Condensed Matter Physics Commons^™

Direct Observation Of Room-Temperature Out-Of-Plane Ferroelectricity And Tunneling Electroresistance At The Two-Dimensional Limit, H. Wang, Z. R. Liu, H. Y. Yoong, Tula R. Paudel, J. X. Xia, R. Guo, W. N. Lin, P. Yang, J. Wang, G. M. Chow, T. Venkatesan, Evgeny Y. Tsymbal, H. Tian, J. S. Chen

Evgeny Tsymbal Publications

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO₃ ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unitcell-thick BiFeO₃ films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO₃ films. …

Kinetic Effects In 2d And 3d Quantum Dots: Comparison Between High And Low Electron Correlation Regimes, Marlina Slamet, Viraht Sahni

Publications and Research

Kinetic related ground state properties of a two-electron 2D quantum dot in a magnetic field and a 3D quantum dot (Hooke's atom) are compared in the Wigner high (HEC) and low (LEC) electron correlation regimes. The HEC regime corresponds to low densities sufficient for the creation of a Wigner molecule. The LEC regime densities are similar to those of natural atoms and molecules. The results are determined employing exact closed-form analytical solutions of the Schrödinger-Pauli and Schrödinger equations, respectively. The properties studied are the local and nonlocal quantal sources of the density and the single particle density matrix; the kinetic …

Large T1 Contrast Enhancement Using Superparamagnetic Nanoparticles In Ultra-Low Field Mri, Xiaolu Yin, Stephen E. Russek, Gary Zabow, Fan Sun, Jeotikatan Mohapatra, Kathryn E. Keenan, Michael A. Boss, Hao Zeng, J. Ping Liu, Alexandrea Viert, Sy-Hwang Liou, John Moreland

Nebraska Center for Materials and Nanoscience: Faculty Publications

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T₂ contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r1 = 615 s−1 mM−1, which is two …

Enhanced Acidity Of Acetic And Pyruvic Acids On The Surface Of Water, Alexis J. Eugene, Elizabeth A. Pillar, Agustín J. Colussi, Marcelo I. Guzman

Chemistry Faculty Publications

Understanding the acid–base behavior of carboxylic acids on aqueous interfaces is a fundamental issue in nature. Surface processes involving carboxylic acids such as acetic and pyruvic acids play roles in (1) the transport of nutrients through cell membranes, (2) the cycling of metabolites relevant to the origin of life, and (3) the photooxidative processing of biogenic and anthropogenic emissions in aerosols and atmospheric waters. Here, we report that 50% of gaseous acetic acid and pyruvic acid molecules transfer a proton to the surface of water at pH 2.8 and 1.8 units lower than their respective acidity constants pK_{a …}

Defect-Assisted Tunneling Electroresistance In Ferroelectric Tunnel Junctions, Konstantin Klyukin, Lingling Tao, Evgeny Y. Tsymbal, Vitaly Alexandrov

Evgeny Tsymbal Publications

Recent experimental results have demonstrated ferroelectricity in thin films of SrTiO₃ induced by antisite Ti_Sr defects. This opens a possibility to use SrTiO₃ as a barrier layer in ferroelectric tunnel junctions (FTJs)—emerging electronic devices promising for applications in nanoelectronics. Here using density functional theory combined with quantum-transport calculations applied to a prototypical Pt/SrTiO₃/Pt FTJ, we demonstrate that the localized in-gap energy states produced by the antisite Ti_Sr defects are responsible for the enhanced electron tunneling conductance which can be controlled by ferroelectric polarization. Our tight-binding modeling, which takes into account multiple defects, shows that …

Developing A Femtosecond Stimulated Raman Spectroscopy Experiment For Solid State Materials, Daniel Hammerland

Electronic Theses and Dissertations

Femtosecond Stimulated Raman Spectroscopy (FSRS) is a ultrafast spectroscopy technique first implemented by chemists to understand isomerization and other ultrafast molecular morphology changes by resolving vibrational dynamics[1, 2, 3]. FSRS has an unparalleled temporal and spectral resolution [4, 1, 5, 6] that arises as a result of a clever combination of picosecond and femtosecond pulses. However, despite this capability, FSRS has yet to be applied to modern materials in condensed matter physics. This thesis explores the design and implementation of FSRS to study two-dimensional materials in order to measure their quantum confined vibrational dynamics on utlrafast time scales.

Plasma Based Synthesis And Surface Modification Of Graphene., Rong Zhao

Electronic Theses and Dissertations

Graphene, an atom thick layer of carbon, has attracted intense scientific interest due to its exceptional electrical, mechanical and chemical properties. Especially, it provides a perfect platform to explore the unique electronic properties in absolute two-dimension. Pristine graphene possesses zero band gap and weakens its competitiveness in the field of semiconductors. In order to induce a band gap and control its semiconducting properties, functionalization and doping are two of the most feasible methods. In the context of functionalization, large area monolayer graphene synthesized by chemical vapor deposition was subjected to controlled and sequential fluorination using radio frequency plasma while monitoring …

Crystallographic Exploration Of Fundamental Technetium Species At Nonambient Conditions, Daniel S. Mast

UNLV Theses, Dissertations, Professional Papers, and Capstones

The study of mater under extreme conditions has yielded fascinating insight into the physical and chemical nature of materials that under more modest conditions are considered mundane but have quite unusual properties when under pressure. Examples of this are the lightest of elements found in the first two rows and in the heaviest elements of the lanthanide and actinide series. Pure elements, though the simplest possible chemical systems, have proven to be among the most complex and interesting. Technetium metal is a simple HCP transition metal that, due to its half-filled d-shell, has a rich chemistry and an important place …

Localization And Scrambling Of Quantum Information With Applications To Quantum Computation And Thermodynamics, Adrian Kristian Chapman

Physics & Astronomy ETDs

As our demand for computational power grows, we encounter the question: "What are the physical limits to computation?" An answer is necessarily incomplete unless it can incorporate physics at the smallest scales, where we expect our near-term high-performance computing to occur. Microscopic physics -- namely, quantum mechanics -- behaves counterintuitively to our everyday experience, however. Quantum matter can occupy superpositions of states and build stronger correlations than are possible classically. This affects how quantum computers and quantum thermodynamic engines will behave.

Though these properties may seem to overwhelmingly defeat our attempts to build a quantum computer at-first-glance, what is remarkable …

Effects Of B And C Doping On Tunneling Magnetoresistance In Cofe/Mgo Magnetic Tunnel Junctions, Andy Paul Chen, John D. Burton, Evgeny Y. Tsymbal, Yuan Ping Feng, Jingsheng Chen

Evgeny Tsymbal Publications

Using density-functional theory calculations, we investigate the dominant defects formed by boron (B) and carbon (C) impurities in a CoFe/MgO/CoFe magnetic tunnel junction (MTJ) and their influence on conductivity and tunneling magnetoresistance (TMR). We find that, in the O-poor conditions relevant to experiment, B forms the substitutional defect B_Co and C forms the interstitial site C_i at the CoFe/MgO interface. The C-doped MTJ is predicted to have a significantly higher TMR than the B-doped MTJ. This is due to interface state densities associated with the majority spin Δ₁-symmetry bands being more heavily suppressed by the B …

Persistent Spin Texture Enforced By Symmetry, Lingling Tao, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Persistent spin texture (PST) is the property of some materials to maintain a uniform spin configuration in the momentum space. This property has been predicted to support an extraordinarily long spin lifetime of carriers promising for spintronics applications. Here, we predict that there exists a class of noncentrosymmetric bulk materials, where the PST is enforced by the nonsymmorphic space group symmetry of the crystal. Around certain high symmetry points in the Brillouin zone, the sublattice degrees of freedom impose a constraint on the effective spin–orbit field, which orientation remains independent of the momentum and thus maintains the PST. We illustrate …

Laser-Induced Recoverable Surface Patterning On Ni50ti50 Shape Memory Alloys, Saidjafarzoda Ilhom

Masters Theses & Specialist Projects

Shape memory alloys (SMAs) are a unique class of smart materials exhibiting extraordinary properties with a wide range of applications in engineering, biomedical, and aerospace technologies. In this study, an advanced, efficient, low-cost, and highly scalable laser-assisted imprinting method with low environmental impact to create thermally controllable surface patterns is reported. Two different imprinting methods were carried out mainly on Ni50Ti50 (at. %) SMAs by using a nanosecond pulsed Nd:YAG laser operating at 1064 nm wavelength and 10 Hz frequency. First, laser pulses at selected fluences were directly focused on the NiTi surface, which generated pressure pulses of up to …

Towards Fundamental Understanding Of Thermoelectric Properties In Novel Materials Using First Principles Simulations, Artem R. Khabibullin

USF Tampa Graduate Theses and Dissertations

Thermoelectric materials play an important role in energy conversion as they represent environmentally safe and solid state devices with a great potential towards enhancing their efficiency. The ability to generate electric power in a reliable way without using non-renewable resources motivates many experimentalists as well as computational physicists to search and design new thermoelectric materials. Several classes of materials have been identified as good candidates for high efficient thermoelectrics because of their inherently low thermal conductivity. The complex study of the crystal and electronic structures of such materials helps to reveal hidden properties and give fundamental understanding, necessary for the …

Aftershocks In Slowly Compressed Bulk Metallic Glasses: Experiments And Theory, Louis W. Mcfaul, Wendelin Wright, Xiaojun Gu, Jonathan T. Uhl, Karin A. Dahmen

Faculty Journal Articles

We observe two distinct interevent time patterns in the slip avalanches of compressed bulk metallic glasses (BMGs). Small slip avalanches cluster together in time, but large slip avalanches recur roughly periodically. We compare the timing patterns of BMG slip avalanches with timing patterns of earthquakes and with the predictions of a mean-field model. The time clustering of small avalanches is similar to the known time clustering of earthquake foreshocks and aftershocks.

Modeling Recombination In Solar Cells, Paul Chery

Macalester Journal of Physics and Astronomy

Solar cells are a competitive alternative to nonrenewable energy sources such as fossil fuels. However, the efficiency of these devices is limited by photogenerated carrier recombination. We use a finite difference numerical model to study recombination phenomena in the absorber layer of solar cells including alternate recombination models and the effects of spatial distribution of recombination centers. We compare the effect of using the constant lifetime approximation for recombination to the full Shockley-Read-Hall expression in Silicon solar cells and find that the constant lifetime approximation holds for high defect densities but not for high photon flux densities. Finally, we simulate …

Wireless Antenna Detection Of Electrostatic Discharge Events, Allen Andersen, Jr Dennison

Conference Proceedings

Wireless intra-spacecraft communication technology is being developed as a weight-saving and design-simplifying measure for signal transfer on space missions. One consideration for this new technology is its interaction with space-environment induced electrostatic discharges (ESD). The short time scales of spacecraft ESD events results in broad frequency signals that can interact with wireless antennae. These interactions present a source of signal noise. However, they may also present a possibility of in-flight wireless ESD monitoring.

We present laboratory measurements of arcing on common spacecraft insulators using commercially available single band 2.4 GHz and dual band 2.4/5.8 GHz Wi-Fi antennas. These wireless detections …

Surface And Interface Effects Of Magnetoimpedance Materials At High Frequency, Tatiana M. Eggers

USF Tampa Graduate Theses and Dissertations

Amorphous and nanocrystalline transition metal magnetic alloys (TMMAs) have been the subjects of fundamental and applied study due to their unique structure. The lack of long-range order in these materials sets the stage for their soft magnetic properties to be tuned for a variety of technological applications, such as sensitive magnetic field sensors, high frequency transformers, and stress sensors. Fundamental investigation of the magnetic and structural properties of these materials is also motivated by their unique amorphous or nanocrystalline-embedded amorphous matrix morphology, which has consequences on both the magnetism seen from both the atomic and macro-scale. The surfaces of these …

Secondary Electron Yield Measurements Of Carbon Nanotube Forests: Dependence On Morphology And Substrate, Brian Wood, Justin Christensen, Gregory Wilson, Jr Dennison, T. -C. Shen

Posters

No abstract provided.

Parameterization Of Secondary And Backscattered Electron Yields For Spacecraft Charging, Justin Christensen, Phil Lundgreen, Jr Dennison

Posters

No abstract provided.

Granular Convection And Crystallization Of A Two-Dimensional Granular Medium, Donley S. Cormode

Honors Projects

Granular media are everywhere from beaches to factories to your kitchen cabinets. There are a rich array of phenomena to study with granular media. These include granular convection, jamming, and crystallization. The systems tend to be macroscopic, so it is easy to collect data. The supplies are low-cost and easy to obtain. Studying granular media gives researchers the opportunity to explore foundational ideas in fields such as crystallography and condensed matter. This paper describes a simple, low cost apparatus used to study a vertically shaken two-dimensional granular medium of glass beads. This paper will also describe a few preliminary studies …