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Title: SURFACTANT DRIVEN ASSEMBLY OF FREEZE-CASTED, POLYMER-DERIVED CERAMIC NANOPARTICLES ON GRAPEHENE OXIDE SHEETS FOR LITHIUM-ION BATTERY ANODES.
Creator: Khater, Ali Zein, Tetard, Laurene, Zhai, Lei, University of Central Florida
Abstract / Description: Traditional Lithium-Ion Batteries (LIBs) are a reliable and cost-efficient choice for energy storage. LIBs offer high energy density and low self-discharge. Recent developments in electric-based technologies push for replacing historically used Lead-Acid batteries with LIBs. However, LIBs do not yet meet the demands of modern technology. Silicon and graphene oxide (GO) have been identified as promising replacements to improve anode materials. Graphene oxide has a unique sheet-like structure...
Show moreTraditional Lithium-Ion Batteries (LIBs) are a reliable and cost-efficient choice for energy storage. LIBs offer high energy density and low self-discharge. Recent developments in electric-based technologies push for replacing historically used Lead-Acid batteries with LIBs. However, LIBs do not yet meet the demands of modern technology. Silicon and graphene oxide (GO) have been identified as promising replacements to improve anode materials. Graphene oxide has a unique sheet-like structure that provides a mechanically stable, light weight material for LIB anodes. Due to its structure, reduced graphene oxide (rGO) is efficiently conductive and resistive to environmental changes. On the other hand, silicon-based anode materials offer the highest theoretical energy density and a high Li-ion loading capacity of various elements [20]. Silicon-based anodes that have previously been studied demonstrated extreme volumetric expansion over long cycles due to lithiation. Polysiloxane may be an interesting alternative as it is a Si-based material that can retain the high Li-ion loading capacity of Si while lacking the unattractive volumetric expansions of Si. Polymer derived ceramic-decorated graphene oxide anodes have been suggested to increase loading capacity, thermal resistance, power density, and mechanical stability of LIBs. Coupled with mechanically stable graphene oxide, polymer derived ceramic nanoparticle decorated graphene oxide anodes are studied to establish their efficiencies under operating conditions.
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Date Issued: 2018
Identifier: CFH2000404, ucf:45765
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000404

Title: Nanoscale Functional Imaging by Tailoring Light-matter Interaction to Explore Organic and Biological Systems.
Creator: Otrooshi, Negar, Tetard, Laurene, Tatulian, Suren, Peale, Robert, Santra, Swadeshmukul, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2019
Identifier: CFE0007897, ucf:52750
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007897

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: Effects of Surfactant Concentrations on Perovskite Emitters Embedded in Polystyrene.
Creator: Calkins, Eric, Dong, Yajie, Tetard, Laurene, Zhai, Lei, University of Central Florida
Abstract / Description: With their simple fabrication, narrow light spectrum, and color tunability, a class of materials known as perovskites are emerging as promising candidates for light emission applications. These materials, when exposed to normal atmospheric conditions show significant degradation. Improved protection has been demonstrated by embedding perovskites in polymers. Furthermore, the addition of a surfactant into the precursor solution has been shown to increase stability and allow for color tuning by...
Show moreWith their simple fabrication, narrow light spectrum, and color tunability, a class of materials known as perovskites are emerging as promising candidates for light emission applications. These materials, when exposed to normal atmospheric conditions show significant degradation. Improved protection has been demonstrated by embedding perovskites in polymers. Furthermore, the addition of a surfactant into the precursor solution has been shown to increase stability and allow for color tuning by exploiting quantum confinement effects. However, the effects of surfactants typically used to stabilize perovskites in solution have not been explored in this polymer embedding strategy. Here we determine the physical and optical emission changes produced by modifying the concentration of octylamine, butylamine, and oleylamine in the perovskite precursor solution prior to embedding into a polystyrene substrate. Using optical emission spectroscopy, we measure emission spectra of perovskite nanocrystals embedded in the polymer. Changes in morphology and dispersion of the perovskite particles within the polymer are observed using UV illuminated optical microscopy. XRD data suggests increased crystallinity with the addition of short chain surfactant. Our measurements in emission show that the location of the emission peak and overall shape of the emission spectra change when longer chain surfactant is added while short chain surfactant reduces nanorod formation without a significant change in particle dispersion or emission. The work suggests that increased long chain surfactant concentration prohibits perovskite crystal growth within the polymer leading to increased optical transparency and quantum confinement effects observable through photo luminescent emission.
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Date Issued: 2017
Identifier: CFE0007119, ucf:51940
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007119

Title: A Multisystem Approach for the Characterization of Bacteria for Sustainable Agriculture.
Creator: Lee, Briana, Tetard, Laurene, Kang, Hyeran, Mason, Chase, University of Central Florida
Abstract / Description: The chemical, physical, and biological properties of bacteria developing resistance have been explored in animal based bacteria while plant bacteria have been largely neglected. Thus, the ability to probe changes in stiffness, adhesion, binding interactions and molecular traits of bacteria causing plant diseases is of great interest to develop a new generation of more potent, yet sustainable, pesticides. Our study aims to investigate the physical and chemical properties of bacterial systems,...
Show moreThe chemical, physical, and biological properties of bacteria developing resistance have been explored in animal based bacteria while plant bacteria have been largely neglected. Thus, the ability to probe changes in stiffness, adhesion, binding interactions and molecular traits of bacteria causing plant diseases is of great interest to develop a new generation of more potent, yet sustainable, pesticides. Our study aims to investigate the physical and chemical properties of bacterial systems, in particular their cell walls. Building upon this fundamental understanding of the cells, we also investigate the physicochemical responses associated to multivalent nanoparticle-based bactericide treatments on bacterial systems identified as pathogens in plant diseases. Here our efforts focus on developing a protocol for the fundamental understanding of Xanthomonas perforans, a strain known for causing bacterial spot in tomatoes and causing close to 50% losses in production. To support the design and accelerate the development of pesticides and treatments against this disease, we evaluate the changes bacteria undergo in the presence of the treatment. Using a silica nanoparticle-based treatment designed with a shell containing multivalent copper and quaternary ammonium, we compare bacteria pre- and post-treatment with infrared spectroscopy, atomic force microscopy (AFM)-based techniques, and TIRF microscopy. Statistical data analysis enables the identification of attributes that can potentially serve as markers to track the bacterial responses to the treatment in the future. Finally, we will discuss the exciting implications of this work, such as potential clues for the development of more potent treatments for resistant bacteria.
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Date Issued: 2018
Identifier: CFE0007038, ucf:52005
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007038

Title: Catalytic Properties of Defect-Laden 2D Material from First-Principles.
Creator: Jiang, Tao, Rahman, Talat, Stolbov, Sergey, Blair, Richard, Tetard, Laurene, University of Central Florida
Abstract / Description: Two dimensional (2D) materials offer excellent opportunities for application as catalysts for energy needs. Their catalytic activity depends on the nature of defects, their geometry and their electronic structure. It thus important that the characteristics of defect-laden 2D materials be understood at the microscopic level. My dissertation focuses on theoretical and computational studies of several novel nanoscale materials using state-of-the-art techniques based on density functional theory ...
Show moreTwo dimensional (2D) materials offer excellent opportunities for application as catalysts for energy needs. Their catalytic activity depends on the nature of defects, their geometry and their electronic structure. It thus important that the characteristics of defect-laden 2D materials be understood at the microscopic level. My dissertation focuses on theoretical and computational studies of several novel nanoscale materials using state-of-the-art techniques based on density functional theory (DFT) with the objective of understanding the microscopic factors that control material functionality.My work has helped establish defect-laden hexagonal boron nitride (dh-BN) as a promising metal-free catalyst for CO2 hydrogenation. Firstly, I showed how small molecules (H2, CO, CO2) interacting with several kinds of defects in dh-BN (with nitrogen or boron vacancy, boron substituted for nitrogen, Stone-Wales defect). I analyzed binding energies and electronic structures of adsorption of molecules on dh-BN to predict their catalytic activities. Then by computational efforts on reaction pathways and activation energy barriers, I found that vacancies induced in dh-BN can effectively activate the CO2 molecule for hydrogenation, where activation occurs through back-donation to the ?* orbitals of CO2 from frontier orbitals (defect state) of the h-BN sheet localized near a nitrogen vacancy (VN). Subsequent hydrogenation to formic acid (HCOOH) and methanol (CH3OH), indicating dh-BN (VN) an excellent metal-free catalyst for CO2 reduction, which may serve as a solution for global energy and sustainability.At the same time, I studied critical steps of the catalytic processes from carbon monoxide and methanol to higher alcohol on single-layer MoS2 functionalized with small Au nanoparticle, indicating C-C coupling feasible on MoS2-Au13, which led to production of acetaldehyde (CH3CHO). Whereas a bilayer 31-atom cluster of gold on MoS2 show excellent catalytic performance on CO hydrogenation to methanol through two effective pathways
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Date Issued: 2019
Identifier: CFE0007823, ucf:52822
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007823

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: High Power Continuous Wave Quantum Cascade Lasers With Increased Ridge Width.
Creator: Todi, Ankesh, Lyakh, Arkadiy, Huo, Qun, Tetard, Laurene, University of Central Florida
Abstract / Description: Quantum Cascade Lasers have recently gained considerable attention for their capability to emit infrared radiation in a broad infrared spectral region, very compact dimensions, and high optical power/efficiency. Increasing continuous wave optical power is one of the main research directions in the field. A straightforward approach to increasing optical power in the pulsed regime is to increase number of stages in the cascade structure. However, due to a low active region thermal conductivity,...
Show moreQuantum Cascade Lasers have recently gained considerable attention for their capability to emit infrared radiation in a broad infrared spectral region, very compact dimensions, and high optical power/efficiency. Increasing continuous wave optical power is one of the main research directions in the field. A straightforward approach to increasing optical power in the pulsed regime is to increase number of stages in the cascade structure. However, due to a low active region thermal conductivity, the increase in number of stages leads to active region overheating in continuous wave operation. In this work, an alternative approach to power scaling with device dimensions is explored: number of stages is reduced to reduce active region thermal resistance, while active region lateral size is increased for reaching high optical power level. Using this approach, power scaling for active region width increase from 10(&)#181;m to 20(&)#181;m is demonstrated for the first time. An analysis based on a simple semi-empirical model suggests that laser power can be significantly improved by increasing characteristic temperature T0 that describes temperature dependence of laser threshold current density.
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Date Issued: 2017
Identifier: CFE0007137, ucf:52299
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007137

Title: Mesoscopic Interactions in Complex Photonic Media.
Creator: Rezvani Naraghi, Roxana, Dogariu, Aristide, Tetard, Laurene, Rahman, Talat, Abouraddy, Ayman, University of Central Florida
Abstract / Description: Mesoscale optics provides a framework for understanding a wide range of phenomena occurring in a variety of fields ranging from biological tissues to composite materials and from colloidal physics to fabricated nanostructures. When light interacts with a complex system, the outcome depends significantly on the length and time scales of interaction. Mesoscale optics offers the apparatus necessary for describing specific manifestations of wave phenomena such as interference and phase memory in...
Show moreMesoscale optics provides a framework for understanding a wide range of phenomena occurring in a variety of fields ranging from biological tissues to composite materials and from colloidal physics to fabricated nanostructures. When light interacts with a complex system, the outcome depends significantly on the length and time scales of interaction. Mesoscale optics offers the apparatus necessary for describing specific manifestations of wave phenomena such as interference and phase memory in complex media. In-depth understanding of mesoscale phenomena provides the required quantitative explanations that neither microscopic nor macroscopic models of light-matter interaction can afford. Modeling mesoscopic systems is challenging because the outcome properties can be efficiently modified by controlling the extent and the duration of interactions.In this dissertation, we will first present a brief survey of fundamental concepts, approaches, and techniques specific to fundamental light-matter interaction at mesoscopic scales. Then, we will discuss different regimes of light propagation through randomly inhomogenous media. In particular, a novel description will be introduced to analyze specific aspects of light propagation in dense composites. Moreover, we will present evidence that the wave nature of light can be critical for understanding its propagation in unbounded highly scattering materials. We will show that the perceived diffusion of light is subjected to competing mechanisms of interaction that lead to qualitatively different phases for the light evolution through complex media. In particular, we will discuss implications on the ever elusive localization of light in three-dimensional random media. In addition to fundamental aspects of light-matter interaction at mesoscopic scales, this dissertation will also address the process of designing material structures that provide unique scattering properties. We will demonstrate that multi-material dielectric particles with controlled radial and azimuthal structure can be engineered to modify the extinction cross-section, to control the scattering directivity, and to provide polarization-dependent scattering. We will show that dielectric core-shell structures with similar macroscopic sizes can have both high scattering cross-sections and radically different scattering phase functions. In addition, specific structural design, which breaks the azimuthal symmetry of the spherical particle, can be implemented to control the polarization properties of scattered radiation. Moreover, we will also demonstrate that the power flow around mesoscopic scattering particles can be controlled by modifying their internal heterogeneous structures.Lastly, we will show how the statistical properties of the radiation emerging from mesoscopic systems can be utilized for surface and subsurface diagnostics. In this dissertation, we will demonstrate that the intensity distributions measured in the near-field of composite materials are direct signatures of the scale-dependent morphology, which is determined by variations of the local dielectric function. We will also prove that measuring the extent of spatial coherence in the proximity of two-dimensional interfaces constitutes a rather general method for characterizing the defect density in crystalline materials. Finally, we will show that adjusting the spatial coherence properties of radiation can provide a simple solution for a significant deficiency of near-field microscopy. We will demonstrate experimentally that spurious interference effects can be efficiently eliminated in passive near-field imaging by implementing a random illumination.
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Date Issued: 2017
Identifier: CFE0006647, ucf:51253
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006647

Title: Tunable Effect of Metal Ions on Polyelectrolyte Mechanics.
Creator: Diaz, Angie, Kang, Hyeran, Zhai, Lei, Tetard, Laurene, University of Central Florida
Abstract / Description: Polyelectrolyte based hydrogel fibers can mimic extracellular matrix and have applications such as drug delivery and tissue scaffolding. Metal ions play a critical role in hydrogel fiber stability via electrostatic interactions, but knowledge of how they modulate mechanical properties of individual polyelectrolyte polymers is lacking. In this study, electrospun polyacrylic acid with chitosan is used as a model system to evaluate ferric ion effect on nanofiber mechanics. Using dark field...
Show morePolyelectrolyte based hydrogel fibers can mimic extracellular matrix and have applications such as drug delivery and tissue scaffolding. Metal ions play a critical role in hydrogel fiber stability via electrostatic interactions, but knowledge of how they modulate mechanical properties of individual polyelectrolyte polymers is lacking. In this study, electrospun polyacrylic acid with chitosan is used as a model system to evaluate ferric ion effect on nanofiber mechanics. Using dark field microscopy imaging and persistence length analysis, we demonstrate that ferric ions modulate the bending stiffness of nanofibers. Young's modulus of individual nanofibers is estimated at values of a few kilopascals, suggesting that electrospun nanofibers possibly exist in a hydrated state. Furthermore, Fourier Transform Infrared (FTIR) spectra indicate the effect of ferric ions on polyacrylic acid molecular bonds. Our results suggest that metal ions can regulate single nanofiber stiffness, thereby providing designs to fabricate hydrogels in a tunable fashion.
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Date Issued: 2018
Identifier: CFE0006993, ucf:51625
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006993

Title: Nanoplasmonics In Two-dimensional Dirac and Three-dimensional Metallic Nanostructure Systems.
Creator: Safaei, Alireza, Chanda, Debashis, Leuenberger, Michael, Mucciolo, Eduardo, Tetard, Laurene, Zhai, Lei, University of Central Florida
Abstract / Description: Surface plasmons are collective oscillation of electrons which are coupled to the incident electric field. Excitation of surface plasmon is a route to engineer the behavior of light in nanometer length scale and amplifying the light-matter interaction. This interaction is an outcome of near-field enhancement close to the metal surface which leads to plasmon damping through radiative decay to outgoing photons and nonradiative decay inside and on the surface of the material to create an...
Show moreSurface plasmons are collective oscillation of electrons which are coupled to the incident electric field. Excitation of surface plasmon is a route to engineer the behavior of light in nanometer length scale and amplifying the light-matter interaction. This interaction is an outcome of near-field enhancement close to the metal surface which leads to plasmon damping through radiative decay to outgoing photons and nonradiative decay inside and on the surface of the material to create an electron-hole pair via interband or intraband Landau damping. Plasmonics in Dirac systems such as graphene show novel features due to massless electrons and holes around the Dirac cones. Linear band structure of Dirac materials in the low-momentum limit gives rise to the unprecedented optical and electrical properties. Electronical tunability of the plasmon resonance frequency through applying a gate voltage, highly confined electric field, and low plasmon damping are the other special propoerties of the Dirac plasmons. In this work, I will summarize the theoretical and experimental aspects of the electrostatical tunable systems made from monolayer graphene working in mid-infrared regime. I will demonstrate how a cavity-coupled nanopatterned graphene excites Dirac plasmons and enhances the light-matter interaction. The resonance frequency of the Dirac plasmons is tunable by applying a gate voltage. I will show how different gate-dielectrics, and the external conditions like the polarization and angle of incident light affect on the optical response of the nanostructure systems. I will then show the application of these nanodevices in infrared detection at room temperature by using plasmon-assisted hot carriers generation. An asymmetric nanopatterned graphene shows a high responsivity at room temperature which is unprecedented. At the end, I will demonstrate the properties of surface plasmons on 3D noble metals and its applications in light-funneling, photodetection, and light-focusing.
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Date Issued: 2019
Identifier: CFE0007904, ucf:52746
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007904

Title: Electronic, Optical, and Magnetic Properties of Graphene and Single-Layer Transition Metal Dichalcogenides in the Presence of Defects.
Creator: Khan, Mahtab, Leuenberger, Michael, Mucciolo, Eduardo, Saha, Haripada, Tetard, Laurene, Schoenfeld, Winston, University of Central Florida
Abstract / Description: Two-dimensional (2D) materials, such as graphene and single-layer (SL) transition metal dichalcogenides (TMDCs), have attracted a lot of attention due to their fascinating electronic and optical properties. Graphene was the first 2D material that has successfully been exfoliated from bulk graphite in 2004. In graphene, charge carriers interacting with the honeycomb lattice of carbonatoms of graphene to appear as massless Dirac fermions. Massless quasiparticles with linear dispersion are also...
Show moreTwo-dimensional (2D) materials, such as graphene and single-layer (SL) transition metal dichalcogenides (TMDCs), have attracted a lot of attention due to their fascinating electronic and optical properties. Graphene was the first 2D material that has successfully been exfoliated from bulk graphite in 2004. In graphene, charge carriers interacting with the honeycomb lattice of carbonatoms of graphene to appear as massless Dirac fermions. Massless quasiparticles with linear dispersion are also observed in surface states of 3D topological insulators and quantum Hall edgestates. My first project deals with the two-dimensional Hong-Ou-Mandel (HOM) type interferenceexperiment for massless Dirac fermions in graphene and 3D topological insulators. Since masslessDirac fermions exhibit linear dispersion, similar to photons in vacuum, they can be used to observethe HOM interference intensity pattern as a function of the delay time between two massless Dirac fermions. My further projects and the major part of this dissertation deal with single-layer (SL) transition metal dichalcogenides (TMDCs), such as MoS$_2$, WS$_2$, MoSe$_2$ and WSe$_2$, which have recently emerged as a new family of two-dimensional (2D) materials with great interest, not only from the fundamental point of view, but also because of their potential application to ultrathin electronic and optoelectronic devices. In contrast to graphene, SL TMDCs are direct band semiconductors and exhibit large intrinsic spin-orbit coupling (SOC), originating from the d orbitals of transition metal atoms. Wafer-scale production of SL TMDCs is required for industrial applications. It has been shown that artificially grown samples of SL TMDCs through various experimental techniques, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and molecular beam epitaxy (MBE), are not perfect, instead certain type of imperfections such as point defects are always found to be present in the grown samples. Defects compromise the crystallinity of the sample, which results in reduced carrier mobility and deteriorated optical efficiency. However, defects are not always unwanted; in fact, defects can play an important role in tailoring electronic, optical, and magnetic properties of materials. Using Density functional theory we investigate the impact of point defects on the electronic, optical, and magnetic properties of SL TMDCs. First, we show that certain vacancy defects lead to localized defect states, which in turn give rise to sharp transitions in in-plane and out-of-plane optical susceptibilities of SL TMDCs. Secondly, we show that a naturally occurring antisite defect Mo$_S$ in PVD grown MoS$_2$ is magnetic in nature with a magneticmoment of 2$\mu_B$, and remarkably exhibit an exceptionally large atomic scale magnetic anisotropy energy (MAE) of ~ 500 eV. Both magnetic moment and MAE can be tuned by shifting the position of the Fermi level which can be achieved either by gate voltage or by chemical doping. Thirdly, we argue that the antisite defect Se$_W$ in WSe$_2$ leads to long lived localized excited states, which can explain the observed single quantum emitters in CVD grown WSe$_2$ samples, with potential application to quantum cryptography.
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Date Issued: 2018
Identifier: CFE0007030, ucf:52047
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007030

Title: A Universal Electrochemical Biosensor for the Detection of Nucleic Acids based on a Four-Way Junction Structure.
Creator: Mills, Dawn, Chumbimuni Torres, Karin, Kolpashchikov, Dmitry, Campiglia, Andres, Dupras, Tosha, Tetard, Laurene, University of Central Florida
Abstract / Description: Electrochemical hybridization sensors have been explored extensively for analysis of specific nucleic acids. However, commercialization of the platform is hindered by the need for attachment of separate oligonucleotide probes complementary to a RNA or DNA target to an electrode's surface. This dissertation demonstrates that a single probe can be used to analyze several nucleic acid targets of different lengths with high selectivity, low cost and can be regenerated in 30 seconds by a simple...
Show moreElectrochemical hybridization sensors have been explored extensively for analysis of specific nucleic acids. However, commercialization of the platform is hindered by the need for attachment of separate oligonucleotide probes complementary to a RNA or DNA target to an electrode's surface. This dissertation demonstrates that a single probe can be used to analyze several nucleic acid targets of different lengths with high selectivity, low cost and can be regenerated in 30 seconds by a simple water rinse. The universal electrochemical four-way junction (4J)-forming (UE4J) sensor consists of a universal DNA stem-loop (USL) probe attached to the electrode's surface and two adaptor strands (m and f) which hybridize to the USL probe and the analyte to form a 4J structure. The UE4J sensor enables a high selectivity by recognition of a single base substitution, even at room temperature. The sensor was monitored with voltammetry and electrochemical impedance spectroscopy using different redox labeling strategies and optimized using synthetic nucleic acid sequences. After the sensor was optimized and fully characterized, it was modified for the detection of the Zika virus. The UE4J sensor presented here opens a venue for a re-useable universal platform that can be adopted at low cost for the analysis of potentially any DNA or RNA targets.
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Date Issued: 2017
Identifier: CFE0007290, ucf:52146
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007290

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: A deoxyribozyme sensor and isothermal amplification for human sex determination.
Creator: Smith, Alexandra, Kolpashchikov, Dmitry, Campiglia, Andres, Harper, James, Beazley, Melanie, Tetard, Laurene, University of Central Florida
Abstract / Description: Ribozymes are known to catalyze biochemical reactions and behave like enzymes. They are naturally occurring and have very diverse functions within a cell. After investigating ribozymes that next step was to find if DNA can exhibit the same characteristics since RNA and DNA only differ by a ribose 2'-hydroxyl group. This evolution in curiosity gave rise to artificial DNA enzymes that can catalyze certain reactions and have been created by in vitro selection methods. Due to the ability to...
Show moreRibozymes are known to catalyze biochemical reactions and behave like enzymes. They are naturally occurring and have very diverse functions within a cell. After investigating ribozymes that next step was to find if DNA can exhibit the same characteristics since RNA and DNA only differ by a ribose 2'-hydroxyl group. This evolution in curiosity gave rise to artificial DNA enzymes that can catalyze certain reactions and have been created by in vitro selection methods. Due to the ability to manipulate and control DNA hybridization, the deoxyribozyme is advantageous to the field of molecular diagnostics. Other hybridization probes like Taqman for PCR (polymerase chain reaction) or a molecular beacon are more conventional methods for molecular diagnostics, but deoxyribozyme-based nucleic acid sensors are overall more sensitive due to their catalytic enhancement of a signal and more selective due to structural design. When the deoxyribozyme is split into two probes, it is very efficient in identifying a minute difference in sequence compared to the monolith structure. This binary deoxyribozyme sensor (BiDz) has two probes, each containing an analyte binding arm, substrate binding arm, and half of the catalytic core. The monolith structure, known as a catalytic molecular beacon (CMB), contains a hairpin that contains the analyte binding arm in the loop and the substrate binding arms in the stem. The catalytic core is fully intact but deemed inactive due to the substrate binding arms being complimentary to an inhibitory sequence forming the stem. Once the sensor binds the analyte, catalytic core is formed/activated and cleaves a substrate containing a fluorophore and quencher. When the substrate is cleaved a fluorescent signal is given off denoting the detection of the target DNA. Deoxyribozyme sensors can be applied to the field of human sex determination by detecting the Amelogenin gene. Found on both sex chromosomes, the Amelogenin gene is the most common marker used for sex determination because it exhibits dimorphism in length and sequence. Sex identification from ancient skeletal remains is crucial to understanding the social structure of our history. When conventional methods, such as metric analysis, are not an option due to the fragmented or prepubescent remains, molecular diagnostics are needed. Amplification of DNA is required to be able to detect the target sequence in human samples. Isothermal loop-mediated amplification (LAMP) is a fast and simple technique that provides ample amounts of amplicon. It is advantageous over PCR because it amplifies at one temperature and no thermal cycler is needed. Two different sensors have been designed to detect the X and Y specific sequences with high selectivity. From a direct comparison between the CMB and BiDZ, the binary structure has shown to be simpler and less expensive to design, and highly selective toward single base substitutions (SNS). While both sensors contain detection limits in the picomolar range, which is consistent with data published by other research groups, the CMB sensors failed to function at higher temperatures (55oC). BiDz sensors are shown to be superior to the CMB design, particularly when selectivity based analysis is desired. For human sex determination, the binary sensor detected sex specific sequences with great selectivity. The sensor then detected LAMP amplified DNA from male and female teeth after 30 minutes of amplification. Combining a binary deoxyribozyme sensor and isothermal amplification can provide a new and valuable method for human sex determination.
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Date Issued: 2017
Identifier: CFE0007133, ucf:52306
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007133

Title: ELECTROMECHANICAL LIFTING ACTUATION OF A MEMS CANTILEVER AND NANO-SCALE ANALYSIS OF DIFFUSION IN SEMICONDUCTOR DEVICE DIELECTRICS.
Creator: Rezadad, Imen, Peale, Robert, Del Barco, Enrique, Tetard, Laurene, Prenitzer, Brenda, University of Central Florida
Abstract / Description: This dissertation presents experimental and theoretical studies of physical phenomena in micro- and nano-electronic devices. Firstly, a novel and unproven means of electromechanical actuation in a micro-electro-mechanical system (MEMS) cantilever was investigated. In nearly all MEMS devices, electric forces cause suspended components to move toward the substrate. I demonstrated a design with the unusual and potentially very useful property of having a suspended MEMS cantilever lift away from...
Show moreThis dissertation presents experimental and theoretical studies of physical phenomena in micro- and nano-electronic devices. Firstly, a novel and unproven means of electromechanical actuation in a micro-electro-mechanical system (MEMS) cantilever was investigated. In nearly all MEMS devices, electric forces cause suspended components to move toward the substrate. I demonstrated a design with the unusual and potentially very useful property of having a suspended MEMS cantilever lift away from the substrate. The effect was observed by optical micro-videography, by electrical sensing, and it was quantified by optical interferometry. The results agree with predictions of analytic and numerical calculations. One potential application is infrared sensing in which absorbed radiation changes the temperature of the cantilever, changing the duty cycle of an electrically-driven, repetitively closing micro-relay.Secondly, ultra-thin high-k gate dielectric layers in two 22 nm technology node semiconductor devices were studied. The purpose of the investigation was to characterize the morphology and composition of these layers as a means to verify whether the transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS) could sufficiently resolve the atomic diffusion at such small length scales. Results of analytic and Monte-Carlo numerical calculations were compared to empirical data to validate the ongoing viability of TEM EDS as a tool for nanoscale characterization of semiconductor devices in an era where transistor dimensions will soon be less than 10 nm.
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Date Issued: 2015
Identifier: CFE0006228, ucf:51075
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006228

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

AFM (3)	+ -
Atomic Force Microscopy (3)	+ -
Graphene (2)	+ -
Raman Spectroscopy (2)	+ -
2D materials (1)	+ -

AFM-IR (1)	+ -
Adhesion (1)	+ -
Asteroid Surfaces (1)	+ -
Catalyst (1)	+ -
Cohesion (1)	+ -
Confocal Raman Microscopy (1)	+ -
DFT (1)	+ -
Defects (1)	+ -
Deoxyribozyme (1)	+ -
Dirac plasmon (1)	+ -
EDS (1)	+ -
Electron Microscopy (1)	+ -
Flat lens (1)	+ -
High-k dielectrics (1)	+ -
Hydrogel (1)	+ -
Inter subband transition (1)	+ -
LAMP (1)	+ -
Laser (1)	+ -
Light funneling (1)	+ -
MEMS (1)	+ -
MOSFET (1)	+ -
Materials Characterization (1)	+ -
Mechanics (1)	+ -
Mesoscopic Optics (1)	+ -
Metal Ions (1)	+ -

ETD Collection (16)	+ -
Honors Collection (1)	+ -

Tetard, Laurene (17)	+ -
University of Central Florida (17)	+ -
Zhai, Lei (6)	+ -
Kang, Hyeran (4)	+ -
Santra, Swadeshmukul (3)	+ -

Blair, Richard (2)	+ -
Campiglia, Andres (2)	+ -
Chumbimuni Torres, Karin (2)	+ -
Kolpashchikov, Dmitry (2)	+ -
Leuenberger, Michael (2)	+ -
Lyakh, Arkadiy (2)	+ -
Mucciolo, Eduardo (2)	+ -
Peale, Robert (2)	+ -
Rahman, Talat (2)	+ -
Abouraddy, Ayman (1)	+ -
Beazley, Melanie (1)	+ -
Britt, Daniel (1)	+ -
Calkins, Eric (1)	+ -
Challapalli, Suryanarayana (1)	+ -
Chanda, Debashis (1)	+ -
Ciaffone, Nicholas (1)	+ -
Del Barco, Enrique (1)	+ -
Diaz, Angie (1)	+ -
Ding, Yi (1)	+ -
Dogariu, Aristide (1)	+ -
Dong, Yajie (1)	+ -
Dove, Adrienne (1)	+ -
Dupras, Tosha (1)	+ -
Harper, James (1)	+ -
Huo, Qun (1)	+ -

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