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Iowa State University

Engineering Physics

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Articles 1 - 30 of 280

Full-Text Articles in Physics

Complex Oscillatory Decrease With Size In Diffusivity Of {100}-Epitaxially Supported 3d Fcc Metal Nanoclusters, King C. Lai, James W. Evans Oct 2019

Complex Oscillatory Decrease With Size In Diffusivity Of {100}-Epitaxially Supported 3d Fcc Metal Nanoclusters, King C. Lai, James W. Evans

Ames Laboratory Accepted Manuscripts

Diffusion and coalescence of supported 3D metal nanoclusters (NCs) leads to Smoluchowski Ripening (SR), a key pathway for catalyst degradation. Variation of the NC diffusion coefficient, DN, with size N (in atoms) controls SR kinetics. Traditionally, a form DN ∼ N−β was assumed consistent with mean-field analysis. However, KMC simulation of a stochastic model for diffusion of {100}-epitaxially supported fcc NCs mediated by surface diffusion reveals instead a complex oscillatory decrease of DN with N. Barriers for surface diffusion of metal atoms across and between facets, along step edges, etc., in this model are selected to accurately capture behavior ...


Interplay Between Superconductivity And Itinerant Magnetism In Underdoped Ba1−Xkxfe2as2 (X = 0.2) Probed By The Response To Controlled Point-Like Disorder, Ruslan Prozorov, Marcin Kończykowski, Makariy A. Tanatar, Hai-Hu Wen, Rafael M. Fernandes, Paul C. Canfield Jul 2019

Interplay Between Superconductivity And Itinerant Magnetism In Underdoped Ba1−Xkxfe2as2 (X = 0.2) Probed By The Response To Controlled Point-Like Disorder, Ruslan Prozorov, Marcin Kończykowski, Makariy A. Tanatar, Hai-Hu Wen, Rafael M. Fernandes, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

The response of superconductors to controlled introduction of point-like disorder is an important tool to probe their microscopic electronic collective behavior. In the case of iron-based superconductors, magnetic fluctuations presumably play an important role in inducing high-temperature superconductivity. In some cases, these two seemingly incompatible orders coexist microscopically. Therefore, understanding how this unique coexistence state is affected by disorder can provide important information about the microscopic mechanisms involved. In one of the most studied pnictide family, hole-doped Ba1−xKxFe2As2 (BaK122), this coexistence occurs over a wide range of doping levels, 0.16 ≲ x ≲ 0.25. We used ...


Interaction Dynamics Between Ferroelectric And Antiferroelectric Domains In A Pbzro3-Based Ceramic, Zhongming Fan, Fei Xue, Goknur Tutuncu, Long-Qing Chen, Xiaoli Tan Jun 2019

Interaction Dynamics Between Ferroelectric And Antiferroelectric Domains In A Pbzro3-Based Ceramic, Zhongming Fan, Fei Xue, Goknur Tutuncu, Long-Qing Chen, Xiaoli Tan

Materials Science and Engineering Publications

The antiferroelectric-ferroelectric phase transition in PbZrO3-based oxides is of both fundamental and practical importance. In ceramics in which such a transition readily occurs, the antiferroelectric and the ferroelectric phases often coexist in individual grains with a coherent interphase interface. In this work, the electric biasing in situ transmission electron microscopy technique is employed to directly observe a unique microstructural dynamic when ferroelectric and antiferroelectric domains are driven by a moderate electric field to interact. It is found that, under monotonic loading, the ferroelectric domain grows until it is blocked by the ferroelectric-antiferroelectric interface. At the same time, a kink is ...


Ultrahigh Elastically Compressible And Strain-Engineerable Intermetallic Compounds Under Uniaxial Mechanical Loading, Gyuho Song, Vladislav Borisov, William Meier, Mingyu Xu, Keith J. Dusoe, John T. Sypek, Roser Valentí, Paul C. Canfield, Seok-Woo Lee Jun 2019

Ultrahigh Elastically Compressible And Strain-Engineerable Intermetallic Compounds Under Uniaxial Mechanical Loading, Gyuho Song, Vladislav Borisov, William Meier, Mingyu Xu, Keith J. Dusoe, John T. Sypek, Roser Valentí, Paul C. Canfield, Seok-Woo Lee

Ames Laboratory Accepted Manuscripts

Intermetallic compounds possess unique atomic arrangements that often lead to exceptional material properties, but their extreme brittleness usually causes fracture at a limited strain of less than 1% and prevents their practical use. Therefore, it is critical for them to exhibit either plasticity or some form of structural transition to absorb and release a sufficient amount of mechanical energy before failure occurs. This study reports that the ThCr2Si2-structured intermetallic compound (CaFe2As2) and a hybrid of its structure (CaKFe4As4) with 2 µm in diameter and 6 µm in height can exhibit superelasticity with strain up to 17% through a reversible, deformation-induced ...


Connection Between Mott Physics And Crystal Structure In A Series Of Transition Metal Binary Compounds, Nicola Lanatà, Tsung-Han Lee, Yong-Xin Yao, Vladan Stevanović, Vladimir Dobrosavljević Mar 2019

Connection Between Mott Physics And Crystal Structure In A Series Of Transition Metal Binary Compounds, Nicola Lanatà, Tsung-Han Lee, Yong-Xin Yao, Vladan Stevanović, Vladimir Dobrosavljević

Ames Laboratory Accepted Manuscripts

The choice that a solid system “makes” when adopting a crystal structure (stable or metastable) is ultimately governed by the interactions between electrons forming chemical bonds. Here we analyze six prototypical binary transition metal compounds and shed light on the connection between Mott physics and the behavior of the energy as a function of the spatial arrangement of the atoms in these systems. Remarkably, we find that the main qualitative features of this complex behavior in the Mott phase of these systems can be traced back to the fact that the strong d-electron correlations influence substantially the charge transfer ...


Effects Of Dopants On The Glass Forming Ability In Al-Based Metallic Alloy, Yang Sun, Feng Zhang, Lin Yang, Huajing Song, Mikhail I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho Feb 2019

Effects Of Dopants On The Glass Forming Ability In Al-Based Metallic Alloy, Yang Sun, Feng Zhang, Lin Yang, Huajing Song, Mikhail I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

The effect of dopants on the metallic glass forming ability is usually considered based on the analysis of changes in the liquid structure or thermodynamics. What is missing in such considerations is an analysis of how a dopant changes the properties of the crystal phases which can form instead of the glass. In order to illuminate this aspect we performed molecular dynamics simulations to study the effects of Mg and Sm dopants on the crystal nucleation in Al. The simulation data were found to be consistent with the experimental observations that addition of Mg to Al does not lead to ...


Ultrafast Nonlinear Transparency Driven At A Telecom Wavelength In An Organic Semiconductor System, Joong-Mok Park, Di Cheng, Aaron Patz, Liang Luo, Fadzai Fungura, Ruth Shinar, Kai-Ming Ho, Joseph Shinar, Jigang Wang Feb 2019

Ultrafast Nonlinear Transparency Driven At A Telecom Wavelength In An Organic Semiconductor System, Joong-Mok Park, Di Cheng, Aaron Patz, Liang Luo, Fadzai Fungura, Ruth Shinar, Kai-Ming Ho, Joseph Shinar, Jigang Wang

Ames Laboratory Accepted Manuscripts

Ultrafast laser-induced transparency is demonstrated using femtosecond (fs) pump-probe experiments in the organic P3HT:PCBM (donor:acceptor) blend structure. For above band gap pumping, ultrafast transient signals strongly depend on the probe photon energy. Most intriguingly, for below band gap pumping at 0.95 eV, or 1.3 µm at a telecom wavelength, a huge transmission increase up to 30% only during the laser pulse ∼100 fs is observed as a pump-driven, quasi-instantaneous suppression of absorption for the high photon-energy energy probe beam. We attribute the observed laser-driven transparency to dynamic Franz-Keldysh effect, at least one order of magnitude stronger ...


Mechanisms Of Enhanced Thermal Stability Of Polarization In Lead-Free (Bi 1/2na 1/2) 0.94ba 0.06tio 3/Zno Ceramic Composites, Zhongming Fan, Lin Zhou, Tae-Hoon Kim, Ji Zhang, Shan-Tao Zhang, Xiaoli Tan Feb 2019

Mechanisms Of Enhanced Thermal Stability Of Polarization In Lead-Free (Bi 1/2na 1/2) 0.94ba 0.06tio 3/Zno Ceramic Composites, Zhongming Fan, Lin Zhou, Tae-Hoon Kim, Ji Zhang, Shan-Tao Zhang, Xiaoli Tan

Ames Laboratory Accepted Manuscripts

(Bi 1/2Na 1/2)TiO 3-based solid solutions, one of the major systems of lead-free piezoelectric ceramics, exhibit a low thermal depolarization temperature ( T d~100°C). It was reported that by incorporating 30 mol% ZnO particles to form a ceramic composite of (Bi 1/2Na 1/2) 0.94Ba 0.06TiO 3/ZnO, the depolarization process can be shifted up to ~250 °C. In the present work, a variety of advanced transmission electron microscopy techniques, including in situ heating, annular bright-field, high-angle annular dark-field, geometric phase analysis, energy-dispersive spectrum and electron energy-loss spectroscopy, are employed to investigate the ...


Nonlinearity In The Dark: Broadband Terahertz Generation With Extremely High Efficiency, Ming Fang, Nian-Hai Shen, Wei E. I. Sha, Zhixiang Huang, Thomas Koschny, Costas M. Soukoulis Jan 2019

Nonlinearity In The Dark: Broadband Terahertz Generation With Extremely High Efficiency, Ming Fang, Nian-Hai Shen, Wei E. I. Sha, Zhixiang Huang, Thomas Koschny, Costas M. Soukoulis

Ames Laboratory Accepted Manuscripts

Plasmonic metamaterials and metasurfaces offer new opportunities in developing high performance terahertz emitters and detectors beyond the limitations of conventional nonlinear materials. However, simple meta-atoms for second-order nonlinear applications encounter fundamental trade-offs in the necessary symmetry breaking and local-field enhancement due to radiation damping that is inherent to the operating resonant mode and cannot be controlled separately. Here we present a novel concept that eliminates this restriction obstructing the improvement of terahertz generation efficiency in nonlinear metasurfaces based on metallic nanoresonators. This is achieved by combining a resonant dark-state metasurface, which locally drives nonlinear nanoresonators in the near field, with ...


Lattice Instability During Solid-Solid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson Oct 2018

Lattice Instability During Solid-Solid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson

Aerospace Engineering Publications

The density functional theory was employed to study the stress-strain behavior and elastic instabilities during the solid-solid phase transformation (PT) when subjected to a general stress tensor, as exemplified for semiconducting Si I and metallic Si II, where metallization precedes the PT, so stressed Si I can be a metal. The hydrostatic PT occurs at 76 GPa, while under uniaxial loading it is 11 GPa (3.7 GPa mean pressure), 21 times lower. The Si I → Si II PT is described by a critical value of the phase-field’s modified transformation work, and the PT criterion has only two parameters ...


Magnetic And Electrocatalytic Properties Of Transition Metal Doped Mos2 Nanocrystals, L. M. Martinez, J. A. Delgado, C. L. Saiz, A. Cosio, Y. Wu, D. Villagran, Kinjal Gandha, C. Karthik, I. C. Nlebedim, S. R. Singamaneni Oct 2018

Magnetic And Electrocatalytic Properties Of Transition Metal Doped Mos2 Nanocrystals, L. M. Martinez, J. A. Delgado, C. L. Saiz, A. Cosio, Y. Wu, D. Villagran, Kinjal Gandha, C. Karthik, I. C. Nlebedim, S. R. Singamaneni

Ames Laboratory Accepted Manuscripts

In this paper, the magnetic and electrocatalytic properties of hydrothermally grown transition metal doped (10% of Co, Ni, Fe, and Mn) 2H-MoS2 nanocrystals (NCs) with a particle size 25–30 nm are reported. The pristine 2H-MoS2 NCs showed a mixture of canted anti-ferromagnetic and ferromagnetic behavior. While Co, Ni, and Fe doped MoS2 NCs revealed room temperature ferromagnetism, Mn doped MoS2 NCs showed room temperature paramagnetism, predominantly. The ground state of all the materials is found to be canted-antiferromagnetic phase. To study electrocatalytic performance for hydrogen evolution reaction, polarization curves were measured for undoped and the doped MoS2 NCs. At ...


Reverse-Engineering Of Graphene On Metal Surfaces: A Case Study Of Embedded Ruthenium, Ann Lii-Rosales, Yong Han, Ka Man Yu, Dapeng Jing, Nathaniel Anderson, David Vaknin, Michael C. Tringides, James W. Evans, Michael S. Altman, Patricia A. Thiel Oct 2018

Reverse-Engineering Of Graphene On Metal Surfaces: A Case Study Of Embedded Ruthenium, Ann Lii-Rosales, Yong Han, Ka Man Yu, Dapeng Jing, Nathaniel Anderson, David Vaknin, Michael C. Tringides, James W. Evans, Michael S. Altman, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy, we show that Ru forms metallic nanoislands on graphite, covered by a graphene monolayer. These islands are air-stable, contain 2–4 layers of Ru, and have diameters on the order of 10 nm. To produce these nanoislands two conditions must be met during synthesis. The graphite surface must be ion-bombarded, and subsequently held at an elevated temperature (1000–1180 K) during Ru deposition. A coincidence lattice forms between the graphene overlayer and the Ru island top. Its characteristics—coincidence lattice constant, corrugation amplitude, and variation of carbon lattice appearance ...


Impact Ignition And Combustion Of Micron-Scale Aluminum Particles Pre-Stressed With Different Quenching Rates, Kevin J. Hill, Nobumichi Tamura, Valery I. Levitas, Michelle L. Pantoya Sep 2018

Impact Ignition And Combustion Of Micron-Scale Aluminum Particles Pre-Stressed With Different Quenching Rates, Kevin J. Hill, Nobumichi Tamura, Valery I. Levitas, Michelle L. Pantoya

Materials Science and Engineering Publications

Pre-stressing aluminum (Al) particles by annealing and quenching alters dilatational strain and is linked to increased particle reactivity. The quenching rate associated with pre-stressing is a key parameter affecting the final stress state within the Al particle, with faster quenching rates theoretically favoring a higher, more desirable stress state. Micron scale Al particles are annealed to 573 K, then quenched at different rates (i.e., 200 and 900 K/min), mixed with bismuth oxide (Bi2O3), and the Al + Bi2O3 mixtures are examined under low-velocity, drop-weight impact conditions. Both quenching rates showed increased impact ignition sensitivity (i.e., between 83% and ...


All-Solid-State Asymmetric Supercapacitor Based On Porous Cobalt Selenide Thin Films, Xincheng Zhang, Jiangfeng Gong, Kaixiao Zhang, Weihua Zhu, Jing-Chang Li, Qingping Ding Sep 2018

All-Solid-State Asymmetric Supercapacitor Based On Porous Cobalt Selenide Thin Films, Xincheng Zhang, Jiangfeng Gong, Kaixiao Zhang, Weihua Zhu, Jing-Chang Li, Qingping Ding

Ames Laboratory Accepted Manuscripts

As a significant semiconductor material, cobalt selenide has enormous potential and extensive application prospects in the field of solar cells, photocatalysis and supercapacitor. In this paper, porous CoSe thin films were successfully fabricated on stainless-steel sheet using a facile, effective electrodeposition technique. Electrochemical tests reveal that the specific capacitance reaches as high as 510 F g−1 at the current density of 1 A g−1 with the capacitance retention of 91% over 5000 cycles. An asymmetric all-solid-state supercapacitor is fabricated using CoSe thin film as the positive electrode and activate carbon as the negative electrode. The combined solid device ...


Structures And Magnetic Properties Of Iron Silicide From Adaptive Genetic Algorithm And First-Principles Calculations, Zejin Yang, Shunqing Wu, Xin Zhao, Manh Cuong Nguyen, Shu Yu, Tongqi Wen, Ling Tang, Fuxiang Li, Kai-Ming Ho, Cai-Zhuang Wang Aug 2018

Structures And Magnetic Properties Of Iron Silicide From Adaptive Genetic Algorithm And First-Principles Calculations, Zejin Yang, Shunqing Wu, Xin Zhao, Manh Cuong Nguyen, Shu Yu, Tongqi Wen, Ling Tang, Fuxiang Li, Kai-Ming Ho, Cai-Zhuang Wang

Ames Laboratory Accepted Manuscripts

We performed a systematic search for low-energy structures of binary iron silicide over a wide range of compositions using the crystal structure prediction method based on adaptive genetic algorithm. 36 structures with formation energies within 50 meV/atom (11 of them are within 20 meV) above the convex hull formed by experimentally known stable structures are predicted. Magnetic properties of these low-energy structures are investigated. Some of these structures can be promising candidates for rare-earth-free permanent magnet.


Current Progress And Future Challenges In Rare-Earth-Free Permanent Magnets, Jun Cui, Matthew J. Kramer, Lin Zhou, Fei Liu, Alexander Gabay, George Hadjipanayis, Balamurugan Balasubramanian, David Sellmyer Jul 2018

Current Progress And Future Challenges In Rare-Earth-Free Permanent Magnets, Jun Cui, Matthew J. Kramer, Lin Zhou, Fei Liu, Alexander Gabay, George Hadjipanayis, Balamurugan Balasubramanian, David Sellmyer

Ames Laboratory Accepted Manuscripts

Permanent magnets (PM) are critical components for electric motors and power generators. Key properties of permanent magnets, especially coercivity and remanent magnetization, are strongly dependent on microstructure. Understanding metallurgical processing, phase stability and microstructural changes are essential for designing and improving permanent magnets. The widely used PM for the traction motor in electric vehicles and for the power generator in wind turbines contain rare earth elements Nd and Dy due to their high maximum energy product. Dy is used to sustain NdFeB's coercivity at higher temperature. Due to the high supply risk of rare earth elements (REE) such as ...


Phase Modulation Of (1t-2h)-Mose2/Tic-C Shell/Core Arrays Via Nitrogen Doping For Highly Efficient Hydrogen Evolution Reaction, Shengjue Deng, Fan Yang, Qinghua Zhang, Yu Zhong, Yinxiang Zeng, Shiwei Lin, Xiuli Wang, Xihong Lu, Cai-Zhuang Wang, Lin Gu, Xinhui Xia, Jiangping Tu Jul 2018

Phase Modulation Of (1t-2h)-Mose2/Tic-C Shell/Core Arrays Via Nitrogen Doping For Highly Efficient Hydrogen Evolution Reaction, Shengjue Deng, Fan Yang, Qinghua Zhang, Yu Zhong, Yinxiang Zeng, Shiwei Lin, Xiuli Wang, Xihong Lu, Cai-Zhuang Wang, Lin Gu, Xinhui Xia, Jiangping Tu

Ames Laboratory Accepted Manuscripts

Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase‐ and morphology‐modulated N‐doped MoSe2/TiC‐C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC‐C nanorod arrays serve as the backbone for MoSe2 nanosheets to form high‐quality MoSe2/TiC‐C shell/core arrays. Impressively, continuous phase modulation of MoSe2 is realized on the MoSe2/TiC‐C arrays. Except for the pure 1T‐MoSe2 and 2H‐MoSe2, mixed (1T‐2H)‐MoSe2 nanosheets are achieved in the ...


Two-Dimensional Crystallization Of Poly(N-Isopropylacrylamide)-Capped Gold Nanoparticles, Wenjie Wang, Jack J. Lawrence, Wei Bu, Honghu Zhang, David Vaknin Jun 2018

Two-Dimensional Crystallization Of Poly(N-Isopropylacrylamide)-Capped Gold Nanoparticles, Wenjie Wang, Jack J. Lawrence, Wei Bu, Honghu Zhang, David Vaknin

Ames Laboratory Accepted Manuscripts

Surface-sensitive X-ray reflectivity and grazing incidence small-angle X-ray scattering reveal the structure of polymer-capped-gold nanoparticles (AuNPs that are grafted with poly(N-isopropylacrylamide); PNIPAM–AuNPs) as they self-assemble and crystallize at the aqueous suspension/vapor interface. Citrate-stabilized AuNPs (5 and 10 nm in nominal diameter) are ligand-exchanged by 6 kDa PNIPAM-thiol to form corona brushes around the AuNPs that are highly stable and dispersed in aqueous suspensions. Surprisingly, no clear evidence of thermosensitive effect on surface enrichment or self-assembly of the PNIPAM–AuNPs is observed in the 10–35 °C temperature range. However, addition of simple salts (in this case ...


Spin Momentum–Locked Surface States In Metamaterials Without Topological Transition, Liang Peng, Yuntian Chen, Yihao Yang, Zhiyu Wang, Faxin Yu, Gaofeng Wang, Nian‐Hai Shen, Baile Zhang, Costas M. Soukoulis, Hongsheng Chen Jun 2018

Spin Momentum–Locked Surface States In Metamaterials Without Topological Transition, Liang Peng, Yuntian Chen, Yihao Yang, Zhiyu Wang, Faxin Yu, Gaofeng Wang, Nian‐Hai Shen, Baile Zhang, Costas M. Soukoulis, Hongsheng Chen

Ames Laboratory Accepted Manuscripts

The photonic analogy of the quantum spin Hall Effect, that is, a photonic topological insulator (PTI), is of great relevance to science and technology in optics based on the promise of scattering‐free surface states. The challenges in realizing such scattering‐free surface states in PTIs and other types of symmetry‐protected topological phases are the result of the exact symmetry needed for creating a pair of time reversal pseudo‐spin states or special boundary conditions, wherein the exact symmetry imposes strict requirements on materials or boundary conditions. Here, it is experimentally demonstrated that scattering‐free edge states can be ...


First-Principles Study Of Electronic Structure And Fermi Surface In Semimetallic Yas, Przemyslaw Swatek Jun 2018

First-Principles Study Of Electronic Structure And Fermi Surface In Semimetallic Yas, Przemyslaw Swatek

Ames Laboratory Accepted Manuscripts

In the course of searching for new systems, which exhibit nonsaturating and extremely large positive magnetoresistance, electronic structure, Fermi surface, and de Haas-van Alphen characteristics of the semimetallic YAs compound were studied using the all-electron full-potential linearized augmented-plane wave (FP-LAPW) approach in the framework of the generalized gradient approximation (GGA). In the scalar-relativistic calculation, the cubic symmetry splits fivefold degenerate Y-d orbital into low-energy threefold-degenerate t(2g) and twofold degenerate doublet e(1g) states at Gamma point around the Fermi energy. One of them, together with the threefold degenerate t(1u) character of As-p orbital, render the YAs semimetal with ...


Controlling Optical Polarization Conversion With Ge2sb2te5-Based Phase-Change Dielectric Metamaterials, Wei Zhu, Ruisheng Yang, Yuancheng Fan, Quanhong Fu, Hongjing Wu, Peng Zhang, Nian-Hai Shen, Fuli Zhang May 2018

Controlling Optical Polarization Conversion With Ge2sb2te5-Based Phase-Change Dielectric Metamaterials, Wei Zhu, Ruisheng Yang, Yuancheng Fan, Quanhong Fu, Hongjing Wu, Peng Zhang, Nian-Hai Shen, Fuli Zhang

Ames Laboratory Accepted Manuscripts

Recent progress in the metamaterial-based polarization manipulation of light highlights the promise of novel polarization-dependent optical components and systems. To overcome the limited frequency bandwidth of metamaterials resulting from their resonant nature, it is desirable to incorporate tunability into metamaterial-based polarization manipulations. Here, we propose a dielectric metamaterial for controlling linear polarization conversion using the phase-change characteristic of Ge2Sb2Te5 (GST), whose refractive index changes significantly when transforming from the amorphous phase to the crystalline phase under external stimuli. The polarization conversion phenomena are systematically studied using different arrangements of GST in this metamaterial. The performance of linear polarization conversion and ...


Phase Field Study Of Surface-Induced Melting And Solidification From A Nanovoid: Effect Of Dimensionless Width Of Void Surface And Void Size, Anup Basak, Valery I. Levitas May 2018

Phase Field Study Of Surface-Induced Melting And Solidification From A Nanovoid: Effect Of Dimensionless Width Of Void Surface And Void Size, Anup Basak, Valery I. Levitas

Physics and Astronomy Publications

The size effect and the effects of a finite-width surface on barrierless transformations between the solid (S), surface melt (SM), and melt (M) from a spherical nanovoid are studied using a phase field approach. Melting (SM → M and S → M) from the nanovoid occurs at temperatures which are significantly greater than the solid-melt equilibrium temperature θe but well below the critical temperature for solid instability. The relationships between the SM and M temperatures and the ratio of the void surface width and width of the solid-melt interface, Δ⎯⎯⎯, are found for the nanovoids of different sizes. Below a critical ratio ...


Synthesis And Characterization Of Ca-Doped Lamnaso, Yong Liu, Warren E. Straszheim, Pinaki Das, Farhan Islam, Thomas W. Heitmann, Robert Mcqueeney, David Vaknin May 2018

Synthesis And Characterization Of Ca-Doped Lamnaso, Yong Liu, Warren E. Straszheim, Pinaki Das, Farhan Islam, Thomas W. Heitmann, Robert Mcqueeney, David Vaknin

Ames Laboratory Accepted Manuscripts

We report on our attempt to hole-dope the antiferromagnetic semiconductor LaMnAsO by substitution of the La3+ site by Ca2+. We use neutron and x-ray diffraction, magnetic susceptibility, and transport techniques to characterize polycrystalline (La1−xCax)MnAsO samples prepared by solid-state reaction and find that the parent compound is highly resistant to substitution with an upper limit x≤0.01. Magnetic susceptibility of the parent and the x=0.002(xnom=0.04) compounds indicate a negligible presence of magnetic impurities (i.e., MnO or MnAs). Rietveld analysis of neutron and x-ray diffraction data shows the preservation of both the tetragonal ...


Hedgehog Spin-Vortex Crystal Stabilized In A Hole-Doped Iron-Based Superconductor, William R. Meier, Qing-Ping Ding, Andreas Kreyssig, Sergey Bud’Ko, Aashish Sapkota, Karunakar Kothapalli, Vladislav Borisov, Roser Valentí, Cristian D. Batista, Peter Orth, Rafael M. Fernandes, Alan I. Goldman, Yuji Furukawa, Anna E. Böhmer, Paul C. Canfield Feb 2018

Hedgehog Spin-Vortex Crystal Stabilized In A Hole-Doped Iron-Based Superconductor, William R. Meier, Qing-Ping Ding, Andreas Kreyssig, Sergey Bud’Ko, Aashish Sapkota, Karunakar Kothapalli, Vladislav Borisov, Roser Valentí, Cristian D. Batista, Peter Orth, Rafael M. Fernandes, Alan I. Goldman, Yuji Furukawa, Anna E. Böhmer, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-doped and Co-doped CaKFe 4As 4 based on thermodynamic, transport, structural and ...


An Open-Source Quadrature-Based Population Balance Solver For Openfoam, Alberto Passalacqua, Frédérique Laurent, Ehsan Madadi-Kandjani, Jeffrey C. Heylmun, Rodney O. Fox Feb 2018

An Open-Source Quadrature-Based Population Balance Solver For Openfoam, Alberto Passalacqua, Frédérique Laurent, Ehsan Madadi-Kandjani, Jeffrey C. Heylmun, Rodney O. Fox

Chemical and Biological Engineering Publications

The extended quadrature method of moments (EQMOM) for the solution of population balance equations (PBE) is implemented in the open-source computational fluid dynamic (CFD) toolbox OpenFOAM as part of the OpenQBMM project. The moment inversion procedure was designed (Nguyen et al., 2016) to maximize the number of conserved moments in the transported moment set. The algorithm is implemented in a general structure to allow the addition of other kernel density functions defined on R+, and arbitrary kernels to describe physical phenomena involved in the evolution of the number density function. The implementation is verified with a set of zero-dimensional cases ...


Nucleation Of Stoichiometric Compounds From Liquid: Role Of The Kinetic Factor, Huajing Song, Yang Sun, Feng Zhang, Cai-Zhuang Wang, Kai-Ming Ho, Mikhail I. Mendelev Feb 2018

Nucleation Of Stoichiometric Compounds From Liquid: Role Of The Kinetic Factor, Huajing Song, Yang Sun, Feng Zhang, Cai-Zhuang Wang, Kai-Ming Ho, Mikhail I. Mendelev

Ames Laboratory Accepted Manuscripts

The nucleation rate depends on the free-energy barrier and the kinetic factor. While the role of the free energy barrier is a text-book subject, the importance of the kinetic factor is frequently underestimated. In this study, we applied the mean first-passage time method, to obtain the free-energy landscape and kinetic factor directly from the molecular dynamics (MD) simulations of the nucleation of the face-centered cubic (fcc) phase in the pure Ni and the B2 phases in the N i 50 A l 50 and C u 50 Z r 50 alloys. The obtained data show that while the free-energy barrier ...


Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong Jan 2018

Phase Transitions And Their Interaction With Dislocations In Silicon, Valery I. Levitas, Hao Chen, Liming Xiong

Aerospace Engineering Publications

In this paper, phase transformations (PTs) in silicon were investigated through molecular dynamics (MD) using Tersoff potential. In the first step, simulations of PTs in single crystal silicon under various stress-controlled loading were carried out. Results shows that all instability points under various stress states are described by criteria, which are linear in the space of normal stresses. There is a region in the stress space in which conditions for direct and reverse PTs coincide and a unique homogeneous phase transition (without nucleation) can be realized. Finally, phase transition in bi-crystalline silicon with a dislocation pileup along the grain boundary ...


Charts Based On Big Data From Fluid Dynamics Simulations Provide A Simple Tool To Estimate How Far From Its Source A Specific Blood Stain Can Be Found, Daniel Attinger Jan 2018

Charts Based On Big Data From Fluid Dynamics Simulations Provide A Simple Tool To Estimate How Far From Its Source A Specific Blood Stain Can Be Found, Daniel Attinger

Mechanical Engineering Publications

The bloodstain pattern analyst sometimes has to judge if a given stain could originate from a specific location. A wide range of values of the maximum distance that a blood drop can travel have been reported from experiments, ranging from less than one meter to more than 10 meter. Here we formulate the problem in a fluid dynamics and big data framework. The fluid dynamics is solved with Newton’s classical equation of motion coupled with well‐established models for the gravity and drag forces that bend the trajectories of drops. The parameters screened are the drop size, initial velocity ...


Early Stage Of Oxidation On Titanium Surface By Reactive Molecular Dynamics Simulation, Liang Yang, Cai-Zhuang Wang, Shiwei Lin, Yang Cao, Xiaoheng Liu Jan 2018

Early Stage Of Oxidation On Titanium Surface By Reactive Molecular Dynamics Simulation, Liang Yang, Cai-Zhuang Wang, Shiwei Lin, Yang Cao, Xiaoheng Liu

Ames Laboratory Accepted Manuscripts

Understanding of metal oxidation is very critical to corrosion control, catalysis synthesis, and advanced materials engineering. Metal oxidation is a very complex phenomenon, with many different processes which are coupled and involved from the onset of reaction. In this work, the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics (MD) simulations using a reactive force field (ReaxFF). We show that oxygen transport is the dominant process during the initial oxidation. Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titanium ...


Effects Of Grain Boundary Disorder On Yield Strength, Valery Borovikov, Mikhail I. Mendelev, Alexander H. King Jan 2018

Effects Of Grain Boundary Disorder On Yield Strength, Valery Borovikov, Mikhail I. Mendelev, Alexander H. King

Materials Science and Engineering Publications

It was recently reported that segregation of Zr to grain boundaries (GB) in nanocrystalline Cu can lead to the formation of disordered intergranular films [1,2]. In this study we employ atomistic computer simulations to study how the formation of these films affects the dislocation nucleation from the GBs. We found that full disorder of the grain boundary structure leads to the suppression of dislocation emission and significant increase of the yield stress. Depending on the solute concentration and heat-treatment, however, a partial disorder may also occur and this aids dislocation nucleation rather than suppressing it, resulting in elimination of ...