Condensed Matter Physics Commons^™

Properties Of Multiferroic Bifeo3 From First Principles, Dovran Rahmedov

Graduate Theses and Dissertations

In this dissertation, a first-principle-based approach is developed to study magnetoelectric effect in multiferoic materials. Such approach has a significant predictive power and might serve as a guide to new experimental works. As we will discuss in the course of this work, it also gives an important insight to the underlying physics behind the experimentally observed phenomena.

We start by applying our method to investigate properties of a generic multiferroic material. We observe how magnetic susceptibility of such materials evolves with temperature and compare this evolution with the characteristic behavior of magnetic susceptibility for pure magnetic systems. Then we focus …

Atomic-Scale Characterization And Manipulation Of Freestanding Graphene Using Adapted Capabilities Of A Scanning Tunneling Microscope, Steven Barber

Graduate Theses and Dissertations

Graphene was the first two-dimensional material ever discovered, and it exhibits many unusual phenomena important to both pure and applied physics. To ensure the purest electronic structure, or to study graphene's elastic properties, it is often suspended over holes or trenches in a substrate. The aim of the research presented in this dissertation was to develop methods for characterizing and manipulating freestanding graphene on the atomic scale using a scanning tunneling microscope (STM). Conventional microscopy and spectroscopy techniques must be carefully reconsidered to account for movement of the extremely flexible sample.

First, the acquisition of atomic-scale images of freestanding graphene …

Reconstructions At The Interface In Complex Oxide Heterostructures With Strongly Correlated Electrons, Benjamin Gray

Graduate Theses and Dissertations

Strongly correlated oxides exhibit a rich spectrum of closely competing orders near the localized-itinerant Mott insulator transition leaving their ground states ripe with instabilities susceptible to small perturbations such as lattice distortions, variation in stoichiometry, magnetic and electric fields, etc. As the field of interfacial engineering has matured, these underlying instabilities in the electronic structure of correlated oxides continue to be leveraged to manipulate existing phases or search for emergent ones. The central theme is matching materials across the interface with disparate physical, chemical, electronic, or magnetic structure to harness interfacial reconstructions in the strongly coupled charge, spin, orbital, and …

Investigation Of Charge Transport In Organic Polymer Donor/Acceptor Photovolatic Materials, Zubair Ahmad, Shahino Mah Abdullah, Khaulah Sulaiman

Zubair Ahmad

Pi-conjugated organic semiconductors have long been used as either holes or electrons transport materials. Recently ambipolar charge carrier transport in these materials have been reported in many investigations. In this paper, we report on the basis of experimental results that the organic semiconductor (donor/acceptor) materials can be as good electrons transporters as these materials are holes transporters. In our study, the solution-processed unipolar diodes based on organic materials P3HT, VOPCPhO and their blends with PCBM have been fabricated. The I-V characteristics of these diodes have been analyzed in the space charge limited current regime. The values of the electron and …

Lessons Learned From The Statistical Analysis Of Measurements Of The Energetic Electron Bombardment Of Epoxy ‘Glue Dots, Justin Christensen, Justin Dekany, Jr Dennison

Presentations

No abstract provided.

Polariton Evaporation: The Blackbody Radiation Nature Of The Low-Frequency Radiation Emitted By Radiative Polaritons To The Surrounding Space, Yosep Schwab, Harkirat S. Mann, Brian N. Lang, Giovanna Scarel

Department of Physics and Astronomy - Faculty Scholarship

Upon formation, radiative polaritons in thin oxide films or crystals emit radiation to the surrounding space. This radiation is confined in a small range of the microwave to far-infrared region of the electromagnetic spectrum, independently of the oxide chemistry. This work shows that the low-frequency radiation is blackbody radiation associated with a temperature directly related to the boson character of the radiative polaritons and to their amount. The proximity of this temperature to absolute zero Kelvin explains the confinement of the frequency. This phenomenon is named polariton evaporation.

Quantum Optics Of Polaritonic Nanocomposites, Chris Racknor

Electronic Thesis and Dissertation Repository

In this thesis, we study the quantum optical interaction in polaritonic nanocomposites. These systems are made by the combination of two or more micro- or nano-scale structures with complementary optical properties, such as polaritonic materials, excitonic materials, photonic crystals (PCs), quantum dots (QDs), waveguides, couplers, metal nanorods (MNRs), bionanoparticles. The nanocomposites systems studied included QDs doped within a polaritonic PC, an excitonic waveguide coupler, and a metamaterial waveguide. Also addressed are systems consisting of MNRs paired with biological labelling dye or QDs.

The application of a strain field, known as the acousto-optic effect, was found to control photon transmission in …

Stochastic Variations Of Cathodoluminescent Intensity Of Bisphenol/Amine Epoxy Exposed To Energetic Electron Bombardment, Justin Christensen, Justin Dekany, Jr Dennison

Presentations

When highly disordered insulating materials are subjected to energetic electron bombardment they can emit photons. This process is termed “cathodoluminescence.” This occurs in the space plasma environment and is an important phenomenon to understand when designing any object to be put into space. Light emitted from spacecraft materials can affect optical detection, and can cause stray-light contamination in space-based observatories. The Materials Physics Group at Utah State University uses an ultra-high vacuum chamber equipped with electron guns and a cryostat to control the sample temperature to simulate the space environment and to observe its affects on sample materials. Previous studies …

Simulation Of Uv Radiation Degradation Of Polymers On Misse-6 In The Low Earth Orbit Environment, Philip Lundgreen, Justin Dekany, Jr Dennison

Presentations

Using a high-Voltage Battery power Supply, we measured the time dependent conductivity for highly disorganized materials, and were able to model the complete conductivity curve for said materials. Previous methods were utilized and improved upon to decrease the error found in conductivity measurements through an “extremely resistive” materials. The data was subsequently analyzed using various curve fitting techniques to measure time taken for a sample to reach conductive equilibrium. The fittings were also used to predict the amount of time required for a sample to completely discharge after it had been fully charged. The objective of this study was to …

Electrostatic Discharge Breakdown Analyses, Sam Hansen, Jr Dennison, Allen Andersen

Presentations

Electrostatic discharge (ESD) and the associated material breakdown is the primary cause for spacecraft damage due to space environment interactions. This phenomenon occurs when the space plasma fluxes charge a craft to high voltages where insulating materials then break down and conduct current. This can damage or destroy onboard electrical systems. This project deals with how suspect materials break down under high voltage exposure. The USU Material Physics Group has acquired hundreds of samples that underwent ESD. The ESD damage sites of these samples have been analyzed for parameters including breakdown size, shape, coloring, and location and material characteristics such …

First-Principles Atomistic Simulations Of Energetic Materials, Aaron Christopher Landerville

USF Tampa Graduate Theses and Dissertations

This dissertation is concerned with the understanding of physico-chemical properties of energetic materials (EMs). Recently, a substantial amount of work has been directed towards calculations of equations of state and structural changes upon compression of existing EMs, as well as elucidating the underlying chemistry of initiation in detonating EMs. This work contributes to this effort by 1) predicting equations of state and thermo-physical properties of EMs, 2) predicting new phases of novel EMs, and 3) examining the initial stages of chemistry that result in detonation in EMs. The motivation for the first thrust, is to provide thermodynamic properties as input …

Magnetic Properties Of Fe-Doped Mnal, Priyanka Manchanda, Arti Kashyap, Jeffrey E. Shield, L. H. Lewis, Ralph Skomski

Ralph Skomski Publications

Electronic and magnetic properties of L1₀-ordered Fe_xMn_1−xAl alloys (x = 0, 0.0625, 0.125, 0.1875, 0.5) are investigated by first-principle supercell calculations. Pristine MnAl exhibits robust ferromagnetism involving the dense-packed Mn atoms in (001) planes of the tetragonal structure. Iron substitution for Mn significantly deteriorates the magnetiza­tion of the alloy. The reduction is a dilution effect, caused by the relatively small Fe moment of about 1.9 μ_B per atom, as compared to the Mn moment, which exceeds 2.4 μ_B. By contrast, 50% Fe substituted for Mn (x = 0.5) …

Faraday Cup Designs For High Efficiency Determination Of Energy- And Angular-Resolved Charged Particle Fluxes, Kent Hartley, Jr Dennison

Senior Theses and Projects

In order to build a spacecraft, we must understand how the construction materials will behave in the space environment (i.e. when subjected to the solar wind). The USU Materials Physics Group performs electron emission tests on spacecraft materials in an Ultra-high vacuum (UHV) test chamber (Fig.1). The chamber utilizes Faraday cups (Fig.2) in order to quantify electron flux at a location within the chamber. This measurement is important in characterizing beam profiles of electron guns used in UHV experiments. Perhaps more importantly, the Faraday cups are used to detect secondary electrons (SE) and back-scattered electrons (BSE) emitted from the surface …

Synthesis And Characterization Of Thermoelectric Nanomaterials, Kamal Kadel

FIU Electronic Theses and Dissertations

As existing energy sources have been depleting at a fast pace, thermoelectric (TE) materials have received much attention in recent years because of their role in clean energy generation and conversion. Thermoelectric materials hold promise in terrestrial applications such as waste heat recovery. Bismuth selenide (Bi₂Se₃), lead telluride (PbTe), skutterudites CoSb₃, and Bi-Sb alloys are among the widely investigated thermoelectric materials.

Synthesis of above mentioned thermoelectric materials in nanostructured form and their characterization were investigated. Highly crystalline Bi₂Se₃, undoped and indium (In) doped PbTe, unfilled and ytterbium (Yb) filled CoSb …

Marshall Space Flight Center Arc/Flare Test Analysis, Charles Bowers, Bob Meloy, Malcolm Niedner, Jim Heaney, Rudy Ivancic, Dennis Skelton, Jr Dennison, Justin Dekany, Amberly Evans Jensen, Gregory Wilson, Todd Schneider

Presentations

No abstract provided.

Spin Transfer Of Quantum Information Between Majorana Modes And A Resonator, Alexey Kovalev

Alexey Kovalev

No abstract provided.

Spin Transfer Of Quantum Information Between Majorana Modes And A Resonator, Alexey Kovalev, Amrit De, Kirill Shtengel

Department of Physics and Astronomy: Faculty Publications

We show that resonant coupling and entanglement between a mechanical resonator and Majorana bound states can be achieved via spin currents in a 1D quantum wire with strong spin-orbit interactions. The bound states induced by vibrating and stationary magnets can hybridize, thus resulting in spin-current induced 4π-periodic torques, as a function of the relative field angle, acting on the resonator. We study the feasibility of detecting and manipulating Majorana bound states with the use of magnetic resonance force microscopy techniques.

Improved Conductivity Measurements Of Highly Disordered Insulating Materials, Phil Lundgreen, Justin Dekany, Jr Dennison

Presentations

By developing a low-noise, high-voltage battery power supply, system noise has been reduced, increasing accuracy of conductivity measurements of highly disordered insulating materials. The method involves a simple parallel plate capacitor setup with the sample sandwiched between electrodes, a voltage potential applied to one electrode, and a measurement device applied to the back electrode measuring current. Previous methods involved use of a commercial power supply with a claimed low noise and high linearity, but with a low AC output ripple. At high voltages (1000 V), however, the noise became apparent in the readings and an unacceptable uncertainty was introduced in …

I. Accurate 50-200 Kev Proton Stopping Cross Sections In Solids Ii. Lateral Growth Of Si Wires On Si (100) Substrate, Sergey Dedyulin

Electronic Thesis and Dissertation Repository

Medium energy ion scattering (MEIS) is used to determine the elemental depth profile in the first few hundred angstroms of a sample. The interpretation of MEIS spectra requires an accurate knowledge of the rate at which the ions lose their energy - the stopping cross section, ε. The rate of energy loss has been fairly well investigated, both experimentally and theoretically, in elemental and compound targets at high energies (E>400 keV/amu). However, in the medium ion energy range where stopping cross section typically has a maximum, experimental data are scarce while most of the existing theories fail to give …

Absorption Of Microwaves In La1Àxsrxmno3 Manganese Powders Over A Wide Bandwidth, G. Li, G. G. Hu, H. D. Zhou, Xiaojuan Fan, X. G. Li

Xiaojuan Fan

We present the frequency dependence of microwave-absorbing properties of La_1-xSr_xMnO₃ (x=0.4, 0.5, 0.6, and 0.7) powders at room temperature. The absorbing properties change gradually with x in the frequency range of 8–12 GHz. The optimal absorption can be achieved for a x=0.4 sample and its microwave loss peak value is about 25 dB. Further experimental results show that the absorption can be attributed to magnetic and dielectric losses and the microwave loss peak corresponds to the maximum dielectric loss tangent tan δ_e near 10.5 GHz. Furthermore, the absorbing properties of the oxides mixed with …