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Physics

University of Kentucky

2016

Articles 1 - 14 of 14

Full-Text Articles in Engineering

Enhanced Metallic Properties Of Srruo3 Thin Films Via Kinetically Controlled Pulsed Laser Epitaxy, Justin K. Thompson, J. Nichols, S. Lee, S. Ryee, John H. Gruenewald, John G. Connell, Maryam Souri, J. M. Johnson, J. Hwang, M. J. Han, H. N. Lee, D. -W. Kim, Sung S. Ambrose Seo Oct 2016

Enhanced Metallic Properties Of Srruo3 Thin Films Via Kinetically Controlled Pulsed Laser Epitaxy, Justin K. Thompson, J. Nichols, S. Lee, S. Ryee, John H. Gruenewald, John G. Connell, Maryam Souri, J. M. Johnson, J. Hwang, M. J. Han, H. N. Lee, D. -W. Kim, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3 (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. Here, we report that high-quality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin …

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Large Linear Magnetoresistance In Heavily-Doped Nb:Srtio3 Epitaxial Thin Films, Hyunwoo Jin, Keundong Lee, Seung-Hyub Baek, Jin-Sang Kim, Byung-Ki Cheong, Bae Ho Park, Sungwon Yoon, B. J. Suh, Changyoung Kim, Sung S. Ambrose Seo, Suyoun Lee Oct 2016

Large Linear Magnetoresistance In Heavily-Doped Nb:Srtio3 Epitaxial Thin Films, Hyunwoo Jin, Keundong Lee, Seung-Hyub Baek, Jin-Sang Kim, Byung-Ki Cheong, Bae Ho Park, Sungwon Yoon, B. J. Suh, Changyoung Kim, Sung S. Ambrose Seo, Suyoun Lee

Physics and Astronomy Faculty Publications

Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin …

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Simultaneous Metal-Insulator And Antiferromagnetic Transitions In Orthorhombic Perovskite Iridate Sr0.94Ir0.78O2.68 Single Crystals, Hao Zheng, Jsaminka Terzic, Feng Ye, X. G. Wan, D. Wang, Jinchen Wang, Xiaoping Wang, P. Schlottmann, Shujuan Yuan, Gang Cao Jun 2016

Simultaneous Metal-Insulator And Antiferromagnetic Transitions In Orthorhombic Perovskite Iridate Sr0.94Ir0.78O2.68 Single Crystals, Hao Zheng, Jsaminka Terzic, Feng Ye, X. G. Wan, D. Wang, Jinchen Wang, Xiaoping Wang, P. Schlottmann, Shujuan Yuan, Gang Cao

Center for Advanced Materials Faculty Publications

The orthorhombic perovskite SrIrO3 is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose an insulating state. We report results of our investigation of bulk single-crystal Sr0.94Ir0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIrO3. It retains the same crystal structure as stoichiometric SrIrO3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring in the basal-plane resistivity at 185 K. Above it, the basal-plane resistivity features an extended regime of almost linear temperature dependence up to 800 K but the strong …

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Observation Of Metallic Surface States In The Strongly Correlated Kitaev-Heisenberg Candidate Na2Iro3, Nasser Alidoust, Chang Liu, Su-Yang Xu, Ilya Belopolski, Tongfei Qi, Minggang Zeng, Daniel S. Sanchez, Hao Zheng, Guang Bian, Madhab Neupane, Yu-Tzu Liu, Stephen D. Wilson, Hsin Lin, Arun Bansil, Gang Cao, M. Zahid Hasan Jun 2016

Observation Of Metallic Surface States In The Strongly Correlated Kitaev-Heisenberg Candidate Na2Iro3, Nasser Alidoust, Chang Liu, Su-Yang Xu, Ilya Belopolski, Tongfei Qi, Minggang Zeng, Daniel S. Sanchez, Hao Zheng, Guang Bian, Madhab Neupane, Yu-Tzu Liu, Stephen D. Wilson, Hsin Lin, Arun Bansil, Gang Cao, M. Zahid Hasan

Center for Advanced Materials Faculty Publications

We report high-resolution angle-resolved photoemission spectroscopy measurements on the honeycomb iridate Na2IrO3. Our measurements reveal the existence of a metallic surface band feature crossing the Fermi level with nearly linear dispersion and an estimated surface carrier density of 3.2 x 1013 cm-2, which has not been theoretically predicted or experimentally observed, and provides the first evidence for metallic behavior on the boundary of this material, whereas the bulk bands exhibit a robust insulating gap. We further show the lack of theoretically predicted Dirac cones at the M¯ points of the surface Brillouin …

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Anisotropic Softening Of Magnetic Excitations In Lightly Electron-Doped Sr2Iro4, X. Liu, M. P. M. Dean, Z. Y. Meng, M. H. Upton, T. Qi, T. Gog, Y. Cao, J. Q. Lin, D. Meyers, H. Ding, Gang Cao, J. P. Hill Jun 2016

Anisotropic Softening Of Magnetic Excitations In Lightly Electron-Doped Sr2Iro4, X. Liu, M. P. M. Dean, Z. Y. Meng, M. H. Upton, T. Qi, T. Gog, Y. Cao, J. Q. Lin, D. Meyers, H. Ding, Gang Cao, J. P. Hill

Center for Advanced Materials Faculty Publications

The magnetic excitations in electron-doped (Sr1−xLax)2IrO4 with x = 0.03 were measured using resonant inelastic x-ray scattering at the Ir L3 edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the antinodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron-doped (Sr1−xLax …

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Size Effect On The Magnetic Phase In Sr4Ru3O10, Yan Liu, Jiyong Yang, Weike Wang, Haifeng Du, Wei Ning, Langsheng Ling, Wei Tong, Zhe Qu, Zhaorong Yang, Minling Tian, Gang Cao, Yuheng Zhang May 2016

Size Effect On The Magnetic Phase In Sr4Ru3O10, Yan Liu, Jiyong Yang, Weike Wang, Haifeng Du, Wei Ning, Langsheng Ling, Wei Tong, Zhe Qu, Zhaorong Yang, Minling Tian, Gang Cao, Yuheng Zhang

Center for Advanced Materials Faculty Publications

High quality Sr4Ru3O10 nanoflakes are obtained by the scotch tape-based micro-mechanical exfoliation method. The metamagnetic transition temperature Tmflake is found to decrease in line with the decrease of thickness, while the ferromagnetic (FM) phase, the ordinary, and anomalous Hall effects (OHE and AHE) are independent on the thickness of the flake. Analysis of the data demonstrates that the AHE reflects the FM nature of Sr4Ru3O10, and the decrease of thickness favors the Ru moments aligned in the ab-plane, which induces a decrease of the metamagnetic transition …

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Hallmarks Of The Mott-Metal Crossover In The Hole-Doped Pseudospin-1/2 Mott Insulator Sr2Iro4, Yue Cao, Qiang Wang, Justin A. Waugh, Theodore J. Reber, Haoxiang Li, Xiaoqing Zhou, Stephen Parham, S. -R. Park, Nicholas C. Plumb, Eli Rotenberg, Aaron Bostwick, Jonathan D. Denlinger, Tongfei Qi, Michael A. Hermele, Gang Cao, Daniel S. Dessau Apr 2016

Hallmarks Of The Mott-Metal Crossover In The Hole-Doped Pseudospin-1/2 Mott Insulator Sr2Iro4, Yue Cao, Qiang Wang, Justin A. Waugh, Theodore J. Reber, Haoxiang Li, Xiaoqing Zhou, Stephen Parham, S. -R. Park, Nicholas C. Plumb, Eli Rotenberg, Aaron Bostwick, Jonathan D. Denlinger, Tongfei Qi, Michael A. Hermele, Gang Cao, Daniel S. Dessau

Physics and Astronomy Faculty Publications

The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed …

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Spatio-Temporal Linear Stability Analysis Of Stratified Planar Wakes: Velocity And Density Asymmetry Effects, Benjamin Emerson, Swapnil Jagtap, J. Mathew Quinlan, Michael W. Renfro, Baki M. Cetegen, Tim Lieuwen Apr 2016

Spatio-Temporal Linear Stability Analysis Of Stratified Planar Wakes: Velocity And Density Asymmetry Effects, Benjamin Emerson, Swapnil Jagtap, J. Mathew Quinlan, Michael W. Renfro, Baki M. Cetegen, Tim Lieuwen

Mechanical Engineering Faculty Publications

This paper explores the hydrodynamic stability of bluff body wakes with non-uniform mean density, asymmetric mean density, and velocity profiles. This work is motivated by experiments [S. Tuttle et al., “Lean blow off behavior of asymmetrically-fueled bluff body-stabilized flames,” Combust. Flame 160, 1677 (2013)], which investigated reacting wakes with equivalence ratio stratification and, hence, asymmetry in the base flow density profiles. They showed that highly stratified cases exhibited strong, narrowband oscillations, suggestive of global hydrodynamic instability. In this paper, we present a local hydrodynamic stability analysis for non-uniform density wakes that includes base flow asymmetry. The results show …

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X-Ray Absorption Spectroscopy Study Of The Effect Of Rh Doping In Sr2Iro4, C. H. Sohn, Deok-Yong Cho, C. -T. Kuo, L. J. Sandilands, Tongfei Qi, Gang Cao, T. W. Noh Mar 2016

X-Ray Absorption Spectroscopy Study Of The Effect Of Rh Doping In Sr2Iro4, C. H. Sohn, Deok-Yong Cho, C. -T. Kuo, L. J. Sandilands, Tongfei Qi, Gang Cao, T. W. Noh

Center for Advanced Materials Faculty Publications

We investigate the effect of Rh doping in Sr2IrO4 using X-ray absorption spectroscopy (XAS). We observed appearance of new electron-addition states with increasing Rh concentration (x in Sr2Ir1−xRhxO4) in accordance with the concept of hole doping. The intensity of the hole-induced state is however weak, suggesting weakness of charge transfer (CT) effect and Mott insulating ground states. Also, Ir Jeff = 1/2 upper Hubbard band shifts to lower energy as x increases up to x = 0.23. Combined with optical spectroscopy, these results suggest a hybridisation-related mechanism, in …

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Direct Band Gap Gallium Antimony Phosphide (GasbXP1-X) Alloys, H. B. Russell, A. N. Andriotis, Madhu Menon, J. B. Jasinski, A. Martinez-Garcia, M. K. Sunkara Feb 2016

Direct Band Gap Gallium Antimony Phosphide (GasbXP1-X) Alloys, H. B. Russell, A. N. Andriotis, Madhu Menon, J. B. Jasinski, A. Martinez-Garcia, M. K. Sunkara

Center for Computational Sciences Faculty Publications

Here, we report direct band gap transition for Gallium Phosphide (GaP) when alloyed with just 1–2 at% antimony (Sb) utilizing both density functional theory based computations and experiments. First principles density functional theory calculations of GaSbxP1−x alloys in a 216 atom supercell configuration indicate that an indirect to direct band gap transition occurs at x = 0.0092 or higher Sb incorporation into GaSbxP1−x. Furthermore, these calculations indicate band edge straddling of the hydrogen evolution and oxygen evolution reactions for compositions ranging from x = 0.0092 Sb up to at least x = 0.065 …

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Growth Control Of Oxygen Stoichiometry In Homoepitaxial Srtio3 Films By Pulsed Laser Epitaxy In High Vacuum, Ho Nyung Lee, Sung S. Ambrose Seo, Woo Seok Choi, Christopher M. Rouleau Jan 2016

Growth Control Of Oxygen Stoichiometry In Homoepitaxial Srtio3 Films By Pulsed Laser Epitaxy In High Vacuum, Ho Nyung Lee, Sung S. Ambrose Seo, Woo Seok Choi, Christopher M. Rouleau

Physics and Astronomy Faculty Publications

In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on …

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The Effects Of Thermal Procedure On Transformation Temperature, Crystal Structure And Microstructure Of Cu-Al-Co Shape Memory Alloy, Y. Aydoğdu, M. Kök, F. Dağdelen, A. Aydoğdu, Ali S. Turabi, Haluk E. Karaca Jan 2016

The Effects Of Thermal Procedure On Transformation Temperature, Crystal Structure And Microstructure Of Cu-Al-Co Shape Memory Alloy, Y. Aydoğdu, M. Kök, F. Dağdelen, A. Aydoğdu, Ali S. Turabi, Haluk E. Karaca

Mechanical Engineering Faculty Publications

The purpose of this study is to investigate the effects of different thermal procedures of the Cu-Al-Co shape memory alloy on its crystal structure, transformation temperature and microstructure. The alloys were subjected to a heat treatment and then cooling was applied at four different conditions. After the thermal process, XRD, DSC, optical microscopy and micro-hardness measurements were carried out. The experimental studies showed that crystal structure, microstructure and transformation temperature of Cu-Al-Co alloy were changed from the cooling conditions.

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Effect Of Spalled Particles Thermal Degradation On A Hypersonic Flow Field Environment, Raghava S. C. Davuluri, Huaibao Zhang, Alexandre Martin Jan 2016

Effect Of Spalled Particles Thermal Degradation On A Hypersonic Flow Field Environment, Raghava S. C. Davuluri, Huaibao Zhang, Alexandre Martin

Mechanical Engineering Faculty Publications

Two-way coupling is performed between a spallation code and a hypersonic aerothermodynamics CFD solver to evaluate the effect of spalled particles on the flow field. Time accurate solutions are computed in argon and air flow fields. A single particle simulations and multiple particles simulations are performed and studied. The results show that the carbon vapor released by spalled particles tend to change the composition of the flow field, particularly the upstream region of the shock.

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Understanding Electrical Conduction In Lithium Ion Batteries Through Multi-Scale Modeling, Jie Pan Jan 2016

Understanding Electrical Conduction In Lithium Ion Batteries Through Multi-Scale Modeling, Jie Pan

Theses and Dissertations--Chemical and Materials Engineering

Silicon (Si) has been considered as a promising negative electrode material for lithium ion batteries (LIBs) because of its high theoretical capacity, low discharge voltage, and low cost. However, the utilization of Si electrode has been hampered by problems such as slow ionic transport, large stress/strain generation, and unstable solid electrolyte interphase (SEI). These problems severely influence the performance and cycle life of Si electrodes. In general, ionic conduction determines the rate performance of the electrode, while electron leakage through the SEI causes electrolyte decomposition and, thus, causes capacity loss. The goal of this thesis research is to design Si …

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