bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetoresistive Properties of Quasiperiodic Metallic Multilayers
Authors: Shima M. , Salamanca-Riba L. , Swartzendruber L. J. 
Published: June 2019

ABSTRACTFibonacci Ni/Cu multilayers were fabricated by electrodeposition for the first time. The deposition of these quasiperiodic as well as periodic multilayers was fully controlled by a computer. X-ray diffraction spectra from a quasiperiodic multilayer built up from blocks of Ni(8ML)/Cu(4.5ML) and Ni(8ML)/Cu(9ML) indicate that the multilayer is of good quality. Since a Fibonacci multilayer has a quasiperiodic nature, the magnetoresistance effect in this system is expected to give more information about the mechanism for magnetic interlayer coupling in the GMR effect. The magnetic and magnetoresistive properties of the quasiperiodic multilayer were compared with those of two periodic multilayers having the equivalent layer thicknesses as the blocks composing the quasiperiodic multilayer. The magnetic and electrical properties of the quasiperiodic multilayer are not the weighted average of the two periodic multilayers.
Electrochemical Processing of Layered Composite Coatings of Nickel - Aluminum - Alumina / Alumina - Yttria Stabilized Zirconia
Authors: Barmak K. , Banovic S. W. , Chan H. M. , Friedersdorf L. E. , Harmer M. P. , Marder A. R. , Petronis C. M. , Puerta D. G. , Susan D. F. 
Published: June 2019

ABSTRACTMultilayered coatings of single and dual particle metal matrix composites, with or without ceramic overlayers, have been produced by a novel combination of electrochemical deposition (electroplating and electrophoretic deposition) and reaction bonding. The coatings contain the following layers in a variety of combinations deposited on Ni substrates: (i) electroplated composites of Ni with Al and/or alumina particles, (ii) precursor Al + A12O3 + yttria stabilized ZrO2 transformed into A12O3 + yttria stabilized ZrO2 by the reaction bonding method, and (iii) yttria stabilized ZrO2. In order to determine the appropriate processing parameters for the multilayered coatings, uniform one-layer coatings were deposited and characterized. We find that in the dual particle Ni-Al-Al2O3 coatings the volume percent of the particles does not show a dependence on deposition current density. However, volume percent alumina in these coatings has a strong dependence on the amount of this particle in the plating bath, while the volume percent Al shows only a weak dependence on its bath content. Comparison of the deposition behavior of these dual particle with single particle coatings, containing Al or alumina only, reveals that the presence of Al in the bath interferes with the codeposition of alumina. This interference, however, is not reciprocal. When coatings containing Al are annealed, Ni and Al react to form a solid solution of Al in Ni (γ) or a two phase mixture of this solid solution and the intermetallic, Ni3Al, (γ-γ') depending on the annealing temperature. Finally, we find that the formation of the reaction bonded alumina plus yttria stabilized zirconia layer requires the oxidation resistance afforded by aluminum in the underlying electroplated layer.
Characterization of High Strength Cu/Ag Multilayered Composites
Authors: Zhai Qing , Kong Dan , Morrone Augusto , Ebrahimi Fereshteh 
Published: June 2019

ABSTRACTIn this study, electrodeposition was employed to produce Cu-Ag multilayered nanocomposites using a single-bath cyanide solution. The silver and the copper layers were applied by electroless deposition and galvanostatic electrodeposition methods, respectively. The as-deposited composite showed a very high strength, which was increased upon annealing at 104°C. Annealing at 149°C caused the strength to drop to a level comparable to the strength of electrodeposited pure copper specimens. In this paper, the effect of heat treatment on the mechanical properties and structure of Cu-Ag multilayered nanocomposites is discussed.
Thermal Stability Of Electrodeposited Nanocrystalline Ni-45%Fe Alloys
Authors: Czerwinski F. , Li H. , Megret F. , Szpunar J. A. , Clark D. G. , Erb U. 
Published: June 2019

ABSTRACTElectrolytically deposited nanocrystalline Ni-45%Fe alloys, composed of γ (f.c.c.) phase, were annealed at 573 and 673 K for time periods up to 20 h in an inert atmosphere of argon. The evolutions of crystallographic texture, grain size, and microhardness were analyzed as a function of annealing parameters. The initial grains, approximately 5 nm in size increased after annealing up to 10–20 nm, however, the growth kinetics and the final grain size depended on the temperature. A correlation was found between the grain size and alloy microhardness. The phase composition was unstable and during annealing the α(b.c.c) phase was detected to precipitate from the γ matrix. The texture of γ phase, consisted of two fibre components of <111> and <200>, and evolved at high temperatures. Although the detailed changes depended on the annealing temperature, in general, the <111> component became stronger at the expense of the <200> component.
Electrochemical Atomic Force Microscopy Study of the Dissolution Kinetics of 304 Stainless Steel
Authors: Mckrell T. J. , Galligan J. M. 
Published: June 2019

ABSTRACTAn electrochemical atomic force microscope (ECAFM) has been employed to observe, in situ, the topographical and electrical changes that occur on 304 stainless steel as a function of an electrical potential. The concurrent acquisition of a polarization curve and topographical data allows direct correlation of variations in the surface roughness with the electrochemical characteristics of the passivation process. Also, the large AFM scan size, employed in this study, allows for the delineation and determination of the interdependence of the surface kinetics at various regions of the surface. Simultaneous measurements of topographical and electrical changes at these regions have established a correspondence of the competing kinetics between the reactions of dissolution and passivation. This provides a way to relate chemical surface reactions to surface topography.
AC and DC Polarization and Cyclic Voltammetric Behavior of Boron-Doped CVD Diamond IN 0.5M NaCl Solution
Authors: Ramesham R. , Rose M. F. 
Published: June 2019

ABSTRACTBoron-doped diamond has been deposited over a Mo substrate by microwave plasma CVD using methane and hydrogen. Boron doping of diamond has been achieved in situ by using a solid boron source while growing the diamond. Impedance spectroscopy of diamond in 0.5 M NaCl solution has been studied. We have observed two time constants at the diamond/solution interface. Solution resistance was found to be constant irrespective of the electrode in the same electrolyte. DC polarization techniques such as linear and Tafel polarization have been used to evaluate the doped diamond/Mo and Mo for corrosion resistance characteristics interms of charge-transfer coefficients and corrosion rate. Cyclic voltammetry has been used to evaluate the doped diamond/Mo to study the background current response and the redox kinetics of ferri/ferrocyanide in 0.5M NaCl solution.
Characterization of Etching Processes on CU Surfaces
Authors: Nakakura C. Y. , Phanse V. M. , Zheng G. , Altman E. I. 
Published: June 2019

ABSTRACTThe etching of single crystal and polycrystalline Cu surfaces by halogens was studied using temperature programmed desorption (TPD), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). For Br2 and Cl2 on Cu(100) and polycrystalline Cu, the etching mechanism could be characterized as a two step process: 1) formation of a bulk Cu(I) halide, and 2) removal of the halide by sublimation. In all cases the first step was found to be adsorption rate limited. Halide formation was observed to consume Cu atoms from the step edge and thus etching can be considered the reverse of step flow growth. While STM showed that Cl2 reacts isotropically with steps on Cu(100), the rate of CuBr formation was observed to be sensitive to the local adsorbate structure at the step edge. For Cl2, it was found that halide removal could be characterized as a simple bulk sublimation process independent of the structure of the underlying Cu. In contrast, a CuBr desorption peak at temperatures lower than anticipated from bulk vapor pressure data was observed. The presence of narrowly spaced steps on the Cu surface was observed to stabilize this low-temperature desorption peak.
Integrated GaAs Diode Technology for Millimeter and Submillimeter-wave Components and Systems
Authors: Crowe Thomas W. , Hesler Jeffrey L. , Bishop William L. , Bowen Willie E. , Bradley Richard F. , Kamaljeet Saini , Marazita Steven M. , Porterfield David W. 
Published: June 2019

ABSTRACTGaAs Schottky barrier diodes remain a workhorse technology for submillimeter-wave applications including radio astronomy, chemical spectroscopy, atmospheric studies, plasma diagnostics and compact range radar. This is because of the inherent speed of these devices and their ability to operate at room temperature. Although planar (flip-chip and beam-lead) diodes are replacing whisker contacted diodes throughout this frequency range, the handling and placement of such small GaAs chips limits performance and greatly increases component costs. Through the use of a novel wafer bonding process we have fabricated and tested submillimeter-wave components where the GaAs diode is integrated on a quartz substrate along with other circuit elements such as filters, probes and bias lines. This not only eliminates the cost of handling microscopically small chips, but also improves circuit performance. This is because the parasitic capacitance is reduced by the elimination of the GaAs substrate and the electrical embedding impedance seen by the diodes is more precisely controlled. Our wafer bonding process has been demonstrated through the fabrication and testing of a fundamental mixer at 585 GHz (Tmix < 1200K) and a 380 GHz subharmonically pumped mixer (Tmix < 1000K). This paper reviews the wafer bonding process and discusses how it can be used to greatly improve the performance and manufacturability of submillimeter-wave components.
Thermochemistry of Substituted Perovskites in the NaTixNb1-xO3-0.5x System
Authors: Xu Hongwu , Navrotsky Alexandra , Balmer M. Lou , Su Yali 
Published: June 2019

AbstractA suite of perovskite phases with the compositions NaTixNb1-xO3-0.5x, 0 ≤ x ≤ 0.2, has been synthesized for the first time using the sol-gel method. Rietveld analysis of powder XRD data reveals that with increasing Ti content, the orthorhombic perovskite structure becomes more cubic-like, as evidenced by the smaller differences among its three cell parameters. Enthalpies of formation of the synthesized phases from the constituent oxides and from the elements have been determined by drop solution calorimetry into molten 3Na2O·4MoO3 solvent at 974 K. As Ti4+ substitutes for Nb5+, the formation enthalpies become less exothermic in a nearly linear manner. This behavior suggests that the Ti→Nb substitution destabilizes the perovskite structure, presumably because of the concomitant occurrence of O2- vacancies, which compensate the charge imbalance between Ti4+ and Nb5+ in the structure.
Microstructural Characterization of Sintered Ba(Mg ⅓ Ta ⅔)O3 Materials by Transmission Electron Microscopy and Convergent Beam Electron Diffraction
Authors: Steeds J. W. , Lin I-N. 
Published: June 2019

AbstractDevelopment of high performance dielectric materials is required to facilitate the trend towards miniaturization of microwave communications circuits. A novel two-step sintering process has been found that enhances the value of (Q-factor) (frequency) (QF)product of Ba(Mg ⅓ Ta ⅔)O3 (BMT). Detailed examination of samples densified in this way gives not only details of the grain size, defect content and state of order of the ordered perovskite grains but also reveals the presence of a number of previously unreported phases. These new phases have been examined by TEM using energy dispersive X-ray analysis to give them approximate chemical composition and convergent beam electron diffraction to determine their crystallography. Large unit cells are found which are evidently related to compounds studied previously in the x 3 BaMnO - system. The results will be discussed in relation to the enhanced performance of the materials.
Dielectric Properties and Microstructure of BaTiO3 Ceramics
Authors: Park Dae-Chul , Itoh Jun-ichi , Sakaguchi Isao , Ohashi Naoki , Yano Toyohiko , Haneda Hajime 
Published: June 2019

AbstractDielectric properties and microstructure were investigated in BaTiO3 ceramics with various additives, Ho2O3, MgO, Ho2O3/MgO, and La2O3. The dielectric constants were increased up to ∼4000 and ∼3000 at 25°C in the 1 mol% Ho-doped and 0.5 mol% Mg-doped BaTiO3 materials, respectively. The BaTiO3 material codoped with 3 mol% Ho + 1.5 mol% Mg led to increase dielectric constant up to ∼6000 at 25°C and the dielectric constant peak around Curie temperature was suppressed at temperature range of from 25°C to 125°C. The size of BaTiO3 grains depended on the content and kind of an additive. Core-shell grains and secondary phase were also dependent on an additive. Core-shell grains were formed completely in Ho-doped BaTiO3 except for 0.5 mol%, but the structure was little observed in Mg- and La-doped BaTiO3 material. Codoped BaTiO3 also formed the core-shell grains.
Calculations of the Electronic and Atomic Structure and Diffusion of Point Defects in KNbO3 Perovskite Crystals and Relevant KTN Solid Solutions
Authors: Eglitis R. I. , Kotomin E. A. , Borstel G. 
Published: June 2019

AbstractIn this paper we review our recent achievements in large scale computer simulations of point defects in advanced perovskite crystals. We have calculated the defect migration energies in the KNbO3 cubic phase using quantum chemical method of the Intermediate Neglect of Differential Overlap (INDO) and classical shell model (SM). The migration energies for the O vacancy obtained by means of these two quite different methods are reasonably close (0.68 eV and 0.79 eV, respectively) and also agree with the only experimental estimate available (ca. 1 eV). Atomic relaxations calculated by these two methods also agree quite well. We used INDO method for a large-scale modeling of the atomic and electronic structure of KNbxTa1-xO3 (KTN) perovskite solid solutions. Results for periodic defect model (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO3 reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of this displacement is close to the EXAFS observation (0.27 a.u.).
The Structure and Stability of Twist Boundaries in SrTiO3 First Principles
Authors: Astala Roope K. , Bristowe Paul D. 
Published: June 2019

AbstractA first principles density funtional computational method has been used to investigate the atomic stucture and energy of various distinct forms of the σ = 5(001) twist grain boundary in SrTiO3. The study focuses on four non-stoichiometric geometries which are all found to be stable to be the most stable. The grain boundary energies are computed as a function of TiO2 chemical potential and these define the limits of stability. The computed volume expansions are consistent with experimental observation and the in plane relaxations lower the boundary symmetry.
Elastic Deformations during Phase Transition in Freestanding BaTiO3 Thin Films.
Authors: Nair Jaya P. , Stavitski Natalie , Zon Ilya , Gartsman Konstantin , Lubomirsky Igor 
Published: June 2019

AbstractElastic deformations during phase transition in freestanding BaTiO3 thin films were investigated. BaTiO3 films were prepared by sol-gel technique or RF magnetron sputtering on silicon substrates, covered by randomly oriented 120 nm thick Al2O3. The as-deposited films were under tensile stress of 100-170 MPa and did not show neither pyroelectric nor piezoelectric properties. Partial substrate removal caused the freestanding films to expand laterally by 0.3-0.5% and corrugate. Dielectric constant of the freestanding films (620±10) was found to be significantly higher than that of the substrate supported films (110±20). The freestanding films showed detectable piezoelectric effect, which indicated that the lateral expansion was originated from the substrate-suppressed cubic-tetragonal phase transition.
Annealing of Radiation Defects in X-Irradiated LiBaF3
Authors: Kulis Peteris , Rogulis Uldis , Springis Maris , Tale Ivars , Veispals Aris , Groza Andis , Ziraps Valters 
Published: June 2019

AbstractResults of application of the glow rate technique GRT for analysis of the activation energy of thermostimulated annealing of X-ray created F-type color centers in LiBaF3 crystals, pure and containing hetero-valence oxygen centers are presented. It is shown that depending on impurity composition in crystal two alternative mechanisms are involved in annealing of color centers. It is proposed that either the anion vacancy governed migration of F- centers resulting in recombination with complementary defects, or the thermal delocalization of radiation created fluorine (Fi) interstitials captured by anti-structure defects followed by recombination with all kinds of complementary F- type centers are responsible for the recombination of radiation defects above RT.
Increase of Magnetic Transition Temperatures by Reduction of Local Disorder for Perovskite Manganites
Authors: Dabrowski B. , Chmaissem O. , Mais J. , Kolesnik S. , Jorgensen J.D. , Short S. 
Published: June 2019

AbstractWe report the synthesis of Sr1-xCaxMnO3 and La0.5Ba0.5MnO3 perovskites over extended cation and oxygen composition ranges and describe the dependence of their phase stability on the tolerance factor t = t(x,T,σ) that is a function of composition, temperature, and oxygen content. We show that magnetic transition temperatures depend strongly on the tolerance factor and charge disorder while dependence on the structural disorder is less important. By reducing charge and structural disorder we have significantly increased the Curie and Neel temperatures for perovskite manganites.
Thermoelastic Properties of (Mg,Fe)SiO3 Perovskite
Authors: Kiefer Boris , Stixrude Lars 
Published: June 2019

AbstractMagnesium rich (Mg1-x,Fex perovskite is thought to be the most abundant mineral in the earth's lower mantle between 660 km and 2900 km depth. We discuss (mg,Fe) solid solutions and their elastic properties at lower mantle pressures. The diffrences of the elastic constants between the Mg-endmember and the iron bearing perovskite with x=0.25 are used to predict the compositional contribution to lateral variations of elastic wave-velocities at high pressures. These predictions are compared and discussed in the context of seismic observations.
Influence of Vanadium Doping on Structural and Ferroelectric Properties of Laser Ablated SrBi2Ta2O9 Thin Films
Authors: Das Rasmi R. , Bhattacharya P. , Pérez W. , Katiyar Ram S. 
Published: June 2019

AbstractPulsed laser deposition technique was used to fabricate SrBi2Ta2O9 (SBT) thin films with partial replacement of penta-valent vanadium ion. In this report, we have doped certain concentrations (0, 5, 10, 15 %) of vanadium at Ta-site of SBT thin films and study their influence on the structural and electrical characteristics. Thin films were grown on platinized silicon substrates using an excimer laser (KrF, 248 nm) with an energy density of ∼ 2.5 J/cm2. Xray diffraction studies confirmed the c-axis suppression of the films at lower processing temperature and at higher annealing temperatures. The decrease in the lattice parameter with vanadium doping was attributed to the smaller ionic radii of vanadium in comparison to Ta. Raman modes of SBT thin films shifted to higher frequencies upon vanadium incorporation at Ta-site. The extra Raman mode observed around ∼860 cm-1, was attributed due to the octahedron stretching vibration in the presence of vanadium at the center of octahedral cage. SBT thin films with 5% V doping exhibit enhanced ferroelectric properties, and the ferroelectric properties were degraded for higher vanadium concentration. The SBT thin films show dielectric constant of about ∼258 with tangential loss of 0.02 at a frequency of 100 kHz. Dielectric constant decreases with increase in V-concentration and attributed to the interdiffusion of bismuth into platinum electrode. The leakage current density of the films was also increased upon vanadium incorporation in SBT thin films.
Epitaxial Perovskite LaVO3/(Ba,Sr)TiO3/(Pb,La)(Zr,Ti)O3/(La,Sr)CoO3 Heterostructures for Ferroelectric Field Effect Memory Devices
Authors: Choi Woong , Sands Tim 
Published: June 2019

AbstractThe ferroelectric field effect was demonstrated in epitaxial perovskite LaVO3/(Ba,Sr)TiO3/(Pb,La)(Zr,Ti)O3/(La,Sr)CoO3 heterostructures grown on (001) SrTiO3 single crystal substrates by pulsed laser deposition. A high degree of c-axis orientation and strong in-plane texture revealed by x-ray diffraction indicated the epitaxial crystallographic relationships between the layers. The heterostructure showed optimal ferroelectric hysteresis with remanent polarizations over 30 μC/cm2. The capacitance measurement as a function of voltage coupled with the measurement of channel resistance revealed the formation of a depletion layer in the semiconducting LaVO3. A ratio of ON- to OFF-state channel resistance of up to 2.5 was observed.
Direct Electron Beam Processing Of Semiconductor Nanostructures
Authors: Park Yeonjoon , Zhao Rian , Specht Petra , Weber Eicke R. 
Published: June 2019

AbstractWe used a high current density focused electron beam to modify a GaAs substrate. To avoid any oxidation or carbon contamination problem, an in-situ electron gun, combined with III-V molecular beam epitaxy (MBE) machine, was used. By changing the substrate temperature and the electron beam dwell time on each spot, different sizes of thermal irradiation marks were created. Fabricated spot-diameters in the sub-micrometer range suggest the possible utilization of this process for novel applications with the MBE growth technique.
Ab Intio Simulations of Quatum Transport: Si Clusters and Fullerene Chains
Authors: Roland Christopher , Meunier Vincent , Larade Brian , Taylor Jeremy , Guo Hong 
Published: June 2019

AbstractThe I-V characteristics of small Sin clusters and short C20 chains between atomistic Al leads were calculated using a new ab initio transport code based on a nonequilibrium Greens function formalism. All of the Si diaplay metallic I-V characteristics with typical conductances ranging between tow and three (units Go = 2e2/h). The transport properties of these molecular devices may be understood in terms of both the bandstructure ofelectrodes, and the molecular levels of the clusters as modified by the lead environment. Turning to the short C20 chains, these behave as short C20 chains, these behave as short nanowires whose tranmission depends sensitively on the orientation and distance between the individual C20 molecules. Transport through the molecular chains is accompained by a significant amount of charge transfer, which however remains localized at the electrode/molecular interface.