Physics Commons^™

Sulfur Vacancies In Photorefractive Sn2P2S6 Crystals, Eric M. Golden, Sergey A. Basun, A. A. Grabar, I. M. Stoika, Nancy C. Giles, D. R. Evans, Larry E. Halliburton

Faculty Publications

A photoinduced electron paramagnetic resonance (EPR) spectrum in single crystals of Sn2P2S6 (SPS) is assigned to an electron trapped at a sulfur vacancy. These vacancies are unintentionally present in undoped SPS crystals and are expected to play an important role in the photorefractive behavior of the material. Nonparamagnetic sulfur vacancies are formed during the initial growth of the crystal. Subsequent illumination below 100 K with 442 nm laser light easily converts these vacancies to EPR-active defects. The resulting S = 1/2 spectrum shows well-resolved and nearly isotropic hyperfine interactions with two P ions and two Sn ions. Partially resolved interactions …

Elucidating Fundamental Mechanisms In Focused Electron- And Ion-Beam Induced Synthesis, Carlos M. Gonzalez

Doctoral Dissertations

A focused electron beam deposition process (FEBID) coupled with in-situ infrared pulsed laser assist (LA-EBID) has been implemented for higher purity tungsten nanowires using W(CO)₆ [tungsten hexacarbonyl] as parent precursor gas. Nanowires made of Co from Co₂(CO)₈ [dicobalt octacarbonyl] and Pt from MeCpPtIVMe₃ [trimethyl methylcyclopentadienyl platinum] have also been realized by using inert focused ion beams of helium and helium and neon, respectively. In all cases, higher electrical conductivities, higher purities and larger grain sizes have been obtained when compared with preceding traditional additive edit techniques. These new approaches will make possible successful nanoscale direct-write …

The Structure And Ferroelectric Properties Of Iron-Doped Lead Titanate, Michael Bartlein

Theses and Dissertations

Multiferroics are a class of poorly understood, but technologically important materials. Lead(II) titanate (PbTiO$_3$) is a known perovskite ferroelectric. By doping PbTiO$_3$ with Fe$^{3+}$ at the Ti site, we produce the multiferroic PbTi$_{1-x}$Fe$_x$O$_3$ (PTFO). Using selected area electron diffraction on a transmission electron microscope, the structure of PTFO is investigated. Of particular interest is identifying the cubic-to-tetragonal transition at the Curie temperature. As the concentration of Fe increases, the crystal becomes more cubic and experiences a lower transition temperature. I also establish a procedure for preparing bulk PTFO samples for ferroelectric testing and present preliminary results establishing ferroelectricity in these …

The Development Of A Laminated Copolyester Electric Guitar, Addison S. Karnes

Electronic Theses and Dissertations

This thesis is an investigation of the fabrication and assembly methodologies employed in the development of a proof-of-principle prototype electric guitar composed of laminated copolyester. The objective of the project was to develop the processes and procedures to create an optimized physical and visual bond between layers to minimize vibratory dissipation, thus maximizing sustain. A high speed CNC router, abrasive waterjet, laser engraver-cutter, as well as various manual fabrication and assembly methods were investigated in the construction of the guitar prototypes. The lamination processes explored include low-temperature, heat-assisted pressure bonding, solvent and chemical welding, and contact adhesives. The project concluded …

Performance Analysis Of A Hybrid Raman Optical Parametric Amplifier In The O- And E-Bands For Cwdm Pons, Sasanthi Peiris, Nicolas Madamopoulos, Neophytos A. Antoniades, Dwight Richards, Roger Dorsinville

Publications and Research

We describe a hybrid Raman-optical parametric amplifier (HROPA) operating at the O- and E-bands and designed for coarse wavelength division multiplexed (CWDM) passive optical networks (PONs). We present the mathematical model and simulation results for the optimization of this HROPA design. Our analysis shows that separating the two amplification processes allows for optimization of each one separately, e.g., proper selection of pump optical powers and wavelengths to achieve maximum gain bandwidth and low gain ripple. Furthermore, we show that the proper design of optical filters incorporated in the HROPA architecture can suppress idlers generated during the OPA process, as well …

Atom-Based Geometrical Fingerprinting Of Conformal Two-Dimensional Materials, Mehrshad Mehboudi

Graduate Theses and Dissertations

The shape of two-dimensional materials plays a significant role on their chemical and physical properties. Two-dimensional materials are basic meshes that are formed by mesh points (vertices) given by atomic positions, and connecting lines (edges) between points given by chemical bonds. Therefore the study of local shape and geometry of two-dimensional materials is a fundamental prerequisite to investigate physical and chemical properties. Hereby the use of discrete geometry to discuss the shape of two-dimensional materials is initiated.

The local geometry of a surface embodied in 3D space is determined using four invariant numbers from the metric and curvature tensors which …

Studies On The Wrinkling Of Thin Polymer Films Floating On Liquid, Kamil B. Toga

Doctoral Dissertations

This dissertation aims to broaden our understanding on wrinkling instabilities occurring on floating polymeric sheets, and tries to establish innovative methods that exploit these patterns in studies on material behavior and interfacial phenomena. We will address three major topics in this thesis including, i) characterization of the conditions required to buckle an annular disc, ii) characterization of wrinkles occurring around a droplet/bubble placed on a membrane that is kept taut at the liquid-air interface, and iii) using wrinkling patterns as a probe to understand the interfacial behavior and dynamics of ultrathin films. The first project in this thesis is about …

Magnetic And Transport Properties Of Nimnal Thin Films, Andriy Vovk, Minghui Yu, Leszek Malkinski, Charles O'Connor, Zhenjun Wang, Eden Durant, Jinke Tang, Vladimir Golub

Jinke Tang

The magnetic and transport properties of Ni₂MnAl thin films prepared using pulse laser deposition were investigated. It was shown that the films are granular and multiphase. Contrary to the data reported earlier we observe nonmonotonic temperature dependence of resistance with minimum in the vicinity of 100 K for the films deposited on substrates held at 773 K and negative magnetoresistance (MR) values of about 2.5% at 5 K and 1.6% at RT in magnetic field of 50 kOe. These values of MR are the highest reported up to date for Ni₂MnAl films. Large negative MR in …

Ultrafine Nife2o4 Powder Fabricated From Reverse Microemulsion Process, Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, Jinke Tang

Jinke Tang

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite.

Effects Of Energetic Irradiation On Materials And Devices Based On Graphene And Topological Insulators, Isaac Childres

Open Access Dissertations

This report focuses on the optical and electronic properties of graphene and topological insulators and how these Dirac fermion systems interact with energetic irradiation. We first present data exploring the effects of electron-beam and oxygen plasma induced disorder on the electronic properties and Raman spectra of graphene. These initial investigations were important for relating Raman peak intensities and weak localization features to each other and to an average disorder length in graphene, L_D. ^ We then integrate gate-effect measurements into the Raman spectroscopy study to fully explore the relationships between carrier density, disorder and Raman spectrum signatures. We …

Creasing Instability Of Hydrogels And Elastomers, Dayong Chen

Doctoral Dissertations

CREASING INSTABILITY OF HYDROGELS AND ELASTOMERS MAY 2014 DAYONG CHEN, B.S., TIANJIN UNIVERISTY M.S., TIANJIN UNIVERSITY M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Ryan C. Hayward Soft polymers placed under compressive stress can undergo an elastic creasing instability in which sharp folds spontaneously form on the free surfaces. This process may play an important role in contexts as diverse as brain morphogenesis, failure of tires, and electrical breakdown of soft polymer actuators. While the creasing instability has been used for collotype printing since as early as the 1850s, the scientific appreciation of this instability …

Optical Resonators And Fiber Tapers As Transducers For Detection Of Nanoparticles And Bio-Molecules, Huzeyfe Yilmaz

McKelvey School of Engineering Theses & Dissertations

In recent years, detection of biological interactions on single molecule level has aspired many researchers to investigate several optical, chemical, electrical and mechanical sensing tools. Among these tools, toroidal optical resonators lead the way in detection of the smallest particle/molecule with the real time measurements. In this work, bio-sensing capabilities of toroidal optical resonators are investigated. Bio-sensing is realized via measuring the analyte-antigen interaction while the antigen is immobilized through a novel functionalization method.

Not long ago, detection of single nanoparticles using optical resonators has been accomplished however the need for cost-effective and practical transducers demands simpler tools. A tapered …

Building Predictive Chemistry Models, Christopher Browne, Nicolas Onofrio, Alejandro Strachan

The Summer Undergraduate Research Fellowship (SURF) Symposium

Density Functional Theory (DFT) simulations allow for sophisticated modeling of chemical interactions, but the extreme computational cost makes it inviable for large scale applications. Molecular dynamics models, specifically ReaxFF, can model much larger simulations with greater speed, but with lesser accuracy. The accuracy of ReaxFF can be improved by comparing predictions of both methods and tuning ReaxFF’s parameters. Molecular capabilities of ReaxFF were gauged by simulating copper complexes in water over a 200 ps range, and comparing energy predictions against ReaxFF. To gauge solid state capabilities, volumetric strain was applied to simulated copper bulk and the strain response functions used …

Structural Dynamics And Charge Transport In Room Temperature Ionic Liquids, Philip James Griffin

Doctoral Dissertations

Room temperature ionic liquids are an important class of materials due to their chemical tunability and numerous advantageous physicochemical properties. As a result, ionic liquids are currently being investigated for use in a wide array of chemical and electrochemical applications. Despite their great potential, however, the relationship between the chemical structure and physicochemical properties of ionic liquids is not well understood.

To this end, this dissertation presents experimental studies of the reorientational structural dynamics and charge transport properties of a variety of room temperature ionic liquids using quasielastic light scattering spectroscopy and broadband dielectric spectroscopy.

Studies of a series of …

Theoretical Studies Of The Growth And Functionality Of Layered Materials, Wei Chen

Doctoral Dissertations

In this thesis, we present several projects on the growth and functionality of layered materials, using density functional theory (DFT) method and phenomenological modeling approach. Beyond the understanding of growth mechanisms and exploration of properties, we propose novel avenues to realize controllable growth processes and layered materials with desirable properties. The contents have three major parts:

(1) Graphene growth on Cu(111) and Ni(111) substrates. We first demonstrate that the inherent multi-orientational degeneracy of the graphene islands on Cu(111) in the early stages of nucleation could result in the prevalence of grain boundaries (GBs). Next, we propose a possible solution to …

A Soft Condensed Matter Approach Towards Mathematical Modelling Of Mass Transport And Swelling In Food Grains, Michael Chapwanya, N. Misra

Articles

Soft condensed matter (SCM) physics has recently gained importance for a large class of engineering materials. The treatment of food materials from a soft matter perspective, however, is only at the surface and is gaining importance for understanding the complex phenomena and structure of foods. In this work, we present a theoretical treatment of navy beans from a SCM perspective to describe the hydration kinetics. We solve the transport equations within a porous matrix and employ the Flory–Huggin’s equation for polymer–solvent mixture to balance the osmotic pressure. The swelling of the legume seed is modelled as a moving boundary with …

A Low Temperature Nonlinear Optical Rotational Anisotropy Spectrometer For The Determination Of Crystallographic And Electronic Symmetries, Darius H. Torchinsky, Hao Chu, Tongfei Qi, Gang Cao, David Hsieh

Center for Advanced Materials Faculty Publications

Nonlinear optical generation from a crystalline material can reveal the symmetries of both its lattice structure and underlying ordered electronic phases and can therefore be exploited as a complementary technique to diffraction based scattering probes. Although this technique has been successfully used to study the lattice and magnetic structures of systems such as semiconductor surfaces, multiferroic crystals, magnetic thin films, and multilayers, challenging technical requirements have prevented its application to the plethora of complex electronic phases found in strongly correlated electron systems. These requirements include an ability to probe small bulk single crystals at the μm length scale, a need …

Radiation-Induced Radicals In Polyurea-Crosslinked Silica Aerogel, Benjamin Michael Walters

Masters Theses

Free radicals are atoms or molecules with an odd number of electrons in an outer shell. Since electrons typically occur in pairs, this leaves one electron that is unpaired. In seek of another electron to pair with, free radicals react with and steal electrons from neighboring molecules, which then become free radicals themselves. This can start a chain reaction, cascading into large scale damage.

Ionizing radiation can tear through molecules, just as bullets can tear through things that we see. If free radicals can be detected, and seen to increase in a material upon radiation exposure, this can indicate molecular …

56th Annual Rocky Mountain Conference On Magnetic Resonance

Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 56th annual meeting of the Rocky Mountain Conference on Magnetic Resonance, co-endorsed by the Colorado Section of the American Chemical Society and the Society for Applied Spectroscopy. Held in Copper Mountain, Colorado, July 13-17, 2014.

Transparent Conducting Oxides: A Δ-Doped Superlattice Approach, Valentino R. Cooper, Sung S. Ambrose Seo, Suyoun Lee, Jun Sung Kim, Woo Seok Choi, Satoshi Okamoto, Ho Nyung Lee

Physics and Astronomy Faculty Publications

Metallic states appearing at interfaces between dissimilar insulating oxides exhibit intriguing phenomena such as superconductivity and magnetism. Despite tremendous progress in understanding their origins, very little is known about how to control the conduction pathways and the distribution of charge carriers. Using optical spectroscopic measurements and density-functional theory (DFT) simulations, we examine the effect of SrTiO3 (STO) spacer layer thickness on the optical transparency and carrier distribution in La δ-doped STO superlattices. We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d …

Nickel Aluminum Shape Memory Alloys Via Molecular Dynamics, Keith Ryan Morrison

Open Access Theses

Shape memory materials are an important class of active materials with a wide range of applications in the aerospace, biomedical, and automobile industries. These materials exhibit the two unique properties of shape memory and superelasticity. Shape memory is the ability to recover its original shape by applying heat after undergoing large deformations. Superelasticity is the ability to undergo large, reversible deformations (up to 10%) that revert back when the load is removed. These special properties originate from a reversible, diffusionless solid-solid phase transformation that occurs between a high temperature austenite phase and a low temperature martensite phase. The development of …

Analysis Of Critical Behavior In Magnetic Materials, Dustin David Belyea

USF Tampa Graduate Theses and Dissertations

This work contains a broad study of a variety of magnetic materials undergoing second order phase transitions. In general this leads to an overall increase in information and analytical methods to further the field of magnetocalorics. Specifically, critical aspects of magnetocaloric materials were compared within systems in relation to structure, stoichiometry, magnetic minority phases and magnetic contaminants. Detailed analyses were developed to quantify techniques which were in the past used mainly in a qualitative way, leading to a more complete understanding of how critical phenomena impacts the magnetocaloric response.

Copper Doping Of Zno Crystals By Transmutation Of 64Zn To 65Cu: An Electron Paramagnetic Resonance And Gamma Spectroscopy Study, Matthew C. Recker, John W. Mcclory, Maurio S. Holston, Eric M. Golden, Nancy C. Giles, Larry E. Halliburton

Faculty Publications

Transmutation of ⁶⁴Zn to ⁶⁵Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the ⁶⁵Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of ⁶⁴Zn nuclei to ⁶⁵Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu²⁺ ions (where ⁶³Cu and ^{65 …}

Synthesis And Characterization Of Magnetic Nanowires Prepared By Chemical Vapor Deposition, Siwei Tang

Doctoral Dissertations

Various metal silicide and germanide magnetic nanowires were synthesized using a home-built CVD [chemical vapor deposition] system. The morphology, composition, and magnetic properties of the nanowires were studied and correlated with growth parameters such as temperature, pressure, time, and source-substrate distance.

One of the compositions targeted for synthesis was MnSi [manganese silicide]. In bulk, this material orders helimagnetically at T_c [curie temperature] = 30K, with a helical pitch of about 20 nm. After extensive study, we learned that the thickness of the silicon dioxide layer on the substrate is a critical parameter for the growth of MnSi nanowires. An …

Discrete Strain Engineering In Graphene, Cedric Marcus Horvath

Graduate Theses and Dissertations

Graphene has a number of fascinating mechanical and electrical properties. Strain engineering in graphene is the attempt to control its properties with mechanical strain. Previous research in this area has come up with an approach using a continuum theory to describe the strain induced gauge fields in graphene; however, this approach is only valid for small strains (5% at most). A discrete framework is being developed in Arkansas that can more accurately calculate the deformation (electrical) and (pseudo-)magnetic gauge fields created by large strains. Computational simulations were carried out and used to get discrete atomic positions for strained, suspended graphene …

Section Abstracts: Astronomy, Mathematics, And Physics With Materials Science

Virginia Journal of Science

Abstracts of the Astronomy, Mathematics, and Physics with Materials Science Section for the 92nd Annual Meeting of the Virginia Academy of Science, May 13-15, 2014, Virginia Commonwealth University, Richmond, Virginia

Triplet Ground State Of The Neutral Oxygen-Vacancy Donor In Rutile Tio2, A. T. Brant, Eric M. Golden, Nancy C. Giles, Shan Yang, M. A. R. Sarker, S. Watauchi, M. Nagao, I. Tanaka, D. A. Tryk, A. Manivannan, Larry E. Halliburton

Faculty Publications

Electron paramagnetic resonance (EPR) is used to investigate the triplet (S = 1) ground state of the neutral oxygen vacancy in bulk rutile TiO₂ crystals. This shallow donor consists of an oxygen vacancy with two nearest-neighbor, exchange-coupled ³⁺ ions located along the [001] direction and equidistant from the vacancy. The spins of the two trapped electrons, one at each ³⁺ ion, align parallel to give the S = 1 state. These neutral oxygen vacancies are formed near 25 K in as-grown oxidized TiO₂ crystals by illuminating with sub-band-gap 442 nm laser light. The angular dependence of the EPR …

Tunneling Into The Mott Insulator Sr2Iro4, John A. Nichols, Noah Bray-Ali, Armin Ansary, Gang Cao, Kwok-Wai Ng

Center for Advanced Materials Faculty Publications

We studied the single-layered iridate Sr₂IrO₄ with a scanning tunneling microscope. The finite low temperature conductance enables the electronic structure of this antiferromagnetic Mott insulator to be measured by tunneling spectroscopy. We imaged the topography of freshly cleaved surfaces and measured differential tunneling conductance at cryogenic temperatures. We found the Mott gap in the tunneling density of states to be 2Δ=615 meV. Within the Mott gap, additional shoulders are observed which are interpreted as inelastic loss features due to magnons.

Large-Scale Solution Synthesis Of Narrow Graphene Nanoribbons, Timothy H. Vo, Mikhail Shekhirev, Donna A. Kunkel, Martha D. Morton, Eric Berglund, Lingmei Kong, Peter M. Wilson, Peter A. Dowben, Axel Enders, Alexander Sinitskii

Nebraska Center for Materials and Nanoscience: Faculty Publications

According to theoretical studies, narrow graphene nanoribbons with atomically precise armchair edges and widths of(1.1 eV), which makes them potentially promising for logic applications. Different top–down fabrication approaches typically yield ribbons with width >10nm and have limited control over their edge structure. Here we demonstrate a novel bottom–up approach that yields gram quantities of high-aspect-ratio graphene nanoribbons, which are only ~1 nm wide and have atomically smooth armchair edges. These ribbons are shown to have a large electronic bandgap of ~1.3 eV, which is significantly higher than any value reported so far in experimental studies of graphene nanoribbons prepared by …

Rheological Studies Of Pmma–Pvc Based Polymer Blend, Ramesh T Subramaniam

Ramesh T Subramaniam

In this research, two systems are studied. In the first system, the ratio of poly (methyl methacrylate) (PMMA) and poly (vinyl chloride) (PVC) is varied, whereas in the second system, the composition of PMMA–PVC polymer blends is varied with dopant salt, lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) with a fixed ratio of 70 wt% of PMMA to 30 wt% of PVC. Oscillation tests such as amplitude sweep and frequency sweep are discussed in order to study the viscoelastic properties of samples. Elastic properties are much higher than viscous properties within the range in the amplitude sweep and oscillatory shear sweep studies. …