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Articles 31 - 60 of 97
Full-Text Articles in Physics
Photoluminescence From Gan Co-Doped With C And Si, Mykhailo Vorobiov
Photoluminescence From Gan Co-Doped With C And Si, Mykhailo Vorobiov
Theses and Dissertations
This thesis devoted to the experimental studies of yellow and blue luminescence (YL and BL relatively) bands in Gallium Nitride samples doped with C and Si. The band BLC was at first observed in the steady-state photoluminescence spectrum under high excitation intensities and discerned from BL1 and BL2 bands appearing in the same region of the spectrum. Using the time-resolved photoluminescence spectrum, we were able to determine the shape of the BLC and its position at 2.87 eV. Internal quantum efficiency of the YL band was estimated to be 90\%. The hole capture coefficient of the BLC …
Geodesic Structure In Schwarzschild Geometry With Extensions In Higher Dimensional Spacetimes, Ian M. Newsome
Geodesic Structure In Schwarzschild Geometry With Extensions In Higher Dimensional Spacetimes, Ian M. Newsome
Theses and Dissertations
From Birkoff's theorem, the geometry in four spacetime dimensions outside a spherically symmetric and static, gravitating source must be given by the Schwarzschild metric. This metric therefore satisfies the Einstein vacuum equations. If the mass which gives rise to the Schwarzschild spacetime geometry is concentrated within a radius of r=2M, a black hole will form. Non-accelerating particles (freely falling) traveling through this geometry will do so along parametrized curves called geodesics, which are curved space generalizations of straight paths. These geodesics can be found by solving the geodesic equation. In this thesis, the geodesic structure in the Schwarzschild geometry …
Quantitative Analysis And Process Of High Speed Live Cell Interferometry Measurements, Daniel Guest
Quantitative Analysis And Process Of High Speed Live Cell Interferometry Measurements, Daniel Guest
Theses and Dissertations
The application of auto focus, using an optical beam deflection technique, to existing live cell interferometry measurements was developed and examined. The benefit to relevant experiments, currently being performed, is shown as well as its performance across various magnifications. Enough information is given so that the system can be reproduced to fit any end users needs.
Investigations Into Structure And Properties Of Atomically-Precise Transition Metal-Chalcogenide Clusters Of Crte And Ligated Cr6te8(Pet3)6, Anthony F. Pedicini
Investigations Into Structure And Properties Of Atomically-Precise Transition Metal-Chalcogenide Clusters Of Crte And Ligated Cr6te8(Pet3)6, Anthony F. Pedicini
Theses and Dissertations
The complete understanding of a clusters electronic structure, the primary mechanisms for its properties and stabilization is necessary in order to functionalize them for use as building blocks within novel materials. First principle theoretical studies have been carried out upon the electronic properties of CrxTey (x = 1 – 6, y = 0 – 8, x + y ≤ 14), as well as for the larger triethylphosphine (PEt3) ligated cluster system of Cr6Te8(PEt3)6. Together, we aim to use the information garnered from the smaller clusters to address …
Nature Of Bonding In Bimetallic Or Ligated Aluminum Clusters, Cam J. Grover
Nature Of Bonding In Bimetallic Or Ligated Aluminum Clusters, Cam J. Grover
Theses and Dissertations
In this study, Amsterdam Density Functional software is used to model bimetallic and ligated aluminum clusters. The stability of the bimetallic clusters is well described by the Jellium model, and the nature of bonding between dopants and aluminum in the bimetallic clusters is analyzed using different criteria. We find that sodium tends to bind ionically, while the bonding of magnesium is not so obvious. We also determine that examining the Mulliken population is the most useful parameter in differentiating bonding character. Calculations on ligated aluminum clusters reveal it behaves fundamentally different than the bimetallic clusters studied in the first part. …
Theoretical And Experimental Analysis Of Optical Properties Of Defects In Gan:, Ibrahima Castillo Diallo
Theoretical And Experimental Analysis Of Optical Properties Of Defects In Gan:, Ibrahima Castillo Diallo
Theses and Dissertations
Using the Heyd-Scuseria-Ernzherof (HSE06) hybrid functional method along with photoluminescence experimental measurements, we analyze the properties of intrinsic defects such as vacancies, interstitials, antisites, and common complexes. By using configurational coordinate diagrams, we estimate the likelihood of defects to be radiative or non-radiative. Our calculations show that gallium vacancies exhibit a large magnetic moment in the neutral charge state and are most likely non-radiative. We also investigate the correlation between the observed infrared PL bands created in 2.5 MeV electron-irradiated GaN samples and the formation of native defects. It is found that gallium-nitrogen divacancies are possible sources of the broad …
Application Of The Fisher Dimer Model To Dna Condensation, John C. Baker Iii
Application Of The Fisher Dimer Model To Dna Condensation, John C. Baker Iii
Theses and Dissertations
This paper considers the statistical mechanics occupation of the edge of a single helix of DNA by simple polymers. Using Fisher's exact closed form solution for dimers on a two-dimensional lattice, a one-dimensional lattice is created mathematically that is occupied by dimers, monomers, and holes. The free energy, entropy, average occupation, and total charge on the lattice are found through the usual statistical methods. The results demonstrate the charge inversion required for a DNA helix to undergo DNA condensation.
Nanopore Thermodynamics Via Infrared Laser Heating, Christopher Angevine
Nanopore Thermodynamics Via Infrared Laser Heating, Christopher Angevine
Theses and Dissertations
Single molecule nanopore spectroscopy is a label-free method for characterizing a wide variety of water-soluble molecules. Recently there have been efforts to expand nanopore sensing to new areas of study. Forensic investigators require an easy to deploy method to identify an unknown number of contributors in a solution. Currently there is no easily available method to distinguish between a single or multiple contributor solution of DNA before being processed by more advanced analytical techniques which has led to wasted time and resources increasing the backlog of samples waiting to be processed. In this work we present a new nanopore technique …
Study Of The Photoluminescence Spectra Of Mg-Doped Gan, Puranjan Ghimire
Study Of The Photoluminescence Spectra Of Mg-Doped Gan, Puranjan Ghimire
Theses and Dissertations
We have studied luminescence properties of Mg-doped GaN grown by hydride vapor phase epitaxy. Steady state photoluminescence (PL) spectra have been analyzed. Exciton, ultraviolet luminescence (UVL) and blue luminescence (BL) bands are the dominant PL bands in the spectra. At low temperature, Exciton and UVL bands show almost no shift with excitation intensity, whereas the BL band blueshifts by almost 0.4 ���� with increasing excitation intensity by seven orders of magnitude. Such shifting nature of bands with excitation intensity is explained by assuming that the BL band is detected from the region of the sample where potential fluctuations are very …
Gravitational Microlensing, Wesley M. Barnes
Gravitational Microlensing, Wesley M. Barnes
Theses and Dissertations
A gravitational microlensing event occurs when a foreground star passes near our line of site to a background source star. The foreground star acts as a lens, perturbing the image of the source star and amplifying the apparent intensity. Because the lens is in motion relative to the source star, the amplification is a function in time, resulting in a characteristic microlensing light curve. If the lens happens to have a planetary companion, the resulting light curve will be perturbed due the planet and the characteristics of the binary system can be ascertained.
Thermal Quenching Of Photoluminescence In Zno And Gan, Nahla Albarakati
Thermal Quenching Of Photoluminescence In Zno And Gan, Nahla Albarakati
Theses and Dissertations
Investigation of the thermal quenching of photoluminescence (PL) in semiconductors provides valuable information on identity and characteristics of point defects in these materials, which helps to better understand and improve the properties of semiconductor materials and devices. Abrupt and tunable thermal quenching (ATQ) of PL is a relatively new phenomenon with an unusual behavior of PL. This mechanism was able to explain what a traditional model failed to explain. Usually, in traditional model used to explain “normal” quenching, the slope of PL quenching in the Arrhenius plot determines the ionization energy of the defect causing the PL band. However, in …
Time-Resolved Photoluminescence Studies Of Point Defects In Gan, Joy Dorene Mcnamara
Time-Resolved Photoluminescence Studies Of Point Defects In Gan, Joy Dorene Mcnamara
Theses and Dissertations
Time-resolved photoluminescence (TRPL) measurements paired with steady-state photoluminescence (SSPL) measurements can help to determine the PL lifetime, shape and position of unresolved bands, capture coefficients, and concentrations of free electrons and defects.PL bands that are obscured in the SSPL spectra can be accurately revealed by TRPL measurements. TRPL measurements are able to show if the PL band originates from an internal transition between different states of the same defect. The main defect-related PL bands in high-purity GaN grown by hydride vapor phase epitaxy (HVPE) which have been investigated are the ultraviolet, blue, green, yellow and red luminescence bands (UVL, BL, …
Understanding And Design Of An Arduino-Based Pid Controller, Dinesh Bista
Understanding And Design Of An Arduino-Based Pid Controller, Dinesh Bista
Theses and Dissertations
This thesis presents research and design of a Proportional, Integral, and Derivative (PID) controller that uses a microcontroller (Arduino) platform. The research part discusses the structure of a PID algorithm with some motivating work already performed with the Arduino-based PID controller from various fields. An inexpensive Arduino-based PID controller designed in the laboratory to control the temperature, consists of hardware parts: Arduino UNO, thermoelectric cooler, and electronic components while the software portion includes C/C++ programming. The PID parameters for a particular controller are found manually. The role of different PID parameters is discussed with the subsequent comparison between different modes …
Fabricating Superhydrophobic And Superoleophobic Surfaces With Multiscale Roughness Using Airbrush And Electrospray, Karam N. Almilaji
Fabricating Superhydrophobic And Superoleophobic Surfaces With Multiscale Roughness Using Airbrush And Electrospray, Karam N. Almilaji
Theses and Dissertations
Examples of superhydrophobic surfaces found in nature such as self-cleaning property of lotus leaf and walking on water ability of water strider have led to an extensive investigation in this area over the past few decades. When a water droplet rests on a textured surface, it may either form a liquid-solid-vapor composite interface by which the liquid droplet partially sits on air pockets or it may wet the surface in which the water replaces the trapped air depending on the surface roughness and the surface chemistry. Super water repellent surfaces have numerous applications in our daily life such as drag …
Electronic Structure And Stability Of Ligated Superatoms And Bimetallic Clusters, William H. Blades
Electronic Structure And Stability Of Ligated Superatoms And Bimetallic Clusters, William H. Blades
Theses and Dissertations
Quantum confinement in small metal clusters leads to a bunching of states into electronic shells reminiscent of shells in atoms. The addition of ligands can tune the valence electron count and electron distribution in metal clusters. A combined experimental and theoretical study of the reactivity of methanol with AlnIm− clusters reveals that ligands can enhance the stability of clusters. In some cases the electronegative ligand may perturb the charge density of the metallic core generating active sites that can lead to the etching of the cluster. Also, an investigation is conducted to understand how the bonding …
The Dawn Of New Quantum Dots: Synthesis And Characterization Of Ge1-Xsnx Nanocrystals For Tunable Bandgaps., Richard J. Esteves
The Dawn Of New Quantum Dots: Synthesis And Characterization Of Ge1-Xsnx Nanocrystals For Tunable Bandgaps., Richard J. Esteves
Theses and Dissertations
Ge1-xSnx alloys are among a small class of benign semiconductors with composition tunable bandgaps in the near-infrared spectrum. As the amount of Sn is increased the band energy decreases and a transition from indirect to direct band structure occurs. Hence, they are prime candidates for fabrication of Si-compatible electronic and photonic devices, field effect transistors, and novel charge storage device applications. Success has been achieved with the growth of Ge1-xSnx thin film alloys with Sn compositions up to 34%. However, the synthesis of nanocrystalline alloys has proven difficult due to larger discrepancies (~14%) in …
Drying Methods For The Fabrication Of Polymer Foam Material, Dalton Echard
Drying Methods For The Fabrication Of Polymer Foam Material, Dalton Echard
Theses and Dissertations
This is a report on the study of the drying of nanoporous polymer foam material fabricated by photolithogtaphic methods. Three drying methods were employed, which were air drying, supercritical drying and freeze drying. After fabrication and drying, physical properties of the polymer foams were measured. These measurements included density of the material, Young’s modulus, surface area, and the shape of the skeletal particles. The measurements determined the effect of the polymer concentration and the effect of drying methods. It was determined that polymer concentration had a much larger effect on the properties of the materials than the drying method.
T-Duality And Double Field Theory, Nicholas T. King
T-Duality And Double Field Theory, Nicholas T. King
Theses and Dissertations
The purpose of this thesis is to study a symmetry of string theory known as T-duality. We focus on a particular example establishing the equivalence between a quantized string moving in a circular space of radius R and a dual string moving in a similar space of radius 1/R . We will show that this duality implies that the momentum of the string in one picture becomes the number of times the string is wound around the circle in the dual picture. We present two proofs of T-duality. The first reflects the standard interpretation of T-duality as an isomorphism of …
Non-Conventional Approaches To Syntheses Of Ferromagnetic Nanomaterials, Dustin M. Clifford
Non-Conventional Approaches To Syntheses Of Ferromagnetic Nanomaterials, Dustin M. Clifford
Theses and Dissertations
The work of this dissertation is centered on two non-conventional synthetic approaches to ferromagnetic nanomaterials: high-throughput experimentation (HTE) (polyol process) and continuous flow (CF) synthesis (aqueous reduction and the polyol process). HTE was performed to investigate phase control between FexCo1-x and Co3-xFexOy. Exploration of synthesis limitations based on magnetic properties was achieved by reproducing Ms=210 emu/g. Morphological control of FexCo1-x alloy was achieved by formation of linear chains using an Hext. The final study of the FexCo1-x chains used DoE to …
Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian
Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian
Theses and Dissertations
Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that …
Cluster Enhanced Nanopore Spectrometry, Amy Chavis
Cluster Enhanced Nanopore Spectrometry, Amy Chavis
Theses and Dissertations
Nanopore sensing is a label-free method used to characterize water-soluble molecules. Recent work describes how Au25(SG)18 clusters improve the single molecule nanopore spectrometry (SMNS) technique when analyzing polyethylene glycol (PEG). This thesis will further study and optimize the enhancement effect resulting from a cluster’s presence. Additionally, a model describing the interaction between a cluster and PEG is developed to assist in understanding this mechanism of enhancement. This thesis will also discuss expanding the SMNS method to detect peptides, using Au25(SG)18 for enhancement, and adjusting solution conditions to improve the sensitivity of the SMNS system …
Enhanced Nanopore Detection Via Diffusion Gradients And Optical Tweezers, Kyle T. Brady
Enhanced Nanopore Detection Via Diffusion Gradients And Optical Tweezers, Kyle T. Brady
Theses and Dissertations
Nanopore-based resistive pulse sensing represents an important class of single-molecule measurements. It provides information about many molecules of interest (i.e. DNA, proteins, peptides, clusters, polymers, etc.) without the need for labeling. Two experiments that are especially well suited for studying with nanopore sensors are DNA sequencing and DNA-protein force measurements. This thesis will describe progress that has been made in both areas.
DNA sequencing has become an active area of research for stochastic single-molecule sensing, with many researchers striving for the ultimate goal of single-molecule de novo DNA sequencing. One intriguing method towards that goal involves the use of a …
Λcdm Cosmology + Chaotic Inflation, Peter A. Farago
Λcdm Cosmology + Chaotic Inflation, Peter A. Farago
Theses and Dissertations
ΛCDM cosmology is described in terms of general relativity and the Robertson-Walker metric. The evolution of the observable universe, currently dominated by dark energy (Λ) and cold dark matter (CDM), is presented in terms of its thermal history. CDM is extended to include an inflation epoch that accelerates the early expansion rate to near exponential levels. It is shown that inflation solves several problems in CDM and produces perturbations in the metric that lead to the observed anisotropies in the Cosmic Microwave Background and the formation of large scale cosmological structures. Various theories of inflation are explored. Predictions of inflation …
Femtosecond Laser Beam Propagation Through Corneal Tissue: Evaluation Of Therapeutic Laser-Stimulated Second And Third-Harmonic Generation, William R. Calhoun Iii
Femtosecond Laser Beam Propagation Through Corneal Tissue: Evaluation Of Therapeutic Laser-Stimulated Second And Third-Harmonic Generation, William R. Calhoun Iii
Theses and Dissertations
One of the most recent advancements in laser technology is the development of ultrashort pulsed femtosecond lasers (FSLs). FSLs are improving many fields due to their unique extreme precision, low energy and ablation characteristics. In the area of laser medicine, ophthalmic surgeries have seen very promising developments. Some of the most commonly performed surgical operations in the world, including laser-assisted in-situ keratomileusis (LASIK), lens replacement (cataract surgery), and keratoplasty (cornea transplant), now employ FSLs for their unique abilities that lead to improved clinical outcome and patient satisfaction.
The application of FSLs in medical therapeutics is a recent development, and although …
Surface Photovoltage Transients For P-Type Algan, Karen L. Phumisithikul
Surface Photovoltage Transients For P-Type Algan, Karen L. Phumisithikul
Theses and Dissertations
There is an understanding of surface photovoltage (SPV) behavior for GaN, yet little is known about the SPV behavior for AlGaN. In this work, a Kelvin probe was used to measure the SPV for p-type AlGaN. Very slow SPV transients were found in AlGaN, which could not be explained with a simple thermionic model. A possible explanation of this behavior is the segregation of impurities to the surface, which causes significant reduction of the depletion region width (down to 2 nm), with carrier tunneling and hopping becoming the dominant mechanisms responsible for the SPV transients. To verify this assumption, …
Silicon Nanostructures For High Capacity Anodes In Lithium Ion Batteries, Tyler M. Selden
Silicon Nanostructures For High Capacity Anodes In Lithium Ion Batteries, Tyler M. Selden
Theses and Dissertations
In this study we looked at several different silicon nanostructures grown for the purpose of optimizing anodes for lithium ion batteries. We primarily focused on two distinct types of structures, nanospirals, and Rugate structures. The samples were designed to have the mechanical robustness to endure the massive expansion caused by lithiation of silicon. All of the samples were grown using an electron beam evaporator. Scanning electron microscope images show that we have achieved the desired structural growth. The spirals were shown to have an average diameter of 343 nm on polished copper, and 366 nm on unpolished copper. The Rugate …
High Speed Atomic Force Microscope Design Using Dvd Optics, Thomas Carlson
High Speed Atomic Force Microscope Design Using Dvd Optics, Thomas Carlson
Theses and Dissertations
We examine the design of a high speed atomic force microscope using an optical pickup from a commercially available compact disc/digital versatile disc drive. An investigation of the commercial optical pickup is done with the goal of determining how it can be used for dimensional measurements on nanometer scale. An evaluation of noise sources, imaging capabilities, and functionality is performed.
Investigating Mechanical Properties Of Metallic Nanowires Using Molecular Dynamics, Alex Khammang
Investigating Mechanical Properties Of Metallic Nanowires Using Molecular Dynamics, Alex Khammang
Theses and Dissertations
Metallic nanowires have useful applications in scanning tunneling microscopes and atomic force microscopes due to their unique sensitivity to force and electricity. These unique properties arise because of the large surface area to volume ratio. One of these properties is that introducing twinning planes the mechanical properties of metallic nanowires can be altered. The effects of twinning planes on metallic nanowires were studied using molecular dynamics simulations. Silver, copper, and nickel nanowires with and without twinning planes were simulated with engineering strain until the first yielding stress was obtained. The radial simulations showed that as the radius of twinned nanowires …
Aromaticity Rules In The Development Of Negative Ions, Brandon Child
Aromaticity Rules In The Development Of Negative Ions, Brandon Child
Theses and Dissertations
Organic molecules are known for their stability due to aromaticity. Superhalogens, on the other hand, are highly reactive anions, whose electron affinity is larger than that of chlorine. This thesis, using first principles calculations, explores possible methods for creation of superhalogen aromatic molecules while attempting to also develop a fundamental understanding of the physical properties behind their creation. The first method studied uses anionic cyclopentadienyl and enhances its electron affinity through ligand substitution or ring annulation in combination with core substitutions. The second method studies the possibilities of using benzene, which has a negative electron affinity (EA), as a core …
Characterization Of Individual Charged Au25(Sg)18 Clusters And Their Enhancement Of Single Molecule Mass Spectrometry, Christopher Angevine
Characterization Of Individual Charged Au25(Sg)18 Clusters And Their Enhancement Of Single Molecule Mass Spectrometry, Christopher Angevine
Theses and Dissertations
Metallic quantum clusters are stable structures that can exhibit many useful magnetic, chemical, and optical properties. Developing clusters for specific applications requires accurate methods for characterizing their physical and chemical properties. Most cluster characterization methods are ensemble-based measurements that can only measure the average values of the cluster properties. Single cluster measurements improve upon this by yielding information about the distribution of cluster parameters. This investigation describes the initial results on a new approach to detecting and characterizing individual gold nanoclusters (Au25(SG)18) in an aqueous solution with nanopore-based resistive pulse sensing. We also present a new application where the clusters …