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Full-Text Articles in Physics

Makerspace Club, Carolyn Brady Oct 2018

Makerspace Club, Carolyn Brady

Honors Expanded Learning Clubs

This is a unique club that allows children to explore the world around them and make projects using materials provided by educators, and to get children thinking about how things work in the world, and how they do. They gain knowledge about success and failure of these things by recreating them.


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 Aug 2018

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

Faculty Publications from Nebraska Center for Materials and Nanoscience

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 ...


Towards A Strong Spin–Orbit Coupling Magnetoelectric Transistor, Peter Dowben, Christian Binek, Kai Zhang, Lu Wang, Wai-Ning Mei, Jonathan P. Bird, Uttam Singisetti, Xia Hong, Kang L. Wang, Dmitri Nikonov Jan 2018

Towards A Strong Spin–Orbit Coupling Magnetoelectric Transistor, Peter Dowben, Christian Binek, Kai Zhang, Lu Wang, Wai-Ning Mei, Jonathan P. Bird, Uttam Singisetti, Xia Hong, Kang L. Wang, Dmitri Nikonov

Peter Dowben Publications

Here, we outline magnetoelectric (ME) device concepts based on the voltage control of the interface magnetism of an ME antiferromagnet gate dielectric formed on a very thin semiconductor channel with large spin–orbit coupling (SOC). The emphasis of the ME spin field-effect transistors (ME spin FET) is on an antiferromagnet spin–orbit read logic device and a ME spin-FET multiplexer. Both spin-FET schemes exploit the strong SOC in the semiconducting channel materials but remain dependent on the voltage-induced switching of an ME, so that the switching time is limited only by the switching dynamics of the ME. The induced exchange ...


Magnetocrystalline Anisotropy Of "-Fe2o3, Imran Ahamed, Rohilt Pathak, Arti Kashyap Dec 2017

Magnetocrystalline Anisotropy Of "-Fe2o3, Imran Ahamed, Rohilt Pathak, Arti Kashyap

Faculty Publications from Nebraska Center for Materials and Nanoscience

The epsilon Fe2O3 phase of iron oxide has been studied to understand the spin structure and the magnetocrystalline anisotropy in the bulk and in thin films of "-Fe2O3 and Co-doped "-Fe2O3. The preferential magnetization direction in the nanoparticles of "-Fe2O3 is along the a-axis [M. Gich et al., Chem. Mater. 18, 3889 (2006)]. Compared to the bulk band gap of 1.9 eV, the thin-film band gap is reduced to 1.3 eV in the Co-free films and to 0.7 eV in the film with partial ...


Texture Development And Coercivity Enhancement In Cast Alnico 9 Magnets, Wenyong Zhang, Shah Valloppilly, Xingzhong Li, Lanping Yue, Ralph Skomski, Iver Anderson, Matthew Kramer, Wei Tang, Jeff Shield, David J. Sellmyer Dec 2017

Texture Development And Coercivity Enhancement In Cast Alnico 9 Magnets, Wenyong Zhang, Shah Valloppilly, Xingzhong Li, Lanping Yue, Ralph Skomski, Iver Anderson, Matthew Kramer, Wei Tang, Jeff Shield, David J. Sellmyer

Faculty Publications from Nebraska Center for Materials and Nanoscience

The effect of Y addition and magnetic field on texture and magnetic properties of arc-melted alnico 9 magnets has been investigated. Small additions of Y (1.5 wt.%) develop a (200) texture for the arc-melted alnico 9 magnet. Such a texture is hard to form in cast samples. To achieve this goal, we set up a high-field annealing system with a maximum operation temperature of 12500 C. This system enabled annealing in a field of 45 kOe with subsequent draw annealing for the solutionized buttons; we have been able to substantially increase remanence ratio and coercivity, from 0.70 ...


Simulation Of Alnico Coercivity, Liqin Ke, Ralph Skomski, Todd D. Hoffman, Lin Zhoue, Wei Tang, Duane D. Johnson, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang Jul 2017

Simulation Of Alnico Coercivity, Liqin Ke, Ralph Skomski, Todd D. Hoffman, Lin Zhoue, Wei Tang, Duane D. Johnson, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang

Faculty Publications from Nebraska Center for Materials and Nanoscience

Micromagnetic simulations of alnico show substantial deviations from Stoner-Wohlfarth behavior due to the unique size and spatial distribution of the rod-like Fe-Co phase formed during spinodal decomposition in an external magnetic field. The maximum coercivity is limited by single-rod effects, especially deviations from ellipsoidal shape, and by interactions between the rods. Both the exchange interaction between connected rods and magnetostatic interaction between rods are considered, and the results of our calculations show good agreement with recent experiments. Unlike systems dominated by magnetocrystalline anisotropy, coercivity in alnico is highly dependent on size, shape, and geometric distribution of the Fe-Co phase, all ...


Effect Of Disorder On The Resistivity Of Cofecral Films, Y. Jin, R. Skomski, P. Kharel, S.R. Valloppilly, D. J. Sellmyer Mar 2017

Effect Of Disorder On The Resistivity Of Cofecral Films, Y. Jin, R. Skomski, P. Kharel, S.R. Valloppilly, D. J. Sellmyer

Faculty Publications from Nebraska Center for Materials and Nanoscience

Structural and electron-transport properties of thin films of the ferrimagnetic Heusler compound CoFeCrAl have been investigated to elucidate structure-property relationships. The alloy is, ideally, a spin-gapless semiconductor, but structural disorder destroys the spin-gapless character and drastically alters the transport behavior. Two types of CoFeCrAl films were grown by magnetron sputtering deposition at 973 K, namely polycrystalline films on Si substrates and epitaxial films on MgO (001) substrates. The resistivity decreases with increasing temperature, with relatively small temperature coefficients of –0.19 cm=K for the polycrystalline films and –0.12 cm=K for the epitaxial films. The residual resistivity of ...


Formation Of Mound-Like Multiscale Surface Structures On Titanium By Femtosecond Laser Processing, Edwin Peng, Alfred Tsubaki, Craig A. Zuhlke, Ryan Bell, Meiyu Wang, Dennis R. Alexander, George Gogos, Jeffrey E. Shield Mar 2017

Formation Of Mound-Like Multiscale Surface Structures On Titanium By Femtosecond Laser Processing, Edwin Peng, Alfred Tsubaki, Craig A. Zuhlke, Ryan Bell, Meiyu Wang, Dennis R. Alexander, George Gogos, Jeffrey E. Shield

Mechanical (and Materials) Engineering -- Dissertations, Theses, and Student Research

Surface Functionalization Technique • Femtosecond Laser Surface Processing (FLSP) • Utilize high power, femtosecond (10-15 s) laser pulses • Produce self-organized, multiscale surface micro/nanostructures • Diverse range of applicable substrates: semiconductors, metals, polymers, & composites

Why? • What are the different types of FLSP structures on Ti? • Physical evidence needed for FLSP formation models • Optimize FLSP of Ti for biomedical & other applications

How? • Obtain evidence of mound growth processes by examining underlying microstructure • Utilize dual beam Scanning Electron Microscope-Focused Ion Beam instrument to cross section surface structures & fabricate transmission electron microscopy samples


Half-Metallic Magnetism In Ti3co5-Xfexb2, Rohit Pathak, Imran Ahamed, W. Y. Zhang, Shah Vallopilly, D. J. Sellmyer, Ralph Skomski, Arti Kashyap Feb 2017

Half-Metallic Magnetism In Ti3co5-Xfexb2, Rohit Pathak, Imran Ahamed, W. Y. Zhang, Shah Vallopilly, D. J. Sellmyer, Ralph Skomski, Arti Kashyap

Faculty Publications from Nebraska Center for Materials and Nanoscience

Bulk alloys and thin films of Fe-substituted Ti3Co5B2 have been investigated by first-principle density-functional calculations. The series, which is of interest in the context of alnico magnetism and spin electronics, has been experimentally realized in nanostructures but not in the bulk. Our bulk calculations predict paramagnetism for Ti3Co5B2, Ti3Co4FeB2 and Ti3CoFe4B2, whereas Ti3Fe5B2 is predicted to be ferromagnetic. The thin films are all ferromagnetic, indicating that moment formation may be facilitated at nanostructural grain boundaries ...


Cooperative And Noncooperative Magnetization Reversal In Alnicos, Raplh Skomski, Liqin Ke, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang, W.Y. Zhang, Jeff E. Shield, D. J. Sellmyer Feb 2017

Cooperative And Noncooperative Magnetization Reversal In Alnicos, Raplh Skomski, Liqin Ke, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang, W.Y. Zhang, Jeff E. Shield, D. J. Sellmyer

Faculty Publications from Nebraska Center for Materials and Nanoscience

It is investigated how magnetostatic interactions affect the coercivity of alnicotype magnets. Starting from exact micromagnetic relations, we analyze two limits, namely cooperative reversal processes operative on short lengths scales and noncooperative reversal processes on long length scales. In alnicos, intrawire interactions are predominantly cooperative, whereas interwire effects are typically noncooperative. However, the transition between the regimes depends on feature size and hysteresis-loop shape, and interwire cooperative effects are largest for nearly rectangular loops. Our analysis revises the common shape-anisotropy interpretation of alnicos.


Epitaxial Strain Controlled Magnetocrystalline Anisotropy In Ultrathin Ferh/Mgo Bilayers, Guohul Zheng, San-Huang Ke, Maosheng Miao, Jinwoong Kim, R, Ramesh, Nicholas Kioussis Jan 2017

Epitaxial Strain Controlled Magnetocrystalline Anisotropy In Ultrathin Ferh/Mgo Bilayers, Guohul Zheng, San-Huang Ke, Maosheng Miao, Jinwoong Kim, R, Ramesh, Nicholas Kioussis

Faculty Publications from Nebraska Center for Materials and Nanoscience

Using ab initio electronic structure calculations we have investigated the effect of epitazial strain on the magnetocrystalline anisotropy (MCA) of ultrathin FeRh/MgO heterostructures. Analysis of the energy- and k-resolved distribution of the orbital character of the band structure reveals that MCA largely arises from the spin-orbit coupling (SOC) between dx2-y2 and dxz/dyz orbitlas of Fe atoms at the FeRh/MhO interface. We demonstrate that the strain has significant effects on the MCA: It not only affects the value of the MCA but also induces a switching of the magnetic easy axis from perpendicular on in-plane ...


Comment On “Electronic Structure Of Mo(1−X)Rex Alloys Studied Through Resonant Photoemission Spectroscopy”, Prescott Evans, Peter A. Dowben Jan 2017

Comment On “Electronic Structure Of Mo(1−X)Rex Alloys Studied Through Resonant Photoemission Spectroscopy”, Prescott Evans, Peter A. Dowben

Peter Dowben Publications

Further analysis of the resonant photoemission data, found within Sundar et al (2016 J. Phys.: Condens. Matter 28 315502), show the intensities do not follow the elemental composition in the Mo1−xRex alloy. Similar trends are observed in the published data for Gd1−xNix alloy films. The analysis of the resonant photoemission intensities suggests that Mo in the Mo1−xRex alloy and Gd in the Gd1−xNix alloy have nearest neighbor bonds to Re and Ni respectively. This means the A–B bond is favored over the average ...


Ch3Nh3Pbi3 Perovskites: Ferroelasticity Revealed, Evgheni Strelcov, Qingfeng Dong, Tao Li, Jungseok Chae, Yuchuan Shao, Yehao Deng, Alexei Gruverman, Jinsong Huang, Andrea Centrone Jan 2017

Ch3Nh3Pbi3 Perovskites: Ferroelasticity Revealed, Evgheni Strelcov, Qingfeng Dong, Tao Li, Jungseok Chae, Yuchuan Shao, Yehao Deng, Alexei Gruverman, Jinsong Huang, Andrea Centrone

Alexei Gruverman Publications

Ferroelectricity has been proposed as a plausible mechanism to explain the high photovoltaic conversion efficiency in organic-inorganic perovskites; however, convincing experimental evidence in support of this hypothesis is still missing. Identifying and distinguishing ferroelectricity from other properties, such as piezoelectricity, ferroelasticity, etc., is typically nontrivial because these phenomena can coexist in many materials. In this work, a combination of microscopic and nanoscale techniques provides solid evidence for the existence of ferroelastic domains in both CH3NH3PbI3 polycrystalline films and single crystals in the pristine state and under applied stress. Experiments show that the configuration of CH ...


Theoretical Approach To Electroresistance In Ferroelectric Tunnel Junctions, Sou-Chi Chang, Azad Naeemi, Dmitri E. Nikonov, Alexei Gruverman Jan 2017

Theoretical Approach To Electroresistance In Ferroelectric Tunnel Junctions, Sou-Chi Chang, Azad Naeemi, Dmitri E. Nikonov, Alexei Gruverman

Alexei Gruverman Publications

In this paper, a theoretical approach comprising the nonequilibrium Green’s function method for electronic transport and the Landau-Khalatnikov equation for electric polarization dynamics is presented to describe polarization-dependent tunneling electroresistance (TER) in ferroelectric tunnel junctions. Using appropriate contact, interface, and ferroelectric parameters, the measured current-voltage characteristic curves in both inorganic (Co/BaTiO3/La0.67Sr0.33MnO3) and organic (Au/PVDF/W) ferroelectric tunnel junctions can be well described by the proposed approach. Furthermore, under this theoretical framework, the controversy of opposite TER signs observed experimentally by different groups in Co/BaTiO3/La0 ...


Anomalous Photovoltaic Effect In Organic-Inorganic Hybrid Perovskite Solar Cells, Yongbo Yuan, Tao Li, Qi Wang, Jie Xing, Alexei Gruverman, Jinsong Huang Jan 2017

Anomalous Photovoltaic Effect In Organic-Inorganic Hybrid Perovskite Solar Cells, Yongbo Yuan, Tao Li, Qi Wang, Jie Xing, Alexei Gruverman, Jinsong Huang

Alexei Gruverman Publications

Organic-inorganic hybrid perovskites (OIHPs) have been demonstrated to be highly successful photovoltaic materials yielding very-high-efficiency solar cells. We report the room temperature observation of an anomalous photovoltaic (APV) effect in lateral structure OIHP devices manifested by the device’s open-circuit voltage (VOC) that is much larger than the bandgap of OIHPs. The persistent VOC is proportional to the electrode spacing, resembling that of ferroelectric photovoltaic devices. However, the APV effect in OIHP devices is not caused by ferroelectricity. The APV effect can be explained by the formation of tunneling junctions randomly dispersed in the polycrystalline films, which allows ...


Spica: Stereographic Projection For Interactive Crystallographic Analysis, Xingzhong Li Jul 2016

Spica: Stereographic Projection For Interactive Crystallographic Analysis, Xingzhong Li

Faculty Publications from Nebraska Center for Materials and Nanoscience

In numerous research fields, especially the applications of electron and X-ray diffraction, stereographic projection represents a powerful tool for researchers. SPICA is a new computer program for stereographic projection in interactive crystallographic analysis, which inherits features from the previous JECP/SP and includes more functions for extensive crystallographic analysis. SPICA provides fully interactive options for users to plot stereograms of crystal directions and crystal planes, traces, and Kikuchi maps for an arbitrary crystal structure; it can be used to explore the orientation relationships between two crystalline phases with a composite stereogram; it is also used to predict the tilt angles ...


A Cylindrically Symmetric “Micro-Mott” Electron Polarimeter, Nathan B. Clayburn, Evan M. Brunkow, S. J. Burtwistle, George H. Rutherford, Timothy J. Gay May 2016

A Cylindrically Symmetric “Micro-Mott” Electron Polarimeter, Nathan B. Clayburn, Evan M. Brunkow, S. J. Burtwistle, George H. Rutherford, Timothy J. Gay

Timothy J. Gay Publications

A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff , or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.16 ± 0.01, where uncertainty in the measurement is due primarily to uncertainty in the incident electron polarization. For an energy loss window of 0.5 keV, Seff reaches its maximum value of 0.24 ± 0.02. The device’s maximum efficiency, I/Io, defined as the detected count rate divided by the incident particle rate, is 3.7 ± 0.2 ...


New Type Of Al-Based Decagonal Quasicrystal In Al60Cr20Fe10Si10 Alloy, Zhanbing He, Haikun Ma, Hua Li, Xingzhong Li, Xiuliang Ma Mar 2016

New Type Of Al-Based Decagonal Quasicrystal In Al60Cr20Fe10Si10 Alloy, Zhanbing He, Haikun Ma, Hua Li, Xingzhong Li, Xiuliang Ma

Faculty Publications from Nebraska Center for Materials and Nanoscience

A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al60Cr20Fe10Si10 alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters ...


On The Ising Character Of The Quantum-Phase Transition In Lihof4, Ralph Skomski Jan 2016

On The Ising Character Of The Quantum-Phase Transition In Lihof4, Ralph Skomski

Ralph Skomski Publications

It is investigated how a transverse magnetic field affects the quantum-mechanical character of LiHoF4, a system generally considered as a textbook example for an Ising-like quantum-phase transition. In small magnetic fields, the low-temperature behavior of the ions is Ising-like, involving the nearly degenerate low-lying Jz = ± 8 doublet. However, as the transverse field increases, there is a substantial admixture of states having | Jz | < 8. Near the quantum-phase-transition field, the system is distinctively non-Ising like, and all Jz eigenstates yield ground-state contributions of comparable magnitude. A classical analog to this mechanism is the micromagnetic single point in magnets with uniaxial anisotropy. Since Ho3+ has J = 8, the ion’s behavior ...


Electron Diffraction Study Of Cobalt-Rich Hf-Co, Xingzhong Li, Yunlong Jin, Jeffrey E. Shield, Ralph Skomski, David J. Sellmyer Jan 2016

Electron Diffraction Study Of Cobalt-Rich Hf-Co, Xingzhong Li, Yunlong Jin, Jeffrey E. Shield, Ralph Skomski, David J. Sellmyer

Faculty Publications from Nebraska Center for Materials and Nanoscience

Intermetallic compounds having compositions from HfCo4 to HfCo8 were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr2Co11 phase in structure, has been observed in the samples with the composition ranges from HfCo6 to HfCo8. The phase, referred to as either Hf2Co11 or HfCo7 phase in the literature, is actually one common phase, having a broad composition range and referred to as μ-phase in the present paper. In addition to the μ-phase, we have ...


Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He Jan 2016

Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He

Faculty Publications from Nebraska Center for Materials and Nanoscience

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We ...


Influence Of Steric Hindrance On The Molecular Packing And The Anchoring Of Quinonoid Zwitterions On Gold Surfaces, Minghui Yuan, Iori Tababe, Jean-Marie Bernard- Schaaf, Qin-Yin Shi, Vicki Schlegel, Rachel Schurhammer, Peter A. Dowben, Bernard Doudin, Lucie Routaboul, Pierre Braunstein Jan 2016

Influence Of Steric Hindrance On The Molecular Packing And The Anchoring Of Quinonoid Zwitterions On Gold Surfaces, Minghui Yuan, Iori Tababe, Jean-Marie Bernard- Schaaf, Qin-Yin Shi, Vicki Schlegel, Rachel Schurhammer, Peter A. Dowben, Bernard Doudin, Lucie Routaboul, Pierre Braunstein

Peter Dowben Publications

Driven by the huge potential of engineering the molecular band offset with highly dipolar molecules for improving charge injection into organic electrics, the anchoring of various N-alkyl substituted quinonoid zwitterions of formula C6H2 (···NHR)2 (···O)2 (R = iPr, Cy, CH2CH(Et)CH2CH2CH2CH3,. . .) on gold surfaces is studied. The N–Au interactions result in an orthogonal arrangement of the zwitterions cores with respect to the surface, and stabilize adsorbed compact rows of molecules. IR spectroscopy is used as a straightforward diagnostic tool to validate the presence of ultra-thin ...


Domain Wall Conductivity In Semiconducting Hexagonal Ferroelectric Tbmno3 Thin Films, D. J. Kim, J. G. Connell, S. S. A. Seo, Alexei Gruverman Jan 2016

Domain Wall Conductivity In Semiconducting Hexagonal Ferroelectric Tbmno3 Thin Films, D. J. Kim, J. G. Connell, S. S. A. Seo, Alexei Gruverman

Alexei Gruverman Publications

Although enhanced conductivity of ferroelectric domain boundaries has been found in BiFeO3 and Pb(Zr,Ti)O3 films as well as hexagonal rare-earth manganite single crystals, the mechanism of the domain wall conductivity is still under debate. Using conductive atomic force microscopy, we observe enhanced conductance at the electrically-neutral domain walls in semiconducting hexagonal ferroelectric TbMnO3 thin films where the structure and polarization direction are strongly constrained along the c-axis. This result indicates that domain wall conductivity in ferroelectric rare-earth manganites is not limited to charged domain walls. We show that the observed conductivity in the TbMnO ...


Anomalously Large Chiral Sensitivity In The Dissociative Electron Attachment Of 10-Iodocamphor, J. M. Dreiling, F. W. Lewis, J. D. Mills, Timothy J. Gay Jan 2016

Anomalously Large Chiral Sensitivity In The Dissociative Electron Attachment Of 10-Iodocamphor, J. M. Dreiling, F. W. Lewis, J. D. Mills, Timothy J. Gay

Timothy J. Gay Publications

We have studied dissociative electron attachment (DEA) between low energy (≤ 0.6 eV) longitudinally polarized electrons and gas-phase chiral targets of 3-bromocamphor (C10H15BrO), 3-iodocamphor (C10H15IO), and 10-iodocamphor. The DEA rate depends on the sign of the incident electron helicity for a given target handedness, and it varies with both the atomic number (Z) and location of the heaviest atom in the molecule. While simple dynamic mechanisms can account for the asymmetry dependence on Z, they fail to explain the large asymmetry variation with the heavy atom location.


Rewriting Magnetic Phase Change Memory By Laser Heating, John Timmerwilke, Sy-Hwang Liou, Shu Fan Cheng, Alan S. Edelstein Jan 2016

Rewriting Magnetic Phase Change Memory By Laser Heating, John Timmerwilke, Sy-Hwang Liou, Shu Fan Cheng, Alan S. Edelstein

Si-Hwang Liou Publications

Magnetic phase change memory (MAG PCM) consists of bits with different magnetic permeability values. The bits are read by measuring their effect on a magnetic probe field. Previously low permeability crystalline bits had been written in high permeability amorphous films of Metglas via laser heating. Here data is presented showing that by applying short laser pulses with the appropriate power to previously crystallized regions they can first be vitrified and then again crystallized. Thus, MAG PCM is rewriteable. Technical issues in processing the bits are discussed and results on thermal modeling are presented.


Phase Separation In Lufeo3 Films, Shi Cao, Xiaozhe Zhang, Kishan Sinha, Wenbin Wang, Jian Wang, Peter A. Dowben, Xiaoshan Xu Jan 2016

Phase Separation In Lufeo3 Films, Shi Cao, Xiaozhe Zhang, Kishan Sinha, Wenbin Wang, Jian Wang, Peter A. Dowben, Xiaoshan Xu

Peter Dowben Publications

The structural transition at about 1000°C, from the hexagonal to the orthorhombic phase of LuFeO3, has been investigated in thin films of LuFeO3. Separation of the two structural phases of LuFeO3 occurs on a length scale of micrometer, as visualized in real space using X-ray photoemission electron microscopy. The results are consistent with X-ray diffraction and atomic force microscopy obtained from LuFeO3 thin films undergoing the irreversible structural transition from the hexagonal to the orthorhombic phase of LuFeO3, at elevated temperatures. The sharp phase boundaries between the structural phases are observed to align with ...


Characterizing Crop Photomultiplier Tube Behavior At 1000 Volts, Zachary T. Smith Jan 2016

Characterizing Crop Photomultiplier Tube Behavior At 1000 Volts, Zachary T. Smith

UCARE Research Products

In an effort to prolong the lifetime of their Photomultiplier tubes (PMTs), the Cosmic Ray Observatory Project (CROP) made the decision to begin operating the PMTs at an operating voltage of 1000 Volts. The aim of this project was to characterize the fundamental behavior of the PMTs at this operating voltage using several tests. These tests include determining the optimal threshold level of the PMTs, the PMT efficiency, and the time stability of the PMT's output.


Electrostatic Charge On Flying Hummingbirds And Its Potential Role In Pollination, Marc Badger, Victor Manuel Ortega-Jimenez, Lisa Von Ribenau, Ashley Smiley, Robert Dudley, Alexei Gruverman , Editor Jan 2015

Electrostatic Charge On Flying Hummingbirds And Its Potential Role In Pollination, Marc Badger, Victor Manuel Ortega-Jimenez, Lisa Von Ribenau, Ashley Smiley, Robert Dudley, Alexei Gruverman , Editor

Alexei Gruverman Publications

Electrostatic phenomena are known to enhance both wind- and insect-mediated pollination, but have not yet been described for nectar-feeding vertebrates. Here we demonstrate that wild Anna's Hummingbirds (Calypte anna) can carry positive charges up to 800 pC while in flight (mean ± s.d.: 66 ± 129 pC). Triboelectric charging obtained by rubbing an isolated hummingbird wing against various plant structures generated charges up to 700 pC. A metal hummingbird model charged to 400 pC induced bending of floral stamens in four plants (Nicotiana, Hemerocallis, Penstemon, and Aloe spp.), and also attracted falling Lycopodium spores at distances of < 2 mm. Electrostatic forces may therefore influence pollen transfer onto nectar-feeding birds.


Spin Density Waves In Periodically Strained Graphene Nanoribbons, Nabil M. Al-Aqtash, Renat F. Sabirianov Jan 2014

Spin Density Waves In Periodically Strained Graphene Nanoribbons, Nabil M. Al-Aqtash, Renat F. Sabirianov

Faculty Publications from Nebraska Center for Materials and Nanoscience

Zigzag graphene nanoribbons (ZGNRs) are antiferromagnetic in the ground state with zero net magnetization due to the compensation of contributions from opposite edges. Uniform deformations (both shear and axial) do not produce magnetization due to symmetry restrictions. However, we report the results of first-principles calculations that predict the induction of spin density waves (SDWs) in ZGNRs under non-uniform periodic strain. Using the density functional theory (DFT) method, we show that a sinusoidal magnetization variation along the axis of the ribbon occurs under a sinusoidal transversal shear strain. SDWs appear due to the presence of a strain gradient that induced asymmetry ...


Positive Exchange Bias In Epitaxial Permalloy/Mgo Integrated With Si (100), S. S. Rao, J. T. Prater, Fan Wu, S. Nori, D. Kumar, Lanping Yue, Sy_Hwang Liou, Jagdish Narayan Jan 2014

Positive Exchange Bias In Epitaxial Permalloy/Mgo Integrated With Si (100), S. S. Rao, J. T. Prater, Fan Wu, S. Nori, D. Kumar, Lanping Yue, Sy_Hwang Liou, Jagdish Narayan

Si-Hwang Liou Publications

In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (100) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni82.5Fe17.5 (permalloy, Py) on Si (100) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we ...