bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric and Pyroelectric Characteristics of Plzt (9.5/65/35) Relaxor Thin Films
Authors: Deb K. K. 
Published: April 2011

AbstractFerroelectric relaxor thin films of lead lanthanide zirconate titanate (PLZT) (9.5/ 65/35) have been deposited by the laser ablation technique onto metallized silicon and lanthanum aluminate substrates. The dielectric and pyroelectric properties of PLZT films and their temperature dependencies have been investigated in some detail in an evaluation of their potential as prospective pyroelectric infrared (IR) detector materials. The temperature at which the dielectric constant of a PLZT film reaches its peak is different from that for the peak pyroelectric coefficient. A lower dielectric constant at which the pyroelectric peak appears contributes to a high figure of merit for PLZT films, so that it is competitive with its ceramic counterpart, as well as with Pb(Mg1/3Nb2/3)O3 (PMN) relaxor ferroelectric ceramic.
GMR and Structure in Sputtered Co90Fe10/Ag Multilayers
Authors: Jarratt J. D. , Barnard J. A. 
Published: April 2011

AbstractGiant magnetoresistance (GMR), structure, and magnetic properties of sputtered (Co90Fe10X Å/Ag Y Å) multilayer films have been investigated. Distinct GMR behaviors including granulartype (GGMR) and ‘discontinuous’ (DGMR) are observed which are strongly dependent on the individual CoFe and Ag layer thicknesses; however, standard multilayer GMR and the associated antiferromagnetic (AFM) coupling is absent. The multilayer structure, individual layer thicknesses, and growth texture were investigated using high and low angle x-ray diffraction (HXRD & LXRD).
Magnetic Coupling in Spin-Valves from Magnetic Circular Dichroism
Authors: Bedrossian P. J. , Tobin J. G. , Waddill G. D. , Jankowski A. F. , Anthony T. C. , Brug J. A. 
Published: April 2011

AbstractWe demonstrate the detection of Magnetic X-ray Circular Dichroism (MXCD) from commercial, thin-film spin valves. Measured x-ray absorption spectra on these devices indicate magnetic polarization of the ferromagnetic constituents, Fe, Co, and Ni.
A Parallel Implementation of Tight-Binding Molecular Dynamics Based on Reordering of Atoms and the Lanczos Eigen-Solver
Authors: Colombot Luciano , Sawyer William , Marict Djordje 
Published: April 2011

AbstractWe introduce an efficient and scalable parallel implementation of tight-binding molecular dynamics (TBMD) which employs reordering of the atoms in order to maximize datalocality of the distributed tight-binding (TB) Hamiltonian matrix. Reordering of the atom labels allows our new algorithm to scale well on parallel machines since most of the TB hopping integrals for a given atom are local to the processing element (PE) therefore minimizing communication. The sparse storage format and the distribution of the required eigenvectors reduces memory requirements per PE. The sparse storage format and a stabilized parallel Lanczos eigen-solver allow consideration of large problem sizes relevant to materials science. In addition, the implementation allows the calculation of the full spectrum of individual eigen-values/-vectors of the TB matrix at each time-step. This feature is a key issue when the dielectric and optical response must be computed during a TBMD simulation. We present a benchmark of our code and an analysis of the overall efficiency.
Parallel Simulations of Rapid Fracture
Authors: Abraham Farid F. 
Published: April 2011

AbstractImplementing molecular dynamics on the IBM SP2 parallel computer, we have studied the fracture of two-dimensional notched solids under tension using million atom systems. Brittle materials are modelled through the choice of interatomic potential function and the speed of the failure process, and our interest is to learn about the dynamics of crack propagation in ideal materials. Recent laboratory findings occur in our simulation experiments, one of the most intriguing is the dynamic instability of the crack tip as it approaches a fraction of the sound speed. A detailed comparison between laboratory and computer experiments is presented, and microscopic processes are identified. In particular, an explanation for the limiting velocity of the crack being significantly less than the theoretical limit is provided.
Gradient-Driven Diffusion Using Dual Control Volume Grand Canonical Molecular Dynamics (DCV-GCMD)
Authors: Swol Frank Van , Heffelfinger Grant S. 
Published: April 2011

AbstractRecently we developed a new nonequilibrium molecular simulation method [1] that allows the direct study of interdiffusion in multicomponent mixtures. The method combines stochastic insertion and deletion moves characteristic of grand canonical (GC) simulations with molecular dynamics (MD) to control the chemical potential μi of a species i. Restricting the insertions and deletions to two separate control volumes (CV's) one can apply different μ's in distinct locations, and thus create chemical potential gradients. DCV-GCMD can be used to study transient phenomena such as the filling of micropores or used in steady-state mode to determine the diffusion coefficients in multicomponent fluid mixtures. We report on the effects of molecular interactions and demonstrate how in a sufficiently nonideal ternary mixture this can lead to up-hill or reverse diffusion. In addition we introduce a novel extension of DCV-GCMD that is specifically designed for the study of gradient-driven diffusion of molecules that are simply too large to be inserted and deleted.
The SEISM* Project: A Software Engineering Initiative for the Study of Materials
Authors: Mula G. , Angius C. , Casula F. , Maxia G. , Porcu M. , Yang Jinlong 
Published: April 2011

AbstractStructured programming is no longer enough for dealing with the large software projects allowed by today's computer hardware. An object-oriented computational model has been developed in order to achieve reuse, rapid prototyping and easy maintenance in large scale materials science calculations. The exclusive use of an object-oriented language is not mandatory for implementing the model. On the contrary, embedding Fortran code in an object-oriented language can be a very efficient way of fulfilling these goals without sacrificing the huge installed base of Fortran programs. Reuse can begin from one's old Fortran programs. These claims are substantiated with practical examples from a professional code for the study of the electronic properties of atomic clusters. Out of the about 20,000 lines of the original Fortran program, more than 70% of them could be reused in the C++ objects of the new version. Facilities for dealing with periodic systems and for scaling linearly with the number of atoms have been added without any change in the computational model.
Clustering and Extended Range Order in Binary Network Glasses
Authors: Nekhayev Dmitry , Kieffer John 
Published: April 2011

AbstractThe clustering in alkali silica glasses (M2O)x(SiO2)1-x, where M is either Na or Rb, and x ranges between 0 and 0.4, was studied using molecular dynamics simulations. Computations were performed using a semi-empirical potential, including two- and three-body terms as well as dynamic partial charge transfer. Characterization of the structures was based on pair correlation functions, neutron static structure factor and ring statistics. Results have shown a much stronger tendency to cluster in case of Na than of Rb. The irregular arrangement of Na is evidenced by a decay pattern in the Na-Na pair correlation function, which can be associated with a fractal dimension. The clustering tendency can be attributed to the differences in the way the network structure is able to accommodate the introduction of modifying cations. As opposed to Rb, the smaller Na cation can fit on sites only slightly larger than is required for Si. This would distort the structure but hardly alter its topology. Rb on the other hand, requires larger interstices, which results in a reconstruction of the network and a significantly different intermediate range order. Na can achieve a similar influence on the network structure if they group in pairs.
Theory of Initial Oxidation Stages on Si(100) Surfaces by Spin-Polarized Generalized Gradient Calculation
Authors: Kato K. , Yamasaki T. , uda T. , Terakura K. 
Published: April 2011

AbstractThe chemical reaction of an O2 molecule on the Si(001) surfaces is studied by the ab initio molecular dynamics with the spin-polarized generalized gradient approximation. The dissociative adsorption of an O2 molecule has been found to occur over two adjacent Si(001) dimers with a spin flip-flop transition. The spin-state transition could cause a substantial retardation for dissociative adsorption of an O2 molecule. The C-type defect after chemisorption of a dissociated O2 molecule, however, shows a spin-triplet state, indicating a barrier-less dissociative chemisorption. These results explain well the overall aspects including preferential oxidation of C-type defects found by recent experimental reports.
Investigation of Crystalline Quartz and Molecular Silicon-Oxygen Compounds with a Simplified LCAO-LDA Method
Authors: Kaschner R. , Seifert G. , Frauenheim Th. , Köhler Th. 
Published: April 2011

AbstractCrystalline and molecular silicon-oxygen compounds are investigated using a simplified LCAO-LDA scheme for the construction of a nonorthogonal tight-binding (TB) Hamiltonian within a two-center approximation. The applicability of this method to the important class of silicon oxides and related molecules is demonstrated. In particular, the properties of the equilibrium structure of α-quartz and several Siloxane molecules are calculated and found to agree well with experiments and self-consistent calculations. To obtain such a good agreement it is necessary to include also the 3d states of Si into the LCAO basis of the wavefunctions.
O(N) Scaling Simulations of Silicon Bulk and Surface Properties Based on a Non-Orthogonal Tight-Binding Hamiltonian
Authors: Bernstein Noam , Kaxiras Efthimios 
Published: April 2011

AbstractWe have implemented a molecular-dynamics algorithm for silicon using a non-orthogonal tight-binding Hamiltonian with the functional form of Menon and Subbaswamy. Parameters for this Hamiltonian were determined by fitting to a database of first-principles total energy calculations of bulk phases and point defect formation energies. These geometries were chosen to reproduce the configurations seen in defective crystalline and amorphous silicon. We have also implemented the non-orthogonal density-matrix method, paying particular attention to data motion locality to facilitate efficient parallelization of the algorithm. The necessary sparse matrix operations (trace, transpose, matrix multiplication) have also been implemented on a single processor workstation with an algorithm which takes O(N) time. Tests of the method's accuracy involved calculations of surface energies and structural reconstructions and activation energies for bulk diffusion through concerted exchange. We present results of a simulation of the melting and rapid quenching of a silicon sample using molecular-dynamics, and examine the resulting structures.
Computer Simulation of Cluster Ion Impacts on a Solid Surface
Authors: Insepov Z. , Yamada I. 
Published: April 2011

AbstractThe sputtering probabilities for normal and oblique cluster ion impacts were calculated by the use of two-dimensional molecular dynamics (MD) calculations. These simulations have revealed the angular dependence of ejecting surface atoms on the cluster incidence angle. The ejecting flux has a symmetrical form with an essential lateral component in the case of normal cluster incidence. For an oblique cluster indidence we found a sharp asymmetry of sputtering orientation. We obtained that the ejecting flux consists of three components: a) fast flying atoms with the velocities higher than the cluster velocity ν ∼ 2.3ν0, b) approximately self-similar component with ν ≈ ν0, and, finally, c) slowly moving tail with ν ≈ 0.2ν0, where ν0 is the cluster velocity. According to our MD results we developed a new model of surface modification phenomena which consists of the Langevin Dynamics based on the Kardar-Parisi-Zhang equation, combined with a Monte-Carlo procedure for crater formation at normal and oblique cluster impacts. We obtained that for a symmetrical crater shape with a size in the order of 20 Å, a significant smoothing occurs after irradiation by ∼ 103 cluster impacts which has been supported by experiment at dose of ∼ 1014 ion/cm2. The rate of the smoothing process can be significantly accelerated if the lateral sputtering phenemenon is taken into account. Simulation of oblique cluster impact on a surface at a grazing angle of 30° by constructing of asymmetric crater shape gives an opposite result: the surface roughness increases. The latter obtaining qualitatively agrees with the experiment.
Dynamic Embrittlement Of Beryllium-Strengthened Copper In Air
Authors: Muthiah Ranjani C. , McMahon C. J. , Guha Amitava 
Published: April 2011

AbstractA precipitation-hardened Cu-0.26%Be alloy is used as a low-temperature model material for “dynamic embrittlement”, or quasi-static diffusion-controlled intergranular brittle fracture. This alloy is shown to undergo intergranular cracking in air at 150°C and to be almost free of this cracking in 2×10−6 Torr vacuum at 200°C. The time to failure is highly stress dependent. The temperature dependence of cracking was found to be 30 kcal/mole. This is about 50% greater than the activation energy for oxygen diffusion in copper, but the present experiments also include an unknown incubation time.
Experimental Analysis Of Instability Effects On The Surface Of Schallamach's Waves Produced By Sliding Friction Of Rubber-Like Materials
Authors: Koudine A. , Barquins M. 
Published: April 2011

AbstractIt is shown that a small ridge exists on the surface of the detachment fold or Schallamach's wave (1971). Such waves take place in the contact area between a moving transparent hemispherical asperity and the smooth, flat surface of a soft elastomer sample. The space-time evolution diagram, composed by juxtaposition of contact area cross-sections, recorded one after the other, proves that there is a correlation between the appearance of these ridges and microdynamic shifting of forward and backward detachment fold limits. A rolling of a rubber band, compressed between two rigid plates, enables us to reproduce the ridges in the macroscale approach.
A Complexed Precursor Approach To The Synthesis Of Ternary Transition Metal Nitrides
Authors: Weil K. S. , Kumta P. N. 
Published: April 2011

ABSTRACTA new chemical synthesis approach has been developed in which ternary transition metal nitride powders are synthesized from hydrolyzed alkanoamine complexed precursors. In this technique, two different metal chlorides are dissolved in a common solvent such as acetonitrile, then reacted with ethanolamine to form a highly viscous solution which settles out of the solvent phase. Simultaneous evaporation of the solvent and forced hydrolysis of the remaining liquid results in the formation of a precipitate which can be filtered and dried. The precursor is heat treated in ammonia to form the corresponding ternary nitride. The approach has been successfully used to synthesize Ni3Mo3N, FeWN2, and Ti3AlN powders, each of which have been characterized using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).
Combustion synthesis of nanosized SiCxNy powders
Authors: Keil D. G. , Calcote H. F. , Gill R. J. 
Published: April 2011

ABSTRACTSilane/acetylene/ammonia flames were used to produce fine powders of composition SiCxNy The experiments were conducted in a spherical reactor at 1 atmosphere total pressure with spark ignition in the center of the chamber. The composition was determined from complete quantitative analysis of the gas products and elemental analysis of the solids. IR spectra indicate little bound hydrogen in the powders, but oxygen was adsorbed on the high surface area powders (60–80 m2/g, N2 BET). The experimental stoichiometries of the nascent powders can be represented as mixtures with weight ratios of Si3N4/SiC ranging from about 0.2 to 2, and variable amounts of excess carbon or silicon. The powders, from TEM, consist of chains of nearly symmetrical particles with diameters around 40 nm. Helium pycnometry densities in the range of 2.9 to 3.2 g/cc are consistent with the theoretical densities for the Si3N4/SiC stoichiometries. The powders were amorphous or nanocrystalline, from X-ray diffraction (Cu Kα). Annealing in argon at 1773 K for 8 h resulted in preferential growth of crystalline SiC domains.
Recent Progress in Gan Based Field Effect Transistors
Authors: Khan M. A. , Chen Q. , Sun C. J. , Yang J. W. , Shur M. S. 
Published: April 2011

ABSTRACTMost types of GaN based Field Effect Transistors – MESFETs, MISFETs, Heterostructure FETs (HFETs), and Doped Channel HFETs (DC-HFETs) have demonstrated a good performance at both room temperature and elevated temperatures. The DC-HFETs demonstrated the best direct current and microwave characteristics among all wide band gap semiconductor devices because of excellent transport properties of two dimensional electron gas at the AlGaN/GaN heterointerface and a large sheet carrier concentration in the device channel. Other advantages of GaN-based materials for FET applications include a very high breakdown field, a very high saturation field, a high peak velocity, a large conduction and valence band discontinuities at the AlN-GaN heterointerface, and a reasonable thermal conductivity (comparable to that of Si). In this paper, we review our recent results obtained for different types of GaN-based transistors.
Effects of Additives on the Stacking Fault Formation During Synthesis of β-Sic Particles by Carbothermal Reduction
Authors: Seo W. S. , Koumoto K. 
Published: April 2011

ABSTRACTThrough the systematic addition of B, and Fe, additive effects on the stacking fault formation and the morphology of the formed particles during synthetic reaction of β-SiC were investigated in the present study. Stacking fault density of the synthesized powders decreased with increasing content of added B and Fe. Whisker content of the synthesized powders and formation mechanism of whiskers are the most closely related to the stacking fault density.
Cubic SiC the Forgotten Polytype
Authors: Jayatirtha H. N. , Spencer M. G. 
Published: April 2011

ABSTRACTThe two most common and most studied forms of SiC are 6H-SiC and 3C-SiC. The 3C-SiC, or cubic modification shares the zincblend lattice structure with other well developed semiconductor materials, such as GaAs and InP. We have grown thick 3C-SiC by the sublimation method. Our results show that it is possible to maintain the 3C polytype even at growth temperatures of 2000°C. Using the sublimation technique we have obtained growth rates as high as 130 microns/hr.
Emissivity of Silicon Carbide Composites as a Function of Temperature and Microstructure
Authors: Sun Ming , Lloyd Isabel K. 
Published: April 2011

ABSTRACTSpectral emissivity normal to the sample surface was investigated as a potential intelligent control parameter for the manufacture of SiC fiber reinforced SiC composites by chemical vapor infiltration (CVI) and microwave assisted CVI. Results indicated that at temperatures between 600 and 1000°C and wavelengths between 1500 and 2100 nm emissivity was sensitive to the sample porosity. It also appeared to be sensitive to the thickness of the oxide layer on the composites. The emissivity was not very sensitive to temperature in this region. It was concluded that emissivity is promising as a probe of density during manufacturing. It may also be useful as a probe of oxide layer formation.
From Precursors to Non-Oxide Ceramics: Pyrolytic Mechanisms Studied by NMR
Authors: Sigmund W. M. , Feike M. , Spiess H. W. , Aldinger F. 
Published: April 2011

ABSTRACTThe pyrolysis of a poly ethylsilazane was studied using a CO2-laser beam heated solid state MAS-NMR probe head. Chemical structures of the intermediate stages could be identified. The analogy of the pyrolysis evolution for the following two different methods could be shown: A) in an inert gas furnace conventionally prepared and B) laser irradiated in the NMR probe head under magic-angle spinning (MAS) conditions. Samples prepared by method A were studied by 29Si MAS-NMR and samples prepared by method B were studied with an appropriate cross polarization time by 29Si CP-MAS-NMR. Both experiments showed the same mechanisms for the pyrolysis as the polymer is transformed into a Si3N4/C ceramic.
New Method for Bonding Poly(Ethylene Oxide) PEO to Surfaces
Authors: Allgor S. J. S. , Merrill E.W. 
Published: April 2011

AbstractA new method has been developed for the covalent attachment of poly(ethylene oxide) to various polymeric surfaces for use in biomedical applications. Methacrylic acid (MA) monomer was first grafted to low-density polyethylene (LDPE) or polystyrene (PS) sheets by placing them in a solution of 10–20% (v/v) methacrylic acid in water followed by electron beam irradiation of 2–4 megarads. The methacrylic acid was grafted to the surface and polymerized, resulting in the polymer surface being extremely hydrophilic. The MA-treated samples were placed in a solution of PEO in water (MW 8000 – lx106 g/mol, concentration 0.05–15 % w/v), where the PEO strongly hydrogen bonds to the MA on the surface. The pieces were either rinsed with water (monolayer formation) or drained of excess solution (multilayer formation), then placed under the electron beam for a dose of 2 megarads to graft the PEO to the MA-treated surface. The grafted PEO was stable on the surface, unable to be removed despite extensive washing with water, soaking in basic solution (which would break the hydrogen bonding of the PEO with the acid), or scraping of excess hydrogel from the surface. The monolayer thickness was found to have no dependence on the molecular weight or concentration of the PEO in solution, nor did it have any dependence on the time that the MA-treated samples were soaking in the PEO solution before the second irradiation. This indicates that the PEO molecules immediately lie flat on the surface with few loops or tails, with no exchange taking place after the initial adsorption. All surfaces were analyzed using X-ray photoelectron spectroscopy (XPS), with high resolution carbon Is scans being the principle means of MA and PEO detection in the top 50 angstroms of the surface.
Spatial Ordering of As Clusters Due to Indium Delta-Doping of LTMBE GaAs
Authors: Bert N. A. , Chaldyshev V. V. , Faleev N. N. , Kunitsyn A. E. , Tret'yakov V. V. , Lubyshev D. I. , Preobrazhenskii V. V. , Semyagin B R. 
Published: April 2011

AbstractWe have shown that two-dimensional layers of arsenic nano-clusters separated by cluster-free GaAs matrix can be formed using indium delta-doping of GaAs films grown by molecular beam epitaxy at low (200°C) temperature. Spatially ordered structures of As clusters have been obtained in the epitaxial LT GaAs films doped with Si donors, Be acceptors and undoped as well.
Optical Study of Carrier Transfer in Strain-induced Quantum Dots
Authors: Gu Yitong , Sturge M. D. , Kash K. , Gaag B. P. Van der , Gozdz A. S. , Florez L. T. , Harbison J. P. 
Published: April 2011

AbstractWe have studied excitation transfer from the host quantum well to strain-confined quantum dots. We find that there is a long-lived intermediate state acting as a reservoir, holding the excitation before it is thermally activated over a barrier to reach the quantum dot. The barrier height increases monotonically with dot size.