Physics Commons^™

Dielectric Properties Of Thin Cr2o3 Films Grown On Elemental And Oxide Metallic Substrates, Ather Mahmood, Mike Street, Will Echtenkamp, Chun Pui Kwan, Jonathan P. Bird, Christian Binek

Christian Binek Publications

In an attempt to optimize leakage characteristics of α-Cr₂O₃ thin films, its dielectric properties were investigated at local and macroscopic scale. The films were grown on Pd(111), Pt(111), and V₂O₃ (0001), supported on Al₂O₃ substrate. The local conductivity was measured by conductive atomic force microscopy mapping of Cr₂O₃ surfaces, which revealed the nature of defects that formed conducting paths with the bottom Pd or Pt layer. A strong correlation was found between these electrical defects and the grain boundaries revealed in the corresponding topographic scans. In comparison, …

Optimization Of Magnetic Chicane For Maximum Electron Beam Compression, Nathan W. Ray, Vida-Michelle Nixon, Matthias Fuchs

UCARE Research Products

Research concerned with optimizing a negatively chirped, relativistic, short electron beam using General Particle Tracer (GPT). The GPT simulations have the ability to include realistic beam effects such as space charge, fringe fields and emittance. A series of electron beam energy spreads were simulated through several different iterations of dipole magnets and, utilizing GPT's optimization ability, the most consistent set of parameters was selected and displayed on the poster. With our presented iteration of parameters we noted a 89.5% compression of the electron beam along the propagating axis.

Origin Of Spin Reorientation Transitions In Antiferromagnetic Mnpt-Based Alloys, P.-H. Chang, I. A. Zhuravlev, K. D. Belashchenko

Department of Physics and Astronomy: Faculty Publications

Antiferromagnetic MnPt exhibits a spin reorientation transition (SRT) as a function of temperature, and off-stoichiometric Mn-Pt alloys also display SRTs as a function of concentration. The magnetocrystalline anisotropy in these alloys is studied using first-principles calculations based on the coherent potential approximation and the disordered local moment method. The anisotropy is fairly small and sensitive to the variations in composition and temperature due to the cancellation of large contributions from different parts of the Brillouin zone. Concentration and temperature-driven SRTs are found in reasonable agreement with experimental data. Contributions from specific band-structure features are identified and used to explain the …

Polarization-Controlled Modulation Doping Of A Ferroelectric From First Principles, Xiaohui Liu, Evgeny Y. Tsymbal, Karin M. Rabe

Evgeny Tsymbal Publications

In a ferroelectric field effect transistor (FeFET), it is generally assumed that the ferroelectric gate plays a purely electrostatic role. Recently it has been shown that in some cases, which could be called “active FeFETs,” electronic states in the ferroelectric contribute to the device conductance as the result of a modulation doping effect in which carriers are transferred from the channel into the ferroelectric layers near the interface. Here we report first-principles calculations and model analysis to elucidate the various aspects of this mechanism and to provide guidance in materials choices and interface termination for optimizing the on-off ratio, using …

Nanostructural Origin Of Semiconductivity And Large Magnetoresistance In Epitaxial Nico2O4/Al2O3 Thin Films, Congmian Zhen, Xiaozhe Zhang, Wengang Wei, Wenzhe Guo, Ankit Pant, Xiaoshan Xu, Jian Shen, Li Ma, Denglu Hou

Xiaoshan Xu Papers

Despite low resistivity (~1 mΩ cm), metallic electrical transport has not been commonly observed in inverse spinel NiCo₂O₄, except in certain epitaxial thin films. Previous studies have stressed the effect of valence mixing and the degree of spinel inversion on the electrical conduction of NiCo₂O₄ films. In this work, we studied the effect of nanostructural disorder by comparing the NiCo₂O₄ epitaxial films grown on MgAl₂O₄ (1 1 1) and on Al₂O₃ (0 0 1) substrates. Although the optimal growth conditions are similar for the …

Time-Resolved Electron (E,2E) Momentum Spectroscopy: Application To Laser-Driven Electron Population Transfer In Atoms, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

Owing to its ability to provide unique information on electron dynamics, time-resolved electron momentum spectroscopy (EMS) is used to study theoretically a laser-driven electronic motion in atoms. Specifically, a chirped laser pulse is used to adiabatically transfer the populations of lithium atoms from the ground state to the first excited state. During this process, impact ionization near the Bethe ridge by time-delayed ultrashort, high-energy electron pulses is used to image the instantaneous momentum density of this electronic population transfer. Simulations with 100 fs and 1 fs pulse durations demonstrate the capability of EMS to image the time-varying momentum density, including …

Elevated Temperature Dependence Of The Anisotropic Visible-To-Ultraviolet Dielectric Function Of Monoclinic Β-Ga2o3, Alyssa Mock, Jeremy Vanderslice, Rafal Korlacki, John A. Woollam, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

We report on the temperature dependence of the dielectric tensor elements of n-type conductive β-Ga2O3 from 22 °C to 550 °C in the spectral range of 1.5 eV–6.4 eV. We present the temperature dependence of the excitonic and band-to-band transition energy parameters using a previously described eigendielectric summation approach [A. Mock et al., Phys. Rev. B 96, 245205 (2017)]. We utilize a Bose-Einstein analysis of the temperature dependence of the observed transition energies and reveal electron coupling with average phonon temperature in excellent agreement with the average over all longitudinal phonon plasmon coupled modes reported previously [M. …

Anisotropy And Phonon Modes From Analysis Of The Dielectric Function Tensor And The Inverse Dielectric Function Tensor Of Monoclinic Yttrium Orthosilicate, Alyssa Mock, Rafal Korlacki, Sean Knight, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

We determine the frequency dependence of the four independent Cartesian tensor elements of the dielectric function for monoclinic symmetry Y₂SiO₅ using generalized spectroscopic ellipsometry from 40–1200 cm⁻¹. Three different crystal cuts, each perpendicular to a principle axis, are investigated. We apply our recently described augmentation of lattice anharmonicity onto the eigendielectric displacement vector summation approach [A.Mock et al., Phys. Rev. B 95, 165202 (2017)], and we present and demonstrate the application of an eigendielectric displacement loss vector summation approach with anharmonic broadening. We obtain an excellent match between all measured and model-calculated dielectric …

Structure And Magnetism Of Mn5ge3 Nanoparticles, Onur Tosun, Mohammed Salehi-Fashami, Balamurugan Balasubramanian, Ralph Skomski, David J. Sellmyer, George C. Hadjipanayis

Nebraska Center for Materials and Nanoscience: Faculty Publications

In this work, we investigated the magnetic and structural properties of isolated Mn₅Ge₃ nanoparticles prepared by the cluster-beam deposition technique. Particles with sizes between 7.2 and 12.6 nm were produced by varying the argon pressure and power in the cluster gun. X-ray diffraction (XRD)and selected area diffraction (SAD) measurements show that the nanoparticles crystallize in the hexagonal Mn₅Si₃-type crystal structure, which is also the structure of bulk Mn₅Ge₃. The temperature dependence of the magnetization shows that the as-made particles are ferromagnetic at room temperature and have slightly different Curie …

Magnetism Of New Metastable Cobalt-Nitride Compounds, Balamuruga Balamurugan, Xin Zhao, Shah R. Valloppilly, Sumit Beniwal, Ralph Skomski, Anandakumar Sarella, Yunlong Jin, Xingzhong Li, Xiaoshan Xu, Huibo Cao, Haohan Wang, Axel Enders, Cai-Zhuang Wang, Kai-Ming Ho, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

The search for new magnetic materials with high magnetization and magnetocrystalline anisotropy is important for a wide range of applications including information and energy processing. There is only a limited number of naturally occurring magnetic compounds that are suitable. This situation stimulates an exploration of new phases that occur far from thermal-equilibrium conditions, but their stabilization is generally inhibited due to high positive formation energies. Here a nanocluster-deposition method has enabled the discovery of a set of new non-equilibrium Co-N intermetallic compounds. The experimental search was assisted by computational methods including adaptive-genetic-algorithm and electronic- structure calculations. Conventional wisdom is that …

Structural, Magnetic, And Electron-Transport Properties Of Epitaxial Mn2Ptsn Films, Y. Jin, Shah R. Valloppilly, Parashu Kharel, Jace Waybright, Pavel V. Lukashev, Xingzhong Li, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

The growth of new magnetic materials on suitable insulating substrates is an important part of the development of spin-electronics devices for memory or information processing. Epitaxial thin films of Mn₂PtSn were grown on a MgO [001] substrate by magnetron co-sputtering of the constituents. Structural, magnetic, and electron-transport properties were investigated. The epitaxial Mn₂PtSn film has an inverse tetragonal structure with the c-axis aligned in the plane of the MgO substrate. The lattice constants determined using XRD and TEM analysis are c=6.124Å and a=b=4.505Å. The orientation of Mn₂PtSn c-axis which …

Multi-Walled Carbon Nanotube-Coated Spiral Coils For Loss Reduction In Wireless Power Transfer Systems, Kamran Keramatnejad, Dawei Li, Hossein Rabiee Golgir, Loic Constantin, Xi Huang, Qiming Zou, Jean-Francois Silvain, Stephen Ducharme, Yongfeng Lu

Stephen Ducharme Publications

Realization of high efficiency and long transmission range in high-frequency wireless power transfer (WPT) systems has always been hindered by the increased resistance due to the eddy current loss occurring in the inductive coils. In this study, multi-walled carbon nanotube-coated copper (MWCNT-Cu) coils are successfully introduced to address this limitation by implementing the frequency-inert MWCNT channels along with using their high-surface areas to realize the electromagnetic shielding of the Cu substrate through multiple reflection mechanisms. At a frequency of 15 MHz, the resistance of the individual MWCNT-Cu coil was reduced to less than 40% of its original value for primitive …

Focused Electron-Beam-Induced Deposition For Fabrication Of Highly Durable And Sensitive Metallic Afm-Ir Probes, Wen Qian, Shuo Sun, Jingfeng Song, Charles Nguyen, Stephen Ducharme, Joesph A. Turner

Stephen Ducharme Publications

We report on the fabrication of metallic, ultra-sharp atomic force microscope tips for localized nanoscale infrared (IR) spectrum measurements by using focused electron-beam-induced deposition of platinum or tungsten. The tip length can be controlled by changing the duration time of the electron beam. Probes of 12.0 ± 5.0 nm radius-of-curvature can be routinely produced with high repeatability and near-100% yield. The near-field-enhancement appears stronger at the extremity of the metallic tip, compared with commercial pristine silicon-nitride probe tip. Finally, the performance of the modified metallic tips is demonstrated by imaging PVDF and PMMA thin films, which shows that spatial resolution …

Isostructural Metal-Insulator Transition In Vo2, D. Lee, B. Chung, Y. Shi, G.-Y. Kim, N. Campbell, F. Xue, K. Song, S.-Y. Choi, J. P. Podkaminer, T. H. Kim, P. J. Ryan, J.-W. Kim, T. R. Paudel, J.-H. Kang, J. W. Spinuzzi, D. A. Tenne, E. Y. Tsymbal, M. S. Rzchowski, L. Q. Chen, J. Lee, And C. B. Eom

Evgeny Tsymbal Publications

No abstract provided.

Tunneling Anomalous Hall Effect In A Ferroelectric Tunnel Junction, M. Y. Zhuravlev, A. Alexandrov, L. L. Tao, And E. Y. Tsymbal

Evgeny Tsymbal Publications

No abstract provided.

Direct Observation Of A Two-Dimensional Hole Gas At Oxide Interfaces, H. Lee, N. Campbell, J. Lee, T. Asel, T. Paudel, H. Zhou, J. W. Lee, B. Noesges, J. Seo, B. Park, L. J. Brillson, S. H. Oh, E. Y. Tsymbal, M. S. Rzchowski, And C. B. Eom

Evgeny Tsymbal Publications

No abstract provided.

Anisotropic Polarization-Induced Conduction At The Ferroelectric/Insulator Interface, Y. Zhang, H. Lu, L. Xie, X. Yan, T. R. Paudel, J. Kim, X. Chen, H. Wang, C. Heikes, L. Li, M. Xu, D. G. Schlom, L.-Q. Chen, R. Wu, E. Y. Tsymbal, A. Gruverman, And X. Q. Pan

Evgeny Tsymbal Publications

No abstract provided.

Direct Imaging Of The Electron Liquid At Oxide Interfaces, Kyung Song, Sangwoo Ryu, Hyungwoo Lee, Tula R. Paudel, Christoph T. Koch, Bumsu Park, Ja Kyung Lee, Si-Young Choi, Young-Min Kim, Jong Chan Kim, Hu Young Jeong, Mark S. Rzchowski, Evgeny Y. Tsymbal, Chang-Beom Eom, And Sang Ho Oh

Evgeny Tsymbal Publications

No abstract provided.

Honeycomb Lattice Na2iro3 At High Pressures: A Robust Spin-Orbit Mott Insulator, Xiaoxiang Xi, Xiangyan Bo, X. S. Xu, P. P. Kong, Z. Liu, X. G. Hong, C. Q. Jin, G. Cao, Xiangang Wan, G. L. Carr

Xiaoshan Xu Papers

The honeycomb iridate Na₂IrO₃ has received much attention as a candidate to realize a quantum spin liquid state, but the nature of its insulating state remains controversial. We found that the material exhibits structural transitions at 3 and 10 GPa. The former is accompanied by 166-meV suppression of the activation gap, but the energies for the low-lying interband transitions change by less than 10 meV. This can be reconciled in a picture in which the application of high pressure barely shifts the electronic bands, but rather merely broadens them. First-principles calculations uncover a strong correlation between the …

Tuning The Neel Temperature Of Hexagonal Ferrites By Structural Distortion, Kishan Sinha, Haohan Wang, Xiao Wang, Liying Zhou, Yuewei Yin, Wenbin Wang, Xuemei Cheng, David J. Keavney, Huibo Cao, Yaohua Liu, Xifan Wu, Xiaoshan Xu

Xiaoshan Xu Papers

To tune the magnetic properties of hexagonal ferrites, a family of magnetoelectric multiferroic materials, by atomic-scale structural engineering, we studied the effect of structural distortion on the magnetic ordering temperature (T_N) in these materials. Using the symmetry analysis, we show that unlike most antiferromagnetic rare-earth transition-metal perovskites, a larger structural distortion leads to a higher T_N in hexagonal ferrites and manganites, because the K₃ structural distortion induces the three-dimensional magnetic ordering, which is forbidden in the undistorted structure by symmetry. We also revealed a nearlinear relation between T_N and the tolerance factor and a …

Saw Assisted Domain Wall Motion In Co/Pt Multilayers, Westin Edrington, Uday Singh, Maya Abo Dominguez, James Rehwaldt Alexander, Rabindra Nepal, Shireen Adenwalla

Shireen Adenwalla Papers

The motion of domain walls in thin ferromagnetic films is of both fundamental and technological interest. In particular, the ability to use drivers other than magnetic fields to control the positions of domain walls could be exciting for memory applications. Here, we show that high frequency dynamic strain produced by surface acoustic waves is an efficient driver of magnetic domain walls in ferromagnetic films with perpendicular anisotropy. A standing surface acoustic wave of resonant frequency 96.6MHz increases the domain wall velocities in thin films of [Co/Pt]n by an order of magnitude compared to magnetic fields alone. This effect is highly …

Indications Of Magnetic Coupling Effects In Spin Cross-Over Molecular Thin Films, Xin Zhang, Alpha T. N'Diaye, Xuanyuan Jiang, Xiaozhe Zhang, Yuewei Yin, Xuegang Chen, Xia Hong, Xiaoshan Xu, Peter Dowben

Xia Hong Publications

Room temperature isothermal reversible spin crossover switching of [Fe(H₂B(pz)₂)₂(bipy)] thin films is demonstrated. The magnetic oxide substrate locks the [Fe{H₂B(pz)₂}₂(bipy)] largely in a low spin state. With an X-ray fluence, excitation to a high spin state occurs, while relaxation back to low spin state is aided by alternating the substrate magnetization.

Includes supplementary materials.

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 field spin …

Spin-Polarized Electron Transmission Through Chiral Halocamphor Molecules, J. M. Dreiling, F. W. Lewis, Timothy J. Gay

Timothy J. Gay Publications

We have measured electron-circularly-dichroic asymmetries when longitudinally-polarized (chiral) electrons are scattered quasi-elastically by chiral halocamphor molecules: 3-bromocamphor (C₁₀H₁₅BrO), 3-iodocamphor (C₁₀H₁₅IO), and 10-iodocamphor. The proposed dynamic origins of these asymmetries are considered in terms of three classical models related to Mott scattering, target electron helicity density, and spin-other-orbit interactions. The asymmetries observed for 3-bromocamphor and 3-iodocamphor scale roughly as Z², where Z is the nuclear charge of the heaviest atom in the target molecule, but the scaling is violated by 10- iodocamphor, which has a smaller asymmetry than that for 3-iodocamphor. …

Investigation Of Toppling Ball Flight In American Football With A Mechanical Field-Goal Kicker, Chase M Pfeifer, Timothy J. Gay, Jeff A. Hawks, Shane Farritor, Judith M. Burnfield

Department of Mechanical and Materials Engineering: Faculty Publications

A mechanical field-goal kicking machine was used to investigate toppling ball flight in American football place-kicking, eliminating a number of uncontrollable impact variables present with a human kicker. Ball flight trajectories were recorded using a triangulation-based projectile tracking system to account for the football’s 3-dimensional position during flight as well as initial launch conditions. The football flights were described using kinematic equations relating to projectile motion including stagnant air drag and were compared to measured trajectories as well as projectile motion equations that exclude stagnant air drag. Measured football flight range deviations from the non-drag equations of projectile motion corresponded …

Tunneling Hot Spots In Ferroelectric Srtio3, Haidong Lu, Daesu Lee, Konstantin Klyukin, Lingling Tao, Bo Wang, Hyungwoo Lee, Tula R. Paudel, Long-Qing Chen, Evgeny Y. Tsymbal, Vitaly Alexandrov, Chang-Beom Eom, And Alexei Gruverman

Evgeny Tsymbal Publications

No abstract provided.

X-Ray-Induced Colossal Persistent Photoconductivity In Current-Perpendicular-To-Plane Thin-Film Junctions, Wei Jin Hu, Tula R. Paudel, Sergei Lopatin, Zhihong Wang, He Ma, Kewei Wu, Ashok Bera, Guoliang Yuan, Alexei Gruverman, Evgeny Y. Tsymbal, And Tom Wu

Evgeny Tsymbal Publications

No abstract provided.

Solid-State Synapse Based On Magnetoelectrically Coupled Memristor, Weichuan Huang, Yue-Wen Fang, Yuewei Yin, Bobo Tian, Wenbo Zhao, Chuangming Hou, Chao Ma, Qi Li, Evgeny Y. Tsymbal, Chun-Gang Duan, And Xiaoguang Li

Evgeny Tsymbal Publications

No abstract provided.

Contributions Of The Lead-Bromine Weighted Bulk Bands To The Occupied Density Of States Of The Hybrid Tri-Bromide Perovskites, A. R. Kirmani, A. E. Mansour, M. I. Saidaminov, X. Cui, D. Shi, A. Alofi, Y. Losovyj, G. Gurung, T. R. Paudel, A. J. Yost, P. A. Dowben, E. Y. Tsymbal, A. Amassian, And K. Katsiev

Evgeny Tsymbal Publications

No abstract provided.

The Promise Of Piezoelectric Polymers, Timothy D. Usher, Kimberley R. Cousins, Renwu Zhang, Stephen Ducharme

Stephen Ducharme Publications

Recent advances provide new opportunities in the field of polymer piezoelectric materials. Piezoelectric materials provide unique insights to the fundamental understanding of the solid state. In addition, piezoelectric materials have a wide range of applications, representing billions of dollars of commercial applications. However, inorganic piezoelectric materials have limitations that polymer ferroelectric materials can overcome, if certain challenges can be addressed. This mini-review is a practical summary of the current research and future directions in the investigation and application of piezoelectric materials with an emphasis on polymeric piezoelectric materials. We will assume that the reader is well versed in the subject …