bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction of Phosphorus With Dislocation Cores in Silicon
Authors: Heggie Malcolm I. , Jones Bob , Umerski Andrey 
Published: March 2011

ABSTRACTSilicon is an ideal model for strong covalent solids because it is an elemental semiconductor amenable to many well-defined structural, mechanical and electronic experiments. It was shown some 25 years ago that electronically active dopants enhance dislocation mobility in silicon, but recently Sumino and co-workers have shown that phosphorus also strongly pins dislocations at low stresses. Almost paradoxically the same dislocations move with enhanced mobility once they are in motion at higher stresses.We have performed local density functional pseudopotential calculations on a molecular fragment taken from the core of a 90° partial dislocation of silicon. The surface dangling bonds were hydrogenated and phosphorus was substituted for silicon in various positions. Our results suggest that there is a strong valence effect in operation that causes phosphorus to bind very strongly to three fold coordinated sites in the core, simultaneously losing electrical activity. It is this binding that inhibits dislocation motion, because motion would require the coordination of phosphorus to change from three-fold to the more energetic fourfold.
Order/Disorder and Phase Diagram of H on Pd(100)
Authors: Tibbits P. , Karimi M. , Ila D. , Dalins I. , Vidali G. 
Published: March 2011

ABSTRACTAn atomistic simulation of H-Pd(100) provided a phase diagram for the c2×2 H overlayer phase. The Embedded Atom Method (EAM) calculated energy of each configuration of atoms and the Metropolis Monte Carlo algorithm equilibrated the structure and generated configurations from which to sample the structure factor for the H overlayer. The procedure provided the expectation of the square of the structure factor modulus, < |S2| >, as a function of temperature at three coverages. The inflection point of the < |S2| > versus T curve estimated the critical temperature for disordering, Tc,, for one value of coverage, θ. The plot of Tc versus θ, the phase boundary for the c2×2 phase, lay about 125 K below the experimentally determined boundary. A comparison of the energies of ordered and disordered phases showed ΔE = 0.016 eV per hydrogen atom. Equating this unrealistically small energy difference to thermal kinetic energy (3/2)kBTc at the critical temperature implies Tc ≈ 100 K. Obtaining – |S2| > values relatively free of noise at such low temperatures required large numbers of Monte Carlo steps. The c2×2 phase is the experimentally determined stable low temperature phase, and was assumed to be the lowest-energy phase possible in this simulation. The very small ΔE indicates that some other ordered phase may be more stable than c2×2 in the EAM model.
Surface and Near-Surface Atom Dynamics During Low Energy Xe Ion Bombardment of Si and Fcc Surfaces
Authors: Murty M. V. R. , Lee H. S. , Atwater Harry A. 
Published: March 2011

ABSTRACTSurface and near-surface processes have been studied during low energy Xe ion bombardment of Si (001) and fcc surfaces using molecular dynamics simulations. Defect production is enhanced near the surface of smooth Si (001) surfaces with respect to the bulk in the energy range 20–150 eV, but is not confined exclusively to the surface layer. The extent and qualitative nature of bombardment-induced dissociation of small fcc islands on an otherwise smooth fcc (001) surface is found to depend strongly on island cohesive energy.
Ab-Initio Simulations to Study the Configurational Entropy of Column IV Microclusters
Authors: Klemm Stefan , Drabold David A. , Sankey Otto F. 
Published: March 2011

ABSTRACTWe directly simulate the dynamics of carbon and silicon clusters to study the relevance of the probability distribution of coordinates to experimentally measured phenomena. We believe that the high temperature conformations are not necessarily related to the ground state minimum, and that care should be exercised when comparing ground state T = 0 calculations to experiments performed at high temperature.
Monte-Carlo Investigation of Avalanche in Adhesion
Authors: Good Brian S. , Banerjea Amitava , Smith John R. , Bozzolo Guillermo H. , Ferrante John 
Published: March 2011

ABSTRACTRecently it has been proposed that as two metal surfaces are gradually brought toward contact, atomic layers can collapse or avalanche together when the interfacial spacing falls below a critical distance. This avalanche can occur regardless of the stiffness of external supports and is accompanied by a discontinuous drop in the adhesive binding energy. Here we re-examine this phenomenon using a simple zero-temperature Monte-Carlo simulation using the Equivalent Crystal Method. In particular, we investigate the effect of loss of registry between the two contacting surfaces in order to delimit the circumstances under which avalanche can occur. We find that the avalanche is suppressed when the two surfaces are sufficiently far out of registry, at least when only a few layers near the surface are allowed to relax.
Transport Properties of Granular Nix(SiO2)100−x Thin Films
Authors: Beamish John R. , Patterson B.M. , Unruh K.M. 
Published: March 2011

ABSTRACTWe have studied the electrical transport behavior of sputter deposited Nix(SiO2)100−x thin films between room temperature and 100 mK and, at selected temperatures, in applied magnetic fields up to 6 T. As the Ni concentration x is reduced, the resistivity increases systematically. At a Ni concentration (nominal) of about x–70 atomic percent (38 volume percent) the room temperature coefficient of resistivity changes sign. For Ni concentrations greater than 70 percent the resistance first decreases with temperature then increases logarithmically at, low temperatures. This increase becomes smaller and the resistivity minimum moves to progressively lower temperatures as the Ni concentration increases. In films with less than x–70 percent Ni, the resistivity has a temperature dependence of the form ρ(T)–ρo exp \(To/T)α] between room temperature and about 5 K. The exponent a is about 1/2 and To increases with decreasing Ni content. Below 1 K, however, the resistivity increases much less rapidly, with a temperature dependence independent of Ni concentration. In all films the magnetoresistance is small and negative.
Far Infrared Magneto-Optical Absorption in Small Bismuth Particles
Authors: Devaty Robert P. , Sherriff Ralph E. 
Published: March 2011

ABSTRACTA semiclassical model based on the measured properties of the free carriers in bulk bismuth successfully accounts for far infrared (ῶ ≤ 60 cm−1) magnetic field dependent resonances observed in free-standing powders of ∼0.5 μm diameter Bi particles prepared by inert gas evaporation. In earlier work, we found that particles with each of the three principal axes aligned parallel to the applied field were required to explain the data. The conclusion that these particles are bulk-like in nature remains valid when an ensemble of randomly oriented particles is treated using a Monte Carlo method.
Anderson Localization in Anisotropically Random Media
Authors: Sheng Ping , Xue Weige , Zhang Zhao-Qing , Chu Q. J. 
Published: March 2011

ABSTRACTDimensional cross-over behavior of Anderson localization is presented. By delineating the physical basis of localization, it is shown that the localization phenomenon is sensitive to the spatial dimension of the randomness. Analytic and numerical results demonstrate that in an anisotropically random medium there is a critical amount of anisotropy which separates the system behavior into a ID-like regime and a 3D-like regime. Dimensional crossover is proposed as a viable experimental approach to observe the mobility edge.
A Quantitative Analysis of Cermet Resistivity Data Using the General Effective Media (GEM) Equation
Authors: Mclachlan David S. 
Published: March 2011

ABSTRACTA General Effective Media (GEM) equation is used to quantitatively describe the resistivity of the W - Al203 and Ni - Si02 cermet systems as a function of the relative volume fractions. The two percolation morphology parameters (øc and t) characterise the microstructure. A constant resistivity pl is assumed for the metal (W or Ni) while, in some cases, it is necessary that the resistivity of the insulator be modeled as the tunneling of electrons, through an oxide barrier, from a thermally excited charged grain to a neutral grain.
Bulk Effective Moduli: Their Calculation and Usage for Describing Physical Properties of Composite Media
Authors: Bergman David J. 
Published: March 2011

ABSTRACTWhile not telling the whole story, the representation of a composite medium by a homogeneous effective medium is often an excellent approximation for describing its macroscopic physical properties. Modern methods for calculating the effective medium properties are reviewed with special emphasis on understanding both successes and limitations. Outstanding problems that can and should be tackled are identified. The successes include calculations of the electrical conductivity, dielectric coefficient, and elastic stiffness moduli of composites with a periodic microstructure, and the simulation of those properties for disordered composites near a percolation threshold by means of discrete models such as a random-resistor-network. For composites where the microstructure is either unknown or very complicated, a whole class of exact bounds have been found for these properties based on various types of limited information. Recently, advances have been made in calculating the weak field magneto-transport and the thermoelectric behavior of two-component composites, and also some types of nonlinear properties. An important challenge remains the calculation of magneto-transport at high magnetic fields. Another is the theoretical treatment of multicomponent composites. A third is to find relations between different effective properties of a composite that can enable us to learn about property A by measuring a different property B. This is especially important when the measurement of A would destroy the sample, as when A is the yield stress, whereas the measurement of B is nondestructive, as when B is a small, nonlinear correction to the usual elastic stiffness moduli.
An Extended Thermodynamic Approach to Transport Phenomena in Porous Media
Authors: Rio J. A. del , Haro M. López de 
Published: March 2011

ABSTRACTA formalism of extended irreversible thermodynamics (EIT) is used to study the physical aspects of heat, momentum and mass transport through porous media.The thermodynamic space is enlarged with respect to that of classical linear irreversible thermodynamics (LIT) to include the mass, heat and momentum fluxes as independent variables. The time evolution equations for such variables are derived self-consistently and reduce to the usual constitutive equations of LIT when the appropriate limits are taken. Equations that involve effects characterized by terms of second order in the gradients of conserved variables (such as the Darcy-Brinkman law) may also be derived within the same formalism. Finally, EIT provides the natural framework beyond LIT to introduce non-isothermal effects in the study of transport phenomena in porous media.
Granular Aspects of High Tc Superconductivity
Authors: Deutscher Guy 
Published: March 2011

ABSTRACTAs Bednorz and Muller noted in their original publication reporting on the discovery of high temperature superconductivity, their oxides present many of the features of granular superconductors. This behavior was first primarily ascribed to poor connectivity of the grains in the bulk ceramic samples. but later studies have pointed out to more fundamental reasons for these similarities. We will discuss them after first reviewing the well established properties of low Tc granular superconductors.
Granular Magnetism
Authors: Chien C.L. 
Published: March 2011

ABSTRACTRecent studies of granular magnetic solids involving Fe and its alloys embedded in either an insulating medium (e.g. SiO2 A12O3) or a metallic medium are described. Below the percolation threshold, isolated magnetic granular exhibit single-domain properties and superparamagnetic relaxation. Giant coercivity has been uncovered in granular Fe-SiO2, with Hc- as high as 3 kOe at 5 K and 1.1 kOe at 300 K. Some recent results on granular Fe in a metallic medium, and other granular magnetic systems will also be discussed.
Digitized Direct Simulation Model of the Microstructural Development of Cement Paste
Authors: Bentz Dale P. , Garboczi Edward J. 
Published: March 2011

ABSTRACTThe complex microstructure of hardened cement paste is produced by hydration reactions between cement particles and the water in which they are suspended. In recent years, algorithms like the diffusion-limited aggregation (DLA) and Eden models have demonstrated that simple growth rules can result in complex aggregated structures. The model described in this paper simulates, via simplified growth rules, the microstructural development ofhydrating cement paste. This model has similarities to DLA, but with the additional novel features of dissolution of solid particles, and a free-space nucleation probability. The percolation aspects and transport properties of the model's pore space are computed and discussed.
Optical Properties of Granular Metallic Media Near the Percolation Transition
Authors: Lafait J. , Berthier S. , Gadenne M. , Gadenne P. 
Published: March 2011

ABSTRACTThis review covers most of new physical aspects opened by the recent interest in the optical properties of heterogeneous media close to the percolation transition: relevant parameters and lengths, caracteristic optical behaviour (transmittance, reflectance and absorptance), theoretical models, dimensionali ty effects, discrimination between optical, electrical and morphological percolation transitions. Morphological aspects are emphasized as the key of optical properties at percolation.
Transport Properties of Granular Porous Media
Authors: Schwartz Lawrence M. 
Published: March 2011

ABSTRACTThis paper is concerned with two related problems: (1) the construction of geometrical models of porous media relevant to granular composites and (2) the description of transport processes in these model systems. We will show that a variety of interesting porous media can be generated by the packing and subsequent modification of spherical grains. This modification may involve a change in either the grain's size, shape, or both. Steady state transport processes such as the flow of electrical current or viscous fluids are controlled by the distribution of pore throat sizes and, within the presentframework, can be studiedefficiently by random walk simulations of diffusion. The techniques developed here are also of interest in connection with dynamic transport processes such as the filtration of fine grained particles into consolidated granular networks. Wediscuss briefly the modeling of such processes as well as the interaction of steady state and dynamic transport.
Effect of Granularity on CuInSe2 Solar Cell Response
Authors: Sites James R. 
Published: March 2011

ABSTRACTPolycrystalline CuInSe2 solar cells, fabricated by evaporation or by selenization of metal films, are granular and relatively porous. Grains are a few hundred nanometers in dimension, and hence about 1% of the atoms are at a surface. Despite the granularity, quantum efficiency is quite high and implies a diffusion length exceeding the grain dimension. The primary photovoltaic loss is excessive forward recombination current. The proposed model consists of single crystal CuInSe2 granules with an indium rich surface layer. When properly passivated, the otherwise uncoordinated indium bonds are terminated by oxygen. However, residual non-passivated crystalline surface states distributed throughout the depletion region provide the paths for enhanced recombination.
Microstructural Changes and Straining Behavior in Transformation Superplasticity in Iron and Steels
Authors: Saotome Yasunori , Iguchi Nobuhiro 
Published: March 2011

ABSTRACTThe microstructural changes associated with phase transformation and the straining behavior in polycrystalline structures during transformational superplastic deformation have betransformatonal superplasticen investigated. In-situ observations have been carried out with specially designed hot-stage microscopes. The strain distribution has been examined by microscopic strain analyses using a micro-grid pattern with 12.7 and 6 μm intervals in pure iron, 0.1%C steel and eutectoid steel. The results are as follows: (1) In the initial stage of Ac3 transformation in pure iron, superplastic strain is induced by the sliding at o/y interface along the prior ferrite grain boundaries and by the grain rotation. In the intermediate stage, the sliding deformation is generated at the migrating tranformation interface associated with the growth of austenite grains. (2) Accumulated strain by sliding has been observed within the previously transformed region during Ac3 transformation in 0.1%C steel. (3) The characteristic straining behavior in the eutectoid steel is due to the behavior at the transformation interface in the microstructure including secondary phase Fe3C particles. These observations suggest that a sliding mechanism at the migrating interface is a principal mechanism of transformation superplasticity.
The Mechanism of Internal Stress Superplasticity
Authors: Derby B. 
Published: March 2011

ABSTRACTThe phenomenon of internal stress superplasticity is reviewed and the theoretical mechanical foundations of current mechanism models of the process examined. These models are shown to be based on two different principles: i.e. a biased internal plastic flow, or an enhanced creep generated by a superposition of internal and external stresses. Mechanical test data is shown to be more consistent with enhanced plasticity models in zinc and metal matrix composites for deformation during thermal cycling.
Superplasticity in Use: A Critical Review of Its Status, Trends and Limits
Authors: Winkler Peter-J. 
Published: March 2011

ABSTRACTThe transformation of the phenomenon Superplasticity into a manufacturing technique has been pushed ahead over the last two decades mainly by the aerospace industries. The possibility of producing complicated structures in one step offers well known economic advantages. The combination of superplastic forming and diffusion bonding further enhances design flexibility thanks to the ability of fabricating multisheet structures.This paper provides an overview of the practical application of Superplasticity in forming components. It focusses on the major aerospace materials i.e. Ti alloys and Al alloys and discusses specific characteristics, the material specifications, and supply situation.Superplastic forming processing is presented including the techniques used for diffusion bonding; design concepts and exemplary SPF and SPF/DB parts are presented.Finally a critical discussion concerning current development trends, and the factors limiting broad application of this manufacturing technique are given. Future prospects are outlined and further research needs emphasized.
Diffusion-Accommodated Grain Boundary Sliding in a Polycrystal
Authors: Hazzledine P. M. , Schneibel J. H. 
Published: March 2011

ABSTRACTA two-dimensional model for diffusional creep (Coble creep) and diffusionaccommodated grain boundary sliding in polycrystals has been developed. The results obtained for small symmetrical clusters of grains reproduce Spingam and Nix's work [Acta Metall. 2M, 1389 (1978)]. For clusters of irregularly shaped grains the material deposition and removal rates, the fluxes along the grain boundaries, the grain boundary tractions as well as the grain boundary sliding rates are irregular and can all be calculated.
Superplastic Forming Characteristics and Microstructural Development of an Aluminium Lithium Alloy (8090)
Authors: Mahon G. J. , Keyte R. , Parson N. C. , Ricks R. A. 
Published: March 2011

ABSTRACTSuperplastic testing of the aluminium-lithium alloy 8090 has been performed in the temperature range 485°C to 550°C. Up to 530°C, raising the test temperature has the effect of increasing the m-value and decreasing the flow stress. Changes in superplastic forming characteristics and microstructure have been followed during straining using a variety of techniques. Jump-strain rate testing reveals that in the optimum temperature range (515°C to 525°C).there is a steady decrease in m-value. Cavitation also occurs, but can be suppressed effectively by applying a hydrostatic pressure during testing. Raising the test temperature above this optimum range to 550°C produces a significant decrease in the m-value and a more rapid fall-off with strain. These observations are explained in terms of recrystallisation and grain growth, and the effectiveness of precipitates in pinning grain boundaries at the various temperatures.
Mechanical Properties of 5083 SPF After Superplastic Deformation
Authors: Dunwoody Barry J , Stracey R J , Barnes A J 
Published: March 2011

ABSTRACTSuperplastic aluminium alloys may be divided into two categories: those which recrystallise dynamically during superplastic deformation, such as the Supral alloys (2004 SPF) and 8090 SPF and, secondly those in which the fine grain necessary for superplasticity is produced by static recrystallisation during thermo-mechanical processing.Both 7475 SPF and 5083 SPF belong to the second category.This paper describes the superplastic forming characteristics of 5083 SPF and its post-formed mechanical properties.Some typical applications will be shown to demonstrate the degree of complexity which is possible with this non-heat treatable alloy.
The Influence of Grain Boundary Structure on Strain-Induced Grain Growth During Superplastic Deformation
Authors: Frost H. J. , Raj R. 
Published: March 2011

ABSTRACTA model is presented to explain the grain growth that is often observed during superplastic deformation. The atomic structure of grain boundaries leads to a coupling between boundary sliding and boundary migration. There is a similar coupling between the absorption or emission of vacancies from a boundary and boundary migration. Because of these couplings, the grain boundary sliding and diffusional flow of superplastic deformation produce extensive boundary migration. We propose that this forced migration leads to random changes in the sizes of grains, and that this evolution of the grain size distribution leads to grain growth.
Superplastic Deformation of an Al-Li-Cu-Zr Alloy under Uniaxial and Biaxial Tension
Authors: Lee Ho-Sung , Mukherjee Amiya K. 
Published: March 2011

ABSTRACTThe superplasticity of an Al-Li-Cu-Zr alloy has been studied under uniaxial tension and biaxial bulging conditions using hydrostatic pressure. An optimum tensile elongation of 850% at a strain rate of 3×10−4 /sec was obtained at 758 K. The maximum true thickness strain was 1.22 for a biaxially deformed specimen under the same conditions. It was shown that strain rate dependent flow hardening was related to necking profile. It was observed that cavity growth during superplastic deformation depended on the type of loading. Under biaxial bulging conditions, the cavities grew by forming cavity fissure networks along the grain boundaries. It was found that, by the superimposition of hydrostatic pressure, cavitation was retarded and the superplastic ductility was increased in both tensile and biaxial deformation.