bluuebunny/crossref_metadata_2025_split huggingface dataset:
'The Role of the Grain Boundary on the Resistivity of Pb(Fe1/2Nb1/2)O3 at Room Temperature
Authors: Lee Sang-Bop , Lee Kwang-Ho , Kim Hwan 
Published: June 2019

AbstractThe effect of changing sintering temperature on the grain boundary properties and the room temperature resistivity (ρRT) of Pb(Fe1/2Nb1/2)O3 (PFN) was investigated. Monitering the temperature dependence of resistivity showed that the ρRT's of 1050°C and 1150°C-sintered specimen were 1011ΩEcm and 104ΩEcm respectively, but the resistivity above 300°C became nearly identical. The previous model, that the low resistivity of PFN is due to the electron hopping between Fe2+ and Fe3+ driven by the reduction of PFN, couldn't explain this phenomenon, and the reconsideration of the Fe reduction revealed that the difference of electron concentration between the 1050°C and 1150°C-sintered specimen couldn't exceed one order of magnitude. The role of the grain boundary was introduced in order to account for this phenomenon.
Calculations of Atomic and Electronic Structure for (100) Surfaces of SrTiO3 Perovskite
Authors: Eglitis R. I. , Heifets E. , Kotomin E. A. , Borstel G. 
Published: June 2019

AbstractWe present and discuss main results of the calculations for the surface relaxation and rumpling of SrTiO3 surfaces with TiO2 and SrO terminations using a wide variety of methods of modern computational physics and chemistry, including the shell model (SM) and ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT). The HF and DFT formalisms with different exchange-correlation functionals are implemented into Crystal-98 computer code using a Gaussian-type basis set. We demonstrate that a hybrid B3PW formalism gives the best results for the bulk SrTiO3 properties. Results are compared with previous ab initio plane-wave LDA calculations and LEED experiments. Our calculations demonstrate an increase of the covalency effects between Ti and O atoms near the surface.
Soft-phonon Dynamics in the Isotopically Induced Ferroelectric Phase Transition of Strontium Titanate
Authors: Yagi Toshirou , Kasahara Masaru , Tsujimi Yuhji , Hasebe Hiroki , Yamaguchi Masashi , Wang Ruiping , Itoh Mitsuru 
Published: June 2019

Abtract:The ferroelectric phase transition of SrTi18O3 (STO8), where the quantum paraelectricity is reduced by the exchange of oxygen atoms 16O for its isotope 18O, has been studied by both Brillouin scattering and Raman scattering. The Brillouin spectra of the c44 and c66 modes in the paraelectric-tetragonal phase show anomalous behavior in the temperature region several degrees above TC accompanied by a central peak. The characteristic shape of the central peak indicates a coupling mechanism between the acoustic mode and an overdamped soft polar mode. Though the ferroelectric soft A2u mode is Raman inactive in the paraelectric phase, it has been observed in the x(yz)-x geometry indicating a local symmetry breaking above TC. Existence of the ferroelectric micro region in the temperature range far above TC is confirmed by the broad spectral component. The soft mode dynamics is concluded in the phase transition of STO18. The doublet spectrum is observed without any of considerable change by the isotope exchange.
Superconductivity Near Ferromagnetism in MgCNi3
Authors: Rosner H. , Weht R. , Johannes M. , Pickett W.E. , Tosatti E. 
Published: June 2019

AbstractSuperconductivity and ferromagnetism have been believed to be incompatible over any extended temperature range until certain specific examples - RuSr2GdCu2O8 and UGe2- have arisen in the past 2-3 years. The discovery of superconductivity above 8 K in MgCNi3, which is primarily the ferromagnetic element Ni and is strongly exchange-enhanced, provides a probable new and different example. This compound is shown here to be near ferromagmnetism, requiring only hole-doping by 12% substitution of Mg by Na or Li. This system will provide the means to prode coupling, and possible coexistence, of these two forms of collective behavior without the requirement of pressure.
Lead Stereochemistry in Incommensurate Ferroelectric Perovskites and in Incommensurate Lead Monoxide
Authors: Baldinozzi Gianguido , Raulot Jean-Marc , Seshadri Ram 
Published: June 2019

AbstractWe have performed Rietveld refinements on neutron and synchrotron diffraction patterns and density functional calculations on various ferroelectric lead perovskites and on α lead monoxide (litharge). These structural data have allowed to shed some light on lead stereochemistry in these compounds. In particular, we discuss the changing in the lead behaviour between the paraelectric cubic phases and the low temperature anti or ferroelectric phases in Pb2CoWO6 and Pb2MgTeO6 (both incommensurate), in Pb2MgWO6 (antiferroelectric) and in PbMg1/3Nb2/3O3 (relaxor). The possible phase transition mechanisms are reviewed and the bonds are compared to those in the aperiodic structure of α-lead monoxide.
Aluminum in Magnesium Silicate Perovskite: Synthesis and Energetics of Defect Solid Solutions
Authors: Navrotsky Alexandra , Schoenitz Mirko , Kojitani Hiroshi , Xu Hongwu , Zhang Jianzhong , Weidner Donald J. , Akaogi Masaki , Jeanloz Raymond 
Published: June 2019

AbstractMgSiO3 - rich perovskite is expected to dominate the Earth's lower mantle (pressures > 25 GPa), with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA+ SiB = MA + MB and SiB = AlB + 0.5 VO. Phase synthesis studies show that both substitutions do occur, and the nonstoichiometric or defect substitution is prevalent along the MgSiO3 - MgAlO2.5 join. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of -0.8±2.2 kJ/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) = MgSi0.9Al0.1O2.95 (perovskite) has a small positive enthalpy of 8.5±4.6 kJ/mol. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite, and may significantly affect the elasticity, rheology and water retention of silicate perovskite in the Earth.
Thermodynamic Properties From Static-Lattice Calculations with Soft Modes
Authors: Ackland Graeme J. , Drummond Neil D. 
Published: June 2019

AbstractWhile phase transition pressures and zero temperature thermodynamic properties can be accurately determined from electronic structure calculation, transition temperatures are more problematic because of the need to sample phase space and quantise vibrations. The quasiharmonic method has proved extremely accurate for calculating thermodynamic properties up to 90% of the melting point without explicit phase space sampling for most materials, but has low temperature divergences for soft mode materials such as perovskites. Here we present a modified quasiharmonic method which avoids these difficulties. Using a simple model system, we demonstrate trends of behaviour in both the classical and quantum limits showing the importance of phonon quantisation in soft-mode behavior.
Ultraviolet-Assisted Pulsed Laser Deposition of Barium Strontium Titanate on Si: Characterization of the Interfacial Layer
Authors: Craciun V. , Craciun D. , Bassim N. D. , Howard J. M. , Singh R. K. 
Published: June 2019

AbstractBarium strontium titanate (BST) thin films were grown directly on Si substrates by the conventional and ultraviolet-assisted pulsed laser deposition techniques. X-ray photoelectron spectroscopy, x-ray diffraction and reflectivity, variable angle spectroscopic ellipsometry, current-voltage, capacitance-voltage, and high-resolution transmission electron microscopy were used to investigate the composition, thickness, and electrical properties of the grown structures. It has been found that at the interface between the Si substrate and the grown dielectric layer, an interfacial layer was always formed. The chemical composition of the layer consisted of SiOx partially mixed with the grown BST, without any evidence of silicate formation.
Particle Size Dependent Magnetoresistance And Magnetothermoelectric Power Of La0.5Pb0.5MnO3 Showing Metal-Insulator Transition
Authors: Banerjee Aritra , Pal S , Chaudhuri B K 
Published: June 2019

AbstractParticle size dependent transport properties (resistivity and thermopower) of La0.5Pb0.5MnO3 has been investigated both in presence and in absence of magnetic field B=0.0-1.5T (maximum). All the samples show metal-insulator transition (MIT) with a peak at the MIT temperature (Tp). Magnetic field decreases the resistivity with an increase in the peak temperature Tp. Particle size, conductivity and Tp of the sample increase with increasing annealing time. High temperature semiconducting (insulating) part of the resistivity curve is divided into two distinct regimes. Resistivity data for T>qθ/2, can be well fitted with the nearest neighbor small polaron hopping (SPH) model. Polaron hopping energy (WH) decreases with increase of particle size. The lower temperature part (Tp>T>qθ/2) of the semiconducting (insulating) regime is found to follow variable range hopping (VRH) model. With the increase of particle size, the temperature range of validity of the VRH mechanism decreases. The low temperature metallic regime (for T<Tp) of the resistivity (both in absence and in presence of field) data fit well with ρ = ρ0 +ρ2.5 T2.5 and transport mechanism in this region is mainly dominated by magnon-carrier scattering (∼T2.5). Particle size has, however, comparatively little effect on Seebeck coefficient (S). In all the samples with different particle sizes, S changes sign below Tp. In contrast to magnetoresistance, application of magnetic field increases S at low temperature (T<Tp) for these samples. Similar to the resistivity results, thermopower data in the metallic phase (both for B=0.0 and 1.5T) can also be analyzed by considering magnon-scattering term along with an additional spin-wave fluctuation term (∼T4).
Ge-rich Si1-XGeX Nanocrystal Formation by the Oxidation of As-Deposited Thin Amorphous Si0.7Ge0.3 Layer
Authors: Yoon Tae-Sik , Kim Ki-Bum 
Published: June 2019

AbstractGe-rich Si1-XGeX nanocrystals are formed by the selective oxidation of Si during the dry oxidation of an amorphous Si0.7Ge0.3 layer. The oxidation kinetics of the alloy film shows the activation energies of linear and parabolic rate constants are about 1.35 and 1.02 eV, respectively, based on the model proposed by Deal and Grove. In addition, as a result of the selective oxidation of Si and Ge pile-up during the oxidation process, Ge-rich Si1-XGeX nanocrystals are formed with the size of 5.6 ± 1.7 nm and the spatial density of 3.6×1011/cm2 at 600°C. At higher temperature of 700 and 800°C, the size of nanocrystal is increased to about 20 nm. The nanocrystals formation by oxidation is thought to be due to higher oxidation rate at grain boundary than at bulk grain. Therefore, the dependence of size on temperature is explained with the grain size determined by solid phase crystallization of amorphous film, oxidation rate, and grain growth.
Nanostructured Polymer Brushes With Reversibly Changing Properties
Authors: Usov Denys , Stamm Manfred , Minko Sergiy , Froeck Christian , Scholl Andreas , Müller Marcus 
Published: June 2019

AbstractWe investigated the interplay between different mechanisms of the lateral and vertical segregation in the synthesized via “grafting from” approach symmetric A/B (where A and B are poly(styrene-co-2,3,4,5,6-pentafluorostyrene) and poly(methylmethacrylate), respectively) polymer brushes upon exposure to different solvents. We used X-ray photoemission electron spectroscopy and microscopy (X-PEEM), AFM, water contact angle measurements, and oxygen plasma etching to study morphology of the brushes. The ripple morphology after toluene (nonselective solvent) revealed elongated lamellar-like domains of A and B polymers alternating across the surface. The dimple-A morphology consisting of round clusters of the polymer A was observed after acetone (selective solvent for B). The top layer was enriched with the polymer B showing that the brush underwent both the lateral and vertical phase segregation. A qualitative agreement with predictions of SCF theory was found.
High Strength Nanoscale Al/Al3Sc Multilayers formed by Interface Reaction
Authors: Phillips M.A. , Clemens B.M. , Nix W.D. 
Published: June 2019

AbstractPolycrystalline Al/Sc multilayer samples are grown via magnetron sputtering. The deposition of Sc onto Al results in significant intermixing between the two components. Substrate curvature, measured in-situ during deposition, reveals behavior similar to that seen in other systems where a slow diffuser is deposited onto a fast diffuser. The multilayer films are further characterized via transmission electron microscopy (TEM), analytical electron microscopy, and X-ray diffraction (XRD), confirming the intermixing and formation of a coherent crystalline phase, likely to be Al3Sc, in the interfacial regions. Nanoindentation hardness tests show that by adding a few percent of Sc to Al films and carefully controlling the location of the Sc, increases in hardness up to 6 times that of a pure Al film can be obtained.
Photoluminescence of Nano-scaled YAG:Ce Phosphor Powders
Authors: Chen In-Gann , Chen Yulin , Hwang Chii-Shyang , Juang F.S. , Chang S.J. , Su Y.K. , Mueller G.O. , Mueller-Mach R. 
Published: June 2019

AbstractFour series of YAG:Ce phosphor powders were synthesized by solid state, co-precipitation, and sol-gel (with two different growth inhibitors, HMDS and PAA respectively) methods, which results in the average particle sizes of 800, 56, 43, and 32 nm respectively. All the nano-scale YAG powders were heat treated below 1000_. Both TEM and XRD results of these nano-scale YAG powders show high degree of crystalline structure. Photoluminescence (PL) characterization shows that the nano-scale YAG phosphor powders emit a higher intensity of luminescence than that of sub-micro sized samples. The effect of different Ce doping level on the PL of (Y3-xCex)Al5O12 shows a maximum at x ∼ 0.01. The Commissiom International de I.Eclairage (CIE) chromaticity coordinates were determined and show different trends of shifts in the resulting PL spectra. Systematic study of the processing parameters characterized by DTA/TGA, XRD, FTIR, and BET will be discussed in detail in the report.
Growth of GaN Nanorods on (0001) Sapphire Substrates by Hydride Vapor Phase Epitaxy
Authors: Kim Hwa-Mok , Kim Doo Soo , Chang Young Wook , Kim Deuk Young , Kang Tae Won 
Published: June 2019

AbstractGaN nanorods were grown on (0001) sapphire substrates by hydride vapor phase epitaxy HVPE) through a self-assemble process. The nanorods were grown at high growth rate, with the c-axis maintained perpendicular to the substrate surface. The dependence of rod diameter and density on growth conditions was systematically investigated. The average diameter was minimized to 80-120 nm and the density of the GaN nanorods was 100×1012 rods/m2.
The Local Electronic structure at Grain Boundaries and Hetero- Interfaces in ZnO Thin Films Grown by Laser Deposition.
Authors: Kvit Alexander , Duscher Gerd , Jin Chunming , Narayan Jagdish 
Published: June 2019

AbstractThe structure and chemistry of interfaces and grain boundaries are known to influence the optical and electrical properties of wide-band gap semiconductors structures. ZnO/AlN/Si(100) heterostructures grown by laser deposition were studied by conventional and high-resolution transmission electron microscopy (HRTEM). The local electronic structure of ZnO grain boundaries was investigated by high resolution Z-contrast imaging using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy in a scanning mode. Zcontrast imaging and EELS were performed simultaneously enabling direct correlations between interface chemistry and local structure to be made. ZnO grain boundaries are composed of a periodic array of a basic structural unit. On the basis of the electron energy-loss near-edge structure (ELNES) of zinc and oxygen edges associated with the ZnO- grain boundaries, the corresponding electronic spectrum was discussed.
Investigation of Oxidation Process of Ultrathin Amorphous and/or Nano-Crystalline Silicon Films
Authors: Mu R. , Wu M. , Liu Y.C. , Ueda A. , Henderson D.O. , Hmelo A. B. , Feldman L.C. 
Published: June 2019

AbstractA series experiments were conducted and reported here on how to employ quartz crystal microbalance (QCM) as a highly mass sensitive sensor to study a-Si film and Si nanocrystals oxidation under ambient oxygen. An experimental calibration procedure has been developed to prevent problems with QCM systems during routine study. With the help of pulsed laser deposition (PLD) technique, one can purposely deposit a thin layer of a heavy element as an insitu calibrant which can be analyzed by RBS quantitatively for QCM. The errors resulted from manufacture's sensor, non-repeatable sensor mounting and handling, temperature cycling history from run to run and so on will be effectively eliminated. Our preliminary results indicate that the oxidation process of a-Si thin films has two stages. A fast oxidation associated with surface and near surface oxidation followed by a slow oxidation. The former is depends on the oxygen vapor pressure in the chamber and the later is oxygen diffusion controlled process.
[ZnSe(dbn)1/2] and [ZnSe(hda)1/2]: Two New Members of Inorganic-Organic Hybrid Semiconductor Nanocomposites Exhibiting A Strong Quantum Confinement Effect
Authors: Huang Xiaoying , Li Jing 
Published: June 2019

AbstractTwo new inorganic-organic hybrid II-VI semiconductor nanostructures have been synthesized by solvothermal reactions. These nanostructures consist of inorganic 2∞[ZnSe] layers and organic bridging diamine molecules as spacers. The crystal structures of [ZnSe(dbn)1/2](1, dbn = 1,4-diaminobutane) and [ZnSe(hda)1/2](2, hda = 1,6-hexanediamine) have been determined by the powder X-ray diffraction method. They are isostructural and crystallize in the orthorhombic crystal system, space group Pbca(No.62), Z = 4. Crystal data for 1: a = 6.646(3), b = 6.473(3), c = 22.31(1) Å, V = 961.2(13) Å3, for 2: a = 6.6252(18), b = 6.4505(17), c = 27.138(7) Å, V = 1159.8(9) Å3. The optical absorption experiments show that both 1 and 2 generate a very large blue shift in the absorption edge (1.5-1.6 eV) due to a strong quantum confinement effect (QCE). Thermogravimetric behavior of both compounds has also been investigated.
Organic Molecules in an Electrical Circuit: An Afm Study of a Negative-Differential-Resistance Molecule
Authors: Ramachandran Ganesh K. , Rawlett Adam M. , Hopson Theresa J. , Nagahara Larry A. , Tsui Raymond K. , Lindsay Stuart M. 
Published: June 2019

Abstract2,5-di(phenylethynyl)-4‘-4“-dithiolate-1-nitrobenzene has been shown to exhibit negative differential resistance (NDR) and spontaneous switching when inserted into inert molecular monolayers between metal contacts. We have used conducting atomic force microscopy to measure the electronic properties of individual dithiolated molecules 2,5-di(phenylethynyl)-4“ 4‘“dithiolate-1-nitrobenzene and 2,5-di(phenylethynyl)-4“4‘“thioacetyl-benzene inserted into an alkanethiol monolayer and chemically bonded to gold nano-contacts to form a covalentlyconnected molecular circuit (bonded contacts). The data show qualitative agreement with previously published results for similar molecules deposited in a nanopore containing several hundred molecules, allowing us to make the important conclusion that the measured negative differential resistance (NDR) is native to the molecule and not an intermolecular phenomenon.
Deterministic Synthesis of ZnO Nanorods
Authors: Heo Y. W. , Varadarajan V. , Kaufman M. , Kim K. , Ren F. , Fleming P. H. , Norton D. P. 
Published: June 2019

AbstractThe deterministic growth of ZnO nanorods using molecular beam epitaxy is reported. The process is catalyst-driven, as single crystal ZnO nanorod growth is realized via nucleation on Ag islands that are distributed on a SiO2-terminated Si substrate surface. Growth occurs at substrate temperatures on the order of 300-500°C. The nanorods exhibit diameters of 15-40 nm and lengths in excess of 1 μm. Nanorod placement can be predefined via location of metal catalyst islands or particles. This, coupled with the relatively low growth temperatures needed, suggests that ZnO nanorods could be integrated on device platforms for numerous applications, including chemical sensors and nanoelectronics.
Automatic Film Formation System For Ultra-Thin Organic Heterostructure By Mass-Controlled Layer-by-layer Sequential Adsorption Method Within One Nanometer Interface Roughness
Authors: Shiratori Seimei , Ito Takahiro 
Published: June 2019

AbstractAn automatic film formation system using an enhanced mass-controlled layer-by-layer sequential adsorption process was newly developed for the fabrication of ultra-thin organic films formed by various polymers, monomers, and inorganic materials. This technique can be applied to both water solutions and volatile solvents. In this process, a quartz crystal microbalance (QCM) was attached to the arm of a robot and the frequency shifts during the adsorption of the materials were monitored. By feeding back the data acquired by the QCM from the deposition to the dipping time, a high quality self-assembly film was produced. As a result, the interface roughness between the layers can be controlled within one nanometer. The cross-sectional TEM (transmission electron microscopy) observation of the films formed by the conventional time controlled dipping method and the newly established mass-controlled dipping method reveals that the interface of the heterostructure of the latter was much smoother than the former. In addition, this automatic dipping system can be applied not only for polyelectrolytes, but also for inorganic materials.
A Novel Patterning Method for Metal-Organic Precursors on a SiOx/Si Substrate Using a Local Electric Field
Authors: Fudouzi Hiroshi , Kobayashi Mikihiko , Shinya Norio , Chikyow Toyohiro , Ahmet Parhat , Naruke Tamami 
Published: June 2019

AbstractThis paper demonstrates a new technique to form a patterned metal-oxide film on a silicon wafer using a local electric field. The idea of the technique involves using an interaction between metal-organic molecules dissolved in a non-polar solvent and a local electric potential field on a substrate. In this paper, an alkoxide and a metal-organic complex were used as metalorganic precursors. The precursor molecules were selectively deposited at the electrified region of the substrate. The deposited precursor films were heated with an electric furnace to form oxide films. Patterned TiOx and Sr-Ti oxide films were formed on a SiOx/Si substrate. These patterned thin films are potentially applicable to electric and optical devices. We believe that this new technique provides a new bottom-up process of molecular assembly for nanofabrication.