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Full-Text Articles in Engineering

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho Jun 2017

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho

Gary Tuttle

A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.


Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles Jun 2017

Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles

Gary Tuttle

We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3thin films. CrxBi2−xTe3 thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2−xTe3. When x = 0.14 and 0.29,ferromagnetism appears in CrxBi2−xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration ...


A New Method For Strengthening Gold, Alan M. Russell, Kai Xu, L. Scott Chumbley, James Parks, Joel Harringa May 2017

A New Method For Strengthening Gold, Alan M. Russell, Kai Xu, L. Scott Chumbley, James Parks, Joel Harringa

Alan M. Russell

Metal-metal composites were first produced in a copper matrix in the 1970’s, and they have since been produced in several other binary metal systems. This strengthening technique reinforces a ductile metal matrix with a ductile metal second phase. In some binary systems, this technique confers extraordinarily high strength and hardness while still maintaining low electrical resistivity. This article reports on the first gold matrix metal-metal composite, which was produced by deformation processing a 90%Au-10%Ag powder compact. The Au-Ag specimen studied had an ultimate tensile strength of 550 MPa and an electrical resistivity only 8% higher than that ...


Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles Mar 2016

Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles

Deborah L. Schlagel

Gd5(Six Ge 1−x)4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3 Ge 2.7 and Gd5Si1.4 Ge 2.6. We have investigated the first order and second orderphase transition temperatures of these samples using magnetic moment vs. temperature andmagnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of ...


The (111) Surface Of Naau2: Structure, Composition, And Stability, Emma Jane Kwolek, Roladn Widmer, Oliver GröNing, Okan Deniz, Holly L. Walen, Chad D. Yuen, Wenyu Huang, Deborah L. Schlagel, Mark Wallingford, Patricia A. Thiel Mar 2016

The (111) Surface Of Naau2: Structure, Composition, And Stability, Emma Jane Kwolek, Roladn Widmer, Oliver GröNing, Okan Deniz, Holly L. Walen, Chad D. Yuen, Wenyu Huang, Deborah L. Schlagel, Mark Wallingford, Patricia A. Thiel

Deborah L. Schlagel

The (111) surface of single-crystal NaAu2 is a model for catalytically active, powdered NaAu2. We prepare and characterize this surface with a broad suite of techniques. Preparation in ultrahigh vacuum consists of the traditional approach of ion bombardment (to remove impurities) and thermal annealing (to restore surface order). Both of these steps, however, cause loss of sodium (Na), and repeated treatments eventually trigger conversion of the surface and near-surface regions to crystalline gold. The bulk has a limited ability to repopulate the surface Na. Under conditions where Na depletion is minimized, electron diffraction patterns are consistent with the bulkterminated structure ...


The (111) Surface Of Naau2: Structure, Composition, And Stability, Emma Jane Kwolek, Roladn Widmer, Oliver GröNing, Okan Deniz, Holly L. Walen, Chad D. Yuen, Wenyu Huang, Deborah L. Schlagel, Mark Wallingford, Patricia A. Thiel Mar 2016

The (111) Surface Of Naau2: Structure, Composition, And Stability, Emma Jane Kwolek, Roladn Widmer, Oliver GröNing, Okan Deniz, Holly L. Walen, Chad D. Yuen, Wenyu Huang, Deborah L. Schlagel, Mark Wallingford, Patricia A. Thiel

Deborah L. Schlagel

The (111) surface of single-crystal NaAu2 is a model for catalytically active, powdered NaAu2. We prepare and characterize this surface with a broad suite of techniques. Preparation in ultrahigh vacuum consists of the traditional approach of ion bombardment (to remove impurities) and thermal annealing (to restore surface order). Both of these steps, however, cause loss of sodium (Na), and repeated treatments eventually trigger conversion of the surface and near-surface regions to crystalline gold. The bulk has a limited ability to repopulate the surface Na. Under conditions where Na depletion is minimized, electron diffraction patterns are consistent with the bulkterminated structure ...


Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles Mar 2016

Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles

Deborah L. Schlagel

Gd5(Six Ge 1−x)4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3 Ge 2.7 and Gd5Si1.4 Ge 2.6. We have investigated the first order and second orderphase transition temperatures of these samples using magnetic moment vs. temperature andmagnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of ...


Growth And Characterisation Of Gd5(Sixge1−X)4 Thin Film, Ravi L. Hadimani, Cajetan Ikenna Nlebedim, Y. Melikhov, David C. Jiles Dec 2015

Growth And Characterisation Of Gd5(Sixge1−X)4 Thin Film, Ravi L. Hadimani, Cajetan Ikenna Nlebedim, Y. Melikhov, David C. Jiles

Ravi L. Hadimani

We report for the first time successful growth of magnetic thin films containing the Gd5(Six Ge1−x)4 phase, which is expected to show giant magnetocaloric properties. The film wasdeposited by Pulsed Laser Deposition (PLD) on a (001) silicon wafer at 200  °C from a polycrystalline Gd5Si2.09 Ge 1.91 target prepared by arc melting. PLD was achieved using a femto second laser with a repetition rate of 1 kHz, and a pulse energy of up to 3.5 mJ. The average film thickness was measured to be 400 nm using a Scanning Electron Microscopy and the composition ...


Microstructure Evolution Of Al–Mg–B Thin Films By Thermal Annealing, Y. Tian, Alan P. Constant, Chester C. H. Lo, James W. Anderegg, Alan M. Russell, J. E. Snyder, P. Molian Sep 2015

Microstructure Evolution Of Al–Mg–B Thin Films By Thermal Annealing, Y. Tian, Alan P. Constant, Chester C. H. Lo, James W. Anderegg, Alan M. Russell, J. E. Snyder, P. Molian

Alan M. Russell

The growth of Al–Mg–B thin films on SiO2/Si(100) substrates was performed by nanosecond pulsed laser deposition at three different substrate temperatures (300 K, 573 K, and 873 K). The as-deposited films were then annealed at 1173 K or 1273 K for 2 h. X-ray photoelectron spectroscopy,x-ray diffraction(XRD), and atomic force microscope were employed to investigate the effects of processing conditions on the composition, microstructure evolution, and surface morphology of the Al–Mg–B films. The substrate temperatures were found to affect the composition of as-deposited films in that the Mg content decreases and C ...


Mechanical Deforming The Alloy Body Having Elongated, Ribbon-Shaped Phases Aligned Along Axis Of The Body, John D. Verhoeven, Timothy W. Ellis, Alan M. Russell, Lawrence L. Jones Sep 2015

Mechanical Deforming The Alloy Body Having Elongated, Ribbon-Shaped Phases Aligned Along Axis Of The Body, John D. Verhoeven, Timothy W. Ellis, Alan M. Russell, Lawrence L. Jones

Alan M. Russell

A high strength, light weight "in-situ" Ti-Y composite is produced by deformation processing a cast body having Ti and Y phase components distributed therein. The composite comprises elongated, ribbon-shaped Ti and Y phase components aligned along an axis of the deformed body.


Aluminum/Alkaline Earth Metal Composites And Method For Producing, Alan M. Russell, Iver E. Anderson, Hyongjune Kim, Andrew E. Freichs Sep 2015

Aluminum/Alkaline Earth Metal Composites And Method For Producing, Alan M. Russell, Iver E. Anderson, Hyongjune Kim, Andrew E. Freichs

Alan M. Russell

A composite is provided having an electrically conducting Al matrix andelongated filaments comprising Ca and/or Sr and/or Ba disposed in the matrixand extending along a longitudinal axis of the composite. The filaments initially comprise Ca and/or Sr and/or Ba metal or alloy and then may be reacted with the Al matrix to form a strengthening intermetallic compound comprising Al andCa and/or Sr and/or Ba. The composite is useful as a long-distance, high voltage power transmission conductor.


A High Specific Strength, Deformation-Processed Scandium-Titanium Composite, Alan M. Russell, Y. Tian, J. D. Rose, T. W. Ellis, L. Scott Chumbley Sep 2015

A High Specific Strength, Deformation-Processed Scandium-Titanium Composite, Alan M. Russell, Y. Tian, J. D. Rose, T. W. Ellis, L. Scott Chumbley

Alan M. Russell

A 59% Sc–41% Ti deformation-processed metal-metal composite was produced by rolling to a true strain of 2.3 at 873 K followed by cold rolling to a total true strain of 3.6. Rolling reduced the original eutectoid microstructure to lamellae of α–Sc and α–Ti with average lamellar thicknesses of 150 nm (Sc) and 120 nm (Ti). The cold-rolled material had an ultimate tensile strength of 942 MPa and a specific strength of 259 J/g. The Sc matrix was oriented with the 〈0001〉 tilted 22° from the sheet normal direction toward the rolling direction, an unusual ...


Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada Feb 2015

Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada

Chemical and Biological Engineering Publications

Magnetotactic bacteria that produce magnetic nanocrystals of uniform size and well-defined morphologies have inspired the use of biomineralization protein Mms6 to promote formation of uniform magnetic nanocrystals in vitro. Small angle X-ray scattering (SAXS) studies in physiological solutions reveal that Mms6 forms compact globular threedimensional (3D) micelles (approximately 10 nm in diameter) that are, to a large extent, independent of concentration. In the presence of iron ions in the solutions, the general micellar morphology is preserved, however, with associations among micelles that are induced by iron ions. Compared with Mms6, the m2Mms6 mutant (with the sequence of hydroxyl/carboxyl containing ...


Metal-Nanowall Grating Transparent Electrodes: Achieving High Optical Transmittance At High Incident Angles With Minimal Diffraction, Ping Kuang, Joong Mok Park, Geyuan Liu, Zhuo Ye, Wai Y. Leung, Sumit Chaudhary, David W. Lynch, Kai-Ming Ho, Kristen P. Constant Jan 2015

Metal-Nanowall Grating Transparent Electrodes: Achieving High Optical Transmittance At High Incident Angles With Minimal Diffraction, Ping Kuang, Joong Mok Park, Geyuan Liu, Zhuo Ye, Wai Y. Leung, Sumit Chaudhary, David W. Lynch, Kai-Ming Ho, Kristen P. Constant

David W. Lynch

A novel architecture has been employed to fabricate transparent electrodes with high conductivity and high optical transmittance at high incident angles. Soft lithography is used to fabricate polymer grating patterns onto which thin metallic films are deposited. Etching removes excess metal leaving tall walls of metal. Polymer encapsulation of the structure both protects the metal and minimizes diffraction. Transmission is dependent upon the height of the walls and encapsulation and varies from 60% to 80% for structures with heights of 1400 nm to 300 nm. In encapsulated structures, very little distortion is visible (either parallel to or perpendicular to standing ...


Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30◦ from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √ 3 times the surface lattice constant, a. Monte Carlo simulations are performed on ...


Deep Brain Transcranial Magnetic Stimulation Using Variable “Halo Coil” System, Y. Meng, Ravi L. Hadimani, Lawrence J. Crowther, Z. Xu, J. Qu Jan 2015

Deep Brain Transcranial Magnetic Stimulation Using Variable “Halo Coil” System, Y. Meng, Ravi L. Hadimani, Lawrence J. Crowther, Z. Xu, J. Qu

Electrical and Computer Engineering Publications

Transcranial Magnetic Stimulation has the potential to treat various neurological disorders non-invasively and safely. The “Halo coil” configuration can stimulate deeper regions of the brainwith lower surface to deep-brain field ratio compared to other coil configurations. The existing “Halo coil” configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current “Halo coil” design along with a graphicaluser interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable “Halo ...


Influence Of Ga-Concentration On The Electrical And Magnetic Properties Of Magnetoelectric Cogaxfe2− Xo4/Batio3 Composite, Yan Ni, Zhen Zhang, Cajetan I. Nlebedim, David C. Jiles Jan 2015

Influence Of Ga-Concentration On The Electrical And Magnetic Properties Of Magnetoelectric Cogaxfe2− Xo4/Batio3 Composite, Yan Ni, Zhen Zhang, Cajetan I. Nlebedim, David C. Jiles

Electrical and Computer Engineering Publications

Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGaxFe2−xO4/BaTiO3composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. An enhancement of the ...


Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Arich menagerie of structures is identified at 5Kfollowing adsorption of lowcoverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their ...


Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles Jan 2015

Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles

Electrical and Computer Engineering Publications

Gd5(Six Ge 1−x)4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3 Ge 2.7 and Gd5Si1.4 Ge 2.6. We have investigated the first order and second orderphase transition temperatures of these samples using magnetic moment vs. temperature andmagnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of the orthorhombic II phase.


Analysis Of Ringing Effects Due To Magnetic Core Materials In Pulsed Nuclear Magnetic Resonance Circuits, Neelam G. Prabhu Gaunkar, N. R. Y. Bouda, Ikenna C. Nlebedim, Ravi L. Hadimani, I. Bulu, K. Ganesan, Y. Q. Song, Mani Mina, David C. Jiles Jan 2015

Analysis Of Ringing Effects Due To Magnetic Core Materials In Pulsed Nuclear Magnetic Resonance Circuits, Neelam G. Prabhu Gaunkar, N. R. Y. Bouda, Ikenna C. Nlebedim, Ravi L. Hadimani, I. Bulu, K. Ganesan, Y. Q. Song, Mani Mina, David C. Jiles

Electrical and Computer Engineering Publications

This work presents investigations and detailed analysis of ringing in a non-resonant pulsednuclear magnetic resonance (NMR) circuit. Ringing is a commonly observed phenomenon in high power switching circuits. The oscillations described as ringing impede measurements in pulsed NMR systems. It is therefore desirable that those oscillations decay fast. It is often assumed that one of the causes behind ringing is the role of the magnetic core used in theantenna (acting as an inductive load). We will demonstrate that an LRC subcircuit is also set-up due to the inductive load and needs to be considered due to its parasitic effects. It ...


Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles Jan 2015

Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles

Electrical and Computer Engineering Publications

We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3thin films. CrxBi2−xTe3 thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2−xTe3. When x = 0.14 and 0.29,ferromagnetism appears in CrxBi2−xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration ...


Thermal Effects On The Magnetic Properties Of Titanium Modified Cobalt Ferrite, Ikenna C. Nlebedim, David C. Jiles Jan 2015

Thermal Effects On The Magnetic Properties Of Titanium Modified Cobalt Ferrite, Ikenna C. Nlebedim, David C. Jiles

Electrical and Computer Engineering Publications

The temperature dependence of the magnetic properties of titanium modified cobalt ferrite is presented. The change of maximum magnetization obtained at H ≈ 2.4 MA/m between any two temperatures increases systematically with composition, which is desirable for applications in devices. Variation in magnetocrystalline anisotropy and coercivity were different from previous studies on cation substituted cobalt ferrite. At lower concentrations, the effect of lower thermal energy dominated the effect of non-magnetic cation substitutions in controlling the anisotropy.The reverse was the case at higher concentrations. The temperature dependence of coercivity is dominated by the contribution of magnetocrystalline anisotropy to coercivity ...


Cu2s3 Complex On Cu(111) As A Candidate For Mass Transport Enhancement, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Christine M. Aikens, Yousoo Kim, Patricia A. Thiel Jan 2015

Cu2s3 Complex On Cu(111) As A Candidate For Mass Transport Enhancement, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Christine M. Aikens, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Sulfur-metal complexes, containing only a few atoms, can open new, highly efficient pathways for transport of metal atoms on surfaces. For example, they can accelerate changes in the shape and size of morphological features, such as two-dimensional nanoclusters, over time. In this study we perform STM under conditions that are designed to specifically isolate such complexes. We find a new, unexpected S-Cu complex on the Cu(111) surface, which we identify as Cu2S3. We propose that Cu2S3 enhances mass transport in this system, which contradicts a previous proposal based on Cu3S3 ...


The (111) Surface Of Naau2: Structure, Composition, And Stability, Emma Jane Kwolek, Roladn Widmer, Oliver GröNing, Okan Deniz, Holly L. Walen, Chad D. Yuen, Wenyu Huang, Deborah L. Schlagel, Mark Wallingford, Patricia A. Thiel Jan 2015

The (111) Surface Of Naau2: Structure, Composition, And Stability, Emma Jane Kwolek, Roladn Widmer, Oliver GröNing, Okan Deniz, Holly L. Walen, Chad D. Yuen, Wenyu Huang, Deborah L. Schlagel, Mark Wallingford, Patricia A. Thiel

Chemistry Publications

The (111) surface of single-crystal NaAu2 is a model for catalytically active, powdered NaAu2. We prepare and characterize this surface with a broad suite of techniques. Preparation in ultrahigh vacuum consists of the traditional approach of ion bombardment (to remove impurities) and thermal annealing (to restore surface order). Both of these steps, however, cause loss of sodium (Na), and repeated treatments eventually trigger conversion of the surface and near-surface regions to crystalline gold. The bulk has a limited ability to repopulate the surface Na. Under conditions where Na depletion is minimized, electron diffraction patterns are consistent with the bulkterminated structure ...


Preface: Special Topic On Supramolecular Self-Assembly At Surfaces, Ludwig Bartels, Karl-Heinz Ernst, Hong-Jun Gao, Patricia A. Thiel Jan 2015

Preface: Special Topic On Supramolecular Self-Assembly At Surfaces, Ludwig Bartels, Karl-Heinz Ernst, Hong-Jun Gao, Patricia A. Thiel

Chemistry Publications

Supramolecular self-assembly at surfaces is one of the most exciting and active fields in Surface Science today. Applications can take advantage of two key properties: (i) versatile pattern formation over a broad length scale and (ii) tunability of electronic structure and transport properties, as well as frontier orbital alignment. It provides a new frontier for Chemical Physics as it uniquely combines the versatility of Organic Synthesis and the Physics of Interfaces. The Journal of Chemical Physics is pleased to publish this Special Topic Issue, showcasing recent advances and new directions.


Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides Dec 2014

Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

Classically, the onset of nucleation is defined in terms of a critical cluster of the condensed phase, which forms from the gradual aggregation of randomly diffusing adatoms. Experiments in Pb/Si(111) at low temperature have discovered a dramatically different type of nucleation, with perfect crystalline islands emerging “explosively” out of the compressed wetting layer after a critical coverage Θc ¼ 1.22 ML is reached. The unexpectedly high island growth rates, the directional correlations in the growth of neighboring islands and the persistence in time of where mass is added in individual islands, suggest that nucleation is a result ...


Microstructure Investigations Of Pt-Modified Γ′-Ni3al + Γ-Ni Coatings On Ni-Based Superalloys, Guanghui Cao, Taoping Ou, Hua Jiang, Alan M. Russell Oct 2014

Microstructure Investigations Of Pt-Modified Γ′-Ni3al + Γ-Ni Coatings On Ni-Based Superalloys, Guanghui Cao, Taoping Ou, Hua Jiang, Alan M. Russell

Alan M. Russell

The microstructure of Pt-modified γ′-Ni3Al + γ-Ni coating on CMSX-4 single-crystal superalloy has been investigated by transmission electron microscopy (TEM). Cross-sectional TEM analyses showed the presence of precipitates in the coating. This precipitate was identified as the hexagonal topologically close-packed (TCP) μ phase with lattice parameters a = 0.473 nm and c = 2.565 nm. The energy-dispersive x-ray (EDX) spectrum of the μ phase suggested a refractory element rich compound comprising the elements Re, W, and Co. Twin domains parallel to (001) were found in the μ phase. The mechanisms of the μ phase and twinning formation were discussed.


The Stability Of Pt Nanofilaments In A Au-Matrix Composite, Kageeporn Wongpreedee, Alan M. Russell Oct 2014

The Stability Of Pt Nanofilaments In A Au-Matrix Composite, Kageeporn Wongpreedee, Alan M. Russell

Alan M. Russell

Au-7 at.% Pt Deformation-processed Metal Metal Composite (DMMC) was isothermally annealed at various times and temperatures. Avrami and Arrhenius relations were used to evaluate the kinetics of the transformation from the initial metastable nanofilamentary microstructure to the equilibrium homogeneous solid solution condition. Results indicated that the activation energy for this transformation was 167 ± 6 kJ/mol. This activation energy is lower than activation energies reported in the literature for planar interface, single crystal Au-Pt diffusion couple experiments. The effects of chemical potential, surface curvature, and strain effects on the empirical activation energies determined in the DMMC of this study are ...


Advances In Deformation Processed Gold Composites, Vladimir Gantovnik, Alan M. Russell, L. Scott Chumbley, Kageeporn Wongpreedee, Dennis Field Oct 2014

Advances In Deformation Processed Gold Composites, Vladimir Gantovnik, Alan M. Russell, L. Scott Chumbley, Kageeporn Wongpreedee, Dennis Field

Alan M. Russell

Conventional metallic composites are comprised of a metal matrix with a ceramic second phase. In recent years, composites have been developed in which both the matrix and the reinforcing phase are ductile metals. In 1998 a 90 vol%Au – 10 vol% Ag metal-metal composite wire was produced and found to possess both high tensile strength (550 MPa) and low electrical resistivity (2.56 m ohm-cm). In that composite, the silver reinforcing phase consisted of sub-micron diameter filaments parallel to the wire axis. This article describes the microstructures, mechanical properties, and electrical resistivity of three gold matrix composites in which the ...


Electrical Transport In Amorphous Semiconducting Almgb14 Films, Y. Tian, G. Li, Joseph Shinar, N. L. Wang, Bruce A. Cook, James W. Anderegg, Alan P. Constant, Alan Mark Russell, J. E. Snyder Oct 2014

Electrical Transport In Amorphous Semiconducting Almgb14 Films, Y. Tian, G. Li, Joseph Shinar, N. L. Wang, Bruce A. Cook, James W. Anderegg, Alan P. Constant, Alan Mark Russell, J. E. Snyder

Alan M. Russell

The electrical transport properties of semiconducting AlMgB14films deposited at room temperature and 573K are reported in this letter. The as-deposited films are amorphous, and they exhibit high n-type electrical conductivity, which is believed to stem from the conduction electrons donated by Al, Mg, and/or Fe impurities in these films. The film deposited at 573K is less conductive than the room-temperature-deposited film. This is attributed to the nature of donor or trap states in the band gap related to the different deposition temperatures.