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Title: CONFOCAL LASER SCANNING MICROSCOPY AS A TOOL FOR THE INVESTIGATION OF TETRACYCLINE FLUORESCENCE IN ARCHAEOLOGICALHUMAN BONE.
Creator: Maggiano, Corey, Waterman, Jane, University of Central Florida
Abstract / Description: Fluorochromes such as tetracycline have been used to label bone for histomorphometric analysis, measuring bone formation, growth, maintenance, and pathology. More recently, similar fluorescence has been observed in ancient human bone. Attributed to tetracycline (TC) exposure, this phenomenon could affect various aspects of health during life and/or preservation of remains postmortem. Standard epifluorescence microscopy is the most common tool employed in the analysis of these labels. Though...
Show moreFluorochromes such as tetracycline have been used to label bone for histomorphometric analysis, measuring bone formation, growth, maintenance, and pathology. More recently, similar fluorescence has been observed in ancient human bone. Attributed to tetracycline (TC) exposure, this phenomenon could affect various aspects of health during life and/or preservation of remains postmortem. Standard epifluorescence microscopy is the most common tool employed in the analysis of these labels. Though valuable, this technique is limited by its inability to penetrate bone three-dimensionally and its inclusion of out-of-focus light, possibly disrupting accurate analysis. Confocal Laser Scanning Microscopy (CLSM) has been demonstrated as a valuable tool for three-dimensional histology. Its application to the study of compact bone fluorescence has been lacking, especially in archaeological and forensic sciences. In the following two papers, modern TC-controlled bone is compared to well preserved archaeological bone recovered from the Dakhleh Oasis, Egypt, using both standard wide-field and more modern confocal techniques for imaging and analysis. Spectral analysis via CLSM shows that both modern and ancient fluorescent labels in bone share the exact same fluorescence emission peak at 525 nm. Differences in the shape of the spectral curve and photobleaching characteristics are discussed. In addition, CLSM's high-resolution two- and three-dimensional imaging capabilities (in polarized light, scattered light, and fluorescence light) are found to increase the flexibility and creativity of investigations into the occurrence of tetracycline labels in archaeological bone and could have added benefits for modern medical and anatomical experimentation.
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Date Issued: 2005
Identifier: CFE0000836, ucf:46680
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000836

Title: DISCRIMINATION OF AUTOMOBILE CARPET FIBERS USING MULTIPLE ANALYTICAL TECHNIQUES AND THE SUBSEQUENT CREATION OF A SEARCHABLE DATABASE.
Creator: Dorrien, Derek, Sigman, Michael, University of Central Florida
Abstract / Description: Forensic fiber examination is an important part of trace evidence analysis. Fibers may be recovered from a crime scene that could link a particular suspect to the scene. Clothing fibers are most frequently encountered but automobile carpeting fibers may also be recovered. An understanding of the frequency of occurrence and the discrimination power of different analytical techniques is needed in order to better establish the evidentiary value of automobile carpet fiber evidence. Seventy-five...
Show moreForensic fiber examination is an important part of trace evidence analysis. Fibers may be recovered from a crime scene that could link a particular suspect to the scene. Clothing fibers are most frequently encountered but automobile carpeting fibers may also be recovered. An understanding of the frequency of occurrence and the discrimination power of different analytical techniques is needed in order to better establish the evidentiary value of automobile carpet fiber evidence. Seventy-five automobile carpet fiber samples were analyzed using a series of techniques ranging from nondestructive to destructive. These techniques included polarized light microscopy, fluorescence microscopy, microspectrophotometry, Fourier-transform infrared spectroscopy, microtomy (cross section analysis), dye extraction and liquid chromatography-mass spectrometry. Based on the information obtained from these techniques an overall discrimination of 98.02% was calculated. Only 55 of 2775 pairwise comparisons were indistinguishable. The information was subsequently entered into a searchable database for general public use.
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Date Issued: 2006
Identifier: CFE0001483, ucf:47103
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001483

Title: Multidimensional Room-Temperature Fluorescence Microscopy for the Nondestructive Analysis of Forensic Trace Textile Fibers.
Creator: Mujumdar, Nirvani, Campiglia, Andres, Sigman, Michael, Harper, James, Rex, Matthew, Peale, Robert, University of Central Florida
Abstract / Description: The purpose of this dissertation is to advance nondestructive methodology for forensic fiber examination. Non-destructive techniques that can either discriminate between similar fibers or match a known to a questioned fiber (-) and still preserve the physical integrity of the fibers for further court examination - are highly valuable in forensic science. A challenging aspect of forensic fiber examinations involves the comparison of fibers colored with visually indistinguishable dyestuffs....
Show moreThe purpose of this dissertation is to advance nondestructive methodology for forensic fiber examination. Non-destructive techniques that can either discriminate between similar fibers or match a known to a questioned fiber (-) and still preserve the physical integrity of the fibers for further court examination - are highly valuable in forensic science. A challenging aspect of forensic fiber examinations involves the comparison of fibers colored with visually indistinguishable dyestuffs. This is not an uncommon situation, as there are numerous indistinguishable fibers pre-dyed with commercial dyes of virtually identical colors. Minimal chemical structural variations are actually encouraged by the dye patent process and commercial competition.The common denominator to forensic methodology is the fact that fiber analysis primarily focuses on the dyes used to color the fibers and do not investigate other potential discriminating components present in the fiber. This dissertation explores a different aspect of fiber analysis as it focuses on the total fluorescence emission of fibers. In addition to the contribution of the textile dye (or dyes) to the fluorescence spectrum of the fiber, we consider the contribution of intrinsic fluorescence impurities (-) i.e. impurities imbedded into the fibers during fabrication of garments - as a reproducible source of fiber comparison. Although fluorescence microscopy is used in forensic labs for single fiber examination, measurements are made with the aid of band-pass filters that provide very limited information on the spectral profiles of fibers. We take the non-destructive nature of fluorescence microscopy to a higher level of selectivity with the collection of room-temperature fluorescence excitation emission matrices (RTF-EEMs). The information contained in the EEMs was first used to select the best excitation wavelength for recording first order data, i.e. two-dimensional fluorescence spectra. Pairwise comparisons involved the following visually indistinguishable fibers: nylon 361 pre-dyed with acid yellow (AY) 17 and AY 23, acrylic 864 pre-dyed with basic green (BG) 1 and BG 4, acetate satin 105B pre-dyed with disperse blue (DB) 3 and DB 14, and polyester 777 pre-dyed with disperse red (DR) 1 and DR 19. With the exception of acrylic 864 fibers dyed with BG1 and BG4, the comparison of two-dimensional spectra via principal component analysis (PCA) provided accurate fiber identification for all the analyzed fibers. The same approach was later applied to the investigation of laundering effects on the comparison of textile fibers. The presence of brighteners and other detergent components adsorbed in the fibers provided spectral fingerprints that enhanced the fiber identification process.The full dimensionality of EEMs was then explored with the aid of parallel factor analysis (PARAFAC), a second order algorithm capable to determine the number of fluorescence components that contribute to an EEM along with their individual excitation and emission profiles. The application of PARAFAC was carried out unsupervised and supervised by linear discrimination analysis (LDA). The classification performances of PARAFAC and LDA-supervised PARAFAC were compared to the one obtained with supervised discriminant unfolded partial least squares (DU-PLS). The best discrimination was obtained with the supervised DU-PLS, which allowed the pairwise differentiation of the four pairs of investigated fibers.DU-PLS was then used to investigate weathering effects on the spectral features of cotton 400 pre-dyed with DB1, nylon 361 pre-dyed with AY17 and acrylic 864 pre-dyed with BG4. The investigated fibers were exposed to humid (Florida) and dry (Arizona) weathering conditions for three, six, nine and twelve months. In all cases, this algorithm was unable to differentiate non-exposed acrylic fibers from exposed acrylic fibers. DU-PLS was able to differentiate non-exposed cotton and nylon fibers from exposed fibers to Florida and Arizona weathering conditions. It was possible to determine the period of exposure to either Florida or Arizona conditions. It was also possible to discriminate between fibers exposed to Florida or Arizona weathering conditions for the same period of time. These results provide the foundation for future studies towards a non-destructive approach capable to provide information on the history of the fiber.
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Date Issued: 2016
Identifier: CFE0006838, ucf:51773
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006838

Title: Optically Induced Forces in Scanning Probe Microscopy.
Creator: Kohlgraf-Owens, Dana, Dogariu, Aristide, Christodoulides, Demetrios, Kik, Pieter, DeWilde, Yannick, University of Central Florida
Abstract / Description: The focus of this dissertation is the study of measuring light not by energy transfer as is done with a standard photodetector such as a photographic film or charged coupled device, but rather by the forces which the light exerts on matter. In this manner we are able to replace or complement standard photodetector-based light detection techniques. One key attribute of force detection is that it permits the measurement of light over a very large range of frequencies including those which are...
Show moreThe focus of this dissertation is the study of measuring light not by energy transfer as is done with a standard photodetector such as a photographic film or charged coupled device, but rather by the forces which the light exerts on matter. In this manner we are able to replace or complement standard photodetector-based light detection techniques. One key attribute of force detection is that it permits the measurement of light over a very large range of frequencies including those which are difficult to access with standard photodetectors, such as the far IR and THz. The dissertation addresses the specific phenomena associated with optically induced force (OIF) detection in the near-field where light can be detected with high spatial resolution close to material interfaces. This is accomplished using a scanning probe microscope (SPM), which has the advantage of already having a sensitive force detector integrated into the system. The two microscopies we focus on here are atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM). By detecting surface-induced forces or force gradients applied to a very small size probe ( diameter), AFM measures the force acting on the probe as a function of the tip-sample separation or extracts topography information. Typical NSOM utilizes either a small aperture ( diameter) to collect and/or radiate light in a small volume or a small scatterer ( diameter) in order to scatter light in a very small volume. This light is then measured with an avalanche photodiode or a photomultiplier tube.These two modalities may be combined in order to simultaneously map the local intensity distribution and topography of a sample of interest. A critical assumption made when performing such a measurement is that the distance regulation, which is based on surface induced forces, and the intensity distribution are independent. In other words, it is assumed that the presence of optical fields does not influence the AFM operation. However, it is well known that light exerts forces on the matter with which it interacts. This light-induced force may affect the atomic force microscope tip-sample distance regulation mechanism or, by modifying the tip, it may also indirectly influence the distance between the probe and the surface. This dissertation will present evidence that the effect of optically induced forces is strong enough to be observed when performing typical NSOM measurements. This effect is first studied on common experimental situations to show where and how these forces manifest themselves. Afterward, several new measurement approaches are demonstrated, which take advantage of this additional information to either complement or replace standard NSOM detection. For example, the force acting on the probe can be detected while simultaneously extracting the tip-sample separation, a measurement characteristic which is typically difficult to obtain. Moreover, the standard field collection with an aperture NSOM and the measurement of optically induced forces can be operated simultaneously. Thus, complementary information about the field intensity and its gradient can be, for the first time, collected with a single probe. Finally, a new scanning probe modality, multi-frequency NSOM (MF-NSOM), will be demonstrated. In this approach, the tuning fork is driven electrically at one frequency to perform a standard tip-sample distance regulation to follow the sample topography and optically driven at another frequency to measure the optically induced force. This novel technique provides a viable alternative to standard NSOM scanning and should be of particular interest in the long wavelength regime, e.g. far IR and THz.
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Date Issued: 2013
Identifier: CFE0004705, ucf:49829
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004705

Title: Interplay of Molecular and Nanoscale Behaviors in Biological Soft Matter.
Creator: Ciaffone, Nicholas, Tetard, Laurene, Kang, Hyeran, Santra, Swadeshmukul, University of Central Florida
Abstract / Description: The complexity of biological soft matter at the sub-micrometer level is fundamentally correlated to the functionalities at the larger scale. Reflecting the level of heterogeneities in the properties of systems remains challenging when probing small scales, due to the mismatch between the area surveyed with the tools offering nanoscale resolution, such as atomic force microscopy (AFM), and the scale of natural variations inherent to biology. Hence, to understand the physiological and...
Show moreThe complexity of biological soft matter at the sub-micrometer level is fundamentally correlated to the functionalities at the larger scale. Reflecting the level of heterogeneities in the properties of systems remains challenging when probing small scales, due to the mismatch between the area surveyed with the tools offering nanoscale resolution, such as atomic force microscopy (AFM), and the scale of natural variations inherent to biology. Hence, to understand the physiological and mechanical alterations that occur within a single cell relative to a cell population, a multiscale approach is necessary. In this work we show that it is possible to observe molecular, chemical and physical alterations in both plant and human cells with a multiscale approach. Biophysical and biochemical traits of cell populations are studied with Fourier Transform infrared spectroscopy (FTIR) and in turn, guide higher resolution discovery with Raman spectroscopy and nanoscale infrared spectroscopy using AFM (NanoIR) to access finer details. We illustrate this with three examples of biological soft matter systems: 1) a preliminary study of cellular interactions with naturally occurring vehicles applicable to human health, 2) a qualitative examination of antibiotics and new pesticide treatments in food crop systems, and 3) a fundamental investigation of the deconstruction mechanisms of plant cells during pre-treatments in preparation for biofuel production.
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Date Issued: 2018
Identifier: CFE0007395, ucf:52058
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007395

Title: Interdiffusion reaction between uranium-zirconium and iron.
Creator: Park, Young Joo, Sohn, Yongho, Coffey, Kevin, Fang, Jiyu, University of Central Florida
Abstract / Description: U-Zr metallic fuels cladded in Fe-alloys are being considered for application in an advanced Sodium-Cooled Fast Reactor (SFR) that can recycle the U-Zr fuels and minimize the long-lived actinide waste. To understand the complex fuel-cladding chemical interaction of the U-Zr metallic fuel with Fe-alloys, a systematic multicomponent diffusion study was carried out using solid-to-solid diffusion couples. The U-10 wt.% Zr vs. pure Fe diffusion couples were assembled and annealed at temperatures,...
Show moreU-Zr metallic fuels cladded in Fe-alloys are being considered for application in an advanced Sodium-Cooled Fast Reactor (SFR) that can recycle the U-Zr fuels and minimize the long-lived actinide waste. To understand the complex fuel-cladding chemical interaction of the U-Zr metallic fuel with Fe-alloys, a systematic multicomponent diffusion study was carried out using solid-to-solid diffusion couples. The U-10 wt.% Zr vs. pure Fe diffusion couples were assembled and annealed at temperatures, 630, 650 and 680(&)deg;C for 96 hours. Development of microstructure, phase constituents, and compositions developed during the thermal anneals were examined by scanning electron microscopy, transmission electron microscopy and X-ray energy dispersive spectroscopy. A complex microstructure consisting of several layers that include phases such as U6Fe, UFe2, ZrFe2, ?-U, ?-U, Zr-precipitates, ?, ?, and ? was observed. Multi-phase layers were grouped based on phase constituents and microstructure, and the layer thicknesses were measured to calculate the growth constant and activation energy. The local average compositions through the interaction layer were systematically determined, and employed to construct semi-quantitative diffusion paths on isothermal U-Zr-Fe ternary phase diagrams at respective temperatures. The diffusion paths were examined to qualitatively estimate the diffusional behavior of individual components and their interactions. Furthermore, selected area diffraction analyses were carried out to determine, for the first time, the exact crystal structure and composition of the ?, ? and ?-phases. The ?, ? and ?-phases were identified as Pnma(62) Fe(Zr,U), I4/mcm(140) Fe(Zr,U)2, and I4/mcm(140) U3(Zr,Fe), respectively.
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Date Issued: 2013
Identifier: CFE0004908, ucf:49616
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004908

Title: Synchrotron based infrared microspectroscopy of carbonaceous chondrites.
Creator: Yesiltas, Mehmet, Peale, Robert, Fernandez, Yan, Britt, Daniel, Reach, William, University of Central Florida
Abstract / Description: Relationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with...
Show moreRelationships between organic molecules and inorganic minerals are investigated in five carbonaceous chondrites, Northwest Africa 852 (CR2), Tagish Lake (C2-ungroupped), Orgueil (CI1), Sutter's Mill (CM), and Murchison (CM2), with micron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for various constituents are determined using statistical correlation analysis. Silicate band is found to be positively correlated with stretching modes of aliphatic hydrocarbons in NWA 852 and Tagish Lake. The former is highly correlated with the hydration band in all meteorites. Negative correlation is observed between water+organics and carbonate bands in all meteorites. Two dimensional infrared maps for NWA 852 and Orgueil show that carbonates are spatially separated from water+organic combination, silicates, OH, and CH distributions. Overlapping of the latter three in NWA 852 and Tagish Lake suggests a possible catalytic role of phyllosilicates in the formation of organics. Additionally, spectroscopic analyses on Sutter's Mill meteorite fragments present multiple distinct mineralogies. Spatial and spectral evidences on this regolith breccia suggest mixing of multiple parent bodies. Ratios of asymmetric CH2 and CH3 band strengths for NWA 852, Tagish Lake, and Sutter's Mill are similar to the average ratio of interplanetary dust particles and Wild 2 cometary dust particles, however significantly exceeds that of interstellar medium objects and several aqueously altered carbonaceous chondrites such as Orgueil. This suggests distinct formation regions and/or parent body processing of organics for these meteorites. Our infrared spectro-microtomography measurements on Murchison meteorite, representing the first such measurement on any kind of meteorite, comprise of three-dimensional reconstructions of specific molecular functional groups for understanding the spatial distributions of these groups.
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Date Issued: 2015
Identifier: CFE0006061, ucf:50966
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006061

Title: Advanced Nanoscale Characterization of Plants and Plant-derived Materials for Sustainable Agriculture and Renewable Energy.
Creator: Soliman, Mikhael, Tetard, Laurene, Vaidyanathan, Raj, Kang, Hyeran, Santra, Swadeshmukul, Zhai, Lei, Chumbimuni Torres, Karin, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2018
Identifier: CFE0007415, ucf:52717
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007415

Title: ON THE USE OF VARIABLE COHERENCE IN INVERSE SCATTERING PROBLEMS.
Creator: Baleine, Erwan, Dogariu, Aristide, University of Central Florida
Abstract / Description: Even though most of the properties of optical fields, such as wavelength, polarization, wavefront curvature or angular spectrum, have been commonly manipulated in a variety of remote sensing procedures, controlling the degree of coherence of light did not find wide applications until recently. Since the emergence of optical coherence tomography, a growing number of scattering techniques have relied on temporal coherence gating which provides efficient target selectivity in a way achieved only...
Show moreEven though most of the properties of optical fields, such as wavelength, polarization, wavefront curvature or angular spectrum, have been commonly manipulated in a variety of remote sensing procedures, controlling the degree of coherence of light did not find wide applications until recently. Since the emergence of optical coherence tomography, a growing number of scattering techniques have relied on temporal coherence gating which provides efficient target selectivity in a way achieved only by bulky short pulse measurements. The spatial counterpart of temporal coherence, however, has barely been exploited in sensing applications. This dissertation examines, in different scattering regimes, a variety of inverse scattering problems based on variable spatial coherence gating. Within the framework of the radiative transfer theory, this dissertation demonstrates that the short range correlation properties of a medium under test can be recovered by varying the size of the coherence volume of an illuminating beam. Nonetheless, the radiative transfer formalism does not account for long range correlations and current methods for retrieving the correlation function of the complex susceptibility require cumbersome cross-spectral density measurements. Instead, a variable coherence tomographic procedure is proposed where spatial coherence gating is used to probe the structural properties of single scattering media over an extended volume and with a very simple detection system. Enhanced backscattering is a coherent phenomenon that survives strong multiple scattering. The variable coherence tomography approach is extended in this context to diffusive media and it is demonstrated that specific photon trajectories can be selected in order to achieve depth-resolved sensing. Probing the scattering properties of shallow and deeper layers is of considerable interest in biological applications such as diagnosis of skin related diseases. The spatial coherence properties of an illuminating field can be manipulated over dimensions much larger than the wavelength thus providing a large effective sensing area. This is a practical advantage over many near-field microscopic techniques, which offer a spatial resolution beyond the classical diffraction limit but, at the expense of scanning a probe over a large area of a sample which is time consuming, and, sometimes, practically impossible. Taking advantage of the large field of view accessible when using the spatial coherence gating, this dissertation introduces the principle of variable coherence scattering microscopy. In this approach, a subwavelength resolution is achieved from simple far-zone intensity measurements by shaping the degree of spatial coherence of an evanescent field. Furthermore, tomographic techniques based on spatial coherence gating are especially attractive because they rely on simple detection schemes which, in principle, do not require any optical elements such as lenses. To demonstrate this capability, a correlated lensless imaging method is proposed and implemented, where both amplitude and phase information of an object are obtained by varying the degree of spatial coherence of the incident beam. Finally, it should be noted that the idea of using the spatial coherence properties of fields in a tomographic procedure is applicable to any type of electromagnetic radiation. Operating on principles of statistical optics, these sensing procedures can become alternatives for various target detection schemes, cutting-edge microscopies or x-ray imaging methods.
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Date Issued: 2006
Identifier: CFE0001387, ucf:47005
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001387

Title: SYNTHESIS, CHARACTERIZATION, AND EVALUATION OF NEW REACTIVE TWO-PHOTON ABSORBING DYES FOR TWO-PHOTON EXCITED FLUORESCENCE IMAGING APPLICATIONS.
Creator: Hales, Katherine, Belfield, Kevin, University of Central Florida
Abstract / Description: Recent, cooperative advances in chemistry, computing, optics, and microelectronics have resulted in extraordinary developments in the biological sciences, resulting in the emergence of a novel area termed ¡¥biophotonics¡¦. The interdisciplinary nature of biophotonics cuts across virtually all disciplines, extending the frontiers of basic cellular, molecular, and biology research. This holds true for the development and application of the novel imaging modality utilizing...
Show moreRecent, cooperative advances in chemistry, computing, optics, and microelectronics have resulted in extraordinary developments in the biological sciences, resulting in the emergence of a novel area termed ¡¥biophotonics¡¦. The interdisciplinary nature of biophotonics cuts across virtually all disciplines, extending the frontiers of basic cellular, molecular, and biology research. This holds true for the development and application of the novel imaging modality utilizing multiphoton absorption and its extraordinary contribution to advances in bioimaging. Intimately involved in the revolution of nonlinear bioimaging has been the development of optical probes for probing biological function and activity. The focus of this dissertation is in the area of probe development, particularly ƒà-conjugated organic probes, optimized for efficient two-photon absorption followed by upconverted fluorescence for multiphoton bioimaging. Specifically, fluorene molecules, with enhanced two-photon absorbing (2PA) properties and high photostability, were prepared and characterized. Contemporary synthetic methods were utilized to prepare target fluorene derivatives expected to be highly fluorescent and, in particular, exhibit high two-photon absorptivity, suitable for two-photon excitation (2PE) fluorescence microscopy. The flexibility afforded through synthetic manipulation for integrating hydrophilic moieties into the fluorophore architecture to enhance compatibility with aqueous systems, more native to biological samples, was attempted. Incorporation of functional groups for direct covalent attachment onto biomolecules was also pursued to prepare fluorene derivatives as efficient 2PA reactive probes. Linear and two-photon spectroscopic characterizations on these novel compounds reveal they exhibit relatively high 2PA cross-sections on the order of ~100 GM units, which is greater than typical, commonly used fluorophores utilized in multiphoton bioimaging. Extensive photostability studies of representative fluorene compounds demonstrate these derivatives are photostable under one- and two-photon excitation conditions, exhibiting photodecomposition quantum yields on the order of 10-5. Additionally, preliminary cytotoxicity studies indicate these fluorene derivatives exhibit minimal cytotoxic effects on proliferating cells. Finally, their utility as high-performance, 2PA fluorescent probes in 2PE fluorescence microscopy imaging of biological samples was demonstrated in both fixed and live cells. Due to the low cytotoxicity, high photostability, efficient 2PA, and high fluorescence quantum yield, the probes were found suitable for relatively long-term, two-photon fluorescence imaging of live cells, representing a significant advance in biophotonics.
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Date Issued: 2005
Identifier: CFE0000685, ucf:46487
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000685

Title: TRANSMISSION ELECTRON MICROSCOPY STUDIES IN SHAPE MEMORY ALLOYS.
Creator: TIYYAGURA, MADHAVI, VAIDYANATHAN, RAJ, University of Central Florida
Abstract / Description: In NiTi, a reversible thermoelastic martensitic transformation can be induced by temperature or stress between a cubic (B2) austenite phase and a monoclinic (B19') martensite phase. Ni-rich binary compositions are cubic at room temperature (requiring stress or cooling to transform to the monoclinic phase), while Ti-rich binary compositions are monoclinic at room temperature (requiring heating to transform to the cubic phase). The stress induced transformation results in the superelastic...
Show moreIn NiTi, a reversible thermoelastic martensitic transformation can be induced by temperature or stress between a cubic (B2) austenite phase and a monoclinic (B19') martensite phase. Ni-rich binary compositions are cubic at room temperature (requiring stress or cooling to transform to the monoclinic phase), while Ti-rich binary compositions are monoclinic at room temperature (requiring heating to transform to the cubic phase). The stress induced transformation results in the superelastic effect, while the thermally induced transformation is associated with strain recovery that results in the shape memory effect. Ternary elemental additions such as Fe can additionally introduce an intermediate rhombohedral (R) phase between the cubic and monoclinic phase transformation. This work was initiated with the broad objective of connecting the macroscopic behavior in shape memory alloys with microstructural observations from transmission electron microscopy (TEM). Specifically, the goals were to examine (i) the effect of mechanical cycling and plastic deformation in superelastic NiTi; (ii) the effect of thermal cycling during loading in shape memory NiTi; (iii) the distribution of twins in martensitic NiTi-TiC composites; and (iv) the R-phase in NiTiFe. Both in situ and ex situ lift out focused ion beam (FIB) and electropolishing techniques were employed to fabricate shape memory alloy samples for TEM characterization. The Ni rich NiTi samples were fully austenitic in the undeformed state. The introduction of plastic deformation (8% and 14% in the samples investigated) resulted in the stabilization of martensite in the unloaded state. An interlaying morphology of the austenite and martensite was observed and the martensite needles tended to orient themselves in preferred orientations. The aforementioned observations were more noticeable in mechanically cycled samples. The observed dislocations in mechanically cycled samples appear to be shielded from the external applied stress via mismatch accommodation since they are not associated with unrecoverable strain after a load-unload cycle. On application of stress, the austenite transforms to martensite and is expected to accommodate the stress and strain mismatch through preferential transformation, variant selection, reorientation and coalescence. The stabilized martensite (i.e., martensite that exists in the unloaded state) is expected to accommodate the mismatch through variant reorientation and coalescence. On thermally cycling a martensitic NiTi sample under load through the phase transformation, significant variant coalescence, variant reorientation and preferred variant selection was observed. This was attributed to the internal stresses generated as a result of the thermal cycling. A martensitic NiTi-TiC composite was also characterized and the interface between the matrix and the inclusion was free of twins while significant twins were observed at a distance away from the matrix-inclusion interface. Incorporating a cold stage, diffraction patterns from NiTiFe samples were obtained at temperatures as low as -160ºC. Overall, this work provided insight in to deformation phenomena in shape memory materials that have implications for engineering applications (e.g., cyclic performance of actuators, engineering life of superelastic components, stiffer shape memory composites and low-hysteresis R-phase based actuators). This work was supported in part by an NSF CAREER award (DMR 0239512).
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Date Issued: 2005
Identifier: CFE0000500, ucf:46462
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000500

Title: INDIVIDUAL CARBON NANOTUBE PROBES AND FIELD EMITTERS FABRICATION AND THEIR PROPERTIES.
Creator: Chai, Guangyu, Chow, Lee, University of Central Florida
Abstract / Description: Since the discovery of carbon nanotubes (CNT) in 1999, they have attracted much attention due to their unique mechanical and electrical properties and potential applications. Yet their nanosize makes the study of individual CNTs easier said than done. In our laboratory, carbon fibers with nanotube cores have been synthesized with conventional chemical vapor deposition (CVD) method. The single multiwall carbon nanotube (MWNT) sticks out as a tip of the carbon fiber. In order to pick up the...
Show moreSince the discovery of carbon nanotubes (CNT) in 1999, they have attracted much attention due to their unique mechanical and electrical properties and potential applications. Yet their nanosize makes the study of individual CNTs easier said than done. In our laboratory, carbon fibers with nanotube cores have been synthesized with conventional chemical vapor deposition (CVD) method. The single multiwall carbon nanotube (MWNT) sticks out as a tip of the carbon fiber. In order to pick up the individual CNT tips, focused ion beam (FIB) technique is applied to cut and adhere the samples. The carbon fiber with nanotube tip was first adhered on a micro-manipulator with the FIB welding function. Afterwards, by applying the FIB milling function, the fiber was cut from the base. This enables us to handle the individual CNT tips conveniently. By the same method, we can attach the nanotube tip on any geometry of solid samples such as conventional atomic force microscopy (AFM) silicon tips. The procedures developed for the FIB assisted individual CNT tip fabrication will be described in detail. Because of their excellent electrical and stable chemical properties, individual CNTs are potential candidates as electron guns for electron based microscopes to produce highly coherent electron beams. Due to the flexibility of the FIB fabrication, the individual CNT tips can be easily fabricated on a sharpened clean tungsten wire for field emission (FE) experimentation. Another promising application for individual CNT tips is as AFM probes. The high aspect ratio and mechanical resilience make individual CNTs ideal for scanning probe microscopy (SPM) tips. Atomic force microscopy with nanotube tips allows us to image relatively deep features of the sample surface at near nanometer resolution. Characterization of AFM with individual CNT tips and field emission properties of single CNT emitters will be studied and presented.
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Date Issued: 2004
Identifier: CFE0000248, ucf:46233
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000248

Title: Nanoscale Spectroscopy in Energy and Catalytic Applications.
Creator: Ding, Yi, Tetard, Laurene, Challapalli, Suryanarayana, Zhai, Lei, Thomas, Jayan, Lyakh, Arkadiy, Blair, Richard, University of Central Florida
Abstract / Description: Emerging societal challenges such as the need for more sustainable energy and catalysis are requiring more sensitive and versatile measurements at the nanoscale. This is the case in the design and optimization of new materials for energy harvesting (solar cells) and energy storage devices (batteries and capacitors), or for the development of new catalysts for carbon sequestration or other reactions of interest. Hence, the ability to advance spectroscopy with nanoscale spatial resolution and...
Show moreEmerging societal challenges such as the need for more sustainable energy and catalysis are requiring more sensitive and versatile measurements at the nanoscale. This is the case in the design and optimization of new materials for energy harvesting (solar cells) and energy storage devices (batteries and capacitors), or for the development of new catalysts for carbon sequestration or other reactions of interest. Hence, the ability to advance spectroscopy with nanoscale spatial resolution and high sensitivity holds great promises to meet the demands of deeper fundamental understanding to boost the development and deployment of nano-based devices for real applications. In this dissertation, the impact of nanoscale characterization on energy-related and catalytic materials is considered. Firstly an introduction of the current energy and environmental challenges and our motivations are presented. We discuss how revealing nanoscale properties of solar cell active layers and supercapacitor electrodes can greatly benefit the performance of devices, and ponder on the advantages over conventional characterization techniques. Next, we focus on two dimensional materials as promising alternative catalysts to replace conventional noble metals for carbon sequestration and its conversion to added-value products. Defect-laden hexagonal boron nitride (h-BN) has been identified as a good catalyst candidate for carbon sequestration. Theoretically, defects exhibit favorable properties as reaction sites. However, the detailed mechanism pathways cannot be readily probed experimentally, due to the lack of tools with sufficient sensitivity and time resolution. A comprehensive study of the design and material processes used to introduce defects in h-BN in view of improving the catalytic properties is presented. The processing-structure-property relationships are investigated using a combination of conventional characterization and advanced nanoscale techniques. In addition to identifying favorable conditions for defect creation, we also report on the first signs of local reactions at defect sites obtained with nanoscale spectroscopy. Next, we explore avenues to improve the sensitivity and time-resolution of nanoscale measurements using light-assisted AFM-based nanomechanical spectroscopy. For each configuration, we evaluate the new system by comparing its performance to the commercial capabilities.Lastly, we provide a perspective on the opportunities for state-of-the-art characterization to impact the fields of catalysis and sustainable energy, as well as the urge for highly sensitive functional capabilities and time-resolution for nanoscale studies.
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Date Issued: 2018
Identifier: CFE0007751, ucf:52387
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007751

Title: Asteroid Surfaces: The Importance of Cohesive Forces.
Creator: Jardine, Keanna, Dove, Adrienne, Tetard, Laurene, Britt, Daniel, University of Central Florida
Abstract / Description: Adhesive forces play a significant role on airless bodies due to their weak gravities. Investigating adhesion at the surface of asteroids and their constituent components is vital to understanding their formation and evolution. Previous research has been done to understand the interaction of micron-sized spheres to planar surfaces and sphere-to-sphere interactions, which have been used to develop models of asteroid surfaces. Our investigation experimentally investigates adhesion through...
Show moreAdhesive forces play a significant role on airless bodies due to their weak gravities. Investigating adhesion at the surface of asteroids and their constituent components is vital to understanding their formation and evolution. Previous research has been done to understand the interaction of micron-sized spheres to planar surfaces and sphere-to-sphere interactions, which have been used to develop models of asteroid surfaces. Our investigation experimentally investigates adhesion through atomic force microscopy (AFM) measurements between JSC-1 simulant particles and several AFM tips, including a typical pyramidal gold tip and microspheres of sizes 2 (&)#181;m and 15 (&)#181;m. The samples of JSC-1 consist of three size ranges: (<) 45 (&)#181;m, 75-125 (&)#181;m, and 125-250 (&)#181;m. For each sample we looked at the magnitude and distribution of the measured adhesive forces. Results show that the pyramidal tip produced larger forces than the spherical tips generally, and the sample that produced larger forces and a larger distribution of those force was the smaller, more powder-like sample with sizes (<)45 (&)#181;m.
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Date Issued: 2018
Identifier: CFE0007755, ucf:52377
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007755

Title: Study of Surface Passivation Behavior of Crystalline Silicon Solar Cells.
Creator: Ali, Haider, Schoenfeld, Winston, Coffey, Kevin, Gaume, Romain, Thomas, Jayan, Chanda, Debashis, University of Central Florida
Abstract / Description: To achieve efficiencies approaching the theoretical limit of 29.4% for industrially manufactured solar cells based on crystalline silicon, it is essential to have very low surface recombination velocities at both the front and rear surfaces of the silicon substrate. Typically, the substrate surfaces feature contacted and uncontacted regions, and recombination should be limited for both to maximize the energy conversion efficiency.Uncontacted silicon surfaces are often passivated by the...
Show moreTo achieve efficiencies approaching the theoretical limit of 29.4% for industrially manufactured solar cells based on crystalline silicon, it is essential to have very low surface recombination velocities at both the front and rear surfaces of the silicon substrate. Typically, the substrate surfaces feature contacted and uncontacted regions, and recombination should be limited for both to maximize the energy conversion efficiency.Uncontacted silicon surfaces are often passivated by the deposition of silicon nitride (SiNx) or an aluminum oxide film with SiNx as capping layer (Al2O3/SiNx stack). Further, proper surface preparation and cleaning of Si wafers prior to deposition also plays an important role in minimizing surface recombination. In the present work, the effect of various cleans based on different combinations of HCl, HF, HNO3, and ozonated deionized water (DIO3) on surface passivation quality of boron-diffused and undiffused {100} n-type Cz Si wafers was studied. It was observed that for SiNx passivated Si, carrier lifetime was strongly influenced by cleaning variations and that a DIO3-last treatment resulted in higher lifetimes. Moreover, DIO3+HF+HCl?HF?DIO3 and HNO3?HF?HNO3 cleans emerged as potential low-cost alternatives to HCl/HF clean in the photovoltaics industry.Transmission electron microscopy (TEM) studies were carried out to get insight into the origin of variation in carrier lifetimes for different cleans. Changes in the surface cleans used were not found to have a significant impact on Al2O3/SiNx passivation stacks.ivHowever, an oxide-last cleaning step prior to deposition of SiNx passivation layers was found to create a 1-2 nm SiOx tunnel layer resulting in excellent carrier lifetimes.For contacted regions, low surface recombination can be achieved using passivated carrier selective contacts, which not only passivate the silicon surface and improve the open circuit voltage, but are also carrier selective. This means they only allow the majority carrier to be transported to the metal contacts, limiting recombination by reducing the number of minority carriers. Typically, carrier selectivity is achieved using a thin metal oxide layer, such as titanium oxide (TiO2) for electron-selective contacts and molybdenum oxide (MoOx) for hole-selective contacts. This is normally coupled with a very thin passivation layer (e.g., a-Si:H, SiOx) between the silicon wafer and the contact.In the present work, TiO2-based electron-selective passivated rear contacts were investigated for n-type c-Si solar cells. A low efficiency of 9.8% was obtained for cells featuring a-Si:H/TiO2 rear contact, which can be attributed to rapid degradation of surface passivation of a-Si:H upon FGA at 350(&)deg;C due to hydrogen evolution leading to generation of defect states which increases recombination and hence a much lower Voc of 365 mV is obtained. On the other hand, 21.6% efficiency for cells featuring SiO2/TiO2 rear contact is due to excellent passivation of SiO2/TiO2 stack upon FGA anneal, which can be attributed to the presence of 1-2 nm SiO2 layer whose passivation performance improves upon FGA at 350(&)deg;C whereas presence of large number of oxygen vacancies in TiO2-x reduces rear contact resistivity.vLikewise, MoOx-based contacts were investigated as hole-selective front contacts for an n-type cell with a boron-doped emitter. It has been previously reported that cell efficiencies up to 22.5% have been achieved with silicon heterojunction solar cells featuring a front contact wherein MoOx is inserted between a-Si:H(i) and hydrogenated indium oxide (IO:H). However, device performance and FF degrades upon annealing beyond 130(&)deg;C. In this work, contact resistivity measurements by TLM technique in combination with TEM studies revealed that degradation of device performance is due to oxygen diffusion into MoOx upon annealing in air which reduces concentration of oxygen vacancies in MoOx and increases contact resistivity. The increase in contact resistivity reduces FF resulting in deterioration of device performance.
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Date Issued: 2017
Identifier: CFE0006554, ucf:51351
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006554

Title: Probing the Influence of Cx43 and Glucose on Endothelial Biomechanics.
Creator: Islam, Md Mydul, Steward, Robert, Kassab, Alain, Mansy, Hansen, Willenberg, Bradley, University of Central Florida
Abstract / Description: Endothelial cells (ECs) form the innermost layer of all vasculature and constantly receive both biochemical and biomechanical signals, yielding a plethora of biomechanical responses. In response to various biochemical or biomechanical cues, ECs have been documented to generate biomechanical responses such as tractions and intercellular stresses between the cell and substrate and between adjacent cells in a confluent monolayer, respectively. Thus far, the ability of endothelial tight junctions...
Show moreEndothelial cells (ECs) form the innermost layer of all vasculature and constantly receive both biochemical and biomechanical signals, yielding a plethora of biomechanical responses. In response to various biochemical or biomechanical cues, ECs have been documented to generate biomechanical responses such as tractions and intercellular stresses between the cell and substrate and between adjacent cells in a confluent monolayer, respectively. Thus far, the ability of endothelial tight junctions and adherens junctions to transmit intercellular stresses has been actively investigated, but the role of gap junctions is currently unknown. In addition, there is no report of the independent influence of hyperglycemia on endothelial biomechanics present in the literature. To fill these gaps, we conducted a two-fold study where we investigated the influence of endothelial gap junction Cx43 and hyperglycemia in endothelial tractions and intercellular stress generation. In the first study, we selectively disrupted and enhanced EC gap junction Cx43 by using 2',5'-dihydroxychalcone and retinoic acid, respectively and in the second study, we cultured ECs in both normal glucose and hyperglycemic condition for 10 days. In both studies, tractions and intercellular stresses were calculated using traction force microscopy (TFM) and monolayer stress microscopy (MSM), respectively. Our results reveal that Cx43 downregulation increased as well as decreased endothelial avg. normal intercellular stresses in response to a low (0.83 (&)#181;M) and a high dose (8.3 (&)#181;M) chalcone treatment, respectively, while Cx43 upregulation decreases avg. normal intercellular stresses in both treatment conditions (2.5 (&)#181;M and 25 (&)#181;M) compared to control. In addition, we observed a decrease in intercellular stresses with hyperglycemic condition compared to control. The results we present here represent, for the first time, detailed and comprehensive biomechanical analysis of endothelial cells under the influence of glucose and the gap junction Cx43. We believe our results will provide valuable insights into endothelial permeability, barrier strength as well as leading to a greater understanding of overall endothelial mechanics.
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Date Issued: 2019
Identifier: CFE0007819, ucf:52805
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007819

Title: SYNTHESIS AND CHARACTERIZATION OF STABLE AND METASTABLE PHASES IN Ni- AND Fe-BASED ALLOY SYSTEMS BY MECHANICAL ALLOYING.
Creator: Al-Joubori, Ahmed, Challapalli, Suryanarayana, Vaidyanathan, Raj, Gou, Jihua, Bai, Yuanli, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: Mechanical Alloying (MA) is a process that involves repeated cold welding, fracturing and rewelding of powder particles in a high-energy ball mill and has been used extensively to synthesize both stable (equilibrium) and metastable phases in a number of alloy systems. This is due to its ability to achieve many effects simultaneously, viz., reduction in grain size, introduction of a variety of crystal defects, disordering of the lattice, and modifying the crystal structures of materials; all...
Show moreMechanical Alloying (MA) is a process that involves repeated cold welding, fracturing and rewelding of powder particles in a high-energy ball mill and has been used extensively to synthesize both stable (equilibrium) and metastable phases in a number of alloy systems. This is due to its ability to achieve many effects simultaneously, viz., reduction in grain size, introduction of a variety of crystal defects, disordering of the lattice, and modifying the crystal structures of materials; all these allowing alloying and phase transformations to occur in powders. In this Dissertation, we have synthesized a number of different alloy phases in Ni- and Fe-based alloy systems using MA.The as-received, blended, and milled powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy techniques to obtain information about the overall microstructure and chemical compositions. The NiX2 (X = Ge and Si) phases were synthesized in the Ni-Ge and Ni-Si systems. MA of Ni-Ge powder blends was investigated to study phase evolution as a function of milling time. On milling the powders for 5 h, the equilibrium NiGe phase started to form, and its amount in the powder increased with increasing milling time. On milling for about 60 h, the equilibrium intermetallic NiGe and Ge powder particles reacted to form the metastable NiGe2 phase. However, on milling for a longer time (75 h), the metastable phase transformed back to the equilibrium NiGe phase.Synthesis of the NiSi2 intermetallic phase depended on the Si content in the initial powder blend. For example, while in the Ni-60 at.% Si powder blend, only the NiSi phase was present homogeneously, the powder blend of the Ni-67 at.% Si composition contained the NiSi phase along with a small amount of unreacted Si. But in the Ni-75 at.% Si and Ni-80 at% compositions, the NiSi phase that had formed earlier (after 2 h of milling) and the remaining free Si powder reacted to form the equilibrium intermetallic NiSi2 phase. This constitution in the milled powder has been attributed to a partial loss of Si content during MA. Formation of Ni(Si) solid solutions with a solubility of about 18.2 at.% and 20.6 at.% for the Ni-75 at.% Si and Ni-80 at.% Si powder blends, respectively, was also achieved in the early stages of MA.In the Fe-C system, we were able to synthesize ferrite, cementite, and mixtures of the two phases. We were able to obtain the Fe-C solid solution phase (ferrite) with a BCC structure and the cementite phase with an orthorhombic structure in the eutectoid Fe-0.8 wt. % C composition, while a homogeneous cementite phase had formed at the higher carbon content of Fe-7.0 wt. % C after 30 h of milling time.In the case of the Fe-18Cr-xNi (x = 8, 12, and 20) system, the current investigation showed that the phase constitution depended significantly on the Ni content in the powder blend. Whereas mostly the martensite or the ferrite and austenite phase mixture was present at lower Ni contents, a completely homogeneous austenite phase was present in the alloy with 20% Ni.
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Date Issued: 2016
Identifier: CFE0006244, ucf:51059
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006244

Title: QUANTITATIVE HIGH-ANGLE ANNULAR DARK FIELD SCANNING TRANSMISSION ELECTRON MICROSCOPY FOR MATERIALS SCIENCE.
Creator: Petrova, Rumyana, Coffey, Kevin, University of Central Florida
Abstract / Description: Scanning transmission electron microscopy (STEM) has been widely used for characterization of materials; to identify micro- and nano-structures within a sample and to analyze crystal and defect structures. High-angle annular dark field (HAADF) STEM imaging using atomic number (Z) contrast has proven capable of resolving atomic structures with better than 2 Å lateral resolution. In this work, the HAADF STEM imaging mode is used in combination with multislice simulations. This combination...
Show moreScanning transmission electron microscopy (STEM) has been widely used for characterization of materials; to identify micro- and nano-structures within a sample and to analyze crystal and defect structures. High-angle annular dark field (HAADF) STEM imaging using atomic number (Z) contrast has proven capable of resolving atomic structures with better than 2 Å lateral resolution. In this work, the HAADF STEM imaging mode is used in combination with multislice simulations. This combination is applied to the investigation of the temperature dependence of the intensity collected by the HAADF detector in silicon, and to convergent beam electron diffraction (CBED) to measure the degree of chemical order in intermetallic nanoparticles. The experimental and simulation results on the high–angle scattering of 300 keV electrons in crystalline silicon provide a new contribution to the understanding of the temperature dependence of the HAADF intensity. In the case of 300 keV, the average high-angle scattered intensity slightly decreases as the temperature increases from 100 K to 300 K, and this is different from the temperature dependence at 100 keV and 200 keV where HAADF intensity increases with temperature, as had been previously reported by other workers. The L10 class of hard magnetic materials has attracted continuous attention as a candidate for high-density magnetic recording media, as this phase is known to have large magnetocrystalline anisotropy, with magnetocrystalline anisotropy constant, Ku, strongly dependent on the long-range chemical order parameter, S. A new method is developed to assess the degree of chemical order in small FePt L10 nanoparticles by implementing a CBED diffraction technique. Unexpectedly, the degree of order of individual particles is highly variable and not a simple function of particle size or sample composition. The particle-to-particle variability observed is an important new aspect to the understanding of phase transformations in nanoparticle systems.
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Date Issued: 2006
Identifier: CFE0001267, ucf:46931
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001267

Title: COHERENCE PROPERTIES OF OPTICAL NEAR-FIELDS.
Creator: Apostol, Adela, Dogariu, Aristide, University of Central Florida
Abstract / Description: Next generation photonics-based technologies will ultimately rely on novel materials and devices. For this purpose, phenomena at subwavelength scales are being studied to advance both fundamental knowledge and experimental capabilities. In this dissertation, concepts specific to near-field optics and experimental capabilities specific to near-field microscopy are used to investigate various aspects of the statistical properties of random electromagnetic fields in the vicinity of optically...
Show moreNext generation photonics-based technologies will ultimately rely on novel materials and devices. For this purpose, phenomena at subwavelength scales are being studied to advance both fundamental knowledge and experimental capabilities. In this dissertation, concepts specific to near-field optics and experimental capabilities specific to near-field microscopy are used to investigate various aspects of the statistical properties of random electromagnetic fields in the vicinity of optically inhomogeneous media which emit or scatter radiation. The properties of such fields are being characterized within the frame of the coherence theory. While successful in describing the far-field properties of optical fields, the fundamental results of the conventional coherence theory disregard the contribution of short-range evanescent waves. Nonetheless, the specific features of random fields at subwavelength distances from interfaces of real media are influenced by the presence of evanescent waves because, in this case, both propagating and nonpropagating components contribute to the detectable properties of the radiation. In our studies, we have fully accounted for both contributions and, as a result, different surface and subsurface characteristics of inhomogeneous media could be explored. We investigated different properties of random optical near-fields which exhibit either Gaussian or non-Gaussian statistics. We have demonstrated that characteristics of optical radiation such as first- and second-order statistics of intensity and the spectral density in the vicinity of random media are all determined by both evanescent waves contribution and the statistical properties of the physical interface. For instance, we quantified the subtle differences which exist between the near- and far-field spectra of radiation and we brought the first experimental evidence that, contrary to the predictions of the conventional coherence theory, the values of coherence length in the near field depend on the distance from the interface and, moreover, they can be smaller than the wavelength of light. The results included in this dissertation demonstrate that the statistical properties of the electromagnetic fields which exist in the close proximity of inhomogeneous media can be used to extract structural information. They also suggest the possibility to adjust the coherence properties of the emitted radiation by modifying the statistical properties of the interfaces. Understanding the random interference phenomena in the near-field could also lead to new possibilities for surface and subsurface diagnostics of inhomogeneous media. In addition, controlling the statistical properties of radiation at subwavelength scales should be of paramount importance in the design of miniaturized optical sources, detectors and sensors.
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Date Issued: 2005
Identifier: CFE0000408, ucf:46410
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000408

Title: CHARACTERIZATION OF MICROSTRUCTURAL AND CHEMICAL FEATURES IN CU-IN-GA-SE-S-BASED THIN-FILM SOLAR CELLS.
Creator: Halbe, Ankush, Heinrich, Helge, University of Central Florida
Abstract / Description: Thin-film solar cells are potentially low-cost devices to convert sunlight into electricity. Improvements in the conversion efficiencies of these cells reduce material utilization cost and make it commercially viable. Solar cells from the Thin-Film Physics Group, ETH Zurich, Switzerland and the Florida Solar Energy Center (FSEC), UCF were characterized for defects and other microstructural features within the thin-film structure and at the interfaces using transmission electron microscopy ...
Show moreThin-film solar cells are potentially low-cost devices to convert sunlight into electricity. Improvements in the conversion efficiencies of these cells reduce material utilization cost and make it commercially viable. Solar cells from the Thin-Film Physics Group, ETH Zurich, Switzerland and the Florida Solar Energy Center (FSEC), UCF were characterized for defects and other microstructural features within the thin-film structure and at the interfaces using transmission electron microscopy (TEM). The present thesis aims to provide a feedback to these groups on their deposition processes to understand the correlations between processing, resulting microstructures, and the conversion efficiencies of these devices. Also, an optical equipment measuring photocurrents from a solar cell was developed for the identification of defect-prone regions of a thin-film solar cell. The focused ion beam (FIB) technique was used to prepare TEM samples. Bright-field TEM along with scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) including elemental distribution line scans and maps were extensively used for characterizing the absorber layer and interfaces both above and below the absorber layer. Energy-filtered transmission electron microscopy (EFTEM) was applied in cases where EDS results were inconclusive due to the overlap of X-ray energies of certain elements, especially molybdenum and sulfur. Samples from ETH Zurich were characterized for changes in the CIGS (Cu(In,Ga)Se2) microstructure due to sodium incorporation from soda-lime glass or from a post-deposition treatment with NaF as a function of CIGS deposition temperature. The CIGS-CdS interface becomes smoother and the small columnar CIGS grains close to the Mo back contact disappear with increasing CIGS deposition temperature. At 773 K the two sodium incorporation routes result in large differences in the microstructures with a significantly larger grain size for the samples after post-deposition Na incorporation. Porosity was observed in the absorber layer close to the back contact in the samples from FSEC. The reason for porosity could be materials evaporation in the gallium beam of the FIB or a processing effect. The porosity certainly indicates heterogeneities of the composition of the absorber layer near the back contact. A Mo-Se rich layer (possibly MoSe2) was formed at the interface between CIGS/CIGSS and Mo improving the quality of the junction. Other chemical heterogeneities include un-sulfurized Cu-Ga deposits, residual Se from the selenization/ sulfurization chamber in CIGS2 and the formation of Cu-rich regions which are attributed to decomposition effects in the Ga beam of the FIB. Wavy absorber surfaces were observed for some of the cells with occasional discontinuities in the metal grids. The 50 nm thick CdS layer, however, remained continuous in all the samples under investigation. For a sample with a transparent back contact, a 10 nm Mo layer was deposited on ITO (indium tin oxide) before deposition of the CIGS2 (Cu(In,Ga)S2) layer. EFTEM maps indicate that a MoS2 layer does not form for such a Mo/MoS2-ITO back contact. Instead, absorber layer material diffuses through the thin Mo layer onto the ITO forming two layers of CIGS2 on either side of Mo with different compositions. Furthermore, an optical beam induced current (OBIC) system with micron level resolution was successfully developed and preliminary photocurrent maps were acquired to microscopically identify regions within a thin-film solar cell with undesirable microstructural features. Such a system, when fully operational, will provide the means for the identification of special regions from where samples for TEM analysis can be obtained using the FIB technique to study specifically the defects responsible for local variations in solar cell properties.
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Date Issued: 2006
Identifier: CFE0001022, ucf:46807
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001022

Atomic Force Microscopy (5)	+ -
Microscopy (3)	+ -
Raman Spectroscopy (3)	+ -
fluorescence microscopy (3)	+ -
microscopy (3)	+ -

two-photon absorption (3)	+ -
Coherence (2)	+ -
Optical Sensing (2)	+ -
Statistical optics (2)	+ -
atomic force microscopy (2)	+ -
photostability (2)	+ -
transmission electron microscopy (TEM) (2)	+ -
two-photon fluorescence microscopy (2)	+ -
304 stainless steel (1)	+ -
AFM (1)	+ -
AFM Nanoindentation (1)	+ -
Adhesion (1)	+ -
Asteroid Surfaces (1)	+ -
Azulene (1)	+ -
Bioimaging (1)	+ -
Bioimaging probe (1)	+ -
Block copolymer (1)	+ -
Carbon nanotube (1)	+ -
Cell Mechanics (1)	+ -
Cohesion (1)	+ -
Computational Imaging and Sensing (1)	+ -
Confocal Microscopy (1)	+ -
Confocal Raman Microscopy (1)	+ -
Database (1)	+ -
Diffusion (1)	+ -

ETD Collection (35)	+ -
Honors Collection (1)	+ -

University of Central Florida (36)	+ -
Dogariu, Aristide (5)	+ -
Tetard, Laurene (5)	+ -
Belfield, Kevin (4)	+ -
Coffey, Kevin (4)	+ -

Peale, Robert (3)	+ -
Britt, Daniel (2)	+ -
Campiglia, Andres (2)	+ -
Challapalli, Suryanarayana (2)	+ -
Fang, Jiyu (2)	+ -
Kaden, William (2)	+ -
Kang, Hyeran (2)	+ -
Riza, Nabeel (2)	+ -
Rolland, Jannick (2)	+ -
Santra, Swadeshmukul (2)	+ -
Sigman, Michael (2)	+ -
Sohn, Yongho (2)	+ -
Thomas, Jayan (2)	+ -
Vaidyanathan, Raj (2)	+ -
Zhai, Lei (2)	+ -
Abouelkhair, Hussain (1)	+ -
Abouraddy, Ayman (1)	+ -
Akhlaghi Bouzan, Milad (1)	+ -
Al-Joubori, Ahmed (1)	+ -
Ali, Haider (1)	+ -
Apostol, Adela (1)	+ -
Atia, George (1)	+ -
Bai, Yuanli (1)	+ -
Baleine, Erwan (1)	+ -
Belfield, Kevin D. (1)	+ -

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