bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic and Electronic Structure of Germanium Clusters at Finite Temperature Using Finite Difference Methods
Authors: Chelikowsky James R. , ÖĞüt Serdar , Jingc X. , Wu K. , Stathopoulos A. , Saad Y. 
Published: April 2011

AbstractDetermining the electronic and structural properties of semiconductor clusters is one of the outstanding problems in materials science. The existence of numerous structures with nearly identical energies makes it very difficult to determine a realistic ground state structure. Moreover, even if an effective procedure can be devised to predict the ground state structure, questions can arise about the relevancy of the structure at finite temperatures. Kinetic effects and non-equilibrium structures may dominate the structural configurations present in clusters created under laboratory conditions. We illustrate theoretical techniques for predicting the structure and electronic properties of small germanium clusters. Spefically, we illustate that the detailed agreement between theoretical and experimental features can be exploited to identify the relevant isomers present under experimental conditions.
Prediction of a Very Hard Triclinic Form of Diamond
Authors: Benedek G. , Facchinetti M. , Miglio L. , Serra S. 
Published: April 2011

AbstractIn a theoretical search for new hypotetical sp3-bonded carbon structure containing five-fold rings as a possible result of fullerene transformation under pressure, we have found a triclinic form of diamond with 16 atoms per unit cell which we called tcl-16. We have calculated the ground state structure, the cohesive energy, the bulk modulus and the electronic density of states by means of tight binding molecular dynamics (TBMD). Finally we have compared the phonon spectra at F to existing Raman data for a non-cubic- phase of diamond.
First-Principles Calculation of the Structure of Mercury
Authors: Mehl Michael J. 
Published: April 2011

AbstractMercury has perhaps the strangest behavior of any of the metals. Although the other metals in column IIB have an hcp ground state, mercury's ground state is the body centered tetragonal βHg phase. The most common phase of mercury is the rhombohedral αHg phase, which is stable from 79K to the melting point and meta-stable below 79K. Another rhombohedral phase, γ71Hg, is believed to exist at low temperatures. First-principles calculations are used to study the energetics of the various phases of mercury. Even when partial spin-orbit effects are included, the calculations indicate that the hexagonal close packed structure is the ground state. It is suggested that a better treatment of the spinorbit interaction might alter this result.
Ab Initio Calculations for SiC-Al Interfaces by Conjugate-Gradient Techniques
Authors: Kohyama Masanori 
Published: April 2011

AbstractConjugate-gradient (CG) techniques for ab initio calculations of large complex systems have been examined for SIC-Al interfaces. The CG method by Bylander, Kleinman and Lee is more efficient than the Teter-Payne-Allan (TPA) method, the modified TPA method and the block Davidson method, although the TPA method is efficient for SiC surfaces. From the relaxed configurations, we have found strong attractive interactions between C and Al atoms, which should play a favorable role for adhesion between SiC and Al.
EELS Studies of B2-Type Transition Metal Aluminides: Experiment and Theory
Authors: Bottonm G. A. , Guo G. Y. , Temmerman W. M. , Szotek Z. , Humphreys C. J. , Wango Yang , Stocks G. M. , Nicholson D. M. C. , Shelton W. A. 
Published: April 2011

AbstractThe electronic structure and bonding character of intermetallic alloys are investigated by a combination of electron energy loss spectroscopy (EELS) experiments and ab initio electronic structure calculations. A detailed comparison is made between experimental spectra and calculations. The changes in electronic structure within a transition metal alurninide series and also due to alloying are studied using EELS spectra. The Korringa-Kohn-Rostoker coherent-potential-approximation method and large supercell models are used to investigate changes in composition and the effect of dopants on the electronic structure.
The Magnetic Structure of Cu0.2Ni0.8 Alloys
Authors: Wang Yang , Stocks G. M. , Nicholson D. M. C. , Shelton W. A. , Szotek Z. , Temmerman W. M. 
Published: April 2011

AbstractThe locally self-consistent multiple scattering method is applied to ab initio spin-polarized local density approximation calculations for ferromagnetic CuNi alloys. The samples used to model the alloys are constructed with experimentally measured short range order parameters. These large cell calculations are performed using the Intel Paragon XP/S massively parallel processing supercomputer. The neutron magnetic diffuse scattering cross sections are calculated and compared with experiment. The dependence of magnetic moment formation on the local environment is discussed.
Derivation of Interatomic Potentials by Inversion of Ab Initio Cohesive Energy Curves
Authors: Bazant M. Z. , Kaxiras Efthimios 
Published: April 2011

AbstractAn analytic procedure for inverting ab initio cohesive energy vs. volume curves to obtain a parameter-free interatomic potential is presented. The procedure determines the radial functions in a cluster potential, assuming an angular dependence. The method is a nonlinear generalization of the ab initio pair potential formula of Carlsson, Gelatt and Ehrenreich to higher orders of cluster expansion [1]. We demonstrate our method by deriving an ab initio cluster potential for silicon with the Stillinger-Weber angular dependence [2]. A novel property of the potential is that bond-bending forces are not monotonic in the bond length, as is the case with most empirical potentials, but rather are peaked at the first neighbor distance. The validity of the inverted potential is discussed along with its use in the development of new interatomic potentials.
Mixed Approach to Incorporate Self-Consistency into Order-N LCAO Methods
Authors: Ordejon Pablo , Artacho E. , Soler J. M. 
Published: April 2011

AbstractWe present a method for selfconsistent Density Functional Theory calculations in which the effort required is proportional to the size of the system, thus allowing the aplication to problems with a very large size. The method is based on the LCAO approximation, and uses a mixed approach to obtain the Hamiltonian integrals between atomic orbitals with Order-N effort. We show the performance and the convergence properties of the method in several silicon and carbon systems, and in a DNA periodic chain.
Fast Algorithms for Composite Materials
Authors: Greengard L. 
Published: April 2011

AbstractWe briefly review recently developed fast algorithms for the evaluation of electrostatic fields in composite materials consisting of a collection of piecewise homogeneous inclusions embedded in a uniform background. These algorithms are based on combining a suitable boundary integral equation with the fast multipole method and a conjugate gradient-like iterative method. The CPU time required grows linearly with the number of points in the discretization of the interface between the inclusions and the background material, bringing large-scale calculations within practical reach.
Isotropic Md Simulations Of Dynamic Brittle Fracture
Authors: Español Pep , Rubio Miguel A. , Zúñiga Ignacio 
Published: April 2011

AbstractWe present results obtained by molecular dynamics simulations on the propagation of fast cracks in triangular 2D lattices. Our aim is to simulate Mode I fracture of brittle isotropic materials. We propose a force law that respects the isotropy of the material. The code yields the correct imposed sound c║, shear c┴ and surface VR wave speeds. Different notch lengths are systematically studied. We observe that initially the cracks are linear and always branch at a particular critical velocity c* ≈0.8VR and that this occurs when the crack tip reaches the position of a front emitted from the initial crack tip and propagating at a speed c = 0.6 8VR.
Dynamic Simulation Of Crack Propagation With Dislocation Emission And Migration
Authors: Zacharopoulos N. , Srolovitz D.J. , LeSAR R.A. 
Published: April 2011

AbstractWe present a simulation procedure for fracture that self-consistently accounts for dislocation emission, dislocation migration and crack growth. We find that the dislocation microstructure in front of the crack tip is highly organized and shows a complex temporal-spatial evolution. The final dislocation microstructure and the number of emitted dislocations immediately proceeding fracture varies rapidly with the loading rate. For high loading rates, fracture occurs at smaller loads with increasing loading rate. However, the load at fracture shows a maximum with respect to loading rates.
Criteria For Progressive Interfacial Debonding With Friction In Fiber-Reinforced Ceramic Composites
Authors: Hsueh Chun-Hway 
Published: April 2011

AbstractCriteria for progressive debonding at the fiber/matrix interface with friction along the debonded interface are considered for fiber-reinforced ceramic composites. The energy-based criterion is adopted to analyze the debond length, the crack-opening displacement, and the displacement of the composite due to interfacial debonding. The analytical solutions are identical to those obtained from the mismatch-strain criterion, in which interfacial debonding is assumed to occur when the mismatch in the axial strain between the fiber and the matrix reaches a critical value. Furthermore, the mismatch-strain criterion is found to bear the same physical meaning as the strength-based criterion.
Interfacial Fracture Between Boron Nitride And Silicon Nitride And Its Applications To The Failure Behavior Of Fibrous Monolithic Ceramics
Authors: Kovar D. , Brady G.A. , Thouless M.D. , Halloran J.W. 
Published: April 2011

AbstractMechanical tests show that fibrous monolithic ceramics can exhibit graceful failure in bending due to marked crack deflection at silicon nitride/boron nitride interfaces. Model sandwich specimens were manufactured from polycrystalline silicon nitride with interphases consisting of mixtures of silicon nitride and boron nitride. The interfacial fracture resistances of the specimens were measured, and the results were correlated to the failure behavior of fibrous monolithic ceramics. It was found that the three modes of failure observed in fibrous monoliths can be correlated with the interfacial fracture resistance. In addition, anisotropy in the properties of the interphases were found to have a profound influence on crack deflection.
Effect Of Aggregate Content On Fracture Behavior Of Concrete
Authors: Xi Y. , Amparano F.E. , Li Zongjin 
Published: April 2011

AbstractEffect of aggregate content on fracture behaviors of concrete is studied by testing on geometrically similar three-point bend beams. The results are analyzed by using a size effect method in which the fracture behavior of concrete is characterized by two parameters, fracture energy Gf and effective fracture process zone cf. Test results showed that with increasing volume fraction of aggregate in the range 45% - 75%: (1) the modulus of elasticity of concrete decreases slightly, (2) fracture energy Gf increases, but the rate is very small; (3) the size of the fracture process zone, cf, decreases, which may be explained by changes in coarseness of grain structures defined in terms of mosaic patterns.
Study Of Fiber Composite Failure Criterion
Authors: Zhou S. J. , Blumenfeld R. , Curtin W.A. , Holian B. L. 
Published: April 2011

AbstractWith a recently developed numerical technique, we have investigated failure processes in real fiber composites. This technique utilizes 3D lattice Green's functions to calculate load transfer from broken to unbroken fibers, and also includes the important effects of fiber/matrix sliding. It is found that the failure processes are more complex than previously thought: The fibers that break or slide are not necessarily located around the largest defect cluster. Rather, the breaking/sliding fibers accumulate, form several large clusters, coalesce and finally cause the fiber composite to fail. Only in some cases does one large defect dominate the damage evolution. Based on our observations of the irregular evolution of the damage, a simple model is developed to describe these different failure modes, and the failure criterion of the fiber composite is also discussed.
Kinetics Of Dislocation Emission From Crack Tips And The Brittle To Ductile Transition Of Cleavage Fracture.
Authors: Argon A.S. , Xu G. , Ortiz M. 
Published: April 2011

AbstractSeveral activation configurations of dislocation embryos emanating from cleavage crack tips at the verge of propagating have been analyzed in detail by the variational boundary integral method, as central elements of the rate controlling process of nucleation governed fracture transitions from brittle cleavage to tough forms, as in the case for BCC transition metals. The configurations include those on inclined planes, oblique planes and crack tip cleavage ledges. Surface ledge production resistance is found to have a very strong embrittling effect. Only nucleation on oblique planes near a free surface and at crack tip cleavage ledges are found to be energetically feasible to explain brittle-to-ductile transition temperatures in the experimentally observed ranges.
Effect Of Crack Blunting On Subsequent Crack Propagation
Authors: SchiØtz J. , Carlsson A. E. , Canel L. -M. , Thomson Robb 
Published: April 2011

AbstractTheories of toughness of materials depend on an understanding of the characteristic instabilities of the crack tip, and their possible interactions. In this paper we examine the effect of dislocation emission on subsequent cleavage of a crack and on further dislocation emission. The work is an extension of the previously published Lattice Greens Function methodology[1, 2, 3]. We have developed a Cavity Greens Function describing a blunt crack and used it to study the effect of crack blunting under a range of different force laws. As the crack is blunted, we find a small but noticeable increase in the crack loading needed to propagate the crack. This effect may be of importance in materials where a dislocation source near the crack tip in a brittle material causes the crack to absorb anti-shielding dislocations, and thus cause a blunting of the crack. It is obviously also relevant to cracks in more ductile materials where the crack itself may emit dislocations.
Novel Applications Of Ceramic Precursors - Tin Coating On Alumina And Functionally Gradient Materials
Authors: Seyferth D. , Narula C. K. , Czubarow P. 
Published: April 2011

ABSTRACTThere are very few demonstrated applications of ceramic precursor technology. Here, we describe two new applications of known ceramic precursors, thin film deposition and the fabrication of functionally gradient materials [FGM]. To demonstrate the thin film deposition, we prepared titanium nitride film on an alumina substrate using (CH3)3SiNHTiCl3precursor by a single dipcoat-fire cycle. The fabrication of copper and aluminum based FGMs was demonstrated using Nicalon®fiber polycarbosilane and poly(methylsilane) precursors as binders and in situ sources of ceramics.
Microstructure and interfaces in TiB2/Ti-46Al-3Cr Alloy Composites
Authors: Si Weimin , Dudley Michael , Li Pengxing , Wu Renjie 
Published: April 2011

ABSTRACTA ternary titanium aluminide alloy, Ti-46Al-3Cr (at%), was discontinuously reinforced with 5 vol% titanium diboride (TiB2), by an in-situ synthesis technique, resulting in a two phase γ(TiAl) (mainly) and α2(Ti3Al) matrix with randomly dispersed TiB2 particle. Interfaces of TiB2-TiAl were investigated by Analytical Electron Microscopy (AEM) and High Resolution Electron Microscopy (HREM). No consistent crystallographic orientation relationship was observed between TiB2 particle and TiAl matrix, and there was no evidence of alloying elements (such as Cr) segregation or interphase formation at the TiB2-TiAl interface. HREM results indicated that no semi-coherent interface between TiB2 and TiAl has been observed. There existed a thin amorphous layer (0.5 to 1.3 nm) at the TiB2-TiAl interface, which may accommodate the large lattice misfit across the interface and enhance the interfacial bonding.
Fabrication and Characterization of CdS Thin Films: Study of the adhesion of Il-VI compound semiconductors for applications to light emitting and absorbing devices
Authors: Kang Hyun Shik , Cho Gi Eun , Kim Kyung Wha , Persans Peter D. 
Published: April 2011

ABSTRACTThe structural and optoelectronic properties of polycrystalline CdS films, fabricated by three different methods, are compared to one another for the purpose of preparing CdTe/CdS solar cells. The three methods were: alternated spraying of cation and anion solution at room temperature, spray pyrolysis, and chemical bath deposition. We studied the surface morphology and crystal quality and texture by scanning electron and optical microscopy and x-ray diffraction. All films had a well-developed wurtzite structure. Films grown by the alternated-spray method and the chemical bath method consist of randomly-oriented crystallites with dimensions <0.5 microns. Annealing at 400°C increases the crystallite size slightly. Films which were grown by pyrolysis at substrate temperatures from 400°C to 500°C were oriented in the <002> direction. For growth by pyrolysis at 500°C, the surface is rough on a lateral scale of 0.1 to 0.3 microns.
A Relationship between Interface Trap Density and Transconductance in 6H-SiC Enhancement Mode Field Effect Transistors
Authors: Dryfuse M. W. , Tabib-Azar M. 
Published: April 2011

ABSTRACTAn explicit analytical expression relating the interface trap densities and transconductance is derived for enhancement mode field effect transistors without any simplifying assumptions regarding the energy distribution of traps. Using this relationship, the interface trap densities were calculated from transconductance data and compared to experimental data and that provided in the literature. Our expression provides a simple and convenient method to reliably estimate interface traps densities from the readily available transconductance data provided in the pertinent literature.
The Influence of Interface Traps on the High Frequency and High Temperature Performance of SiC Field Effect Transistors
Authors: Aydin H. , Dryfuse M. W. , Tabib-Azar M. 
Published: April 2011

ABSTRACTFast and slow interface traps can considerably deteriorate the performance of field effect transistors. Slow interface traps, by slowly changing their charge occupancy, contribute to a drift in the quiescent operation point of the transistor, while fast traps deteriorate the device performance by contributing to both amplitude and phase current noise. They also result in a non-equilibrium surface depletion layer between gate and source which increases the gate-to-source parasitic resistance and deteriorates the device transconductance. We examine these different effects and present some preliminary data regarding interface traps in boron-doped 611-SiC.
The thermoelectric performance of silicon carbide semiconductor made from rice hull
Authors: A E. Maed , Komatsu M. 
Published: April 2011

ABSTRACTThermoelectric properties (Thermoelectromotive force and electrical conductivity) of porous silicon carbide ceramics are evaluated. Porous silicon carbide ceramics are made from rice hull by reacting silica and carbon, both of which are included in rice hull, using hotpressing method[1].When nitrogen gas is used as enviromental gas for hotpressing, this material becomes n-type semiconductor. It shows comparably high themoelectromotive force. Thermoelectric properties of this material change with the processing conditions.The relationship between thermoelectric properties and microstructure is also evaluated.
Effects of Charged Substrates on Attachment of Primary Bone Marrow Stromal Cells
Authors: Qiu Q. , Sayer M. , Wan J. , Kawaja M. D. , Shen X. , Davies J. E. 
Published: April 2011

AbstractThe effects of charged substrates on the attachment of rat primary bone marrow stromal cells have been investigated using a novel cell culture chamber. Cells were cultured on the surfaces of a conductive and optically transparent indium tin oxide (ITO) coating. When a voltage was applied to the ITO electrodes, positive and negative charges were induced on the ITO electrodes. After 24 hours exposure to 0.8V, more cells attached to the anode than either the cathode or control both in presence or absence of serum in the culture medium. Protein desorption profiles also indicated that the enhanced attachment of cells to the anode was not controlled by the adsorption of serum proteins. The surface texture of ITO was analyzed using atomic force microscopy, the thickness by transmission electron microscopy, and crystallinity using glancing angle x-ray diffraction.
ESCA Detection of Surface Carboxyl Group Concentration of Polyanhydrides
Authors: Ciwen J.-X , Gardella J. A. , Santos C. A. , Mathiowitz E. 
Published: April 2011

AbstractWe present in this paper the surface derivatization of polyanhydrides with triethylamine for labeling the hydroxyl group. The reaction was verified with diffuse reflectance FTIR spectroscopy. Surface derivatization of poly(fumaric-co-sebacic)anhydride of 50:50 and 20:80 compositions was performed and ESCA measurements showed the surface nitrogen concentration in good agreement with stoichiometry values.
Does The 1.25 eV Luminescence of Coherently Strained InGaAs Insertions in GaAs Originate from Quantum Dots?
Authors: Lazzari J.-L. , Klann R. , Mazuelas A. , Trampert A. , Wassermeier M. , Brandt O. , Ploog K. H. 
Published: April 2011

AbstractWe study the growth of InAs/AlxGa1-xAs/GaAs heterostructures as well as their structural and optical properties. Structurally coherent InAs islands with a narrow size distribution are found to be formed only in a very narrow range of InAs coverage. In striking contrast, the photoluminescence band in the 1.15–1.35 eV spectral range, which is commonly attributed to the emission from InAs quantum dots, is present for all of our structures, regardless the presence or absence of InAs islands and their strain state. Moreover, for constant InAs coverage this PL band follows not the Γ gap but the L gap of the AlxGa1-xAs barrier. This latter result is in disagreement with effective mass calculations for three-dimensionally confined excitons.
Reversible Electrochromic Effect in Fullerene Thin Films Utilizing Alkali and Transition Metals
Authors: Konesky G. A. 
Published: April 2011

AbstractA simple apparatus is described to rapidly assess the Electrochromic effect of Alkali and Transition Metal species of intercalated Fullerene thin films. Optical transmission loss during the Coloring phase is monitored at 880, 635, 583 and 565 nm while electrochemical intercalation proceeds. The process is repeated during the reverse polarity Bleaching phase. Results are presented for electrolyte systems based on Butyrolactone or water for Ag, Cr, Cu, Mg and Ba species.
Energy Up-Conversion at GaAs-GaInP2 and GaAs-AlGaInP2 Interfaces Caused by Cold Auger Processes
Authors: Driessen F. A. J. M. , Cheong H. M. , Mascarehas A. 
Published: April 2011

AbstractEfficient, low-temperature luminescence at energies far above that of the exciting cw-laser is reported at junctions of GaAs-GaInP2 and GaAs-AlxGa1−x.InP2. The signal originates from the high-band gap layers and disappears only if the excitation energy is tuned below the GaAs band gap, as monitored by up-converted photoluminescence excitation spectroscopy. This shows that the non-linear process is induced by the generation of electrons and holes in the GaAs. Furthermore, it is found that the up-conversion is only observed if the (A1)GaInP2 layers are CuPtB long-range ordered. The reason for this is the inherent presence of metastable states in these ordered alloys. It is argued that cold Auger processes cause the nonlinear effect at these type I interfaces.