bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of InSb Thin Film as a Magnetic Sensor Material Using In/Sb/In Multilayer Structure
Authors: Yun Chong-Man , Lee Seung-Ki , Han Min-Koo , Yun Mun-Soo
Published: March 2011

This paper proposes the novel processing technique on the formation of InSb thin film which may not be influenced by the vapor pressure difference between In and Sb. Three layers which are composed of In with 1000 A of thickness, Sb with 5000 A and In with 4000 A are deposited sequentially at room temperature. During post heat treatment of these layers, InSb compound phase begins to form and the outer In layer suppresses the reevaporation of more volatile material, Sb. Since multiple single layers are sequentially evaporated, the problem of the severe vapor pressure difference betweentwoevaporating materialsmaynotcontributetothestoichiometriccomposition which may be the most critical parameter to determine the quality of films. The characterization of a fabricated InSb thin film by X-ray diffraction and scanning electron microscope shows that the proposed multilayer method may be a powerful technique to form a high quality InSb compound thin film.
Micromagnetic Processes in Steels
Authors: Beale A. D. , Hetherington M. G. , Jakubovics J. P. , Lewis B. A. , Scruby C. B.
Published: March 2011

Magnetoacoustic emission (MAE) and Barkhausen emission (BE) measurements have been carried out on steel specimens heat treated to produce various microstructures ranging from martensitic/bainitic to ferritic/pearlitic. The magnetic domain structure of the specimens has been studied using transmission electron microscopy, and micromagnetic processes have been observed using an in-situ magnetizing device. The results are used in the interpretation of the MAE and BE measurements.
Magnetic Materials for New Sensors — Sensor Magnetics —
Authors: Mohri K.
Published: March 2011

”Magnetics sensors” are the key devices to establish intelligent electronics measurement and control systems for development of high level factory automations ( FA ). Various magnetics sensors having quick response, high sensitivity and robustness have been widely developed in these years using amorphous magnetic alloys, magnetoresistive ( MR ) elements, soft ferrites, and high temperature superconductors. These high-performance sensors are spreading in use in the fields of Power-Electronics ( Power Magnetics ), Mechatronics, Medical Electronics ( Medical Magnetics), Information Apparatus, Security Electronics ( Security Magnetics ) etc..

Relations between new magnetic materials and high-performance sensors are summarized and a principle for constitution of these sensors is proposed.
Magnetic and Microstructural Studies On Co-Cr Films Investigated Using NMR
Authors: Yoshida Kazuetsu , Kakibayashi Hiroshi , Yasuoka Hiroshi
Published: March 2011

The compositional distribution of Co-Cr vacuum evaporated films is investigated using the 59Co nuclear magnetic resonance technique. The dependence of the spin-echo spectra of Co-Cr films and powders on Cr concentration is measured. The spectra of the films evaporated at 260°C are found to be similar to those of powder samples with the Cr concentration of approximately 6 at%, although the Cr concentration of the films is between 10 at% and 24 at%. It is concluded that the Cr concentration of the ferromagnetic regions in Co-Cr films remains at 6 at%, although Cr concentration increased to 25 at%. The spin-echo spectra of the films evaporated at 160°C show that the Cr concentration in ferromagnetic regions is slightly higher than that found in the films deposited at 265 °C. This implies that segregation is less developed in the 160°C films The relationship between the magnetic properties and the segregation is also discussed
Magneto-Optical Spectroscopy of RE/TM Alloys and TM/CO Multilayers
Authors: Weller D. , Rcim W.
Published: March 2011

This paper reviews on magneto-optical spectroscopy of alloys, metallic multilayers and interference enhancement structures for magneto-optic (MO) recording. Mainly rare earth transition metal (RE-TM) alloys and Co/transition metal (Co/X) multilayers will be discussed. The read out performance in MO write/read tests is given by tile reflectivity and Kerr rotation strongly depends on the wavelength. While the magneto-optical transitions in the near infrared (IR:≈820nm) are dominated by tile 3d magnetic transition metals Fe and Co, the properties in the ultraviolet (UV: <400nm) can be dominated by either rare earths like Nd or Pr in RE-TM alloys or by exchange polarized Pt or Pd in Co/X multilayers and their respective alloys.

In an attempt to correlate the magneto-optic Kerr effect to electronic properties we have systematically investigated alloys and multilayers with x-ray photoemission (XPS) and polar magneto-optical Kerr spectroscopy (0.5–5.3eV range). It is found that electronic 4f levels in Nd or Pr contribute to the Kerr elffct via Γ→, d transitions in the order of 0.3°. Exchange polarized Pd and Pt in Co/X multilayers give rise to a room temperature Kerr rotation in the same order of magnitude via excitations of the 4d and 5d bands, respectively. These effects clearly depend on film compositions and thickness ratios.,
TEM Samples of Semiconductors Prepared by a Small-Angle Cleavage Technique
Authors: McCaffrey J. P.
Published: March 2011

A small-angle cleavage technique has been developed for transmission electron microscopy (TEM) of semiconductors and related materials. In this technique, samples are prepared by back-thinning the material to a prescribed thickness, back-scribing the material at a specific angle to a standard cleavage plane, and cleaving along these scribe lines. A second cleave is made along the standard cleavage plane to intersect the first cleave, forming a thin wedge. This wedge is mounted on a grid, providing an electron transparent tip free of ion milling artifacts.
Preparation of Cross-Sectional TEM Samples of Fe-Zn Couples
Authors: Giannuzzi L. A. , Howell P. R. , Pickering H. W. , Bidter W. R.
Published: March 2011

A preparation technique for the production of cross-sectional transmission electron microscope (TEM) samples from the interdiffusion regions of Fe-Zn binary couples is described. To alleviate the problem of unequal ion milling rates between the Fe and Zn, a 0.75mm thick Fe sheet has been double plated with a thick electrodeposited Zn coating to achieve a total couple thickness of ˜3mm. After slicing the couple in cross-section, the Fe region of the sample is dimpled to perforation near the Fe-Zn interface. Final thinning for TEM analysis is obtained by ion milling using a liquid nitrogen cold stage and sector speed control. The ion milling procedure is stopped when the perforated hole in the Fe-side of the couple extends through the faster eroding Zn-side of the interface. This technique, in modified form, is expected to be suitable for commercial steels coated with Zn-based alloys.
Preparation of Microindentations In Cross-Section
Authors: Morris Jonathan C. , Pharr George M. , Callahan Daniel L.
Published: March 2011

The increased usage of indentation testing for the determination of the toughness of brittle materials has raised many questions about the nature and extent of plastic deformation in these materials. Of particular interest is the behavior of single crystal silicon in indentation (hardness) testing. Recent studies point to some interesting properties of silicon under indentation loading and unloading. The least understood of these properties is the apparent phase change and subsequent cracking that the crystalline silicon experiences upon indentation. The pressure induced phase transformation is thought to proceed by crystalline Si changing to metallic and then changing to amorphous. Accompanying this phase transformation is usually a characteristic cracking pattern.

It is the goal of a larger study to characterize the deformation process during indentation. This can be best achieved by producing an electron transparent cross section of a microindentation which is suitable for structural characterization using a Transmission Electron Microscope (TEM). The various conventional and unconventional methods we have attempted to employ to produce suitable samples, the problems we have encountered, preliminary results, and proposed modifications are discussed.
Tem Specimen Preparation of Tial Alloy Powders Produced by Plasma Rotating Electrode Process
Authors: Nishida M. , Chiba A. , Tateyama T. , Tomoshige R. , Morita K. , Aoyagi E.
Published: March 2011

TEM specimens of PREPed Ti -48 at.% Al powders can be prepared reproducibly in a straight-forward manner. There are two kinds of powders with respect to surface and crosssectional morphologies. One is with an Widmanstitten-like structure and or a surface relief of martensitic phase and the other is with a dendritic structure. The primary phase during solidification and relative cooling rate in both the powders are discussed by comparing the macroscopic and microscopic features.
Preparation of Large Thin Area Vlsi Tem Specimens by Dimpling With A “Flatting Tool”
Authors: Humiston Helen L. , Tracy Bryan M. , Lawrence M. , Dass A.
Published: March 2011

An alternative VLSI TEM specimen preparation technique has been developed to produce 100μm diameter electron transparent thin area by using a conventional dimpler with a texmet padded ‘flatting tool’ for dimpling and a microcloth padded ‘flatting tool’ for polishing, followed by low angle ion milling. The advantages of this technique are a large sampling area and shorter milling times than conventional specimen preparation methods. In the following, we report the details of the modified dimpling technique. The improvements in available electron transparency, and a decrease in ion milling time are demonstrated with the preparation of planar and cross section VLSI device samples.
Precision Ion Polishing System -A New Instrument for TEM Specimen Preparation of Materials
Authors: Alani Reza , Swann Peter R.
Published: March 2011

The article describes the design, construction and performance of a new bench top instrument for high speed ion beam thinning and polishing of materials. In this system, the combination of very low angle ion milling and powerful ion guns has led to the rapid production of high quality TEM specimens. The main subassemblies are (1) a work chamber (2) gas control system (3) vacuum system and (4) electrical system. The work chamber consists of a pair of newly designed Penning type ion guns and Faraday cups to measure ion currents. The Whisperlok™ mechanism provides specimen rotation, pneumatically driven airlock for very fast specimen exchange and transmission/reflection illumination for specimen viewing. The ion guns are mounted to deliver a nominal, 4° milling angle on the specimen surface with precision alignment of ±2° about horizontal and vertical axes. The actual thinning is undertaken from one side using a single, post-type specimen holder which minimizes the specimen heating and contamination. The ion beam current of each gun can be individually optimized by varying the flow rate of the ionizing gas. The main chamber is evacuated by diaphragm and molecular drag pumps to produce a clean, dry vacuum in the 10−6Torr range. The discharge and accelerating voltages required for the operation of each gun are provided by a dual high voltage power supply capable of delivering ion energies in the range; 1 keV to 6keV. TEM micrographs of typical ion polished specimens of semiconductors, metals, ceramics and composites are included to illustrate the performance of the instrument.
Synthesis, Characterization, and Dynamics of a Rod/Sphere Organoceramic Composite Liquid
Authors: Tracy Mark A. , Pecora R.
Published: March 2011

Composite liquids – liquids composed of polymers, particles, and small molecule solvents – constitute an important class of synthetic and naturally occurring materials. Examples include molecular composites, ceramic precursors, lubricants, adhesives, and the cytoplasm in biological cells. Due to the complexity of these liquids, experimental studies of precisely defined systems are essential in developing an understanding of the interactions between all components in the liquid. Unfortunately, such fundamental studies have been relatively rare due to both the difficulty of synthesizing precisely defined composite liquids and the lack of adequate experimental methods to monitor the motions of the various constituents.

We have recently reported the synthesis, characterization and some studies of the dynamics of a rod/sphere composite liquid system [1]. In our case the “polymer” constituent is a rigid rod polymer, poly(γ-benzyl-α,L-glutamate) (PBLG). Rigid rod polymers are frequently used in composite liquids as viscosity enhancers. PBLG is commercially available in a wide range of molecular weights and its static and dynamic behavior in dilute and nondilute solutions has been studied. It, in addition, forms mesophases in the concentrated regime. The ceramic “particles” in our composite liquid are coated silica spheres. These spheres are synthesized by the method of Stober et. al. [2] and coated with an organic coating (3-(trimethoxysilyl)propyl methacrylate (TPM)) following a procedure based on that of Philipse et. al. [3] to render them dispersible in organic solvents. The spheres with sizes in the range from 10 nm up to almost 1μm can be synthesized with a relatively narrow size distribution. The solvent in our studies is dimethylformamide (DMF). Both polymer and particle are dispersible as singlets (nonaggregating) in these solvents and the PBLG retains its rigid (or nearly rigid) rod conformation. The diffusion of both the polymer and the sphere in the composite liquid is measured by dynamic light scattering (DLS) [4]. In this paper, we focus on the spheres and examine the effects of rod concentration and rod length on the diffusion of different size spheres. This study suggests that the solution microstructure has an important influence on sphere diffusion.
Sol-Gel Synthesis of Ceramic-Organic Nano Composites
Authors: Schmidt Helmut K.
Published: March 2011

Sol-gel synthesis can be used for generating nano particles from a variety of compositions. In order to avoid aggregation and undesired gelation, it is necessary to react the particle surfaces with ligands reducing their interaction but allowing the incorporation into desired matrices. Three examples (semiconducting and metal quantum dots, ZrO2 and Al2O3 containing composites) are described, their properties and some applications for optics and protective coatings are discussed.
Microstructure Development and Mechanical Properties of Ce-TZP/La- β-Alumina Composites
Authors: Fujii Takashi , Muragaki Hironobu , Hatano Hiraku , Hirano Shin-Ichi
Published: March 2011

Simultaneous additions of lanthanum aluminate(LAL) and Al2O3to Ce-TZP (12mol% CeO2-ZrO2) lead to the in-situ formation of lanthanum- β-alumina(LBA) platelets (∼1.0.μ m in width and 5 ∼10 μ m in length) in the Ce-TZP matrix during sintering. The composites showed a fracture toughness(SEPB method) of 9.5 MPa · m0.5and fracture strength of 960 MPa. which are remarkably improved from Ce-TZP sintered body (8.5 MPa · m0.5and 560 MPa).

The composites also exhibit the no degradation by hydrothermal treatment.
In-Situ Phase Separation of an Amine-Terminated Siloxane in Epoxy Matrices
Authors: Bergstrom D. F. , Burns G. T. , Decker G. T. , Durall R. L. , Fryrear D. , Gornowicz G. A. , Tokunoh M. , Odagiri N.
Published: March 2011

We have developed an amino-functional silicone resin to toughen epoxies which, when prereacted with the epoxy function in resins, undergoes in-situ phase separation during final epoxy curing. SEM analyses of the morphology of fracture surfaces of MY720- DDS, Epon 828-DDS and other epoxy matrices modified with the silicone resin showed rough surfaces with the formation of very uniform <10 μm spheres. Silicon and sulfur elemental distribution mapping showed silicon rich spheres embedded in an epoxy matrix. We report cavitation, particle debonding and pull-out, and an increases in fracture surface area as possible modes of toughening. Silicone modified materials give improvements in slow strain rate G1c fracture toughness measurements of 250–400%, similar to carboxy terminated polybutadiene-acrylonitrile copolymer (CTBN) modifiers, but with a much smaller flexural modulus loss. The Tg of the modified epoxy matrices are maintained, moisture resistance is improved, and flammability is reduced.
Laser or Flood Exposure Generated Electrically Conducting Patterns in Polymers
Authors: Bargon Joachim , Baumann Reinhard
Published: March 2011

Electrically conducting patterns can be generated in insulating polymers or composites either via UV-flood exposure through a mask or via laser irradiation. Various lithographic concepts starting either from conventional or custom tailored polymers or from special composites have been developed and tested. Thereby electrically conducting polymers are photogenerated either directly from a self-developing photosensitive precursor or via a twocomponent redox approach using one of the components as a vapor in an otherwise dry process. The electrically conducting patterns so obtained may be reinforced by plating them with metals electrogalvanically. These processes may also be combined with laser induced ablation, whereby the intensity of the laser beam may be gated to either induce electrical conductivity of the substrate or to ablate it without rendering it conductive. Analogously, thin films of electrically conducting polymers on top of insulating polymer layers can be patterned directly using excimer laser ablation.
Molecular Weight Dependence of Domain Structure in Silica-Siloxane Molecular Composites
Authors: Ulibarri Tamara A. , Beaucage Greg , Schaefer Dale W. , Olivier Bernard J. , Assink Roger A.
Published: March 2011

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The morphology of the in situ filled material showed a definite dependence on the molecular weight of the precursor polymer. The scale, R, of the glassy domains follows de Gennes' description of phase separation in a crosslinked system (R ∝ M1/2).
Effect of Impurities on the Electronic Structureof Grain Boundaries and Intergranular Cohesionin Tungsten
Authors: Krasko Genrich L.
Published: March 2011

The cohesion of a grain boundary (GB) is believed to be the controlling factor limiting theductility of high-strength metallic alloys, and particularly W. Intergranular embrittlement isusually associated with segregation of impurities at the GBs. Impurities present in ppmconcentrations can result in a dramatic decrease in plasticity. This paper reviews recent results onboth semi-empirical and first-principles modelling of the energetics and the electronic structuresof impurities on a Σ3 (111) GB in W. Our calculations have shown that impurities, such as N, O,P, S, and Si weaken the intergranular cohesion resulting in “loosening” the GB. The presence ofB and C on the contrary, enhances the interatomic interaction across the GB. The so-called site-competition effect should play an important role affecting impurity distribution in W GBs.Among the impurities analyzed, B in the GB has the lowest energy, and thus would tend todisplace other impurity atoms from the GB. Microalloying with 10-50 ppm B may be an effectiveway of improving tungsten's ductility. These results are important for understanding thefundamental physics of intergranular embrittlement.
An AB Initio Calculation of the Pd-V FCC Superstructure Phase Diagram with Fourth Nearest Neighbor Cluster Interactions
Authors: Tepesch Patrick D. , Ceder G. , Wolverton C. , Fontaine D. De
Published: March 2011

The Monte Carlo technique was used to calculate the phase diagram of the fee superstructures in the Pd-V system using up to fourth nearest neighbor, concentration independent, pair and multiplet interactions. The interactions were computed by the method of Direct Configurational Averaging using a Linearized Muffin-Tin Orbital Hamiltonian cast into the tight binding form. The phase diagram was computed with a fast Monte Carlo simulation technique using environment sampling. The two fee ground states in experimental diagram are predicted to be stable. The computed transition temperatures are higher than those found experimentally.
Calculations of Alloy Phases with a Direct Monte-Carlo Method
Authors: Faulkner J. S. , Wang Yang , Horvath Eva A. , Stocks G. M.
Published: March 2011

A method for calculating the boundaries that describe solid-solid phase transformations in the phase diagrams of alloys is described. The method is first-principles in the sense that the only input is the atomic numbers of the constituents. It proceeds from the observation that the crux of the Monte-Carlo method for obtaining the equilibrium distribution of atoms in an alloy is a calculation of the energy required to replace an A atom on site i with a B atom when the configuration of the atoms on the neighboring sites, κ is specified, δHκ(A→B) = EB(κ)−EA(κ).Normally, this energy difference is obtained by introducing interatomic potentials, vij ,into an Ising Hamiltonian, but we calculate it using the embedded cluster method (ECM). In the ECM an A or B atom is placed at the center of a cluster of atoms with the specified configuration κ ,and the atoms on all the other sites in the alloy are simulated by the effective scattering matrix obtained from the coherent potential approximation. The interchange energy is calculated directly from the electronic structure of the cluster. The table of δHκ(A→B)'s for all configurations κ and several alloy concentrations is used in a Monte Carlo calculation that predicts the phase of the alloy at any temperature and concentration. The detailed shape of the miscibility gaps in the palladium-rhodium and copper-nickel alloy systems are shown.
New Technique for AB Initio Atomistic Potentials and Application to Thermal Expansion of Ni/Cr Alloys
Authors: Mei J. , Cooper B.R. , Hao Y.G. , Lim S.P. , VanScoy F.L.
Published: March 2011

A scheme of developing ab initio many body potentials based on total energy calculations within density functional theory (DFT) is presented and demonstrated for transition metal alloys. An ab initio interatomic potential for Ni/Cr alloys is constructed with no input from experimental data. Molecular dynamics simulations have been performed to study thermal expansions. The coefficient of thermal expansion (CTE) has been calculated over a wide range of temperature, and good agreement is obtained between theory and experiment.
How Small a System is Too Small for Studying Liquid Behavior?
Authors: Grabow Marcia. H.
Published: March 2011

Although it is often convenient to perform computer simulations with small systems, in liquids the structure obtained using a small system may not be the same that would be obtained in the thermodynamic limit. In this paper we address the question specifically for the case of Stillinger-Weber silicon, identifying the region of density and temperature where small systems give different results from larger systems.
Tight-Binding Molecular Dynamics Study of Liquid and Amorphous Carbon
Authors: Wang C. Z. , Ho K. M. , Chan C. T.
Published: March 2011

Tight-binding molecular-dynamics simulations are performed to study the structure of liquid and amorphous carbon. Comparisons of our results with ab initiomolecular dynamics (Car-Parrinello) results and experimental data show that the scheme has sufficient accuracy and efficiency for realistic simulation study of the structural properties of complex carbon systems.
Bond Rotations at the Si(100) Surface: Anharmonicity, Chaotic Dynamics, and Signature of Tilted-Dimer Reconstruction
Authors: Gryko J. , Allen R. E.
Published: March 2011

In our first-principles-based molecular dynamics simulations for Si(100), we have found that the total energy U(θ) is rather flat with respect to the bond-rotation angle θ for |θ| <10°, with shallow minima at the positions θ = ± θ0 corresponding to a tilted-dimer geometry. Here we calculate the Fourier transform of the atomic displacements, u(ω), and find a characteristic bond-rotation mode with v − 5 THz. This mode is primarily associated with the upper atom in a dimer, and appears to be a signature of the tilted-dimer reconstruction. At low temperature the vibrations are nearly harmonic, but at high temperature there is strong anharmonicity, and θ appears to exhibit chaotic behavior.
Pseudohamiltonians and Quantum Monte Carlo
Authors: Bosin A. , Fiorentini V. , Lastri A. , Bachelet G. B.
Published: March 2011

A new method is presented for the generation of valence-only local hamiltonians, or pseudohamiltonians, within the DFT-LDA framework. At the moment these promise to be very useful tools to overcome the problem of eliminating the core electrons from many QMC calculations.
Application of Density Functional Theory to Al Distribution in Mordenite
Authors: Fitzgerald G , Coe C. G. , Klotz H.C. , Macdougall J.E.
Published: March 2011

Mordenite zeolites are well known for their acid cracking abilities, but are often hindered by coke formation which limits their life. The dealumination and generation of Bronsted acid sites in the MOR structure will have significant implications as to their catalytic activity. Density functional theory (DFT) has been applied to determine preferred aluminum siting in the Na-mordenite zeolite structure. DFT correctly reproduces the 6-31G* Hartree-Fock predictions for the relative stabilities of the four T sites of mordenite in a T(OH)4 cluster. Larger cluster sizes influence the preferred Al siting with DFT predicting T2 as the preferred tetrahedral site. Since DFT computational requirements are considerably smaller than Hartree-Fock theory, it is an attractive alternative for studying zeolites. The calculations performed were based on fixed geometries obtained from crystallographic data. Further work employing local geometry optimization in the vicinity of the substituted Al is underway.
Transferable Total Energy Parametrization for Metals
Authors: Sigalas M. , Papaconstantopoulos D.A.
Published: March 2011

We have investigated total energy expressions that consist of a term describing the eigenvalue sum and a pair potential term. Such expressions can be used to fit the results of first principles total energy calculations at given structures, and then obtain the total energy of another configuration of atoms avoiding the complexity of further ab initio calculations.

In this work we present a method of fitting APW total energy results to a non-orthogonal tight-binding Hamiltonian from which the sum of the eigenvalues is derived and to a pair potential represented by a 5th order polynomial. We fit total energies for the fee and bec structures and we then obtain the elastic constants Cij in good agreement with both full potential LAPW calculations and experiment. We present results of this method for Ir.
Ergodicity and Convergence of Fluctuations in Parrinello-Rahman Molecular Dynamics
Authors: Li M. , Johnson W. L. , Goddard W. A.
Published: March 2011

Distortion and rotation of a molecular dynamics cell used in Parrinello-Rahman molecular dynamics are found to lead to slow convergence, or nonconvergence of fluctuations from thermodynamic averages. The variations are shown to be related to nonconservation of the total angular momentum and translational symmetry variance of the dynamics. A modified equation of motion is presented which eliminates these variations. It is shown that the ergodicity is achieved in the MD ensemble generated by the new equations of motion. However, the rate of convergence is strongly affected by the choice of the MD cell mass W. Simulation results show that not all values of Wcan be used to give a desired convergence of fluctuations from thermodynamic averages in finite simulations. The fastest convergence is achieved by using the optimal cell mass.
Classical and Quantum Simulations for Large Systems on Parallel Computers
Authors: Vashishta Priya , Kalia Rajiv K. , Yu Jin
Published: March 2011

Molecular dynamics (MD) method is used to investigate structural transformation and the loss of intermediate range order in SiO2 glass at very large positive pressures and the modification of SiO2 glass network at very large negative pressures. The nature of molecular vibrations in solid C60 has been studied with tight binding molecular dynamics (TBMD) method. Implementations of simulation algorithms on parallel computers are also discussed.

In a-SiO2 at high pressures, the height of the first sharp diffraction peak in S(q) is considerably diminished and its position shifts to larger wave vectors. At twice the normal density, Si-O bond length increases, Si-O coordination changes from 4 to 6, and O-Si-O band-angle changes from 109° to 90°. This is clearly a tetrahedral to octahedral transformation, which is observed recently by Meade, Hemley, and Mao in their diffraction experiments using synchrotron radiation.

MD simulations of porous silica are carried out in the density range 2.2 - 0.1 g/cm3 Internal surface area, pore surface-to-volume ratio, gyration radius, and fractal dimension are studied as a function of density. Simulations are in good agreement with the experimental results obtained by x-ray scattering. The results reveal a crossover of the structural correlations between short- to intermediate-range (< 8 Å) and fractal- to large-scale-regime (10 ~ 100 Å).

Dispersion and density of states (DOS) of inter- and intra-molecular phonons are calculated for orientationally ordered and disordered solid C60 using the TBMD method. Inter-molecular phonon DOS extends up to 7.6 meV and shows libron peaks at 2.4 meV and 3.7 meV in the orientationally ordered phase. Orientational disorder softens libron modes. Intra-molecular phonons below 70 meV also show significant dispersion. Our results are in good agreement with the recent inelastic neutron scattering experiments.

MD is a numerical approach which involves the solution of Newton's equations for particles in the system. The multiple-time-step (MTS) approach reduces this computation significantly by exploiting the different time scales for short-range and intermediate-range interactions. Using the linked-list scheme, parallel algorithms are designed to implement on the in-house 8-node iPSC/860, a MIMD (multiple instruction multiple data) machine. Our group has also developed a quantum dynamical simulation scheme for Computational Nanoelectronics based on the quantum molecular dynamics (QMD) method. The QMD algorithm has been implemented on the in-house 8,192-node MasPar, a SIMD (single instruction multiple data) architecture.
Dimerization on GaN(001) Surfaces
Authors: Tsai Min-Hsiung , Dow John D.
Published: March 2011

The GaN(OOl) surface is polar with either N- or Ga-termination. We predict that the Ga-terminated surface does not dimerize, but instead the surface Ga atoms relax into the vacuum by about ≈0.38 Å. The N-terminated surface is predicted to form a c(2×4) structure with N2 dimers in rows of length two. This is to be contrasted with the (2×1) Si(001) surface, on which the dimer rows are infinitely long, and with the (2×4) GaAs(OO1) surface, on which the rows are three dimers long.
Mechanical Response of High Performance Polymers: Abpbo, Abpbi and Abpbt
Authors: Çağin Tahir
Published: March 2011

Light weight, high strength fibers and films produced from stiff chain polymers are good candidates for use as structural materials. Over the last decade, considerable success has been achieved in synthesizing high strength fibers and films. Due to their thermal and oxidative stability aromatic heterocyclic stiff chain polymers such as ABPBO, ABPBT, and ABPBI are especially good candidates. We first describe the finite theory of elasticity as applied in atomistic modelling and simulations of anisotropic solids and then use this description to investigate the mechanical response of these crystalline polymers as a function of applied hydrostatic pressure and uniaxial tension and compression along the chain direction in molecular mechanics simulations. In addition to these finite stress-strain experiments, I will also present the results of the first elastic stiffness matrix calculations performed on these high performance polymers.
Cluster Calculation of B and A1 Impurities in Amorphous Silicon
Authors: Cogordan J. A. , Sansores L. E. , Valladares A. A.
Published: March 2011

We report our results of molecular structure calculations for B and A1 impurities. From our unoptimized ab initio calculations, we found the molecular electronic wave function to be unstable for both impurities. This instability was removed through a geometry optimization process. Local densities of states (LDOS) were computed for the optimized geometries. They show a rise of a peak at the tail of the valence LDOS; this feature is due to p orbitals of B and Al. The contribution is slightly higher for B than for A1 impurities. Charge contour plots are presented.
Diffusion Characteristics of Vacancies in Aluminum Interconnects.
Authors: Nandedkar A. S.
Published: March 2011

Computer simulations were performed to investigate the migration energy of vacancies in A1 in the presence of grain boundary, dislocation and various imposed forces (such as stress gradients and electro-migration). The energy values were significantly smaller when the vacancy moved into the grain boundary or a dislocation core than in opposite direction. This makes these defects sinks for vacancies from which they are unlikely to migrate out. The major time required for the movement of vacancies is thus limited to within a single grain. Calculations of migration time from the center of the grain to the grain boundary gives time needed for void formation. Calculations of this time assuming an electrical potential gradient along the metal line gave estimates consistent with experimental observations. The increased values of migration energy under compressive stresses suggest that void formation could be deterred by applying such stresses.
Diffusion of Gold Into Silicon. W-Shaped Concentration Profiles of Gold.
Authors: Vaysleyb A.V. , Malinsky J.
Published: March 2011

Diffusion of gold atoms into silicon crystals was considered. It was shown that W-shaped gold profiles in silicon can be explained in the framework of both the dissociative and the kickout mechanisms.
Extension of a New Semiempirical Method (BFS) and the Study of Ground State Properties of Binary Alloys
Authors: Bozzolo Guillermo , Ferrante John
Published: March 2011

We extend the method of Bozzolo, Ferrante and Smith (BFS) for the study of alloy energetics to include a description of the local environment in specific ordered structures. The concept of bond-diagrams is introduced and applied to fcc binary compounds. A simple example of the parameterization of the bond-diagrams is done with reference to available first-principles calculations of Ni-Pt ordered alloys.
Calculation of the Thermopower of Ni-P Amorphous Alloys
Authors: Swihart James C. , Yang Hyungjin , Nicholson Donald M.C.
Published: March 2011

We have modeled the Ni-P amorphous alloy system by a set of supercells on which we have carried out calculations of electronic and transport properties. The thermopower is determined by calculating the energy dependence of the dc electrical conductivity from the Kubo formalism. At 15% P we find -0.015 μV/K2 for the thermopower divided by the temperature, while for 25% P the calculated value is +0.008 μV/K2, in reasonable agreement with experiment, particularly with regard to the change of sign with concentration.
Electronic Structure of Ordered and Disordered Ternary Intermetallics
Authors: Wolverton C. , De Fontaine D.
Published: March 2011

A cluster expansion for energetics is combined with a direct, real-space method of studying the electronic structure of ordered and disordered ternary intermetallics. The electronic structure calculations are based on an explicit averaging of local quantities over a small number of randomly chosen configurations. Quantities such as densities of states, one-electron energies, etc., are computed within the framework of the first-principles tight-binding linear muffin-tin orbital method (TB-LMTO). Effective pair interactions, which describe the ordering tendencies of the alloy, are computed for the full ternary alloy. With this technique, then, the effects on ordering trends of ternary additions to a binary alloy may be obtained. Results for Ag-Pd-Rh and Ni-Al-Cu are shown. The self-consistency of these calculations is checked against the fully self-consistent ordered LMTO calculations.
Electronic Structure and Phase Stability Properties in Ternary Substitutional Alloys
Authors: Traiber Ariel J.S. , Sluiter Marcel , Turchi Patrice E.A. , Allen Samuel M.
Published: March 2011

Electronic structure and stability properties of ternary-metal alloys are examined using an extension of the Coherent Potential Approximation -Generalized Perturbation Method approach within the Tight-Binding description of the chemically random alloy. In particular, we report on calculations of density of states, mixing energies and effective cluster interactions which build up the ordering energy. The study focuses on the Ti-V-Fe system and its binary components.
Monte Carlo and Molecular Dynamics Validation of an N-Body Potential for Cu3Au
Authors: Rey-losada Carlos , Hayoun Marc , Pontikis Vassilis
Published: March 2011

We present the results of Monte Carlo and Molecular Dynamics simulations of some thermodynamical properties of Cu3Au. The calculations rely on an empirical n-body potential that reproduces satisfactorily the critical temperature, Tc, the temperature dependence of the lattice constant and atomic vibrational amplitudes as well as Cowley's short-range order parameters above Tc. Our results show that relaxation effects decrease considerably the formation energy of antisite defects and therefore should explicitly be considered for a realistic description of the transition.
The Effects of Aromaticity and Reduced Bond Length Alternation on Linear and Third-Order Polarizabilities of Conjugated Organic Chromophores
Authors: Gorman Christopher B. , Marder Seth R.
Published: March 2011

The geometries, the linear (α) and third-order (γ) polarizabilities of several bipolaron model compounds and cyanines are computed using the semi-empirical AM1 parameterization. The effects of aromaticity, charge localization and bond length alternation are considered.
Quantum Simulation of Amorphous Silicon: Preparation, Structure and Properties
Authors: Colombo L. , Servalli G.
Published: March 2011

Within a tight-binding molecular dynamics scheme we investigate pure amorphous silicon (a-Si) obtained by direct quenching from the melt. Using different rates for the cooling process, we demonstrate that both structural and electronic properties of a-Si depend on the sample preparation. Possible size-effects are also investigated using 64- and 216-atom supercells. Finally, we discuss the reliability and transferability of the present scheme for large scale simulations of covalent materials.
Model of the Semiconductor-to-Semimetal Transition Modulation at Teraherz Frequencies
Authors: Cheng T. K. , Acioli L. , Vidal J. , Zeiger H. J. , Ippen E. P. , Dresselhaus G. , Dresselhaus M. S.
Published: March 2011

We present experimental data which show that large amplitude coherent lattice vibrations can be impulsively excited using short optical pulses of light. Furthermore, using a quasi-equilibrium model, we show how the these coherent lattice vibrations suggest a ~ 7 THz modulation of the semiconductor-to-metal transition in Ti2O3.
Dynamical Ising Model Simulations of Nucleation and Growth in Copper-Cobalt Alloys
Authors: Cerezo Alfred , Hyde Jonathan M. , Miller Michael K. , Setna Rohan P. , Smith George D. W.
Published: March 2011

A simple dynamical Ising model on a fixed lattice with a single bond energy parameter has been used to simulate the kinetics of diffusion during solid-state phase transformations in binary metallic alloys. The results of these simulations are compared with direct real-space measurements of the atomic distributions of elements in alloys, obtained with the position-sensitive atom probe. Despite the simplicity of the model, there is good quantitative agreement between the development of micro-structure in the simulation and the nucleation and growth of cobalt-rich precipitates in copper-cobalt alloys.
Elastic Instabilities and Amorphization of Crystalline Silica Under Pressure
Authors: Chelikowsky James R. , Binggeli Nadia
Published: March 2011

Solid state amorphization can occur when a crystalline phase is compressed at a sufficiently low temperature to inhibit kinetically the transformation to a stable high pressure crystalline phase. An example of such a vitrification transformation occurs in α-quartz, the most stable phase of SiO2 at standard temperature and pressure conditions. Under pressure at room temperature α-quartz gradually transforms to an amorphous form in the range of 25-30 GPa. The driving force for this amorphization is not clear, and speculation has centered on mechanical instabilities of the quartz crystal under pressure. The elastic properties of α-quartz are studied as a function of pressure using both classical interatomic potentials, and ab initio pseudopotentials. In both cases, we find that the α-quartz structure becomes mechanically unstable at about 30GPa. This finding supports a picture in which the amorphization of quartz is triggered by the onset of a lattice shear-instability. The microscopic origin of this elastic softening is intimately related to the presence of an oxygen close-packed cubic arrangement in the quartz high pressure structure.
First-Principles Calculation of Force Constants and Full Phonon Dispersions
Authors: Wei Siqing , Chou M. Y.
Published: March 2011

We calculated the real-space force constants and full phonon dispersion curves for elemental semiconductors (silicon and germanium) under the local-density approximation with the Hellmann-Feynman forces. The force constants are obtained through super- cell calculations for planar displacements in three different symmetry directions. From these real-space force constants the dynamical matrix for an arbitrary wave vector in the Brillouin zone can be constructed. The procedure is simple in concept and requires no complicated computer programing. It is also possible in principle to handle the anharmonic effects.
Quantum Dynamical Simulation of Many Electron-Phonon Coupled Systems on Parallel Computers
Authors: Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya
Published: March 2011

A quantum dynamical simulation method is developed to investigate coupled many electron-phonon systems. Both electron and phonon wave functions are numerically propagated in time. The method is applied to the study of resonant tunneling of an electron through double quantum dots. Phonon-induced electron localization is observed. The space- splitting Schrödinger solver and dynamical-simulated-annealing Poisson solver are implemented on an 8,192-node MP-1 computer from MasPar.
Simple Flexible Boundary Conditions for the Atomistic Simulation of Dislocation Core Structure and Motion
Authors: Pasianot Roberto , Savino Eduardo J. , Xie Zhao-Yang , Farkas Diana
Published: March 2011

Flexible boundary codes for the atomistic simulation of dislocations and other defects have been developed in the past mainly by Sinclair [1], Gehlen et al.[2], and Sinclair et al.[3]. These codes permitted the use of smaller atomic arrays than rigid boundary codes, gave descriptions of core non-linear effects and allowed fair assessments of the Peierls stress for dislocation motion. Green functions (continuum or discrete) or surface traction forces were used to relax the boundary atoms.

A much simpler approach is followed here. Core and mobility effects at the boundary are accounted for by a dipole tensor centered at the dislocation line, whose components constitute six more parameters of the minimization process. Results are presented for [100] dislocations in NiAl. It is shown that, within the limitations of the technique, reliable values of the Peierls stress are obtained.
Analogy Between the Groundstate of an Antiferromagnet and the Mode of Quasi-Static Deformation of a Packing of Spheres.
Authors: Evesque P.
Published: March 2011

We report on local and global processes during the mechanical deformation of packings of spheres. We demonstrate that solid friction imposes a counter-rotation interaction to two adjacent grains during the deformation in order to minimize losses. This is equivalent to introduce an anti-ferromagnetic spin-like interaction in the structure; the search for the deformation process is quite similar to that one of finding the groundstate of an anti- ferromagnetic disordered structure with special boundary conditions. We demonstrate experimentally that boundaries may produce leading frustration processes; in this case, they govern most of the deformation mode and cancel mostly the influence of bulk mechanical properties (at least in the case when global “antiferromagnetic” order of the bulk is allowed by the absence of frustration). Frustration due to triangular local structure is described and existence of “anti-ferromagnetic-like” domains is proved; these domains are induced by the adequation between the boundary conditions and the deformation process and the domain wall is a stress-localization band as named in classical soil mechanics.
Catalytic Effect of Some Oxides on Calcination of Sodium Nitrate
Authors: Sembira A. N. , Perez M. M.
Published: March 2011

The calcination process used for sodium nitrate could be the most important part of the liquid-waste calcination process used in high-level-waste (HLW) disposal. A French process that involves conversion of the solution of nitrate fission products into a solid mixture of oxides and undecomposed nitrates. These products are then mixed with a glass-making mixture (called a frit) in an induction melting pot.

In 1984, Utake et.al., (1) suggested the use of the Sol-Gel technique to decrease the calcination temperature of NaNO3.

In this work, we used the thermal-analysis technique to study the catalytic effect of some glass network formers like SiO2, B2O3 and of some network modifiers like A12O3, Fe2O3, MgO, TiO2 ZnO. The best effect was achieved by adding 20% diatomaceous earth (Kieselguhr) and 20% B2O3 In that case, the calcination temperature onset decreased from 780°C to 565°C.

The advantages of this process are as follows:

1. The proposed additives (Kieselguhr and B2O3) are glass network formers that have to be added anyway in the next piocess step.

2. In the proposed process, no sodium is added, and the only process change suggested is that the glass formers (or part of them) should added at the calcination step, rather than at the glass-melting step.

3. The proposed modification is easily achieved and is expected to improve the homogenization of the final product.
Plutonium Leaching from a Reference Nuclear Waste Glass in Synthetic Interstitial Claywater
Authors: Wang Lian , Van Iseghem P. , Maes A.
Published: March 2011

The steady-state concentration of Pu was measured upon leaching Pu doped glass in synthetic interstitial claywater (SIC) and humic acid free interstitial solution (IS). The solubility of PuO2·xH2O(am) was determined in the same chemical condition. The results then were compared with the Pu solubility calculated by using a published solubility product and complex stability constants. The humic acid (HA) influence on the Pu leaching from the glass and the colloid formation were investigated.