bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Surface Atomic Structures for III-V(110)-p(1x1)-Sb(1ML):Chemical Bonding and Electronic Structure
Authors: LaFemina John P. , Duke C. B. , Maflhiot C. 
Published: March 2011

ABSTRACTTight-binding total energy computations are used to examine the chemical bonding and electronic structure for two new minimum-energy surface atomic structures for p(lxl) overlayers of Sb on III-V(110) surfaces. The bonding in each of these structures is unique, having no analog in either the bulk or small molecule coordination chemistry of these materials, and is a phenomenon uniquely associated with the constrained epitaxical growth of the Sb overlayer.
Oxygen Dissociation and Adsorption on Si(100) Reconstructed Surfaces
Authors: Miyamoto Yoshiyuki , Oshiyama Atsushi 
Published: March 2011

ABSTRACTA detailed picture of dissociation and adsorption of oxygen on the Si(100) reconstructed surface is presented on the basis of the total-energy band structure and force calculations within the local density approximation with use of the normconserving nonlocal pseudopotentials. Dissociation of an oxygen molecule occurs at any site on the Si(100) surface. The resulting oxygen atom is adsorbed on several (meta)stable sites depending on which site the preceding molecule dissociates. Peculiar relaxation of the top-layer Si atoms is found upon oxygen adsorption. Calculated vibrational energy and valence density of states in the most stable geometry are reasonably consistent with the experimental data available, i.e., HREELS and UPS. Finally, we have found that an oxygen molecule penetrates through the oxygen-covered Si(100) surface, on which the Si dangling bonds are terminated, and then dissociates in the vicinity of the Si bond center site.
Classical Potentials for Covalent Solids and Clusters: Application to Silicon and Silicon Dioxide
Authors: Chelikowsky James R. , Glassford Keith M. 
Published: March 2011

ABSTRACTPairwise interactions lead to close-packed structures which can be easily described by classical potentials. However, covalent solids such as silicon or silica form open structures which cannot be described by such interactions. We have developed new interatomic force fields which describe the phase stability of silicon and small silicon clusters. We consider three body forces which are adjusted to describe “covalent” →, “metallic” phase transitions instead of small amplitude atomic vibrations. These forces result in a highly accurate phase diagram for crystalline polytypes. Our force filed can be easily modified to describe energies and structures of Sin vapor phase clusters. A key aspect of the cluster problem is the transfer of bond strength from dangling bonds to back bonds. We show as a function of this back bond strength that a covalent →. metallic “first order” structural phase transition occurs in the cluster structures. We also examine the role of three body forces in silica in light of recent pressure measurements. We find that the recently developed pairwise forces are not sufficient to predict accurately the pressure dependence of the structural parameters.
Application of the Embedded Atom Method to Pb and Be
Authors: Karimi M. , Yang Z. , Tibbits P. , Ila D. , Dalins I. , Vidali G. 
Published: March 2011

ABSTRACTWe have derived the embedding energy functional and two body potential of the Embedded Atom Method (EAM) using decreasing exponentials for both the electron density and the two body potential. The embedding function was obtained from the equation of state given by Rose et al. Because of the form of the embedding function, the equilibrium lattice constant, cohesive energy, and bulk modulus are automatically satisfied. The two parameters Φe and γ of the two body potential were determined by fitting to shear modulus and the single vacancy formation energy. Contributions of up to the third nearest neighbors were included in the evaluation of the charge density ρ and the two body potential Φ. The stability and anisotropy of each structure were estimated and compared with the available experimental data.
Calculation of Local Fields for Clusters of Ellipsoids Within the T-Katrix Approach
Authors: Gomez Manuel , Fonseca Luis F. , Cruz Luis , Vargas William 
Published: March 2011

ABSTRACTA T-matrix formalism is used to calculate local electric fields around clusters of prolate ellipsoids in the long wavelength regime. The calculations are performed as a function of interparticle distance as well as angle of orientation. The observed red shifts in the resonant wavelengths of the characteristic peaks are shown to obey an exponential relationship as a function of interparticle separation and a sinusoidal relationship as a function of angle of rotation of the ellipsoid. The behavior of the cluster is discussed and the two effects, of separation and rotation, are compared.
Conductivity Fluctuations in Two-Component Finite Systems
Authors: Axell Jörgen , Helsing Johan 
Published: March 2011

ABSTRACTIn all applications and experimental setups one has to do measurements on finite samples with some average properties. Due to statistical fluctuations in the realization of the specific sample one has, there will be a spread in the measured properties. In this paper we consider electrical conduction in a two-phase material, where the two phases have different conductivities. We study the size dependence of the fluctuations in the effective conductivity and give the dependence of the sample size and the dependence of the resistance ratio, especially when the latter is close to one. A simple model and numerical simulations are presented.
Particle Interaction Model of Permittivity Enhancement in Metal-Insulator Composites
Authors: Doyle W. T. , Jacobs I. S. 
Published: March 2011

ABSTRACTA simple effective spherical cluster model of generalized susceptibility enhancements in disordered monodisperse suspensions of conducting spheres is compared with experimental measurements of reduced permittivity and conductance. Good agreement with experiment is obtained by treating the suspension in the Clausius-Mossotti approximation as a mixture of isolated spheres and compact spherical metallized clusters.
Dielectric Properties of Percolating Nanocrystals
Authors: Marquardt P. , Nimtz G. 
Published: March 2011

ABSTRACTMicrowave spectroscopy revealed a non-metallic effective dielectric function of non- supported nanocrystal networks. This new result is in agreement with the size-induced metal-insulator transition (SIMIT) observed in isolated sub-μm conductors. Separating the particle contribution ε = ε1 + iε2 from the measured effective dielectric response leads to the conclusion that percolating networks of SIMIT particles are characterized by an enormous positive value of El and a conductivity σ ∼ ε2 much smaller than expected for metallic networks. Another non-metallic feature of the networks is the weak thermal influence on ε1 and ε2. All properties change sensitively with the filling factor f of the network. Their unusual dielectric properties make low- density nanocrystal networks candidates for applications e.g. as high permittivity capacitor materials or temperature-independent resistors.
Electrical Conduction in Granular Metal Films
Authors: Morris J.E. , Mello A. , Adkins C.J. 
Published: March 2011

ABSTRACTIn the early 1970's, Abeles et al developed a widely accepted model for electrical conduction in granular metal films based upon an assumed correlation between metal particle size and inter-particle tunneling gap width. The paper critically examines this assumption and other aspects of the theory. No observation of any such correlation has been reported, nor should it be expected, particularly in discontinuous films. The latter point requires separate considerations of the very different structures of discontinuous metal films, granular metals and cermets, using the “granular” term here in a more limited sense than usual.Other aspects of the theory considered include its implied percolation topology and the field effect. Experimental data are also re-evaluated in terms of other common models. The paper concludes with a brief review of recent work in discontinuous metal films with suggestions for future theoretical and experimental work.
Numerical Simulation of Hopping Conductivity in Granular Metals
Authors: Chen L. F. , Sheng Ping , Abeles B. , Zhou M. Y. 
Published: March 2011

ABSTRACTElectrical conduction in granular metals is simulated by mapping the hopping conductance between pairs of metal grains onto a simple cubic lattice with bonds between neighbors. By considering a log-normal distribution of grain sizes and the effect of disorder potential, the numerically calculated network conductance exhibit clear deviation from simple activation. Plotting -log a vs. T-½, where σ denotes conductivity and T the temperature, gives good straight line behavior with slopes comparable to those measured experimentally. Our results are noted to differ from those of Adkins et al.
Field Effect Experiments on Discontinuous Metal Films
Authors: Adkins C J 
Published: March 2011

ABSTRACTWe describe experiments in which the energetics of electrical conduction in discontinuous metal films are probed by inducing carriers electrostatically into the films. Both conductivity and thermopower show field effects that are generally of the expected form but they are very much smaller than the classic model for conduction in these systems would predict. Furthermore, in some cases at least, they can be shown to result from dielectric relaxation processes rather than from direct modification of basic transport energetics.We discuss possible explanations, including that large potential disorder is present and that transport is controlled by energy structure that moves with the chemical potential, as would be the case i correlation energies determined carrier mobility. Experiments that measure the charging energies of the metal particles directly suggest that correlation is important, and we argue that progress in understanding conduction in granular metals depends on development of a model in which correlation energies play a critical role in controlling transport.
Use of Dielectric Mixture Equations for Estimating Permittivities of Solids from Data on Pulverized Samples
Authors: Nelson Stuart O. , You Tian-Su 
Published: March 2011

ABSTRACTThe complex permittivities of solid and pulverized samples of two plastics, Rexolite 1422 and Kynar, were measured at frequencies of 2.45, 11.5, and 22.0 GHz at 25°C by the short-circuited waveguide technique. Several dielectric mixture equations and extrapolation of functions of the real and imaginary parts of the permittivity that are linear with bulk density were then used to estimate the permittivities at solid-material densities from measurements on the pulverized samples. For these materials, the best estimates of the permittivities were provided by extrapolations that are consistent with the Complex Refractive Index and Landau and Lifshitz, Looyenga mixture equations. The Bottcher mixture equation often gave values very close to the Landau and Lifshitz, Looyenga equation, and the Bruggeman-Hanai, Rayleigh, and Lichtenecker mixture equations gave increasingly larger permittivity estimates in that order.
Oxygen-Induced Reversible Structural Change of Supported fine Silver Particles Observed by In Situ Optical Absorption and X-ray Diffraction
Authors: Yanase Akihisa , Komiyama Hiroshi , Tanaka Kazunobu 
Published: March 2011

ABSTRACTIn situ measurements of optical absorption and x-ray diffraction for small supported silver particles were performed under defined atmospheres at temperatures below 723 K. We found, for the first time, reversible changes both in optical absorption spectrum and lattice parameter of silver particles against the cyclic exchange of ambient gases between 5% H2/He and 1% 02/He. The present data indicate that the adsorption of oxygen results in a reduction in surface stress of silver particles, leading to a change in the shape of particles.
Dynamical Properties of Weakly Coupled Josephson Systems
Authors: Lee K. H. , Xia T.-K. , Stroud D. 
Published: March 2011

ABSTRACTWe review recent work on the dynamical behavior of coupled resistively-shunted Josephson junctions, with emphasis on our own calculations. We present a model which allows for the inclusion of finite temperature, disorder, d.c. and a. c. applied currents, and applied magnetic fields. We discuss applications to (a) calculations of critical currents and IV characteristics; (b) harmonic generation and microwave absorption by finite clusters of Josephson junctions; (c) critical energies for vortex depinning; and (d) quantized voltage plateaus in arrays subjected to combined d.c. and a. c. currents. Possible connections to the behavior of granular high-temperature superconductors are briefly discussed.
Quantum Fluctuations in Granular Superconductors
Authors: Fishman R.S. 
Published: March 2011

ABSTRACTA 1/z expansion is used to study the coupling of phase fluctuations in an array of superconducting grains. By lowering Tc. and increasing the critical grain diameter αc,fluctuations suppress the long-range order in the material. When the temperature T is of order U = e2/C, where C is the grain capacitance, peaks appear in the fluctuation corrections to both the specific heat and the short-range order parameter. These peaks are induced by the coupling between thermal fluctuations of the charge and quantum fluctuations of the phase on neighboring grains.
Superconductivity and Tunneling Spectroscopy in Granular and Homogeneous Quench Condensed thin Films
Authors: Valles J. M. , Dynes R. C. 
Published: March 2011

ABSTRACTQuench-condensed films of simple superconductors can be deposited with a morphology which is either granular (grain sizes on the scale of tens of angstroms) or homogeneous. Transport and tunneling studies of the normal and superconducting states of these films as a function of sheet resistance have revealed profound differences between them. In uniform films Tc. and the energy gap decrease continuously with decreasing film thickness. Superconductivity is destroyed by the reduction of the amplitude of the order parameter. In granular films, the grains are sufficiently large to support superconductivity in each grain. Long range phase coherence is destroyed by intergrain phase coherence breaking.
On The Optimized Mixing of Order and Disorder in High-Tc Ceramic Superconductors
Authors: Mezzelli E. 
Published: March 2011

ABSTRACTCoherent excitations of localized states, represented by a selfsimilar Cayley tree, produce a gap in the density of states, which is deeper as the number of generations increases.The model can suitably describe systems in which an optimized concentration of “defects” allows self similarity of the state-tree and coherent coupling between clusters of localized states.A renormalization of the state-tree leads to a hierarchy of the energy eigenvalues.
Percolation Effects in the Mechanical Properties of Granular Ni-A12O3 thin films
Authors: Schlesinger T.E. , Gavrin A. , Cammarata R.C. , Chien C.-L. 
Published: March 2011

ABSTRACTThe mechanical properties of sputtered Ni-Al2O3 granular thin films were investigated by low load microharaness testing. It was found that the microhardness of these films displayed a percolation threshold at a nickel volume fraction of about 0.6, below which the hardness is greatly enhanced. This behavior is qualitatively similar to the electrical and magnetic properties of these types of films. A percolation threshold in hardness can be understood as due to a change in the mechanism for plastic deformation.
Magnetic and Structural Properties of Granular Iron-Silicon Dioxide Thin Films
Authors: Carey M.J. , Parker F.T. , Berkowitz A.E. 
Published: March 2011

ABSTRACTFe-SiO2 granular films were produced by co-sputtering from separate Fe and SiO2 targets. Films deposited on silicon nitride membranes were thin enough to observe directly by transmission electron microscopy (TEM). The coercive force (Hc) was strongly dependent on temperature and volume fraction of Fe as observed in previous investigations, but with lower Hc. Two features of the films with low Fe concentrations were remarkable. The hysteresis loops show high remanence, and the room temperature TEM images show stable domain structure and ripple patterns. This behavior is inconsistent with a model of non-percolating, non-interacting superparamagnetic Fe grains.
Transport of Toluene in Microporous Vycor Class
Authors: Abeles Ben , Chen L. F. , Johnson J. W. , Drake J. M. 
Published: March 2011

ABSTRACTA quasi-equilibrium model is developed for capillary condensation flow, in which surfacediffusion is included. The model is in excellent agreement with the experimental data for the flow of toluene in untreated Vycor glass and in Vycor glass whose pores were derivatized with C18H38. The observed increase in viscosity with decreasing pore size is ascribed to a stagnant monolayer adsorbed to the pore walls. The surface diffusion coefficient at 22ºC is 5 x 10-5 cm2/secfor both the derivatized and untreated samples.
Characterization of the Electric Field in Electrophotographic Granular Systems
Authors: Schein L. B. 
Published: March 2011

ABSTRACTWithin all electrophotographic (or xerographic) copiers and laser printers are development systems where the image is reproduced. Usually these development systems contain 200 μm diameter metallic, magnetic balls called carrier particles. Attached electrostatically to these balls are 10μm diameter polymer particles called toner which eventually end up on the paper forming the black images given to customers. The process bywhich the toner leaves the carrier and ends up on the paper is driven by electric fieldsin the development system. These fields are determined by the applied voltage and the dielectric properties of the granular mixture of metal carrier balls, polymeric toner, andair. The average electric field is determined by the dielectric constant of this granular mixture. But on a microscopic scale that a toner would experience, i.e. 10 μm, the electric field has significant structure. This structure has been determined both experimentally and theoretically. For example, the electric field peaks underneath a chainof carrier particles (which are chained up by a magnetic field). Models of the development process clearly indicate that toner particles transfer from the carrier particles only when the toner particles are directly under a carrier chain, where one would expect the field to be a maximum. However, recently we have succeeded in showing experimentally that the value of the electric field that the toner particles experience is the average field, described by the dielectric constant. Theoretical questions concerning the calculation of the electric field in a granular system raised by this unexpected result will bediscussed.
Oxide Nonlinear Conductors: A Review
Authors: Levinson Lionel M. , Philipp Herbert R. 
Published: March 2011

ABSTRACTOxide nonlinear conductors are granular electronic ceramic materials whose electrical behavior is dominated by grain boundary interfaces states. The material is typically comprised of relatively conducting oxide grains with electrical barriers at the grain boundaries induced by segregated impurity ions. Oxide nonlinear conductors can exhibit a highlynonlinear current-voltage relationship with a 5% change in voltage serving to increase the current flow an order of magnitude or more.This review outlines our understanding of the microstructure, grain boundary properties and electrical behavior of these variable resistor or “varistor” granular materials. ZnO varistors currently have widespread application in protecting power and signal level electrical circuits against dangerous voltage surges and a brief overview will be given of the applications of this material.
Diffusion Bonding of Superplastic 7075 Aluminum Alloy
Authors: Yan Huang , Jianzhong Cui , Longxiang Ma 
Published: March 2011

ABSTRACTBecause of the presence of surface oxide films, aluminum alloys are very difficult to join by diffusion bonding processes when there are no interlayers between mating surfaces. In the present investigation, the diffusion bonding of superplastic 7075 aluminum alloy has been carried out using a special method for surface treatment in the temperature range 500∼520°C, at pressures of 2.07∼3.OMPa, times of 90∼150min and a vaccum of 1×10−5torr. The joint strength obtained is the same as the base metal strength of the alloy, and the joint microstructure is indistinguishable from that of the base metal. In this paper, the effect of the superplastic treatment of the alloy on the bonding process is discussed, and it is proposed that the bonding mechanism is the migration of the initial bond interface caused both by the diffusion of atoms and by the growth of grains during the diffusion bonding process.
Developement of SPF and SPF/DB Techniques for Ti and Al Alloys and their Applications
Authors: Wenhai Ji , Zhenguo Wang , Feiling Song 
Published: March 2011

ABSTRACTThis paper deals with the new development of both SPF of an Al alloy and SPF/DB of an Ti alloy.Based on a theoretical model, a pressure versus time curve was determined for optimizing the SPF parameters. The effects of applied back pressure and reverse billowing on the performance of 7475 and Al-Cu-Li-Mg-Zr alloys are discussed.Some essential technological factors which affect the quality of the SPF/DB of the Ti-6A1–4V alloy have been studied, such as the effect of an o layer on the strength of the base metal, the gas filling method and the pre-forming of parts with curved surfaces etc. Examples of applications to the manufacturing of airplane spars and undercarriage doors are also shown in this paper.
Mechanical Properties of TiAl and (TiAl+Ti3 Al) Alloys Produced by Mechanical Alloying
Authors: Ochiai S. , Kobayashi M. , Michimura K. 
Published: March 2011

ABSTRACTTwo representative titanium aluminides containing 48 and 52 at. pct Al were produced by a mechanical alloying (MA) process for the purpose of attaining fine microstructures. For the MA apparatus, an attritor mill and a conventional ball mill were both used and the results compared. Mechanically alloyed powders were consolidated by hot pressing. In addition to morphological changes in the powders during MA, microstructures and mechanical properties of the consolidated products were studied. In particular, the MA alloy with 48 at. pct Al comprised of both TiAl and Ti 33Al phases showed a high strain rate sensitivity exponent, above 0.3. This suggests a possibility of developing superplastic deformation.
Microstructure Change During High Strain Rate Superplastic Deformation in a PM 7475 AL-0. 7ZR Alloy
Authors: Matsuki K. , Tokizawa M. , Murakami Y. 
Published: March 2011

ABSTRACTImprovements of superplasticity in the high strain rate range have been achieved in a 7475 Al alloy with 0. 7 wt% Zr produced from rapidly solidified powder (PM7475-0.7Zr alloy), and the superplastic properties and microstructural changes with strain have been investigated.The PM 7475-0.7 Zr alloy has a cold rolling structure, but on heating to the superplastic temperature of 520°C, the alloy developed a very fine subgrain structure of average subgrain size of less than 1 μm. The fine structure was stabilized with metastable cubic Al3Zr precipitate dispersions, and there exist a large number of less than 5° misorientation subboundaries together with a small number of highly misoriented ones.After 117% strain at the high strain rate of 2. 5×10−1 S−1 the subboundaries with the misorientation of 5° – 15° Were observed to increase. During the initial stage of the deformation, m value and the contribution of boundary sliding to the deformation also increased with strain, and thus the alloy behaved superplastically during the following deformation.The improvements of superplasticity with strain in the early stage of the high strain rate deformation of the alloy were interpreted to be closely related with the increase in misorientation of subboundaries stabilized with finely dispersed metastable Al3Zr precipitates.