bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linear-Response Calculations of Electron-Phonon Coupling Parameters and Free Energies of Defects
Authors: Quong Andrew A. , Liu Amy Y. 
Published: April 2011

AbstractLinear-response theory provides an efficient approach for calculating the vibrational properties of solids. Moreover, because the use of supercells is eliminated, points with little or no symmetry in the Brillouin zone can be handled. This allows accurate determinations of quantities such as real-space force constants and electron-phonon coupling parameters. We present highly converged calculations of the spectral function α2F(ω) and the average electron-phonon coupling for Al, Pb, and Li. We also present results for the free energy of vacancy formation in Al calculated within the harmonic approximation.
Phase Stability of the Sigma Phase in Fe-Cr Based Alloys
Authors: F Marcel Il. , Esfurjani Sluiter. Koivan , Kawazoe Yoshiyuki 
Published: April 2011

AbstractThe FeCr sigma phase is a good example of a complex structure: it. has 30 atoms in the unit cell and 5 inequivalent lattice sites, and it belongs to the class of tetrahedrally close packed structures, also known as Frank-Kaspar structures. So far. such structures have riot been treated within a first-principles statistical thermodynamics framework. It will be shown that dtlme to advances in algorithms and hardware important features of the phase stability of complex phases can be computed. The factors which affect the stability of the sigma phase have been studied using carefully selected supercells for electronic total energy calculations. cluster variation calc:ulations in the tet.rahedron approximation were performed to evaluate the effect of partial disorder and of finite temperature. The preferred occupancy of the 5 lattice sites has been investigated and is compared with experimental determinations.
Ab Initio Study of Expitaxial Growth on a Si(100) Surface in the Presence of Steps
Authors: Milman V. , Pennycook S. J. , Jesson D. E. 
Published: April 2011

AbstractThe motion of a Si adatom over the reconstructed Si(100) surface with single-height rebonded (SB) step is studied using the pseudopotential total energy method. The step is shown to act as a good sink for adatoms descending onto the lower ledge. This is due to the presence of deep traps at the rebonded dimer row on the lower terrace and to the negative Ehrlich-Schwoebel barrier (the activation barrier for descent from the edge is 0.23 eV lower than for the motion on a flat surface). The diffusion characteristics of the adatom on both terraces are virtually unaffected by the presence of the step. The dimer buckling sequence on a lower terrace depends strongly on the position of the adatom along the diffusion path.
Electronic Structure and Stability of Ordered Vacancy Phases of NbN
Authors: Ethridge E. C. , Erwin S. C. , Pickett W. E. 
Published: April 2011

AbstractA recently reported metastable phase of NbN with a superconducting Tc=16.4 K is characterized using full potential electronic structure methods. This new phase, which has Pm3m (cubic) symmetry, can be described as the B1 (rocksalt) structure with 25% ordered vacancies on each sublattice. We compare the equation of state and electronic spectrum of this Pm3m phase with its rocksalt counterpart [1] and with Nb4N3 in the 14/mmm (tetragonal) phase, which allows the characterization of N vacancies without accompanying Nb vacancies. For Pm3m NbN, the calculated lattice constant is 5% smaller than reported and the energy is 1.00 eV/molecule higher than B1 NbN, suggesting that the newly reported phase is something other than a stoichiometric Pm3m phase of NbN. We report on the energy surface for tetragonal distortions of this phase, from which we evaluate its structural stability and obtain Poisson's ratio.
Ab-Initio Calculations of the Electronic Structure and Properties of Titanium Carbosulfide
Authors: Ramalingam Bala , McHenry Michael E. , Garrison Warren M. , MacLaren James M. 
Published: April 2011

AbstractTitanium carbosulfide (Ti2CS) is frequently found as an inclusion phase in Ti - containing steels. It is of considerable interest because, whenever present in preference to the more common manganese sulfide (MnS), it significantly improves the toughness (a very desirable property) of the steel. Currently, to the best of our knowledge, there is no data, either computational or experimental, regarding the structural properties of Ti2CS. This data is needed to understand the influence of the Ti2CS inclusions on the toughness of the host material.In this paper, our results from the ab-initio calculations, using the LKKR-ASA (Layer Korringa Kohn Rostoker method in the Atomic Spheres Approximation) on the equilibrium ground state properties of bulk Ti2CS are presented and discussed. In particular, attention is focused upon (a) the Energy – Atomic Volume curve generated to calculate the equilibrium lattice constant and the bulk modulus, and (b) the density of states calculations. The application of these results to the subsequent study of an interface involving the carbosulfide and the host matrix is also illustrated.
O(N) Multiple Scattering Method for Relativistic and Spin Polarized Systems
Authors: Beiden S. V. , Guo G. Y. , Temmerman W. M. , Szotek Z. , Gehring G. A. , Wang Yang , Stocks G. M. , Nicholson D. M. C. , Shelton W. A. , Ebert H. 
Published: April 2011

AbstractWe have implemented the fully relativistic and spin-polarized extension of the O(N) real space locally self-consistent multiple scattering formalism [1]. Here we present preliminary results for the spin and orbital magnetic moments and magneto-crystalline anisotropy in iron metal. The spin and orbital moments are in good agreement with the results of conventional electronic structure methods. In addition we present preliminary results for the magnetocrystalline anisotropy obtained in the frozen potential approximation.
Polarization, Dynamical Charge, and Bonding in Partly Covalent Polar Insulators
Authors: Resta R. , Massidda S. , Posternak M. , Baldereschi A. 
Published: April 2011

AbstractWe have investigated the macroscopic polarization and dynamical charges of some crystalline dielectrics presenting a mixed ionic/covalent character. First principles investigations have been done within the Hartree-Fock, LDA, and model GW approaches. All calculations have been performed on the same footing, using the all-electron FLAPW scheme. Apparently similar oxides have strikingly different behaviors: some (like the ferroelectric perovskites) have giant dynamical charges, while others (like ZnO) are quite normal and display dynamical charges close to the nominal static ones. We find the rationale for such differences.
Dynamics And Morphology Of Cracks In Silicon Nitride Films: A Molecular Dynamics Study On Parallel Computers
Authors: Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya 
Published: April 2011

AbstractMultiresolution molecular dynamics approach on parallel computers has been used to investigate fracture in ceramic materials. In microporous silica, critical behavior at fracture is analyzed in terms of pore percolation and kinetic roughening of fracture surfaces. Crack propagation in amorphous silicon nitride films is investigated, and a correlation between the speed of crack propagation and the morphology of fracture surfaces is observed. In crystalline silicon nitride films, temperature-assisted void formation in front of a crack tip slows down crack propagation.
Simulation Of Dislocations In Ordered Ni3Al By Atomic Stiffness Matrix Method
Authors: Hsu Y. E. , Chaki T.K. 
Published: April 2011

AbstractA simulation of structure and motion of edge dislocations in ordered Ni3Al was performed by atomic stiffness matrix method. In this method the equilibrium positions of the atoms were obtained by solving a set of linear equations formed by a stiffness matrix, whose terms consisted of derivatives of the interaction potential of EAM (embedded atom method) type. The superpartial dislocations, separated by an antiphase boundary (APB) on (111), dissociated into Shockley partials with complex stacking faults (CSF) on (111) plane. The core structure, represented by the Burgers vector density distribution and iso-strain contours, changed under applied stresses as well as upon addition of boron. The separation between the superpartials changed with the addition of B and antisite Ni. As one Shockley partial moved out to the surface, a Shockley partial in the interior moved a large distance to join the lone one near the surface, leaving behind a long CSF strip. The decrease in the width of the APB upon addition of B and antisite Ni has been explained by a reduction of the strength of directional bonding between Ni and Al as well as by the dragging of B atmosphere by the superpartials.
The Composition Of Polymer Composite Fracture Surfaces As Studied By Xps
Authors: Wiegand Donald A. , Pinto James J. 
Published: April 2011

AbstractThe composition of the fracture surfaces of a composite made up of a polycrystalline organic nonpolymeric filler and a binder composed of a copolymer was studied by XPS. Because the binder and the filler of the composite each have at least one element not in common it is possible to easily distinguish between the binder and filler by XPS. A measure of the relative amounts of binder and filler on the fracture surfaces, therefore, could be made as a function of the sample temperature, T, and the strain rate during fracture. The ratio of filler to binder, F/B, increases with decreasing T at constant strain rate and is least sensitive to strain rate at T's below TG, the quasi static glass transition T. At higher T, F/B increases with strain rate at constant T. These results indicate that as the binder becomes stronger and stiffer due to a decrease in T or an increase in strain rate more of the fracture processes take place in the filler whose properties are expected to be less sensitive to T and strain rate. These results are related to the fracture properties as observed by uniaxial compression.
Molecular-Dynamics Simulations Of Fracture: An Overview Of System Size And Other Effects
Authors: Holian B. L. , Zhou S.J. , Lomdahl P.S. , Gronbech-Jensen N. , Beazley D.M. , RAVELO R. 
Published: April 2011

AbstractWe have studied brittle and ductile behavior and their dependence on system size and interaction potentials, using molecular-dynamics (MD) simulations. By carefully embedding a single sharp crack in two- and three-dimensional crystals, and using a variant of the efficient sound-absorbing reservoir of Holian and Ravelo [Phys. Rev. B 51, 11275 (1995)], we have been able to probe both the static and dynamic crack regimes. Our treatment of boundary and initial conditions allows us to elucidate early crack propagation mechanisms under delicate overloading, all the way up to the more extreme dynamic crack-propagation regime, for much longer times than has been possible heretofore (before unwanted boundary effects predominate). For example, we have used graphical display of atomic velocities, forces, and potential energies to expose the presence of localized phonon-like modes near the moving crack tip, just prior to dislocation emission and crack-branching events. We find that our careful MD method is able to reproduce the ZCT brittle-ductile criterion for short-range pair potentials [static lattice Green's function calculations of Zhou, Carlsson, and Thomson, Phys. Rev. Letters 72, 852 (1994)].We report on progress we have made in large-scale 3D simulations in samples that are thick enough to display realistic behavior at the crack tip, including emission of dislocation loops. Such. calculations, using our careful treatment of boundary and initial conditions - especially important in 3D - have the promise of opening up new vistas in fracture research.
Fracture Surface Fractal Dimension Determined Through An Extensive 3-D Reconstruction
Authors: Ammann J.J. , Nazar A.M. 
Published: April 2011

AbstractAn efficient image processing method is developed to determine the fractal dimension from a high resolution 3-D reconstruction of fracture surface. The third dimension of the fracture surface is obtained from a stereo pair. The elevation is locally determined through a recursive window matching algorithm centered on the cross-correlation operation. The method allows to reach high vertical and horizontal resolutions of the elevation map.The fractal dimension is obtained by an implementation of the slit-island method. A series of contour lines is extracted from the reconstructed surface. The images of the contour lines are progressively reduced in size and at every step the curve length is estimated. The result is then normalized according to the scale factor to build a Kolmogorov plot.The performance of this method is demonstrated on a synthetic image generated by a fracture surface mathematical model.
High-Pressure Behavior of Iron Sulfide
Authors: Fei Y. , Prewitt C. T. 
Published: April 2011

ABSTRACTA high-temperature diamond-anvil cell has been developed for in situ characterization of material properties at high pressure and temperature. Using this technique, we have studied the phase relations and physical properties of iron sulfide, FeS, up to 30 GPa and 900 K. In situ X-ray diffraction measurements revealed five polymorphs of FeS, which are closely related to a simple NiAs-type hexagonal structure. In addition to confirming the previously observed phase transitions, we observed a new hexagonal phase of FeS with axial ratio (c/a ) close to ideal closepacking value of 1.63 at high pressure and high temperature. The compression behavior of this new high P-T phase was studied up to 25 GPa at 500 K, 600 K, and 800 K. There is an abrupt shortening of the c axis at about 6 GPa, which may result from an electronic transition, possibly a spin-pairing transition. The c-axis shortening across the electronic transition means that the high P-T phase has substantially shorter interlayer Fe-Fe distances, which would lead to metallization of FeS at high pressure. Changes in density and chemical bonding of FeS at high pressure and temperature will affect the solution and melting behavior in systems such as Fe-FeS. These changes also have important implications for understanding sulfur-bearing iron-cores of planetary bodies.
Crystal Phases and Lattice Dynamics of Slip-Cast β'-Sialons
Authors: Loong C.-K. , Richardson J. W. , Suzuki S. , Ozawa M. 
Published: April 2011

ABSTRACTThe crystal structures and phonon densities of states (DOS) of β'-Sialon ceramics, Si6-zAlzOzN8-z (0 ≤ z ≤ 6), prepared by a novel slip-cast method were studied by neutron scattering techniques. A Rietveld analysis of the diffraction patterns shows that samples of z < 4 form a single-phase solid solution of Si-A1-O-N isostructural to β-Si3N4 (space group P63/m). Within this structure there is a consistent preferred occupation of 0 on the 2c sites and N on the 6h sites. For z > 4 the materials exhibit multiple-phase structure. The observed phonon DOS of the 0 ≤ z ≤ 4 ceramics displays phonon bands at about 50 and 115 meV. These features are considerably broader than the corresponding ones in β-Si3N4 powder. As z increases, effects due to atomic disorder lead to an overlap of the two phonon bands and a complete fill up of the phonon gap at ˜100 meV.
Large Lattice Mismatch Epitaxy
Authors: Mahajan S. 
Published: April 2011

ABSTRACTDuring the early stages of lattice mismatch epitaxy, island growth is observed in several systems. The evolution of this morphology is attributed to a large value of the substrate/layer interface energy. Origins of misfit and threading dislocations are also considered. Nucleation of misfit dislocations could occur either from steps present on surfaces of islands or from substrate/island edges. Arms of glide loops terminating at the surface in the first case form threading segments in the layer, whereas the coalescence of islands in which misfit dislocations are not aligned with respect to each other lead to threading dislocations in the second case. Existing approaches for lowering threading dislocation densities are also evaluated. A novel approach involving controlled, self-assembly of islands is presented to achieve the preceding objective.
Multilayer Enzyme Assembly for the Development of a Novel Fiber Optic Biosensor
Authors: Gao Harry H. , Chen Zhongping , Kumar Jayant , Marx Kenneth A. , Tripathy Sukant K. , Kaplan David L. 
Published: April 2011

AbstractWe have developed a technique to immobilize a multilayer enzyme assembly on an optical fiber surface. The technique utilizes a bifunctional amino coupling agent to link between different layers of enzymes. The method offers the flexibility of controlling the number of enzymes on a fiber surface. Multilayers of enzyme — Alkaline Phosphatase have been characterized using ellipsometry and surface plasma resonance. Chemiluminecence experiments have been conducted as a function of number of enzyme layers. The results indicated that at least 3 layers of enzyme can be assembled on a fiber surface. Utilising the new immobilization technique, a novel fiber optic biosensor system for the detection of organophosphorous-based pesticide has been developed. The detection mechanism is the pesticide inhibition of alkaline phosphatase catalyzed chemiluminescence. As a model analyte, paraoxon with ppb level concentration has been detected.
A Dual Constant Composition Study of the Kinetics of Mineralization and Demineralization of Bone Substitutes
Authors: Tucker B.E. , Gorlinea G.L. , Carney D.E. , Nancollas G.H. , Bearcroft J.A. 
Published: April 2011

AbstractCalcium phosphates are widely used as implantable materials in both dental andorthopaedic applications. Seven different bone substitutes (BS), including Interpore CorallineHAP, Cortical Bio-Oss, Endobon, Cancellous Bio-Oss, Dense HAP (hydroxyapatite), Collagraftgranules, and Porous HAP, have been evaluated using the Dual Constant Composition (DCC)kinetics methods. DCC measurements of the kinetics of dissolution and re-mineralization of theBS materials offer considerable advantages for the characterization of minor calcium-containingsurface species due to the insensitivity of conventional physical chemical methods such as X-raydiffraction and ESCA. Each sample was pre-conditioned (PC) in 0.15 M NaCl prior to the DCCkinetics procedures. The fastest dissolving material, Collagraft granules, showed a dissolution ratemore than two orders of magnitude larger than Dense HAP. Interestingly, the relativesupersaturation with respect to HAP (σ) following PC was normally negative, whereas withplasma sprayed HAP coated implants, these a values were as high as 20. Surface impurities mayplay a major role following in vivo implantation, since resorption is probably a major reparativemechanism. It is therefore essential to understand the dissolution behavior. Moreover, in a remineralizationmode, trace surface phases may determine the phase and morphology of the newlydeposited bone mineral.
Growth of GaAs/AlGaAs Quantum Dots Using Self-Organized InP Stressors
Authors: Hanna M. C. , Lu Z. H. , Cahill A. F. , Heben M. J. , Nozik A. J. 
Published: April 2011

AbstractGaAs quantum dots were formed in a near surface quantum well (QW) by producing lateral confinement with self-organized InP stressors grown in situ by metal organic chemical vapor deposition (MOCVD). We report here the influence of growth conditions on InP island formation on AlGaAs/GaAs single QW structures and also the influence of the QW structure on the optical properties of the GaAs quantum dots. We observe strong photoluminscence up to room temperature from the strain-induced quantum dots with energy redshifts of 70 meV below the QW peak.
Growth and Characterization of BRS GaInAsp-GaAs Laser Emitting At 0.8μm by Gas-Source Molecular Beam Epitaxy
Authors: Jelen C. , Slivken S. , Diaz J. , Erdtmann M. , Kim S. , Wu D. , Razeghi M. 
Published: April 2011

AbstractGaInAsP-GaAs buried ridge structure lasers emitting at 0.8μm have been fabricated on material grown in two steps by low pressure metalorganic chemical vapor deposition and gas-source molecular beam epitaxy. Preliminary laser results are reported, and the feasibility of using gas-source molecular beam epitaxy for the regrowth of sophisticated laser system is demonstrated.
Growth and Capacitance Spectroscopy of Self Assembled Quantum Dots
Authors: Medeiros-Ribeiro G. , Schmidt K. H. , Leonard D. , Cheng Y. M. , Petroff P. M. 
Published: April 2011

AbstractThe growth of InAs on GaAs self assembled quantum dots and their electronic properties is studied. The limit for coherent island growth is calculated with a simple model and compared to the experimentally observed values. Cross section transmission electron micrography and atomic force micrography are used to investigate this limit. The electronic properties studies involved the use of capacitance spectroscopy to map out the density of states in these structures as well as to probe the temperature dependence of the Coulomb Blockade effect in this system. It was found that Coulomb Blockade could be observed at temperatures in excess of 77K, representing an attractive approach for single electronics operating at high temperatures.
On the Moss-Burstein Shift in Quantum Confined Optoelectronic Ternary and Quaternary Materials
Authors: Ghatajc Kamakhya P. , Nag B. , Biswas S. N. 
Published: April 2011

AbstractIn this paper we have studied, the Burstein-Moss shift (BMS) in quantum wires (QWs) and quantum dots (QDs) of ternary and quaternary types of optoelectronic materials on the basis of a newly formulated electron dispersion law which occours as a result of heavy doping. It has been found, taking Hg1−xCdx.Te and In1−x.Gax.AsyP1−y lattice matched to InP as examples, that the BMS increases with :Lncreasing electron concentration and decreases with increasing film thickness in oscillatory manners for both types of quantum confinements, although the variations are totally band structure dependent. The numerical values of BMS is greatest in QDs and least in QWs together with the fact that the BMS in quaternary materials is greater than that of ternary comupounds. In addition the theoretical analysis is a quantitative agreement with the experimental datas as given elsewhere.
Influence of Structure on the Formation of Dislocation in LBO Crystal
Authors: Hu X. B. , Jiang S. S. , Huang X. R. , Zeng W. , Liu W. J. , Zheng Y. D. , Zhao Q. L. , Chen C. T. 
Published: April 2011

AbstractDislocations in LiB3O5(LBO) single crystal were investigated by white-beam synchrotron radiation topography(WBSRT). The WBSRT revealed that the grown-in dislocations are mainly pure screw or edge types with the Burgers vectors in the low index directions on (010) lattice plane. Based on the structure analysis, the formation cause of dislocations can be interpreted in terms of the loose packing of B-O rings and the low density of Li+on (010) lattice plane.
Theory of Surface Dimerization-induced Ordering in GaInP Alloys
Authors: Zhang S. B. , Froyen Sverre , Zunger Alex 
Published: April 2011

AbstractWe identify via thermodynamic energy minimization the role of subsurface strain (caused by surface reconstruction and dimerization) in the ordering of Ga0.51n0.5P alloys. Depending on the growth conditions, the alloy surfaces can have either β2(2×4), c(4×4) or c(8×6) reconstructions, with characteristic 2×1, 1×2 and 2×3 RHEED patterns. We show that (i) the 1×2 reconstruction will lead to a CUPtA surface ordering, (ii) a 2×1 reconstruction will lead to a CuPtB ordering, (iii) a 2×3 reconstruction will lead to a 3-period ordering, and (iv) single (double) bilayer steps are stable at low (high) anion chemical potential. These results are in good agreement with recent experimental observations.