bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Microstructure of National Bureau of Standards Reference Fly Ashes
Authors: Qian J. C. , Lachowski E. E. , Glasser F. P. 
Published: March 2011

ABSTRACTA suite of three fly ashes, National Bureau of Standards* Standard Reference Materials (SRMs) 2689, 2690 and 2691, was studied by transmission electron microscopy and by analytical electron microscopy (aem): sample preparation techniques are described. The chemical compositions of the glassy phase, analyzed by aem, showed a wide dispersion of values although the mean composition of the glass remained close to that of the whole fly ash.The microstructure of these materials is complex: besides crystalline inclusions, the aluminasilica glasses have undergone phase separation on a nanometer scale, and consist of two glassy phases. Since liquid-liquid phase separation has also been found in British fly ashes, it appears to be a characteristic feature of the glassy phase in Class F ashes and is also encountered in occasional Al-Si rich particles in Class C ashes. High iron content glass was found in fly ash SRM 2689, and its phase separation and crystallization were investigated.
Pseudoatomic Orbital Compact Basis Sets: Applications to Metallic Systems
Authors: Jansen Robert W. , Klein B. H. 
Published: March 2011

AbstractA self-consistent orbital-based scheme is applied to metallic systems and is found to be efficient for these materials. The technique uses the local density approximation in the pseudopotential framework, but replaces the planewave basis by a basis pseudoatomic orbitals constructed directly from the pseudoatoms. Free electron-like wavefunction components are handled by orthogonalizing the orbital basis to a few low energy planewaves as needed for good eigenvalue and total energy convergence. The method is fast and versatile enough to be used for a variety of problems. Applications to bulk bandstructures, total energies, and forces in Al and Nb are presented.
First-Principles Phonon Calculations for LA2CUO4
Authors: Cohen R. E. , Pickett W. E. , Krakauer Henry 
Published: March 2011

AbstractFull potential linearized augmented plane wave (LAPW) total energy calculations predict that the breathing mode in La2CuO4 is a high frequency mode, in agreement with experiment and contrary to previously published results. We also find the experimentally observed tilt mode to be unstable within the local density approximation (LDA). Eight other modes were studied, as well as the static structural parameters, and excellent agreement with experiment was found, indicating that LDA gives accurate total energies and static density response for the high temperature superconductors. Our results also suggest that phonons in the high Tc superconductors are not heavily dressed by magnetic or excitonic fluctuations, and thus that the isotope effect observed in the oxide superconductors is probably due to direct involvement of phonons in the superconductivitymechanism.
Quantum Chemical Molecular Dynamics
Authors: Caro A. , Victoria M. 
Published: March 2011

AbstractWe propose a simple electronic model for the cohesive energy of metals which explicitely considers eigenfunctions and eigenvectors in a single-particle LCAO approach. From them, forces are obtained to perform molecular dinamics or static relaxation. As a first application we compare the model predictions to full many-body ab-initio and Embedded Atom Model calculations of structure and energetics of small metallic clusters. Adventages and limitations of this approach as well as size restrictions are discussed.
Solid Solutions of AB2C4 Defect Semiconductors
Authors: de Pascale T.M. , Marinelli M. , Meloni F. , Mula G. , Serra M. , Borghesi A. , Guizzetti G. , Nosenzo L. 
Published: March 2011

AbstractAB2C4 defect semiconductors can be thought of as generalized zincblende compounds, in which the presence of two different cations and of vacant sites favours the formation of several crystalline phases. In this work we present a theoretical study of the structural stability of the ZnxCdl-xIn2S4 solid solutions. The end compounds crystallize in a layer (x = 1) and in a spinel structure (x = 0). Total energy first principle calculations have been performed for both phases and for various values of x. The theoretical structural stability diagram compares very well with experiment.
Vibrational Localization and Vibrational Spectra in Amorphous Silicon
Authors: Biswas R. , Bouchard A. M. , Kamitakahara W. A. , Grest G. S. , Soukoulis C. M. 
Published: March 2011

AbstractAmorphous silicon structures have been generated by quenching liquid silicon configurations using molecular-dynamics simulations. Localized vibrational modes have been identified in these models. The presence of under-coordinated atoms in these a-Si models leads to extra resonant modes at low frequencies. The vibrational densities of states, and dynamic structure factors for localized, resonant and extended modes, are discussed and compared with neutron scattering data. The amorphous networks have also been adapted to model amorphous silicon-germanium systems. Densities of states and localization characteristics have been calculated for a-SixGe1-x alloys and a-Si/a-Ge superlattices, and are compared to Raman measurements.
Structure of Unhydrogenated Amorphous Silicon Carbide
Authors: Kelires P. C. , Tersoff I. 
Published: March 2011

AbstractSimulations of unhydrogenated amorphous silicon carbide, formed by condensing a vapor of silicon and carbon atoms, indicate partial chemical ordering, with heteronuclear bonds predominating. We find no evidence of phase separation. Carbon atoms are predominantly three-fold coordinated while silicon atoms have four-fold coordination. By combining these results with results of experimental studies, we speculate on the role of hydrogenation in determining the structure of amorphous silicon carbide.
Properties of Liquid As: A First Principles Calculation
Authors: Li X.-P. , Allen P.B. , Car R. , Parrinello M. 
Published: March 2011

AbstractThe structural and electronic properties of liquid arsenic are calculated using density-functional quantum theory to calculate forces and trajectories of atoms. A semiconducting gap of 0.4 eV is found, and a coordination number of 2.8, close to the experimental values of 0.5 eV and 3. Our results support the existence of a Peierls-type distortion in liquid arsenic.
Native Defects in Diamond, Sic, and Si: Energetics and Self-Diffusion
Authors: Antonelli A. , Wang C. , Bemholc J. , Davis R. F. 
Published: March 2011

AbstractWe have investigated, via first principles total energy calculations, the energetics of elementary native defects in group IV semiconductors. Its implications on the relative abundance of these defects and self-diffusion phenomena are analyzed. The results show that in diamond the self-diffusion is dominated by vacancies, because the interstitial and direct exchange mechanisms have much greater activation energy. In SiC stoichiometry plays an important role. For Si-rich compound, Sic-antisite is the dominant defect in the intrinsic and p-type material, while the carbon vacancy is dominant in the n-type material. For C-rich material, the Csi-antisite is dominant regardless the position of the Fermi level. In Si, it well-known that the vacancy, interstitial and direct exchange mechanisms have very similar activation energies. Our results suggest that self-diffusion experiments carried out at various pressures can determine the relative contribution of each of these mechanisms.
Atomistic Simulation of Ionic and Electronic Defects in YBa 2 Cu3O7
Authors: Baetzold Roger C. , Islam M. Saiful 
Published: March 2011

AbstractAn empirical two-body potential model has been developed in order to describe the electronic and ionic defect properties of orthorhombic YBa 2 Cu307. The potential model was derived starting from known potentials and calculated potentials and fits the crystal structure to better than 0.03 A for the major bonds. Oxygen vacancy formation and hole trapping as a localized polaron are most favorable at the chain oxygen ion site. Hole trapping on Cu + ions is most favorable for ions in the copper-oxygen plane. Divalent impurity ions such as Ni+2, Zn+2 and Cd+2 can dissolve in the crystal preferentially at the Cu+2 plane site.
Derivation of Many-Body Potentials for Examining Defect Behavior in Bcc Niobium
Authors: Eridon James M. , Rao Satish 
Published: March 2011

AbstractMany-body potentials, in either the Embedded Atom or Finnis-Sinclair form, have gained wide popularity recently. The major difficulty in implementing the method concerns the derivation of suitable forms for the pair potential, electron density, and embedding, function which reproduce a range of empirically observable parameters such as elastic constants, defect formation energies, and defect Green's functions. This is a particularly difficult problem for niobium, which shows a variety of anomalous features in its phonon dispersion. Embedding functions which match only elastic constants may do a poor job of reproducing short wavelength behavior, and hence provide poor defect modeling. A straightforward method of deriving embedding functions for homonuclear BCC andFCC metals will be presented which provides excellent agreement with experimental phonon dispersion curves and elastic constants, as well as Griineisen coefficients, vacancy formation energies, lattice constants and heats of sublimation. The results of the application of a set of many-body potentials derived in this fashion to nitrogen irradiated niobium will be presented.
Point and Extended Defect Properties in H.C.P. Metals Revealed by Atomic-Scale Calculations
Authors: Bacon D.J. 
Published: March 2011

AbstractRecent modelling of defects in the h.c.p, metals is discussed, including the properties of vacancies and self-interstitials, and the structure of twin-boundary dislocations. Most simulations have used pair potentials, and their strengths and weaknesses are described. It is shown that an understanding of the atomic structure of h.c.p, defects is at last emerging.
Atomic Structure of a 60° Dislocation in Bulk Silicon and Germanium, and at Ge/Si Interface.
Authors: Nandedkar A. S. , Narayan J. 
Published: March 2011

AbstractAtomic structures of 60° dislocations were calculated in bulk Si and Ge ,and at Ge/Si interfaces, using energy minimization techniques. An empirical three body potential developed by Stillinger-Weber was used for Si ,and the same potential with modified parameters was used for Ge. Two different configurations of a 60° dislocation (shuffle and glide) were compared. Energetics of a 60° dislocation in shuffle configuration in bulk Si and Ge , and at Ge/Si interfaces are discussed.
Electronic Structure of Extended Defects in Close-Packed Metals
Authors: Crampin S. , Vvedensky D.D. , Maclaren J.M. , Eberhart M.E. 
Published: March 2011

AbstractStacking faults in close-packed metals are known to play a crucial role in determining mechanical behaviour. Extending recent layer Korringa-Kohn-Rostoker calculations on twin faults in a variety of FCC crystals, we study in detail the aluminium defect and develop an atomistic understanding of the modifying behaviour of small concentrations of impurity atoms.
Molecular Dynamics Study of A Model Langmuir-Blodgett Film
Authors: Bareman James P. , Cardini Gianni , Klein Michael L. 
Published: March 2011

AbstractMolecular dynamics calculations have been carried out on a primitive model of a Langmuir-Blodgett film. The model consists of a patch of 151 molecules, each with a head group and a 19 pseudoatom tail, physisorbed on a planar substrate at room temperature. The aggregated patch is found to be a stable entity for the duration of the calculation (200 ps), with structural features similar to those found in previous calculations on a monolayer system which employed periodic boundary conditions but no explicit headgroup. Results are presented for the density distribution normal to the surface, the average chain tilt angle distribution and for the number of gauche defects.
First Principles Study of Hydrogen Adsorption and Diffusion on Transition Metal Surfaces: Application to the Ru (0001) Surface
Authors: Chelikowsky-al James R. , Chou M.-Y. 
Published: March 2011

AbstractHydrogen adsorption and diffusion on the (0001) surface of ruthenium is investigated using ab initio pseudopotentials within the local density approximation. The adsorption energies at a number of different sites and bond lengths were investigated via total energy calculations. Using these calculated values a potential surface was constructed and an estimate for the activation barrier for hydrogen diffusion was obtained. The calculated value of 4.0 kcal is in good accord with the value of ≈ 4 kcal as determined from laser-induced thermal desorption experiments.
Computer-Generated Structural Models for a-Si:H
Authors: Lewis Laurent J. , Mousseau Normand , Drolet FranÇois 
Published: March 2011

AbstractA new algorithm for generating fully-coordinated hydrogenated amorphous silicon models with periodic boundary conditions is presented. The hydrogen is incorporated into an a-Si matrix by a bond-switching process similar to that proposed by Wooten, Winer, and Weaire, making sure that four-fold coordination is preserved and that no rings with less than 5 members are created. After each addition of hydrogen, the structure is fully relaxed. The models so obtained, to be used as input to molecular dynamics simulations, are found to be in good agreement with experiment. A model with 12 at.% H is discussed in detail.
Hyperfine Interactions in Dangling-Bond Defects
Authors: Cook Michael , White C.T. 
Published: March 2011

AbstractIn a recent theoretical study of the Pb center at the Si(lll)/SiO2 interface, 1,2 we pointed out the importance of spin-polarization effects for the accurate theoretical description of ESR hyperfine interactions. The small superhyperfine tensor in the Pb center, for example, could not have been definitely assigned to a subset of the second neighbors of the defect atom rather than its nearest neighbors without an explicit consideration of spin polarization effects.
Thermodynamics, Kinetics and Interface Morphology of Reactions Between Metals and GaAs
Authors: Lin Jen-Chwen , Chang Y. Austin 
Published: March 2011

ABSTRACTThe chemical stability of interfaces between metals and GaAs was discussed in terms of reaction sequence and diffusion path concepts. The factors which determine interface morphology were also given. These general ideas can be applied to any interfacial reactions between two dissimilar materials.
Characterization of Interfaces Between Polymers and Metals by Static Sims
Authors: Van Ooij W.J. 
Published: March 2011

AbstractThe use of static Secondary Ion Mass Spectrometry (SIMS) in the characterization of polymer surfaces and interfaces between polymers and metals is described. Examples are given of the use of SIMS to study the effects of plasma treatments on polyimide surfaces and for the analysis of the interface in metallized polytetrafluoroethylene (PTFE).
Xps Identification of Al-Pva Complex
Authors: Akhter S. , Jo S.K. , Zhou X.-L. , White J.M. 
Published: March 2011

AbstractAluminum was deposited on a polyvinyl alcohol film surface by reaction with trimethyl aluminum at 300 K. XPS analysis indicated a carbon free deposition of a monolayer of Al. The Al forms an oxy-carbide complex, AIOC, which exhibits a stoichiometry of 1:1:1 for Al, 0 and C. Within this complex Al is bonded to both C and 0 resulting in the appearance of low binding energy peaks in C(ls) and O(ls) spectra. The complex is oriented such that Al forms the outer-most layer. The Al modified surface was hydrophobic compared to the hydrophilic PVA. A reaction mechanism is proposed based on XPS and mass spectrometric data.
New Simulation of Polymers on Surfaces
Authors: Aguilera-Granja F. , Kikuchi Ryoichi 
Published: March 2011

AbstractA new method of simulation based on the output of the analytical equilibrium calculation of the Cluster Variational Method (CVM) is used to obtain information about the properties of the polymers adsorbed on a surface. We find a strong preferential adsorption of longer chains, in agreement with experimental observations. This tendency is more pronounced in neutral polymers than in polyelectrolytes. Other geometrical properties like trains, tails, and loops of adsorbed polymers are also calculated.
Interfacial Shear Strength of Ion Beam Modified UHMW-PE Fibers in Epoxy Matrix Composites
Authors: Ozzello A. , Grummon D. S. , Drzal L. T. , Kalantar J. , Loh I-H. , Moody R. A. 
Published: March 2011

AbstractUltra-high molecular weight polyethylene fibers possess exceptional strength and stiffness combined with low density. Their use as reinforcements in polymer matrix composites has, however, been limited by poor fiber adhesion. In the present study, individual fibers of UHMW-PE (Allied-Signal SPECTRA-1000) were modified by direct implantation of N+, Ti+ and Ar+ ions, at energies between 30 and 100 KeV, to doses ranging between 1x1014 and lx1015 ions/cm2. Fiber tensile strength was generally unaffected by these irradiations. Single-fiber droplet pull-off tests using DGEBA Epoxy with m-PDA curing agent have shown that ion beam surface modification of the fibers can give an increase of over 300% in interfacial shear strength (ISS). The improvements were found to vary with dose but were relatively insensitive to implant species. TEM observation of transverse microtomed sections confirmed a substantial improvement in fiber-matrix adhesion for ion beam modified UHMW-PE composites.
Electrophoretically Applied Dielectrics for Amorphous Metal Foils Used in Pulsed Power Saturable Reactors.
Authors: Sharp D. J. , Harjes H. C. , Mann G. A. 
Published: March 2011

AbstractAmorphous metal foil-wound inductors have been tested as ferromagnetic saturable inductive elements for pulsed-power (multi-terawatt) switching modules in the inertial confinement fusion program at Sandia National Laboratories. Saturation switching may provide large 100 ns current bursts necessary to accelerate ion beams for the fusion fuel pellet implosion required, for example, in PBFA (particle beam fusion accelerator) operation.In simulated capacitor testing premature dielectric breakdown of thin polyethylene terephthalate film insulation in the inductor windings occurs at considerably below 2500 V. This appears to be due to inadvertant dielectric damage from micro-spikes on the amorphous foil surface. Electron micrographs and dielectric breakdown data illustrate that electrophoretically-applied dielectric coatings, deposited from organic aqueous colloid dispersions, can be used to provide insulating coatings on the foil which provide a 240% improvement (6000 V) in the breakdown strength of wound amorphous foil inductors.The theory and operation of a dedicated electrophoretic continuous coating system is described. The machine was constructed and successfully applied for dielectric coating of amorphous metal foil. Additional possible applications exist for practical dielectric coating of metallic films or foils used in various commercial wound-type capacitor structures.
Solvent and Curing Effects on Diffusion at Polyimide Interfaces
Authors: Tead S. F. , Kramer E. J. , Russell T. P. , Volksen W. 
Published: March 2011

AbstractInterdiffusion at interfaces between deuterated polyamic acid (d-PAA) and polyimide (PI) films was investigated with forward recoil spectrometry, an ion beam analysis technique. The PI films were prepared by spin - coating a solution of PAA on a silicon substrate, followed by an anneal at a temperature Ti, which produced partial or complete conversion of the PAA to PI. An overlayer of d-PAA was added in one set of samples by spin - coating from solution and in another set by transferring (in the absence of solvents) a dry d-PAA film onto the PI surface. The bilayer samples were then either annealed at a temperature Td or allowed to stand at room temperature. Bilayers prepared by spin - coating d-PAA from solution directly on partially cured PI films had interdiffusion distances w that decreased with increasing values of Ti to immeasurable levels by Ti = 200 °C. The decrease in w with increasing Ti is thought to be caused by a positive Flory parameter between PAA and PI which increases with the imide fraction in the PI film; the result is an increasing immiscibility between the swollen polymer layers. No interdiffusion occurred in the solventless - transfer samples for any combination of temperatures Ti or Td from room temperature up to 400 °C. Post - annealing of spin - coated bilayers at a temperature Td up to 400 °C was ineffective in producing any additional interdiffusion. Both of these results indicate that thermally activated interdiffusion (even for initially unimidized samples) does not exist in the absence of solvents, an effect attributed to the rapid increase of the glass transition temperature of the polymer with imidization.
Determination of the Bond Strength of a Metal Coating on a Substrate
Authors: Sachse Wolfgang , Kim Kwang Yul , Conway H. D. 
Published: March 2011

AbstractThis paper reviews the principles and describes new procedures for determining the bond strength of a metal film on a substrate. Considered are mechanical, electrical, acoustical and thermal measurements. Particular attention is placed on techniques which permit an unambiguous connection to be made between measured quantitites and the parameters by which the adhesive strength of a coating on a substrate can be determined.
Characterization of Nanophase Materials by X-Ray Diffraction and Computer Simulation
Authors: Eastman J. A. , Thompson L. J. 
Published: March 2011

AbstractX-ray diffraction experiments on nanophase Pd have been performed with the primary goal of determining the nature of grain boundary structures in nanophase materials. A kinematical diffraction analysis has been developed to interpret x-ray θ-2θ data by comparing actual scans with scans produced by computer simulation. This simulation program has been used to explore the effects on diffracted intensity of a variety of microstructural and grain boundary structural parameters such as void concentration, grain size, grain boundary width, and changes in interplanar spacing and density in grain boundary regions. It has been found that a reasonable match to experimental data is produced by at least two model structures; in one, the material contains randomly positioned voids or vacancies, while in the other, the interplanar spacings in grain boundary regions are varied with respect to the spacings found in the grain interiors.
Influence of Substrate on Cracking of Vapour-Deposited Thin Films Due to Residual Stresses
Authors: Fisher Robert M. , Duan J.Z. 
Published: March 2011

AbstractThe influence of the substrate material on the column and grain microstructure, the residual stresses, crack patterns and delamination of Cr films has been investigated using TEM, SEM, and X-ray diffraction. The inter-influence of these factors which determine the long term reliability of microelectronics is discussed. When interfacial adhesion is very low, as may be the case with some polymer substrates, cracking occurs discontinuously during film formation each time the stress exceeds the critical value for fracture.