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Title: Effects of Allotropic Transformations on Interdiffusion Behavior in Binary Systems.
Creator: Ewh, Ashley, Sohn, Yongho, Suryanarayana, Challapalli, Coffey, Kevin, University of Central Florida
Abstract / Description: Diffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding....
Show moreDiffusion plays a significant role in most materials systems by controlling microstructural development. Consequently, the overall properties of a material can be largely dependent upon diffusion. This study investigated the interdiffusion behavior of three binary systems, namely, Mo-Zr, Fe-Mo, and Fe-Zr. The main interest in these particular metals is for application in nuclear fuel assemblies. Nuclear fuel plates generally consist of two main components which are the fuel and the cladding. Due to diffusional interactions that can occur between these two components, a third is sometimes added between the fuel and cladding to serve as a diffusion barrier layer. Fe, Mo, and Zr can act as either cladding or barrier layer constituents and both Mo and Zr also serve as alloying additions in uranium based metallic fuels. Therefore, a fundamental understanding of the diffusional interactions in these systems is critical in predicting the performance and lifetime of these fuels. In order to study this diffusion behavior, a series of solid-to-solid diffusion couples were assembled between Fe, Mo, and Zr. These couples were then diffusion annealed isothermally for various predetermined times over a range of temperatures, including some both above and below the allotropic transformation temperatures for Fe and Zr. Following the diffusion anneal, the couples were water quenched, cross-sectioned, and prepared for microstructural and compositional characterization. A combination of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to obtain micrographs showing the microstructure and to collect compositional data for identifying intermediate phases and determining concentration profiles across the interdiffusion zone.Based on this characterization, the phases that developed in the diffusion zones were identified. In the Mo-Zr system, a large Zr solid solution layer developed in the couples annealed at and above 850(&)deg;C and a thin (~1-2 ?m) layer of Mo2Zr formed in all couples. Growth constants and concentration dependent interdiffusion coefficients were calculated for the Mo2Zr and Zr solid solution phases, respectively. In the Fe-Mo system, both the ?-Fe2Mo and ?-Fe7Mo6 phases were observed in couples annealed at 900(&)deg;C and below while ?-Fe7Mo6 and ?-Fe solid solution layers were observed in couples annealed above 900(&)deg;C. The relevant growth constants and activation energies for growth were calculated. In the Fe-Zr system, the couple annealed at 750(&)deg;C developed an FeZr2 and an FeZr3 layer while the couple annealed at 850(&)deg;C developed an Fe2Zr and Fe23Zr6 layer in the diffusion zone. The results of this analysis were then compared to available information from literature and the corresponding binary phase diagrams for each system. The results are discussed with respect to the effects of the allotropic transformations of Fe and Zr on the interdiffusion behavior in these systems.
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Date Issued: 2012
Identifier: CFE0004374, ucf:49422
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004374

Title: A Mixed-Methods Approach to Examining the Memphis Crisis Intervention Team (CIT) Model: An exploratory study of program effectiveness and institutionalization processes.
Creator: Magers, Megan, Potter, Roberto, Rosky, Jeffrey, Adams, Kenneth, Lin, Hefang, University of Central Florida
Abstract / Description: The present study utilized a mixed-methods strategy to examine the effectiveness, diffusion, and institutionalization of the Memphis Crisis Intervention Team (CIT) model. To evaluate the effectiveness of the training component of the CIT model, a panel research design was employed in which a sample of 179 law enforcement officers and 100 correctional officers in nine Florida counties were surveyed on the first day of training (pretest), the last day of training (posttest), and one month...
Show moreThe present study utilized a mixed-methods strategy to examine the effectiveness, diffusion, and institutionalization of the Memphis Crisis Intervention Team (CIT) model. To evaluate the effectiveness of the training component of the CIT model, a panel research design was employed in which a sample of 179 law enforcement officers and 100 correctional officers in nine Florida counties were surveyed on the first day of training (pretest), the last day of training (posttest), and one month following their completion of CIT training (follow-up). These surveys measured the extent to which CIT training achieved several officer-level objectives, including increased knowledge of mental illness and the mental health referral process, improved self-efficacy when responding to mental health crises, and enhanced perceptions of verbal de-escalation skills, mental health services in the community, and the mental health referral process. The results of these surveys revealed officers experienced a statistically significant increase on every measure of training effectiveness between the pretest and posttest data collection points. However, a significant decline was found among the 117 officers that responded to the follow-up survey on the measures associated with self-efficacy and perceptions of verbal de-escalation, which points to a measurable decay in the effectiveness of the training in the intermediate timeframe with regard to these two measures. To examine the extent to which the diffusion of the CIT model resembles a social movement in the field of criminal justice and to explore the impact of CIT institutionalization on the organizational structure of criminal justice agencies, an online survey was distributed to 33 representatives of law enforcement and correctional agencies known to participate in the CIT program in the nine Florida counties in which officers were surveyed. The results of this survey indicate interagency communication and external pressure from mental health providers and advocates largely contribute to the decision of criminal justice agencies to adopt the CIT model. In addition, the findings of this survey suggest criminal justice agencies modify their organizational structure in a number of different ways to internalize and institutionalize the CIT model. By coupling a training program evaluation with an assessment of diffusion and institutionalization, this study makes a unique contribution to organizational and evidence-based literature.
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Date Issued: 2013
Identifier: CFE0004884, ucf:49671
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004884

Title: STRUCTURAL, ELECTRONIC, VIBRATIONAL AND THERMODYNAMICAL PROPERTIES OF SURFACES AND NANOPARTICLES.
Creator: Yildirim, Handan, Rahman, Talat S., University of Central Florida
Abstract / Description: The main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the Ã‚Â"bottom-upÃ&...
Show moreThe main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the Ã‚Â"bottom-upÃ‚Â" approach for which the knowledge gathered at the scale of atoms and NPs serves as a base to build, at the macroscopic scale, materials with desired physical and chemical properties. We use a variety of theoretical and computational tools with different degrees of accuracy to study problems in different time and length scales. Interactions between the atoms are derived using both Density Functional Theory (DFT) and Embedded Atom Method (EAM), depending on the scale of the problem at hand. For some cases, both methods are used for the purpose of comparison. For revealing the local contributions to the vibrational dynamics and thermodynamics for the systems possessing site-specific environments, a local approach in real-space is used, namely Real Space GreenÃ‚Â's Function method (RSGF). For simulating diffusion of atoms/clusters and growth on metal surfaces, Molecular Statics (MS) and Molecular Dynamics (MD) methods are employed.
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Date Issued: 2010
Identifier: CFE0003064, ucf:48300
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003064

Title: AN INVESTIGATION OF COUNSELOR EDUCATORS' ATTITUDES TOWARDS EVIDENCE-BASED PRACTICES AND PERCEIVED BARRIERS TO THE INCORPORATION OF EVIDENCE-BASED PRACTICES IN COUNSELOR EDUCATION CURRICULA.
Creator: Patel, Samir, Hagedorn, Bryce, University of Central Florida
Abstract / Description: The overall purpose of this study was to investigate counselor educatorsÃ‚Â' attitudes towards evidence-based practices (EBPs) and perceived barriers to the inclusion of EBPs in counselor education curricula. Additionally, this study aimed to assess whether counselor educatorsÃ‚Â' level of agreement towards the presence of motivational interviewing (MI) principles in the counseling relationship impacted attitudes towards EBPs. As such, this...
Show moreThe overall purpose of this study was to investigate counselor educatorsÃ‚Â' attitudes towards evidence-based practices (EBPs) and perceived barriers to the inclusion of EBPs in counselor education curricula. Additionally, this study aimed to assess whether counselor educatorsÃ‚Â' level of agreement towards the presence of motivational interviewing (MI) principles in the counseling relationship impacted attitudes towards EBPs. As such, this researcher analyzed four research questions using two instruments and a demographic questionnaire. Two hundred sixty nine counselor educators (39.8% response rate) from the Association of Counselor Education and Supervision responded to an electronic survey, which consisted of the Evidence-Based Practice Attitude Scale (EBPAS; Aarons, 2004), the BARRIERS Scale (Funk, Champagne, Wiese, & Tornquist, 1991), and a demographic questionnaire. Specifically, this study investigated four research questions to determine: (a) the difference in attitude towards adopting EBPs among counselor educators with respect to specific individual factors (i.e. specialized training in evidence-based practices, years of professoriate experience, and primary counselor education focus); (b) the difference in perceived barriers towards adopting EBPs into counselor education curricula among counselor educators with respect to organizational factors (i.e. type of program, status of CACREP accreditation, and faculty position); (c) the influence of EBP attitude on perceived barriers to the inclusion of EBPs in counselor education curricula; and (d) the correlation between counselor educators reported level of agreement towards MI principlesÃ‚Â' presence in the counseling relationship and their attitude towards EBPs. Multivariate analyses of variance (MANOVA) were computed to analyze the data for the first two research questions, while linear regressions were utilized to compute the data for the last two research questions. In terms of individual factors, study results indicated that neither specialized training in EBPs nor years of professoriate experience resulted in significant differences with regards to attitudes towards EBPs. However, data analysis did reveal a significant difference between counselor educators with a clinical focus and counselor educators with a vocational focus. With regards to organizational factors influence on perceived barriers to the inclusion of EBPs in counselor education curricula, analyses revealed that neither CACREP accreditation nor faculty position resulted in any significant differences. Although, analysis did reveal that counselor educators in masters only programs perceived significantly less barriers to the inclusion of EBPs than did counselor educators in doctorate granting programs. Furthermore, results suggested a negative correlation between attitude towards EBPs and barriers towards the inclusion of EBPs in counselor education curricula, and a positive correlation between counselor educatorsÃ‚Â' agreement towards the inclusion of MI principles in the counseling relationship and their attitudes towards EBPs. Limitations of the study, implications for this study, and recommendations for future research as it relates to EBPs in counselor education and the counseling profession are addressed.
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Date Issued: 2010
Identifier: CFE0003063, ucf:48293
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003063

Title: Anthropogenic Organic Chemical Removal from a Surficial Groundwater and Mass Transfer Modeling in a Nanofiltration Membrane Process.
Creator: Jeffery, Samantha, Duranceau, Steven, Lee, Woo Hyoung, Sadmani, A H M Anwar, Yestrebsky, Cherie, University of Central Florida
Abstract / Description: This dissertation reports on research related to trace organic compounds (TrOCs) in surficial groundwater supplies and their subsequent removal from nanofiltration (NF) membranes. The research was conducted along coastal South Florida in cooperation with the Town of Jupiter Water Utilities, Jupiter, FL (Town). The focus of the research was to determine the extent of reclaimed water impacts on surficial groundwater supplies and subsequent effects on the Town's NF water treatment plant. Routine...
Show moreThis dissertation reports on research related to trace organic compounds (TrOCs) in surficial groundwater supplies and their subsequent removal from nanofiltration (NF) membranes. The research was conducted along coastal South Florida in cooperation with the Town of Jupiter Water Utilities, Jupiter, FL (Town). The focus of the research was to determine the extent of reclaimed water impacts on surficial groundwater supplies and subsequent effects on the Town's NF water treatment plant. Routine monitoring of fourteen TrOCs in reclaimed water and at the water treatment facility revealed varying degrees of TrOC detection in the environment. Certain TrOCs, including caffeine and DEET, were detected in a majority of the water sampling locations evaluated in this work. However, subsequent dilution with highly-treated reverse osmosis (RO) permeate from alternative supplies resulted in TrOCs below detection limits in potable water at the point-of-entry (POE). Pilot testing was employed to determine the extent of TrOC removal by NF. Prior to evaluating TrOC removal, hydraulic transients within the pilot process were first examined to determine the required length of time the pilot needed to reach steady-state. The transient response of a center-port NF membrane process was evaluated using a step-input dose of a sodium chloride solution. The pilot was configured as a two-stage, split-feed, center-exit, 7:2 pressure vessel array process, where the feed water is fed to both ends of six element pressure vessels, and permeate and concentrate streams are collected after only three membrane elements. The transient response was described as a log-logistic system with a maximum delay time of 285 seconds for an 85% water recovery and 267 gallon per minute feed flowrate.Eleven TrOC pilot unit experiments were conducted with feed concentrations ranging from 0.52 to 4,500 ?g/L. TrOC rejection was well-correlated with compound molecular volume and polarizability, with coefficient of determination (R2) values of 0.94. To enhance this correlation, an extensive literature review was conducted and independent literature sources were correlated with rejection. Literature citations reporting the removal effectiveness of an additional sixty-one TrOCs by loose NF membranes (a total of 95 data points) were found to be well-correlated with molecular volume and polarizability, with R2 values of 0.72 and 0.71, respectively.Of the TrOC's detected during this research, the anthropogenic solute caffeine was selected to be modeled using the homogeneous solution diffusion model (HSDM) and the HSDM with film theory (HSDM-FT). Mass transfer coefficients, K_w (water) K_s (caffeine), and k_b (caffeine back-transport) were determined experimentally, and K_s was also determined using the Sherwood correlation method. Findings indicate that caffeine transport through the NF pilot could be explained using experimentally determined K_s values without incorporating film theory, since the HSDM resulted in a better correlation between predicted and actual caffeine permeate concentrations compared to the HSDM-FT and the HSDM using K_s obtained using Sherwood applications. Predicted versus actual caffeine content was linearly compared, revealing R2 values on the order of 0.99, 0.96, and 0.99 for the HSDM without FT, HSDM-FT, and HSDM using a K_s value obtained using the Sherwood correlation method. However, the use of the HSDM-FT and the Sherwood number resulted in the over-prediction of caffeine concentrations in permeate streams by 27 percent and 104 percent, respectively.
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Date Issued: 2016
Identifier: CFE0006331, ucf:51545
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006331

Title: Modeling Mass Transfer and Assessing Cost and Performance of a Hollow Fiber Nanofiltration Membrane Process.
Creator: Yonge, David, Duranceau, Steven, Sadmani, A H M Anwar, Lee, Woo Hyoung, Clausen, Christian, University of Central Florida
Abstract / Description: Bench-scale water treatment testing of three next generation hollow-fiber (HF) nanofiltration (NF) membranes was conducted to characterize divalent ion rejection capabilities and investigate removal mechanisms. Existing mathematical models were investigated to describe solute transport using synthetic magnesium sulfate solutions including the size exclusion model, homogenous solution diffusion (HSD) model, dimensional analysis, and the HSD model incorporating film theory. Solute transport for...
Show moreBench-scale water treatment testing of three next generation hollow-fiber (HF) nanofiltration (NF) membranes was conducted to characterize divalent ion rejection capabilities and investigate removal mechanisms. Existing mathematical models were investigated to describe solute transport using synthetic magnesium sulfate solutions including the size exclusion model, homogenous solution diffusion (HSD) model, dimensional analysis, and the HSD model incorporating film theory. Solute transport for two of the membranes were described by HSD theory and were predictive of their 90% divalent ion removal. A third membrane was more accurately modeled using size exclusion and was found to be predictive of its 40% divalent ion rejection. Feed ionic strength variation was shown to significantly impact rejection. In this work, semi-empirical models were developed to describe solute transport under varying feed ionic strength conditions. Bench-scale testing of aerated groundwater confirmed the HFNF membrane divalent ion rejection capabilities. Pilot testing of a commercially available HFNF membrane was shown to remove divalent ions and dissolved organic carbon (DOC) by 10% and 25%, respectively. Financial evaluations indicated that HFNF offered cost savings over traditional spiral-wound (SW) NF, $0.60/kgal versus $0.85/kgal operating costs, respectively. Traditional SWNF membranes produced superior water quality achieving 90% divalent ion removal and 96% DOC removal but required media and membrane filtration pretreatment. When considering the costs of constructing a new 2 million gallon per day (permeate) HFNF process, conceptual cost comparisons revealed that HFNF technologies could reduce capital costs by approximately $1 million, and operating costs by $0.27/kgal for an 85% recovery plant.
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Date Issued: 2016
Identifier: CFE0006549, ucf:51346
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006549

Title: Theoretical And Computational Studies Of Diffusion Of Adatom Islands And Reactions Of Molecules On Surfaces.
Creator: Shah, Syed Islamuddin, Rahman, Talat, Kara, Abdelkader, Schelling, Patrick, Coffey, Kevin, University of Central Florida
Abstract / Description: The work presented in this dissertation focuses on the study of post deposition spatial and temporal evolution of adatom islands and molecules on surfaces using ab initio and semiemperical methods. It is a microscopic study of the phenomena of diffusion and reaction on nanostructured surfaces for which we have developed appropriate computational tools,as well as implemented others that are available. To map out the potential energy surface on which the adatom islands and molecules move, we...
Show moreThe work presented in this dissertation focuses on the study of post deposition spatial and temporal evolution of adatom islands and molecules on surfaces using ab initio and semiemperical methods. It is a microscopic study of the phenomena of diffusion and reaction on nanostructured surfaces for which we have developed appropriate computational tools,as well as implemented others that are available. To map out the potential energy surface on which the adatom islands and molecules move, we have carried out ab initio electronic structure calculations based on density functional theory (DFT) for selected systems. For others, we have relied on semiempirical interatomic potentials derived from the embedded atom method. To calculate the activation energy barriers, we have employed the (")drag(") method in most cases and verified its reliability by employing the more accurate nudged elastic band method for selected systems. Temporal and spatial evolution of the systems of interest have been calculated using the kinetic Monte Carlo (KMC), or the more accurate (complete) Self Learning kinetic Monte Carlo (SLKMC) method in the majority of cases, and ab initio molecular dynamics simulations in others. We have significantly enhanced the range of applicability of the SLKMC method by introducing a new pattern recognitionscheme which by allowing occupancy of the (")fcc(") and (")hcp(") sites (and inclusion of (")top(") site in the pattern recognition as well) is capable of simulating the morphological evolution of three dimensional adatom islands, a feature not feasible via the earlier - proposed SLKMC method. Using SLKMC (which allows only fcc site occupancy on fcc(111) surface), our results of the coarsening of Ag islands on the Ag(111) surface show that during early stages, coarsening proceeds as a sequence of selected island sizes, creating peaks and valleys in the island-size distribution. This island size selectivity is independent of initial conditions andresults from the formation of kinetically stable islands for certain sizes as dictated by the relative energetics of edge atom detachment/attachment processes together with the large activation barrier for kink detachment.On applying the new method, SLKMC-II, to examine the self diffusion of smalladatom islands (1-10 atoms) of Cu on Cu(111), Ag on Ag(111) and Ni on Ni(111), wefind that for the case of Cu and Ni islands, diffusion is dominated by concerted processes(motion of island as a whole), whereas in the case of Ag, islands of size 2-9 atoms diffusethrough concerted motion whereas the 10-atom island diffuses through single atom processes.Effective energy barriers for the self diffusion of these small Cu islands is 0.045 eV/atom,for Ni it is 0.060 eV/atom and for Ag it is 0.049 eV/atom, increasing almost linearly withisland size.Application of DFT based techniques have allowed us to address a few issues stemmingfrom experimental observations on the effect of adsorbates such as CO on the structure and stability of bimetallic systems (nanoparticles and surfaces). Total energy calculationsof Ni-Au nanoparticles show Ni atoms to prefer to be in the interior of the nanoparticle.CO molecules, however, prefer to bind to a Ni atom if present on the surface. Using abinitio molecular dynamics simulations, we confirm that the presence of CO molecule induces diffusion of Ni atom from the core of the Ni-Au nanoparticle to its surface, making the nanoparticle more reactive. These results which help explain a set of experimental data are rationalized through charge transfer analysis.Similar to the case of Ni-Au system, it is found that methoxy (CH$_{3}$O) may also induce diffusion of inner atoms to the surface on bimetallic Au-Pt systems. Our total energy DFT calculations show that it is more favorable for methoxy to bind to a Pt atom in the top Au layer than to a Au atom in Au-Pt system thereby explaining experimental observations.To understand questions related to the dependence of product selectivity on ambientpressure for ammonia decomposition on RuO2(110), we have carried out an extensivecalculation of the reaction pathways and energy barriers for a large number of intermediate products. On combining the reaction energetics from DFT, with KMC simulations, we showthat under UHV conditions, selectivity switches from N2 ( ? 100 % selectivity) at T = 373Kto NO at T = 630K, whereas under ambient conditions, N2 is still the dominant productbut maximum selectivity is only 60%. An analysis based on thermodynamics alone shows a contradiction between experimental data at UHV with those under ambient pressure. Ourcalculations of the reaction rates which are essential for KMC simulations removes this apparentinconsistency and stresses the need to incorporate kinetics of processes in order toextract information on reaction selectivity.
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Date Issued: 2013
Identifier: CFE0005254, ucf:50584
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005254

Title: INTERDIFFUSION BEHAVIOR OF U-MO ALLOYS IN CONTACT WITH AL AND AL-SI ALLOYS.
Creator: Perez, Emmanuel, Sohn, Yong-Ho, University of Central Florida
Abstract / Description: U-Mo dispersion and monolithic fuels embedded in Al-alloy matrix are under development to fulfill the requirements of research reactors to use low-enriched molybdenum stabilized uranium alloys as fuels. The system under consideration in this study consisted of body centered cubic (gamma) U-Mo alloys embedded in an Al structural matrix. Significant interaction has been observed to take place between the U-Mo fuel and the Al matrix during manufacturing of the fuel-plate system assembly and...
Show moreU-Mo dispersion and monolithic fuels embedded in Al-alloy matrix are under development to fulfill the requirements of research reactors to use low-enriched molybdenum stabilized uranium alloys as fuels. The system under consideration in this study consisted of body centered cubic (gamma) U-Mo alloys embedded in an Al structural matrix. Significant interaction has been observed to take place between the U-Mo fuel and the Al matrix during manufacturing of the fuel-plate system assembly and during irradiation in reactors. These interactions produce Al-rich phases with physical and thermal properties that adversely affect the performance of the fuel system and can lead to premature failure. In this study, interdiffusion and microstructural development in the U-Mo vs. Al system was examined using solid-to-solid diffusion couples consisting of U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. pure Al, annealed at 600°C for 24 hours. The influence of Si alloying addition (up to 5 wt.%) in Al on the interdiffusion microstructural development was also examined using solid-to-solid diffusion couples consisting of U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. pure Al, Al-2wt.%Si, and Al-5wt.%Si annealed at 550°C for 1, 5 and 20 hours. To further clarify the diffusional behavior in the U-Mo-Al and U-Mo-Al-Si systems, Al-rich 85.7Al-11.44U-2.86Mo, 87.5Al-10U-2.5Mo, 56.1Al-18.9Si-21.9U-3.1Mo and 69.3Al-11.9Si-18.8U (at.%) alloys were cast and homogenized at 500°C to determine the equilibrium phases of the system. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) and X-ray diffraction (XRD) were employed to examine the phase development in the diffusion couples and the cast alloys. In ternary U-Mo-Al diffusion couples annealed at 600°C for 24 hours, the interdiffusion microstructure consisted of finely dispersed UAl3, UAl4, U6Mo4Al43, and UMo2Al20 phases while the average composition throughout the interdiffusion zone remained constant at approximately 80 at.% Al. The interdiffusion microstructures observed by EPMA, SEM and TEM analyses were correlated to explain the observed morphological development in the interdiffusion zones. The concept of thermodynamic degrees of freedom was used to justify that, although deviations are apparent, the interdiffusion zones did not significantly deviate from an equilibrium condition in order for the observed microstructures to develop. Selected diffusion couples developed periodic bands within the interdiffusion zone as sub-layers in the three-phase regions. Observation of periodic banding was utilized to augment the hypothesis that internal stresses play a significant role in the phase development and evolution of U-Mo vs. pure Al diffusion couples. The addition of Si (up to 5 wt.%) to the Al significantly reduced the growth rate of the interdiffusion zone. The constituent phases and composition within the interdiffusion zone were also modified. When Si was present in the Al terminal alloys, the interdiffusion zones developed layered morphologies with fine distributions of the (U,Mo)(Al,Si)3 and UMo2Al20 phases. The U6Mo4Al43 phase was observed scarcely in Si depleted regions within the interdiffusion zone. The phase development and evolution of the interdiffusion zone was described in terms of thermodynamic degrees of freedom with minimal deviations from equilibrium.
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Date Issued: 2011
Identifier: CFE0003747, ucf:48778
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003747

Title: ELECTRON INJECTION-INDUCED EFFECTS IN III-NITRIDES: PHYSICS AND APPLICATIONS.
Creator: Burdett, William Charles, Chernyak, Leonid, University of Central Florida
Abstract / Description: This research investigated the effect of electron injection in III-Nitrides. The combination of electron beam induced current and cathodoluminescence measurements was used to understand the impact of electron injection on the minority carrier transport and optical properties. In addition, the application of the electron injection effect in optoelectronic devices was investigated.The impact of electron injection on the minority carrier diffusion length was studied at various temperatures in Mg...
Show moreThis research investigated the effect of electron injection in III-Nitrides. The combination of electron beam induced current and cathodoluminescence measurements was used to understand the impact of electron injection on the minority carrier transport and optical properties. In addition, the application of the electron injection effect in optoelectronic devices was investigated.The impact of electron injection on the minority carrier diffusion length was studied at various temperatures in Mg-doped p-GaN, p-AlxGa1-xN, and p-AlxGa1-x N/GaN superlattices. It was found that the minority carrier diffusion length experienced a multi-fold linear increase and that the rate of change of the diffusion length decreased exponentially with increasing temperature. The effect was attributed to a temperature-activated release of the electrons, which were trapped by the Mg levels.The activation energies for the electron injection effect in the Mg-doped (Al)GaN samples were found to range from 178 to 267 meV, which is close to the thermal ionization energy of the Mg acceptor. The activation energy observed for Al0.15Ga0.85N and Al0.2Ga0.8N was consistent with the deepening of the Mg acceptor level due to the incorporation of Al into the GaN lattice. The activation energy in the homogeneously doped Al0.2Ga0.8N/GaN superlattice indicates that the main contribution to the electron injection effect comes from the capture of injected electrons by the wells (GaN). The electron injection effect was successfully applied to GaN doped with an impurity (Mn) other than Mg. Electron injection into Mn-doped GaN resulted in a multi-fold increase of the minority carrier diffusion length and a pronounced decrease in the band-to-band cathodoluminescence intensity. The activation energy due to the electron injection effect was estimated from temperature-dependent cathodoluminescence measurements to be 360 meV. The decrease in the band-to-band cathodoluminescence is consistent with an increase in the diffusion length and these results are attributed to an increase in the minority carrier lifetime due to the trapping of injected electrons by the Mn levels.A forward bias was applied to inject electrons into commercially built p-i-n and Schottky barrier photodetectors. Up to an order of magnitude increase in the peak (360 nm) responsivity was observed. The enhanced photoresponse lasted for over four weeks and was attributed to an electron injection-induced increase of the minority carrier diffsuion length and the lifetime.
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Date Issued: 2004
Identifier: CFE0000080, ucf:46109
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000080

Title: MYSPACE OR OURSPACE: A MEDIA SYSTEM DEPENDENCY VIEW OF MYSPACE.
Creator: Schrock, Andrew, Brown, Timothy, University of Central Florida
Abstract / Description: MySpace is a type of "social networking" website where people meet, socialize, and create friendships. The way MySpace members, particularly younger individuals, interact online underscores the changing nature of mass media. Media system dependency states that individuals become reliant on media in their daily life because of fundamental human goals. This reliance, termed a dependency, leads to repeated use. Media system dependency was applied in the current study to explain how and why...
Show moreMySpace is a type of "social networking" website where people meet, socialize, and create friendships. The way MySpace members, particularly younger individuals, interact online underscores the changing nature of mass media. Media system dependency states that individuals become reliant on media in their daily life because of fundamental human goals. This reliance, termed a dependency, leads to repeated use. Media system dependency was applied in the current study to explain how and why individuals became habitual MySpace users. To attain results a survey was administered to a convenience sampling of 401 adult undergraduates at the University of Central Florida. Members reported MySpace dependency had a moderate correlation to MySpace use, and they actively used the website an average of 1.3 hours of use per day. Results indicated members use MySpace to primarily satisfy play and interaction orientation dependencies. MySpace use was found to have a correlation with number of MySpace friends. "Number of friends created" in turn had a correlation with MySpace dependency, as people returned to interact with their friends. Individual factors were also found to be a source of influence in MySpace dependency. These individual factors were demographics, psychological factors related to use of the Internet, and psychological factors related to use of MySpace. Factors related to MySpace, extroversion and self-disclosure, were positively correlated with intensity of dependency. The influence of factors related to the Internet was partly supported; computer self-efficacy was not significantly related to MySpace dependency, while computer anxiety was significantly related to MySpace dependency. Speed of connection to the Internet and available time to use the Internet were not related to MySpace dependency. Additionally, significant differences were found between genders in overall dependency, extroversion, self-disclosure, computer anxiety, and computer self-efficacy. These findings provide evidence that MySpace members were little, if at all, constrained by factors related to use of the Internet, but were attracted to the websites for similar reasons as real-life relationships. Finally, MySpace is just one of the large number of online resources that are predominantly social, such as email, message boards, and online chat. This study found that through a "technology cluster" MySpace members use these other social innovations more frequently than non-members. However, members also used significantly more non-social innovations, which may indicate that MySpace members are part of a larger technology cluster than anticipated or perhaps are in the same category of innovation adopter.
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Date Issued: 2006
Identifier: CFE0001451, ucf:47057
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001451

Title: THE EFFECT OF COLLOIDAL STABILITY ON THE HEAT TRANSFER CHARACTERISTICS OF NANOSILICA DISPERSED FLUIDS.
Creator: Venkataraman, Manoj, Kumar, Ranganathan, University of Central Florida
Abstract / Description: Addition of nano particles to cooling fluids has shown marked improvement in the heat transfer capabilities. Nanofluids, liquids that contain dispersed nanoparticles, are an emerging class of fluids that have great potential in many applications. There is a need to understand the fundamental behavior of nano dispersed particles with respect to their agglomeration characteristics and how it relates to the heat transfer capability. Such an understanding is important for the development and...
Show moreAddition of nano particles to cooling fluids has shown marked improvement in the heat transfer capabilities. Nanofluids, liquids that contain dispersed nanoparticles, are an emerging class of fluids that have great potential in many applications. There is a need to understand the fundamental behavior of nano dispersed particles with respect to their agglomeration characteristics and how it relates to the heat transfer capability. Such an understanding is important for the development and commercialization of nanofluids. In this work, the stability of nano particles was studied by measuring the zeta potential of colloidal particles, particle concentration and size. Two different sizes of silica nano particles, 10 nm and 20 nm are used in this investigation at 0.2 vol. % and 0.5 vol. % concentrations. The measurements were made in deionized (DI) water, buffer solutions at various pH, DI water plus HCl acid solution (acidic pH) and DI water plus NaOH solution (basic pH). The stability or instability of silica dispersions in these solutions was related to the zeta potential of colloidal particles and confirmed by particle sizing measurements and independently by TEM observations. Low zeta potentials resulted in agglomeration as expected and the measured particle size was greater. The heat transfer characteristics of stable or unstable silica dispersions using the above solutions were experimentally determined by measuring heat flux as a function of temperature differential between a nichrome wire and the surrounding fluid. These experiments allowed the determination of the critical heat flux (CHF), which was then related to the dispersion characteristics of the nanosilica in various fluids described above. The thickness of the diffuse layer on nano particles was computed and experimentally confirmed in selected conditions for which there was no agglomeration. As the thickness of the diffuse layer decreased due to the increase in salt content or the ionic content, the electrostatic force of repulsion cease to exist and Van der Waal's force of agglomeration prevailed causing the particles to agglomerate affecting the CHF. The 10nm size silica particle dispersions showed better heat transfer characteristics compared to 20nm dispersion. It was also observed that at low zeta potential values, where agglomeration prevailed in the dispersion, the silica nano particles had a tendency to deposit on the nickel chromium wire used in CHF experiments. The thickness of the deposition was measured and the results show that with a very high deposition, CHF is enhanced due to the porosity on the wire. The 10nm size silica particles show higher CHF compared to 20nm silica particles. In addition, for both 10nm and 20nm silica particles, 0.5 vol. % concentration yielded higher heat transfer compared to 0.2 vol. % concentration. It is believed that although CHF is significantly increased with nano silica containing fluids compared to pure fluids, formation of particle clusters in unstable slurries will lead to detrimental long time performance, compared to that with stable silica dispersions.
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Date Issued: 2005
Identifier: CFE0000837, ucf:46676
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000837

Title: Theoretical Studies of Nanostructure Formation and Transport on Surfaces.
Creator: Aminpour, Maral, Rahman, Talat, Stolbov, Sergey, Roldan Cuenya, Beatriz, Blair, Richard, University of Central Florida
Abstract / Description: This dissertation undertakes theoretical and computational research to characterize and understand in detail atomic configurations and electronic structural properties of surfaces and interfaces at the nano-scale, with particular emphasis on identifying the factors that control atomic-scale diffusion and transport properties. The overarching goal is to outline, with examples, a predictive modeling procedure of stable structures of novel materials that, on the one hand, facilitates a better...
Show moreThis dissertation undertakes theoretical and computational research to characterize and understand in detail atomic configurations and electronic structural properties of surfaces and interfaces at the nano-scale, with particular emphasis on identifying the factors that control atomic-scale diffusion and transport properties. The overarching goal is to outline, with examples, a predictive modeling procedure of stable structures of novel materials that, on the one hand, facilitates a better understanding of experimental results, and on the other hand, provide guidelines for future experimental work. The results of this dissertation are useful in future miniaturization of electronic devices, predicting and engineering functional novel nanostructures. A variety of theoretical and computational tools with different degrees of accuracy is used to study problems in different time and length scales. Interactions between the atoms are derived using both ab-initio methods based on Density Functional Theory (DFT), as well as semi-empirical approaches such as those embodied in the Embedded Atom Method (EAM), depending on the scale of the problem at hand. The energetics for a variety of surface phenomena (adsorption, desorption, diffusion, and reactions) are calculated using either DFT or EAM, as feasible. For simulating dynamic processes such as diffusion of ad-atoms on surfaces with dislocations the Molecular Dynamics (MD) method is applied. To calculate vibrational mode frequencies, the infinitesimal displacement method is employed. The combination of non-equilibrium Green's function (NEGF) and DFT is used to calculate electronic transport properties of molecular devices as well as interfaces and junctions.
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Date Issued: 2013
Identifier: CFE0005298, ucf:50504
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005298

Title: An Investigation of Boaters' Attitudes toward and Usage of Targeted Mobile Apps.
Creator: Bowerman, Kamra, Delorme, Denise, Brown, Timothy, Neuberger, Lindsay, University of Central Florida
Abstract / Description: The purpose of this study was to understand boaters' adoption and usage of smartphones and mobile apps as well as to obtain their opinion on potential features of a targeted mobile app being developed as part of a broader interdisciplinary Florida Sea Grant outreach project. Data were gathered from an online survey of a sample of 164 boaters from the surrounding Central Florida area. In contrast with previous empirical mobile app studies, many respondents reported using mobile apps for...
Show moreThe purpose of this study was to understand boaters' adoption and usage of smartphones and mobile apps as well as to obtain their opinion on potential features of a targeted mobile app being developed as part of a broader interdisciplinary Florida Sea Grant outreach project. Data were gathered from an online survey of a sample of 164 boaters from the surrounding Central Florida area. In contrast with previous empirical mobile app studies, many respondents reported using mobile apps for information-seeking versus escape gratifications. Further more than half of the respondents' age sixty-five and over indicated using smartphones and mobile apps. These findings reflected recent national trend data showing shifting gratifications and an increase in technology use among older American adults. In regards to the planned mobile app, the study's respondents had favorable reactions to its potential features and indicated an above average intent toward downloading the app.
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Date Issued: 2013
Identifier: CFE0004655, ucf:49902
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004655

Title: computational study of traveling wave solutions and global stability of predator-prey models.
Creator: Zhu, Yi, Qi, Yuanwei, Rollins, David, Shuai, Zhisheng, Zhai, Lei, University of Central Florida
Abstract / Description: In this thesis, we study two types of reaction-diffusion systems which have direct applications in understanding wide range of phenomena in chemical reaction, biological pattern formation and theoretical ecology.The first part of this thesis is on propagating traveling waves in a class of reaction-diffusion systems which model isothermal autocatalytic chemical reactions as well as microbial growth and competition in a flow reactor. In the context of isothermal autocatalytic systems, two...
Show moreIn this thesis, we study two types of reaction-diffusion systems which have direct applications in understanding wide range of phenomena in chemical reaction, biological pattern formation and theoretical ecology.The first part of this thesis is on propagating traveling waves in a class of reaction-diffusion systems which model isothermal autocatalytic chemical reactions as well as microbial growth and competition in a flow reactor. In the context of isothermal autocatalytic systems, two different cases will bestudied. The first is autocatalytic chemical reaction of order $m$ without decay. The second is chemical reaction of order $m$ with a decay of order $l$, where $m$ and $l$ are positive integers and $m(>)l\ge1$. A typical system is $A + 2B \rightarrow3B$ and $B\rightarrow C$ involving three chemical species, a reactant A and an auto-catalyst B and C an inert chemical species.We use numerical computation to give more accurate estimates on minimum speed of traveling waves for autocatalytic reaction without decay, providing useful insight in the study of stability of traveling waves. For autocatalytic reaction of order $m = 2$ with linear decay $l = 1$, which hasa particular important role in biological pattern formation, it is shown numerically that there exist multiple traveling waves with 1, 2 and 3 peaks with certain choices of parameters.The second part of this thesis is on the global stability of diffusive predator-prey system of Leslie Type and Holling-Tanner Type in a bounded domain $\Omega\subset R^N$ with no-flux boundary condition. By using a new approach, we establish much improved global asymptotic stability of a unique positiveequilibrium solution. We also show the result can be extended to more general type of systems with heterogeneous environment and/or other kind of kinetic terms.
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Date Issued: 2016
Identifier: CFE0006519, ucf:51359
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006519

Title: A Holistic Analysis of the Long-Term Challenges (&) Potential Benefits of the Green Roof, Solar PV Roofing, and GRIPV Roofing Markets in Orlando, Florida.
Creator: Kelly, Carolina, Tatari, Omer, Oloufa, Amr, Mayo, Talea, Zheng, Qipeng, University of Central Florida
Abstract / Description: Green roofs and roof-mounted solar PV arrays have a wide range of environmental and economic benefits, including significantly longer roof lifetimes, reductions in urban runoff, mitigation of the urban heat island (UHI) effect, reduced electricity demand and energy dependence, and/or reduced emissions of greenhouse gases (GHGs) and other harmful pollutants from the electricity generation sector. Consequently, green roofs and solar panels have both become increasingly popular worldwide, and...
Show moreGreen roofs and roof-mounted solar PV arrays have a wide range of environmental and economic benefits, including significantly longer roof lifetimes, reductions in urban runoff, mitigation of the urban heat island (UHI) effect, reduced electricity demand and energy dependence, and/or reduced emissions of greenhouse gases (GHGs) and other harmful pollutants from the electricity generation sector. Consequently, green roofs and solar panels have both become increasingly popular worldwide, and promising new research has emerged for their potential combination in Green Roof Integrated Photovoltaic (GRIPV) roofing applications. However, due to policy resistance, these alternatives still have marginal market shares in the U.S., while GRIPV research and development is still severely limited today. As a result, these options are not yet sufficiently widespread in the United States as to realize their full potential, particularly due to a variety of policy resistance effects with respect to each specific alternative. The steps in the System Dynamics (SD) methodology to be used in this study are summarized as follows. First, based on a comprehensive review of relevant literature, a causal loop diagram (CLD) will be drawn to provide a conceptual illustration of the modeled system. Second, based on the feedback relationships observed in this CLD, a stock-flow diagram (SFD) will be developed to form a quantitative model. Third, the modeled SFD will be tested thoroughly to ensure its structural and behavioral validity with respect to the modeled system in reality using whatever real world data is available. Fourth, different policy scenarios will be simulated within the model to evaluate their long-term effectiveness. Fifth, uncertainty analyses will be performed to evaluate the inherent uncertainties associated with the analyses in this study. Finally, the results observed for the analyses in this study and possible future research steps will be discussed and compared as appropriate.
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Date Issued: 2018
Identifier: CFE0007406, ucf:52741
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007406

Title: Design and Characterization of High Temperature Packaging for Wide-Bandgap Semiconductor Devices.
Creator: Grummel, Brian, Shen, Zheng, Sundaram, Kalpathy, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description: Advances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor...
Show moreAdvances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor device packaging with high reliability at high temperatures is necessary. Transient liquid phase (TLP) die-attach has shown in literature to be a promising bonding technique for this packaging need. In this work TLP has been comprehensively investigated and characterized to assess its viability for high-temperature power electronics applications. The reliability and durability of TLP die-attach was extensively investigated utilizing electrical resistivity measurement as an indicator of material diffusion in gold-indium TLP samples. Criteria of ensuring diffusive stability were also developed. Samples were fabricated by material deposition on glass substrates with variant Au(-)In compositions but identical barrier layers. They were stressed with thermal cycling to simulate their operating conditions then characterized and compared. Excess indium content in the die-attach was shown to have poor reliability due to material diffusion through barrier layers while samples containing suitable indium content proved reliable throughout the thermal cycling process. This was confirmed by electrical resistivity measurement, EDS, FIB, and SEM characterization. Thermal and mechanical characterization of TLP die-attached samples was also performed to gain a newfound understanding of the relationship between TLP design parameters and die-attach properties. Samples with a SiC diode chip TLP bonded to a copper metalized silicon nitride substrate were made using several different values of fabrication parameters such as gold and indium thickness, Au(-)In ratio, and bonding pressure. The TLP bonds were then characterized for die-attach voiding, shear strength, and thermal impedance. It was found that TLP die-attach offers high average shear force strength of 22.0 kgf and a low average thermal impedance of 0.35 K/W from the device junction to the substrate. The influence of various fabrication parameters on the bond characteristics were also compared, providing information necessary for implementing TLP die-attach into power electronic modules for high-temperature applications. The outcome of the investigation on TLP bonding techniques was incorporated into a new power module design utilizing TLP bonding. A full half-bridge inverter power module for low-power space applications has been designed and analyzed with extensive finite element thermo-mechanical modeling. In summary, TLP die-attach has investigated to confirm its reliability and to understand how to design effective TLP bonds, this information has been used to design a new high-temperature power electronic module.
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Date Issued: 2012
Identifier: CFE0004499, ucf:49276
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004499

Title: Analysis of steady state micro-droplet evaporation to enhance heat dissipation from tiny surfaces.
Creator: Voota, Harish, Putnam, Shawn, Kauffman, Jeffrey, Vasu Sumathi, Subith, University of Central Florida
Abstract / Description: Steady state droplet evaporation experiments are conducted to understand (1) Droplet contact line influence on evaporation rate and (2) Droplet contact angle correlation to evaporation rate. Experiments are performed on a polymer substrate with a moat like trench (laser patterned) to control droplet contact line dynamics. A bottom-up methodology is implemented for droplet formation on the patterned substrate. Droplet evaporation rates on substrate temperatures 22???T_Substrate?70? and contact...
Show moreSteady state droplet evaporation experiments are conducted to understand (1) Droplet contact line influence on evaporation rate and (2) Droplet contact angle correlation to evaporation rate. Experiments are performed on a polymer substrate with a moat like trench (laser patterned) to control droplet contact line dynamics. A bottom-up methodology is implemented for droplet formation on the patterned substrate. Droplet evaporation rates on substrate temperatures 22???T_Substrate?70? and contact angles 80(&)deg;???110(&)deg; are measured. For a pinned microdroplet (CCR), volumetric infuse rate influences droplet contact angle. Results illustrate droplet contact line impact on evaporation rate . Moreover, these results coincide with previously published results and affirm that evaporation rate efficiency reduces with contact line depinning. Additionally, from all the analyzed experimental cases, evaporation rate scales proportional to the microdroplet contact angle (i.e. ?_(LG )??). In conclusion, these experiments shed new light on steady state evaporation of a microdroplet and its corresponding observations. Vital research findings can be used to enhance heat dissipation from tiny surfaces.
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Date Issued: 2015
Identifier: CFE0006235, ucf:51067
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006235

Title: Deposition and characterization studies of boron carbon nitride (BCN) thin films prepared by dual target sputtering.
Creator: Prakash, Adithya, Sundaram, Kalpathy, Kapoor, Vikram, Yuan, Jiann-Shiun, Jin, Yier, Chow, Louis, University of Central Florida
Abstract / Description: As complementary metal-oxide semiconductor (CMOS) devices shrink to smaller size, the problems related to circuit performance such as critical path signal delay are becoming a pressing issue. These delays are a result of resistance and capacitance product (RC time constant) of the interconnect circuit. A novel material with reduced dielectric constants may compromise both the thermal and mechanical properties that can lead to die cracking during package and other reliability issues. Boron...
Show moreAs complementary metal-oxide semiconductor (CMOS) devices shrink to smaller size, the problems related to circuit performance such as critical path signal delay are becoming a pressing issue. These delays are a result of resistance and capacitance product (RC time constant) of the interconnect circuit. A novel material with reduced dielectric constants may compromise both the thermal and mechanical properties that can lead to die cracking during package and other reliability issues. Boron carbon nitride (BCN) compounds have been expected to combine the excellent properties of boron carbide (B4C), boron nitride (BN) and carbon nitride (C3N4), with their properties adjustable, depending on composition and structure. BCN thin film is a good candidate for being hard, dense, pore-free, low-k dielectric with values in the range of 1.9 to 2.1. Excellent mechanical properties such as adhesion, high hardness and good wear resistance have been reported in the case of sputtered BCN thin films. Problems posed by high hardness materials such as diamonds in high cutting applications and the comparatively lower hardness of c-BN gave rise to the idea of a mixed phase that can overcome these problems with a minimum compromise in its properties. A hybrid between semi-metallic graphite and insulating h-BN may show adjusted semiconductor properties. BCN exhibits the potential to control optical bandgap (band gap engineering) by atomic composition, hence making it a good candidate for electronic and photonic devices. Due to tremendous bandgap engineering capability and refractive index variability in BCN thin film, it is feasible to develop filters and mirrors for use in ultra violet (UV) wavelength region. It is of prime importance to understand process integration challenges like deposition rates, curing, and etching, cleaning and polishing during characterization of low-k films. The sputtering technique provides unique advantages over other techniques such as freedom to choose the substrate material and a uniform deposition over relatively large area. BCN films are prepared by dual target reactive magnetron sputtering from a B4C and BN targets using DC and RF powers respectively. In this work, an investigation of mechanical, optical, chemical, surface and device characterizations is undertaken. These holistic and thorough studies, will provide the insight into the capability of BCN being a hard, chemically inert, low-k, wideband gap material, as a potential leader in semiconductor and optics industry.
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Date Issued: 2016
Identifier: CFE0006378, ucf:51496
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006378

Title: Structure, stability, vibrational, thermodynamic, and catalytic properties of metal nanostructures: size, shape, support, and adsorbate effects.
Creator: Behafarid, Farzad, Roldan Cuenya, Beatriz, Chow, Lee, Heinrich, Helge, Kara, Abdelkader, Schoenfeld, Winston, University of Central Florida
Abstract / Description: Recent advances in nanoscience and nanotechnology have provided the scientific community with exciting new opportunities to rationally design and fabricate materials at the nanometer scale with drastically different properties as compared to their bulk counterparts. In this dissertation, several challenges have been tackled in aspects related to nanoparticle (NP) synthesis and characterization, allowing us to make homogenous, size- and shape-selected NPs via the use of colloidal chemistry,...
Show moreRecent advances in nanoscience and nanotechnology have provided the scientific community with exciting new opportunities to rationally design and fabricate materials at the nanometer scale with drastically different properties as compared to their bulk counterparts. In this dissertation, several challenges have been tackled in aspects related to nanoparticle (NP) synthesis and characterization, allowing us to make homogenous, size- and shape-selected NPs via the use of colloidal chemistry, and to gain in depth understanding of their distinct physical and chemical properties via the synergistic use of a variety of ex situ, in situ, and operando experimental tools. A variety of phenomena relevant to nanosized materials were investigated, including the role of the NP size and shape in the thermodynamic and electronic properties of NPs, their thermal stability, NP-support interactions, coarsening phenomena, and the evolution of the NP structure and chemical state under different environments and reaction conditions.
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Date Issued: 2012
Identifier: CFE0004779, ucf:49796
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004779

Title: The Influence of Alloying Additions on Diffusion and Strengthening of Magnesium.
Creator: Kammerer, Catherine, Sohn, Yongho, Coffey, Kevin, Challapalli, Suryanarayana, Gordon, Ali, University of Central Florida
Abstract / Description: Magnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate...
Show moreMagnesium alloys are being developed as advanced materials for structural applications where reduced weight is a primary motivator. Alloying can enhance the properties of magnesium without significantly affecting its density. Essential to alloy development, inclusive of processing parameters, is knowledge of thermodynamic, kinetic, and mechanical behavior of the alloy and its constituents. Appreciable progress has been made through conventional development processes, but to accelerate development of suitable wrought Mg alloys, an integrated Materials Genomic approach must be taken where thermodynamics and diffusion kinetic parameters form the basis of alloy design, process development, and properties-driven applications.The objective of this research effort is twofold: first, to codify the relationship between diffusion behavior, crystal structure, and mechanical properties; second, to provide fundamental data for the purpose of wrought Mg alloy development. Together, the principal deliverable of this work is an advanced understanding of Mg systems. To that end, the objective is accomplished through an aggregate of studies. The solid-to-solid diffusion bonding technique is used to fabricate combinatorial samples of Mg-Al-Zn ternary and Mg-Al, Mg-Zn, Mg-Y, Mg-Gd, and Mg-Nd binary systems. The combinatorial samples are subjected to structural and compositional characterization via Scanning Electron Microscopy with X-ray Energy Dispersive Spectroscopy, Electron Probe Microanalysis, and analytical Transmission Electron Microscopy. Interdiffusion in binary Mg systems is determined by Sauer-Freise and Boltzmann-Matano methods. Kirkaldy's extension of the Boltzmann-Matano method, on the basis of Onsager's formalism, is employed to quantify the main- and cross-interdiffusion coefficients in ternary Mg solid solutions. Impurity diffusion coefficients are determined by way of the Hall method. The intermetallic compounds and solid solutions formed during diffusion bonding of the combinatorial samples are subjected to nanoindentation tests, and the nominal and compositionally dependent mechanical properties are extracted by the Oliver-Pharr method.In addition to bolstering the scantly available experimental data and first-principles computations, this work delivers several original contributions to the state of Mg alloy knowledge. The influence of Zn concentration on Al impurity diffusion in binary Mg(Zn) solid solution is quantified to impact both the pre-exponential factor and activation energy. The main- and cross-interdiffusion coefficients in the ternary Mg solid solution of Mg-Al-Zn are reported wherein the interdiffusion of Zn is shown to strongly influence the interdiffusion of Mg and Al. A critical examination of rare earth element additions to Mg is reported, and a new phase in thermodynamic equilibrium with Mg-solid solution is identified in the Mg-Gd binary system. It is also demonstrated that Mg atoms move faster than Y atoms. For the first time the mechanical properties of intermetallic compounds in several binary Mg systems are quantified in terms of hardness and elastic modulus, and the influence of solute concentration on solid solution strengthening in binary Mg alloys is reported. The most significant and efficient solid solution strengthening is achieved by alloying Mg with Gd. The Mg-Nd and Mg-Gd intermetallic compounds exhibited better room temperature creep resistance than intermetallic compounds of Mg-Al. The correlation between the concentration dependence of mechanical properties and atomic diffusion is deliberated in terms of electronic nature of the atomic structure.
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Date Issued: 2015
Identifier: CFE0005815, ucf:50043
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005815

Diffusion (14)	+ -
diffusion (14)	+ -
interdiffusion (5)	+ -
GaN (3)	+ -
Interdiffusion (3)	+ -

diffusion length (3)	+ -
diffusion of innovations (3)	+ -
Aluminum (2)	+ -
CATER (2)	+ -
DFT (2)	+ -
Diffuser (2)	+ -
Intermetallics (2)	+ -
Magnesium (2)	+ -
Nanoindentation (2)	+ -
Separation (2)	+ -
TEM (2)	+ -
cathodoluminescence (2)	+ -
diffusion coefficient (2)	+ -
impurity diffusion (2)	+ -
ionic strength (2)	+ -
molybdenum (2)	+ -
nanofiltration (2)	+ -
uranium (2)	+ -
zirconium (2)	+ -
Ab-initio (1)	+ -
Accountable Care Organizations (1)	+ -
Adsorption cooling cycle (1)	+ -
Aerodynamics (1)	+ -
Al (1)	+ -
Al2O3 (1)	+ -

ETD Collection (58)	+ -
Honors Collection (2)	+ -

University of Central Florida (60)	+ -
Sohn, Yongho (12)	+ -
Coffey, Kevin (11)	+ -
Kapat, Jayanta (5)	+ -
Sundaram, Kalpathy (4)	+ -

An, Linan (3)	+ -
Chernyak, Leonid (3)	+ -
Chow, Lee (3)	+ -
Chow, Louis (3)	+ -
Deng, Weiwei (3)	+ -
Dogariu, Aristide (3)	+ -
Duranceau, Steven (3)	+ -
Fang, Jiyu (3)	+ -
Heinrich, Helge (3)	+ -
Orlovskaya, Nina (3)	+ -
Rahman, Talat (3)	+ -
Stolbov, Sergey (3)	+ -
Yuan, Jiann-Shiun (3)	+ -
Blair, Richard (2)	+ -
Brown, Timothy (2)	+ -
Gordon, Ali (2)	+ -
Kammerer, Catherine (2)	+ -
Kar, Aravinda (2)	+ -
Kara, Abdelkader (2)	+ -
Kolpashchikov, Dmitry (2)	+ -
Lee, Woo Hyoung (2)	+ -
Park, Young Joo (2)	+ -
Perez, Emmanuel (2)	+ -
Roldan Cuenya, Beatriz (2)	+ -
Sadmani, A H M Anwar (2)	+ -

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