bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Green Function Cellular Method and Its Relation to Multiple Scattering Theory
Authors: Butler W. H. , Zhang X.-G , Gonis A. 
Published: March 2011

ABSTRACTWe investigate techniques for solving the wave equation which are based on the idea of obtaining exact local solutions within each potential cell, which are then joined to form a global solution. We derive full potential multiple scattering theory (MST) from the Lippmann-Schwinger equation and show that it as well as a closely related cellular method are techniques of this type. This cellular method appears to have all of the advantages of MST and the added advantage of having a secular matrix with only nearest neighbor interactions. Since this cellular method is easily linearized one can rigorously reduce electronic structure calculations to the problem of solving a nearest neighbor tight-binding problem.
Self-Consistent-Field Kkr-Cpa Calculations in the Atomic-Sphere Approximations
Authors: Singh Priabhakar P. , Gonis A. , Fontaine Didier De 
Published: March 2011

ABSTRACTWe present a formulation of the Korringa-Kohn-Rostoker coherent potential approximation (KKPt-CPA) for the treatment of substitutionally disordered alloys within the KKR atomic-sphere approximation (ASA). This KKR-ASA-CPA represents the first step toward the implementation of a full cell potential CPA, and combines the accuracy of the KKR-CPA method with the flexibility of treating complex crystal structures. The accuracy of this approach has been tested by comparing the self-consistent-field (SCF) KKR-ASA-CPA calculations of Cu-Pd alloys with experimental results and previous SCF-KKR-CPA calculations.
First Principles Calculation of Residual Resistivity
Authors: Nicholson D. M. , Brown R. H. , Butler W. H. , Yang H. , Swihart J. W. , Allen P. B. , Mehta A. , Schwartz L. M. 
Published: March 2011

ABSTRACTThe list of physical properties which are important in the design of materials and which are routinely calculated from first principles within the local density approximation to density functional theory is continually growing. In this paper we discuss the application of multiple scattering theory to the calculation of the residual resistivity of disordered alloys. Progress has been made on two fronts. First, the coherent potential approximation for the resistivity, which sums to all orders a limited set of multiple scattering diagrams, has given resistivities in agreement with experiment for alloys where the site occupation is roughly random. Second, the linearized KKR was used to evaluate the Kubo formula for several large configurations of atoms and obtain the resistivity with all multiple scattering paths included. This method is not limited to random alloys, but can be applied to short range ordered and amorphous alloys provided the resistivity is high enough to limit the mean free path to a single unit cell.
Calculations of Spin-Wave Energy Gap in Transition Metals
Authors: Antropov V.P. , Liechtenstein A.I. 
Published: March 2011

ABSTRACTAnalytical expressions for the total energy derivative with respect to the magnetic moment rotations have been derived in the relativistic local-spin density functional approach and multiple scattering theory. The spin-wave stiffness constant as well as the gap in the spin-wave spectrum due to relativistic anisotropy effects is calculated in KKR-ASA approximation for bcc Fe. This is compared with other theoretical calculations and available experimental data.
Can Polar Interface Energies be Calculated by Means of Supercells?
Authors: Lambrecht W. R. L. , Amador C. , Segall B. 
Published: March 2011

ABSTRACTTwo problems associated with the calculation of polar interface energies in semiconductors or insulators are discussed: (1) the stoichiometry of the associated interface region, and (2) the impossibility of constructing a supercell with two equivalent interfaces in certain cases. An approach for calculating the energy of a single interface is introduced. It utilizes local quantities obtained from supercell calcualtions and the electrostatic energy of the isolated single interface. Results are presented for GaAs inversion domain boundaries and NaCl antiphase boundaries. The problem associated with charge transfer between two different interfaces is discussed.
Electronic Structure of Planar Faults and Point Defects in High Temperature Intermetallics
Authors: Maclaren J.M. , Woodward C. 
Published: March 2011

ABSTRACTFirst principles electronic structure calculations, using the layer Korringa-Kohn-Rostoker method, are reported for isolated planar faults in TiAl. The calculated fault energies are discussed in the context of suggested superdislocation separation reactions. The influence of dilute impurities on fault energies are treated using the coherent potentialapproximation. Using this approach, the variation of fault energies in TiAl resulting from stoichiometry changes and from the addition of Mn axe calculated, and compared to recent experimental data.
Lie Group Calculation of the Green Function of Disordered Systems
Authors: Brouder Christian 
Published: March 2011

ABSTRACTWithin the framework of the muffin-tin multiple-scattering theory, the scattering path operators are given by the inverse of a matrix consisting of atomic t-matrices and a structural matrix. The influence of the displacement of an atomic centre on the structural matrix can be described analytically using Lie group techniques. From this analytical expression and the standard perturbation expansion of the Lippmann-Schwinger equation, it is possible to write the Green function of a disordered system as a series of terms whichare averages over configurations. These averages can be calculated analytically from themoments of the interatomic distances. Special terms of this series are then summed up toinfinity using Dyson equation. This formalism is computationally very effective to calculate electronic properties of systems with thermal or structural disorder. In this paper, the theoretical basis of this approach is briefly described and the convergence properties of the expansions are investigated.
Observation of Elastic Wave Localization
Authors: Ye Ling , Cody George , Zhou Minyao , Sheng Ping , Norris Andrew 
Published: March 2011

ABSTRACTSpatial localization of bending waves was observed on a steel plate (72"X72"X1") decorated with lucite blocks (3.5"X3.5"X3") arranged in either a periodic or a random array. The exponential decay length of the localized modes is as short as 12 cm at 2.8 kHz, and increases with frequency as (f0 - f)-1, where f0 = 3.5 kHz is a quasi-mobility edge. The experimental data and finiteelement calculations suggest that the observed localization ofbending waves is due to the strong resonant scattering of bending waves by the shear modes of lucite/steel system. The generic nature of this localization phenomenon suggests its potential use as a attenuation mechanism for bending waves.
Photoemission of CO/CU(100). Non-Relativistic Spin- and Angle-Resolved Normal Emission
Authors: Schneeweiss R. , König U. , Redinge J. , Weinberger P. , Schneider C. M. , Kirschner J. 
Published: March 2011

ABSTRACTThe Co/Cu(100) system is the first system known where the contributions to the spin polarisation of spin-orbit coupling and the ferromagnetic overlayer were clearly distinguished experimentally. In order to get a first understanding of the photoemission data non-relativistic spin-polarized photoemission calculations are performed for one and two overlayers of Co on Cu(100).
The Wave Function in Multiple Scattering Theory
Authors: Butler W. H. , Zhang X. -G. 
Published: March 2011

ABSTRACTThe wave function in Multiple Scattering Theory (MST) is a locally exact solution to the Schrödinger equation for any ℓ truncation (ℓmax), except at the the muffin-tin boundaries (or cell boundaries in a full cell calculation) where it and its derivative generally have discontinuities. These discontinuities vanish only in the limit ℓmax → ∞. Furthermore, the MST wave function as usually calculated is not correctly normalized which means the density of states calculated from the Green function does not agree with that calculated from the Lloyd formula. Here we obtain an alternative wave function from the usual MST secular equation which is smooth and continuous everywhere and which is correctly normalized.
Dielectric Permittivities at X-Band Frequencies of Conductive Fibers Aligned in Polymer Matrices
Authors: Ho Yung-Shou , Lodge J. , Schoen P. E. 
Published: March 2011

AbstractComposites have been formed of Cycom, nickel-coated graphite fibers, aligned at concentrations of up to 6 weight percent in polymer matrices. Dielectric constants up to approximately 70 have been measured for these samples at x band frequencies. The results have been compared with a single non-interacting particle theory.
Statistical Mechanics of Phase Transitions with a Hierarchy of Structures
Authors: Berker A. Nihat , Caflisch Robert G. , Kardar Mehran 
Published: March 2011

AbstractRescaling (renormalization-group) [1] and restructuring [2] transformations are used in the statistical mechanics of systems with different complexities at different length scales, starting with the microscopic scale. These transformations are effected by a partial trace of the partition function, yielding effective coupling constants that incorporate the free energy contribution of the structures and length scales that are summed out of the problem. An example of this approach is a quantitative treatment [3] of the phase diagram of krypton adsorbed onto graphite. At the smallest length scales, adatom adsorption (first and second layer) and vibrations at adsorption sites are considered. At the next scale, sublattice formation and vacancy occurrence on the hexagonal graphite surface are considered. At a larger scale, heavy and superheavy domain wall formation, wall crossings and annihilations (dislocations) [4] are considered. This problem is treated by a sequence of 5 different transformations. Starting with the microscopic potentials, phase diagrams are obtained in temperature versus pressure or coverage, featuring disordered, commensurate and incommensurate solid phases, in good agreement with experiments [5]. The mechanism for reentrant phase transitions is divulged. Such solutions can be considered approximate treatments of physical systems or, alternatively, exact solutions of “hierarchical models” [6]. This “realizability” on hierarchical lattices insures the robustness of the approximation.
Orientation in Biomimetic Polymer-Mineral Composites
Authors: Burdon Jeremy , Calvert Paul 
Published: March 2011

AbstractMechanisms for the production of oriented precipitates are reviewed in the context of the orientation in mineralized biological tissues. Organic crystals have been oriented in polymer matrices by crystallization in a temperature gradient and by crystallization within a drawn crystalline polymer. Elongated oxide particles can be formed in a polymer by drawing of a material which contains phase-separated droplets of alkoxide, followed by hydrolysis of the alkoxide. Highly elongated rod-like or disc-like particles can be formed. Alternatively drawn films of a polymer blend can be swollen with alkoxide and hydrolysed to produce elongated chains of particles.
Hierarchial Structure and Physical Properties of Natural Cellulosic Fibers
Authors: Rebenfeld Ludwig 
Published: March 2011

AbstractNatural cellulosic fibers have in common the fact that cellulose is the key polymeric component in the structure, although the chemical composition varies widely depending on the specific source of the fibers. Cellulose is a long-chain linear condensation polymer of β-D-glucose with three free hydroxyl groups on each monomeric unit, resulting in strong inter- and intramolecular hydrogen bonds. Because of the hydrogen bond network, and also due to restricted rotation around the polymeric 1,4- β-linkage, cellulose is a rigid and stiff chain with a Tg well above the chemical decomposition temperature.Despite the high Tg native cellulose is invariably highly crystalline as a result of the biosynthetic process. In naturally occurring cellulosic fibers, the cellulose crystallites are aggregated into fibrils which constitute the underlying building blocks of the fiber. In cotton, the fibrils are laid down during the development or growth of the fiber in the form of concentric layers. The fibrils are disposed at an angle of 23° with respect to the fiber axis and thus they describe a helical pattern. The sense of the helix reverses frequently along the length of the fiber. This morphology is unique to cotton; other cellulosic fibers such as ramie and jute have similar fibrillar structures, but fibrillar angles in the 5 to 10 degree range, with no reversals. Wood fibers, on the other hand, are structurally more heterogeneous and may be considered as composites.
Conductive Composite Fibers with a Rigid-Rod Matrix
Authors: Beltsios Konstantinos , Carr S. H. 
Published: March 2011

AbstractConductive composite fibers are prepared by dry-jet wet-spinning of a strong-acid solution of rod-like polymers and phthalocyanine(Pc) compounds. A model yielding a hierarchical structure for a pure rigid-rod fiber is described first. The inclusion of NiPc in the spinning dope leads upon coagulation to isolated NiPc domains that are predicted to correspond to body centered cells (exhibiting various degrees of disorder). The observed dependence of fiber conductivity of composition is explained in terms of tunneling and percolation processes.
Raman and Optical Characterization of Porous Silicon
Authors: Harvey J. F. , Shen H. , Lux R. A. , Dutita M. , Pamulapati J. , Tsu R. 
Published: March 2011

ABSTRACTRaman spectra from electrochemically etched porous silicon are correlated with photoluminescence (PL) data from the same spots of the sample. This correlation is consistent with optical properties of quantum confinement. The dielectric constant determined from angle resolved ellipsometry gives values far below that of bulk silicon. This reduction is due to the combined effects of voids as well as quantum confinement. The PL spectrum shows a weak high energy peak around 2.8eV in addition to the strong broad peak at 1.5 to 1.9eV. The temperature dependence of PL resembles that of bound excitons such as Si:S, having a thermal dissociation energy of 100 meV near room temperature. The radiation life time changes from tens of microseconds near room temperature to a few milliseconds at liquid helium temperatures. The rapid increase in lifetime and decrease in PL intensity at low temperatures indicates that phonons are probably involved.
Visible Electroluminescence of Porous Silicon Devices with a Solid State Contact
Authors: Richter A. , Lang W. , Steiner P. , Kozlowski F. , Sandmaier H. 
Published: March 2011

ABSTRACTThe photoluminescence and electroluminescence of light emitting porous silicon (LEPOS) is described. The porous silicon is made by anodic dissolution of silicon in HF with an applied electrical current and illumination with visible light. Photoluminescence is observed using ultraviolet light, visible electroluminescence is achieved by applying a voltage to a solid state contact on top of the porous layer. The luminescence, the structure and the composition of the LEPOS are studied.
Composition and Morphology of Luminescent Porous Si
Authors: Petrova-Koch V. , Kux A. , Müller F. , Muschik T. , Koch F. , Lehmann V. 
Published: March 2011

ABSTRACTUsing thermal effusion of H together with a weighing of the remaining Si we determine the composition of luminescing porous Si. From studies of the IR vibration spectrum and its change with effusion we. argue that the H of freshly prepared microporous Si is bound in the dihydride form SiH2. We thus obtain a surface to volume ratio and a characterisicic linear dimension of the porous surface layer. The paper concludes with some observations on photo- and electroluminescence.
Sims Analysis of the Contamination of Porous Silicon by Ambient Air
Authors: Canham L T , Blackmore G W 
Published: March 2011

ABSTRACTMicroporous silicon layers contain an enormous surface area (> 500 m2 cm−3) that influences their structural, optical and electrical properties. When freshly etched the pore wall surface can be extremely clean and composed primarily of hydrogen and fluorine. Extended storage in ambient air however will convert this clean hydride surface into that of a contaminated native oxide.Using dynamic SIMS profiling we demonstrate here that slow oxidation at room temperature by ambient air is accompanied by impregnation with atmospheric boron and sulphur but that levels of calcium and sodium for example, remain exceedingly low. We conclude that the pore wall surface is very efficiently protected from particulate - related airborne species but is susceptible to contamination from small molecules present in the atmosphere at trace levels.
Raman Scattering in Electrochemically Prepared Porous Silicon
Authors: Wu Y. -J. , Zhao X. -S. , Persans P. D. 
Published: March 2011

ABSTRACTPorous silicon of various porosity has been prepared by electrochemical etching of silicon with different doping levels. Room temperature photoluminescence in the visible range is observed from the powder scraped from the top layer of the etched samples. In this paper we use Raman scattering to characterize the source of the high efficiency photoluminescence. We have also studied microcrystalline silicon prepared by thermal annealing of hydrogenated amorphous silicon/amorphous silicon oxide multilayers.
The Structure of Porous Silicon Revealed by Electron Microscopy
Authors: Cullis A. G. , Canham L. T. , Dosser O. D. 
Published: March 2011

ABSTRACTThis detailed electron microscope study of porous silicon compares the different structures of macro-, meso- and microporous material. Mesoporous silicon of high porosity (∼-80%) exhibits efficient red photoluminescence at room temperature. Transmission electron microscopy provides strong direct evidence that this visible luminescence arises from dramatic carrier confinement in quantum-size, crystalline silicon structures. Images of undulating, interconnected ‘quantum wires’ of widths <3nm are shown.
Piezoresistance and Quantum Confinement in Microcrystalline Silicon
Authors: Foresi J. S. , Moustakas T. D. 
Published: March 2011

ABSTRACTWe report piezoresistance studies in microcrystalline silicon films produced by reactive sputtering from a silicon target in an atmosphere of hydrogen and argon. The microcrystalline silicon films are two phase materials consisting of 50-100Å diameter silicon crystallites embedded in an amorphous Si-Hx matrix. The conductivity of the films was found to decrease significantly when the films were put under compression. Conductivity decreases of up to 100% were observed; this large conductivity changes with strain indicate that microcrystalline silicon is ideally suited for highly sensitive strain gauge applications. The results can be qualitatively accounted for in a model which assumes quantum confinement of carriers in 50Å diameter silicon crystallites separated by tunnelable amorphous Si-Hx barriers.
Current–Voltage Characteristics of Porous Silicon Made from A P/N Junction Structure
Authors: Hsu Y. J. , Samanta L. K. , Wang K. C. , Chen P. C. , Hwang H. L. 
Published: March 2011

ABSTRACTWe have made studies on the TRANSVERSE transport properties of the porous Si made from a novel P/N junction structure. The structures of porous Si were examined for various electrochemical etching conditions and they were correlated with the electrical data. The junciton was fabricated by shallow diffusion, with porous Si formed perpendicular to the junction and between two indium ohmic contacts. This structure confines currents to the direction parallel to the surface. Distinct feature on I–V curves have been observed, including sudden rise of currents and the existence of negative differential resistances (NDR). The characteristics appeared stable and depended on the polarity of bias. Suggestions are made that the porous Si could be composed of microcrystals, and feasibility of carrier transport through quantum boxes responsible for the electrical behaviors are discussed.
Backfill Modification Using Geochemical Principles to Optimize High Level Nuclear Waste Isolation in a Geological Repository
Authors: Langmuir Donald , Apted Michael J. 
Published: March 2011

ABSTRACTThe clay backfill that will surround a buried high level nuclear waste package in most national repository programs, could be modified to play a greater role as a barrier to radionuclide (RN) releases. The RN steady state release (Mb) rate from a clay backfill to adjacent rock is directly proportional to backfill porosity (ε), RN diffusion rate In the backfill (Ds), and RN solubility at the waste form surface (C*), and Inversely proportional to RN half-life (λ) and RN retardation coefficient (R) in the backfill [1]. We propose ways to reduce ε, Ds and C* and Increase R for important radionuclides, mostly through the addition of reactive minerals to the backfill. Silica, calcite and anhydrite may be added to precipitate and clog porosity. Increased backfill compaction similarly reducesε, Ds and Mb for all the RN's. Strongly sorbent phases can be added to selectively adsorb both cationic and anionic RN's (e.g. 1–129). However, adsorption will not Importantly reduce peak release rates of most long-lived RN's. The backfill can be poised at reducing Eh's with mineral additives to lower Ds and so immobilize radioisotopes of NI, Np, Pa, Pu, Se, Tc and U. Minerals of stable or more stable isotopes of Cs, NI, Se, Sn and U can be added to lower Ds values of the RN's and to coprecipitate them in solid solution. Phosphorite-apatites, which are known to have high selectivities for rare earths and RN's, may be added to coprecipitate Am, Np, Pu, Sr, Th and U.
Alumina as a Matrix for Fixation of Fission Products
Authors: Zimmer Erich , Scharf K. , Schmidt S.-O. 
Published: March 2011

ABSTRACTFission products and α-emitters from reprocessing plants ( HAW ) are incorporatedinto a ceramic matrix consisting of 90 w/o α-AI2O3 The amount of HAW in the product is 10 w/o. The matrix is produced by a sol-gel technique using a boehmite powder and a SiO2 sol as starting materials. To reduce the sintering temperature seeding with α-AI2O3 particlesis applied. The first step of the process is mixing of the starting materials with the nitric acid containing HAW. This results in the production of a gel. The gel is extruded and subsequently dried at 105ºC. Calcination is carried out in a hydrogen containing atmosphere. Finally, the material is sintered at 1300ºC. During heat treatment only minor volatilization is observed. Even cesium is almost completely retained sinceit forms an aluminosilicate (Cs2O. xSiO2. yAI2O3; feldspar type). The waste product has a total leach rate of 4 * 10-7g * cm-2 d-1 at 97ºC as determined in a Soxhlet apparatus. Under the same conditions, specific leaching rates of radiologically important nuclides, such as cesium and strontium, are approximately 10-6 g * cm-2 d-1. The process has the advantage that commercially available starting materialscan be used. In addition, only a moderate sintering temperature is required and pressingbefore or during sintering is not necessary.
Alternative Synroc Formulations
Authors: Vance E.R. , Smith K.L. , Thorogood G.J. , Begg B.D. , Moricca S.S. , Angel P.J. , Stewart M.W.A. , Blackford M.G. , Ball C.J. 
Published: March 2011

ABSTRACTPerovskite is the least durable of the resistate minerals comprising Synroc-C and it is desirable to reduce its abundance in Synroc. Kinetic limitations and competition with Csapparently affect the incorporation of Sr into hollandite during hot-pressing at 1200ºC/20 MPa so that ∼ 10% of perovskite (a value below the percolation limit) is probably an optimum target. Zirconolite-rich Synroc formulations have been prepared for actinide-rich wastes. Background XRD and TEM studies have also been performed to study the crystal-chemical behaviour of Nd (a simulant of trivalent actinides) in zirconolite. Either rare-earth compensated perovskite or freudenbergite in Synroc can evidently be used to immobilise Na-bearing HLW.