bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Atomic and Electronic Structures of Grain Boundaries in Silicon-Carbide and Silicon
Authors: Kohyama M. , Kose S. , Kinoshita M. , Yamamoto R. 
Published: March 2011

ABSTRACTThe atomic and electronic structure of the {122} Σ=9 grain boundary in cubic SiC has been calculated for the first time using the self-consistent tight-binding (SCTB) method. An atomic model consisting of zigzag arrangement of 5-membered and 7-membered rings similar to that in the same boundary in Si or Ge has been constructed from a HREM image, although Si-Si and C-C wrong bonds are repeated alternately at the interface in this model. We have also performed calculations of the same boundary in Si using the SCTB method for comparison, and have obtained the results similar to those previously obtained by other theoretical schemes. The calculated boundary energy in SiC has shown that the present atomic model can exist stably as compared with the two surfaces, and the calculated boundary electronic structure in SiC has no deep states in the gap as well as that in Si. However, it has been found that the the increase in the electrostatic energy caused by the wrong bonds is a large part of the present boundary energy in SiC differently from that in Si, and it has been shown that the wrong bonds introduce the wrong-bond localised states at the band edges and within the valence band.
The Relationship between the Microscopic Properties of Semiconducting Grain Boundaries and their Orientation
Authors: Tarnow Eugen , Arias Tomas , Bristowe P. D. , Dallot P. , Francis G. P. , Joannopoulos J. D. , Payne M. C. 
Published: March 2011

ABSTRACTThe microscopic structure of a tilt and a twist boundary in germanium are explored using a state-of-the-art total energy calculation. The structure of the tilt boundary (Σ = 5 (310)) is found to be simple as it exhibits a well defined minimum energy structure, consistent with previous experimental and theoretical results on this and other tilt boundaries. The structure of the twist boundary (Σ = 5 (100)), however, is found to be very complex. The boundary bonds are distorted and weak, and their weakness makes the twist boundary exhibit a wealth of local energy minima. The different types of energy minima for the twist boundaries are identified and studied in some detail. We summarize the consequence of the orientation of the two crystal grains upon the microscopic structure of the boundaries, and speculate about future applications.
Computer Simulation of Grain Boundary Structures in Ni3 Al
Authors: Lin Dongliang , Lin T. L. , Chen Da 
Published: March 2011

ABSTRACTThe embedded atom type potentials and static relaxation method combined with steepest gradient computational technique have been used to simulate the grain boundary cohesive energies, the distribution of electron density and stress field in the grain boundary region, and other related problems of [100], [110] and [111] symmetric tilt grain boundaries in Ni3 Al with different grain boundary geometrical index and composition. Their relations with the segregation of boron, behaviors of the grain boundary, and especially the stoichiometrical effect of B induced ductility have also been studied and discussed.
The Nature of Crack Tip Fields in Atomic Scale Models of Aluminum
Authors: Hoagland R. G. , Daw M. S. , Foiles S. M. , Baskes M. I. 
Published: March 2011

ABSTRACTThe stresses, displacement gradients, and Eshelby's F and M integrals are obtained for two crack orientations in an EAM atomic model of aluminum. For a sharp crack, the stresses are shown to agree quite well with the linear elastic prediction, and F is essentially path independent and also in good agreement with the linear elastic prediction. When dislocation emission and blunting ensues, the path independence of F disappears. In addition, for circular contours with origin at the crack tip, the M-integral is linear in contour radius with slope equal to twice the surface energy and zero intercept for a sharp crack, but acquires a nonzero intercept as blunting occurs. The shift in intercept is related to the movement of singularities away from the origin.
On the Dynamical Spin Susceptibility of Paramagnetic La2CuO4
Authors: Winter H. , Szotek Z. , Temmerman W. M. 
Published: March 2011

ABSTRACTThe self-consistent one-electron wave functions and energy bands obtained by the LMTO-ASA method within the local density approximation (LDA) are used to calculate the wave vector and frequency dependent non-interacting spin susceptibility of paramagnetic La2CuO4 in the body-centred tetragonal (bct) structure. We show that the tendency towards the antiferromagnetic instability is strongly dependent on the effects of the matrix elements which lead to a substantial depression of the susceptibility, especially near the X-point. The Fermi surface nesting properties, although important for the susceptibility, are by far not sufficient for the instability and the interband transitions turn out to be of great significance. Our results indicate that the susceptibility is at least 3 times too small to drive this system through a transition to the antiferromagnetic state, and we discuss possible reasons for this failure.
Molecular Dynamics Simulations of Grain-Boundary Diffusion for Varying TILT Angle Geometries
Authors: Plimpton Steven J. 
Published: March 2011

ABSTRACTThe effect of structure and geometry on grain boundary self-diffusion is investigated. Using static structures found by relaxation techniques (conjugate gradients) as starting points for a molecular dynamic simulation of a bicrystal model, diffusion coefficients and activation energies are calculated for (100) fcc Al and bcc α-Fe tilt boundaries. These quantities are derived by monitoring the mean-squared displacement of atoms in the grain boundary region as the simulation progresses and as the temperature of the simulated solid is changed. The angular, directional, and structural dependence of the simulated diffusion are discussed and compared to experimental measures and theoretical predictions. The implementation of the molecular dynamics algorithm on a parallel supercomputer is also briefly discussed to illustrate the performance benefits these computers make possible.
Electronic Structure of Epitaxial Silicon Interfaces
Authors: Fujitani Hideaki , Asano Setsuro 
Published: March 2011

ABSTRACTUsing the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA), we studied the electronic structure of the Si(111) interface for four different materials: CaF2, NiSi2, CoSi2, and YSi2. We examined how the interface states and Schottky barrier height depend on the interface atomic structure.
Theory of Structural and Electronic Properties of Silicon Nitride and Carbon Nitride
Authors: Liu Amy Y. , Cohen Marvin L. 
Published: March 2011

ABSTRACTUsing a first principles pseudopotential total energy approach with a localized basis for the electronic wave functions, we have investigated the structural and bonding properties of β-Si3N4 and β-C3N4, which is a proposed structure for carbon nitride. The latter system is used as a prototype for studying the properties of possible covalent C-N solids. For β-Si3N4, calculated structural properties such as lattice constant and bulk modulus are in excellent agreement with experimental values. This gives support for the predicted properties of β-C3N4.β/C3N4 is found to be a good candidate for a new low-compressibility solid, with compressibility comparable to diamond. Despite similarities between β-Si3N4 and β-C3N4 in terms of crystal structure and valency of constituent elements, differences are found in their electronic bonding properties. A comparison of the bonding in β-Si3N4 and β-C3N4 with other first and second row semiconductors is useful for understanding trends in the structural properties of these materials.
Diffusion of Light in Antarctic Sea Ice
Authors: Buckley R G , Trodahl H J 
Published: March 2011

ABSTRACTIt is important to understand the diffusion sun light in sea ice as this interaction exerts a strong influence over the weather in polar regions and over the growth of microbial communities in the sub-ice water column. Sea ice is a granular composite of ice, brine, air and at low temperatures precipitated salts, in which the proportion and disposition of these components vary with depth, with temperature and thermal history. It is demonstrated that by using a simple in situ technique, supported by Monto Carlo simulations, the diffusive transport of light through a weakly absorbing composite such as sea ice can be characterised. The radiation field both within and emergent from the ice is found to reflect the anisotropic structure of the ice, in particular, the scattering is found to be highly anisotropic so that the light is channelled predominantly vertically. The technique will be illustrated with experimental results collected in McMurdo Sound, Antarctica.
A Quantum Percolation Model for Magnetoconductance of Granular Metal Films
Authors: Zhang Zhao-Qing , Sheng Ping 
Published: March 2011

ABSTRACTA quantum percolation model is introduced to study the magnetoconductance of granular metal films. This model incorporates the granular property of the films and enables us to study the magnetoconductance in the strong scattering regime. Our calculations show a sign change in magnetoconductance as the temperature varies. There also exist oscillations in the magnetoconductance as the magnetic field is increased. Both observations are consistent with some recent experimental data.
Conduction Mechanisms in Discontinuous Copper Films
Authors: BiegaŃski P. , Mozrzymas-Dobierzewska E. 
Published: March 2011

ABSTRACTCopper films of coverage coefficients ranging between 0.2 and 1 were evaporated onto glass substrates under vacuum conditions (p ≃ 10−8 Torr). For these films, the temperature dependences of resistance were measured in vacuo in situ. Making use of the obtained data TCR values, as a function of coverage coefficient and the activation energy for the films with different coverage coefficients were established. The resistance of films was found to change, and TCR values approaching zero for coverage coefficients between 0.63 and 0.75. This interval (∆qc) can be regarded as the percolation interval for discontinuous Cu films.
Infrared Optical Guided Modes in Plasma Deposited Gold Clusters Embedded in a Polymer Matrix
Authors: Parmigiani F. , Jurichi M. , Kay E. , Swalen J.D. 
Published: March 2011

ABSTRACTMeasurements of the refractive index of discontinuous metallic films, consisting of gold clusters embedded in a dielectric matrix prepared in a capacitively coupled coplanar diode radio frequency discharged system, are reported.These composite films were analyzed to determine the metal volume fraction, the thickness and the cluster size.Optical characterizations in the visible and near infrared regions of the electromagnetic spectrum, particularly, in the near-IR region (Nd/YAG laser wavelength 1.0642 μm), where the absorption coefficient of these materials is very low (k < 0.001) were performed. Optical guided modes analysis allowed careful measurement of the effective medium refractive index.
Study on Thermal Hysteresis of Elastic Modulus in Granular Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O
Authors: Wang Yening , Sun Linhai , Wu Jin , Gu Min 
Published: March 2011

ABSTRACTA large thermal hysteresis ( > 100 K) of elastic modulus was measured for coarse grained Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O. Whereas, only a small thermal hysteresis (2∼3 K) near the velocity minima at 240 K, and 150 K was observed in Bi2 Sr2 CaCu2 O8 single crystal, which were found to be associated with phaselike transitions (PLT). The investigations of isothermal recovery of modulus for coarse grained YBCO and BSCCO disclose that the large thermal hysteresis may be attributed to the defects of pore size generated in the interconnecting region between grains as a result of PLT of weak first order but covering a wide temperature range. The mechanism of a large thermal hysteresis for coarse grained samples has been discussed in detail.
Magnetic Penetration Depth Measurements and Inhomogeneity in YBa2Cu3O7−δ Superconducting Thin Films
Authors: Anlage Steven M. , Langley Brian W. , Halbritter Jurgen , Eom Chang-Beom , Switz Neil , Geballe T. H. , Beasley M. R. 
Published: March 2011

ABSTRACTThe microstrip resonator technique has been applied to study the temperature dependence of the magnetic penetration depth in high quality YBa2Cu3O7−δ thin films. The temperature dependence at low temperatures comes out directly from measured data, with no assumptions about transmission line geometry, dielectric properties, or a model for the temperature dependence of the penetration depth. One can interpret the data in terms of either an exponential decay of λ(T) at low temperatures or as a power law decay. The energy gaps obtained from the exponential decay at low temperature are found to be significantly smaller than weak coupled BCS theory and power-law exponents are in the range of 1.3 to 3.2. These results will be discussed in terms of microscopic theories and the possibility that materials properties dominate the measurement.
Superconductivity in Granular Snx (SiO2)100−x Thin Films
Authors: Beamish John R. , Patterson B.M. , Unruh K.M. 
Published: March 2011

ABSTRACTThe resistivity of sputter deposited Snx (SiO2)100−x films has been measured for Sn concentration x between 50 and 90 atomic percent. Films with more than 53 percent Sn are superconducting at low temperatures with transition temperatures slightly above that of bulk Sn. The enhancement is 0.11 K for the 90 percent film, increasing to 0.24 K in the 55 percent film. As the metal concentration decreases, the transition region broadens, with the resistance beginning to decrease about 1 K above the transition in the highest resistance films. The films remain superconducting in substantial magnetic fields. In the 55 percent film, a magnetic field of 1 T reduces the transition temperature by 1 K and a field greater than 2 T is needed to eliminate superconductivity. At the largest field of 6 T, there is no sign of superconductivity in any sample, and the resistances increase down to the lowest temperatures measured (100 mK).
Synthesis and Magnetic Characteristics of Granular Co Dispersions in a Polymer Matrix
Authors: Kay Eric , Laurent C. , Parkin S.S.P. , Mauri D. 
Published: March 2011

ABSTRACTWe have produced thin film composite matrices containing granular transition metals in the zero valent state and have found onset of percolation at a much lower volume fraction than was the case for Au, albeit for significantly smaller transition metal particles. At volume fractions below percolation these granular composites are superparamagnetic down to 6°K. Remanent magnetization and hysteretic ferromagnetic behavior was not observed until we were slightly above the onset of electrical percolation. We interpret this result as indicative of ferromagnetic ordering among the transition metal grains. No significant reduction in magnetic moment due to size effects or to chemical interaction with the matrix was observed. A very small size dispersion of the metal clusters was indicated both from magnetic a well as electron microscopy measurements.
Structural and Magnetic Properties of Fe/Al2O3, Granular Systems
Authors: Dormann J.L. , Fiorani D. 
Published: March 2011

ABSTRACTSeveral samples of granular material consisting of Fe small particles dispersed in an alumina matrix were studied by means of various techniques. Structural results show that the particle surface is partially oxidized with occurrence of bonds with the matrix. Depending on the particle size, one observes b.c.c. a-Fe or amorphous structure. Magnetic properties are relevant of superparamagnetism phenomena, but the strong magnetic interactions between particles (due to the close compact arrangement) lead to a phase transition at zero temperature. It is also briefly discussed the magnetic volume determination and the influence on the properties of the magnetic disorder arising at the particle surface.
Elements of the Diagenesis of Sedimentary Rocks
Authors: Cohen Morrel H. 
Published: March 2011

ABSTRACTThree of the most important elements of the diagenesis of sedimentary rocks are consolidation, porosity reduction, and pressure dissolution or cementation. These are discussed qualitatively with special emphasis on the central role of contact formation in controlling both the driving forces and the kinetics of morphological change. It is shown, in particular, that the equilibrium forces would drive the rocks towards collapse of their porosity earlier in diagenesis were they not prevented by kinetic barriers. At greater depths these barriers are effectively removed by pressure concentration at the small contacts. We propose an explicit, qualitative mechanism leading to the observed morphologies and identify specific problems for quantitative analysis.
Influence of Microgeometry on Membrane Potential of Shaly Sands
Authors: Sen Pabitra N. 
Published: March 2011

ABSTRACTThe microgeometry of the pore space influences the membrane potential Em. and theDC electrical conductivity σ of a shaly sand in a similar manner, independent of the details of the geometry: Em and σ being related via the conductivities of cations and σanions;σ=σcation + σ onion, and Em α σ cation/(σcation + σanion). This explicit relationship is used to investigate the role of the geometrical factors which influence both Em and σ in a related manner. The dependence of σ on the water conductivity σw can be well approximated with four geometrical parameters which can be obtained from the slopes and the interceptsof σ vs. σw curve at high and low salinities. We show that these geometrical factors appear in the expression for Em a well. These geometrical parameters (one of them is the formation factor) vary from rock to rock, and any trend in these parameters depend on the local geology.
Structure and Reactivity of Granular Noble Metal Catalysts
Authors: Deckman H. W. , Fung S. C. , Matturro M. G. , McHenry J. A. 
Published: March 2011

ABSTRACTThe deactivation / reactivation behavior of fresh granular Pt metal catalysts supported on alumina is used to obtain information about the nature of catalytically activesites. It is found that relatively fresh catalysts can in some cases be reactivated by evolving only ∼1/100 of a monolayer of molecules off the Pt metal. This implies that either less than ∼1/100 of the surface is catalytically active with a site turnover frequency of greater than ∼100 reactions/(site-sec) orthat the reactivation process does not evolve small cracked molecules from the catalyticsites and involves some other physical or chemical change of the catalyst surface.
Noncrystalline Solids Prepared by Compacting Nanometer — Sized Particles
Authors: Weissmüller J. , Jing J. , Krämer A. , Birringer R. , Gonser U. , Gleiter H. 
Published: March 2011

ABSTRACTA new method of preparing amorphous solids is presented. X-ray diffraction, thermal stability and Mgssbauer spectroscopy give evidence for an atomic structure with reduced short–range order in Si75Auz5 and Pd72FeloSil8 alloys prepared by this method.
Fabricaton Of Granular Materials by High-Pressure Sputitering
Authors: Chow G.M. , Holtz R.L. , Chien C.L. , Edelstein A.S. 
Published: March 2011

ABSTRACTA brief study of the fabrication of granular materials by high-pressure sputtering is presented. This method utilizes sputtering at high pressures (p > 100 mTorr) in a thermal gradient to produce nanoscale particles, which are then embedded in a matrix by normal sputtering (p ∼ a few mTorr). The shape, size and the degree of aggregationof these nanoscale crystals can be changed by varying such processing parameters as the sputtering gas pressure and the target voltage. Examples are presented of nanocomposite films containing Mo nanocrystals (grain size ranging from 3 to 20 nm ) in an Al matrix.
Kinetics of Grain Growth Across Bond Interface During Diffusion Bonding
Authors: Yan Huang , Jianzhong Cui , Longxiang Ma 
Published: March 2011

ABSTRACTGenerally, the elimination of the voids in bond interface is considered to be the rate-controlling mechanism for diffusion bonding. In an earlier paper, the author proposed a new theoretical model for solid-state diffusion bonding of similar matals, in which the grain growth across the bond interface was considered to be the governing mechanism for diffusion bonding. The aim of the model is to understand how the joint strength is affected both by process variables (temperature, pressure, time) and by the microstructures of the materials being joined. In this paper, the mechanism of grain growth and recrystallization is discussed, and the calculation of an appropriate kinetic equation is made based on a diffusion bonding experiment on a hot-rolled 7075 aluminum alloy. The calculated results basically agree with those of the experiment.
Commercial Production, Superplastic Performance and Property Determination of 8090 SPF Alloy
Authors: Grimes Roger , Dunwoody Barry J. , Jones John A. 
Published: March 2011

ABSTRACT8090SPF alloy sheet has been in commercial production for about three years. This paper describes some of the property statistics of the commercially produced material, including tensile and superplastic results.Properties have been determined for test components formed with back pressure with different levels of superplastic strain. Results from tensile and corrosion tests are presented.
m-δ Relationship and Structural Evolution during a Constant Strain-Rate Superplastic Deformation of an Aluminum Alloy
Authors: Zhou Shanyou , Zhang Dongming , Lin Dongliang , Lin T. L. 
Published: March 2011

ABSTRACTAt 515° C with a constant strain-rate of 6.7× 10−3 min−1,tensile specimen of LC4 aluminum alloy with an initial average grain size of 8.7μm exhibited good superplasticity. A fracture elongation of 4649% was obtained. Under such deformation conditions, the m-δrelationship belongs to the mL=mmax type , with a maximum m value of 0.78 at 94% strain. The m-δ relationship can be expressed as δI(%)= (CI ×0.0067(mI−0.5) −1) × 100. During superplastic deformation, three kinds of structural evolution take place, namely the formation of precipitate-free zones adjacent to grain boundaries due to diffusional creep, grain coarsening and cavity generation. The m-δ relationship of superplasticity of the alloy mentioned above can be explained on the basis of the structural evolution during superplastic deformation.
High Rate Superplastic Deformation Mechanisms in IN90211 Mechanically Alloyed Aluminum
Authors: Bieler Thomas R. , Mukherjee Amiya K. 
Published: March 2011

ABSTRACTIN90211 has exhibited superplastic elongations above 500% at high homologous temperatures (0.76–0.82 Tm). A high strain rate and flow stress for optimum elongation was measured (1–5/sec, 20–60 MPa, 425–485 °C). The apparent strain rate sensitivity of m≈0.25 differs from the usual m≈0.5 observations of superplastic deformation. An analysis of the data at several strains indicates a highly temperature dependent threshold stress is present, with either a n=2 or n=3 assumption for the stress exponent. The magnitude of the threshold stresses in IN90211 are smaller than usually observed in a dispersion strengthened matrix (1–20% instead of ≈50% of the Orowan stress). Experimental evidence from creep experiments supports the n=3 deformation mechanism as the rate limiting step of deformation.