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Title: SURFACE CHARACTERIZATION OF THIN FILM ZNO CAPACITORS BY CAPACITANCE-VOLTAGE MEASUREMENTS.
Creator: Smith, Linda, del Barco, Enrique, University of Central Florida
Abstract / Description: The main objective of the research was the fabrication and characterization of MOS/MIS capacitors with ZnO as the insulating layer. Comparison with the already well known behavior of MOS/MIS capacitors with SiO2 as insulator was used to facilitate determination of the ZnO characteristics. Moreover, thermal annealing of the samples led to increased understanding of the role of defects on the dielectric properties of the ZnO layers in the MOS/MIS devices. Hall-effect transport measurements and...
Show moreThe main objective of the research was the fabrication and characterization of MOS/MIS capacitors with ZnO as the insulating layer. Comparison with the already well known behavior of MOS/MIS capacitors with SiO2 as insulator was used to facilitate determination of the ZnO characteristics. Moreover, thermal annealing of the samples led to increased understanding of the role of defects on the dielectric properties of the ZnO layers in the MOS/MIS devices. Hall-effect transport measurements and x-ray diffraction (XRD) spectroscopy are used to analyze the structure and electronic surface characteristics of the ZnO insulator. Capacitance-voltage (C-V) measurements are used to understand the effect of surface interface charges and fixed oxide charges in the MOS/MIS (metal-oxide (insulator)-semiconductor) capacitor. The results of the Hall-effect measurement will reveal several things; the sheet resistance, carrier concentration, and mobility as well as confirm the type of silicon used. The optical spectrophotometry measurement confirmed the band gap of 3.2 eV for ZnO. The x-ray diffraction data confirmed a (002) orientation polycrystalline wurtzite ZnO structure. Initial capacitance-voltage measurement of SiO2 and ZnO revealed that the capacitance was larger for SiO2 than for ZnO. This study also explores the impact of thermal annealing on the performance of the ZnO capacitors. Hall-effect measurements are used to evaluate the influence of thermal annealing on the resistivity, carrier concentration and mobility as a function of annealing temperature. ZnO is an n-type semiconductor; this n-type conductivity is due to deviations from the stoichiometry as a result of oxygen vacancies and interstitial zinc. After ZnO samples were annealed at different temperatures, the Hall-effect measurements were performed. After thermal annealing, the mobility increased significantly by two orders of magnitude, but both the carrier concentration and the sheet density decreased. A threshold voltage (turn-on) of –1V was observed for the ZnO sample annealed at 980oC. ZnO is very versatile material with the potential for use in field effect transistors, solar cells, sensors, surface acoustic wave devices and photodiodes due to the high conductivity and high transmittance in the visible part of the spectrum. ZnO as an insulator works through analytical solutions, but not necessarily through this investigation. The difference in oxide thickness during rf magentron sputtering change the capacitance for ZnO making it lower. For n-type substrates it appears that the capacitance after annealing was higher than the capacitance before annealing. After annealing, a stretched out capacitance-voltage curve indicates the presence of trapped oxide charges and an unsmoothed surface. A high resistivity material could be used for some devices. However, typically low resistivity materials are used. After ZnO samples were annealed (unetched) at different temperatures, the Hall-effect were performed and the mobility increased significantly by two orders of magnitude, but the sheet density decreased along with the carrier concentration. The only sample that appears to come to a high frequency C-V in equilibrium is the ZnO sample annealed at 980oC. The depletion region was distinguishable and the transition point (threshold voltage) was found to be at -1 V.
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Date Issued: 2007
Identifier: CFE0001630, ucf:47176
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001630

Title: TEMPERATURE DEPENDENCE OF DYNAMICAL SPIN INJECTION IN A SUPERCONDUCTING NIOBIUM THIN FILM.
Creator: Townsend, Tyler S, Del Barco, Enrique, University of Central Florida
Abstract / Description: Spintronics is a research field that focuses on the manipulation of the quantum mechanical spin of charge carriers in solid state materials for future technological applications. Creating large spin currents with large relaxation times is sought after in the field of spintronics which may be aided by combining spintronics with superconductivity. This thesis provides a phenomological study of the effective change in ferromagnetic resonance linewidth, by dynamical spin injection into a...
Show moreSpintronics is a research field that focuses on the manipulation of the quantum mechanical spin of charge carriers in solid state materials for future technological applications. Creating large spin currents with large relaxation times is sought after in the field of spintronics which may be aided by combining spintronics with superconductivity. This thesis provides a phenomological study of the effective change in ferromagnetic resonance linewidth, by dynamical spin injection into a permalloy-copper-niobium tri-layer in the superconducting state. The ferromagetic resonance linewidth was measured from 2-14 K. It was observed that there was a change in the behavior of the resonance as well as a change in the linewidth from the between 6-8 K. An observed change in the resonance field, H_r, shows a clear non monotonic behavior as a function of temperature below 7-8 K. The decrease in linewidth was attributed to the suppression of the spin sinking mechanisms due to the superconducting state of niobium.
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Date Issued: 2017
Identifier: CFH0000224, ucf:44685
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0000224

Title: CONTROLLED DEPOSITION OF MAGNETIC MOLECULES AND NANOPARTICLES ON ATOMICALLY FLAT GOLD SURFACES.
Creator: Haque, Md. Firoze, del Barco, Enrique, University of Central Florida
Abstract / Description: In this thesis I am presenting a detailed study to optimize the deposition of magnetic molecules and gold nanoparticles in atomically flat surfaces by self-assembling them from solution. Epitaxially grown and atomically flat gold surface on mica is used as substrate for this study. These surfaces have roughness of the order one tenth of a nanometer and are perfect to image molecules and nanoparticles in the 1-10 nanometers range. The purpose of these studies is to find the suitable parameters...
Show moreIn this thesis I am presenting a detailed study to optimize the deposition of magnetic molecules and gold nanoparticles in atomically flat surfaces by self-assembling them from solution. Epitaxially grown and atomically flat gold surface on mica is used as substrate for this study. These surfaces have roughness of the order one tenth of a nanometer and are perfect to image molecules and nanoparticles in the 1-10 nanometers range. The purpose of these studies is to find the suitable parameters and conditions necessary to deposit a monolayer of nano-substance on chips containing gold nanowires which will eventually be used to form single electron transistors by electromigration breaking of the nanowire. Maximization of the covered surface area is crucial to optimize the yield of finding a molecule/nanoparticle near the gap formed in the nanowire after electromigration breaking. Coverage of the surface by molecules/nanoparticles mainly depends on the deposition time and concentration of the solution used for the self-assembly. Deposition of the samples under study was done for different solution concentrations and deposition times until a self-assembly monolayer covering most of the surface area is obtained. Imaging of the surfaces after deposition was done by tapping-mode AFM. Analysis of the AFM images was performed and deposition parameters (i.e. coverage or molecule/particle size distribution) were obtained. The subjects of this investigation were a molecular polyoxometalate, a single-molecule magnet and functionalized gold nanoparticles. The obtained results agree with the structure of each of the studied systems. Using the optimized deposition parameters found in this investigation, single-electron transport measurements have been carried out. Preliminary results indicate the right choice of the deposition parameters.
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Date Issued: 2008
Identifier: CFE0002338, ucf:47795
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002338

Title: SPIN QUANTUM DYNAMICS IN MOLECULAR MAGNETS.
Creator: Henderson, John, del Barco, Enrique, University of Central Florida
Abstract / Description: Molecular magnets are ideal systems to probe the realm that borders quantum and classical physics, as well as to study decoherence phenomena in nanoscale systems. The control of the quantum behavior of these materials and their structural characteristics requires synthesis of new complexes with desirable properties which will allow probing of the fundamental aspects of nanoscale physics and quantum information processing. Of particular interest among the magnetic molecular materials are...
Show moreMolecular magnets are ideal systems to probe the realm that borders quantum and classical physics, as well as to study decoherence phenomena in nanoscale systems. The control of the quantum behavior of these materials and their structural characteristics requires synthesis of new complexes with desirable properties which will allow probing of the fundamental aspects of nanoscale physics and quantum information processing. Of particular interest among the magnetic molecular materials are single-molecule magnets (SMMs) and antiferromagnetic (AFM) molecular wheels in which the spin state of the molecule is known to behave quantum mechanically at low temperatures. In previous experiments the dynamics of the magnetic moment of the molecules is governed by incoherent quantum tunneling. Short decoherence times are mainly due to interactions between molecular magnets within the crystal and interactions of the electronic spin with the nuclear spin of neighboring ions within the molecule. This decoherence problem has imposed a limit to the understanding of the molecular spin dynamics and the sources of decoherence in condensed matter systems. Particularly, intermolecular dipolar interactions within the crystal, which shorten the coherence times in concentrated samples, have stymied progress in this direction. Several recent works have reported a direct measurement of the decoherence time in molecular magnets. This has been done by eliminating the dephasing created by dipolar interactions between neighboring molecules. This has been achieved by a) a dilution of the molecules in a liquid solution to decrease the dipolar interaction by separating the molecules, and b) by polarizing the spin bath by applying a high magnetic field at low temperatures. Unfortunately, both approaches restrict the experimental studies of quantum dynamics. For example, the dilution of molecular magnets in liquid solution causes a dispersion of the molecular spin orientation and anisotropy axes, while the large fields required to polarize the spin bath overcome the anisotropy of the molecular spin. In this thesis I have explored two methods to overcome dipolar interactions in molecular magnets: a) studying the dynamics of molecular magnets in single crystals where the separation between magnetic molecules is obtained by chemical doping or where the high crystalline quality allows observations intrinsic to the quantum mechanical nature of the tunneling of the spin, and b) studying the electronic transport through an individual magnetic molecule which has been carefully placed in a single-electron transistor device. I have used EPR microstrip resonators to measure Fe17Ga molecular wheels within single crystals of Fe18 AFM wheels, as well as demonstrating, for the first time in a Single Molecule Magnet, the complete suppression of a Quantum Tunneling of the Magnetization transition forbidden by molecular symmetry.
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Date Issued: 2009
Identifier: CFE0002799, ucf:48117
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002799

Title: SINGLE-ELECTRON TRANSPORT SPECTROSCOPY STUDIES OF MAGNETIC MOLECULES AND NANOPARTICLES.
Creator: Haque, Md. Firoze, del Barco, Enrique, University of Central Florida
Abstract / Description: Magnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles...
Show moreMagnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles are found to behave ferromagnetically for diameters below a few nanometers. Some of these manifestations are still intriguing, and novel research approaches are necessary to advance towards a more complete understanding of these exciting nanoscale systems. In particular, the ability to study an isolated individual nanoscale system (i.e just one molecule or nanoparticle) is both challenging technologically and fundamentally essential. It is expected that accessing to the energy landscape of an isolated molecule/nanoparticle will allow unprecedented knowledge of the basic properties that are usually masked by collective phenomena when the systems are found in large ensembles or in their crystal form. Several approaches to this problem are currently under development by a number of research groups. For instance, some groups are developing deposition techniques to create patterned thin films of isolated magnetic nanoparticles and molecular magnets by means of optical lithography, low-energy laser ablation, or pulsed-laser evaporation or specific chemical functionalization of metallic surfaces with special molecular ligands. However, it is still a challenge to access the properties of an individual molecule or nanoparticle within a film or substrate. I have studied molecular nanomagnets and ferromagnetic noble metal nanoparticles by means of a novel experimental approach that mixes the chemical functionalization of nano-systems with the use of single-electron transistors (SETs). I have observed the Coulomb-blockade single-electron transport response through magnetic gold nanoparticles and single-molecule magnet. In particular, Coulomb-blockade response of a Mn4-based SET device recorded at 240 mK revealed the appearance of two diamonds (two charge states) with a clear switch between one and the other is indicative of a conformational switching of the molecule between two different states. The excitations inside the diamonds move with magnetic field. The curvature of the excitations and the fact of having them not going down to zero energy for zero magnetic field, indicated the presence of magnetic anisotropy (zero-field splitting) in the molecule. In addition, the high magnetic field slope of the excitations indicates that transitions between charge states differ by a net spin value equal to 9 (dS = 9), as expected from the behavior of Mn4 molecules in their crystalline form. Anticrossings between different excitations are indicative of quantum superpositions of the molecular states, which are observed for the first time in transport measurements through and individual SMM.
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Date Issued: 2011
Identifier: CFE0003718, ucf:48776
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003718

Title: Comparison Of Casimir , Elastic, Electrostatic Forces For A Micro-Cantilever.
Creator: Alhasan, Ammar, Peale, Robert, Del Barco, Enrique, Chow, Lee, University of Central Florida
Abstract / Description: Casimir force is a cause of stiction (adhesion) between metal surfaces in Micro-Electro Mechanical Systems (MEMS). Casimir Force depends strongly on the separation of the two surfaces and the contact area. This thesis reviews the theory and prior experimental demonstrations of the Casimir force. Then the Casimir attractive force is calculated for a particular MEMS cantilever device, in which the metal cantilever tip is required to repeatedly touch and release from a metal tip pad on the...
Show moreCasimir force is a cause of stiction (adhesion) between metal surfaces in Micro-Electro Mechanical Systems (MEMS). Casimir Force depends strongly on the separation of the two surfaces and the contact area. This thesis reviews the theory and prior experimental demonstrations of the Casimir force. Then the Casimir attractive force is calculated for a particular MEMS cantilever device, in which the metal cantilever tip is required to repeatedly touch and release from a metal tip pad on the substrate surface in response to a periodic driving electrostatic force. The elastic force due to the bending of the cantilever support arms is also a consideration in the device operation. The three forces are calculated analytically and compared as a function of cantilever tip height. Calculation of the electrostatic force uses coefficients of capacitance and electrostatic induction determined numerically by the finite element method, including the effect of permittivity for the structural oxide. A condition on the tip area to allow electrostatic release of the tip from the surface against Casimir sticking and elastic restoring forces is established.
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Date Issued: 2014
Identifier: CFE0005123, ucf:50713
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005123

Title: Spin and Charge Transport in Graphene Based Devices.
Creator: Anguera Antonana, Marta, Del Barco, Enrique, Peale, Robert, Bhattacharya, Aniket, Schoenfeld, Winston, University of Central Florida
Abstract / Description: The present dissertation is comprehended in two main parts. The first part is focused on understanding the mechanisms behind spin current to charge current interconversion (i.e. the spin Hall angle), where the spin current is generated by means of spin pumping. The measurement of a positive spin Hall angle of magnitude 0.004 in Uranium is reported in Chapter 2. These results support the idea that the electronic configuration may be at least as important as the atomic number in governing spin...
Show moreThe present dissertation is comprehended in two main parts. The first part is focused on understanding the mechanisms behind spin current to charge current interconversion (i.e. the spin Hall angle), where the spin current is generated by means of spin pumping. The measurement of a positive spin Hall angle of magnitude 0.004 in Uranium is reported in Chapter 2. These results support the idea that the electronic configuration may be at least as important as the atomic number in governing spin Hall effects. In Chapter 3, the design of a spintronics device designed to interconvert charge and spin currents in CVD graphene is presented. The second part of the thesis is centered in the study of transport through single molecules with the use of three-terminal devices. The first evidence of a molecular double quantum dot is detailed in Chapter 5. The conclusions are supported by self-assembled monolayers (SAMs) and single-electron transistors (SETs) measurements. Using gold electrodes for SETs measurements has its disadvantages, two of the main ones being: the junctions are not stable at room temperature and it does not allow for transport measurements in the presence of light. Graphene electrodes, on the other hand, have been reported to be stable at temperatures above room temperature and have no absorption in the visible range. Along those lines, the development of a multilayer graphene-based SET is reported in Chapter 6. Finally, a new technique, based on CVD graphene transistors, that will allow three-terminal measurements on an STM is described in Chapter 7.
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Date Issued: 2017
Identifier: CFE0006715, ucf:51897
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006715

Title: Light Matter Interaction in Single Molecule Magnets.
Creator: Cebulka, Rebecca, Del Barco, Enrique, Klemm, Richard, Mucciolo, Eduardo, Luis, Fernando, University of Central Florida
Abstract / Description: This dissertation includes a series of experimental realizations which focus on studying the coupling between photons and single-molecule magnets (SMMs) in both the weak and strong coupling regimes. In the weak coupling regime, the aim is to achieve coherent control over the time evolution of the spin of SMMs while applying rapid microwave pulses at sub-Kelvin temperatures, where polarization of the spin bath may be achieved without large magnetic fields, allowing the suppression of dipolar...
Show moreThis dissertation includes a series of experimental realizations which focus on studying the coupling between photons and single-molecule magnets (SMMs) in both the weak and strong coupling regimes. In the weak coupling regime, the aim is to achieve coherent control over the time evolution of the spin of SMMs while applying rapid microwave pulses at sub-Kelvin temperatures, where polarization of the spin bath may be achieved without large magnetic fields, allowing the suppression of dipolar dephasing. The continuing results of this experiment will be to provide a window into fundamental sources of decoherence in single-crystal SMMs in an energy range not thoroughly investigated. We expect that these conditions would allow us to study the quantum dynamics of the spins as governed by the intrinsic molecular magnetic anisotropy, which should give rise to non-well-defined Rabi oscillations of the spin state, including metastable precessional spin states. In the strong coupling regime, high quality factor superconducting CPW resonators have been designed and fabricated to investigate the vacuum Rabi splitting between a photon and the SMM spin. The proposed setup will permit measurements of coherent collective coupling between molecular spins and a low number of photons, ideally down to a single photon. This experiment may ultimately provide the opportunity for reaching the strong coupling regime with a single spin. Finally, this thesis also documents a research study into the impact of service-learning methodology on students' depth of learning and critical thinking skills during a novel nanoscale science and technology course offered in the UCF Physics Dept. The overall learning of students was assessed and results clearly showed improvement in both multiple choice pre/post-tests and critical reflection papers. We associate this improvement at least partially to the service-learning experience.
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Date Issued: 2019
Identifier: CFE0007442, ucf:52728
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007442

Title: Undergraduate Student Agreement With Reformed Introductory Physics Classes.
Creator: Wilcox, Matthew, Chini, Jackie, Del Barco, Enrique, Saitta, Erin, Sivo, Stephen, University of Central Florida
Abstract / Description: In this study, I investigate student (")buy-in("), defined as students' proper understanding of and agreement with the class format, for introductory studio physics classes that incorporate lectures, labs, and group problem-solving activities into one interactive environment. I also investigate the ways in which instructors try to gain student buy-in to their class. Research has shown that student resistance to reformed instruction is a barrier to an instructor's use of research-based...
Show moreIn this study, I investigate student (")buy-in("), defined as students' proper understanding of and agreement with the class format, for introductory studio physics classes that incorporate lectures, labs, and group problem-solving activities into one interactive environment. I also investigate the ways in which instructors try to gain student buy-in to their class. Research has shown that student resistance to reformed instruction is a barrier to an instructor's use of research-based instructional strategies that are common to the studio class. Expectancy value theory suggests that by gaining student buy-in to the reformed class format, student resistance will decrease thus allowing a more effective class. I created a survey to measure student agreement with their class and another survey to determine the strategies that instructors use to gain student buy-in. I describe the responses to the surveys and use hierarchical models to determine if student agreement predicts their performance in the class and if the instructor strategies have an effect on student agreement. To triangulate these findings, I also interviewed instructors and students. From the surveys, I found that students disagree with the time spent lecturing and the importance and time spent reading outside of class. This is important because student agreement with the time spent in class predicts favorable attitudes about physics and their agreement with the time spent outside of class predicts a higher expected final grade. From the interviews, I discovered that both instructors and students believe that using evidence to justify the class format would be an effective strategy to gain agreement. However, few instructors used evidence due to a lack of prepared materials. Future work should develop materials to support instructors in presenting evidence about studio's effectiveness and investigate the impact on student buy-in and other outcomes.
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Date Issued: 2018
Identifier: CFE0007265, ucf:52197
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007265

Title: Experimental confirmation of ballistic nanofriction and quasiparticle interference in Dirac materials.
Creator: Lodge, Michael, Ishigami, Masahiro, Kaden, William, Schelling, Patrick, Del Barco, Enrique, Roy, Tania, University of Central Florida
Abstract / Description: This dissertation is broadly divided into two parts. The first part details the development and usage of an experimental apparatus to measure the dry nanofriction for a well-defined interface at high sliding speeds. I leverage the sensitivity of a quartz crystal microbalance (QCM) to determine the drag coefficient of an ensemble of gold nanocrystals sliding on graphene at speeds up to 11 cm/s. I discuss the theories of velocity-dependent friction, especially at high sliding speeds, and QCM...
Show moreThis dissertation is broadly divided into two parts. The first part details the development and usage of an experimental apparatus to measure the dry nanofriction for a well-defined interface at high sliding speeds. I leverage the sensitivity of a quartz crystal microbalance (QCM) to determine the drag coefficient of an ensemble of gold nanocrystals sliding on graphene at speeds up to 11 cm/s. I discuss the theories of velocity-dependent friction, especially at high sliding speeds, and QCM modeling. I also discuss our synthesis protocols for graphene and molybdenum disulfide, as well as our protocol for fabricating a clean, graphene-laminated QCM device and nanocrystal ensemble. The design and fabrication of our QCM oscillator circuit is presented in detail. The quantitatively-measured the drag coefficient is compared against molecular dynamics simulations at both low and high sliding speeds. We show evidence of a predicted ultra-low friction regime and find that the interaction energy between gold nanocrystals and graphene is lower than previously assumed. In the second part of this dissertation, I detail the band structure measurement of a novel semimetal using scanning tunneling microscopy. In particular, I measured the energy-dependenceof quasiparticle interference patterns at the surface of zirconium silicon sulfide (ZrSiS), a topological nodal line semimetal whose charge carrier quasiparticles possess a pseudospin degree offreedom. The aims of this study were to (1) discover the shape of the band structure above the Fermi level along a high-symmetry direction, (2) discover the energetic location of the line node inthe same high-symmetry direction, and (3) discover the selection rules for k transitions. This study confirms the predicted linearity in E(k) of the band structure above the Fermi level. Additionally,we observe an energy-dependent mechanism for pseudospin scattering. This study also provides the first experimentally-derived estimation of the line node position in E(k).
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Date Issued: 2018
Identifier: CFE0007218, ucf:52222
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007218

Title: Sub-Terahertz Spin Pumping from an Insulating Antiferromagnet.
Creator: Vaidya, Priyanka, Del Barco, Enrique, Neupane, Madhab, Nakajima, Yasuyuki, Hernandez, Florencio, University of Central Florida
Abstract / Description: The combination of the spin transfer torque and spin Hall effects, or their reciprocal dynamical spin pumping and inverse spin Hall effects, respectively, enable reading and controlling the magnetization state in spintronics devices which are at the verge of mass commercialization as the next generation of energy-efficient and fast magnetic random-access memory applications with the use of ferromagnetic elements, e.g., the spin valve. However, these effects have remained elusive in...
Show moreThe combination of the spin transfer torque and spin Hall effects, or their reciprocal dynamical spin pumping and inverse spin Hall effects, respectively, enable reading and controlling the magnetization state in spintronics devices which are at the verge of mass commercialization as the next generation of energy-efficient and fast magnetic random-access memory applications with the use of ferromagnetic elements, e.g., the spin valve. However, these effects have remained elusive in antiferromagnetic-based devices up to date, despite the fascinating advantages offered by the absence of stray fields (zero net magnetization), Terahertz spin dynamics, and the widespread availability of metallic, insulating and semiconducting antiferromagnetic materials. In this thesis I report the first demonstration of sub-Terahertz dynamical spin pumping at the interface between an antiferromagnet and a non-magnetic material; more specifically a uniaxial insulating antiferromagnet MnF2 and heavy metal Pt. The measured ISHE signal generated by the corresponding spin-charge current interconversion in the platinum layer is modulated by the handedness of the circularly polarized sub-THz irradiation. This effect results directly from the opposite chirality of each of the fundamental dynamical modes of the antiferromagnet. Contrary to the case of ferromagnets, this observation in an antiferromagnetic system allows unambiguously differentiating coherent spin pumping from incoherent spin Seeback effect, by which electric signals result from thermal activation. A complete study of the generated electric signals at the antiferromagnetic resonances, the spin-flop mode and the transition between the two regimes as the microwave polarization is continuously varied from circular to linear polarizations enabled an understanding of the different phenomena governing interconversion of spin dynamics and charge currents at the MnF2/Pt interface.
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Date Issued: 2019
Identifier: CFE0007870, ucf:52776
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007870

Title: Normally-Off Computing Design Methodology Using Spintronics: from Devices to Architectures.
Creator: Roohi, Arman, DeMara, Ronald, Abdolvand, Reza, Wang, Jun, Fan, Deliang, Del Barco, Enrique, University of Central Florida
Abstract / Description: Energy-harvesting-powered computing offers intriguing and vast opportunities to dramatically transform the landscape of Internet of Things (IoT) devices and wireless sensor networks by utilizing ambient sources of light, thermal, kinetic, and electromagnetic energy to achieve battery-free computing. In order to operate within the restricted energy capacity and intermittency profile of battery-free operation, it is proposed to innovate Elastic Intermittent Computation (EIC) as a new duty-cycle...
Show moreEnergy-harvesting-powered computing offers intriguing and vast opportunities to dramatically transform the landscape of Internet of Things (IoT) devices and wireless sensor networks by utilizing ambient sources of light, thermal, kinetic, and electromagnetic energy to achieve battery-free computing. In order to operate within the restricted energy capacity and intermittency profile of battery-free operation, it is proposed to innovate Elastic Intermittent Computation (EIC) as a new duty-cycle-variable computing approach leveraging the non-volatility inherent in post-CMOS switching devices. The foundations of EIC will be advanced from the ground up by extending Spin Hall Effect Magnetic Tunnel Junction (SHE-MTJ) device models to realize SHE-MTJ-based Majority Gate (MG) and Polymorphic Gate (PG) logic approaches and libraries, that leverage intrinsic-non-volatility to realize middleware-coherent, intermittent computation without checkpointing, micro-tasking, or software bloat and energy overheads vital to IoT. Device-level EIC research concentrates on encapsulating SHE-MTJ behavior with a compact model to leverage the non-volatility of the device for intrinsic provision of intermittent computation and lifetime energy reduction. Based on this model, the circuit-level EIC contributions will entail the design, simulation, and analysis of PG-based spintronic logic which is adaptable at the gate-level to support variable duty cycle execution that is robust to brief and extended supply outages or unscheduled dropouts, and development of spin-based research synthesis and optimization routines compatible with existing commercial toolchains. These tools will be employed to design a hybrid post-CMOS processing unit utilizing pipelining and power-gating through state-holding properties within the datapath itself, thus eliminating checkpointing and data transfer operations.
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Date Issued: 2019
Identifier: CFE0007526, ucf:52619
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007526

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: Density-Functional Theory+Dynamical Mean-Field Theory Study of the Magnetic Properties of Transition-Metal Nanostructures.
Creator: Kabir, Alamgir, Rahman, Talat, Kara, Abdelkader, Del Barco, Enrique, Kik, Pieter, University of Central Florida
Abstract / Description: In this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using...
Show moreIn this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using available codes, to study the magnetic properties of small (2 to 5-atom) Fe and FePt clusters provide meaningful results: dynamical effects lead to a reduction of the cluster magnetic moment as compared to that obtained from DFT or DFT+U (U being the Coulomb repulsion parameter). We have subsequently developed our own nanoDFT+DMFT code and applied it to examine the magnetization of iron particles containing10-147 atoms. Our results for the cluster magnetic moments are in a good agreement with experimental data. In particular, we are able to reproduce the oscillations in magnetic moment with size as observed in the experiments. Also, DFT+DMFT does not lead to an overestimation of magnetization for the clusters in the size range of 10-27 atoms found with DFT and DFT+U. On application of the nanoDFT+DMFT approach to systems with mixed geometry (-) Fe2O3 film, which are periodic (infinitely extended), in two directions, and finite in the third. Similar to DFT+U, we find that the surface atom magnetic moments are smaller compared to the bulk. However, the absolute values of the surface atoms magnetic moments are smaller in DFT+DMFT. In parallel, we have carried out a systematic study of magnetic anisotropy in bimetallic L10 FePt nanoparticles (20-484 atoms) by using two DFT-based approaches: direct and the torque method. We find that the magnetocrystalline anisotropy (MCA) of FePt clusters is larger than that of the pure Fe and Pt ones. We explain this effect by a large hybridization of 3d Fe- and 5d Pt-atom orbitals, which lead to enhancement of the magnetic moment of the Pt atom, and hence to a larger magnetic anisotropy because of large spin-orbit coupling of Pt atoms. In addition, we find that particles whose (large) central layer consists of Pt atoms, rather than Fe, have larger MCA due to stronger hybridization effects. Such 'protected' MCA, which does not require protective cladding, can be used in modern magnetic technologies.
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Date Issued: 2015
Identifier: CFE0006038, ucf:50971
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006038

Title: Microscopic Theory of the Knight Shift.
Creator: Hall, Bianca, Klemm, Richard, Fernandez, Yan, Rahman, Talat, Del Barco, Enrique, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description: This dissertation is the beginning of the development of a microscopic theory of the Knight shift. The Knight shift experiment has been used in superconductivity research throughout history, however, a complete understanding of the Knight shift in conventional as well as unconventional superconductors does not yet exist. Motivated by the results of a literature review, which discusses Knight shift anomalies in multiple superconducting materials, this research studies a new model of the Knight...
Show moreThis dissertation is the beginning of the development of a microscopic theory of the Knight shift. The Knight shift experiment has been used in superconductivity research throughout history, however, a complete understanding of the Knight shift in conventional as well as unconventional superconductors does not yet exist. Motivated by the results of a literature review, which discusses Knight shift anomalies in multiple superconducting materials, this research studies a new model of the Knight shift, which involves the processes involved in nuclear magnetic resonance measurements in metals.The result of this study is a microscopic model of nuclear magnetic resonance in metals. The spins of the spin-1/2 local nucleus and its surrounding orbital electrons interact with the arbitrary constant ${\bf B}_0$ and perpendicular time-oscillatory magnetic inductions ${\bf B}_1(t)$ and with each other via an anisotropic hyperfine interaction. An Anderson-like Hamiltonian describes the excitations of the relevant occupied local orbital electrons into the conduction bands, each described by an anisotropic effective mass with corresponding Landau orbits and an anisotropic spin ${\bf g}$ tensor. Local orbital electron correlation effects are included using the mean-field decoupling procedure of Lacroix. The metallic contributions to the Knight shift resonance frequency and linewidth shifts are evaluated to leading orders in the hyperfine and Anderson excitation interactions. While respectively proportional to $(B_1/B_0)^2$ and a constant for weak $B_0(>)(>)B_1$, both shifts are shown to depend strongly upon ${\bf B}_0$ when a Landau level is near the Fermi energy.
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Date Issued: 2015
Identifier: CFE0005954, ucf:50808
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005954

Title: convective heat transfer in quasi-one-dimensional magnetic fluid in horizontal field and temperature gradients.
Creator: Huang, Jun, Luo, Weili, Schulte, Alfons, Del Barco, Enrique, Kassab, Alain, University of Central Florida
Abstract / Description: In this work we studied the convective heat transfer in a magnetic fluid in both zero and applied magnetic fields. The natural convection is observed in a quasi-one dimensional magnetic fluid in a horizontal temperature gradient. The horizontal non-homogeneous magnetic fields were applied across the sample cell either parallel or anti-parallel to the temperature gradient. The temperature profile was measured by eight thermocouples and temperature sensitive paint. The flow velocity field and...
Show moreIn this work we studied the convective heat transfer in a magnetic fluid in both zero and applied magnetic fields. The natural convection is observed in a quasi-one dimensional magnetic fluid in a horizontal temperature gradient. The horizontal non-homogeneous magnetic fields were applied across the sample cell either parallel or anti-parallel to the temperature gradient. The temperature profile was measured by eight thermocouples and temperature sensitive paint. The flow velocity field and streamlines were obtained by optical flow method. Calculated Nusselt numbers, Rayleigh number, and Grashof number show that the convective flow is the main heat transfer mechanism in applied fields in our geometry. It was found that when the field gradient is parallel with temperature gradient, the fields enhance the convective heat transfer while the fields inhibit it in anti-parallel configuration by analyzing the temperature difference across the sample, flow patterns, and perturbation Q field in applied fields. Magnetic Rayleigh number and magnetic Grashof number show that the thermomagnetic convections dominate in high magnetic fields. It is shown that the physical nature of the field effect is corresponding to the magnetic body force which is perpendicular to the gravity in our experiments. When the direction of the magnetic body force is same with temperature gradient in parallel configuration, the body force increases the convective heat transfer; while it has opposite effect in anti-parallel configuration.Our study will not only shed light on the fundamental mechanisms for thermomagnetic convection but also help to develop the potential field-controlled heat transfer devices.
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Date Issued: 2015
Identifier: CFE0005957, ucf:50810
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005957

Title: Internal Degrees of Freedom and Spin Transitions in Single Molecule Magnets.
Creator: Atkinson, James, Del Barco, Enrique, Chen, Bo, Mucciolo, Eduardo, Luis, Fernando, University of Central Florida
Abstract / Description: This thesis covers a range of work detailing the transitions between spin eigenstates in molecular magnet systems. Broadly speaking, these transitions can be divided into two kinds: Those that involve a the tunneling of spin through a potential barrier to a resonant state on the other side, a phenomenon known as quantum tunneling of magnetization, and those that occur through the absorption or emission of a photon. In this latter case, the energy of the photon must match the difference...
Show moreThis thesis covers a range of work detailing the transitions between spin eigenstates in molecular magnet systems. Broadly speaking, these transitions can be divided into two kinds: Those that involve a the tunneling of spin through a potential barrier to a resonant state on the other side, a phenomenon known as quantum tunneling of magnetization, and those that occur through the absorption or emission of a photon. In this latter case, the energy of the photon must match the difference between two eigenstates with a difference in angular momentum of ?. We will detail research performed on single molecule magnets, a class of systems that has established itself as an exemplar of higher-order spin interaction. Specifically, we will present the results of studies focused on two Manganese based systems, both of which represent good examples of single molecule magnet behavior. By performing magnetization measurements below the temperature threshold where these systems' polarizations become hysteretic, we find that the precise form of the observed resonant tunneling features (which includes evidence for strong interference of geometric phase a.k.a. Berry phase) can be related to the specifics of the intramolecular interaction. We have analyzed our results using the (")giant spin(") model (which approximates the system as a single spin) as well as with a (")multi-spin(") method which considers all interactions between the ions in the molecular core. We will also discuss the results of measurements performed on a crystalline sample under stress (uniaxial pressure). The data has been analyzed in a framework in which a physical distortion is modelled as a modification of the molecular anisotropy, with different directions of applied stress represented as changes to different parameters governing the molecular energy landscape. This analysis includes simulation of the magnetic relaxation through a master equation approach to the spin-phonon interaction.Finally, our discussion will outline efforts toward understanding the coherent behavior of spin systems. The (")weak(") and (")strong(") coupling between a photon and spin represent two regimes of an interaction by which the information within a spin can be accessed and manipulated. We will discuss the challenges involved in exploring these regimes, both from a theoretical and experimental standpoint. The purpose of this experiment dovetails with those outlined above in attempting to form an intimate basis of knowledge describing the universal relationships to spin at the most fundamental level.
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Date Issued: 2016
Identifier: CFE0006524, ucf:51381
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006524

Title: Charge and Spin Transport in Low-Dimensional Materials.
Creator: Ahmadi, Amin, Mucciolo, Eduardo, Del Barco, Enrique, Ishigami, Masa, Guo, Jing, University of Central Florida
Abstract / Description: My research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon...
Show moreMy research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon nanotube. The second part of my study was concerned to the dynamicalspin injection and spin currents in low-dimensional materials. We have developed an atomisticmodel to express the injected spin current in terms of the systems Greens function. The newformulation provides a framework to study the spin injection and relaxation of a system with anarbitrary structure.
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Date Issued: 2017
Identifier: CFE0006550, ucf:51343
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006550

Title: Light Trapping in Thin Film Crystalline Silicon Solar Cells.
Creator: Boroumand Azad, Javaneh, Chanda, Debashis, Peale, Robert, Del Barco, Enrique, Flitsiyan, Elena, Schoenfeld, Winston, University of Central Florida
Abstract / Description: This dissertation presents numerical and experimental studies of a unified light trapping approach that is extremely important for all practical solar cells. A 2D hexagonal Bravais lattice diffractive pattern is studied in conjunction with the verification of the reflection mechanisms of single and double layer anti-reflective coatings in the broad range of wavelength 400 nm - 1100 nm. By varying thickness and conformity, we obtained the optimal parameters which minimize the broadband...
Show moreThis dissertation presents numerical and experimental studies of a unified light trapping approach that is extremely important for all practical solar cells. A 2D hexagonal Bravais lattice diffractive pattern is studied in conjunction with the verification of the reflection mechanisms of single and double layer anti-reflective coatings in the broad range of wavelength 400 nm - 1100 nm. By varying thickness and conformity, we obtained the optimal parameters which minimize the broadband reflection from the nanostructured crystalline silicon surface over a wide range of angle 0(&)deg;-65(&)deg;. While the analytical design of broadband, angle independent anti-reflection coatings on nanostructured surfaces remains a scientific challenge, numerical optimization proves a viable alternative, paving the path towards practical implementation of the light trapping solar cells. A 3 (&)#181;m thick light trapping solar cell is modeled in order to predict and maximize combined electron-photon harvesting in ultrathin crystalline silicon solar cells. It is shown that the higher charge carrier generation and collection in this design compensates the absorption and recombination losses and ultimately results in an increase in energy conversion efficiency. Further, 20 (&)#181;m and 100 (&)#181;m thick functional solar cells with the light trapping scheme are studied. The efficiency improvement is observed numerically and experimentally due to photon absorption enhancement in the light trapping cells with respect to a bare cell of same thickness.
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Date Issued: 2017
Identifier: CFE0006936, ucf:51654
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006936

Title: Integration of Fundamental Research and CER: The Role of Authenticity in Developing Views on the Nature of Teaching, Learning, and Doing Science.
Creator: Donnelly, Julie, Hernandez, Florencio, Del Barco, Enrique, Saitta, Erin, Yestrebsky, Cherie, Underwood, Sonia, University of Central Florida
Abstract / Description: This dissertation is an integration of fundamental research and chemical education. It begins with two nonlinear spectroscopic studies of compounds important to the study of brain chemistry. In Chapter 2, we present a novel method using quantum mechanics for modelling ligand docking and the potential of nonlinear circular dichroism for elucidating the mechanism of cannabinoids docking to their receptor, a contribution to studies of varying psychological effects of cannabinoids. Considering...
Show moreThis dissertation is an integration of fundamental research and chemical education. It begins with two nonlinear spectroscopic studies of compounds important to the study of brain chemistry. In Chapter 2, we present a novel method using quantum mechanics for modelling ligand docking and the potential of nonlinear circular dichroism for elucidating the mechanism of cannabinoids docking to their receptor, a contribution to studies of varying psychological effects of cannabinoids. Considering existent challenges with measuring this phenomenon, in Chapter 3, we evaluate two-photon absorption properties of Thioflavin T (ThT) in varying glycerol/water content solutions and discuss the enhancement of nonlinear absorption due to small micelle formation. Our results represent the potential to enhance the applications of ThT for imaging Amyloid beta plaques in vitro and ex vivo and its potential application in vivo. Next, we consider the benefits of incorporating modern research into the undergraduate curriculum. In Chapter 4, we describe the integration of nonlinear optics into the physical chemistry laboratory in a course-based undergraduate research experience and the effects on student learning and perceptions. In Chapter 5, we expand our impact to secondary students by describing the development and assessment of the Orlando Chemistry Training, Enrichment, and Tutoring (OCTET) camp and its success in conveying chemistry concepts and inspiring students to pursue chemistry. In Chapter 6, we combine the successes of the previous two studies and incorporate a research component into OCTET. We study the effect on participants' views about science and show the impact on their practical knowledge about doing science. Finally, in Chapter 6, we extend the implementation of authentic learning to the classroom, present the implementation of active learning in physical chemistry, and describe students' perceptions. The results presented in this dissertation demonstrate successful integration of fundamental research into education and the powerful impact on all parties.
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Date Issued: 2018
Identifier: CFE0006997, ucf:51620
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006997

STM (3)	+ -
graphene (3)	+ -
MEMS (2)	+ -
SET (2)	+ -
Spin Pumping (2)	+ -

TEM (2)	+ -
molecular electronics (2)	+ -
single molecule magnets (2)	+ -
spintronics (2)	+ -
AFM (1)	+ -
Anti-reflective Coating (1)	+ -
Anticrossing (1)	+ -
Antiferromagnetic Resonance (1)	+ -
Antiferromagnets (1)	+ -
Atomic Number Contrast (1)	+ -
CM-LUT (1)	+ -
CMLUT (1)	+ -
CNFET (1)	+ -
CNFET LUT (1)	+ -
CNFET MTJ write (1)	+ -
CNFET PCSA (1)	+ -
Casimir Force (1)	+ -
Characterization (1)	+ -
Density functional theory(DFT) (1)	+ -
Dirac semimetal (1)	+ -
Dynamical mean-field theory (DMFT) (1)	+ -
EDS (1)	+ -
Electronic Circular Dichroism (1)	+ -
Electronic transport (1)	+ -
FIB (1)	+ -

ETD Collection (28)	+ -
Honors Collection (1)	+ -

University of Central Florida (29)	+ -
Del Barco, Enrique (25)	+ -
Mucciolo, Eduardo (6)	+ -
Peale, Robert (6)	+ -
Hernandez, Florencio (4)	+ -

Ishigami, Masa (4)	+ -
del Barco, Enrique (4)	+ -
Chow, Lee (3)	+ -
Schoenfeld, Winston (3)	+ -
Chen, Bo (2)	+ -
DeMara, Ronald (2)	+ -
Flitsiyan, Elena (2)	+ -
Haque, Md. Firoze (2)	+ -
Klemm, Richard (2)	+ -
Kuebler, Stephen (2)	+ -
Luis, Fernando (2)	+ -
Rahman, Talat (2)	+ -
Saitta, Erin (2)	+ -
Abdolvand, Reza (1)	+ -
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Alhasan, Ammar (1)	+ -
Anguera Antonana, Marta (1)	+ -
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