Condensed Matter Physics Commons^™

Dual-Defect Model Of Electrostatic Discharge In Polymeric Dielectrics, Allen Andersen, Jr Dennison

Presentations

Electrostatic discharge (ESD) is a serious concern for spacecraft, high voltage power transmission, and other applications. A parallel plate capacitor geometry under high vacuum was used to apply increasing voltages across insulating samples until ESD breakdown and to apply sub-critical fields and observe time-to-breakdown. Transient arcing was frequently observed prior to complete ESD breakdown in both cases. Results are presented for two prototypical polymeric materials, low density polyethylene (LDPE) and polyimide (PI or Kapton HN™) in terms of both statistical and physics-based models.

Many electrical aging models are described by defect creation within the material from bond stress due to …

Small Satellite Space Environments Effects Test Facility, Jr Dennison, Kent Hartley, Lisa Montierth Phillipps, Justin Dekany, James S. Dyer, Robert Johnson

Presentations

No abstract provided.

Wigner High-Electron-Correlation Regime Of Nonuniform Density Systems: A Quantal-Density-Functional-Theory Study, Douglas Achan, Lou Massa, Viraht Sahni

Publications and Research

The Wigner regime of a system of electrons in an external field is characterized by a low electron density and a high electron-interaction energy relative to the kinetic energy. The low-correlation regime is in turn described by a high electron density and an electron-interaction energy smaller than the kinetic energy. The Wigner regime of a nonuniform-electron-density system is investigated via quantal density functional theory (QDFT). Within QDFT, the contributions of electron correlations due to the Pauli exclusion principle, Coulomb repulsion, and correlation-kinetic effects are separately delineated and explicitly defined. The nonuniform-electron-density system studied is that of the Hooke's atom in …

Small Satellite Space Environments Effects Test Facility, Jr Dennison, Kent Hartley, Lisa Montierth Phillipps, Justin Dekany, James S. Dyer, Robert H. Johnson

Conference Proceedings

A versatile test facility has been designed and built to study space environments effects on small satellites and system components. Testing for potentially environmental-induced modifications of small satellites is critical to avoid possible deleterious or catastrophic effects over the duration of space mission. This is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments (such as polar or geosynchronous orbits), make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics (often including untested off-the-shelf components). The vacuum chamber described here is particularly well suited for …

Environmental Testing Of Lasers For Jpl's Cold Atom Laboratory, Carey L. Baxter

STAR Program Research Presentations

NASA’s Cold Atom Lab (CAL) is a multi-user facility designed to study ultra-cold quantum gases in the microgravity environment of the International Space Station (ISS). One of the main goals of CAL is to explore the unknown territory of extremely low temperatures—possibly as low as the picokelvin range!—where new and fascinating quantum phenomena can be observed. At such temperatures matter stops behaving as particles and instead becomes macroscopic matter waves. CAL will be remotely controlled to perform a multitude of experiments and is scheduled to launch in 2016. In order to anticipate problems that might occur during and post-launch, including …

Nanoscale Manipulation Of Pristine And Functionalized Freestanding Graphene Using Scanning Tunneling Microscopy, Matthew Ackerman

Graduate Theses and Dissertations

Over the past ten years the 2D material graphene has attracted an enourmous amount of attention from researchers from across diciplines and all over the world. Many of its outstanding electronic properties are present only when it is not interacting with a substrate but is instead freestanding. In this work I demonstrate that pristine and functionalized freestanding graphene can be imaged using a scanning tunneling microscope (STM) and that imaging a flexible 2D surface is fundamentally different from imaging a bulk material due to the attraction between the STM tip and the sample. This attraction can be used to manipulate …

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 …

Electron And Hole Drift Mobility Measurements On Thin Film Cdte Solar Cells, Qi Long, Steluta A. Dinca, Eric A. Schiff, Ming Yu, Jeremy Theil

Physics - All Scholarship

We report electron and hole drift mobilities in thin film polycrystalline CdTe solar cells based on photocarrier time-of-flight measurements. For a deposition process similar to that used for high-efficiency cells, the electron drift mobilities are in the range of 10–100 cm²/Vs, and holes are in the range of 1–10 cm²/Vs. The electron drift mobilities are about a thousand times smaller than those measured in single crystal CdTe with time-of-flight; the hole mobilities are about ten times smaller. Cells were examined before and after a vapor phase treatment with CdCl₂; treatment had little effect on …

Chemically Induced Jahn–Teller Ordering On Manganite Surfaces, Zheng Gai, Wenzhi Lin, John D. Burton, K. Fuchigami, Paul C. Snijders, T. Z. Ward, Evgeny Y. Tsymbal, J. Shen, Stephen Jesse, Sergei V. Kalinin, Arthur P. Baddorf

Evgeny Tsymbal Publications

Physical and electrochemical phenomena at the surfaces of transition metal oxides and their coupling to local functionality remains one of the enigmas of condensed matter physics. Understanding the emergent physical phenomena at surfaces requires the capability to probe the local composition, map order parameter fields and establish their coupling to electronic properties. Here we demonstrate that measuring the sub-30-pm displacements of atoms from high-symmetry positions in the atomically resolved scanning tunnelling microscopy allows the physical order parameter fields to be visualized in real space on the single-atom level. Here, this local crystallographic analysis is applied to the in-situ-grown manganite surfaces. …

Nonlinear Transport In Nanoscale Phase Separated Colossal Magnetoresistive Oxide Thin Films, V. R. Singh, L. Zhang, Anil Rajapitamahuni, N. Devries, Xia Hong

Materials Research Science and Engineering Center: Faculty Publications

We report a study of the I-V characteristics of 2.5–5.4 nm epitaxial La_1xSr_xMnO₃ (x = 0.33 and 0.5) and La_0.7Ca_0.3MnO₃ thin films. While La_0.67Sr_0.33MnO₃ films exhibit linear conduction over the entire temperature and magnetic field ranges investigated, we observe a strong correlation between the linearity of the I-V relation and the metal-insulator transition in highly phase separated La_0.5Sr_0.5MnO₃ and La_0.7Ca_0.3MnO₃ films. Linear I-V behavior has been observed in the high temperature paramagnetic insulating phase, and …

Below Gap Optical Absorption In Gaas Driven By Intense, Single-Cycle Coherent Transition Radiation, J. Goodfellow, Matthias Fuchs, D. Daranciang, S. Ghimire, F. Chen, H. Loos, D. A. Reis, A. S. Fisher, A. M. Lindenberg

Matthias Fuchs Publications

Single-cycle terahertz fields generated by coherent transition radiation from a relativistic electron beam are used to study the high field optical response of single crystal GaAs. Large amplitude changes in the sub-band-gap optical absorption are induced and probed dynamically by measuring the absorption of a broad-band optical beam generated by transition radiation from the same electron bunch, providing an absolutely synchronized pump and probe geometry. This modification of the optical properties is consistent with strong-field-induced electroabsorption. These processes are pertinent to a wide range of nonlinear terahertz-driven lightmatter interactions anticipated at accelerator-based sources.

Quantum Levitation Using Metamaterials, Venkatesh K. Pappakrishnan

Doctoral Dissertations

The emergence of an attractive vacuum force (Casimir force) between two purely dielectric materials can lead to an increase in the friction and the stiction effects in nanoscale devices, resulting in degradation or decreased performance. Thus, it is of high practical importance that the conditions for the reversal of the Casimir force from attractive to repulsive are identified. Although the repulsive Casimir force has been considered for high dielectric materials as an intermediate (between the plates) medium, so far no realistic system has been proposed that can demonstrate quantum levitation with air/vacuum as a host medium. Since air is the …

Variations In Cathodoluminescent Intensity Of Spacecraft Materials Exposed To Energetic Electron Bombardment, Justin Dekany, Justin Christensen, Jr Dennison, Amberly Evans Jensen, Gregory Wilson, Todd Schneider, Charles W. Bowers, Robert Meloy

Presentations

Various highly insulating materials used in spacecraft construction can exhibit glow (electron-induced luminescence or cathodoluminescence) when exposed to the space plasma environment. Measurements of the absolute and relative cathodoluminescent intensity per incident electron flux of spacecraft materials are essential to predict and mitigate consequences for optical detection and for stray light contamination in space-based observatories. They also provide important information about the defect structure and electron transport properties of these materials. Previous studies have focused on how the relative spectral radiance of cathodoluminescent materials varies with changes in environmental conditions, including electron energy, current density, absorbed power density, and temperature. …

Variations In Cathodoluminescent Intensity Of Spacecraft Materials Exposed To Energetic Electron Bombardment, Justin Dekany, Justin Christensen, Jr Dennison, Amberly Evans Jensen, Gregory Wilson, Todd Schneider, Charles W. Bowers, Robert Meloy

Conference Proceedings

Many contemporary spacecraft materials exhibit cathodoluminescence when exposed to electron flux from the space plasma environment. A quantitative, physics-based model has been developed to predict the intensity of the glow as a function of incident electron current density and energy, temperature, and intrinsic material properties. We present a comparative study of the absolute spectral radiance for several types of dielectric and composite materials based on this model which spans three orders of magnitude. Variations in intensity are contrasted for different electron environments, different sizes of samples and sample sets, different testing and analysis methods, and data acquired at different test …

The Dynamic Interplay Between Spacecraft Charging, Space Environment Interactions And Evolving Materials, Jr Dennison

Conference Proceedings

While the effects on spacecraft charging from varying environmental conditions and from the selection of different construction materials have been studied extensively, modification of materials properties by exposure to the space plasma environment can also have profound effects on spacecraft charging. Given the increasingly demanding nature of space missions, there is a clear need to extend our understanding of the dynamic nature of material properties that affect spacecraft charging and to expand our knowledge base of materials’ responses to specific environmental conditions so that we can more reliably predict the long term response of spacecraft to their environment. This paper …

Density Of State Models And Temperature Dependence Of Radiation Induced Conductivity, Jodie Corbridge Gillespie, Jr Dennison, Alec M. Sim

Presentations

Radiation induced conductivity (RIC) occurs when incident ionizing radiation deposits energy and excites electrons into the conduction band of insulators. The increased number of charge carriers, and hence the magnitude of the enhanced conductivity, is dependent on a number of factors including temperature and the spatial and energy dependence and occupation of the material’s distribution of localized trap states within the band gap—or density of states (DOS). Expressions for RIC in terms of the filling of the DOS up to an effective Fermi level were largely developed by Rose [RCA Review, 1951], and were extended by Fowler [ …

Electrostatic Discharge And Endurance Time Measurements Of Spacecraft Materials: A Defect-Driven Dynamic Model, Allen Andersen, Jr Dennison, Alec Sim, Charles Sim

Presentations

Electrostatic discharge (ESD) is the primary cause of space environment induced failures and malfunctions. As mission lifetimes and the sensitivity and complexity of instrumentation increase, so does the need for describing the influence of the electrical aging processes on ESD. This research studies the electrostatic field strength (F_ESD) of polymeric insulators as a function of applied field and the time-to-breakdown for F < F_ESD. A dynamic physics-based model for time-to-breakdown is much more valuable than an empirical static model, since it provides the ability to predict the statistical lifetime of dielectric materials subjected to prolonged stress from …

Defects Density Of States Model Of Cathodoluminescent Intensity And Spectra Of Disordered Sio2,, Amberly Evans Jensen, Jr Dennison

Presentations

Electron beam measurements have shown that disordered SiO2 exhibits luminescent behavior, which varies with incident beam energy and current density, sample temperature (T), exposure time, and wavelength. A simple model based on the electronic band structure and defect density of states—used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO 2 as a function of these variables. Insulating SiO2 has a band gap of ~8.9 eV. Hence thermal excitation from the valence to conduction band is highly improbable; excitation is through collisions of the incident high …

Electrostatic Discharge And Endurance Time Measurements Of Spacecraft Materials: A Defect-Driven Dynamic Model, Allen Andersen, Jr Dennison, Alec M. Sim, Charles Sim

Conference Proceedings

Electrostatic breakdown leads to the majority of anomalies and failures attributed to spacecraft interactions with the plasma space environment. It is therefore critical to understand how electrostatic field strength (FESD) of spacecraft materials varies due to environmental conditions such as duration of applied electric field, rate of field change, history of exposure to high fields, and temperature. We have developed a dual-defect, thermodynamic, mean-field trapping model in terms of recoverable and irrecoverable defect modes to predict probabilities of breakdown. Fits to a variety of measurements of the dependence of FESD of insulating polymers on endurance time, voltage ramp rate, and …

Small Satellite Space Environments Effects Test Facility, Jr Dennison, Kent Hartley, Lisa Montierth Phillipps, Robert Johnson, Justin Dekany, James Dyer

Presentations

A versatile space environments test facility has been designed and built to study the effects on small satellites and system components. Testing for potentially environmental-induced modifications of small satellites is critical to avoid possible deleterious or catastrophic effects over the duration of space missions. This is increasingly more important as small satellite programs have longer mission lifetimes, expand to more hash environments (such as polar or geosynchronous orbits), make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics (often including untested off-the-shelf components). Our vacuum chamber is particularly well suited for cost-effective, …

Synergistic Models Of Electron Emission And Transport Measurements Of Disordered Sio2, Jr Dennison, Justin Dekany, Jodie Corbridge Gillespie, Phil Lundgreen, Allen Andersen, Amberly Evans Jensen, Gregory Wilson, Alec Sim, Ryan Hoffmann

Presentations

A critical component in the prediction and mitigation of spacecraft charging issues is an accurate model of the charging, transport and electron emission properties of a broad array of materials used in the construction of spacecraft. The increased sensitivity, longer-duration missions, and ventures into more demanding environments only serve to heighten this need. One important way for the spacecraft charging community to address this issue is to expand the role of more fundamental materials physics. This includes the development of unifying theoretical models of the charge transport equations based on the creation, distribution, and occupancy of defect densities of states. …

Density Of State Models And Temperature Dependence Of Radiation Induced Conductivity, Jodie Corbridge Gillespie, Jr Dennison, Alec M. Sim

Conference Proceedings

Expressions are developed for radiation induce conductivity (RIC) over an extended temperature range, based on density of states models for highly disordered insulating materials. A general discussion of the DOS of can be given using two simple types of DOS distributions of defect states within the bandgap for disordered materials are considered, one that monotonically decreases within the bandgap and one with a distribution peak within the band gap. Three monotonically decreasing models (exponential, power law, and linear), and two peaked models (Gaussian and delta function) are considered, plus limiting cases with a uniform DOS for each type. Variations using …

Defects Density Of States Model Of Cathodoluminescent Intensity And Spectra Of Disordered Sio2, Amberly Evans Jensen, Jr Dennison

Conference Proceedings

Electron beam measurements have been made that show disordered SiO 2 exhibits luminescent behavior, and that it varies with incident beam energy and current density, sample temperature and wavelength. A simple model based on the electronic band structure and defect density of states—initially used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO 2 as a function of these variables. Insulating SiO 2 has a band gap of ~8.9 eV. Hence thermal excitation from the valence to conduction band is highly improbable; excitation is through collisions …

Long-Range Electronic Reconstruction To A Dxz,Yz-Dominated Fermi Surface Below The Laalo3/Srtio3 Interface, Alexander Paul Petrović, A. Pare, Tula R. Paudel, K. Lee, S. Holmes, Crispin H. W. Barnes, A. David, T. Wu, Evgeny Y. Tsymbal, C. Panagopoulos

Evgeny Tsymbal Publications

Low dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions - i.e. the interfacial ‘‘depth’’ - remains unclear. Examining LaAlO₃/SrTiO₃ heterostructures at previously unexplored carrier densities n_2D 14 cm^-2 , we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferential d_xz,yz orbital occupancy extending over at least 100 nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO₃ emerge simultaneously at higher n_2D. …

Dynamics And Manipulation Of Nanomagnets, Liufei Cai

Dissertations, Theses, and Capstone Projects

This thesis presents my work on the spin dynamics of nanomagnets and investigates the possibility of manipulating nanomagnets by various means. Most of the work has been published\cite{LC-PRB2010, LC-PRB2012, LC-PRB2013, LC-EPL2014}. Some has been submitted for publication\cite{LC-arxiv2014}. The structure of this thesis is as follows.

In Chapter 1, I present the theory of manipulation of a nanomagnet by rotating ac fields whose frequency is time dependent. Theory has been developed that maps the problem onto Landau-Zener problem. For the linear frequency sweep the switching phase diagrams are obtained on the amplitude of the ac field and the frequency sweep rate. …

Optical Properties Of De Vries Liquid Crystals And A Look At Ultra Thin Freely Suspended Smectic Films, Joshua P. Fankhauser

Physics

Liquid crystals exist as a fourth state of matter. They are anisotropic and due to this order, they affect light that passes through them, making them ideal candidates for optical study. By employing a basic technique for measuring a liquid crystal's birefringence and tilt angle, one is able to study a number of other properties such as the electroclinic effect. In addition, smectic liquid crystals have been studied intently because of their ability to create stable ultra-thin films of quantized layer thickness. These thin films have been studied due to the fact that they are an ideal system for investigating …

The Soft Mode Driven Dynamics Of Ferroelectric Perovskites At The Nanoscale: An Atomistic Study, Kevin Mccash

USF Tampa Graduate Theses and Dissertations

The discovery of ferroelectricity at the nanoscale has incited a lot of interest in perovskite ferroelectrics not only for their potential in device application but also for their potential to expand fundamental understanding of complex phenomena at very small size scales. Unfortunately, not much is known about the dynamics of ferroelectrics at this scale. Many of the widely held theories for ferroelectric materials are based on bulk dynamics which break down when applied to smaller scales. In an effort to increase understanding of nanoscale ferroelectric materials we use atomistic resolution computational simulations to investigate the dynamics of polar perovskites. Within …

Kinetics Of Solid Phase Crystallization Of A-Ge Thin Films, John D. Graham

Macalester Journal of Physics and Astronomy

A method was developed to investigate the solid-phase crystallization (SPC) reaction undergone by germanium thin films. Amorphous films were grown by the radio-frequency (RF) magnetron sputtering and then annealed for a maximum of 6 hours at two temperatures: 446°C and 460°C. Crystallinity was measured by resistivity measurements, as well as crystal peak height and area taken from X-ray diffractometer (XRD) data. Initial data shows qualitative agreement with a nucleation-growth model for the observed kinetic process. However, observed peak narrowing phenomena suggests a comprehensive model of XRD measurements of polycrystalline thin films is needed for a rigorous interpretation of the results.

Subwavelength Visualization Of Light In Thin Film Waveguides With Photoelectrons, Joseph P. Fitzgerald, Robert Campbell Word, Rolf Könenkamp

Physics Faculty Publications and Presentations

We report the visualization and quantitative analysis of electromagnetic surface fields at solid surfaces with the potential for λ/50 resolution. To illustrate this capability, we investigate patterns in two-photon photoemission images of light-diffracting structures in waveguiding, transparent thin films. The obtained micrographs show interference patterns between incident and guided light with a remarkable sensitivity to subwavelength features. We demonstrate that photoemission rates are directly related to the surface field strengths and develop a subwavelength method to calculate the surface fields from optical properties and surface topology based on the two-dimensional Kirchhoff diffraction integral. Calculated images based on this theoretical approach …

Improved Measurements In Conductivity For Highly Disorganized Resistive Materials, Phil Lundgreen

Senior Theses and Projects

Determining the electrical properties of highly insulating materials can be a challenging task. These materials are designed to greatly resist the flow of electrical current. This makes them useful for various applications including terrestrial transmission lines, spacecraft charging, and capacitor-driven charge storage devices. Every year over 370 billion kWhr are lost during transportation along power lines in the US. That is roughly $36B which is thrown away each year due to inefficiency in our power transmission network (1). Due to the fact that satellites are isolated from ground, charging caused by the plasma environment found at typical orbital radii (2) …