show moreThe role of sensor technology is obvious in improvement and optimization of many industrial processes. The sensor films, which are considered the core of chemical sensors, have the capability to detect the presence and concentration of a specific chemical substance. Such sensor films achieve selectivity by detecting the interaction of the specific chemical substance with the sensor material through selective binding, adsorption and permeation of analyte. This research focuses on development and verification of a comprehensive mathematical model of mixed metal oxide thin film growth using spray pyrolysis technique (SPT). An experimental setup is used to synthesize mixed metal oxide films on a heated substrate. The films are analyzed using a variety of characterization tools. The results are used to validate the mathematical model. There are three main stages to achieve this goal: 1) A Lagrangian-Eulerian method is applied to develop a CFD model of atomizing multi-component solution. The model predicts droplet characteristics in flight, such as spatial distribution of droplet size and concentration. 2) Upon reaching the droplets on the substrate, a mathematical model of multi-phase transport and chemical reaction phenomena in a single droplet is developed and used to predict the deposition of thin film. The various stages of droplet morphology associated with surface energy and evaporation are predicted. 3) The processed films are characterized for morphology and chemical composition (SEM, XPS) and the data are used to validate the models as well as investigate the influence of process parameters on the structural characteristics of mixed metal oxide films. The structural characteristics are investigated of nano structured thin films comprising of ZnO, SnO2, ZnO+In2O3 and SnO2+In2O3 composites. The model adequately predicts the size distribution and film thickness when the nanocrystals are well-structured at the controlled temperature and concentration.
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Date Issued: 2014
Identifier: CFE0005817, ucf:50048
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005817

Title: BLOCK COPOLYMER STABILIZED SELF-ASSEMBLED MAGNETIC NANOPARTICLES.
Creator: ZHANG, LI, BELFIELD, KEVIN, University of Central Florida
Abstract / Description: Magnetic materials are currently being developed in the areas of pharmacology and medicinal chemistry for use in applications such as drug delivery and magnetic resonance imaging. Magnetic fluids are being used in audio equipment and hard disk drives. Their suspension in a particular fluid is promoted by the adsorption or reaction of steric or electrostatic stabilizers, which are appropriate for the particular medium. Critical to the success of these magnetic fluids is the development of the...
Show moreMagnetic materials are currently being developed in the areas of pharmacology and medicinal chemistry for use in applications such as drug delivery and magnetic resonance imaging. Magnetic fluids are being used in audio equipment and hard disk drives. Their suspension in a particular fluid is promoted by the adsorption or reaction of steric or electrostatic stabilizers, which are appropriate for the particular medium. Critical to the success of these magnetic fluids is the development of the steric stabilizers, which must prevent the coagulation of the metal particles. Polymeric materials are one of the most suitable nonmagnetic media to disperse the magnetic nanoparticles, forming polymeric nanocomposites in ferrofluids. We have developed strategies in molecular nanoscience to design polymeric systems for stabilization of magnetic nanoparticles. Ring opening metathesis polymerization (ROMP) was used to prepare a series of novel, well-defined diblock copolymers of bicyclo[2.2.1]hept-5-ene 2-carboxylic acid 2-cyanoethyl ester and bicyclo[2.2.1]hept-2-ene, consisting of both anchoring and steric stabilizing blocks. Both ester and cyano groups were incorporated into the polymers to chelate and stabilize the iron oxide magnetic nanoparticles. These polynorbornene-based copolymers were characterized by GPC, along with 1H NMR, FTIR, DSC, and TGA. Using diblock copolymers as stabilizers, nanostructured maghemite (ã-Fe2O3) magnetic ferrofluids were prepared in toluene or cyclohexanone via thermal decomposition of Fe(CO)5 and then the oxidation of iron nanoparticles. Transmission electron microscopic (TEM) images showed a highly crystalline structure of the ã-Fe2O3 nanoparticles, with average particle size varying from 5 to 7 nm. Polymer films containing iron oxide nanoclusters were also prepared from the diblock copolymers. For comparison, a commercial triblock copolymer (BASF PluronicR F127) surfactant was used to prepare stabilized ferrofluids. In addition to ã-Fe2O3 nanoparticles, other types of magnetic nanoparticles, such as FePt, were investigated using this triblock copolymer as a stabilizer. The results indicated that the norbornene diblock copolymers could also be used for the preparation of FePt stabilized magnetic ferrofluids in the future research work.
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Date Issued: 2004
Identifier: CFE0000230, ucf:46272
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000230

Title: STUDY OF OXIDE BREAKDOWN, HOT CARRIER AND NBTI EFFECTS ON MOS DEVICE AND CIRCUIT RELIABILITY.
Creator: Liu, Yi, Yuan, Jiann.S., University of Central Florida
Abstract / Description: As CMOS device sizes shrink, the channel electric field becomes higher and the hot carrier (HC) effect becomes more significant. When the oxide is scaled down to less than 3 nm, gate oxide breakdown (BD) often takes place. As a result, oxide trapping and interface generation cause long term performance drift and related reliability problems in devices and circuits. The RF front-end circuits include low noise amplifier (LNA), local oscillator (LO) and mixer. It is desirable for a LNA to...
Show moreAs CMOS device sizes shrink, the channel electric field becomes higher and the hot carrier (HC) effect becomes more significant. When the oxide is scaled down to less than 3 nm, gate oxide breakdown (BD) often takes place. As a result, oxide trapping and interface generation cause long term performance drift and related reliability problems in devices and circuits. The RF front-end circuits include low noise amplifier (LNA), local oscillator (LO) and mixer. It is desirable for a LNA to achieve high gain with low noise figure, a LO to generate low noise signal with sufficient output power, wide tuning range, and high stability, and a mixer to up-convert or down-convert the signal with good linearity. However, the RF front-end circuit performance is very sensitive to the variation of device parameters. The experimental results show that device performance is degraded significantly subject to HC stress and BD. Therefore, RF front-end performance is degraded by HC and BD effects. With scaling and increasing chip power dissipation, operating temperatures for device have also been increasing. Another reliability concern, which is the negative bias temperature instability (NBTI) caused by the interface traps under high temperature and negative gate voltage bias, arises when the operation temperature of devices increases. NBTI has received much attention in recent year and it is found that NIT is present for all stress conditions and NOT is found to occur at high VG. Therefore, the probability of BD in pMOSFET increases with temperature since trapped charges during the NBTI process increase, thus resulting in percolation, a main cause of oxide degradation. The above effects can cause significant degradations in transistors, thus leading to the shifts of RF performance. This dissertation focuses on the following aspects: (1) RF performance degradation in nMOSFET and pMOSFET due to hot carrier and soft breakdown effects are examined experimentally and will be used for circuit application in the future. (2) A modeling method to analyze the gate oxide breakdown effects on RF nMOSFET has been proposed. The device performance drifts due to gate oxide breakdown are examined, breakdown spot resistance and total gate capacitance are extracted before and after stress for 0.16 um CMOS technology. (3) LC voltage controlled oscillator (VCO) performance degradation due to gate oxide breakdown effect is evaluated. (4) NBTI, HCI and BD combined effects on RF performance degradation are investigated. A physical picture illustrating the NBTI induced BD process is presented. A model to evaluate the time-to-failure (TTF) during NBTI is developed. DCIV method is used to extract the densities of NIT and NOT. Measurements show that there is direct correlation between the steplike increase in the gate current and the oxide-trapped charge (NOT). However, Breakdown has nothing to do with interface traps (NIT). (5) It is found that the degradation due to NSH stress is more severe than that of NS stress at high temperature. A model aiming to evaluate the stress-induced degradation is also developed.
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Date Issued: 2005
Identifier: CFE0000505, ucf:46465
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000505

Title: ANALYSIS OF THE PREVENTION OF BIOCORROSION CAUSED BY DESULFOVIBRIO ALASKENSIS G20.
Creator: Boring, Michael, Self, William, University of Central Florida
Abstract / Description: Desulfovibrio alaskensis G20 and other sulfate-reducing bacteria cause significant damage to metal pipelines and other infrastructure through a metabolic pathway that releases toxic hydrogen sulfide into their surroundings. The biocorrosion that results from the release of hydrogen sulfide creates significant economic burden, and can pose health risks for those exposed to this chemical. They are commonly present in the form of biofilms, an extracellular matrix composed of bacterial cells,...
Show moreDesulfovibrio alaskensis G20 and other sulfate-reducing bacteria cause significant damage to metal pipelines and other infrastructure through a metabolic pathway that releases toxic hydrogen sulfide into their surroundings. The biocorrosion that results from the release of hydrogen sulfide creates significant economic burden, and can pose health risks for those exposed to this chemical. They are commonly present in the form of biofilms, an extracellular matrix composed of bacterial cells, polysaccharides, proteins, nucleic acids, and other materials. These biofilms are difficult to remove, and they provide protection to the bacteria within from anti-bacterial treatments. Desulfovibrio alaskensis G20 is a strain derived from a wild-type bacterium collected from an oil well corrosion site and is a model organism for understanding biofilm formation of sulfate-reducing bacteria and how these biofilms can be prevented or inhibited by techniques such as cerium oxide nanoparticle coating. To this end, samples of Desulfovibrio alaskensis G20 were grown anaerobically in 24-well and 96-well plates, and the resultant biofilm growth was measured through spectrophotometry. Several different environmental parameters were tested, including temperature, electron donor molecules, basal and enriched growth media, and oxidative stress, revealing several affinities for production of biofilm growth.
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Date Issued: 2017
Identifier: CFH2000263, ucf:45942
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000263

Title: CERIUM OXIDE NANOPARTICLES FOR THE DETECTION OF ANTIMICROBIAL RESISTANCE.
Creator: Noll, Alexander, Perez, J. Manuel, University of Central Florida
Abstract / Description: The rise of antimicrobial resistance demands the development of more rapid screening methods for the detection of antimicrobial resistance in clinical samples to both give the patient the proper treatment and expedite the treatment of patients. Cerium oxide nanoparticles may serve a useful role in diagnostics due to their ability to exist in a mixed valence state and act as either oxidizing agents or reducing agents. Considering that cerium oxide nanoparticles have been shown to shift in...
Show moreThe rise of antimicrobial resistance demands the development of more rapid screening methods for the detection of antimicrobial resistance in clinical samples to both give the patient the proper treatment and expedite the treatment of patients. Cerium oxide nanoparticles may serve a useful role in diagnostics due to their ability to exist in a mixed valence state and act as either oxidizing agents or reducing agents. Considering that cerium oxide nanoparticles have been shown to shift in absorbance upon oxidation, a useful method of antimicrobial resistance detection could be based on the oxidation of cerium oxide nanoparticles. Herein, an assay is described whereby cerium oxide nanoparticle oxidation is a function of glucose metabolism of bacterial samples in the presence of an antimicrobial agent. Cerium oxide nanoparticles were shown to have an absorbance in the range of 395nm upon oxidation by hydrogen peroxide whereas mixed valence cerium oxide nanoparticles lacked an absorbance around 395nm. In the presence the hydrogen peroxide-producing glucose oxidase and either increasing concentrations of glucose or bacterial medium supplemented with increasing concentrations of glucose, cerium oxide nanoparticles were shown to increase in absorbance at 395nm. This oxidation assay was capable of measuring differences in the absorbance of E. coli and S. aureus samples grown in the presence of inhibitory and non-inhibitory concentrations of ampicillin in as little as six hours. Therefore, this cerium oxide nanoparticle oxidation assay may be very useful for use in clinical laboratories for the detection of antimicrobial resistance due to the relatively low cost, no requirement for specialized equipment and, most importantly, the reduced incubation time of the assay to as little as six hours compared to current gold standard antimicrobial resistance detection methods that require 24 hours. This assay may thus also help partially circumvent the issue of knowledge of antimicrobial resistance in infected patients before prescribing improper regimens.
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Date Issued: 2011
Identifier: CFH0003760, ucf:44780
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0003760

Title: PRODUCTION, CONTROL AND ACTUATION OF MICRON-SIZED PARTICLES IN AMICROFLUIDIC T-JUNCTION.
Creator: Wilson, James, Kumar, Ranganathan, University of Central Florida
Abstract / Description: This research is directed towards understanding the mechanisms associated with the manufacture of solid microspheres less than 100 [micro]m, from liquid droplets with nanosuspensions in a microfluidic T-junction, which are heated downstream of the channel. Preliminary material characterization tests on colloidal suspensions of alumina and copper oxide demonstrate promising temperature dependent viscosity results indicating solidification in the temperature range of 40degC-50degC. The...
Show moreThis research is directed towards understanding the mechanisms associated with the manufacture of solid microspheres less than 100 [micro]m, from liquid droplets with nanosuspensions in a microfluidic T-junction, which are heated downstream of the channel. Preliminary material characterization tests on colloidal suspensions of alumina and copper oxide demonstrate promising temperature dependent viscosity results indicating solidification in the temperature range of 40degC-50degC. The solidification mechanism is referred to as Temperature Induced Forming and is described by polymeric bridges formed between nanoparticles in suspension at elevated temperatures, resulting in a solid structure. The polymer network results from the ionization of alumina at elevated temperatures whereby polymeric binders adhere to newly formed charged sites on the alumina particle. This study aims to investigate the aspects of manufacturing microstructures in microfluidic Tjunctions, droplet morphology, size and frequency of production. Preliminary low solid concentration experiments (1%-10% volume concentration of alumina in H2O) have indicated solidification and a regression in droplet diameter when heated near the saturation temperature of the water used to disperse the particles. The microstructures from this solidification process are uniform and are estimated to be 30 [micro]m in size.
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Date Issued: 2013
Identifier: CFH0004387, ucf:44996
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004387

Title: Malondialdehyde (MDA) and Glutathione Peroxidase (GPx) are elevated in Crohns disease-associated with Mycobacterium avium subspecies paratuberculosis (MAP).
Creator: Qasem, Ahmad, Naser, Saleh, Masternak, Michal, Parthasarathy, Sampath, Andl, Claudia, University of Central Florida
Abstract / Description: Inflamed tissue in Crohn's disease (CD) are continuously producing toxic oxygen metabolites leading to cellular injury and apoptosis. Here, we are evaluating the role of Mycobacterium avium subspecies paratuberculosis (MAP) in oxidative stress in CD by evaluation of lipid peroxidation and antioxidant defense activity. Specifically, we measured malondialdehyde (MDA) level and selenium-dependent glutathione peroxidase (GPx) activity in the plasma from patients and cattle infected with MAP. The...
Show moreInflamed tissue in Crohn's disease (CD) are continuously producing toxic oxygen metabolites leading to cellular injury and apoptosis. Here, we are evaluating the role of Mycobacterium avium subspecies paratuberculosis (MAP) in oxidative stress in CD by evaluation of lipid peroxidation and antioxidant defense activity. Specifically, we measured malondialdehyde (MDA) level and selenium-dependent glutathione peroxidase (GPx) activity in the plasma from patients and cattle infected with MAP. The level of MAP antibodies in bovine sera was determined by IDEXX kit whereas detection of MAP DNA was performed by IS900-based nPCR. A total of 42 cattle (21 infected with MAP and 21 healthy controls), 27 CD subjects, 27 of CD-healthy relatives, 66 subjects with various diseases and 34 non-related healthy subjects were investigated. Overall, GPx activity was significantly higher in MAP infected humans (0.80941(&)#177;0.521) versus MAP (-ve) samples (0.42367(&)#177;0.229 units/ml), P(<)0.01. Similarly, the average of GPx activity in cattle infected with MAP was 1.59(&)#177;0.65 units/ml compared to 0.46907(&)#177;0.28 units/ml in healthy cattle (P(<)0.01). Although it was not statistically significant, MDA average level was higher in MAP infected human samples versus MAP (-ve) controls (1.11(&)#177;0.185 nmol/ml versus 0.805(&)#177;0.151 nmol/ml, respectively). Similarly, MDA average level in CD samples that are MAP+ (1.703(&)#177;0.231 nmol/ml) was higher than CD samples that are MAP (-ve) (1.429(&)#177;0.187 nmol/ml). In cattle, MDA average level in MAP infected samples was significantly higher at 3.818(&)#177;0.45 nmol/ml compared to 0.538(&)#177;0.18 nmol/ml in healthy cattle (P(<)0.01). Clearly, the data demonstrated that MAP infection is associated with oxidative stress and resulting in the pathophysiology of worsening of the condition of CD patients.
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Date Issued: 2016
Identifier: CFE0006699, ucf:51906
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006699

Title: COMPARATIVE STUDY OF ETHANOL AND METHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ALKALINE AND ACID SOLUTIONS: ELECTRO-CATALYTIC PERFORMANCE AND REACTION KINETICS.
Creator: Hidalgo, Carlos, Diaz, Diego, University of Central Florida
Abstract / Description: A comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by...
Show moreA comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by potentiodynamic and potentiostatic methods in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions at various concentrations of ethanol and methanol. The kinetics of ethanol and methanol on a Pt/ceria composite electrode were measured in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions using a rotating disk electrode (RDE). Cyclic voltammetry was employed in temperatures ranging from 15 to 55°C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. The temperature dependence of the electro-catalytic activities afforded the determination of apparent activation energies for ethanol and methanol oxidation.
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Date Issued: 2011
Identifier: CFE0003628, ucf:48853
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003628

Title: Transient Safe Operating Area (TSOA) for ESD applications.
Creator: Malobabic, Slavica, Liou, Juin, Shen, Zheng, Yuan, Jiann-Shiun, Vinson, James, University of Central Florida
Abstract / Description: A methodology to obtain design guidelines for gate oxide input pin protection and high voltage output pin protection in Electrostatic Discharge (ESD) time frame is developed through measurements and Technology Computer Aided Design (TCAD).A set of parameters based on transient measurements are used to define Transient Safe Operating Area (TSOA). The parameters are then used to assess effectiveness of protection devices for output and input pins.The methodology for input pins includes...
Show moreA methodology to obtain design guidelines for gate oxide input pin protection and high voltage output pin protection in Electrostatic Discharge (ESD) time frame is developed through measurements and Technology Computer Aided Design (TCAD).A set of parameters based on transient measurements are used to define Transient Safe Operating Area (TSOA). The parameters are then used to assess effectiveness of protection devices for output and input pins.The methodology for input pins includes establishing ESD design targets under Charged Device Model (CDM) type stress in low voltage MOS inputs.The methodology for output pins includes defining ESD design targets under Human Metal Model (HMM) type stress in high voltage Laterally Diffused MOS (LDMOS) outputs. First, the assessment of standalone LDMOS robustness is performed, followed by establishment of protection design guidelines. Secondly, standalone clamp HMM robustness is evaluated and a prediction methodology for HMM type stress is developed based on standardized testing. Finally, LDMOS and protection clamp parallel protection conditions are identified.
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Date Issued: 2012
Identifier: CFE0004405, ucf:49363
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004405

Title: NONLINEAR FEMTOSECOND NEAR INFRARED LASER STRUCTURING IN OXIDE GLASSES.
Creator: Royon, Arnaud, Richardson, Martin, University of Central Florida
Abstract / Description: Three-dimensional femtosecond laser structuring has a growing interest because of its ease of implementation and the numerous possible applications in the domain of photonic components. Structures such as waveguides, diffraction gratings, optical memories or photonic crystals can be fabricated thanks to this technique. Its use with oxide glasses is promising because of several advantages; they are resistant to flux and ageing, their chemical composition can easily be changed to fit the well...
Show moreThree-dimensional femtosecond laser structuring has a growing interest because of its ease of implementation and the numerous possible applications in the domain of photonic components. Structures such as waveguides, diffraction gratings, optical memories or photonic crystals can be fabricated thanks to this technique. Its use with oxide glasses is promising because of several advantages; they are resistant to flux and ageing, their chemical composition can easily be changed to fit the well-defined requirements of an application. They can already be found in Raman amplifiers, optical fibers, fiber lasers, and other devices. This thesis is based on two axes. The first axis consists in characterizing the linear and nonlinear optical properties of bulk vitreous materials in order to optimize their composition with a particular application in view. Within this context, the nonlinear optical properties, their physical origins (electronic and nuclear) as well as their characteristic response times (from a few femtoseconds to a few hundreds of picoseconds) are described within the Born-Oppenheimer approximation. Fused silica and several sodium-borophosphate glasses containing different concentrations in niobium oxide have been studied. Results show that the nonlinear optical properties of fused silica are mainly from electronic origin, whereas in the sodium-borophosphate glasses, the contribution from nuclear origin becomes predominant when the concentration of niobium oxide exceeds 30%. The second axis is based on the structuring of materials. Three commercially available fused silica samples presenting different fabrication conditions (therefore distinct impurity levels) and irradiated with a near infrared femtosecond laser have been studied. The laser induced defects have been identified by means of several spectroscopic techniques. They show the formation of color centers as well as a densification inside the irradiated area. Their linear refractive index and nonlinear third-order susceptibility properties have been measured. Moreover, the structuring of fused silica at the subwavelength scale into "nanogratings" is observed and the form of birefringence induced by these structures is discussed. In addition to the fused silica samples, several oxide glasses presenting very distinct chemical compositions have been studied. A sodium-borophosphate glass containing niobium oxide exhibits micro-cracks and nano-crystallites following irradiation. A silicate glass with or without a silver component reveals fluorescent rings or "nanograting" structures. A zinc phosphate glass containing silver also presents fluorescent ring structures, with a size of the order of 80 nm, well below the diffraction limit. Pump-probe microscope techniques have been performed on this glass to investigate the laser-glass interaction. The absorption mechanism is determined to be four-photon absorption. The generated free electron density is ~ 1017 cm-3, which suggests the conclusion that an electron gas rather than a plasma is formed during the laser irradiation.
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Date Issued: 2009
Identifier: CFE0002666, ucf:48200
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002666

Title: DENSITY FUNCTIONAL THEORY STUDY OF MOLECULES AND CRYSTALS CONTAINING D AND F METALS.
Creator: Gangopadhyay, Shruba, Masunov, Artem, University of Central Florida
Abstract / Description: Density Functional Theory (DFT) method is applied to study the crystal structure of transition metal and lanthanide oxides, as well as molecular magnetic complexes. DFT is a widely popular computational approach because it recasts a many-body problem of interacting electrons into an equivalent problem of non-interacting electrons, greatly reducing computational cost. We show that for certain structural properties like phase stability, lattice parameter and oxygen migration energetics pure DFT...
Show moreDensity Functional Theory (DFT) method is applied to study the crystal structure of transition metal and lanthanide oxides, as well as molecular magnetic complexes. DFT is a widely popular computational approach because it recasts a many-body problem of interacting electrons into an equivalent problem of non-interacting electrons, greatly reducing computational cost. We show that for certain structural properties like phase stability, lattice parameter and oxygen migration energetics pure DFT can give good agreement with experiments. But moving to more sensitive properties like spin state energetic certain modifications of standard DFT are needed. First we investigated mixed ionic-electronic conducting perovskite type oxides with a general formula ABO3 (where A =Ba, Sr, Ca and B = Co, Fe, Mn). These oxides often have high mobility of the oxygen vacancies and exhibit strong ionic conductivity. They are key materials that nd use in several energy related applications, including solid oxide fuel cell (SOFC), sensors, oxygen separation membranes, and catalysts. Different cations and oxygen vacancies ordering are examined using plane wave pseudopotential density functional theory. We nd that cations are completely disordered, whereas oxygen vacancies exhibit a strong trend for aggregation in L-shaped trimer and square tetramer structure. On the basis of our results, we suggest a new explanation for BSCF phase stability. Instead of linear vacancy ordering, which must take place before the phase transition into brownmillerite structure, the oxygen vacancies in BSCF prefer to form the nite clusters and preserve the disordered cubic structure. This structural feature could be found only in the rst-principles simulations and cannot be explained by the effect of the ionic radii alone. In order to understand vacancy clustering and phase stability in oxygen-deficient barium strontium cobalt iron oxide (BSCF), we predict stability and activation energies for oxygen vacancy migration. Using symmetry constrained search and Nudged Elastic Band method, we characterize the transition states for an oxygen anion moving into a nearby oxygen vacancy site that is surrounded by different cations and find the activation energies to vary in the range 30-50 kJ/mol in good agreement with experimental data. Next we study spin alignments of single molecule magnets (SMM). SMMs are a class of polynuclear transition metal complexes, which characterized by a large spin ground state and considerable negative anisotropy. These properties lead to a barrier for the reversal of magnetization. For these reasons SMM are expected to be promising materials for molecular spintronics and quantum computing applications. To design SMM for quantum computation, we need to accurately predict their magnetic properties. The most important property is, Heisenberg exchange coupling constant (J). This constant appears in model Heisenberg Hamiltonian that can be written in general form as here Jij represents the coupling between the two magnetic centers i and j with the spin states Si and Sj. The positive J values indicate the ferromagnetic ground state and the negative ones indicate the antiferromagnetic ground state. We found pure DFT is not accurate enough to predict J values. We employ density functionals with a Hubbard U term that helps to counteract the unphysical delocalization of electrons due to errors in pure exchange-correlation functionals. Unlike most previous DFT+U studies, we calibrate U parameters for both metal and ligand atoms using five binuclear manganese complexes as the benchmarks. We note delocalization of the spin density onto acetate ligands due to À-back bonding, inverting spin-polarization of the acetate oxygen atoms relative to that predicted from superexchange mechanism. This inversion may affect performance of the models assuming strict localization of the spins on magnetic centers for the complexes with bridging acetate ligands. Next, we apply DFT+U methodology for Mn12(mda) and Mn12(ada) complexes to calculate all six nearest neighbor Jij value. Our result shows both qualitative and quantitative agreement with experiments unlike other DFT studies. Using the optimized geometry of the ground spin state instead of less accurate experimental geometry was found to be crucial for this good agreement. The protocol tested in this study can be applied for the rational design of single-molecule magnets for molecular spintronics and quantum computing applications. Finally we apply hybrid DFT methodology to calculate geometrical parameters for cerium oxides. We review the experimental and computational studies on the cerium oxide nanoparticles, as well as stoichiometric phases of bulk ceria. Electroneutral and nonpolar pentalayers are identified as building blocks of type A sesqioxide structure. The idealized structure of the nanoparticles is described as dioxide covered by a single pentalayer of sesquioxide, which explains the exceptional stability of subsurface vacancies in nanoceria. The density functional theory (DFT) predictions of the lattice parameters and bulk moduli for the Ce(IV) and Ce(III) oxides at the hybrid DFT level are also presented. The calculated values for both compounds agree with experiment and allow to predict changes in the lattice parameter with decreasing size of the nanoparticles. The results validate hybrid DFT as a promising method for future study the structure of oxygen vacancies and catalytic properties of ceria nanoparticles.
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Date Issued: 2011
Identifier: CFE0003741, ucf:48762
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003741

Title: ADSORPTION BEHAVIOUR OF POLYACRYLIC ACID ON CERIUM OXIDE NANOSTRUCTURES: EXPERIMENTAL AND PREDICTIVE MODEL.
Creator: Haghighat Mesbahi, Ali, Seal, Sudipta, Fang, Jiyu, Bai, Yuanli, University of Central Florida
Abstract / Description: Cerium oxide-based slurries are crucial for chemical mechanical polishing (CMP) in electronic industry. For these slurry systems, poly(acrylic acid) (PAA) is heavily utilized to provide colloidal stability. Some of the important parameters in the colloid stability are molecular weight (MW) and concentration of stabilizer, size of the nanoparticle in the slurry and the pH of system. By determining the colloidal stability of a discrete number of slurry formulations and relating these to certain...
Show moreCerium oxide-based slurries are crucial for chemical mechanical polishing (CMP) in electronic industry. For these slurry systems, poly(acrylic acid) (PAA) is heavily utilized to provide colloidal stability. Some of the important parameters in the colloid stability are molecular weight (MW) and concentration of stabilizer, size of the nanoparticle in the slurry and the pH of system. By determining the colloidal stability of a discrete number of slurry formulations and relating these to certain slurry component parameters, a possible model can be produced to predict the influence of these parameters on the particle stability. Direct quantification of colloidal stability is difficult, however, polymer adsorption has been well established to correlate with the stability and therefore it can be used to quantify the colloidal stability.For the current thesis, surface area of cerium oxide, molecular weight of PAA, and the relative weight fraction of PAA were varied in two different nanomaterial systems, such as nanocubes and nanorods. To obtain the best fit of these variables, as they relate to polymer adsorption, fittings were performed using two advanced modeling techniques; namely, artificial neural network and adaptive neuro-fuzzy inference system. The precision of these techniques were compared each other and with the more simple, though largely imprecise, multi-variable linear regression. It was determined that the GENFIS-3 model shows the best performance for describing polymer adsorption on the nanocube and nanorod systems with an average relative deviation of only 6.5%. Additionally, these models suggest that the relative fraction of PAA has the most significant effect on the stability of cerium oxide-based CMP slurries. The greater precision of these advanced modeling methods can explain the better slurry performance with greater colloidal stability.
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Date Issued: 2015
Identifier: CFE0006315, ucf:51542
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006315

Title: The Study of Physiochemical Properties of Cerium Oxide Nanoparticles and its Application in Biosensors.
Creator: Barkam, Swetha, Seal, Sudipta, Heinrich, Helge, Gaume, Romain, University of Central Florida
Abstract / Description: Biosensors continue to get smaller and faster with the advancement in nanotechnology through the use of nanomaterials to achieve high sensitivity and selectivity. However, the continued reliance on biomolecules or enzymes in the biosensor assembly poses the problem of reproducibility, storage and complexity. This dissertation research address some of the challenges by investigating the physiochemical properties of nanoparticles to understand its interaction with biological systems and develop...
Show moreBiosensors continue to get smaller and faster with the advancement in nanotechnology through the use of nanomaterials to achieve high sensitivity and selectivity. However, the continued reliance on biomolecules or enzymes in the biosensor assembly poses the problem of reproducibility, storage and complexity. This dissertation research address some of the challenges by investigating the physiochemical properties of nanoparticles to understand its interaction with biological systems and develop enzyme free biosensors. In this study, we have demonstrated a novel strategy to integrate cerium oxide nanoparticles (CNPs) as an efficient transducer through rigorous screening for developing enzyme/label free biosensors for detecting analytes such as dopamine associated with neurodegenerative diseases and limonin for fruit quality management. CNPs have been proven to exhibit antioxidant properties attributed to its dynamic change in surface oxidation states (Ce4+ to Ce3+ and vice versa) mediated at the oxygen vacancies on the surface of the CNPs. It is also well-established that nanoparticles are resourceful novel materials with a plethora of applications in the field of nanomedicine.It is of significant importance to study the changes in physiochemical properties of different synthesized CNPs for effective use in biomedical applications. In one of the studies, the effects of different anions in the precursor of the cerium salts used for synthesizing CNPs using the same synthesis method, were extensively studied. It has been demonstrated that the physicochemical properties such as dispersion stability, hydrodynamic size, and the signature surface chemistry, antioxidant catalytic activity, oxidation potentials of different CNPs have been significantly altered with the change of anions in the precursor salts. . The increased antioxidant property of CNPs prepared using the precursor salts containing NO3(&)#175; and Cl(&)#175; ions have been extensively studied using in-situ UV-Visible spectroscopy which reveal that the change in oxidation potentials of CNPs with the change in concentration of anions. Thus, this work demonstrated that the physicochemical and antioxidant properties of CNPs can be tuned by anions of the precursor during the synthesis process.After standardizing the synthesis process, CNPs have been immobilized on highly ordered polymer nanopillars to develop an optical sensor for dopamine detection. Dopamine, is one of the main neurotransmitters which plays a significant role in central nervous system and its deficiency leads to neurological disorders such as Parkinson's disease, schizophrenia etc. Current biosensors in the literature use invasive detection techniques and lacks sensitivity to detect physiological clinically relevant concentrations of dopamine. The interaction between CNPs and dopamine have been extensively studied using UV-visible spectro-electrochemical studies to achieve the right surface chemistry (35-70% Ce4+). The sensor exhibits high sensitivity (1fM detection in simulated body fluid), high selectivity (in acetic acid, sheep plasma) and increased robustness with several cycles of usage.Furthermore, we have developed a CNPs based biosensor by integrating it on a transistor platform for improved sensitivity and better adhesion by immobilizing in silk fibroin matrix. In the final study, CNPs integrated in silk fibroin (SF) polymer electrospun nanofibers incorporated on an organic electrochemical transistor platform, is used to develop a limonin sensor. It has been established that the concentration of limonin in citric fruit predicts the quality in terms of bitter taste from the HLB bacteria infected fruits. A unique in-house electrospinning set-up using drum as collector was used to develop SF (extracted from cocoon) nanofibers used as CNP (synthesized in-situ in fibers) transducer carrier, both of which have a specific interaction with limonin. This novel biosensor has exhibited high sensitivity (100nM in PBS) and selectivity (citric acid, sugar etc.) with improved robustness in terms of reuse. The broader impact of the study is to develop holistic diagnostic non-invasive biosensors that can directly be used to detect the analytes using samples from humans and/or on field for fruit quality determination, which is a huge stepping stone in the advancement of nanotechnology based biosensors. This will fuel future generation of enzyme free biosensors which can utilize similar concepts for the detection of other analytes. The biosensor could be printed on a flexible substrate to advance wearable smart biosensor and could eventually enable users to wirelessly monitor the analyte concentrations using smartphones.
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Date Issued: 2017
Identifier: CFE0006931, ucf:51662
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006931

Title: Electronic Transport Investigation of Chemically Derived Reduced Graphene Oxide Sheets.
Creator: Joung, Daeha, Khondaker, Saiful, Chow, Lee, Leuenberger, Michael, Zhai, Lei, University of Central Florida
Abstract / Description: Reduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is...
Show moreReduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is of great significance for determining its potential application. In this dissertation, I demonstrate fabrication of high-yield solution based graphene field effects transistor (FET) using AC dielectrophoresis (DEP) and investigate the detailed electronic transport properties of the fabricated devices. The majority of the devices show ambipolar FET properties at room temperature. However, the mobility values are found to be lower than pristine graphene due to a large amount of residual defects in RGO sheets. I calculate the density of these defects by analyzing the low temperature (295 to 77K) charge transport data using space charge limited conduction (SCLC) with exponential trap distribution. At very low temperature (down to 4.2 K), I observe Coulomb blockade (CB) and Efros-Shklovskii variable range hopping (ES VRH) conduction in RGO implying that RGO can be considered as a graphene quantum dots (GQD) array, where graphene domains act like QDs while oxidized domains behave like tunnel barriers between QDs. This was further confirmed by studying RGO sheets of varying carbon sp2 fraction from 55 (-) 80 % and found that both the localization length and CB can be tuned. From the localization length and using confinement effect, we estimate tunable band gap of RGO sheets with varying carbon sp2 fraction. I then studied one dimensional RGO nanoribbon (RGONR) and found ES VRH and CB models are also applicable to the RGONR. However, in contrast to linear behavior of decrease in threshold voltage (Vt) with increasing temperature (T) in the RGO, sub linear dependence of Vt on T was observed in RGONR due to reduced transport pathways. Finally, I demonstrate synthesis and transport studies of RGO/nanoparticles (CdS and CeO2) composite and show that the properties of RGO can be further tuned by attaching the nanoparticles.
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Date Issued: 2012
Identifier: CFE0004785, ucf:49743
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004785

Title: Manufacturing of Single Solid Oxide Fuel Cells.
Creator: Torres-Caceres, Jonathan, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
Abstract / Description: Solid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials...
Show moreSolid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials and manufacturing methods is necessary to reduce costs and improve efficiency to make the technology commercially viable.The goal of the research is to optimize and simplify the production of single SOFCs using high performance ceramics. This includes the use of 8mol% Y2O3-ZrO2 (YSZ) and 10mol% Sc2O3-1mol%CeO2-ZrO2 (SCSZ) layered electrolytes which purport higher conductivity than traditional pure YSZ electrolytes. Prior to printing the electrodes onto the electrolyte, the cathode side of the electrolyte was coated with 20mol% Gd2O3-CeO2 (GDC). The GDC coating prevents the formation of a nonconductive La2Zr2O7 pyrochlore layer, which forms due to the interdiffusion of the YSZ electrolyte ceramic and the (La0.6Sr0.4)0.995Fe0.8Co0.2O3 (LSCF) cathode ceramic during sintering. The GDC layer was deposited by spin coating a suspension of 10wt% GDC in ethanol onto the electrolyte. Variation of parameters such as time, speed, and ramp rate were tested. Deposition of the electrodes onto the electrolyte surface was done by screen printing. Ink was produced using a three roll mill from a mixture of ceramic electrode powder, terpineol, and a pore former. The pore former was selected based on its ability to form a uniform well-connected pore matrix within the anode samples that were pressed and sintered. Ink development involved the production of different ratios of powder-to-terpineol inks to vary the viscosity. The different inks were used to print electrodes onto the electrolytes to gauge print quality and consistency. Cells were produced with varying numbers of layers of prints to achieve a desirable thickness. Finally, the densification behaviors of the major materials used to produce the single cells were studied to determine the temperatures at which each component needs to be sintered to achieve the desired density and to determine the order of electrode application, so as to avoid over-densification of the electrodes. Complete cells were tested at the National Energy Technology Laboratory in Morgantown, WV. Cells were tested in a custom-built test stand under constant voltage at 800(&)deg;C with 3% humidified hydrogen as the fuel. Both voltage-current response and impedance spectroscopy tests were conducted after initial startup and after 20 hours of operation. Impedance tests were performed at open circuit voltage and under varying loads in order to analyze the sources of resistance within the cell. A general increase in impedance was found after the 20h operation. Scanning electron micrographs of the cell microstructures found delamination and other defects which reduce performance. Suggestions for eradicating these issues and improving performance have been made.
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Date Issued: 2013
Identifier: CFE0004946, ucf:49641
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004946

Title: The Study of Photo-reduction of Cerium Oxide Nanoparticles in Presence of Dextran: An Attempt in Understanding the Functionality of the System.
Creator: Barkam, Swetha, Seal, Sudipta, Heinrich, Helge, Gaume, Romain, University of Central Florida
Abstract / Description: Malignant melanoma cancer is the sixth common cancer diagnosed in the United States. Surgery, chemotherapy and radiation are some of the successful techniques in killing tumor cells. However, in these techniques, it is not easy to distinguish tumor cells from the healthy once which inadvertently get exposed to chemical agent/radiation. Therefore it is required to develop an anti-cancer agent which selectively kills the cancer cells, while still protecting the normal tissues. In our...
Show moreMalignant melanoma cancer is the sixth common cancer diagnosed in the United States. Surgery, chemotherapy and radiation are some of the successful techniques in killing tumor cells. However, in these techniques, it is not easy to distinguish tumor cells from the healthy once which inadvertently get exposed to chemical agent/radiation. Therefore it is required to develop an anti-cancer agent which selectively kills the cancer cells, while still protecting the normal tissues. In our preliminary work, we have shown that Dextran (1000Da) coated Cerium oxide nanoparticles (Dex-CNPs) selectively kills the cancer cells (50% killing at a concentration of 150?M) without inducing toxicity to the normal cells. However, the mechanism involved on how CNPs/Dex-CNPs attain the selectivity and efficiently kill the tumor cells is still unknown. In this study we have synthesized Dextran coated ceria nano particles (Dex- CNPs) with different surface oxidation state ratio (Ce4+/Ce3+). This will provide an in depth understanding of the key chemical and physical properties of the system that can improve its efficacy. The varied surface oxidation of the particles is achieved by exposing Dex-CNPs to light which initiates a color change from dark to pale yellow indicating the reduction of Ce4+ to Ce3+. Interestingly we have found that the Dex-CNPs exposed to light have reduced cytotoxicity towards squamous cell carcinoma cell line (CCL30) compared to the protected once. Characterization of the same revealed that Dex- CNPs exposed to light have decreased Ce4+ /Ce3+ surface oxidation ratio compared to the other. This provides more insight in useful synthesis of Dex-CNPs in terms of storage and handling. In summary, higher Ce4+ /Ce3+ surface oxidation ratio is more efficient in hindering tumor growth by effectively hindering the tumor-stoma interaction.
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Date Issued: 2013
Identifier: CFE0005301, ucf:50508
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005301

Title: The Impact of Growth Conditions on Cubic ZnMgO Ultraviolet Sensors.
Creator: Boutwell, Ryan, Schoenfeld, Winston, Likamwa, Patrick, Kik, Pieter, Chernyak, Leonid, University of Central Florida
Abstract / Description: Cubic Zn1-xMgxO (c-Zn1-xMgxO) thin films have opened the deep ultraviolet (DUV) spectrum to exploration by oxide optoelectronic devices. These extraordinary films are readily wet-etch-able, have inversion symmetric lattices, and are made of common and safe constituents. They also host a number of new exciting experimental and theoretical challenges. Here, the relation between growth conditions of the c-Zn1-xMgxO film and performance of fabricated ultraviolet (UV) sensors is investigated....
Show moreCubic Zn1-xMgxO (c-Zn1-xMgxO) thin films have opened the deep ultraviolet (DUV) spectrum to exploration by oxide optoelectronic devices. These extraordinary films are readily wet-etch-able, have inversion symmetric lattices, and are made of common and safe constituents. They also host a number of new exciting experimental and theoretical challenges. Here, the relation between growth conditions of the c-Zn1-xMgxO film and performance of fabricated ultraviolet (UV) sensors is investigated. Plasma-Enhanced Molecular Beam Epitaxy was used to grow Zn1-xMgxO thin films and formation conditions were explored by varying the growth temperature, Mg source flux, oxygen flow rate, and radio-frequency (RF) power coupled into the plasma. Material review includes the effect of changing conditions on the film's optical transmission, surface morphology, growth rate, crystalline phase, and stoichiometric composition. Oxygen plasma composition was investigated by spectroscopic analysis under varying oxygen flow rate and applied RF power and is correlated to device performance. Ni/Mg/Au interdigitated metal-semiconductor-metal detectors were formed to explore spectral responsivity and UV-Visible rejection ratio (RR). Zn1-xMgxO films ranged in Mg composition from x = 0.45 - 1.0. Generally, x increased with increasing substrate temperature and Mg source flux, and decreased with increasing oxygen flow rate and RF power. Increasing x was correlated with decreased peak responsivity intensity and increased RR. Device performance was improved by increasing the ratio of O to O+ atoms and minimizing O2+ in the plasma. Peak responsivity as high as 500 A/W was observed in visible-blind phase-segregated Zn1-xMgxO devices, while cubic phase solar-blind devices demonstrated peak responsivity as high as 12.6 mA/W, and RR of three orders of magnitude. Optimal conditions are predicted for the formation of DUV Zn1-xMgxO sensors.
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Date Issued: 2013
Identifier: CFE0005087, ucf:50735
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005087

Title: PROBING AND TUNING THE SIZE, MORPHOLOGY, CHEMISTRY AND STRUCTURE OF NANOSCALE CERIUM OXIDE.
Creator: Kuchibhatla, Satyanarayana, Seal, Sudipta, University of Central Florida
Abstract / Description: Cerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be...
Show moreCerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be enhanced in the nanoceria. In most the practical scenarios, it is necessary to have a stable suspension of ceria nanoparticles (CNPs) over longer periods of time. However, the existing literature is confined to short term studies pertaining to synthesis and property evaluation. Having understood the need for a comprehensive understanding of the CNP suspensions, this dissertation is primarily aimed at understanding the behavior of CNPs in various chemical and physical environments. We have synthesized CNPs in the absence of any surfactants at room temperature and studied the aging characteristics. After gaining some understanding about the behavior of this functional oxide, the synthesis environment and aging temperature were varied, and their affects were carefully analyzed using various materials analysis techniques such as high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS). When the CNPs were aged at room temperature in as-synthesized condition, they were observed to spontaneously assemble and evolve as fractal superoctahedral structures. The reasons for this unique polycrystalline morphology were attributed to the symmetry driven assembly of the individual truncated octahedral and octahedral seed of the ceria. HRTEM and Fast Fourier Transform (FFT) analyses were used to explain the agglomeration behavior and evolution of the octahedral morphology. Some of the observations were supported by molecular dynamic simulations. Poly (ethylene glycol) (PEG) and ethylene glycol (EG) were used to control the kinetics of this morphology evolution. The ability to control the agglomeration of CNPs in these media stems from the lower dielectric constant and an increased viscosity of the EG and PEG based solvents. CNPs when synthesized and aged in frozen conditions, i.e. in ice, were found to form one dimensional, high aspect ratio structures. A careful analysis has provided some evidence that the CNPs use the porous channels in ice as a template and undergo oriented attachment to form nanorods. When the aging treatment was done near freezing temperature in solution, the nanorods were not observed, confirming the role of channels in ice. When synthesized in aqueous media such as DI water, PEG and EG; CNPs were observed to exhibit a reversible oxidation state switching between +3 and +4. Band gap values were computed from the optical absorption data. The changes in the band gap values observed were attributed to the changes in the oxidation state of CNPs as opposed to the quantum confinement effects, as expected in other nanoparticle systems. The work presented in this dissertation demonstrates, with evidence, that in order to obtain a comprehensive understanding of the properties of nanoscale materials it is of paramount importance to monitor their behavior over relatively longer periods of time under various ambient environments. While the solution based techniques offer a versatility and low cost route to study the fundamental properties of nanomaterials, they suffer some inherent problems such as precursor contamination and uncontrolled chemical reactions. Especially when analyzing the behavior of ceria-based materials for applications like solid oxide fuel cells, a great control in the density and crystalline quality are desired. In order to achieve this, as a first step pure ceria thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE). The ceria films were analyzed using various in situ and ex situ techniques to study the crystal structure, growth mode and epitaxial quality of the films. It was observed that the epitaxial orientation of the ceria films could be tuned by varying the deposition rate. When the films were grown at low deposition rate (< 8 Å/min) ceria films with epitaxial (200) orientation were observed where as the films grown at high deposition rates (up to 30 Å/min) showed (111) orientation. Theoretical simulations were used to confirm some of the experimental facts observed in both nanoparticles and thin films.
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Date Issued: 2008
Identifier: CFE0002163, ucf:47499
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002163

Title: CLASS-E CASCODE POWER AMPLIFIER ANALYSIS AND DESIGN FOR LONG TERM RELIABILITY.
Creator: Kutty, Karan, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description: This study investigated the Class-E power amplifier operating at 5.2 GHz. Since the operation of this amplifier applies a lot of stress on the switching transistor, a cascode topology was applied in order to reduce the drain-source voltage stress. Such an amplifier was designed and optimized in order to improve stability, power added efficiency, and matching. A layout for the said design was then created to be fabrication-ready using the TSMC 0.18 um technology. Post-layout simulations were...
Show moreThis study investigated the Class-E power amplifier operating at 5.2 GHz. Since the operation of this amplifier applies a lot of stress on the switching transistor, a cascode topology was applied in order to reduce the drain-source voltage stress. Such an amplifier was designed and optimized in order to improve stability, power added efficiency, and matching. A layout for the said design was then created to be fabrication-ready using the TSMC 0.18 um technology. Post-layout simulations were performed in order to realize a more realistic circuit performance with the layout design in mind. Long-term stress effects, such as oxide breakdown, on the key transistors were modeled and simulated in order to achieve an understanding of how leakage currents affect the overall circuit performance. Simulated results were compared and contrasted against theoretical understanding using derived equations. Recommendations for future advancements were made for modification and optimization of the circuit by the application of other stress reduction strategies, variation in the class-E topology, and improvement of the driver stage.
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Date Issued: 2010
Identifier: CFE0003360, ucf:48477
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003360

Title: Investigating Novel Water Treatment Methods and Monitoring Techniques for Sulfide-Laden Groundwater Supplies.
Creator: Yoakum, Benjamin, Duranceau, Steven, Lee, Woo Hyoung, Sadmani, A H M Anwar, Moore, Sean, University of Central Florida
Abstract / Description: This dissertation reports on research related to novel water treatment and monitoring techniques for sulfide-laden groundwater supplies. The dissertation is divided into several chapters with four core chapters focused on investigations studying a novel water treatment method or monitoring technique. The first investigation assessed the efficacy of multi-pass spray aeration treatment to remove trihalomethanes (THMs) and to reduce the total THM formation potential (TTHMFP) of an aerated water...
Show moreThis dissertation reports on research related to novel water treatment and monitoring techniques for sulfide-laden groundwater supplies. The dissertation is divided into several chapters with four core chapters focused on investigations studying a novel water treatment method or monitoring technique. The first investigation assessed the efficacy of multi-pass spray aeration treatment to remove trihalomethanes (THMs) and to reduce the total THM formation potential (TTHMFP) of an aerated water column post-aeration. A recirculating spray aeration pilot unit was constructed to make this assessment. To assess the effect of multi-pass spray aeration on the TTHMFP, water was recirculated through a fabricated spray nozzle for various lengths of time. Results showed that multi-pass spray aeration can remove chloroform, dichlorobromomethane, dibromochloromethane and bromoform to below detection levels ((<) 0.7 ppb) for the waters investigated. Additionally, spray aeration reduced the TTHMFP of chlorinated water. Results suggest multi-pass spray aeration may be a viable treatment option for some bromide container waters. Results also indicate that multi-pass spray aeration removes bromide from the bulk water in the form of organically bound volatile compounds.The second investigation assessed the efficacy of using pre-existing tray aeration infrastructure to comply with disinfection by-product (DBP) regulations. To assess the efficacy of tray aerators to reduce the concentration TTHMs a pilot tray aerator was constructed. Results showed that after five tray passes (each pass consisting of water being passed over five trays) the concentration of TTHMs was below the detection limit ((<) 0.7 ppb) for the water investigated. To assess the efficacy of tray aeration at full-scale, a water treatment plant and the distribution system it serves were monitored for eight months. Results showed an approximate 40 ppb reduction in the TTHM concentration at two on-site monitoring locations and the one off-site monitoring location (initial concentrations being approximately 54 ppb, 60 ppb and 73 ppb, respectively). Results suggest that the utility managing the full-scale system could comply with DBP regulations by using the pre-existing tray aeration infrastructure to reduce formed THMs on-site where regulated haloacetic acids are not predominant.The third investigation assessed the efficacy of using biological activated carbon (BAC) to remove disinfection by-product precursor matter to comply with DBP regulations. To research this method, a pilot scale BAC filter was operated for three independent test runs. In addition, two full-scale WTPs using BAC were monitored over time. Results showed an approximate 40 percent removal of dissolved organic carbon (DOC) during the three pilot runs and an approximate 55 percent removal of DOC during full-scale monitoring. Results showed that the reduction in DOC reduced the TTHMFP of BAC treated water. Results suggest that BAC treatment could be a viable treatment option to comply with DBP regulations in the sulfide-laden water studied.The fourth investigation assessed the suitability of oxidation reduction potential (ORP) to monitor the effectiveness of an oxidizing media filter used to remove sulfur from a sulfide-laden groundwater. Results showed that ORP was more useful as a measurement technique as compared to free chlorine residual when assessing filter bed health and regeneration effectiveness. It was determined that when the ORP measurement taken from within the oxidative media layer was below 500 mV, the filter bed was not providing treatment, and manganese could be released. Results showed a significant increase in turbidity ((>) 2 NTU) and total manganese ((>) 0.05 mg/L) occurred when the ORP within the filter bed dropped below 400 mV. More frequent cycling of the filters was found to be an effective treatment option to maintain ORP values above an identified 400 mV operational threshold.
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Date Issued: 2017
Identifier: CFE0007141, ucf:52317
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007141

graphene oxide (6)	+ -
oxidation (6)	+ -
graphene (5)	+ -
nanoparticles (5)	+ -
Modeling (4)	+ -

Nanoparticles (4)	+ -
cerium oxide nanoparticles (4)	+ -
Ceria (3)	+ -
Cerium Oxide (3)	+ -
Cerium oxide nanoparticles (3)	+ -
Ferrate (3)	+ -
Oxidation (3)	+ -
SOFC (3)	+ -
Solid Oxide Fuel Cells (3)	+ -
XRD (3)	+ -
catalysis (3)	+ -
cerium oxide (3)	+ -
chlorine dioxide (3)	+ -
iron (3)	+ -
potassium permanganate (3)	+ -
surface chemistry (3)	+ -
AFM (2)	+ -
Angiogenesis (2)	+ -
Catalysis (2)	+ -
Cerium Oxide Nanoparticles (2)	+ -
Cerium oxide (2)	+ -
Corrosion (2)	+ -
Disinfection by-products (2)	+ -
EXAFS (2)	+ -
Fuel Cells (2)	+ -

ETD Collection (83)	+ -
Honors Collection (7)	+ -

University of Central Florida (90)	+ -
Seal, Sudipta (15)	+ -
Zhai, Lei (13)	+ -
Heinrich, Helge (8)	+ -
Duranceau, Steven (7)	+ -

Orlovskaya, Nina (7)	+ -
Self, William (7)	+ -
Sundaram, Kalpathy (5)	+ -
Yuan, Jiann-Shiun (5)	+ -
An, Linan (4)	+ -
Blair, Richard (4)	+ -
Chopra, Manoj (4)	+ -
Lee, Woo Hyoung (4)	+ -
Raghavan, Seetha (4)	+ -
Schoenfeld, Winston (4)	+ -
Yestrebsky, Cherie (4)	+ -
Chow, Lee (3)	+ -
Clausen, Christian (3)	+ -
Das, Tuhin (3)	+ -
Gaume, Romain (3)	+ -
Kuebler, Stephen (3)	+ -
Kwok, Kawai (3)	+ -
Likamwa, Patrick (3)	+ -
Nam, Boo Hyun (3)	+ -
Parthasarathy, Sampath (3)	+ -
Randall, Andrew (3)	+ -
Reinhart, Debra (3)	+ -
Roldan Cuenya, Beatriz (3)	+ -
Sohn, Yongho (3)	+ -
Vaidyanathan, Raj (3)	+ -

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