bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractAn 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

AbstractThe 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

ABSTRACTComposite 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

ABSTRACTSol-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

ABSTRACTSimultaneous 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

ABSTRACTWe 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

ABSTRACTElectrically 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTA 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

ABSTRACTAlthough 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

ABSTRACTTight-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

ABSTRACTIn 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

ABSTRACTA 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

ABSTRACTMordenite 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

ABSTRACTWe 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

ABSTRACTDistortion 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

ABSTRACTMolecular 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

ABSTRACTThe 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

ABSTRACTLight 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.