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Iowa State University

Series

Materials Science and Engineering

2013

Materials Science and Engineering

Articles 1 - 9 of 9

Full-Text Articles in Physics

Low-Energy Planar Magnetic Defects In Bafe2as2: Nanotwins, Twins, Antiphase, And Domain Boundaries, Suffian N. Khan, Aftab Alam, Duane D. Johnson Nov 2013

Low-Energy Planar Magnetic Defects In Bafe2as2: Nanotwins, Twins, Antiphase, And Domain Boundaries, Suffian N. Khan, Aftab Alam, Duane D. Johnson

Ames Laboratory Publications

In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study, using density-functional theory, the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated nanotwins (twin nuclei), and spin excitations proposed and/or observed. These nanoscale defects have a very low surface energy (22–210 m Jm−2), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries—making a uniform-moment picture inappropriate for long-range magnetic order in real samples. Nanotwins explain features in measured pair distribution functions so should ...


Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant Jul 2013

Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant

Iowa State University Patents

A multi-channel polarized thermal emitter (PTE) is presented. The multi-channelPTE can emit polarized thermal radiation without using a polarizer at normal emergence. The multi-channel PTE consists of two layers of metallic gratings on a monolithic and homogeneous metallic plate. It can be fabricated by a low-cost soft lithography technique called two-polymer microtransfer molding. The spectral positions of the mid-infrared (MIR) radiation peaks can be tuned by changing the periodicity of the gratings and the spectral separation between peaks are tuned by changing the mutual angle between the orientations of the two gratings.


Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson Mar 2013

Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson

Ames Laboratory Publications

Formation energies of native defects in Bi2(TexSe3−x), with comparison to ideal Bi2Te2S, are calculated in density-functional theory to assess transport properties. Bi2Se3 is found to be n type for both Bi- and Se-rich growth conditions, while Bi2Te3 changes fromn to p type going from Te- to Bi-rich conditions, as observed. Bi2Te2Se and Bi2Te2S are generally n type, explaining observed heavily doped n-type behavior in most samples. A (0/−) transition level at 16 meV above valence-band maximum ...


Stability Maps To Predict Anomalous Ductility In B2 Materials, Ruoshi Sun, Duane D. Johnson Mar 2013

Stability Maps To Predict Anomalous Ductility In B2 Materials, Ruoshi Sun, Duane D. Johnson

Ames Laboratory Publications

While most B2 materials are brittle, a new class of B2 (rare-earth) intermetallic compounds is observed to have large ductility. We analytically derive a necessary condition for ductility (dislocation motion) involving ⟨111⟩ versus ⟨001⟩ slip and the relative stability of various planar defects that must form. We present a sufficient condition for antiphase boundary bistability on {11¯0} and {112¯} planes that allows multiple slip systems. From these energy-based criteria, we construct two stability maps for B2 ductility that use only dimensionless ratios of elastic constants and defect energies, calculated via density functional theory. These two conditions fully explain and ...


Manufacturing Method Of Photonic Crystal, In Sung Park, Tae Ho Lee, Jin Ho Ahn, Rana Biswas, Kristen P. Constant, Kai-Ming Ho, Jae-Hwang Lee Jan 2013

Manufacturing Method Of Photonic Crystal, In Sung Park, Tae Ho Lee, Jin Ho Ahn, Rana Biswas, Kristen P. Constant, Kai-Ming Ho, Jae-Hwang Lee

Iowa State University Patents

A manufacturing method of a photonic crystal is provided. In the method, a high-refractive-index material is conformally deposited on an exposed portion of a periodic template composed of a low-refractive-index material by an atomic layer deposition process so that a difference in refractive indices or dielectric constants between the template and adjacent air becomes greater, which makes it possible to form a three-dimensional photonic crystal having a superior photonic bandgap. Herein, the three-dimensional structure may be prepared by a layer-by-layer method.


Site-Preference And Valency For Rare-Earth Sites In (R-Ce)2fe14b Magnets, Aftab Alam, Mahmud Khan, R. William Mccallum, Duane D. Johnson Jan 2013

Site-Preference And Valency For Rare-Earth Sites In (R-Ce)2fe14b Magnets, Aftab Alam, Mahmud Khan, R. William Mccallum, Duane D. Johnson

Ames Laboratory Publications

Rare-earth (R) permanent magnets of R2Fe14B have technological importance due to their high energy products, and they have two R-sites (Wyckoff 4f and 4g, with four-fold multiplicity) that affect chemistry and valence. Designing magnetic behavior and stability via alloying is technologically relevant to reduce critical (expensive) R-content while retaining key properties;cerium, an abundant (cheap) R-element, offers this potential. We calculate magnetic propertiesand Ce site preference in ( R1−xCex) 2Fe14B [R = La,Nd] using density functional theory (DFT)methods—including a DFT + U scheme to treat localized 4f-electrons. Fe moments compare well ...


Chapter 14 – Evolutionary Algorithms Applied To Electronic-Structure Informatics: Accelerated Materials Design Using Data Discovery Vs. Data Searching, Duane D. Johnson Jan 2013

Chapter 14 – Evolutionary Algorithms Applied To Electronic-Structure Informatics: Accelerated Materials Design Using Data Discovery Vs. Data Searching, Duane D. Johnson

Ames Laboratory Publications

We exemplify and propose extending the use of genetic programs (GPs) – a genetic algorithm (GA) that evolves computer programs via mechanisms similar to genetics and natural selection – to symbolically regress key functional relationships between materials data, especially from electronic structure. GPs can extract structure–property relations or enable simulations across multiple scales of time and/or length. Uniquely, GP-based regression permits “data discovery” – finding relevant data and/or extracting correlations (data reduction/data mining) – in contrast to searching for what you know, or you think you know (intuition). First, catalysis-related materials correlations are discussed, where simple electronic-structure-based rules are revealed ...


Communication: Structure, Formation, And Equilibration Of Ensembles Of Ag-S Complexes On An Ag Surface, Selena M. Russell, Yousoo Kim, Da-Jiang Liu, James W. Evans, Patricia A. Thiel Jan 2013

Communication: Structure, Formation, And Equilibration Of Ensembles Of Ag-S Complexes On An Ag Surface, Selena M. Russell, Yousoo Kim, Da-Jiang Liu, James W. Evans, Patricia A. Thiel

Chemistry Publications

We have utilized conditions of very low temperature (4.7 K) and very low sulfur coverage to isolate and identify Ag-S complexes that exist on the Ag(111) surface. The experimental conditions are such that the complexes form at temperatures above the temperature of observation. These complexes can be regarded as polymeric chains of varying length, with an Ag4S pyramid at the core of each monomeric unit. Steps may catalyze the formation of the chains and this mechanism may be reflected in the chain length distribution.


Anisotropic Coarsening: One-Dimensional Decay Of Ag Islands On Ag(110), Yong Han, Selena M. Russell, Anthony R. Layson, Holly L. Walen, Chad D. Yuen, Patricia A. Thiel, James W. Evans Jan 2013

Anisotropic Coarsening: One-Dimensional Decay Of Ag Islands On Ag(110), Yong Han, Selena M. Russell, Anthony R. Layson, Holly L. Walen, Chad D. Yuen, Patricia A. Thiel, James W. Evans

Chemistry Publications

Scanning tunneling microscopy studies show that coarsening of arrays of rectangular single-layer Ag islands on Ag(110) at 220 K and below occurs by one-dimensional (1D) decay of narrower islands, which maintain roughly constant width in the 〈001〉 direction. Adatoms mainly detach from the island ends with 〈001〉 step edges. 1D decay derives from the absence of corner rounding diffusion from 〈001〉 to 〈1̅ 10〉 edges and from inhibited nucleation of new layers on 〈1̅ 10〉 edges. In contrast, rounding from 〈1̅ 10〉 to 〈001〉 edges is active. The island decay rate exhibits an unexpectedly low effective Arrhenius energy due ...