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open access

Degradation Mechanisms and Dynamics of Silicon Telluride: A Guide to the Effective Fabrication and Characterization of Silicon Telluride-Based Devices

Description: Silicon telluride (Si2Te3) and many other tellurium containing compounds show emergent Raman peaks located at ~120 cm-1 and ~140 cm-1 as they age. The origin of these two emergent peaks is controversial in the literature and has been attributed to myriad causes such as the intrinsic Raman modes of the telluride materials, surface oxidation, defects, double resonances, and tellurium precipitates. The controversial nature of these peaks has led to the misidentification of highly degraded materia… more
Date: December 2023
Creator: Hathaway, Evan Allen
Partner: UNT Libraries

Transport of Proton, Hydrogen and Alpha Particles through Atomic Hydrogen Environment

Description: Using multiple theoretical methods, comprehensive calculations are performed to create a new and more comprehensive data set for elastic scattering and related transport cross sections for collisions of (H$^+$ + H), (H + H) and (He$^{2+}$ + H) in the center-of-mass energy frame. In proton-atomic hydrogen collisions, we have significantly updated and extended previous work of elastic scattering, charge transfer and related transport integral and differential cross sections in the center-of-mass … more
This item is restricted from view until January 1, 2025.
Date: December 2023
Creator: Zaman, Tamanna
Partner: UNT Libraries

Extending the Capabilities of Continuum Embeddings in First-Principle Simulations of Materials

Description: In recent years, continuum models of solvation have had exceptional success in materials simulations as well as condensed matter physics. They can easily capture the effects of disordered systems, such as neutral liquids or electrolytes solutions, on material interfaces without the need for expensive statistical sampling. The Environ library (www.quantum-environ.org) implements different continuum models and correction schemes, which is the focus of this presentation. Recently refactored into a… more
This item is restricted from view until June 1, 2024.
Date: May 2023
Creator: Medrano, Gabriel
Partner: UNT Libraries
open access

Near-Infrared Spectroscopy of High Redshift Quasars: Bringing Distant Quasars into View

Description: The Gemini Near Infrared Spectrograph - Distant Quasar Survey (GNIRS-DQS) is the largest uniform, homogeneous survey of its kind, covering 260 quasars at 1.5 ≤ z ≤ 3.5. This unique survey, coupled with data from the Sloan Digital Sky Survey (SDSS), enables new investigations into redshifts, supermassive black hole masses (MBH), and accretion rates at high redshift through spectroscopic coverage of important rest-frame UV-optical emission lines. The importance of this survey is highlighted in th… more
Date: May 2023
Creator: Dix, Cooper Wilhelm
Partner: UNT Libraries
open access

Placing High-Redshift Quasars in Perspective: Unifying Distant Quasars with Their Lower Redshift Counterparts through Near-Infrared Spectroscopy

Description: I present spectroscopic measurements for 260 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample of Sloan Digital Sky Survey (SDSS) quasars at 1.5 < z < 3.5. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C IV λ1549, Mg II λλ2798, 2803, Hβ λ4861, and [O III] λλ4959, 5007 emission lines, in each source. The spectral… more
Date: May 2023
Creator: Matthews, Brandon M.
Partner: UNT Libraries

Twisted Moire Photonic Crystals: Their Nano-Fabrications, Optical Properties, and Applications in Light Extraction

Description: In this dissertation, I report the results of my research on twisted moiré photonic crystals which can be formed through multi-beam holographic interference without a physical rotation and later fabricated by electron-beam lithography. Their optical properties, such as photonic bandgaps, multiple resonance modes, and quality factor are presented. Randomized moire photonic crystals in lattice are also studied. The applications of moire photonic crystals in improving light extraction efficiency … more
This item is restricted from view until June 1, 2024.
Date: May 2023
Creator: Alnasser, Khadijah Saleh T.
Partner: UNT Libraries

Investigating Accretion Mechanisms and Host Galaxy Environments of z~4 Quasars

Description: Observations of quasars at the highest accessible redshifts have revealed supermassive black holes (SMBHs) with masses much too massive to be accounted for by the growth mechanisms observed in the local universe. Masses up to 10 10 M ⊙ up to z~7 seem to suggest some type of secular evolution or external influence to feed the earliest SMBHs at extremely high rates. Observations at such redshifts come at expensive technical cost and require significant dedicated space-telescope observing time. Howe… more
Date: December 2022
Creator: Thomas, Marcus
Partner: UNT Libraries
open access

Optical Control of Coherent Quantum Systems

Description: Optical control of coherent quantum systems has many methods and applications. In this defense we will discuss the effects of an electric field interacting with molecules with dipole moments. The theoretical study of such molecules will consist of two-level atom and a three-level atom in the λ configuration. The methods that will be discussed are population trapping using both bright and dark starts obtained by both STIRAP and CHIRAP pulses. The application to be discussed is how to create a ro… more
Date: December 2022
Creator: Roy, Colin Dean
Partner: UNT Libraries

Ultrasonic Wave Propagation and Localization in a Nonreciprocal Phononic Crystal

Description: Ultrasonic wave propagation through a two-dimensional nonreciprocal phononic crystal with asymmetric aluminum rods in viscous water is studied for its application in Anderson localization and trapping of acoustic energy. A one-dimensional disorder in the otherwise 2D periodic crystal is introduced by disorienting the asymmetric rods along the rows and by keeping them equally oriented along the columns. An exponential decay of sound waves travelling along the direction of disorder is observed de… more
Date: December 2022
Creator: Dhillon, Jyotsna
Partner: UNT Libraries

Developing Ultra-Fast Plasmonic Spiking Neuron via Integrated Photonics

Description: This research provides a proof of concept and background theory for the physics behind the state-of-the-art ultra-fast plasmonic spiking neurons (PSN), which can serve as a primary synaptic device for developing a platform for fast neural computing. Such a plasmonic-powered computing system allows localized AI with ultra-fast operation speed. The designed architecture for a plasmonic spiking neuron (PSN) presented in this thesis is a photonic integrated nanodevice consisting of two electro-opti… more
This item is restricted from view until September 1, 2024.
Date: August 2022
Creator: Goudarzi, Abbas, Sr.
Partner: UNT Libraries
open access

Scaling, Power-Law First Return Times, and Non-Ergodicity

Description: This dissertation is a collection of papers on anomalous phenomena in physics, biology, and sociology. These phenomena are primarily analyzed in terms of their temporal and spatiotemporal statistical properties. The analysis is based on both numerical simulations and, in some cases, real-world physiological and sociological data. The primary methods of analysis are diffusion entropy analysis, power spectral analysis, multifractal analysis, and survival (or waiting-time) analysis.
Date: August 2022
Creator: Lambert, David Robert
Partner: UNT Libraries
open access

Band Theory and Beyond: Applications of Quantum Algorithms for Quantum Chemistry

Description: In the past two decades, myriad algorithms to elucidate the characteristics and dynamics of molecular systems have been developed for quantum computers. In this dissertation, we explore how these algorithms can be adapted to other fields, both to closely related subjects such as materials science, and more surprising subjects such as information theory. Special emphasis is placed on the Variational Quantum Eigensolver algorithm adapted to solve band structures of a periodic system; three distin… more
Date: May 2022
Creator: Sherbert, Kyle Matthew
Partner: UNT Libraries
open access

Defect Modulated Properties of Molybdenum Disulfide Monolayer Films

Description: In this dissertation work, the study focuses on large areal growth of MoS2 monolayers and a study of the structural, optical and electrical properties of such monolayers before and after transfer using a polymer-lift off technique. This work will discuss the issue of contact resistance and the effect of defects (both intrinsic and extrinsic) on the overall quality of the monolayer films. The significance of this dissertation work is that a reproducible strategy for monolayer MoS2 film growth an… more
Date: May 2022
Creator: Jiang, Yan
Partner: UNT Libraries
open access

Ionized Molecular Hydrogen Confinement Using Electron Space-Charge: A Plasma Trap

Description: An ion trap has been constructed that creates a potential well suitable for confining ions with the space charge of an electron cloud. The trap uses the concept of artificially structured boundaries, regions of overlapping electric and magnetic fields, to confine particles in a relatively field free volume. Measurements are presented from the build-up of ionized molecular hydrogen over time. Molecular hydrogen is introduced into the confinement volume by direct electron bombardment ionization o… more
Date: May 2022
Creator: Kiester, Allen Scott
Partner: UNT Libraries
open access

Nonreciprocal and Non-Spreading Transmission of Acoustic Beams through Periodic Dissipative Structures

Description: Propagation of a Gaussian beam in a layered periodic structure is studied analytically, numerically, and experimentally. It is demonstrated that for a special set of parameters the acoustic beam propagates without diffraction spreading. This propagation is also accompanied by negative refraction of the direction of phase velocity of the Bloch wave. In the study of two-dimensional viscous phononic crystals with asymmetrical solid inclusions, it was discovered that acoustic transmission is nonre… more
Date: May 2022
Creator: Zubov, Yurii
Partner: UNT Libraries

Ongoing Developments on Continuum Solvation Models

Description: This work explores a continuum representation for diffuse layer models, thereby endowing continuum embedding models the ability to capture electrostatic phenomena in the environment such as the existence of electrolyte ions, and the nature of ionic liquids. It introduces a new field-aware continuum model that adjusts the size of the quantum regime per atom based on the distribution of charge in a system. The model accounts for the asymmetric nature of solvent distribution when applied to cation… more
Date: May 2022
Creator: Truscott, Matthew Anthony Si Ren
Partner: UNT Libraries
open access

Relaxation Time Approximations in PAOFLOW 2.0

Description: Electronic transport properties have been used to classify and characterize materials and describe their functionality. Recent surge in computational power has enabled computational modelling and accelerated theoretical studies to complement and accelerate experimental discovery of novel materials. This work looks at methods for theoretical calculations of electronic transport properties and addresses the limitations of a common approximation in the calculation of these properties, namely, the … more
Date: May 2022
Creator: Jayaraj, Anooja
Partner: UNT Libraries
open access

Computational Techniques for Accelerated Materials Discovery

Description: Increasing ubiquity of computational resources has enabled simulation of complex electronic systems and modern materials. The PAOFLOW software package is a tool designed to construct and analyze tight binding Hamiltonians from the solutions of DFT calculations. PAOFLOW leverages localized basis sets to greatly reduce computational costs of post-processing QE simulation results, enabling efficient determination of properties such as electronic density, band structures in the presence of electric… more
Date: December 2021
Creator: Cerasoli, Franklin
Partner: UNT Libraries
open access

Information and Self-Organization in Complex Networks

Description: Networks that self-organize in response to information are one of the most central studies in complex systems theory. A new time series analysis tool for studying self-organizing systems is developed and demonstrated. This method is applied to interacting complex swarms to explore the connection between information transport and group size, providing evidence for Dunbar's numbers having a foundation in network dynamics. A complex network model of information spread is developed. This network in… more
Date: December 2021
Creator: Culbreth, Garland
Partner: UNT Libraries
open access

Towards Increased Precision of the 4He:23P1→23P2 Transition Measurement Using Laser Spectroscopy

Description: Significant sub-systems were created and others enhanced providing a platform for an order of magnitude precision increase of the small 4He interval - 23P1→23P2 laser spectroscopy measurement, as well as other helium transitions. These measurements serve as tests of helium theory and quantum electro-dynamics in general. Many improvements to the original experiment are discussed and characterized. In particular, counting speed increased 10x, the signal level was doubled, a novel Doppler shift mi… more
Date: December 2021
Creator: Cameron, Garnet
Partner: UNT Libraries
open access

Classical Simulations of the Drift of Magnetobound States of Positronium

Description: The production and control of antihydrogen at very low temperatures provided a key tool to test the validity for the antimaterial of the fundamental principles of the interactions of nature such as the weak principle of equivalence (WEP), and CPT symmetry (Charge, Parity, and Time reversal). The work presented in this dissertation studies the collisions of electrons and positrons in strong magnetic fields that generate magnetobound positronium (positron-electron system temporarily bound due to … more
Date: August 2021
Creator: Aguirre Farro, Franz
Partner: UNT Libraries
open access

The Electrochemical Etching Process of a Tungsten Wire

Description: This study produced and analyzed shaped tungsten wire tips formed through electrochemical etching. Specifically, the cone length and the radius of curvature of the tip were analyzed. Having the tips move dynamically through an electrolytic solution, such as potassium hydroxide, and tuning the initial starting depth of the tungsten wire along with the dynamic speed of the tungsten wire as it passed throughout the solution allowed various types of tip profiles to be produced. The tip's radius of … more
Date: August 2021
Creator: Richardson, Aaron Michael
Partner: UNT Libraries

Low-Energy Electron Irradiation of 2D Graphene and Stability Investigations of 2D MoS2

Description: In this work, we demonstrate the mechanism for etching exfoliated graphene on SiO2 and other technological important substrates (Si, SiC and ITO), using low-energy electron sources. Our mechanism is based on helium ion sputtering and vacancy formation. Helium ions instead of incident electrons cause the defects that oxygen reacts with and etches graphene. We found that etching does not occur on low-resistivity Si and ITO. Etching occurs on higher resistivity Si and SiC, although much less than … more
Date: August 2021
Creator: Femi Oyetoro, John Dideoluwa
Partner: UNT Libraries
open access

A Study of Anomalous Conduction in n-Type Amorphous Silicon and Correlations in Conductivity and Noise in Gold Nanoparticle-Ligand Arrays

Description: This work explores two very different structural systems: n-type hydrogenated amorphous silicon (a-Si:H) and gold nanoparticles (AuNPs) suspended in a matrix of organic ligands. For a-Si:H, examination of the gas-phase concentration of dopant (1-6% PH3/SiH4) and argon diluent effects includes the temperature dependent conductivity, low-frequency electronic noise, and Raman spectroscopy to examine structure. It is found that a-Si:H samples grown with high dopant concentration or with argon dilut… more
Date: August 2021
Creator: Western, Brianna J
Partner: UNT Libraries
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