Physical Sciences and Mathematics Commons^™

Ultra-Low Temperature Measurements Of London Penetration Depth In Iron Selenide Telluride Superconductors, Andrei Diaconu

University of New Orleans Theses and Dissertations

The newly discovered iron based superconductors have captivated the attention of the scientific community due to the unusual mechanism behind their superconductivity and their promise as the next generation high temperature superconductors. After a century of superconductor research, the physical mechanism behind high temperature superconductivity is still not understood. These new materials bring renewed hope in elucidating the pairing mechanism responsible with high temperature superconductors and achieving the ultimate goal of the field, room temperature superconductivity. Consequently, a deeper understanding of the intriguing properties of iron based materials is essential.

A great deal about the pairing mechanism of Cooper electron …

Rheology Of Solutions Of Polyisophrene And Polyisoprene-Carbon Nanotube Composites, Ruiping Ge

Electronic Thesis and Dissertation Repository

The addition of a small amount of carbon nanotubes to a polymer matrix can result in large changes in its mechanical properties. In this work, we study the rheological behavior of solutions of polyisoprene (PI) in chloroform and suspensions of multi-walled carbon nanotubes (MWCNT) and single-walled carbon nanotubes (SWCNT) in these PI solutions using shear rheometry.

We perform rheological measurements to study the viscoelastic properties of solutions of trans-PI in chloroform for polymer concentrations ranging from 1.0 wt% to 10.0 wt%. Oscillatory strain sweep tests show a concentration-and-frequency independent critical strain of that defines the limit of the linear viscoelastic …

Numerical Study Of Hubbard Model For Iron-Based Superconductors, Qinlong Luo

Doctoral Dissertations

This thesis addresses the numerical and analytical study of the iron-based superconductors, mainly using the multi-orbital Hubbard model and Hartree-Fock approximation. The text starts with an introduction to the new iron-based superconductors, followed by a theoretical description of the multi-orbital Hubbard model and Hartree-Fock approximations. The numerical study of the Hubbard model in momentum space is described next, where the phase diagrams for three- and five-orbital Hubbard models are provided. The physically ``realistic" regime of couplings is highlighted, to guide future theoretical work into the proper region of parameters of Hubbard models for iron-based superconductors. What goes next is the …

A Holographic Model Of Striped Superconductors, Suman Ganguli

Doctoral Dissertations

One of the most prominent distinguishing features in strongly correlated electron systems, such as the high Tc (critical temperature) cuprates and the most recent iron pnictides, is the presence of "competing orders" that are related to the breaking of the lattice symmetries. Does the ubiquitous presence of such inhomogeneous orders in strongly correlated superconductors have a deep connection to superconductivity? The answer to this question is crucial for identifying the mechanism of superconductivity, at least in the cuprates. Amidst serious difficulties within conventional theoretical framework to deal with strongly interacting degrees of freedom at finite density, "AdS/CFT correspondence" or "gauge/gravity …

Magneto-Optical Properties Of Complex Oxides, Peng Chen

Doctoral Dissertations

Complex oxides give rise to rich physics and exotic cross-coupled electronic and magnetic properties. This is because of the competing interaction between charge, structure, and magnetism in the materials. In this dissertation I present a spectroscopic investigation of several model complex oxides under external stimuli of magnetic field and temperature. The compounds of interest include BiFeO₃ [bismuth ferrite] nanoparticles and tetragonal film, Bi_1-xNd_xFeO₃ [neodymium doped bismuth ferrite], α-Fe₂O₃ [hematite], Ni₃V₂O₈ [nickel vanadate], and RIn_1-xMn_xO₃ [manganese doped rare earth indium oxide]. …

Enhancing The Performance Of Organic Thin Film Transistors By Cross-Linking The Organic Gate Dielectric, Soheila Naderi Gohar

Electronic Thesis and Dissertation Repository

Amongst various surface modification techniques, hyperthermal hydrogen induced cross-linking (HHIC) has been used to modify the surface of polymeric samples. In this novel and innovative technique neutral hydrogen projectiles with appropriate kinetic energy are produced to generate carbon radicals on the impacted surface through the collision-induced C-H bond breaking. Subsequently, this phenomenon results in cross-linking hydrocarbon chains in the treated polymeric samples.

Verifying the validity of cross-linking process through experiments is the target of first part of presented dissertation. Spin-coated poly(methyl methacrylate) (PMMA) films on silicon wafer were exposed to hydrogen projectiles for different durations, while the other conditions related …

Photothermal Deflection Spectroscopy Of Amorphous, Nanostructured And Nanocomposite Thin Films, Muhammad Shafiq Ahmed

Electronic Thesis and Dissertation Repository

The energy needs of the modern world are growing day by day, while sources of non-renewable fossil fuels are limited, so there is a need to efficiently use the existing resources and explore renewable energy sources. In order to harvest, store and efficiently utilize renewable energy, we need to explore new materials and improve the performance of existing ones. Among others, hydrogenated amorphous silicon (a-Si:H) with high optical absorption in the visible range of electromagnetic spectrum, is a low cost material for solar cells. But the efficiency of such solar cells is comparatively low because of intrinsic defects associated with …

Dynamic Light Scattering Study Of Hydroxyapatite Formation: Effect Of Osteopontin And Bone Sialoprotein, Maryam Mozaffari

Electronic Thesis and Dissertation Repository

Biomineralization is the process by which living organisms synthesize minerals. Some bone-related proteins, such as bone sialoprotein (BSP), have been found to enhance biomineralization, while others, including osteopontin (OPN), act as inhibitors of this process. Dynamic light scattering was used to investigate the effect of several native and recombinant proteins and peptides on the formation and growth of hydroxyapatite (HA) crystals from solutions of Ca²⁺ and PO₄^3- ions. We studied two isoforms of OPN, the OPN-derived peptides P0, P3, OPAR and pOPAR, and recombinant BSP. X-ray diffraction was used to identify the precipitate as HA crystals. Native …

Modeling The Atomic And Electronic Structure Of Metal-Metal, Metal-Semiconductor And Semiconductor-Oxide Interfaces, Ganesh Krishna Hegde

Open Access Dissertations

The continuous downward scaling of electronic devices has renewed attention on the importance of the role of material interfaces in the functioning of key components in electronic technology in recent times. It has also brought into focus the utility of

atomistic modeling in providing insights from a materials design perspective. In this thesis, a combination of Semi Empirical Tight-Binding (TB), first-principles Density

Functional Theory and Reactive Molecular Dynamics (MD) modeling is used to study aspects of the electronic and atomic structure of three such 'canonical' material interfaces - Metal-Metal, Metal-Semiconductor and Semiconductor oxide interfaces.

An important contribution of this thesis …

Investigating The Influence Of Interface And Vacancy Defects On The Growth Of Silicon Quantum Dots In Sio2, John Phelan

Electronic Thesis and Dissertation Repository

The effects of interface and vacancy defects on silicon quantum dot (Si-QD) growth are investigated using measurements of Time Resolved Photoluminescence (TRPL), Photoluminescence (PL) Spectroscopy and Electron Paramagnetic Resonance (EPR). Thermally grown SiO₂ thin films (280nm) were irradiated with high energy (400keV – 1MeV) silicon ions in order to introduce defects into the Si-QD growth layer of SiO₂. A noticeable increase in PL emission intensity is seen with the highest energy pre-implanted sample over a single implant sample. TRPL results show increased radiative lifetimes for the lower energy (400keV) pre-implant while little or no difference is seen …

Diffusionless Transition In Tricosane And Reversible Inhibition Of Calcium Oxalate Monohydrate: Two Studies Of Crystal Growth, Shailesh S. Nene

Electronic Thesis and Dissertation Repository

The process of crystal growth has been intensively studied, for both its academic interest and industrial importance. I report here two studies of crystal growth.

The normal alkanes are an interesting, both in terms of their intrinsic properties and because many biological materials contain hydrocarbon domains. The normal alkanes often exhibit complicated phase behaviour, with phase diagrams containing multiple solid phases. We report here a curious pattern of twinned domains seen in one phase of tricosane (C23H48), which we have studied by X-ray diffraction, as well as by optical and atomic force microscopy. This pattern is seen in the rotator …

The Study Of Nanophotonic Switching Mechanisms In Photonic And Metallic Heterostructures, Joel Cox

Electronic Thesis and Dissertation Repository

In this thesis, nanophotonic switching mechanisms and light-matter interactions are explored in photonic and metallic heterostructures and nanocomposites. These heterostructures are made using various combinations of photonic crystals (PCs), quantum dots (QDs), and graphene or metal nanoparticles (MNPs).

PC heterostructures are formed by combining different PCs so that photons in a specific energy range can propagate in certain regions along one direction and cannot propagate in others. This band structure engineering is used to form photonic quantum wells (PQWs) that have discrete energy states along one dimension. By simulating the photon transmission along the direction of confinement, resonant photon tunnelling …

Design And Construction Of A Nernst Effect Measuring System, Warner E. Sevin

University of New Orleans Theses and Dissertations

An experimental Nernst effect measuring system is designed and constructed. The ability to measure the Nernst effect allows completion of a thermoelectric suite of measurements consisting of electrical conductivity, the Seebeck effect, the Hall effect, and the Nernst effect. This suite of measurements gives information about electron transport, carrier concentration, and electron scattering within a thermoelectric sample. Programs were designed in LabView to control the various instruments in the measuring system. Measurements of the Nernst effect were taken on two thermoelectric samples, bismuth nickel telluride and bismuth antimony telluride. These measurements were taken at both constant temperature and constant magnetic …

Neutron Scattering Study Of The Iron Based Superconductors, Miaoyin Wang

Doctoral Dissertations

In most iron-based and copper-oxide superconductors, the T_c [superconducting critical temperature] gradually increases upon charge carrier doping or isovalent doping. In the under-doped regime of electron-doped BaFe₂As₂ [Barium Iron 2 Arsenic 2], the superconductivity appears before the complete suppression of AF [antiferromagnetic] long-range order, creating a SC-AF [superconducting-antiferromagnetic] coexisting area. The interplay between long-range magnetic order and superconductivity was studied using a triple-axis thermal neutron spectrometer under an in-plane magnetic field. The suppression of superconductivity and the enhancement of long-range AF order were discovered under 11 Tesla, suggesting the competing nature of these two phases and …

Complex Magnetism In Noncentrosymmetric Magnets, Nirmal Jeevi Ghimire

Doctoral Dissertations

Broken inversion symmetry in a crystal lattice allows an extra term called the Dzyaloshinskii-Moriya (DM) interaction in the magnetic Hamiltonian. The DM interaction tends to align spins in perpendicular orientation and therefore competes with the exchange interaction that favors collinear spins. This competition results in different modulated chiral magnetic structures depending on the relative strength of the two interactions. Skyrmion, soliton and magnetic blue phases are some of the anticipated structures. This dissertation extends the search for these exotic magnetic structures using various techniques to study the magnetism in the noncentrosymmetric magnets Cr₁₁Ge₁₉ [chromium eleven germanium nineteen], …

Structural Properties Of Ferroelectric Lead (Zirconium0.5,Titanium0.5)Oxygen3 Nanotube Array And Electronic Structure Of Lao Delta-Doped Strontium Titanate, Rajendra Prasad Adhikari

Graduate Theses and Dissertations

In this Dissertation we begin with two introductions on: 1) ferroelectricity and related phenomena, and 2) novel properties of Oxide electronics and the generation of two dimensional electron gas. We then give theoretical background of density functional theory (including LDA+U) and pseudopotentials. The first part of research work is about structural, polarization, and dielectric properties of ferroelectric Lead Zirconate Titanate (PZT) solid solution in the form of a nanotube array, embedded in a matrix medium of different ferroelectric strengths. We use the effective Hamiltonian derived from first-principles and finite-temperature Monte Carlo methods to determine the various properties. We revealed different …

Field Control Of The Surface Electroclinic Effect In Liquid Crystal Displays, Dana Hipolite

Physics

Liquid crystals (LCs) are a fascinating class of materials exhibiting a range of phases intermediate between liquid and crystalline. Smectic LCs consist of elongated molecules arranged in a periodic stack (along z) of liquid like layers. In the smectic-A (Sm-A) phase, the average molecular long axis (director) points along z. In the smectic-C (Sm-C) phase, it is tilted relative to z, thus picking out a special direction within the layers. Typically, the Sm-A* to Sm- C* transition will occur as temperature is decreased. In chiral smectics (Sm-*A or Sm-C*) it is possible to induce director titling (i.e. the Sm-C* phase) …

Multiscale Study Of Batio3 Nanostructures And Nanocomposites, Lydie Louis Louis

Graduate Theses and Dissertations

Advancements in integrated nanoelectronics will continue to require the use of unique materials or systems of materials with diverse functionalities in increasingly confined spaces.

Hence, research on finite-dimensional systems strive to unearth and expand the knowledge of fundamental physical properties in certain key materials which exhibit numerous concurrent and exploitable functions.

Correspondingly, ferroelectric nanostructures, which particularly display a plethora of complex phenomena, prevalent in countless fields of research, are noteworthy candidates. Presently, however, the assimilation of zero-(0D) and one-dimensional (1D) ferroelectric into micro- or nano-electronics has been lagging, in part due to a lack of applied and fundamental studies but …

Influence Of Microstructure On The Propagation Of Fatigue Cracks In Inconel 617, Benjiman Michael Albiston

Boise State University Theses and Dissertations

Inconel 617 is a candidate material for use in the intermediate heat exchanger of the Next Generation Nuclear Plant. Because of the high temperatures and the fluctuations in stress and temperature, the fatigue behavior of the material is important to understand. The goal of this study was to determine the influences of the microstructure during fatigue crack propagation. For this investigation, Inconel 617 compact tension samples, fatigue tested by Julian Benz at the Idaho National Laboratory, were obtained. The testing conditions included two environments at 650 °C (lab air and impure-He) and varied testing parameters including: loading waveform (triangular, trapezoidal), …

The Measurement Of The Dielectric Constant Of Concrete Pipes And Clay Pipes, David Mcgraw

Doctoral Dissertations

To optimize the effectiveness of the rehabilitation of underground utilities, taking in consideration limitation of available resources, there is a need for a cost effective and efficient sensing systems capable of providing effective, in real time and in situ, measurement of infrastructural characteristics. To carry out accurate non-destructive condition assessment of buried and above ground infrastructure such as sewers, bridges, pavements and dams, an advanced ultra-wideband (UWB) based radar was developed at Trenchless Technology Centre (TTC) and Centre for Applied Physics Studies (CAPS) at Louisiana Tech University (LTU). One of the major issues in designing the FCC compliant UWB radar …

Analysis Of An Unusual Liquid Crystal Phase Transition, Loni Ann Fuller

Physics

Liquid crystals are a unique phase of matter that resemble a state between a solid and liquid. Within these properties, liquid crystal molecules have the ability to align and create layers. From this phenomenon, many electro-optical effects can be investigated, such as measuring the tilt angle between molecules at different temperatures and applied electric fields and also measuring the birefringence, which is a unique property of liquid crystals in which the index of refraction of the sample behaves differently along different axes. In order to better understand these electro- optical effects, we designed a more precise protocol of measuring this …

Novel Bimetallic Plasmonic Nanomaterials, Ritesh Sachan

Doctoral Dissertations

Plasmonic nanomaterials have attracted a lot of attention recently due to their application in various fields such as chemical and biological sensing, catalysis, energy harvesting and optical devices. However, there is a need to address several outstanding issues with these materials, including cost-effective synthesis, tunability in plasmonic characteristics, and long term stability. In this thesis, we have focused on bimetallic nanoparticles (NPs) of Ag and Co due to their immiscibility as well as their individual properties. First, a pulsed laser induced dewetting route was used to synthesize Ag-Co bimetallic plasmonic NPs. An synthesis parameter space was derived to show the …

Haldane Pseudopotentials And Landau Level Mixing In The Quantum Hall Effect, Rachel Elizabeth Wooten

Doctoral Dissertations

The discovery of the quantum Hall effect in 1980 opened to physics one of the simplest systems for studying many-body correlations. Numerical techniques and trial wavefunctions have proven useful for describing the novel collective behavior of the electrons, but have not fully explained all features of the fractional quantum Hall effect. For example, it is predicted that Landau level mixing should have a moderate effect on the system for all but the very strongest magnetic fields, but this effect has not been extensively studied. Among the tools most useful to modeling and describing the quantum Hall system is the Haldane …

Alkane Adsorption On Mgo(100): Volumetric Isotherm, Inelastic Neutron Scattering, And Computational Studies, Andrew Spencer Hicks

Doctoral Dissertations

Volumetric adsorption isotherms and computational molecular dynamics (MD) simulations were performed for nonane and decane adfilms on MgO(100) nanocubes. From the isotherms, variety of thermodynamic quantities are calculated. These values, along with visual inspection of the isotherms, indicate a layer by layer trend from 2D to 3D behavior. This is attributed to the increasing importance of vertical adsorbate-adsorbate interactions as distance from the surface increases. Additionally, a 2D phase transition is observed for the first adsorbed layer as indicated by the evolution of the widths of the isotherm first derivative peaks. These experimental results are complemented by the MD calculations, …

Growth And Electric Field Control Of Phase Separated Manganites, Hangwen Guo

Doctoral Dissertations

Perovskite Manganites have received numerous attentions due to exotic behaviors such as colossal magnetoreistance (CMR) and electronic phase separation (EPS). The purpose of my research is to answer fundamental questions about the growth properties of manganites and electric field control of the EPS properties.

Experimental study was conducted on controlling the growth mode of La_0.7Sr_0.3MnO₃[Lanthanum Strontium Manganese Oxide] thin films using pulsed laser deposition. Different thin film morphology, crystallinity and stoichiometry have been observed depending on growth parameters. To understand the microscopic origin, the thermodynamic processes were theoretically analyzed and a growth diagram was …

Carbon Nitride And Conjugated Polymer Composite Materials, Josh Byers

Electronic Thesis and Dissertation Repository

The semiconductor and photovoltaic properties of carbon nitride (CNx) thin films prepared using a reactive magnetron sputtering technique were investigated both individually and as composites with the organic conjugated polymers polybithiophene (PBT) and poly(3-hextlthiophene) (P3HT). At low nitrogen content, the film structure was dominated by graphitic sp² percolation networks, whereas at higher nitrogen contents CNx films started to demonstrate semiconductor properties, as evidenced by the occurrence of photoconductivity and the development of a space charge region. When CNx was deposited onto a PBT substrate, it was found to function as an acceptor material improving the photocurrent generation both in …

Density Functional Theory And The Calculation Of Tcmg2O4 Spinel Lattice Parameters, Jon Karlo Macias

Physics

The cohesive energy, lattice constant and bulk modulus of two simple HCP crystal structures of magnesium and technetium were calculated using the vienna ab initio simulation package (VASP) which is based on density functional theory (DFT). The same properties were determined for TcMg₂O₄ spinel. The theoretical results of the lattice constant of the pure crystals were compared to experimental results and found to be in excellent agreement with a difference of less than 2%. The results for the lattice constant of the TcMg₂O₄ spinel were found to be in excellent agreement as well with …

The Study Of Optoelectronics In Semiconductor And Metallic Nanoparticle Hybrid Systems, Daniel G. Schindel

Electronic Thesis and Dissertation Repository

This thesis examines optoelectronics of photonic crystals and photonic nanofibers, especially with quantum dots and metallic nanoparticles doped into them. The simulations produced focus on the quantum dots, which are presented in an ensemble of 3-level systems.

In order to consider a photonic nanofiber in isolation, a model was developed for the density of photonic states. We studied two profiles, a square cross-section and a circular cross-section. In addition, we consider two architectures, one where a photonic crystal surrounds a dielectric fiber, and one where the fiber is another photonic crystal. We found several photonic nanofibers with a single bound …

Low Energy Positron Interactions With Biological Molecules, Indika Lasantha Wanniarachchi

Wayne State University Dissertations

Calculations of the positron density distribution which can be used for positrons bound to midsize and larger molecules have been tested for smaller molecules and subsequently applied to investigate the most likely e+e- annihilation sites for positrons interacting with biological molecules containing C, H, O, and N. In order to allow consideration of positrons bound to extended molecules with regions of different character and no particular symmetry, atom-centered positron basis sets of Gaussian-type functions were developed for positrons bound to molecules containing O, N, C, H, Li, Na, and Be. Testing shows that there is no need to scale the …

Diffusion Of Gold Nanoparticles In Synthetic And Biopolymer Solutions, Indermeet Kohli

Wayne State University Dissertations

Soft matter systems of colloidal particles, polymers, amphiphiles and liquid crystals are ubiquitous in our everyday life. Food, plastics, soap and even human body is comprised of soft materials. Research conducted to understand the behavior of these soft matter systems at molecular level is essential for many interdisciplinary fields of study as well as important for many technological applications.

We used gold nanoparticles (Au NPs) to investigate the length-scale dependent dynamics in semidilute poly(ethylene glycol) (PEG)-water, bovine serum albumin (BSA)-phosphate buffer, dextran and particulate solutions. In case of PEG-water solutions, fluctuation correlation spectroscopy was used to measure the diffusion coefficients …