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Articles 31 - 49 of 49
Full-Text Articles in Condensed Matter Physics
Schottky Barrier Formation At The Au To Rare Earth Doped Gan Thin Film Interface, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben
Schottky Barrier Formation At The Au To Rare Earth Doped Gan Thin Film Interface, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben
Peter Dowben Publications
The Schottky barriers formed at the interface between gold and various rare earth doped GaN thin films (RE = Yb, Er, Gd) were investigated in situ using synchrotron photoemission spectroscopy. The resultant Schottky barrier heights were measured as 1.68 ± 0.1 eV (Yb:GaN), 1.64 ± 0.1 eV (Er:GaN), and 1.33 ± 0.1 eV (Gd:GaN). We find compelling evidence that thin layers of gold do not wet and uniformly cover the GaN surface, even with rare earth doping of the GaN. Furthermore, the trend of the Schottky barrier heights follows the trend of the rare earth metal work function.
Scanning Capacitance Spectroscopy On N+-P Asymmetrical Junctions In Multicrystalline Si Solar Cells, Chun-Sheng Jiang, Jennifer T. Heath, Helio R. Moutinho, Mowafak M. Al-Jassim
Scanning Capacitance Spectroscopy On N+-P Asymmetrical Junctions In Multicrystalline Si Solar Cells, Chun-Sheng Jiang, Jennifer T. Heath, Helio R. Moutinho, Mowafak M. Al-Jassim
Faculty Publications
We report on a scanning capacitance spectroscopy (SCS) study on the n+-p junction of multicrystalline silicon solar cells. We found that the spectra taken at space intervals of ∼10 nm exhibit characteristic features that depend strongly on the location relative to the junction. The capacitance-voltage spectra exhibit a local minimum capacitance value at the electrical junction, which allows the junction to be identified with ∼10-nm resolution. The spectra also show complicated transitions from the junction to the n-region with two local capacitance minima on the capacitance-voltage curves; similar spectra to that have not been previously reported in …
Ionic Conductivity And Related Studies In Methyl Cellulose Based Polymer Electrolytes And Application In Supercapacitors., Noor Erwani Azura Shuhaimi
Ionic Conductivity And Related Studies In Methyl Cellulose Based Polymer Electrolytes And Application In Supercapacitors., Noor Erwani Azura Shuhaimi
Student Works (2010-2019)
Solid polymer electrolytes based on methyl cellulose (MC) were investigated. Two MC based polymer electrolytes systems were prepared using solution cast technique. These are MC-ammonium nitrate (NH4NO3) system and MC-NH4NO3 system plasticized with poly (ethylene glycol), (PEG). NH4NO3 was chosen as the proton source to make MC, a biodegradable polymer conductive. The room temperature conductivity of pure MC is 3.08 × 10-11 S cm-1. The conductivity is increased up to 2.10 × 10-6 S cm-1 with addition of 25 wt.% NH4NO3. To enhance conductivity of MC-NH4NO3 system, PEG was added to 75MC25AN solution in different concentrations (from 5 to 25 …
Electron-Phonon Interactions And Quantum Confinement Effects On Optical Transitions In Nanoscale Silicon Films, Vimal Kumar Kamineni
Electron-Phonon Interactions And Quantum Confinement Effects On Optical Transitions In Nanoscale Silicon Films, Vimal Kumar Kamineni
Legacy Theses & Dissertations (2009 - 2024)
Theoretical studies have attributed the temperature dependence of the linear optical response (dielectric function) of bulk semiconductors to electron-phonon interactions and thermal expansion of the lattice. However, the role of phonons in the optical properties of nanoscale structures is often overlooked. This thesis systematically investigates the impact of both carrier confinement and electron-phonon interactions using nanoscale films of silicon in crystalline silicon quantum wells (c-Si QW). Spectroscopic ellipsometry (SE) is a linear optical technique used to of extract the dielectric function and thickness of very thin films. X-ray reflectivity (XRR) was used as the complementary thickness metrology method. The dielectric …
Band Structures Of Layered Carbon/Boron Nitride Materials With Commensurate Lattices, Christopher C. Wells
Band Structures Of Layered Carbon/Boron Nitride Materials With Commensurate Lattices, Christopher C. Wells
Legacy Theses & Dissertations (2009 - 2024)
The electronic structures of systems consisting of hexagonal boron nitride layers and graphite sheets have been investigated in detail using density functional theory methods with two exchange correlation functions (local density approximation and generalized gradient approximation). The experimental data of graphene, graphite, monolayer hexagonal BN, and hexagonal BN were reproduced well with computational models. The commensurate models used in the investigation were generated by taking the averages of the lattice constants for graphite and h-BN.
Structure And Magnetism Of Mnau Nanoclusters, X. Wei, Damien Le Roy, Ralph Skomski, Xingzhong Li, Zhiguang Sun, Jeffrey E. Shield, M. J. Kramer, David J. Sellmyer
Structure And Magnetism Of Mnau Nanoclusters, X. Wei, Damien Le Roy, Ralph Skomski, Xingzhong Li, Zhiguang Sun, Jeffrey E. Shield, M. J. Kramer, David J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
Equiatomic MnAu clusters with average sizes of 4 and 10 nm are produced by inert-gas condensation. As-produced clusters are used to form both dense cluster films and films with clusters embedded in a W matrix with a cluster volume fraction of 25%. Both structure and magnetism are size-dependent. Structural analysis of the 10 nm clusters indicate a distorted tetragonal body-centered cubic structure with lattice parameters a=0.315 and c=0.329 nm. The 4 nm clusters have a partially ordered tetragonal L10 structure with lattice parameters a=0.410 nm and c=0.395 nm. Magnetic properties of the clusters show evidence at …
High Temperature And Pressure Resonant Ultrasound Spectroscopy Study Of Metal Hydride Systems, Rasheed Adebisi
High Temperature And Pressure Resonant Ultrasound Spectroscopy Study Of Metal Hydride Systems, Rasheed Adebisi
Electronic Theses and Dissertations
The goal of this dissertation is to characterize the elastic properties of palladium hydride near the tri-critical point as a classic example of metal hydride systems using the resonant ultrasound spectroscopy. A high temperature and high pressure resonant ultrasound spectroscopy system which include the RUS cell and the direct contact transducer set-up was designed and constructed. The temperature and pressure dependent of elastic moduli of palladium hydride and palladium crystals were obtained at five isotherms near the critical temperature, 293 °C and for pressure range of 250–500 psi. A strong softening of the shear modulus was observed at temperature and …
Magnetism Of Cluster-Deposited Y–Co Nanoparticles, Balamuruga Balamurugan, Ralph Skomski, Xingzhong Li, V. R. Shah, George C. Hadjipanayis, Jeffrey E. Shield, David J. Sellmyer
Magnetism Of Cluster-Deposited Y–Co Nanoparticles, Balamuruga Balamurugan, Ralph Skomski, Xingzhong Li, V. R. Shah, George C. Hadjipanayis, Jeffrey E. Shield, David J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
Nanoparticles of YCo2, YCo3, and YCo5 are produced by cluster-deposition and investigated both structurally and magnetically. The nanoparticles have sizes of less than 10 nm and are superparamagnetic at 300 K, irrespective of stoichiometry. As-produced nanoparticles exhibit disordered structures with magnetic properties differing from those of the bulk particles. The temperature-dependent magnetization curves of the nanoparticles reveal blocking temperatures from 110 to 250 K, depending on stoichiometry. The magnetic anisotropy constant K1 of disordered YCo5 nanoparticles of 7.8 nm in size is 3.5×106ergs/cm3, higher than those of the disordered YCo …
Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Cheettu Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden
Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Cheettu Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden
Faculty Publications
The electronic conductivity and thermodynamic stability of mixed n-type and p-type doped SrTiO3 have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained ab initio thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO3 at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of n- and p-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20% Nb-doped Sr-deficient SrTiO3 to a non-Sr-deficient phase …
Unitary-Quantum-Lattice Algorithm For Two-Dimensional Quantum Turbulence, Bo Zhang, George Vahala, Linda L. Vahala, Min Soe
Unitary-Quantum-Lattice Algorithm For Two-Dimensional Quantum Turbulence, Bo Zhang, George Vahala, Linda L. Vahala, Min Soe
Electrical & Computer Engineering Faculty Publications
Quantum vortex structures and energy cascades are examined for two-dimensional quantum turbulence (2D QT) at zero temperature. A special unitary evolution algorithm, the quantum lattice algorithm, is employed to simulate the Bose-Einstein condensate governed by the Gross-Pitaevskii (GP) equation. A parameter regime is uncovered in which, as in 3D QT, there is a short Poincare recurrence time. It is demonstrated that such short recurrence times are destroyed by stronger nonlinear interaction. The similar loss of Poincare recurrence is also seen in the 3D GP equation. Various initial conditions are considered in an attempt to discern if 2D QT exhibits inverse …
Metastability Of Free Cobalt And Iron Clusters: A Possible Precursor To Bulk Ferromagnetism, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John Bowlan, Walt A. De Heer
Metastability Of Free Cobalt And Iron Clusters: A Possible Precursor To Bulk Ferromagnetism, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John Bowlan, Walt A. De Heer
Xiaoshan Xu Papers
Homonuclear cobalt and iron clusters CoN and FeN measured in a cryogenic molecular beam exist in two states with distinct magnetic moments (μ), polarizabilities, and ionization potentials, indicating distinct valences. The μ is approximately quantized: μN ~ 2NμB in the ground states and μN* ~ NμB in the excited states for Co; μN ~ 3N μB and μN * ~ NμB for Fe. At a large size, the average μ of the two states converges to the bulk value with diminishing ionization potential differences. …
Mesoscale Flux-Closure Domain Formation In Single-Crystal Batio3, R. G.P. Mcquaid, L. J. Mcgilly, Pankaj Sharma, Alexei Gruverman, J. M. Gregg
Mesoscale Flux-Closure Domain Formation In Single-Crystal Batio3, R. G.P. Mcquaid, L. J. Mcgilly, Pankaj Sharma, Alexei Gruverman, J. M. Gregg
Alexei Gruverman Publications
Over 60 years ago, Charles Kittel predicted that quadrant domains should spontaneously form in small ferromagnetic platelets. He expected that the direction of magnetization within each quadrant should lie parallel to the platelet surface, minimizing demagnetizing fields, and that magnetic moments should be configured into an overall closed loop, or flux-closure arrangement. Although now a ubiquitous observation in ferromagnets, obvious flux-closure patterns have been somewhat elusive in ferroelectric materials. This is despite the analogous behaviour between these two ferroic subgroups and the recent prediction of dipole closure states by atomistic simulations research. Here we show Piezoresponse Force Microscopy images of …
Metallic And Insulating Oxide Interfaces Controlled By Electronic Correlations, H. W. Jang, D. A. Felker, C. W. Bark, Y. Wang, Manish K. Niranjan, C. T. Nelson, Y. Zhang, D. Su, C. M. Folkman, S. H. Baek, S. Lee, K. Janicka, Y. Zhu, X. Q. Pan, D. D. Fong, Evgeny Y. Tsymbal, M. S. Rzchowski, Chang-Beom Eom
Metallic And Insulating Oxide Interfaces Controlled By Electronic Correlations, H. W. Jang, D. A. Felker, C. W. Bark, Y. Wang, Manish K. Niranjan, C. T. Nelson, Y. Zhang, D. Su, C. M. Folkman, S. H. Baek, S. Lee, K. Janicka, Y. Zhu, X. Q. Pan, D. D. Fong, Evgeny Y. Tsymbal, M. S. Rzchowski, Chang-Beom Eom
Evgeny Tsymbal Publications
The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO3) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local …
Transport Spin Polarization Of High-Curie Temperature Mnbi Films, Parashu Kharel, P. Thapa, Pavel V. Lukashev, Renat F. Sabirianov, Evgeny Y. Tsymbal, D. J. Sellmyer, Boris Nadgorny
Transport Spin Polarization Of High-Curie Temperature Mnbi Films, Parashu Kharel, P. Thapa, Pavel V. Lukashev, Renat F. Sabirianov, Evgeny Y. Tsymbal, D. J. Sellmyer, Boris Nadgorny
Evgeny Tsymbal Publications
We report on the study of the structural, magnetic, and transport properties of highly textured MnBi films with the Curie temperature of 628 K. In addition to detailed measurements of resistivity and magnetization, we measure transport spin polarization of MnBi by Andreev reflection spectroscopy and perform fully relativistic band-structure calculations of MnBi. A spin polarization from 51% ± 1% to 63% ± 1% is observed, consistent with the calculations and with an observation of a large magnetoresistance in MnBi contacts. The band-structure calculations indicate that in spite of almost identical densities of states at the Fermi energy, the large disparity …
A Giant Tunneling Electroresistance Effect Driven By Electrically Controlled Spin Valve At A Complex Oxide Interface, John D. Burton, Evgeny Y. Tsymbal
A Giant Tunneling Electroresistance Effect Driven By Electrically Controlled Spin Valve At A Complex Oxide Interface, John D. Burton, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
A giant tunneling electroresistance effect may be achieved in a ferroelectric tunnel junction by exploiting the magnetoelectric effect at the interface between the ferroelectric barrier and a magnetic La1-xSrxMnO3 electrode. Using first-principles density-functional theory we demonstrate that a few magnetic monolayers of La1-xSrxMnO3 near the interface act, in response to ferroelectric polarization reversal, as an atomic-scale spin valve by filtering spin-dependent current. This produces more than an order of magnitude change in conductance, and thus constitutes a giant resistive switching effect.
Resonant Photoemission Of Rare Earth Doped Gan Thin Films, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben
Resonant Photoemission Of Rare Earth Doped Gan Thin Films, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben
Peter Dowben Publications
The 4d → 4f Fano resonances for various rare earth doped GaN thin films (RE = Gd, Er, Yb) were investigated using synchrotron photoemission spectroscopy. The resonant photoemission Fano profiles show that the major Gd and Er rare earth 4f weight is at about 5–6 eV below the valence band maximum, similar to the 4f weights in the valence band of many other rare earth doped semiconductors. For Yb, there is very little resonant enhancement of the valence band of Yb doped GaN, consistent with a largely 4f14 occupancy.
Superplastic Boronizing On Duplex Stainless Steel (Dss) Using Compression Method., Yong Siu Fung
Superplastic Boronizing On Duplex Stainless Steel (Dss) Using Compression Method., Yong Siu Fung
Student Works (2010-2019)
The formation and growth of boride phases on duplex stainless steel (DSS) during superplastic boronizing (SPB) were studied in comparison with conventional boronizing (CB) from previous research. SPB is a surface hardening technique that combines boronizing with superplastic deformation. It utilizes the ultra high plasticity phenomenon in metal while carrying out boronizing in which boron atoms are diffused into the metal substrate to form hard boronized layer. The SPB process was conducted under compression mode at a strain rate of 2 × 10-4 s-1, at three different temperature conditions (1223 K, 1273 K, 1373 K) and strains (0.2 to 0.6). …
Analysis Of Electrodeposited Nickel-Iron Alloy Film Composition Using Particle-Induced X-Ray Emission, Alyssa Frey, Nicholas Wozniak, Timothy Nagi, Matthew Keller, J. Mark Lunderberg, Graham F. Peaslee, Paul Deyoung, Jennifer R. Hampton
Analysis Of Electrodeposited Nickel-Iron Alloy Film Composition Using Particle-Induced X-Ray Emission, Alyssa Frey, Nicholas Wozniak, Timothy Nagi, Matthew Keller, J. Mark Lunderberg, Graham F. Peaslee, Paul Deyoung, Jennifer R. Hampton
Faculty Publications
The elemental composition of electrodeposited NiFe thin films was analyzed with particle-induced X-ray emission (PIXE). The thin films were electrodeposited on polycrystalline Au substrates from a 100mM NiSO4, 10 mM FeSO4, 0.5M H3BO3, and 1M Na2SO4 solution. PIXE spectra of these films were analyzed to obtain relative amounts of Ni and Fe as a function of deposition potential and deposition time. The results show that PIXE can measure the total deposited metal in a sample over at least four orders of magnitude with similar fractional uncertainties. The technique is …
Hydrodynamic Correlation Functions Of A Driven Granular Fluid In Steady State, Katharina Vollmayr-Lee, Timo Aspelmeier, Annette Zippelius
Hydrodynamic Correlation Functions Of A Driven Granular Fluid In Steady State, Katharina Vollmayr-Lee, Timo Aspelmeier, Annette Zippelius
Faculty Journal Articles
No abstract provided.