Condensed Matter Physics Commons^™

Synthesis, Characterization, And Simulation Of Two-Dimensional Materials, Lawrence Hudy

Theses and Dissertations

ABSTRACT

SYNTHESIS, CHARACTERIZATION, AND SIMULATION OF TWO-DIMENSIONAL MATERIALS

by

Lawrence Hudy

The University of Wisconsin-Milwaukee, 2023Under the Supervision of Professor Michael Weinert

This dissertation focuses on my journey through many aspects of surface science leading to the first principles investigation of transition metal dichalcogenides studying the impact of defects, twist, and decreasing interlayer separation to probe their effect on the electronic properties of these materials. My journey started out learning many aspects of material science such as methods for material synthesis and characterization but later ended on simulation of material properties using density functional theory. In the first experiments, we …

Computational Modeling Of Superconductivity From The Set Of Time-Dependent Ginzburg-Landau Equations For Advancements In Theory And Applications, Iris Mowgood

Computational and Data Sciences (PhD) Dissertations

A full review of the research conducted and published during my PhD studies in Computational and Data Sciences at Chapman University, under the advisement of Dr. Armen Gulian, are presented. Using the set of time-dependent Ginzburg-Landau (TDGL) equations with inclusion of the interference current and the non-equilibrium phonon term, we modeled the dynamics of superconductors in various theory revealing states and practical purposes. A review of the history and phenomenon of superconductivity, including modern applications, is introduced. The Josephson effect and associated Josephson junction are discussed for comparison to our analogous results with the 1-D superconducting wire. The mathematics of …

Response Of The Isothermal Mode Grüneisen Tensor Across Phase Boundaries, Jasmine K. Hinton

UNLV Theses, Dissertations, Professional Papers, and Capstones

The assumptions for the 1912 Grüneisen parameter are reviewed, particularly in the cases of anisotropy, high temperatures, and across phase boundaries. Two main case studies are shown: β-Sn, and Cd. The main techniques of this work involve resistively heated diamond anvil cells with both optical Raman spectroscopy and x-ray diffraction. It is found in Sn that the isothermal mode Grüneisen tensor along increasing isotherms diverges from the single-valued temperature aggregate at the onset of melt, and this is proposed to use as a method of exploring melt phase boundaries in other systems. This method is examined once again on another …

Stoichiometric Determination Of Hydride Materials At Extreme Conditions, Gregory Alexander Smith

UNLV Theses, Dissertations, Professional Papers, and Capstones

Hydrogen was predicted to be a high-temperature superconductor at near-megabar conditions in 1968,[1] but only recently was been experimentally observed.[2] This is due to the extraneous metrological constraint of requiring 5 megabars of pressure to stabilize. A more practical approach for synthesis of high-temperature superconductors has been pro-posed through the use of hydride compounds. Recently, a surge of rare earth hydrides have achieved critical superconducting transition temperatures (T_C ) close to room temperature.[3, 4, 5, 6] However, due to limitations of the necessary instrumentation to achieve megabar pressures, many techniques traditionally used to measure stoichiometry are unavailable.Three works presented in …

Development And Characterization Of Germanium Detectors For Searching Rare-Event Physics, Rajendra Panth

Dissertations and Theses

High-purity germanium (HPGe) detector has an excellent energy resolution and low-energy detection threshold ideal for searching rare-event physics such as dark matter and neutrinoless double beta decay searches. Understanding the electrical contact properties and the Ge detector properties is key to enhancing the use of Ge detectors for a wide range of applications. Amorphous Ge (a-Ge) is one of the passivation materials used to passivate Ge detectors, which also provides the barrier height to the charge injection. Several a-Ge contact Ge detectors were fabricated and tested at the University of South Dakota (USD) and Max-Planck-Institut (MPI) für Physik in Munich …

Attempts To Measure Nanosecond Resolved Electronic Dynamics Of Charge Density Wave Phase Transition In 1t-Tas2, Ben Campbell

Honors Theses and Capstones

Scanning tunneling microscopes allow for atomic spatial resolution but the resulting images are necessarily time-averaged and fast dynamics are lost. Pump-probe spectroscopy is a common optical technique used to measure ultrafast electronic dynamics but the integration of optical pump-probe spectroscopy into an STM requires specialized knowledge and equipment. Alternatively, an all-electronic pump-probe spectroscopy technique has recently been developed for use with an STM that replaces the laser pulses of optical pump-probe with voltage pulses. In this paper, I implemented an all-electronic pump-probe scheme into an existing scanning tunneling microscope using an arbitrary waveform generator and a lock-in amplifier. I developed …

Ab-Initio And Empirical Simulations Of Aluminum And Copper Metal, William Wolfs

UNLV Theses, Dissertations, Professional Papers, and Capstones

In this work, I perform detailed calculations on the bulk and electronic properties of aluminum and copper metal. Originally, I was motivated by experimental work on the solidsolid phase changes in pure aluminum. These phase changes were well predicted by density functional theory(DFT) but difficult or impossible to predict using embedded atom method potentials(EAM). EAM potentials are in wide use to describe many properties of bulk materials, and it seemed worrying that something so basic as a phase change could not be predicted. I began running high precision calculations with DFT and compared the results to EAM potentials which had …

Study Of Weakly Bound Cluster Anions Using Self Interaction Corrected Density Functional Scheme, Peter Obinna Ufondu

Open Access Theses & Dissertations

The Kohn–Sham formulation of density functional theory (DFT) is a widely used quantum mechanical theory to study chemical and materials properties. The practical application of DFT requires an approximation to the exchange–correlation (XC) functional. These approximations suffer from self-interaction errors due to the incomplete cancellation of the self-Coulomb energy with the approximate self-exchange and correlation energy for one-electron densities. Systems with weakly-bound electrons impose great challenges to semi-local density functional approximations. We use recently developed local scaled self-interaction correction (LSIC) by Zope et al and the Perdew-Zunger SIC method using the Fermi-Löwdin orbitals to calculate the vertical detachment energies (VDEs) …

Understanding The Magnetic Properties Of Ii-Vi Semiconductor Nanocrystals, Alex Khammang

Electronic Theses and Dissertations

Semiconductor nanocrystals (NC) are well known for their unique size tunable optical properties making them suitable candidates for devices such as light emitting diodes (LEDs), solar cells, and cellular labels. II-VI semiconductors in the bulk form behave diamagnetically, but can inherit paramagnetic (PM) or ferromagnetic (FM) properties at the nanoscale. Reports suggest that the emergence of weak PM or FM behavior in undoped NCs are attributed to the increased surface to volume ratio compared for NCs. Traditionally, these NCs only obtain magnetic properties after doping with certain transition metals, such as Co, Mn, or Fe. Many mechanisms have been proposed …

Density Functional Theory Study Of Two-Dimensional Boron Nitride Films, Pradip R. Niraula

Dissertations, Theses, and Capstone Projects

Since graphene was isolated in 2004, the number of two-dimensional (2D) materials and their scientific relevance have grown exponentially. Besides graphene, one of the most important and technolocially promizing 2D materials that has emerged in recent years is hexagonal boron nitride, in its monolayer or multilayer form. In my thesis work, I used density functional theory (DFT) calculations to investigate the properties of boron nitride films. In particular, I first studied the properties (i.e. formation energy, defect states, and structure) of point charged defects in monolayer and bilayer hexagonal boron nitride, and subsequently, I focused on the linear and nonlinear …

Electrodynamics Modeling Of Plasmonic-Organic Hybrid Waveguides, Marcus Michel

Pomona Senior Theses

Optical fibers have multiple advantages over conventional electrical connections, such as lower energy losses and higher bandwidth. To use optics for chip-to-chip communication, electro-optic (EO) modulators need to be scaled down to be incorporated on integrated circuits. This size reduction has been accomplished using plasmonic-organic hybrid (POH) waveguides, which make use of nonlinear organic EO materials and surface plasmon polaritons to achieve light modulation in devices with lengths on the micron scale. As these devices are just starting to be developed, there are many avenues for their potential optimization. In order to streamline and reduce the cost of the optimization …

First-Principles Simulations Of Materials Under Extreme Conditions, Kien Nguyen Cong

USF Tampa Graduate Theses and Dissertations

The investigation of materials at extreme conditions of high pressure and temperature (high-PT), has been one of the greatest scientific endeavors in condensed mater physics, chemistry, astronomy, planetary, and material sciences. Being subjected to high-PT conditions, materials exhibit dramatic changes in both atomic and electronic structure resulting in an emergence of exceptionally interesting phenomena including structural and electronic phase transitions, chemical reactions, and formation of novel compounds with never-previously observed physical and chemical properties. Although new exciting experimental developments in static and dynamic compression combined with new diagnostics/characterization methods allow to uncover new processes and phenomena at high P-T conditions, …

Applied Symmetry For Crystal Structure Prediction, Scott William Fredericks

UNLV Theses, Dissertations, Professional Papers, and Capstones

This thesis presents an original open-source Python package called PyXtal (pronounced "pi-crystal") that generates random symmetric crystal structures for use in crystal structure prediction (CSP). The primary advantage of PyXtal over existing structure generation tools is its unique symmetrization method. For molecular structures, PyXtal uses an original algorithm to determine the compatibility of molecular point group symmetry with Wyckoff site symmetry. This allows the molecules in generated structures to occupy special Wyckoff positions without breaking the structure's symmetry. This is a new feature which increases the space of search-able structures and in turn improves CSP performance.

It is shown that …

Morphological Study Of Voids In Ultra-Large Models Of Amorphous Silicon, Durga Prasad Paudel

Dissertations

The microstructure of voids in pure and hydrogen-rich amorphous silicon (a:Si) network was studied in ultra-large models of amorphous silicon, using classical and quantum- mechanical simulations, on the nanometer length scale. The nanostructure, particularly voids of device grade ultra-large models of a:Si was studied, in which observed three-dimensional realistic voids were extended using geometrical approach within the experimental limit of void-volume fractions. In device-grade simulated models, the effect of void morphology; size, shape, number density, and distribution on simulated scattering intensities in small- angle region were investigated. The evolution of voids on annealing below the crystallization temperature …

Extended-Range Oscillations And The First Sharp Diffraction Peak In Amorphous Silicon: A Systematic Study, Devilal Dahal

Master's Theses

The first sharp diffraction peak (FSDP), which characterizes the static structure factor of many glassy systems near the wave vector region of 1-2 Å^-1 has been observed depending on the temperature, pressure and the degree of annealing of the system. The presence of the FSDP is indicative of the intermediate range order (IRO). In current work, we study the role of the extended- range oscillations on the parameters of the FSDP, i.e., intensity, position, area, and the full width at half maximum (FWHM) by using high-quality simulated models of amorphous silicon. The radial distance up to half of the …

Toward Devices For Exploring Pt-Symmetry In Electronic Transport Of Graphene, Michael Carovillano

Senior Honors Papers / Undergraduate Theses

Parity-time symmetry, or PT -symmetry is the principle that in quantum mechanics a non- Hermitian Hamiltonian is capable of returning real eigenstates and real spectra.Recent research has demonstrated real world observation of PT -symmetry in electronics and optics. We aim to expand the regime of observed PT -symmetry through measurement of the electronic transport of graphene devices. Drawing from analogous experiments, we plan to use balanced ohmic resistance acting as both loss and relative gain to induce the required unbroken PT -symmetry regime. This paper analyzes techniques used in fabrication of such devices as well as the basis of the …

High-Pressure High-Temperature Exploration Of Phase Boundaries Using Raman Spectroscopy, Jasmine Kashmir Hinton

UNLV Theses, Dissertations, Professional Papers, and Capstones

Metastability of states can provide interesting properties that may not be readily accessible in a material’s ground state. Many materials show high levels of polymorphism, indicating a rich energy landscape and a potential for metastable states. Melt crystallization techniques provide a potential route to these states. We use a resistively heated diamond anvil cell (DAC) with fine control of a system’s pressure and temperature to explore these systems. Raman spectroscopy is used to track subtle structural changes across phase boundaries. Organic systems, such as glycine and aspirin, were our initial interest due to their high polymorphism and reported low melting …

Topological Insulating States In Photonics And Acoustics, Xiang Ni

Dissertations, Theses, and Capstone Projects

Recent surge of interest in topological insulators, insulating in their interior but conducting at the surfaces or interfaces of different domains, has led to the discovery of a variety of new topological states, and their topological invariants are characterized by numerous approaches in the category of topological band theory. The common features shared by topological insulators include, the topological phase transition occurs if the bulk bandgap is formed due to the symmetries reduction, the topological invariants exist characterizing the global properties of the material and inherently robust to disorder and continuous perturbations irrespective of the local details. Most importantly, these …

Theoretical Studies Of The Structure And Stability Of Metal Chalcogenide Crntem (1≤N≤6, 1≤M≤8) Clusters, Fnu Sweta Prabha

Theses and Dissertations

In the presented work, first principle studies on electronic structure, stability, and magnetic properties of metal chalcogenide, Cr_nTe_m clusters have been carried out within a density functional framework using generalized gradient functions to incorporate the exchange and correlation effects. The energetic and electronic stability was investigated, and it was found that they are not always correlated as seen in the cluster Cr₆Te₈ which has smaller gap between its HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) and a high electron affinity of 3.39 eV indicating lower electronic stability whereas higher fragmentation …

Effects Of High Pressure On Photochemical Reactivity Of Organic Molecular Materials Probed By Vibrational Spectroscopy, Jiwen Guan

Electronic Thesis and Dissertation Repository

Chemical transformations of molecular materials induced by high pressure and light radiation exhibit novel and intriguing aspects that have attracted much attention in recent years. Particularly, under the two stimuli, entire transformations of molecular species can be realized in condensed phases without employing additional chemical constraints, e.g., the need of solvents, catalysts or radical initiators. This new synthetic approach in chemistry therefore satisfies increasing need for production methods with reduced environmental impacts. Motivated by these promises, my Ph. D thesis focuses on this state-of-the-art branch of high-pressure photochemistry. Specifically, high pressure is employed to create the necessary reaction conditions to …

Emergent Phenomena In Quantum Critical Systems, Kun Chen

Doctoral Dissertations

A quantum critical point (QCP) is a point in the phase diagram of quantum matter where a continuous phase transition takes place at zero temperature. Low-dimensional quantum critical systems are strongly correlated, therefore hosting nontrivial emergent phenomena. In this thesis, we first address two decades-old problems on quantum critical dynamics. We then reveal two novel emergent phenomena of quantum critical impurity problems. In the first part of the thesis, we address the linear response dynamics of the $(2+1)$-dimensional $O(2)$ quantum critical universality class, which can be realized in the ultracold bosonic system near the superfluid (SF) to Mott insulator (MI) …

Simulating The Electrical Properties Of Random Carbon Nanotube Networks Using A Simple Model Based On Percolation Theory, Roberto Abril Valenzuela

Physics

Carbon nanotubes (CNTs) have been subject to extensive research towards their possible applications in the world of nanoelectronics. The interest in carbon nanotubes originates from their unique variety of properties useful in nanoelectronic devices. One key feature of carbon nanotubes is that the chiral angle at which they are rolled determines whether the tube is metallic or semiconducting. Of main interest to this project are devices containing a thin film of randomly arranged carbon nanotubes, known as carbon nanotube networks. The presence of semiconducting tubes in a CNT network can lead to a switching effect when the film is electro-statically …

An Analysis Of Frenkel Defects And Backgrounds Modeling For Supercdms Dark Matter Searches, Matthew Stein

Physics Theses and Dissertations

Years of astrophysical observations suggest that dark matter comprises more than ~80 % of all matter in the universe. Particle physics theories favor a weakly-interacting particle that could be directly detected in terrestrial experiments. The Super Cryogenic Dark Matter Search (SuperCDMS) Collaboration operates world-leading experiments to directly detect dark matter interacting with ordinary matter. The SuperCDMS Soudan experiment searched for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei in low-temperature germanium detectors.

During the operation of the SuperCDMS Soudan experiment, ²¹⁰Pb sources were installed to study background rejection of the Ge detectors. Data from these sources …

Vibrational Relaxation Theory For Systems Embedded In Microscopically Specified Reservoirs, Anastasia Aemilia Ierides

Physics & Astronomy ETDs

This dissertation is a study of the theoretical framework of the practical as well as fundamental problem of the process of relaxation to equilibrium of quantum mechanical systems. The fundamental aspect is concerned with the simultaneous occurrence of decoherence and population equilibration. The practical aspect deals with experimental observations of vibrational relaxation of molecules embedded in liquids or solids. The systems include, but are not limited to, the nondegenerate dimer and harmonic oscillator, in one case weak and in the other strong, interaction with a thermal bath. The time dependence of the energy and the temperature dependence of the relaxation …

Nonlinear Dynamic Studies Of Pattern-Forming And Biomedical Systems, Doaa Taha

Wayne State University Dissertations

Nonlinear phenomena are ubiquitous in nature and in almost every discipline of science. Various nonlinear dynamic theories are being developed to investigate a wide range of complex nonlinear systems. In this work, we study two types of nonlinear phenomena. The first type involves understanding and controlling the properties and dynamics of two-dimensional (2D) material systems. We develop a binary phase field crystal (PFC) model which simultaneously addresses diffusive dynamics of large-scale systems and resolves material microstructures, and apply the model to the study of two material systems. (1) We use this PFC model to investigate the self assembly of 2D …

Designing Active Granular Squares, Christopher C. Olson

Masters Theses

The goal of this thesis has been to find a means of i) designing an active square particle, and ii) continuously varying its degree of activity with the objective of understanding the effects of activity on the various phases of granular matter. The motivations, results and limitations of our methods of creating active particles are discussed in this thesis. The applicability of a stochastic model based on the Langevin equation in 2D as well as implications for future experiments are also discussed.

Polarization Charge Density In Strained Graphene, Noah Wilson

Graduate College Dissertations and Theses

Graphene, the world's first truly two-dimensional material, is unique for having an electronic structure described by an effective Lorentz invariant theory. One important consequence is that the ratio or Coulomb energy to kinetic energy is a constant, depending only on conditions within the lattice rather than on the average charge density as in a typical Galilean invariant material. Given this unusual property, a natural question would be how do phenomena, such as screening of a Coulomb impurity, happen in graphene? Moreover, how does the addition of uniaxial strain enhance or diminish this behavior? Here I discuss our work to calculate …

Thermoelectric Properties Of Nano-Meso-Micro Β-Mno2 Powders As A Function Of Electrical Resistance: Experiment And Theory, Morgan Hedden

Senior Honors Projects, 2010-2019

In this work, the thermoelectric properties of Beta-MnO² powders as a function of electrical resistance are measured and compared to theoretical models. The discovery of a giant Seebeck coefficient by Song et al. in these powders rejuvenated interest in understanding the physical mechanism behind it. A simple pestle and mortar method was used to modify the MnO² powder sizes. We and the largest S coefficient, power factor, and thermal conductivity values were found to be S=-316 uV/K, (sigma)S² =5.8x10^-7 W/mK² and k=0.2096 W/(mK), all observed at a particle electrical resistance of R=9.8 Ohms. From these …

Novel Physical Properties Of Non-Trivial Magnetic Materials: Cr1/3nbs2, Mnsi And Fe3gete2, Jieyu Yi

Doctoral Dissertations

Helimagnets and quasi-two-dimensional layered materials have attracted much recent interest due to their rich physical properties and potential for spintronics applications. In this dissertation, the helimagnets Cr_1/3NbS₂ [chromium one-third niobium disulfide] and thin-film MnSi [manganese silicide] as well as the layered magnetic material Fe₃GeTe₂ [iron three germanium ditelluride] were extensively and carefully studied. Cr_1/3NbS₂ was previously reported to be helimagnet with a transition temperature of approximately 120 K. Cr_1/3NbS₂ has a layered structure with Cr³⁺ ions intercalating between NbS­₂ sheets, and is easily cleaved. Using in-situ …

Dynamics And Manipulation Of Nanomagnets, Liufei Cai

Dissertations, Theses, and Capstone Projects

This thesis presents my work on the spin dynamics of nanomagnets and investigates the possibility of manipulating nanomagnets by various means. Most of the work has been published\cite{LC-PRB2010, LC-PRB2012, LC-PRB2013, LC-EPL2014}. Some has been submitted for publication\cite{LC-arxiv2014}. The structure of this thesis is as follows.

In Chapter 1, I present the theory of manipulation of a nanomagnet by rotating ac fields whose frequency is time dependent. Theory has been developed that maps the problem onto Landau-Zener problem. For the linear frequency sweep the switching phase diagrams are obtained on the amplitude of the ac field and the frequency sweep rate. …