bluuebunny/crossref_metadata_2025 huggingface dataset:
Reward Expectation Modulates Local Field Potentials, Spiking Activity and Spike-Field Coherence in the Primary Motor Cortex
Authors: An Junmo , Yadav Taruna , Hessburg John P. , Francis Joseph T.
Published: June 2019

Reward modulation (M1) could be exploited in developing an autonomously updating brain-computer interface (BCI) based on a reinforcement learning (RL) architecture. For an autonomously updating RL-based BCI system, we would need a reward prediction error, or a state-value representation from the user’s neural activity, which the RL-BCI agent could use to update its BCI decoder. In order to understand the multifaceted effects of reward on M1 activity, we investigated how neural spiking, oscillatory activities and their functional interactions are modulated by conditioned stimuli related reward expectation. To do so, local field potentials (LFPs) and single/multi-unit activities were recorded simultaneously and bilaterally from M1 cortices while four non-human primates (NHPs) performed cued center-out reaching or grip force tasks either manually using their right arm/hand or observed passively. We found that reward expectation influenced the strength of α (8–14 Hz) power, α-γ comodulation, α spike-field coherence (SFC), and firing rates (FRs) in general in M1. Furthermore, we found that an increase in α-band power was correlated with a decrease in neural spiking activity, that FRs were highest at the trough of the α-band cycle and lowest at the peak of its cycle. These findings imply that α oscillations modulated by reward expectation have an influence on spike FR and spike timing during both reaching and grasping tasks in M1. These LFP, spike, and spike-field interactions could be used to follow the M1 neural state in order to enhance BCI decoding (An et al., 2018; Zhao et al., 2018).
La ansiedad y el aprendizaje de una lengua extranjera desde la perspectiva de adolescentes
Authors: López Montero Rosberly
Published: June 2019

Este trabajo analiza los factores más comunes que le producen ansiedad a un grupo de adolescentes a la hora de aprender inglés como lengua extranjera en un programa perteneciente al proyecto de Acción Social “ED-2884” de la Sede del Pacífico de la Universidad de Costa Rica. El instrumento empleado en este estudio está basado en la escala para ansiedad en el aula de lengua extranjera (FLCAS, por sus siglas en inglés), elaborado por Horwitz et al. (1986). El estudio indica que la ansiedad por el aprendizaje de un idioma es mayormente producida por el habla espontánea y la presión por obtener buenas calificaciones, mientras que los exámenes de comprensión auditiva y equivocarse no pareciera generar problema para estos aprendices.
Colonizar con la mirada
Authors: Gil-Fernández Rosalía
Published: June 2019

El propósito de este artículo es visualizar y analizar sí la mirada hegemónica hacia la mujer, establecida durante la conquista latinoamericana aún se prolonga en la contemporaneidad, y sí esta mirada, perpetúa un discurso de poder estructurado e impuesto mediante técnicas específicas de sujeción y apropiación, que han contribuido en la construcción de una subjetividad marginada.La propuesta es que la mirada que produce desigualdades podría revertirse por medio de la divulgación de las voces de la otredad, como una posible resistencia al poder colonial, reflejado en la Colonialidad del Poder que prevalece en la modernidad. Palabras clave: mirada, poder, mujer, cuerpo, colonia.
El Rol del estudiante en el fenómeno del Compromiso Académico en Educación Superior
Authors: Maluenda Albornoz Jorge Ignacio , Moraga Villablanca Felipe , Díaz Mujica Alejandro
Published: June 2019

El gran interés surgido frente al estudio del Compromiso Académico, debido a su vinculación con el desempeño y el abandono de los estudios universitarios, ha traído como consecuencia la existencia de una investigación prolífera y distintas aproximaciones. El objetivo de este trabajo es analizar las diferencias conceptuales y metodológicas entre las aproximaciones a este fenómeno. Se realiza un ensayo que analiza críticamente las principales líneas de trabajo, las teorías, los conceptos y sus modelos explicativos, así como los potenciales efectos sobre su desarrollo. Se concluye la posibilidad de que, la concepción del Compromiso Académico opere desde un enfoque top-down donde la construcción científica de la teoría, modelos teóricos y conceptos afecte la práctica cotidiana, los significados y marcos de funcionamiento en la educación. Las conceptualizaciones predominantes sobre el Compromiso Académico podrían estar favoreciendo un rol pasivo del estudiante, además de incrementar la responsabilidad de los sistemas educativos sobre la producción de entornos que puedan favorecerlo.
Morphological study of the midbrain tectum in ostrich (Struthio camelus) embryo
Authors: Koushafar Z. , Mohammadpour A.
Published: June 2019

In this study the morphological features of the optic tectum in ostrich embryo were studied macroscopically and microscopically. After gross anatomical study, fixed specimens of the optic lobes in 30th, 36th and 40th embryonic days were processed for paraffin sections. Sections were stained by Harris haematoxylin and eosin (H&E), Luxol Fast Blue/Cresyl Echt Violet and Malory PTAH dyes. The optic lobes had large volumes even on the 30th embryonic day and increased proportionally to age. The optic lobe consisted of two parts: gray matter (outer) and white matter (inner). The first external layer of the optic lobe e.g. molecular layer consisted of neural fibres, neuroglia and scarce small neurons. The most common appearance of the optic lobes was characterised by small to medium-sized neurons (rounded to pyramid-shaped with large and pale nucleus consistong of obvious nucleoli arranged in three layers whose thickness increased in the deeper one) supported by neuroglia. Larger size neurons and occasionally multipolar neurons were presented in the interior compared with these layers. The lateral mesencephalic nucleus was detectable in the optic lobe base even on 30th embryonic day and was composed of few multipolar neurons supported by neuroglia. The tectal ventricles were lined with simple cuboidal ciliated ependymal cells in the embryonic period. As embryonic age increased, the ratio of tectal ventricle volume to its thickness decreased. Special stainings showed that Nissl bodies and myelin fibres, also glial fibres were available from the 30th embryonic day and that their density, especially myelin fibres density, increased with age.
Computational study of Mg insertion into amorphous silicon: advantageous energetics over crystalline silicon for Mg storage
Authors: Legrain Fleur , Malyi Oleksandr I. , Tan Teck L. , Manzhos Sergei
Published: June 2019

We show in a theoretical density functional theory study that amorphous Si (a-Si) has more favorable energetics for Mg storage compared to crystalline Si (c-Si). Specifically, Mg and Li insertion is compared in a model a-Si simulation cell. Multiple sites for Mg insertion with a wide range of binding energies are identified. For many sites, Mg defect formation energies are negative, whereas they are positive in c-Si. Moreover, while clustering in c-Si destabilizes the insertion sites (by about 0.1/0.2 eV per atom for nearest-neighbor Li/Mg), it is found to stabilize some of the insertion sites for both Li (by up to 0.27 eV) and Mg (by up to 0.35 eV) in a-Si. This could have significant implications on the performance of Si anodes in Mg batteries.
Beyond “Train-the-Trainer:” A Preliminary Report on a New Scaffolding Strategy for Science Communication Workshop Dissemination
Authors: Alpert Carol Lynn
Published: June 2019

This paper reports on the development and results to date of a new strategy to disseminate a well-validated, successful science communication workshop program to multiple campuses hosting National Science Foundation (NSF) Research Experience for Undergraduates or REU-like research programs. The REU Science Communication Workshop program (REU SCW) is based on the premise that the most effective pedagogy for science communication skills development is one in which students practice iteratively using their own research material, with expert coaching and facilitated peer feedback. After testing several models for widespread dissemination, the most promising capacity-building strategy is one that scaffolds the traditional “train-the-trainer” approach with a new “piggyback” professional development model.
Proliferation and Osteogenic Differentiation of Mesenchymal Stem Cells on Biodegradable Calcium-deficient Hydroxyapatite Tubular Bacterial Cellulose Composites
Authors: Favi Pelagie , Dhar Madhu , Neilsen Nancy , Benson Roberto
Published: June 2019

Advanced biomaterials that mimic the structure and function of native tissues and permit stem cells to adhere and differentiate is of paramount importance in the development of stem cell therapies for bone defects. Successful bone repair approaches may include an osteoconductive scaffold that permits excellent cell adhesion and proliferation, and cells with an osteogenic potential. The objective of this study was to evaluate the cell proliferation, viability and osteocyte differentiation of equine-derived bone marrow mesenchymal stem cells (EqMSCs) when seeded onto biocompatible and biodegradable calcium-deficient hydroxyapatite (CdHA) tubular-shaped bacterial cellulose scaffolds (BC-TS) of various sizes. The biocompatible gel-like BC-TS was synthesized using the bacterium Gluconacetobacter sucrofermentans under static culture in oxygen-permeable silicone tubes. The BC-TS scaffolds were modified using a periodate oxidation to yield biodegradable scaffolds. Additionally, CdHA was deposited in the scaffolds to mimic native bone tissues. The morphological properties of the resulting BC-TS and its composites were characterized using scanning electron microscopy. The ability of the BC-TS and its composites to support and maintain EqMSCs growth, proliferation and osteogenic differentiation in vitro was also assessed. BC-TS and its composites exhibited aligned nanofibril structures. MTS assay demonstrated increasing proliferation and viability with time (days 1, 2 and 3). Cell-scaffold constructs were cultured for 8 days under osteogenic conditions and the resulting osteocytes were positive for alizarin red. In summary, biocompatible and biodegradable CdHA BC-TS composites support the proliferation, viability and osteogenic differentiation of EqMSCs cultured onto its surface in vitro, allowing for future potential use for tissue engineering therapies.
Nanostructured Ceramic and Ceramic-Polymer Composites as Dual Functional Interface for Bioresorbable Metallic Implants
Authors: Johnson Ian , Tian Qiaomu , Liu Huinan
Published: June 2019

Millions of medical implants and devices (e.g., screws, plates, and pins) are used each year worldwide in surgery, and traditionally the components have been limited to permanent metals (e.g., stainless steel, titanium alloys) and polyester-based absorbable polymers. Because of clinical problems associated with these traditional materials, a novel class of biodegradable metallic materials, i.e., magnesium-based alloys, attracted great attention and clinical interests. Magnesium (Mg) is particularly attractive for load-bearing orthopedic applications because it has comparable modulus and strength to cortical bone. Controlling the interface of Mg with the biological environment, however, is the key challenge that currently limits this biodegradable metal for broad applications in medical devices and implants. This paper will particularly focus on creating nanostructured interface between the biodegradable metallic implant and surrounding tissue for the dual purposes of (1) mediating the degradation of the metallic implants and (2) simultaneously enhancing bone tissue regeneration and integration. Nanophase hydroxyapatite (nHA) is an excellent candidate as a coating material due to its osteoconductivity that has been widely reported. Applying nHA coatings or nHA containing composite coatings on Mg alloys is therefore promising in serving the needed dual functions. The composite of nHA and poly(lactic-co-glycolic acid) (PLGA) as a dual functional interface provides additional benefits for medical implant applications. Specifically, the polymer phase promotes interfacial adhesion between the nHA and Mg, and the degradation products of PLGA and Mg neutralize each other. Our results indicate that nHA and nHA/PLGA coatings slow down Mg degradation rate and enhance adhesion of bone marrow stromal cells, thus promising as the next-generation multifunctional implant materials. Further optimization of the coatings and their interfacial properties are still needed to bring them into clinical applications.
Correlation of Stress Relaxation and Microstructure Change in Polycrystalline Thin Films on Substrates: Au on Si <100> at RT
Authors: Vermeulen A. C. , Delhez R. , Mittemeijer E. J.
Published: June 2019

Stress relaxation in polycrystalline layers can be explained by processes, in which the microstructure plays a dominant role. The microstructure itself may also be subjected to changes. With X-ray diffraction information about both the stress and the microstructure can be obtained without destroying the specimen and without disturbing the stress relaxation process.

In this paper a model system is studied: Au on Si<100>. The specimens showed a simultaneous decrease of macrostress and dislocation density with time at room temperature. This could be interpreted on the basis of a model founded on thermally activated dislocation motion. It followed that the grain size is an important parameter for the change of the dislocation density.
The Modified Gibbs-Wulff Construction and Critical Nucleus Morphology at an Interface
Authors: Lee J. K. , Choy J. H. , Choi Y.
Published: June 2019

The conditions for the equilibrium shape of a second-phase particle nucleating either at a planar interface or at a spherically curved interface are reviewed under the assumption that the interfacial structure of the nucleation site has a torque of an appropriate strength. The results are then incorporated into the modified Gibbs-Wulff construction in order to demonstrate a graphical representation of both the equilibrium shape and the free energy barrier for heterogeneous nucleation.
Initial Evolution of Cobalt Silicides in The Cobalt/Amorphous-Silicon Thin Film System
Authors: Miura Hideo , Ma En , Thompson Carl V.
Published: June 2019

The initial phase formation sequence for reactions in cobalt/ amorphous-silicon multi-layer thin films has been investigated using a combination of differential scanning calorimetry, thin film X-ray diffraction, and transmission electron microscopy. Multilayer thin films with various overall atomic concentration ratios and various bilayer thicknesses were used in this study. It was found that crystalline CoSi is always the first phase to nucleate in the interdiffused amorphous layer which preexisted at the as-deposited coba It/amorphous-si licon interface. The CoSi nucleates at temperatures as low as about 530 K, but does not grow until the next phase, which is Co2 Si when excess Co is available, starts to nucleate and grow. The activation energy of the CoSi nucleation was found to be 1.-6±0.1 eV.
On the Diffusion Behaviour in Stressed Ni-Zr Couples
Authors: Mazzone G. , Montone A. , Antisari M. Vittori
Published: June 2019

Solid state reactions at the interface of bulk Ni-Zr couples have been induced at several temperatures by compressive plastic deformation. The reaction product is an amorphous phase whose thickness increases with applied load and sample temperature. In addition, similar samples have been thermally reacted in order to measure the thermal interdiffusion coefficent in the same conditions. Measurements on stressed couples show that the interdiffusion coefficent (several orders of magnitude larger than the corresponding thermal value) follows a dual regime Arrhenius behaviour. The activation energy is independent of load and of the order of 0.2 eV in the low temperature regime extending up to 550 K. A different behaviour characterized by a single value of the activation energy in the whole temperature range has been observed in thermally treated samples.
Molecular Dynamics Simulation of the Effect of Interfaces in Melting and Solid-State Amorphization
Authors: Wolf Dieter , Yip Sidney
Published: June 2019

A newly developed molecular dynamics code was used to study the effect of free surfaces, grain boundaries and voids in the process of melting. It was found that conventional “thermodynamic melting” occurs via nucleation of the liquid at the extended defects with subsequent growth into the crystal. In the absence of interfaces, or when this transition is kinetically hindered, however, a second type of melting transition can be triggered by an elastic instability first described by Born (“mechanical melting”). It is suggested that the distinct characteristic features associated with the two types of melting are actually observed in solid-state amorphization experiments. A unified thermodynamics-based description, in the form of an extended phase diagram, of melting and solid-state amorphization is proposed which brings out the parallels between these two phenomena and suggests that their underlying causes are apparently the same. By investigating the effect of surface stresses on the structure and elastic behavior of free-standing thin films, we discuss how these concepts need to be modified in thin-film and small-grained materials.
Effect of Annealing on the Dielectric Properties and Microstructure of Tantalum Oxide T14in Films
Authors: Chun Chang Hwan , Kim Geun Hong , Yi Kyoung-Soo
Published: June 2019

Effects of heat treatments on the dielectric properties of tantalum oxide thin films(250Å) deposited on the p-Si substrates by RF reactive sputtering were investigated. The leakage current density was considerably reduced from 10-9 to 10-12A/μm2 at an electric field of 2MV/cm after rapid thermal annealing in O2 at 1000°C, while little leakage reduction was observed after annealing at 500°C.

The structural changes of tantalum oxide thin film after annealing were examined using high resolution transmission electron microscopy. The leakage reduction after annealing can be attributed to crystallization and reoxidation of the amorphous tantalum oxide thin film.
Phase Transformations in Sputtered Ni-Ti Film: Effects of Heat Treatment and Precipitates
Authors: Busch J. D. , Berkson Mitchell H. , Johnson A. D.
Published: June 2019

This research investigated the influence of heat treatment and precipitation on the phase transformation temperatures of sputter-deposited nickel-titanium films. Films 5 to 10 microns thick were subjected to isochronal and isothermal heat treatments in vacuum. Four-point resistance measutements were made and the TP, TR, Ma, and Mc temperatures identified. The correlation between transformation temperatures and the film's microstructure was studied using transmission electron microscopy. Existence of Ti2Ni and Ti11Ni14 precipitates was seen to adversely influence the phase transformation temperatures. It was concluded that precipitate-free film is preferable for mechanical actuator applications.
Structural and Electrical Properties of Titanium-Nickel Films Deposited Onto Silicon Substrates
Authors: Collen Kathleen R. , Ellis Arthur B. , Busch J. D. , Johnson A. D.
Published: June 2019

Thin films of the shape memory alloy NiTi have been sputter-deposited onto ptype silicon substrates. Films that are initially amorphous may be crystallized by vacuum annealing. The crystalline films exhibit the B2->B19′ phase change associated with the shape memory effect while remaining in contact with the silicon substrate. Transition temperatures were determined by resistance measurements and x-ray diffraction. The NiTi - Si contacts are diodes, as evidenced by their current-voltage characteristics; however, the effect of the phase change on the barrier height could not be determined.
How Strong is the Electron Correlation in Conjugated Polymers
Authors: Wu C. Q.
Published: June 2019

Correlation effects on the band gap are studied to get the strength of electron interactions in conjugated polymers. In the presence of an additional electron or hole, the correlation induces a polarization cloud around the additional particle, which forms a polaron. For the excitation energy of a polaron, there is a competition between a loss of correlation energy in the ground state and a gain of polarization energy due to the scattering through the additional particle. The calculation has been done both for the Hubbard Model and long-range interactions. For polyacetylene, we obtain the on-site repulsion U = 4.4 eV and the nearest-neighbor interaction V = 0.8 eV. The polarization effect of Σ electrons and theoretical results on the effective interaction are discussed. The strength of effective interactions should depends on physical processes.
Energetics of Epitaxial Monolayers Deposited on a (111) Surface of an FCC Crystal: Application to a Cu Monolayer on Au(111)
Authors: Zypman F. R. , Fonseca L. F. , Blum L.
Published: June 2019

We study a system in which a monolayer of atoms of one kind are deposited epitaxialy onto a (111) surface of an FCC crystal using the Tight Binding approximation. First, we obtain an analytical expression for the energy spectrum of the system. This turns out to be an interesting result from the mathematical standpoint due to its simplicity, and to the fact that no artificial boundary conditions (like periodic or vanishing) were imposed on the wave functions. All the spectral information is shown to be contained in the roots of a quadratic polynomial. Then, for Cu on Au, we study the density of states and wave function decay out from the outer layer. This is done at zero and finite voltage applied between an electrode and bulk Gold, immersed in an electrolyte. This problem is of interest in electrochemistry.
Electrochemical Heteroepitaxial Growth of Molecular Films on Ordered Substrates
Authors: Last Julie A. , Hooks Daniel E. , Yip Christopher M. , Ward Michael D.
Published: June 2019

Electrocrystallization of the organic superconductor bis(ethylenedithio)tetrathiafulvalene triiodide, (ET)2I3, on a highly ordered pyrolytic graphite (HOPG) substrate has been visualized using in situ atomic force microscopy (AFM). Previous studies have revealed the formation of a coincident epitaxial monolayer with a structure identical to that of a (001) layer of the superconducting beta phase of this material prior to bulk crystal growth. However, the symmetry of the HOPG substrate leads to domain boundary defects during self assembly of the separately growing domains. The number of defects is significantly reduced after an electrochemical annealing process in which the potential is cycled about the monolayer deposition potential. Annealing of these films is important if they are to be used in electronic devices as the defects may serve as barriers to electron transport in the two-dimensional layers.

In addition to (ET)2I3, monolayer growth also has been visualized during electrocrystallization of (ET)2ReO4 on HOPG. The role of coincident epitaxy with HOPG in the monolayer formation and molecular orientation will be discussed.

Structurally modified substrates have also been investigated. Studies of the electrocrystallization of (ET)2I3 on HOPG, thermally treated to produce well-defined monolayer depth pit structures, have demonstrated that (ET)2I3 monolayer growth can occur inside the pit structures. The presence of monolayer domain boundaries within large pits indicates that multiple, independent nucleation events can occur in the pits, providing an opportunity to determine critical nucleation sizes by varying the pit dimensions. Recently we have discovered that MoS2 substrates can be electrochemically etched, giving rise to monolayer deep triangular pits.
Electrolyte Electroreflectance of Boron Phosphide (BP)
Authors: Schroten E. , Goossens A. , Schoonman J.
Published: June 2019

An electrolyte electroreflectance study has been performed on boron phosphide thin films epitaxially grown on silicon (100) substrates. To our knowledge, this paper is the first report on the electrolyte electroreflectance spectrum of BP. All our boron phosphide of 1.5 μm thick films show a pronounced peak at the energy 4.25 eV, indicating a critical point in the valence or conduction band of the semiconductor. Photoreflectance measurements confirm these results. The 4.25 eV energy level is much lower than previously reported direct bandgap values of BP. The electrolyte electroreflectance spectrum of much thinner layers shows, besides the 4.25 eV peak, some other features at still lower incident photon energies caused by interference effects.
Electrochemical Deposition of Metals on Semiconductors
Authors: Oskam Gerko , Long John G. , Nikolova Maria , Searson Peter C.
Published: June 2019

The general concepts governing the electrochemical deposition of metal films on semiconductors are discussed, and recent results on the fabrication of Schottky junctions consisting of silicon electrodeposited with platinum, copper and gold are presented. In order to obtain good adherent metal films, the density of nuclei should be high and the films should be grown at low current densities where the charge transfer process is rate limiting. This situation can be realized using potential controlled electrochemical deposition. For metal deposition on silicon, the surface should be pretreated in HF to dissolve the oxide layer. Furthermore, the surface should be stable during deposition which can be achieved by tailoring the deposition solutions and by using electrochemical deposition at negative potentials. It is shown that by using this approach, n-type silicon / Pt, Au, and Cu Schottky junctions can be fabricated of a quality comparable to that of junctions prepared by sputter and vapor deposition techniques.
Magnetoresistive Properties of Quasiperiodic Metallic Multilayers
Authors: Shima M. , Salamanca-Riba L. , Swartzendruber L. J.
Published: June 2019

Fibonacci 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

Multilayered 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

In 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

Electrolytically 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

An 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

Boron-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

The 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

GaAs 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

A 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

Development 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

Dielectric 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

In 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

A 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

Elastic 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

Results 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

We 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

Magnesium 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

Pulsed 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

The 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

We 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.