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Articles 1 - 20 of 20
Full-Text Articles in Physics
Removal Of Multiple-Tip Artifacts From Scanning Tunneling Microscope Images By Crystallographic Averaging, Jack C. Straton, Bill Moon, Taylor T. Bilyeu, Peter Moeck
Removal Of Multiple-Tip Artifacts From Scanning Tunneling Microscope Images By Crystallographic Averaging, Jack C. Straton, Bill Moon, Taylor T. Bilyeu, Peter Moeck
Physics Faculty Publications and Presentations
Crystallographic image processing (CIP) techniques may be utilized in scanning probe microscopy (SPM) to glean information that has been obscured by signals from multiple probe tips. This may be of particular importance for scanning tunneling microscopy (STM) and requires images from samples that are periodic in two dimensions (2D). The image-forming current for double-tips in STM is derived with a slight modification of the independent-orbital approximation (IOA) to allow for two or more tips. Our analysis clarifies why crystallographic averaging works well in removing the effects of a blunt STM tip (that consists of multiple mini-tips) from recorded 2D periodic …
Homogeneous Cosmology With Aggressively Expanding Civilizations, S. Jay Olson
Homogeneous Cosmology With Aggressively Expanding Civilizations, S. Jay Olson
Physics Faculty Publications and Presentations
In the context of a homogeneous Universe, we note that the appearance of aggressively expanding advanced life is geometrically similar to the process of nucleation and bubble growth in a first-order cosmological phase transition. We exploit this similarity to describe the dynamics of life saturating the Universe on a cosmic scale, adapting the phase transition model to incorporate probability distributions of expansion and resource consumption strategies. Through a series of numerical solutions spanning several orders of magnitude in the input assumption parameters, the resulting cosmological model is used to address basic questions related to the intergalactic spreading of life, dealing …
General Formalism For Singly-Thermostated Hamiltonian Dynamics, John D. Ramshaw
General Formalism For Singly-Thermostated Hamiltonian Dynamics, John D. Ramshaw
Physics Faculty Publications and Presentations
A general formalism is developed for constructing modified Hamiltonian dynamical systems which preserve a canonical equilibrium distribution by adding a time evolution equation for a single additional thermostat variable. When such systems are ergodic, canonical ensemble averages can be computed as dynamical time averages over a single trajectory. Systems of this type were unknown until their recent discovery by Hoover and colleagues. The present formalism should facilitate the discovery, construction, and classification of other such systems by encompassing a wide class of them within a single unified framework. This formalism includes both canonical and generalized Hamiltonian systems in a state …
Enhanced Li Capacity In Functionalized Graphene: A First Principle Study With Van Der Waals Correction, Rajiv K. Chouhan, Pushpa Raghani
Enhanced Li Capacity In Functionalized Graphene: A First Principle Study With Van Der Waals Correction, Rajiv K. Chouhan, Pushpa Raghani
Physics Faculty Publications and Presentations
We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material …
Emergence Of Room-Temperature Ferroelectricity At Reduced Dimensions, D. A. Tenne
Emergence Of Room-Temperature Ferroelectricity At Reduced Dimensions, D. A. Tenne
Physics Faculty Publications and Presentations
The enhancement of the functional properties of materials at reduced dimensions is crucial for continuous advancements in nanoelectronic applications. Here, we report that the scale reduction leads to the emergence of an important functional property – ferroelectricity, challenging the long-standing notion that ferroelectricity is inevitably suppressed at the scale of a few nanometers. A combination of theoretical calculations, electrical measurements, and structural analyses provides evidence of room-temperature ferroelectricity in strain-free epitaxial nanometer-thick films of otherwise non-ferroelectric SrTiO3. We show that electrically-induced alignment of naturally existing polar nanoregions is responsible for the appearance of a stable net ferroelectric polarization …
Confocal Raman Spectroscopy And Afm For Evaluation Of Sidewalls In Type Ii Superlattice Fpas, D. A. Tenne
Confocal Raman Spectroscopy And Afm For Evaluation Of Sidewalls In Type Ii Superlattice Fpas, D. A. Tenne
Physics Faculty Publications and Presentations
We propose to utilize confocal Raman spectroscopy combined with high resolution atomic force microscopy (AFM) for nondestructive characterisation of the sidewalls of etched and passivated small pixel (24 μm×24 μm) focal plane arrays (FPA) fabricated using LW/LWIR InAs/GaSb type-II strained layer superlattice (T2SL) detector material. Special high aspect ratio Si and GaAs AFM probes, with tip length of 13 μm and tip aperture less than 7°, allow characterisation of the sidewall morphology. Confocal microscopy enables imaging of the sidewall profile through optical sectioning. Raman spectra measured on etched T2SL FPA single pixels enable us to quantify the …
Magnetic Structure And Ordering Of Multiferroic Hexagonal Lufeo3, Daniel A. Hillsberry, Eric L. Thies, Dmitri A. Tenne
Magnetic Structure And Ordering Of Multiferroic Hexagonal Lufeo3, Daniel A. Hillsberry, Eric L. Thies, Dmitri A. Tenne
Physics Faculty Publications and Presentations
We report on the magnetic structure and ordering of hexagonal LuFeO3 films of variable thickness grown by molecular-beam epitaxy (MBE) on YSZ (111) and Al2O3 (0001) substrates. These crystalline films exhibit long-range structural uniformity dominated by the polar P63cm phase, which is responsible for the paraelectric to ferroelectric transition that occurs above 1000 K. Using bulk magnetometry and neutron diffraction, we find that the system orders into a ferromagnetically-canted antiferromagnetic state via a single transition below 155 K regardless of film thickness, which is substantially lower than that previously reported in hexagonal LuFeO …
Epitaxial Crn Thin Films With High Thermoelectric Figure Of Merit, Eric L. Thies, Daniel A. Hillsberry, Dmitri A. Tenne
Epitaxial Crn Thin Films With High Thermoelectric Figure Of Merit, Eric L. Thies, Daniel A. Hillsberry, Dmitri A. Tenne
Physics Faculty Publications and Presentations
A large enhancement of the thermoelectric figure of merit is reported in single crystalline films of CrN. The strong reduction of the lattice thermal conductivity in the rock-salt phase of this material is shown to be related to intrinsic lattice instabilities, which is similar to the resonant bonding effect proposed for cubic IV-VI compounds. These results demonstrate that useful ideas from classic thermoelectrics and phase change materials can be extended to transition metal nitrides and oxides.
Novel Magnetic And Optical Properties Of Sn1−XZnXO2 Nanoparticles, Nevil A. Franco, Kongara M. Reddy, Josh Eixenberger, Dmitri A. Tenne, Charles B. Hanna, Alex Punnoose
Novel Magnetic And Optical Properties Of Sn1−XZnXO2 Nanoparticles, Nevil A. Franco, Kongara M. Reddy, Josh Eixenberger, Dmitri A. Tenne, Charles B. Hanna, Alex Punnoose
Physics Faculty Publications and Presentations
In this work, we report on the effects of doping SnO2 nanoparticles with Zn2+ ions. A series of ∼2–3 nm sized Sn1−x ZnxO2 crystallite samples with 0 ≤ x ≤ 0.18 were synthesized using a forced hydrolysis method. Increasing dopant concentration caused systematic changes in the crystallite size, oxidation state of Sn, visible emission, and band gap of SnO2 nanoparticles. X-ray Diffraction studies confirmed the SnO2 phase purity and the absence of any impurity phases. Magnetic measurements at room temperature showed a weak ferromagnetic behavior characterized by an open hysteresis loop. Their …
Heterojunction Metal-Oxide-Metal Au-Fe3O4-Au Single Nanowire Device For Spintronics, K. M. Reddy, Nitin P. Padture, Alex Punnoose, Charles Hanna
Heterojunction Metal-Oxide-Metal Au-Fe3O4-Au Single Nanowire Device For Spintronics, K. M. Reddy, Nitin P. Padture, Alex Punnoose, Charles Hanna
Physics Faculty Publications and Presentations
In this report, we present the synthesis of heterojunction magnetite nanowires in alumina template and describe magnetic and electrical properties from a single nanowire device for spintronics applications. Heterojunction Au-Fe-Au nanowire arrays were electrodeposited in porous aluminum oxide templates, and an extensive and controlled heat treatment process converted Fe segment to nanocrystalline cubic magnetite phase with well-defined Au-Fe3O4 interfaces as confirmed by the transmission electron microscopy. Magnetic measurements revealed Verwey transition shoulder around 120 K and a room temperature coercive field of 90 Oe. Current–voltage (I-V) characteristics of a single Au-Fe3O4-Au nanowire have …
Magnetoresistance Characteristics In Individual Fe3O4 Single Crystal Nanowire, K. M. Reddy, Nitin P. Padture, Alex Punnoose, Charles Hanna
Magnetoresistance Characteristics In Individual Fe3O4 Single Crystal Nanowire, K. M. Reddy, Nitin P. Padture, Alex Punnoose, Charles Hanna
Physics Faculty Publications and Presentations
We report on the magnetoresistance (MR) and electron transport measurements observed on asingle crystal magnetite nanowire prepared using a hydrothermal synthesis method. High-resolution electron microscopy revealed the single crystal magnetite nanowires with 80–120 nm thickness and up to 8 μm in length. Magnetic measurements showed the typical Verwey transition around 120 K with a 100 Oe room temperature coercivity and 45 emu/g saturationmagnetization, which are comparable to bulk magnetite. Electrical resistance measurements in 5-300 K temperature range were performed by scanning gate voltage and varying appliedmagnetic field. Electrical resistivity of the nanowire was found to be around 5 × …
Structure Of Local Quantum Operations And Classical Communication: Finite Versus Infinite Rounds, Scott M. Cohen
Structure Of Local Quantum Operations And Classical Communication: Finite Versus Infinite Rounds, Scott M. Cohen
Physics Faculty Publications and Presentations
Every measurement that can be implemented by local quantum operations and classical communication (LOCC) using an infinite number of rounds is the limit of a sequence of measurements, where each measurement in the sequence requires only a finite number of rounds. This rather obvious and well-known fact is nonetheless of interest as it shows that these infinite-round measurements can be approximated arbitrarily closely simply by using more and more rounds of communication. Here we demonstrate the perhaps less obvious result that (at least) for bipartite systems, the reverse relationship also holds. Specifically, we show that every finite-round bipartite LOCC measurement …
Gasb Thermophotovoltaic Cells Grown On Gaas By Molecular Beam Epitaxy Using Interfacial Misfit Arrays, Bor-Chau Juang, Ramesh B. Laghumavarapu, Brandon J. Foggo, Paul J. Simmonds, Andrew Lin, Baolai Liang, Diana L. Huffaker
Gasb Thermophotovoltaic Cells Grown On Gaas By Molecular Beam Epitaxy Using Interfacial Misfit Arrays, Bor-Chau Juang, Ramesh B. Laghumavarapu, Brandon J. Foggo, Paul J. Simmonds, Andrew Lin, Baolai Liang, Diana L. Huffaker
Physics Faculty Publications and Presentations
There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm2. In addition, the …
Prussian Green: A High Rate Capacity Cathode For Potassium Ion Batteries, Prasanna Pradigi, Joseph Thiebes, Mitchell Swan, Gary Goncher, David Evans, Raj Solanki
Prussian Green: A High Rate Capacity Cathode For Potassium Ion Batteries, Prasanna Pradigi, Joseph Thiebes, Mitchell Swan, Gary Goncher, David Evans, Raj Solanki
Physics Faculty Publications and Presentations
The influence of the precursors, namely potassium ferrocyanide and potassium ferricyanide on the particles sizes of Prussian Blue (PB) and Prussian Green (PG), under identical reaction conditions have been investigated. It was found that the particle sizes influence the gravimetric capacity utilization of these materials as cathodes for aqueous potassium (K+ ) ion batteries. The PG particle sizes were on the order of 50-75 nm, whereas PB particles size were on the order of 2-10 microns. The PG cathodes demonstrated a reversible capacity of 121.4 mAhr/g, with a coulombic efficiency of 98.7% compared to PB cathodes which demonstrated 53.8 …
Hybrid Type-I Inas/Gaas And Type-Ii Gasb/Gaas Quantum Dot Structure With Enhanced Photoluminescence, Hai-Ming Ji, Baolai Liang, Paul J. Simmonds, Bor-Chau Juang, Tao Yang, Robert J. Young, Diana L. Huffaker
Hybrid Type-I Inas/Gaas And Type-Ii Gasb/Gaas Quantum Dot Structure With Enhanced Photoluminescence, Hai-Ming Ji, Baolai Liang, Paul J. Simmonds, Bor-Chau Juang, Tao Yang, Robert J. Young, Diana L. Huffaker
Physics Faculty Publications and Presentations
We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL.These hybrid QD structures show potential for high efficiency QD solar cell applications.
Dust Devils And Dustless Vortices On A Desert Playa Observed With Surface Pressure And Solar Flux Logging, Ralph D. Lorenz, Brian K. Jackson
Dust Devils And Dustless Vortices On A Desert Playa Observed With Surface Pressure And Solar Flux Logging, Ralph D. Lorenz, Brian K. Jackson
Physics Faculty Publications and Presentations
Dust devils are convective vortices rendered visible by lofted dust, and may be a significant means of injecting dust into the atmosphere, on both Earth and Mars. The fraction of vortices that are dust-laden is not well-understood, however. Here we report a May/June 2013 survey on a Nevada desert playa using small stations that record pressure and solar flux with high time resolution (2 Hz): these data allow detection of vortices and an estimate of the dust opacity of the subset of vortices that geometrically occult the sun. The encounter rate of vortex pressure drops of 0.3 hPa or larger …
A Multiyear Dust Devil Vortex Survey Using An Automated Search Of Pressure Time Series, Brian Jackson, Ralph Lorenz
A Multiyear Dust Devil Vortex Survey Using An Automated Search Of Pressure Time Series, Brian Jackson, Ralph Lorenz
Physics Faculty Publications and Presentations
Dust devils occur in arid climates on the Earth and ubiquitously on Mars, where they likely dominate the supply of atmospheric dust and influence climate. Martian dust devils have been studied with a combination of orbiting and landed spacecraft, while most studies of terrestrial dust devils have involved manned monitoring of field sites, which can be costly both in time and personnel. As an alternative approach, we describe a multiyear in situ survey of terrestrial dust devils using pressure loggers deployed at El Dorado Playa in Nevada, USA, a site known for dust devil activity. Analogous to previous surveys for …
Class Of Unambiguous State Discrimination Problems Achievable By Separable Measurements But Impossible By Local Operations And Classical Communication, Scott M. Cohen
Physics Faculty Publications and Presentations
We consider an infinite class of unambiguous quantum state discrimination problems on multipartite systems, described by Hilbert space H, of any number of parties. Restricting consideration to measurements that act only on H, we find the optimal global measurement for each element of this class, achieving the maximum possible success probability of 1/2 in all cases. This measurement turns out to be both separable and unique, and by our recently discovered necessary condition for local quantum operations and classical communication (LOCC) it is easily shown to be impossible by any finite-round LOCC protocol. We also show that, quite generally, if …
Comparative Metal Oxide Nanoparticle Toxicity Using Embryonic Zebrafish, Leah C. Wehmas, Catherine Anders, Jordan Chess, Alex Punnoose, Cliff B. Pereira, Juliet A. Greenwood, Robert L. Tanguay
Comparative Metal Oxide Nanoparticle Toxicity Using Embryonic Zebrafish, Leah C. Wehmas, Catherine Anders, Jordan Chess, Alex Punnoose, Cliff B. Pereira, Juliet A. Greenwood, Robert L. Tanguay
Physics Faculty Publications and Presentations
Engineered metal oxide nanoparticles (MO NPs) are finding increasing utility in the medical fields as anticancer agents. Before validation of in vivo anticancer efficacy can occur, a better understanding of whole-animal toxicity is required. We compared the toxicity of seven widely used semiconductor MO NPs made from zinc oxide (ZnO), titanium dioxide, cerium dioxide and tin dioxide prepared in pure water and in synthetic seawater using a five-day embryonic zebrafish assay. We hypothesized that the toxicity of these engineered MO NPs would depend on physicochemical properties. Significant agglomeration of MO NPs in aqueous solutions is common making it challenging to …
Infrared Radiography: Modeling X-Ray Imaging Without Harmful Radiation, Otto Zietz, Elliot E. Mylott, Ralf Widenhorn
Infrared Radiography: Modeling X-Ray Imaging Without Harmful Radiation, Otto Zietz, Elliot E. Mylott, Ralf Widenhorn
Physics Faculty Publications and Presentations
Planar x-ray imaging is a ubiquitous diagnostic tool and is routinely performed to diagnose conditions as varied as bone fractures and pneumonia. The underlying principle is that the varying attenuation coefficients of air, water, tissue, bone, or metal implants within the body result in non-uniform transmission of x-ray radiation. Through the detection of transmitted radiation, the spatial organization and composition of materials in the body can be ascertained. In this paper, we describe an original apparatus that teaches these concepts by utilizing near infrared radiation and an up-converting phosphorescent screen to safely probe the contents of an opaque enclosure.