Physics Commons^™

Evolution Of Magnetism In The Single-Crystal Honeycomb Iridates (Na1−XLiX)2Iro3, Gang Cao, Tongfei Qi, L. Li, Jsaminka Terzic, Vincent Shian Cao, Shujuan Yuan, M. Tovar, Ganpathy Murthy, Ribhu K. Kaul

Physics and Astronomy Faculty Publications

We report the successful synthesis of single crystals of the layered iridate (Na_1−xLi_x)₂IrO₃, 0 ≤ x ≤ 0.9, and a thorough study of its structural, magnetic, thermal, and transport properties. This compound allows a controlled interpolation between Na₂IrO₃ and Li₂IrO₃, while maintaining the quantum magnetism of the honeycomb Ir⁴⁺ planes. The measured phase diagram demonstrates a suppression of the Néel temperature T_N at an intermediate x, indicating that the magnetic orders in Na₂IrO₃ and Li₂IrO_{3 …}

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 …

Impact Of Alkaline Doping And Reducing Conditions On Lafeo3, Geoffrey L. Beausoleil Ii

Geoffrey L Beausoleil II

Efficient and reliable materials for gas separation, syngas production, and hybrid nuclear power plants must be capable of reliably operating at a high-temperature range of 700-1000°C and under exposure to highly oxidizing and reducing conditions. Candidate materials for these applications include alkaline metal doped lanthanum ferrite.

In the first study, the impact of A site substitution by different alkaline metals on lanthanum ferrite (LMF, M=Ca, Sr, and Ba) was investigated. The study focused on thermal expansion near the Néel transition temperature and a magneto-elastic contribution to thermal expansion was identified for each sample. Iron oxidation, Fe3+ to Fe4+, was identified …

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 …

Polarization-Coupled Transport Behavior In Ultrathin Ferroelectric Heterostructures, Haidong Lu

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Ferroelectric polarization-coupled resistive switching behavior in ferroelectric tunnel junctions (FTJs), the tunneling electroresistance (TER) effect, is a recently predicted new phenomenon, which attracts interest due to potential application in the next generation non-volatile ferroelectric random access memories (FeRAMs). In this dissertation, we demonstrate the TER effect in FTJ devices by means of scanning probe microscopy (SPM) techniques. We have investigated several device configurations for enhancement of polarization stability and for demonstration of the resistive switching behavior: (i) using the SPM probe as a top electrode; (ii) using heterostructures with engineered interfacial atomic terminations; (iii) using metal electrodes; (iv) adding an …

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]. …

Magnetic Anisotropy And Exchange In (001) Textured Fept-Based Nanostructures, Tom George

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Hard-magnetic L1₀ phase FePt has been demonstrated as a promising candidate for future nanomagnetic applications, especially magnetic recording at areal densities approaching 10 Tb/in². Realization of FePt’s potential in recording media requires control of grain size and intergranular exchange interactions in films with high degrees of L1₀ order and (001) crystalline texture, including high perpendicular magnetic anisotropy. Furthermore, a write-assist mechanism must be employed to overcome the high coercivity of L1₀ FePt nanograins. The research described in this dissertation examines potential solutions to the aforementioned problems. Specifically, a nonepitaxial method of fabricating highly (001) textured …

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 …

Interface States In Cofe2o4 Spin-Filter Tunnel Junctions, Pavel V. Lukashev, John D. Burton, Alexander Smogunov, Julian P. Velev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Spin-filter tunneling is a promising way to generate highly spin-polarized current, a key component for spintronics applications. In this paper we explore the tunneling conductance across the spin-filter material CoFe₂O₄ interfaced with Au electrodes, a geometry which provides nearly perfect lattice matching at the CoFe₂O₄/Au(001) interface. Using density functional theory calculations we demonstrate that interface states play a decisive role in controlling the transport spin polarization in this tunnel junction. For a realistic CoFe₂O₄ barrier thickness, we predict a tunneling spin polarization of about −60%. We show that this value …

Structure And Dynamics Of Model Systems: From Ferrofluids To Brain Membranes, Matthew A. Barrett

Matthew J. Barrett

Soft condensed matter systems are a very diverse and challenging subject to study. To understand the complex macro-properties of such systems one approach is to characterize the microscopic structure and dynamics. A powerful technique for determining micro and nanoscale properties is scattering of radiation sources. Light, electron and neutron scattering techniques provide insight into the complicated molecular structures and the processes happening on these small scales. We have used neutron and x-ray scattering techniques to determine structural and dynamical information from two different types of soft condensed matter systems. The microscopic nature of a cobalt magnetic fluid was studied using …

Polarization-Controlled Ohmic To Schottky Transition At A Metal/Ferroelectric Interface, Xiaohui Liu, Yong Wang, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO₃ (n-BTO). The coexistence of a ferroelectric phase and conductivity opens the door to new functionalities that may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling, we explore the effect that the switchable polarization of n-BTO has on the electronic properties of the SrRuO₃/n-BTO (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The …

Imaging Molecular Structures With Atomic Force Microscopy, Unurbat Erdenemunkh, Tyler Flanagan

Student Works

As part of the LEEP project we repaired the Atomic Force Microscopy (AFM), and wrote a user manual on using AFM. Then we scanned Self Assembly of Copolymer Films collaboration with Prof. Sergio Granados –Focil and Copper Oxide Nanocubes with Professor Prof.Luis Smith.

Reflectance Anisotropy Of Gd5si2ge2 And Tb5si2.2ge1.8, S. J. Lee, Joong Mok Park, J. E. Snyder, David C. Jiles, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Pecharsky, David W. Lynch

Professor David Lynch

Reflectance difference (RD) spectra for the a–b plane of the single crystals of Gd5Si2Ge2and b–c planes of Gd5Si2Ge2 and Tb5Si2.2Ge1.8 were obtained in the photon energy range of 1.5–5.5 eV. Several peaks were observed for these crystals in the measured spectrum range. Similar features were observed in the RD spectra for the b–c planes ofGd5Si2Ge2 and Tb5Si2.2Ge1.8, while different features were observed for the a–b plane and b–c plane of Gd5Si2Ge2. The RD spectra for the crystals arise not only from the surface anisotropy but also from the bulk anisotropy due to the monoclinic structure of the bulk crystal.

Characterization Of Polylactic Acid Films For Food Packaging As Affected By Dielectric Barrier Discharge Atmospheric Plasma, Shashi Pankaj, Luke O'Neill, N. Misra, Paula Bourke

Articles

Dielectric barrier discharge (DBD) air plasma is a novel technique for in-package decontamination of food, but it has not been yet applied to the packaging material. Characterization of commercial polylactic acid (PLA) films was done after in-package DBD plasma treatment at different voltage and treatment time to evaluate its suitability as food packaging material. DBD plasma increased the roughness of PLA film mainly at the site in contact with high voltage electrode at both the voltage levels of 70 and 80 kV. DBD plasma treatments did not induce any change in the glass transition temperature, but significant increase in the …

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 …

Effects Of Silver Nanoparticles Towards The Efficiency Of Organic Solar Cells, Khairus Syifa Hamdan, Shahino Mah Abdullah, Khaulah Sulaiman

Shahino Mah Abdullah

We report an alternative approach to enhance the optical and electrical performance of a vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine:poly(3hexylthiophene) (VOPcPhO:P3HT) blending system by integrating plasmonic spherical silver into an active layer of organic solar cells. Studies of the influence of the size distribution and optical properties of the silver nanoparticles were carried out using UV–Vis spectroscopy and field emission scanning electron microscopy, respectively. Electrical characteristics with and without the presence of metallic nanostructures were analyzed using J–V characteristics to observe the plasmonic effects on the performance in the VOPcPhO:P3HT organic solar cells.

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 …

On The Transition From Diffusion-Limited To Kinetic-Limited Regimes Of Alloy Solidification, Sergey Sobolev

Sergey Sobolev

An abrupt transition from diffusion-limited solidification to diffusionless, kinetic-limited solidification with complete solute trapping is explained as a critical phenomenon which arises due to local non-equilibrium diffusion effects in the bulk liquid. The transition occurs when the interface velocityVpasses through the critical pointV=VD, where V=VDis the bulk liquid diffusive velocity. Analytical expressions are developed for velocity–temperature and velocity–undercooling functions, using local non-equilibrium partition coeffi-cient based on the Jackson et al. kinetic model and the local non-equilibrium diffusion model of Sobolev. The calculated functions dem-onstrate a sharp break in the velocity–undercooling and velocity–temperature relationships at the critical pointV=VD. At this point …

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 …

Wave Function For Time-Dependent Harmonically Confined Electrons In A Time-Dependent Electric Field, Yu-Qi Li, Xiao-Yin Pan, Viraht Sahni

Publications and Research

The many-body wave function of a system of interacting particles confined by a time-dependent harmonic potential and perturbed by a time-dependent spatially homogeneous electric field is derived via the Feynman path-integral method. The wave function is comprised of a phase factor times the solution to the unperturbed time-dependent Schrödinger equation with the latter being translated by a time-dependent value that satisfies the classical driven equation of motion. The wave function reduces to that of the Harmonic Potential Theorem wave function for the case of the time-independent harmonic confining potential.

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 …

Novel Nanostructured Rare-Earth-Free Magnetic Materials With High Energy Products, Bhaskar Das

B. Das

Novel nanostructured Zr2Co11-based magnetic materials are fabricated in a single step process using cluster-deposition method. The composition, atomic ordering, and spin structure are precisely controlled to achieve a substantial magnetic remanence and coercivity, as well as the highest energy product for non-rare-earth and Pt-free permanent-magnet alloys.

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 …

Polarization Discontinuity Induced Two-Dimensional Electron Gas At Zno/Zn(Mg)O Interfaces: A First-Principles Study, Jesuan Betancourt, J. J. Saavedra-Arias, John D. Burton, Yasuyuki Ishikawa, Evgeny Y. Tsymbal, Julian P. Velev

Evgeny Tsymbal Publications

The discovery of a high-mobility two-dimensional electron gas (2DEG) in wurtzite ZnO/Zn(Mg)O heterostructures is promising for applications due to the high mobility of the carriers. In this paper, we study the formation and properties of the 2DEG at ZnO/Zn(Mg)O interfaces using first-principles calculations based on hybrid density functional theory. The 2DEG arises from the polarization discontinuity at the interface between the two materials. The uncompensated bound charge at the interface gives rise to an electric field in the bulk of ZnO which confines free carriers close to the interface. We find that the type of the confined carriers is determined …

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 …

Bulk Fermi Surface And Momentum Density In Heavily Doped La₂₋ₓsrₓcuo₄ Using High-Resolution Compton Scattering And Positron Annihilation Spectroscopies, W. Al-Sawai, B. Barbiellini, Y. Sakurai, M. Itou, P. E. Mijnarends, R. S. Markiewicz, S. Kaprzyk, S. Wakimoto, M. Fujita, S. Basak, H. Lin, Yung Jui Wang, S. W. H. Eijt, H. Schut, K. Yamada, A. Bansil

Susmita Basak

We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La₂₋ₓSrₓCuO₄ by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra …

Use Of Zwitterionic Molecules For Forming A Hole Or Electron Transport Layer, Bernard Doudin, Pierre Braunstein, Lucie Routaboul, Guillaume Dalmas, Zhengzheng Zhang, Peter Dowben

Peter Dowben Publications

The invention relates to the use of zwitterionic molecules for forming a hole or electron transport layer. The preferred zwitterionic molecules of the invention are derivatives of p-benzoquinonemonoimines. The invention is useful in the field of electronic devices in particular.