Condensed Matter Physics Commons^™

Voltage Modulated Infrared Reflectance Study Of Soluble Organic Semiconductors In Thin Film Transistors, Emily Geraldine Bittle

Theses and Dissertations--Physics and Astronomy

Soluble organic semiconductors have attracted interest due to their potential in making flexible and cheap electronics. Though their use is being implemented in electronics today, the conduction mechanism is still under investigation. In order to study the charge transport, this study examines the position, voltage, and frequency dependence of charge induced changes in far infrared absorption in soluble organic semiconductors in thin-film transistor structures. Measurements are compared to a simple model of a one-dimensional conductor which gives insight into the charge distribution and timing in devices. Main results of the study are dynamic measurements of charge taken by varying the ...

Nuclear Magnetic Resonance Studies Of Sodiumaluminohexahydride (Na3alh6), Tim J. Ellis-Caleo

Undergraduate Research Symposium

Many applications of modern physics require the investigator to understand the behavior of specific atoms in compounds. The behavior and structure of molecules such as sodiumaluminohexahydride (Na3AlH6) is relevant to the field of hydrogen storage [1]. In this study, we used nuclear magnetic resonance to examine the behavior of sodium, aluminum and hydrogen atoms in the compound sodiumaluminohexahydride. Sodiumaluminohexahydride consists of a covalently bonded AlH6 anion that forms an ionic bond with a sodium cation [2]. Particularly, we investigated the atomic motion at various temperatures by looking at the motional averaging of the atoms as a function of temperature from ...

Complex Rare-Earth Antimonide Suboxides For Thermoelectric Applications, Peng Li Wang

Open Access Dissertations and Theses

Thermoelectric (TE) materials are able to convert heat directly into electricity and vice versa. This special property makes them valuable for a variety of applications involving power generation and refrigeration. In the search for potential high-performance TE materials, a number of rare-earth (RE) antimonide suboxide phases have been investigated.This presentation will focus on two classes of rare-earth antimonide suboxides: the RE₃Sb₃O₃ and RE₈Sb_3-dO₈ phases (C2/m space group) based on the RE–O frameworks and the anti-ThCr₂Si₂ type RE₂SbO₂ compounds ...

Growth And Characterization Of Hexagonal Lu-Fe-O Multiferroic Thin Films, Wenbin Wang

Doctoral Dissertations

In the quest for new types of information processing and storage, complex oxides stand out as one of the most promising material classes. The multiple functionalities of complex oxides naturally arise from the delicate energy balance between the various forms of order (structural, electronic, magnetic). In particular, multiferroic and magnetoelectric oxides which simultaneously exhibit more than one type of ferroic orders have many advantages over existing materials. Widespread practical applications will require a single-phase multiferroic material with a transition temperature that lies considerably above room temperature, large electric and magnetic polarizations, and strong coupling between ferroic orders.

Recently, multiferroic LuFe ...

Condensed Matter From Gauge/Gravity Duality, Jason Edward Therrien

Doctoral Dissertations

Currently strongly coupled systems present the greatest challenge to theoretical physics. For years conventional methods of approach have failed to describe these systems analytically. In recent years it has been shown that there is a duality between weakly coupled and strongly coupled systems, the Gauge Theory/Gravity Duality. In this dissertation I will discuss how the AdS/CFT is used to describe strongly coupled condensed matter systems as well as present the work done by the author and collaborators.

Charge, Bonding, And Magneto-Elastic Coupling In Nanomaterials, Qi Sun

Doctoral Dissertations

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials because they are intimately connected to charge, structure, and magnetism, and a quantitative analysis of their behavior can reveal microscopic aspects of chemical bonding and spin-phonon coupling. To investigate these effects, we measured infrared vibrational properties of bulk and nanoscale MoS₂ [molybdenum disulfide], MnO [manganese(II) oxide], and CoFe₂O₄ [cobalt iron oxide]. From an analysis of frequencies, oscillator strengths, and high-frequency dielectric constants, we extracted Born and local effective charges, and polarizability for MoS₂ and MnO. For MoS₂ nanoparticles ...

Structure And Dynamics Of High Temperature Superconductors, Jennifer Lynn Niedziela

Doctoral Dissertations

High temperature superconductivity in iron based compounds has presented a series of complex problems to condensed matter physics since being discovered in 2008. The stalwart basis of condensed matter physics is the “strength in numbers" aspect of crystalline periodicity. Perfect crystalline periodicity has made possible the reduction of the questions of structural and electronic properties to single dimensions, increasing the tractability of these problems. Nevertheless, modern complex materials stretch these assumptions to their limits, and it is at this point where our work starts. Using neutron and x-ray scattering, we have conducted a series of studies on the structural disorder ...

Ab-Initio And Model Studies Of Spin Fluctuation Effects In Transport And Thermodynamics Of Magnetic Metals, James K. Glasbrenner

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

Magnetic materials are vital to many devices and the manipulation of spins is central to the operation of novel devices such as spin transistors. It is important to understand the effect of spin fluctuations on such systems. In this dissertation, first-principles calculations and models further the understanding of spin fluctuation effects in the transport and thermodynamics of magnetic metals.

A simple classical spin-fluctuation Hamiltonian with a single itinerancy parameter is studied using the mean-field approximation, Monte Carlo simulations, and a generalized Onsager cavity field method. The results of these different methods are in agreement. It is found that the thermodynamics ...

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

University of Western Ontario - 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 ...

In-Plane Anisotropy Of Ultrathin Co/W(110) Films And The Néel Transition In Bilayer Ultrathin Coo/Co/W(110) Films, Andrew P. Bartlett Mr.

Open Access Dissertations and Theses

The study of ultrathin magnetic films offers novel magnetic phenomena due to the reduced symmetry of these 2D systems. The magnetic anisotropy differentiates behaviour in ultrathin films from the bulk environment, as additional anisotropies emerge from the ultrathin film thickness and the inherent strain of ultrathin films. In this work, the in-plane magnetic anisotropy of strained ferromagnetic (FM) ultrathin Co(0001) films grown on a W(110) substrate is measured over a range of temperatures (150-320 K). Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) were used to determine the film structure and thickness. The anisotropy is derived ...

Modeling Electronic Structure And Spectroscopy In Correlated Materials And Topological Insulators, Yung Jui Wang

Physics Dissertations

Current major topics in condensed matter physics mostly focus on the investigation of materials having exotic quantum phases. For instance, Z₂ topological insulators have novel quantum states, which are distinct from ordinary band insulators. Recent developments show that these nontrivial topological phases may provide a platform for creating new types of quasiparticles in real materials, such as Majorana fermions. In correlated systems, high-T_c superconducting cuprates are complicated due to the richness of their phase diagram. Surprisingly, the discovery of iron pnictides demonstrates that high-T_c superconductivity related phenomena are not unique to copper oxide compounds. Many people believe ...

Non-Equilibrium Topographies: Surface Tension Driven Flows Reveal Polymer Properties At The Nanoscale, Joshua D. Mcgraw

Open Access Dissertations and Theses

The most important results in this thesis are those concerned with the levelling of a stepped film’s height profile. Films are prepared such that their height profiles are well described by a Heaviside step function and to a good approximation, they are invariant in one dimension. The temporal dependence of the levelling gives rheological information about the molecules making up the stepped films. For the range of heights that is much larger that the typical size of molecules making up the film, we use classical hydrodynamics to model the flows in these stepped films. Having measured the temporal and ...

Synthesis And Characterization Of Copper Nanoparticles And Copper-Polymer Nanocomposites For Plasmonic Photovoltaic Applications, Sabastine Chukwuemeka Ezugwu

Electronic Thesis and Dissertation Repository

Deposition techniques for the fabrication of metal nanostructures influence their morphological properties, which in turn control their optical behavior. Here, copper nanoparticles (np-Cu’s) were grown using a deposition system that was specifically set up during this work, and is based on a radio frequency (RF) sputtering source that can operate at high temperature and under bias voltage. The effect of deposition conditions (RF power, chamber pressure and substrate bias voltage) on RF sputtered np-Cu’s using RF sputtering has been studied. The study included a comparison between the morphological and optical properties of as-grown np-Cu’s and thermally treated ...

Numerical Study Of The Transition Metal Oxides And The Transport Properties Of Iron Pnictides, Shuhua Liang

Doctoral Dissertations

Strongly correlated materials such as the manganites and iron pnictides are studied here with several computational techniques. Both types of materials contain transition metals. Thus, our computational models are based on the double exchange mechanism, the super exchange mechanism and the crystal field theory to describe the d electrons. In manganites, we focus on its multiferroic properties induced by the Dzyaloshinskii-Moriya interaction. In the BiFeO3 , we use classical Monte Carlo simulations to study the magnetic critical transition transition. In iron pnictides, we study the interplay between the Fermi surface orbital order and the ground state magnetic order.

Iron Pnictides: Superconductivity In Multi-Orbital Systems, Andrew David Nicholson

Doctoral Dissertations

This work focuses on the development and implementation of microscopic models as well as their numerical and analytical study to elucidate the properties of the iron pnictides. There are many first principle and phenomenological studies of these materials, but there is a need for unbiased numerical calculations following an approach similar to the one used in the study of the Hubbard and t-J models for the cuprates.

First a two orbital model for the pnictides, focusing on two hybridized Fe-d orbitals (dxz and dyz) is formulated, including hoppings between nearest and next nearest neighbors as well as on site Coulomb ...

Magnetic Excitations In The Iron Based Superconductors, Leland Weldon Harriger

Doctoral Dissertations

Presented within are neutron scattering studies detailing the spin dynamics of BaNi$_{x}$Fe$_{2-x}$As$_{2}$ for x = 0 (parent), 0.04 (underdoped), and 0.1 (optimal) dopings, and FeSe$_{x}$Te$_{1-x}$ for x = 0 (parent), 0.3 (underdoped), and 0.4 (optimal) dopings. These recently discovered Fe-based superconducting compounds are strikingly similar, in many respects, to the cuprate class of unconventional superconductors and share qualitatively similar phase diagrams consisting of a long range ordered magnetic ground state in the parents which, upon doping, is supplanted in favor of superconductivity. The dopings discussed ...

Morphology-Properties Studies In Laser Synthesized Nanostructured Materials, Nozomi Shirato

Doctoral Dissertations

Synthesis of well-defined nanostructures by pulsed laser melting is an interesting subject from both a funda- mental and technological point of view. In this thesis, the synthesis and functional properties of potentially useful materials were studied, such as tin dioxide nanostructured arrays, which have potential applications in hydrogen gas sensing, and ferromagnetic Co nanowire and nanomagnets, which are fundamentally im- portant towards understanding magnetism in the nanoscale. First, the formation of 1D periodic tin dioxide nanoarrays was investigated with the goal of forming nanowires for hydrogen sensing. Experimental obser- vations combined with theoretical modeling successfully explained the mechanisms of structure ...

Influence Of Quantum Dot Structure On The Optical Properties Of Group Iv Materials Fabricated By Ion Implantation, Eric G. Barbagiovanni

Electronic Thesis and Dissertation Repository

In nanostructures (NSs), to acquire a fundamental understanding of the electronic states by studying the optical properties is inherently complicated. A widely used simplification to this problem comes about by developing a model for a small scale representation of types of NSs and applying it to a hierarchy of fabrication methods. However, this methodology fails to account for structural differences incurred by the fabrication method that lead to differences in the optical properties. Proper modelling is realized by first considering the proper range of experimental parameters individually as inputs to a theoretical model and applying the correct parameters to the ...

Electron-Phonon Coupling And Structural Phase Transitions On Au/Mo(112), Keisuke Fukutani

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

The electronic structures, many-body interactions and Fermi surface topologies of Au/Mo(112) were investigated in detail and were found to play important roles in the newly discovered order-disorder structural phase transition of the system. First, the high-resolution angle-resolved photoemission spectroscopy was utilized to characterize the electronic band structure of Mo(112) in far greater details than before. This elucidated the existence of several surface-derived states and their dispersion relations in high precisions near the Fermi level, as well as the symmetries of the bulk and surface electronic states, which are in good quantitative agreement with the ab-initio calculations. Such ...