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- Title
- QUANTITATIVE THICKNESS MAPPING IN HIGH-ANGLE ANNULAR DARK-FIELD (HAADF) SCANNING TRANSMISSION ELECTRON MICROSCOPY (STEM).
- Creator
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Nukala, Haritha, Heinrich, Helge, University of Central Florida
- Abstract / Description
-
Only a few methods are currently available for the measurement of sample thicknesses in Transmission Electron Microscopy (TEM). These methods, Convergent-Beam Electron Diffraction (CBED) and thickness mapping in Energy-Filtered TEM (EFTEM), are either elaborate or complex. In this present work, I have investigated and come up with a simple straight-forward method to measure the local thickness of a TEM sample with the atomic number (Z-contrast) imaging using High-Angle Annular Dark Field ...
Show moreOnly a few methods are currently available for the measurement of sample thicknesses in Transmission Electron Microscopy (TEM). These methods, Convergent-Beam Electron Diffraction (CBED) and thickness mapping in Energy-Filtered TEM (EFTEM), are either elaborate or complex. In this present work, I have investigated and come up with a simple straight-forward method to measure the local thickness of a TEM sample with the atomic number (Z-contrast) imaging using High-Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM). HAADF STEM shows atomic number contrast for high scattering angles of the electrons, owing to predominant electron scattering at the potential of the nucleus similar to Rutherford scattering. The characterization of materials by STEM helps to identify microstructures and nanostructures within a sample and to analyze defects in samples. HAADF STEM imaging is capable of resolving atomic structures with better than 2 Å lateral resolution. However, HAADF STEM has so far not been systematically used to measure sample thicknesses. In Z-contrast imaging, it was known that the intensity of the electrons scattered to high angles increases with increase in the atomic number (Z) of the element/compound with increasing thickness of the sample based on the equation, I ~ t.Zα Where t, is the thickness and α, is a parameter between 1 and 2. This project was started with this simple approach, but the experimental results within the thesis show that the relation between the intensity and the atomic number is not well described by this equation. A more reliable parameter, σZ, the interaction coefficient of the material was calculated. Samples containing Ag2Al platelets in Al matrix were used for calibration purposes. Additional samples containing layers of known elements/compounds were obtained from TriQuint Semiconductors and from the Physics department of UCF to calculate σ for various elements/compounds. These experimental values were used to measure the local thicknesses in nanoparticles and also the total volume of the nanoparticles. This quantitative HAADF STEM analysis represents a new method, which can be added to the list of methods used for the purpose of measurement of the local thickness of a sample in the TEM. This method is especially useful for the thickness measurement of nanoparticles. The other two methods, CBED and thickness maps in EFTEM are strongly affected by the sample orientation and therefore not appropriate for the study of nanoparticle thicknesses, whereas orientation effects are negligible for the conditions used in this HAADF STEM analysis.
Show less - Date Issued
- 2008
- Identifier
- CFE0002309, ucf:47859
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002309
- Title
- SYNTHESIS AND CHARACTERIZATION OF POLYMER-DERIVED POROUS SICN CERAMICS.
- Creator
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wei, yun, An, Linan, University of Central Florida
- Abstract / Description
-
The synthesis and characterization of porous SiCN ceramics produced by the method of polymer-derived ceramics were studied in this work. The polymer-to-ceramic conversion technique is a novel revolution in the methods for fabricating porous materials with controlled morphologies and tailored properties. The porous SiCN ceramics can be successfully prepared from thermal decomposition of polymeric precursors (polysilazane) and the pore former (polyvinyl alcohol (PVA)). The fabrication...
Show moreThe synthesis and characterization of porous SiCN ceramics produced by the method of polymer-derived ceramics were studied in this work. The polymer-to-ceramic conversion technique is a novel revolution in the methods for fabricating porous materials with controlled morphologies and tailored properties. The porous SiCN ceramics can be successfully prepared from thermal decomposition of polymeric precursors (polysilazane) and the pore former (polyvinyl alcohol (PVA)). The fabrication procedures involved the mixing of the pre-ceramic precursor with appropriate concentration of the PVA, curing, pyrolysis and subsequent PVA removal, leaving pores in the ceramic matrix. The material obtained revealed a homogeneous amorphous microstructure consisting of Si, C and N elements. The effects of the concentration and the particle size of PVA on the bulk density, open porosity, line shrinkage, microstructure, pore size, permeability, mechanical behavior, oxidation behavior and thermal stability were examined in this thesis. An increase in both concentration and particle size of PVA contribute to a decrease in the bulk density and an increase in the open porosity and line shrinkage. The morphology development, in particular, was investigated by scanning electron microscopy (SEM). The properties in terms of the pore size and permeability were measured by the water expulsion method. The mechanical behavior of the porous SiCN ceramic was characterized by the three- point bending strength test, thermal shock strength test and hertzian indentation strength test. The flexural strength and hertzian indentation strength of these porous ceramics at room temperature decrease with an increase in porosity. However, the flexural strength after thermal shock was significantly improved by increasing the temperature change. The oxidation behavior and thermal stability of porous SiAlCN ceramics were also explored by the mass change versus oxidation time and temperature. The phase evolution at different temperatures was also investigated by XRD analysis.
Show less - Date Issued
- 2008
- Identifier
- CFE0002359, ucf:47792
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002359
- Title
- Nanoscale Functional Imaging by Tailoring Light-matter Interaction to Explore Organic and Biological Systems.
- Creator
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Otrooshi, Negar, Tetard, Laurene, Tatulian, Suren, Peale, Robert, Santra, Swadeshmukul, University of Central Florida
- Abstract / Description
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ABSTRACTProbing molecular systems with light has been critical to deepen our understanding of life sciences. However, conventional analytical methods fail to resolve small quantities of molecules or the heterogeneity in molecules assembled into complex systems. This bottleneck is mostly attributed to light diffraction limit. In recent years, the successful implementation of new approaches to achieve sub-wavelength chemical speciation with an Atomic Force Microscope (AFM) has paved the way to...
Show moreABSTRACTProbing molecular systems with light has been critical to deepen our understanding of life sciences. However, conventional analytical methods fail to resolve small quantities of molecules or the heterogeneity in molecules assembled into complex systems. This bottleneck is mostly attributed to light diffraction limit. In recent years, the successful implementation of new approaches to achieve sub-wavelength chemical speciation with an Atomic Force Microscope (AFM) has paved the way to a deeper understanding of the effect of local composition and structure on the functional properties of a larger scale system. The combination of infrared light, to excite the vibrational modes of a sample, and AFM detection to monitor the resulting local photothermal expansion has emerged as a powerful approach. In this work, we explore new applications of AFM-infrared (IR) to further the understanding of proteins and bacterial cells. We first consider the vibrational modes and secondary structure of proteins. We show that beyond the localized IR fingerprint of the system, light polarization could affect the response of the protein. To investigate this further, we combine the AFM-IR measurements with plasmonic substrates to tune the electromagnetic field. Using plasmonic structures, we map the electromagnetic field confinement using nanomechanical infrared spectroscopy. We detect and quantify, in the near field, the energy transferred to the lattice in the form of thermal expansion resulting from the heat generated. We compare the photothermal expansion patterns in the structures under linearly and circular polarized illumination. The results suggest the formation of hot spots, of great interest for biomolecules detection. Using a model system, poly-L-lysine, we show that the IR spectrum and the vibrational circular dichroism fingerprint of a chiral biological system can be probed at the nanoscale, far beyond the conventional limits of detection. The second part of the study focuses on utilizing the capabilities of AFM-IR to investigate bacterial cells and their responses to nanoparticle-based treatments. We highlight the potential of these new capabilities to further dive into the fundamental molecular mechanism of antibacterial activity and of development of drug resistance. We conclude this work by providing a perspective on the impact nanoscale functional imaging and spectroscopy can have on life sciences and beyond.
Show less - Date Issued
- 2019
- Identifier
- CFE0007897, ucf:52750
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007897
- Title
- Advanced Nanoscale Characterization of Plants and Plant-derived Materials for Sustainable Agriculture and Renewable Energy.
- Creator
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Soliman, Mikhael, Tetard, Laurene, Vaidyanathan, Raj, Kang, Hyeran, Santra, Swadeshmukul, Zhai, Lei, Chumbimuni Torres, Karin, University of Central Florida
- Abstract / Description
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The need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced...
Show moreThe need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced worldwide.Here we will present our advanced characterization approach to study the effects of external stresses on plants, and resulting opportunities for biomass valorization with an impact on the food-energy-water nexus.First, the adaption of plants to the pressure imposed by gravity in poplar reaction wood will be discussed. We will show that a multiscale characterization approach is necessary to reach a better understanding of the chemical and physical properties of cell walls across a transverse section of poplar stem. Our Raman spectroscopy and statistical analysis reveals intricate variations in the cellulose and lignin properties. Further, we will present evidence that advanced atomic force microscopy can reveal nanoscale variations within the individual cell wall layers, not attainable with common analytical tools. Next, chemical stresses, in particular the effect of Zinc-based pesticides on citrus plants, will be considered. We will show how multiscale characterization can support the development of new disease management methods for systemic bacterial diseases, such as citrus greening, of great importance for sustainable agriculture. In particular, we will focus on the study of new formulations, their uptake and translocation in the plants following different application methods. Lastly, we will consider how plant reactions to mechanical and chemical stresses can be controlled to engineer biomass for valorization applications. We will present our characterization of two examples: the production of carbon films derived from woody lignocellulosic biomass and the development of nanoscale growth promoters for food crop. A perspective of the work and discussion of the broader impact will conclude the presentation.
Show less - Date Issued
- 2018
- Identifier
- CFE0007415, ucf:52717
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007415
- Title
- EXPERIMENTAL TECHNIQUES FOR NONLINEAR MATERIAL CHARACTERIZATION: A NONLINEAR SPECTROMETER USING A WHITE-LIGHT CONTINUUM Z-SCAN.
- Creator
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Balu, Mihaela, Van Stryland, Eric, University of Central Florida
- Abstract / Description
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The main goal of this dissertation is to introduce and demonstrate a new method for the rapid determination of the nonlinear absorption spectra and the dispersion of the nonlinear refraction of optical materials in the visible and near IR spectral regions. However, conventional methods like, white-light continuum pump-probe and Z-scan techniques were used to measure the peak 2PA cross-sections for a number of commercially available photoinitiators. In the new method mentioned above, a high...
Show moreThe main goal of this dissertation is to introduce and demonstrate a new method for the rapid determination of the nonlinear absorption spectra and the dispersion of the nonlinear refraction of optical materials in the visible and near IR spectral regions. However, conventional methods like, white-light continuum pump-probe and Z-scan techniques were used to measure the peak 2PA cross-sections for a number of commercially available photoinitiators. In the new method mentioned above, a high energy, broadband femtosecond white-light continuum is used to replace the single wavelength source conventionally used in a Z-scan experiment. In a Z-scan experiment, the transmittance of a focused beam through a sample is monitored as the sample travels through the focus, in the Z direction, along the focused beam. Providing the sample exhibits nonlinear absorption and/or refraction, the detector monitors a change in transmittance and/or a change in the beam divergence (if the energy is partially collected through an aperture in front of the detector). Replacing the single wavelength source with a white-light continuum allows for a much faster way of measuring nonlinear absorption/refraction spectra. This could eliminate the need for using other tunable sources (e.g. Optical Parameter Generators/Amplifiers) for nonlinear measurements. These sources made nonlinear spectroscopy using Z-scan experiments a time consuming task. This new source/method allows for rapid and simultaneous measurement of the nonlinear absorption spectrum and the dispersion of the nonlinear refraction. We have confirmed the functionality of the continuum as a source for nonlinear optical characterization of materials by using it to perform Z-scans on the well characterized semiconductors ZnSe and ZnS and on solutions of organic dyes.
Show less - Date Issued
- 2006
- Identifier
- CFE0001241, ucf:46934
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001241
- Title
- A METHODOLOGY FOR INSTRUMENTED INDENTATION STUDIES OF DEFORMATION IN BULK METALLIC GLASSES.
- Creator
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Sridharan, Subhaashree, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
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Bulk Metallic Glasses (BMGs), also known as amorphous metals, are of considerable scientific and commercial interest due to their random or chaotic structure. Given their potential use as engineering materials, there is a concomitant need to establish their mechanical properties. However, BMGs are not conveniently available in sufficient volumes (especially experimental and combinatorial compositions), making property determination via conventional tensile or compression testing problematic....
Show moreBulk Metallic Glasses (BMGs), also known as amorphous metals, are of considerable scientific and commercial interest due to their random or chaotic structure. Given their potential use as engineering materials, there is a concomitant need to establish their mechanical properties. However, BMGs are not conveniently available in sufficient volumes (especially experimental and combinatorial compositions), making property determination via conventional tensile or compression testing problematic. Instrumented indentation is ideally suited for this purpose because the testing requires only small sampling volumes and can probe multiaxial deformation characteristics at various length scales. In this technique, conducted generally on a sub-micron regime, the depth of penetration of an indenter, usually a diamond, is measured as a function of the applied load and expressed graphically as load (P) - displacement (h) curves from which a host of mechanical properties can be extracted and studied. In this work, a methodology for using instrumented indentation at nano- and micro- scales to determine the mechanical response of BMGs was developed and implemented. The implementation primarily focused on deformation in the elastic regime but included preliminary results related to the onset of inelastic deformation. The methodology developed included calibration techniques, formulations to extract the machine compliances, verifications using standards and verification for uniqueness of instrument deformation under a spherical indenter. The methodology was different for the two platforms used based on the load-depth response characteristics of the instrument. In the case of the Micro Test platform, the load-depth response of the instrument was linear. In the case of the Nano Test platform, the instrument load-depth response followed a 3/2 power law, representative of Hertzian behavior. The load-depth response of the instrument was determined by subtracting the theoretical response from the corresponding raw load-depth response obtained by elastically indenting a standard steel specimen of known modulus. The true response of the sample was then obtained by subtracting the instrument's response from the corresponding uncorrected load-depth response (raw data). An analytical model to describe the load-train compliance was developed. The methodology was verified using quartz and tungsten standards. Indentation experiments were conducted on Zr41.25Ti13.75Cu12.5Ni10Be22.5 (Vitreloy 1), Cu60Hf25Ti15, Cu60Zr30Ti10 and Fe60Co7Zr10Mo5W2B16 bulk metallic glasses using spherical indenters with diameters 2.8 mm and 100 m. The spherical geometry results in a simpler stress distribution under the indenter (when compared to a sharp geometry) and furthermore by recourse to spherical indenters the onset of plastic deformation was delayed. In the case of the Zr-based BMG, the experiments showed that the elastic response did not depend on the diameter of the indenter used indicative of the absence of residual stresses in the sample. Large scale plastic deformation was observed when the sample was indented using a smaller diameter indenter. Log scale analysis (i.e., examining the results on a log load vs. log depth response to check for deviation from Hertzian behavior) showed a deviation from a 3/2 fit indicating a deviation from elastic behavior. The onset implied a yield strength value of ~ 4 GPa, higher than the value reported in the literature (~ 2 GPa). Hence, it is believed that the first signs of plastic deformation occurred at lower loads than the predicted loads from the log scale analysis procedure and is expected to occur as discrete bursts. Discrete plastic events or "pop-ins" were observed in the load-depth indentation responses under quasistatic loading conditions, which were believed to be associated with shear band activity. An attempt was made to formulate a mathematical model based on three yield criteria (Drucker-Prager, Mohr-Coulomb and von Mises). Based on the von Mises predictions and comparable experiments on a quartz standard, it was established that the pop-ins observed were real and not an instrument artifact. Multiple load cycles following partial unload experiments showed that the pop-ins affected the subsequent indentation response. The moduli and the yield strength values obtained for the Cu-based BMGs were comparable to the values reported in the literature. There was significant scatter in the indentation data from the Fe-based BMG. Porosity and lack of 100 % compaction were believed to be the reasons for scatter in the data. The financial support of NSF through grant DMR 0314212 is gratefully acknowledged.
Show less - Date Issued
- 2006
- Identifier
- CFE0001442, ucf:47047
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001442
- Title
- NOISE CHARACERIZATION FOR PROPOSED UCF PHYISCAL SCIENCE BUILDING SITES.
- Creator
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Martinez, Jorge, Peale, Robert, University of Central Florida
- Abstract / Description
-
Today's Advance Technology Facilities require low noise levels and increased noise monitoring. Ambient noise can interfere with the accuracy and precision of experiments and manufacturing processes. Therefore preconstruction site surveys are needed to develop strategies for mitigating noise. Vibration and low frequency electromagnetic fields are particularly detrimental for sensitive instruments, and they are also difficult to mitigate. However a large part of these costs can be avoided...
Show moreToday's Advance Technology Facilities require low noise levels and increased noise monitoring. Ambient noise can interfere with the accuracy and precision of experiments and manufacturing processes. Therefore preconstruction site surveys are needed to develop strategies for mitigating noise. Vibration and low frequency electromagnetic fields are particularly detrimental for sensitive instruments, and they are also difficult to mitigate. However a large part of these costs can be avoided or minimized if a quiet building site is selected in the first place. Accelerometers and gauss meters combined with a computer for acquisition and analysis provide a low cost method of evaluating noise levels at proposed building sites. This work examines low frequency vibration and electromagnetic fields at two proposed sites for the planned Physical Science Building at the University of Central Florida.
Show less - Date Issued
- 2006
- Identifier
- CFE0001507, ucf:47156
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001507
- Title
- MECHANICAL CHARACTERIZATION AND NUMERICAL SIMULATION OF A LIGHT-WEIGHT ALUMINUM A359 METAL-MATRIX COMPOSITE.
- Creator
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DeMarco, James, Gordon, Ali, University of Central Florida
- Abstract / Description
-
Aluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of...
Show moreAluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of material through edge cracking during the hot rolling process which is applied to reduce thick billets of as-cast material to usable sheets. In the current work, mechanical characterization and numerical modeling of as-cast aluminum A359-SiCp-30% is employed to determine the properties of the composite and identify their dependence on strain rate and temperature conditions. Tensile and torsion tests were performed at a variety of strain rates and temperatures. Data obtained from tensile tests were used to calibrate the parameters of a material model for the composite. The material model was implemented in the ANSYS finite element software suite, and simulations were performed to test the ability of the model to capture the mechanical response of the composite under simulated tension and torsion tests. A temperature- and strain rate-dependent damage model extended the constitutive model to capture the dependence of material failure on testing or service conditions. Trends in the mechanical response were identified through analysis of the dependence of experimentally-obtained material properties on temperature and strain rate. The numerical model was found to adequately capture strain rate and temperature dependence of the stress-strain curves in most cases. Ductility modeling allowed prediction of stress and strain conditions which would lead to rupture, as well as identification of areas of a solid model which are most likely to fail under a given set of environmental and load conditions.
Show less - Date Issued
- 2011
- Identifier
- CFE0004007, ucf:49177
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004007
- Title
- THE ANATOMY OF A FIGHT SCENE: CHARACTERIZATION THROUGH STAGE COMBAT AND MOVEMENT.
- Creator
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Davis, Nona, Boyd, Belinda, University of Central Florida
- Abstract / Description
-
The study of stage combat is designed to fabricate the illusion of physical combat without causing harm to the performers. Most research in this field does not take into account the characterization of the actor during the training of a fight scene. An actor primarily learns the stunt choreography of the scene and often times the subtleties of the character is often forgotten. Scenes that involve physical contact are an essential aspect of the dramatic action. My aim is to eventually devise a...
Show moreThe study of stage combat is designed to fabricate the illusion of physical combat without causing harm to the performers. Most research in this field does not take into account the characterization of the actor during the training of a fight scene. An actor primarily learns the stunt choreography of the scene and often times the subtleties of the character is often forgotten. Scenes that involve physical contact are an essential aspect of the dramatic action. My aim is to eventually devise a process that will consistently create fight scenes that maintain the integrity of the fight director's work as well as the mastery of the actor's character composition. I am aware this is an ambitious project therefore will I approach this endeavor in two stages. This document will cover the first stage of this project: the investigation of the current process of several professionals who have varying experiences with fight choreography. I will propose and explore the significance of a series of questions a director, actor and fight choreographer should answer before embarking upon a fight sequence successfully. Questions such as: How important is the stunt physiologically and psychologically on the character? Does gender play a role in a fight sequence? Do size, age, and race play a role on character choice in a sequence? Why did the character choose that weapon? Where did that character learn to fight and why in that style?
Show less - Date Issued
- 2011
- Identifier
- CFE0003627, ucf:48862
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003627
- Title
- High Temperature Materials Characterization and Sensor Application.
- Creator
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Ren, Xinhua, Gong, Xun, Wahid, Parveen, Wu, Xinzhang, An, Linan, University of Central Florida
- Abstract / Description
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This dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate...
Show moreThis dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent of the material. The dielectric properties of Silicon Carbonitride (SiCN) and Silicoboron Carbonitride (SiBCN) ceramics, developed at UCF Advanced Materials Processing and Analysis Center (AMPC) are characterized from 25 to 1300oC. It is observed that the dielectric constant and loss tangent of SiCN and SiBCN materials increase monotonously with temperature. This temperature dependency provides the valuable basis for development of wireless passive temperature sensors for high-temperature applications. Second, wireless temperature sensors are designed based on the aforementioned high-temperature ceramic materials. The dielectric constant of high-temperature ceramics increases monotonically with temperature and as a result changes the resonant frequency of the resonator. Therefore, the temperature can be extracted by measuring the change of the resonant frequency of the resonator. In order for the resonator to operate wirelessly, antennas need to be included in the design. Three different types of sensors, corresponding to different antenna configurations, are designed and the prototypes are fabricated and tested. All of the sensors successfully perform at temperatures over 1000oC. These wireless passive sensor designs will significantly benefit turbine engines in need of sensors operating at harsh environments.
Show less - Date Issued
- 2012
- Identifier
- CFE0004791, ucf:49727
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004791
- Title
- Nano-pipette as nanoparticle analyzer and capillary gated ion transistor.
- Creator
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Rudzevich, Yauheni, Chow, Lee, Heinrich, Helge, Schulte, Alfons, Yuan, Jiann-Shiun, University of Central Florida
- Abstract / Description
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The ability to precisely count inorganic and organic nanoparticles and to measure their size distribution plays a major role in various applications such as drug delivery, nanoparticles counting, and many others. In this work I present a simple resistive pulse method that allows translocations, counting, and measuring the size and velocity distribution of silica nanoparticles and liposomes with diameters from 50 nm to 250 nm. This technique is based on the Coulter counter technique, but has...
Show moreThe ability to precisely count inorganic and organic nanoparticles and to measure their size distribution plays a major role in various applications such as drug delivery, nanoparticles counting, and many others. In this work I present a simple resistive pulse method that allows translocations, counting, and measuring the size and velocity distribution of silica nanoparticles and liposomes with diameters from 50 nm to 250 nm. This technique is based on the Coulter counter technique, but has nanometer size pores. It was found that ionic current drops when nanoparticles enter the nanopore of a pulled micropipette, producing a clear translocation signal. Pulled borosilicate micropipettes with opening 50 ~ 350 nm were used as the detecting instrument. This method provides a direct, fast and cost-effective way to characterize inorganic and organic nanoparticles in a solution. In this work I also introduce a newly developed Capillary Ionic Transistor (CIT). It is presented as a nanodevice which provides control of ionic transport through nanochannel by gate voltage. CIT is Ionic transistor, which employs pulled capillary as nanochannel with a tip diameter smaller than 100 mm. We observed that the gate voltage applied to gate electrode, deposited on the outer wall of a capillary, affect a conductance of nanochannel, due to change of surface charge at the solution/capillary interface. Negative gate voltage corresponds to lower conductivity and positive gate increases conductance of the channel. This effect strongly depends on the size of the channel. In general, at least one dimension of the channel has to be small enough for electrical double layer to overlap.
Show less - Date Issued
- 2014
- Identifier
- CFE0005880, ucf:50882
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005880
- Title
- EFFECT OF SOURCE WATER BLENDING ON COPPER RELEASE IN PIPE DISTRIBUTION SYSTEM: THERMODYNAMIC AND EMPIRICAL MODELS.
- Creator
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Xiao, Weizhong, Taylor, James S., University of Central Florida
- Abstract / Description
-
This dissertation focuses on copper release in drinking water. Qualitative and quantitative assessment of Cu and Fe corrosion by process water quality was assessed over one year in a field study using finished waters produced from seven different treatment process and eighteen pilot distribution systems (PDSs) that were made from unlined cast iron and galvanized steel pipes, and lined cement and PVC pipes taken from actual distribution systems. Totally seven different waters were studied,...
Show moreThis dissertation focuses on copper release in drinking water. Qualitative and quantitative assessment of Cu and Fe corrosion by process water quality was assessed over one year in a field study using finished waters produced from seven different treatment process and eighteen pilot distribution systems (PDSs) that were made from unlined cast iron and galvanized steel pipes, and lined cement and PVC pipes taken from actual distribution systems. Totally seven different waters were studied, which consisted of three source waters: groundwater, surface, and simulated brackish water designated as G1, S1, and RO. With certain pre-established blending ratios, these three waters were blended to form another three waters designated as G2, G3, and G4. Enhanced surface water treatment was CFS, ozonation and GAC filtration, which was designated as S1. The CFS surface water was nanofiltered, which is S2. All seven finished waters were stabilized and chloraminated before entering the PDSs. Corrosion potential was compared qualitatively and quantitatively for all seven waters by monitoring copper and iron release from the PDSs. This dissertation consists of four major parts.(1) Copper corrosion surface characterization in which the solid corrosion products formed in certain period of exposure to drinking water were tried to be identified with kinds of surface techniques. Surface characterization indicated that major corrosion products consists of cuprite (Cu2O) as major underneath corrosion layer and tenorite (CuO), cupric hydroxide (Cu(OH)2) on the top surface. In terms of dissolution/precipitation mechanism controlling the copper concentration in bulk solution, cupric hydroxide thermodynamic model was developed.(2) Theoretical thermodynamic models were developed to predict the copper release level quantitatively based on controlling solid phases identified in part (1). These models are compared to actual data and relative assessment is made of controlling solid phases. (3) Non-linear and linear regression models were developed that accommodated the release to total copper for varying water quality. These models were verified using independent data and provide proactive means of assessing and controlling copper release in a varying water quality environment. (4) Simulation of total copper release was conducted using all possible combinations of water quality produced by blending finished waters from ground, surface and saline sources, which involves the comparison of copper corrosion potentials among reverse osmosis, nanofiltration, enhanced coagulation, lime softening, and conventional drinking water treatment.
Show less - Date Issued
- 2004
- Identifier
- CFE0000042, ucf:46069
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000042
- Title
- THE SHEFFER B-TYPE 1 ORTHOGONAL POLYNOMIAL SEQUENCES.
- Creator
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Galiffa, Daniel, Ismail, Mourad, University of Central Florida
- Abstract / Description
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In 1939, I.M. Sheffer proved that every polynomial sequence belongs to one and only one $type$. Sheffer extensively developed properties of the $B$-\emph{Type 0} polynomial sequences and determined which sets are also orthogonal. He subsequently generalized his classification method to the case of arbitrary $B$-\emph{Type k} by constructing the generalized generating function $A(t)\mathrm=\sum_^\infty$, with $H_i(t)=h_t^i+h_t^+\cdots,\phantomh_\neq 0$. Although extensive research has been...
Show moreIn 1939, I.M. Sheffer proved that every polynomial sequence belongs to one and only one $type$. Sheffer extensively developed properties of the $B$-\emph{Type 0} polynomial sequences and determined which sets are also orthogonal. He subsequently generalized his classification method to the case of arbitrary $B$-\emph{Type k} by constructing the generalized generating function $A(t)\mathrm=\sum_^\infty$, with $H_i(t)=h_t^i+h_t^+\cdots,\phantomh_\neq 0$. Although extensive research has been done on characterizing polynomial sequences, no analysis has yet been completed on sets of type one or higher ($k\geq1$). We present a preliminary analysis of a special case of the $B$-\emph{Type 1} ($k=1$) class, which is an extension of the $B$-\emph{Type 0} class, in order to determine which sets, if any, are also orthogonal sets. Lastly, we consider an extension of this research and comment on future considerations. In this work the utilization of computer algebra packages is indispensable, as computational difficulties arise in the $B$-\emph{Type 1} class that are unlike those in the $B$-\emph{Type 0} class.
Show less - Date Issued
- 2009
- Identifier
- CFE0002551, ucf:47655
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002551
- Title
- DESIGN, ANALYSIS, AND OPTIMIZATION OF DIFFRACTIVE OPTICAL ELEMENTS UNDER HIGH NUMERICAL APERTURE FOCUSING.
- Creator
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Jabbour, Toufic, Kuebler, Stephen, University of Central Florida
- Abstract / Description
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The demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical...
Show moreThe demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical lithography, microscopy and direct laser writing are but a few of the many applications in which a properly designed DOE can significantly improve optical performance of the system. Designing DOEs for use in high-NA applications is complicated by electric field depolarization that occurs with tight focusing. The linear polarization of off-axis rays is tilted upon refraction towards the focal point, generating additional transverse and longitudinal polarization components. These additional field components contribute significantly to the shape of the PSF under tight focusing and cannot be neglected as in scalar diffraction theory. The PSF can be modeled more rigorously using the electromagnetic diffraction integrals derived by Wolf, which account for the full vector character of the field. In this work, optimization algorithms based on vector diffraction theory were developed for designing DOEs that reshape the PSF of a 1.4-NA objective lens. The optimization techniques include simple exhaustive search, iterative optimization (Method of Generalized Projections), and evolutionary computation (Particle Swarm Optimization). DOE designs were obtained that can reshape either the transverse PSF or the irradiance distribution along the optical axis. In one example of transverse beam shaping, all polarization components were simultaneously reshaped so their vector addition generates a focused flat-top square irradiance pattern. Other designs were obtained that can be used to narrow the axial irradiance distribution, giving a focused beam that is superresolved relative to the diffraction limit. In addition to theory, experimental studies were undertaken that include (1) fabricating an axially superresolving DOE, (2) incorporating the DOE into the optical setup, (3) imaging the focused PSF, and (4) measuring aberrations in the objective lens to study how these affect performance of the DOE.
Show less - Date Issued
- 2009
- Identifier
- CFE0002844, ucf:48063
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002844
- Title
- A Framework for Miniaturized Mechanical Characterization of Tensile, Creep, and Fatigue Properties of SLM Alloys.
- Creator
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Torres-Caceres, Jonathan, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
- Abstract / Description
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With the heightened design complexity that may be achieved through additive manufacturing (AM) comes an equally complex set of distinct material characteristics. To properly characterize new materials for use in selective laser melting (SLM), extensive analysis is necessary. Traditional testing techniques, however, can be prohibitive in time and cost incurred. The small punch test (SPT) has been developed for such purposes, where material is scarce or costly. Although lacking standardization,...
Show moreWith the heightened design complexity that may be achieved through additive manufacturing (AM) comes an equally complex set of distinct material characteristics. To properly characterize new materials for use in selective laser melting (SLM), extensive analysis is necessary. Traditional testing techniques, however, can be prohibitive in time and cost incurred. The small punch test (SPT) has been developed for such purposes, where material is scarce or costly. Although lacking standardization, SPT has been successfully employed with various materials to assess material properties such as the yield and ultimate strength and verified by traditional testing results. With the accompaniment of numerical simulations for use in the inverse method and determining correlation factors, several methods exist for equating SPT results with traditional results. There are, however, areas of weakness with SPT which require development, and the solution of the inverse method can be demanding of time and resources. Additionally, the combination of SPT and SLM is relatively unexplored in literature, though studies have shown that SPT is sensitive to the types of structures and unique material characteristics present in SLM components. The present research therefore focuses on developing a framework for characterizing SLM materials via the small punch test. Several types of SLM materials in various orientations and processing states are small punch tested to evaluate the ability of the SPT to track the effects of these as they cause the materials to evolve. A novel cyclic test method is proposed to fill the gap in SPT fatigue testing. Results from these tests are evaluated via numerical modelling using the inverse method solved with the least squares method. Samples were also inspected using digital microscopy to connect fracture morphology to processing parameter variations. A framework is thus presented with which SPT may be utilized to more economically and expeditiously characterize SLM materials.
Show less - Date Issued
- 2018
- Identifier
- CFE0007109, ucf:51952
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007109
- Title
- The Characterization of Condom Lubricants and Personal Hygiene Products using DART-TOFMS and GC- MS and The Investigation of Gold Nanoparticle Behavior in Water and the Interaction with Blood Serum Proteins.
- Creator
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Moustafa, Yasmine, Huo, Qun, Bridge, Candice, Sigman, Michael, Baudelet, Matthieu, Popolan-Vaida, Denisia, Ni, Liqiang, University of Central Florida
- Abstract / Description
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This dissertation is divided into two independent research projects. First, condom lubricants, sexual lubricants, and personal hygiene products (PHPs) were studied using direct analysis in real time-time-of-flight-mass spectrometry (DART-TOFMS) and gas chromatography-mass spectrometry (GC-MS). The purpose addressed the concern of perpetrators resorting to new tactics, i.e. using condoms to remove seminal fluid that could provide a DNA link to a suspect, leading to the need of the...
Show moreThis dissertation is divided into two independent research projects. First, condom lubricants, sexual lubricants, and personal hygiene products (PHPs) were studied using direct analysis in real time-time-of-flight-mass spectrometry (DART-TOFMS) and gas chromatography-mass spectrometry (GC-MS). The purpose addressed the concern of perpetrators resorting to new tactics, i.e. using condoms to remove seminal fluid that could provide a DNA link to a suspect, leading to the need of the consideration of condom lubricants as pieces of sexual assault evidence. Due to condom lubricants having a chemical composition resembling PHPs, the investigation of both sample groups was analyzed to prevent false positives. Although past research has focused on the identification of major lubricant groups and additives, the discernment between such samples is insufficient. The discriminatory capability and rapid analysis of samples using DART-TOFMS was illustrated through resolution among the sample groups and higher classification rates. Here, lubricant analysis was introduced as a viable source of evidence, with a scheme detailing their discrimination from common hygiene products using DART-TOFMS as a robust tool for the analysis of sexual assault evidence. Second, gold nanoparticles (AuNPs) were characterized using dynamic light scattering (DLS), Ultraviolet-Visible spectroscopy (UV-VIS), dark field Imaging (DFM), and Transmission electron microscopy (TEM). Following characterization, AuNPs were used in protein adsorption study from blood serum concentration and to observe how the differences in their characterization affected their interactions with blood serum proteins. AuNPs are an interest in the bioanalytical sector due to their optical properties, scattering of light, and high surface-to-volume ratio. A common issue plagues the field: the difficulty of inter/intra laboratory reproducibility from one characterization technique. This further affects the understanding of how AuNPs may react for diagnostic and other applications. The importance of a comprehensive characterization protocol for AuNP products and the need for manufacturers to include product specifications is demonstrated in this study.
Show less - Date Issued
- 2019
- Identifier
- CFE0007842, ucf:52814
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007842
- Title
- Improved system for fabrication and characterization of nanophotonic devices by multi-photon lithography.
- Creator
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Sharma, Rashi, Kuebler, Stephen, Zou, Shengli, Huo, Qun, Beazley, Melanie, Phanstiel, Otto, University of Central Florida
- Abstract / Description
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A new system for multi-photon lithography (MPL) was developed and used to fabricate three-dimensional (3D) structures with higher aspect ratio, better resolution, improved fidelity, and reduced structural distortion relative to a conventional implementation of MPL.A set of curved waveguides (Rbend = 19 (&)#181;m, and 38 (&)#181;m) and straight waveguides (length = 50 (&)#181;m, Rbend = ?) were fabricated in an epoxide photopolymer and optically characterized using light having a wavelength in...
Show moreA new system for multi-photon lithography (MPL) was developed and used to fabricate three-dimensional (3D) structures with higher aspect ratio, better resolution, improved fidelity, and reduced structural distortion relative to a conventional implementation of MPL.A set of curved waveguides (Rbend = 19 (&)#181;m, and 38 (&)#181;m) and straight waveguides (length = 50 (&)#181;m, Rbend = ?) were fabricated in an epoxide photopolymer and optically characterized using light having a wavelength in vacuum of ?0 = 2.94 (&)#181;m. The optical performance of the waveguides was compared to novel spatially-variant photonic crystals (SVPCs) previously studied in the group. The waveguides were found to guide light with 90% lower efficiency, due to mode leakage. The study provides further evidence that SVPCs operate not through total internal reflection, but rather through self-collimation, as designed.3D uniform-lattice photonic crystals (ULPCs) were fabricated by MPL using a commercial acrylate photopolymer. The ULPCs were optically characterized at ?0 = 1.55 (&)#181;m. A laser beam with adjustable bandwidth was used to measure the self-collimation in the ULPCs. For the low bandwidth beam, vertically polarized light was self-collimated, whereas horizontally polarized light diverged. The transmission efficiency of the ULPCs was also measured as a function of fill factor. The ULPC having a fill factor of 48% exhibited 80% transmission.An etching process was also developed for non-destructively removing Au/Pd coatings that must be deposited onto structures to image them by scanning electron microscopy. The structural and optical integrity of the samples was found to be maintained despite etching. The sputter-coated sample sustained no structural damage when exposed to the ?0 = 1.55 (&)#181;m. However, the metal coating resulted in diminished transmission efficiency due to the high reflection of the 1.55 (&)#181;m beam by the metal coating.
Show less - Date Issued
- 2018
- Identifier
- CFE0007767, ucf:52380
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007767
- Title
- Direct measurement of thicknesses, volumes or compositions of nanomaterials by quantitative atomic number contrast in high-angle annular dark-field scanning transmission electron microscopy.
- Creator
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Yuan, Biao, Heinrich, Helge, Sohn, Yongho, Coffey, Kevin, Fang, Jiyu, Roldan Cuenya, Beatriz, University of Central Florida
- Abstract / Description
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The sizes, shapes, volumes and compositions of nanoparticles are very important parameters determining many of their properties. Efforts to measure these parameters for individual nanoparticles and to obtain reliable statistics for a large number of nanoparticles require a fast and reliable method for 3-D characterization. In this dissertation, a direct measurement method for thicknesses, volumes or compositions of nanomaterials by quantitative atomic number contrast in High-Angle Annular...
Show moreThe sizes, shapes, volumes and compositions of nanoparticles are very important parameters determining many of their properties. Efforts to measure these parameters for individual nanoparticles and to obtain reliable statistics for a large number of nanoparticles require a fast and reliable method for 3-D characterization. In this dissertation, a direct measurement method for thicknesses, volumes or compositions of nanomaterials by quantitative atomic number contrast in High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM) is presented. A HAADF detector collects electrons scattered incoherently to high angles. The HAADF signal intensity is in first-order approximation proportional to the sample thickness and increases with atomic number. However, for larger sample thicknesses this approach fails. A simple description for the thickness dependence of the HAADF-STEM contrast has been developed in this dissertation. A new method for the calibration of the sensitivity of the HAADF detector for a FEI F30 transmission electron microscope (TEM) is developed in this dissertation. A nearly linear relationship of the HAADF signal with the electron current is confirmed. Cross sections of multilayered samples provided by TriQuint Semiconductors in Apopka, FL, for contrast calibration were obtained by focused ion-beam (FIB) preparation yielding data on the interaction cross section per atom.To obtain an absolute intensity calibration of the HAADF-STEM intensity, Convergent Beam Electron Diffraction (CBED) was performed on Si single crystals. However, for samples prepared by the focused ion beam technique, CBED often significantly underestimates the sample thickness. Multislice simulations from Dr. Kirkland's C codes are used for comparison with experimental results. TEM offers high lateral resolution, but contains little or no information on the thickness of samples. Thickness maps in energy-filtered TEM (EFTEM), CBED and tilt series are so far the only methods to determine thicknesses of particles in TEM. In this work I have introduced the use of wedge-shaped multilayer samples prepared by FIB for the calibration of HAADF-STEM contrasts. This method yields quantitative contrast data as a function of sample thickness. A database with several pure elements and compounds has been compiled, containing experimental data on the fraction of electrons scattered onto the HAADF detector for each nanometer of sample thickness. The use of thick samples reveals an increased signal at the interfaces of high- and low-density materials. This effect can be explained by the transfer of scattered electrons from the high density material across the interface into the less-absorbing low-density material. The calibrations were used to determine concentration gradients in nanoscale Fe-Pt multilayers as well as thicknesses and volumes of individual Au-Fe, Pt, and Ag nanoparticles. Volumes of nanoparticles with known composition can be determined with accuracy better than 15%. Porosity determination of materials becomes available with this method as shown in an example of porous Silicon.?
Show less - Date Issued
- 2012
- Identifier
- CFE0004464, ucf:49355
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004464
- Title
- A Novel Nonlinear Mason Model and Nonlinear Distortion Characterization for Surface Acoustic Wave Duplexers.
- Creator
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Chen, Li, Wahid, Parveen, Malocha, Donald, Richie, Samuel, Briot, Jean-Bernard, University of Central Florida
- Abstract / Description
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Surface acoustic wave (SAW) technology has been in use for well over one century. In the last few decades, due to its low cost and high performance, this technology has been widely adopted in modern wireless communication systems, to build filtering devices at radio frequency (RF). SAW filters and duplexers can be virtually found inside every mobile handset. SAW devices are traditionally recognized as passive devices with high linear signal processing behavior. However, recent deployments of...
Show moreSurface acoustic wave (SAW) technology has been in use for well over one century. In the last few decades, due to its low cost and high performance, this technology has been widely adopted in modern wireless communication systems, to build filtering devices at radio frequency (RF). SAW filters and duplexers can be virtually found inside every mobile handset. SAW devices are traditionally recognized as passive devices with high linear signal processing behavior. However, recent deployments of third generation (3G) and fourth generation (4G) mobile networks require the handsets to handle an increasing number of frequency bands with more complex modulation /demodulation schemes and higher data rate for more subscribers. These requirements directly demand more stringent linearity specifications on the front end devices, including the SAW duplexers. In the past, SAW duplexer design was based on empirically obtained design rules to meet the linearity specifications. Lack of predictability and an understanding of the root cause of the nonlinearity have limited the potential applications of SAW duplexers. Therefore, research on the nonlinearity characterization and an accurate modeling of SAW nonlinearity for mobile device applications are very much needed.The Ph.D. work presented here primarily focuses on developing a general nonlinear model for SAW resonators/duplexers. Their nonlinear characteristics were investigated by measuring the harmonic and intermodulation distortions of resonators. A nonlinear Mason model is developed and the characterization results are integrated into SAW duplexer design flows to help to simulate the nonlinear effects accurately and improve the linearity performance of the products.In this dissertation, first, a novel nonlinear Mason equivalent circuit model including a third order nonlinear coefficient in the wave propagation is presented. Next, the nonlinear distortions of SAW resonators are analyzed by measuring large-signal harmonic and intermodulation spurious emission on resonators using a wafer probe station. The influence of the setups on the measurement reliability and reproducibility is discussed. Further, the nonlinear Mason model is validated by comparing its simulation results with harmonic and intermodulation measurements on SAW resonators and a WCDMA Band 5 duplexer. The Mason model developed and presented here is the first and only nonlinear physical model for SAW devices based on the equivalent circuit approach. By using this new model, good simulation measurement agreements are obtained on both harmonic and intermodulation distortions for SAW resonators and duplexers. These outcomes demonstrate the validity of the research on both the characterization and modeling of SAW devices. The result obtained confirms that the assumption of the representation of the 3rd order nonlinearity in the propagation by a single coefficient is valid.
Show less - Date Issued
- 2013
- Identifier
- CFE0004967, ucf:49565
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004967
- Title
- Understanding the Role of Defects in the Radiation Response of Nanoceria.
- Creator
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Kumar, Amit, Seal, Sudipta, Heinrich, Helge, Cho, Hyoung, Leuenberger, Michael, Zhai, Lei, Devanathan, Ram, University of Central Florida
- Abstract / Description
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Nanoscale cerium oxide (nanoceria) have shown to possess redox active property , and has been widely studied for potential use in catalysis, chemical-mechanical planarization, bio-medical and solid oxide fuel cell (SOFC), etc. The redox state of nanoceria can be tuned by controlling the defects within the lattice and thus its physical and chemical properties. Perfect ceria lattice has fluorite structure and the research in last decade has shown that oxide and mixed oxide systems with...
Show moreNanoscale cerium oxide (nanoceria) have shown to possess redox active property , and has been widely studied for potential use in catalysis, chemical-mechanical planarization, bio-medical and solid oxide fuel cell (SOFC), etc. The redox state of nanoceria can be tuned by controlling the defects within the lattice and thus its physical and chemical properties. Perfect ceria lattice has fluorite structure and the research in last decade has shown that oxide and mixed oxide systems with pyrochlore and fluorite have better structural stability under high energy radiation. However, the current literature shows a limited number of studies on the effect of high energy radiation on nanoceria. This dissertation aims at understanding the phenomena occurring on irradiation of nanoceria lattice through experiments and atomistic simulation.At first, research was conducted to show the ability to control the defects in nanoceria lattice and understand the effect in tailoring its properties. The defect state of nanoceria was controlled by lower valence state rare earth dopant europium. Extensive materials characterization was done using high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to understand the effect of dopant chemistry in modifying the chemical state of nanoceria. The defects originating in the lattice and redox state was quantified with increasing dopant concentration. The photoluminescence property of the control and doped nanoceria were evaluated with respect to its defect state. It was observed that defect plays an important role in modifying the photoluminescence property and that it can be tailored in a wide range to control the optical properties of nanoceria.Having seen the importance of defects in controlling the properties of nanoceria, further experiments were conducted to understand the effect of radiation in cerium oxide thin films of different crystallinity. The cerium oxide thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE) growth. The thin films were exposed to high energy radiation over a wide range of fluence (1013 to 1017 He+ ions/cm3). The current literature does not report the radiation effect in nanoceria in this wide range and upto this high fluence. The chemical state of the thin film was studied using in-situ XPS for each dose of radiation. It was found that radiation induced defects within both the ceria thin films and the valence state deviated further towards non-stoichiometry with radiation. The experimental results from cerium oxide thin film irradiation were studied in the light of simulation. Classical molecular dynamics and Monte Carlo simulation were used for designing the model ceria nanoparticle and studying the interaction of the lattice model with radiation. Electronic and nuclear stopping at the end of the range were modeled in ceria lattice using classical molecular dynamics to simulate the effect of radiation. It was seen that displacement damage was the controlling factor in defect production in ceria lattice. The simulation results suggested that nanosized cerium oxide has structural stability under radiation and encounters radiation damage due to the mixed valence states. A portion of the study will focus on observing the lattice stability of cerium with increasing concentration of the lower valence (Ce3+) within the lattice. With this current theoretical understanding of the role of redox state and defects during irradiation, the surfaces and bulk of nanoceria can be tailored for radiation stable structural applications.
Show less - Date Issued
- 2012
- Identifier
- CFE0004396, ucf:49375
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004396
