bluuebunny/crossref_metadata_2025_split huggingface dataset:
Precision Tem Sample Preparation Using Focused Ion Beam Marking Strategies
Authors: Sanborn Christopher E. , Myers Sharon A. 
Published: March 2011

AbstractFocused ion beam (FIB) etching has been shown to be an effective method for TEM sample prep. The system uses a finely focused beam of gallium ions to remove surface material from selected areas. When used in conjunction with a metal-organic gas source, a conductive layer can be deposited in specific areas.In a production atmosphere, it is not always possible to use the FIB equipment for the length of time required to completely prepare a cross-sectional sample. Instead, the FIB has been used to indicate specific areas, such as blown fuses or shorts by “marking” the area so that it is easily optically located. Unconventional TEM sample prep techniques were developed to prepare the cross-sectional samples from specific target areas.
Reduced Amorphization of Ion-Milled Silicon Cross-Section Transmission Electron Microscope Samples by Dynamic Annealing During Milling.
Authors: Bahnck D. , Hull R. 
Published: March 2011

AbstractWe have developed an experimental apparatus for heating samples in the temperature range 50–400°C during ion milling. We find that heating to temperatures > 250°C during milling greatly reduces ion sputtering amorphization of the sample surfaces, due to dynamic reannealing of point defects. This allows thinner regions of crystalline sample to be imaged, without the signal being swamped by noise due to milling amorphization. At temperatures ≥300°C, however implantation defects am formed. We discuss the advantages of this technique for high resolution imaging.
Topographic Kinetics and Practice of Low Angle Ion Beam Thinning
Authors: Barna Árpád 
Published: March 2011

AbstractThe thinning technique is based on a simple geometrical model, describing the changes in the surface topography during ion beam etching. A high ion beam density makes jt possible that a thinning with an incidence angle of 0.5–7° ( measured from the sample surface) can take place within a reasonable time. Our method is applicable to a wide range of materials and to XTEM preparation.
Interpenetrating Organometallic Polymer Networks (IOPN's): Novel Advanced Materials
Authors: Corain B. , Zecca M. , Corvaja C. , Palma G. , Lora S. , Jerabek K. 
Published: March 2011

ABSTRACTA cross-linked copolymer of vinylferrocene and dimethyl-acrylamide is generated inside the less dense microporous domains of a cross-linked polydimethylacrylamide matrix. I.S.E.C. and E.S.R. data reveal that the obtained composite is in fact an I.P.N.(Interpenetrating Polymer Network) material.
A Novel Epoxy Resin Toughened by HTBN Liquid Rubber
Authors: Han Xiaozu , Yun Zhankui , Guo Fenchun 
Published: March 2011

ABSTRACTA novel toughened epoxy resin was obtained by using an epoxy-terminated prepolymer prepared from epoxy resin and hydroxy-terminated butadiene-acryl-onitrile copolymer (HTBN), and an amine curing agent. The cured, toughened resin has excellent mechanical properties due to the two-phase structure which was observed using SEM and TEM. When the HTBN content is 15 phr, the rubber phase separates effectively and the specimen presents a fine two-phase structure. However, when the HTBN content reaches 25 phr, the morphology appears continuous.
Variable Frequency Conductivity of Layered Polypyrrole / V2O5 Composites
Authors: DeGroot D. C. , Schindler J. L. , Kannewurf C. R. , Liu Y.-J. , Wu C.-G. , Kanatzidis M. G. 
Published: March 2011

ABSTRACTThe frequency dependent electrical properties of the intercalated polypyrrole/V2O5 system have been measured. This study continues the investigation into the charge transport mechanisms that have been identified in these layered polymer/inorganic composites. The polypyrrole/V2O5 material is prepared by in-situ oxidative polymerization of pyrrole in the intralamellar space of the V2O5 xerogel. This process produces a layered, two-dimensional structure in which the charge transport properties result from two parallel conduction paths: the polypyrrole chains and the V2O5 layers. Impedance spectroscopy data have been collected from free-standing film samples of the layered polypyrrole/V2O5. The experiments were conducted over the frequency range of 10 Hz to 0.5 GHz and a temperature range of 77 to 310 K. The polypyrrole/V2O5 impedance results are presented in various equivalent forms and compared to data collected from pristine V2O5·nH2O, and reduced Cs0.14V2O5·nH2O.
Al2O3-ZrO2 Ceramics with Submicron Microstructures Obtained through Microwave Sintering, Plasma Sintering and Shock Compaction
Authors: McKittrick J. , Tunaboylu B. , Katz J. D. , Nellis W. 
Published: March 2011

ABSTRACTSubmicron and nanocrystalline grain sizes were achieved in the Al2O3-ZrO2 eutectic composition through conventional, microwave and plasma sintering of rapidly solidified starting powders and through shock compaction of commercial powders. Post sintering studies revealed nanocrystalline intragranular ZrO2 in the 1–2 μm Al2O3 grains, which is thought to be a result of the solidification synthesis. Additions of B2O3 greatly increased the final density through liquid phase sintering. Shock compression of commercial powders produced dense, crack-free, fine grained ceramics with loading pressures up to 9.1 GPa and a metastable ZrO2 phase under higher pressures.
Synthesis of Carbon/Ferrite Composite by In-Situ Pressure Pyrolysis of Organometallic Polymers
Authors: Hirano Shin-Ichi , Yogo Toshinobu , Kikuta Koichi , Fukuda Makoto 
Published: March 2011

ABSTRACTFerrite particle-dispersed carbon composite were synthesized by in-situ pressure pyrolysis of organometallic polymers at temperatures from 500 to 700°C under 125 MPa. Magnetite-dispersed carbon composite could be prepared from 550 to 700°C at 125 MPa. Nickel and nickel zinc ferrite particles were dispersed in carbon matrices at 550°C and 500°C, respectively, under 125 MPa. The morphology of the carbon matrix can be controlled by the pyrolysis conditions and the amount of coexistent supercritical water. Carbon spherulites of several micrometers dispersed with ferrite particles less than 100 nm were successfully synthesized by pressure pyrolysis of organometallic polymers in the presence of supercritical water. The saturation magnetization of magnetite-, nickel ferrite- and nickel zinc ferrite-dispersed carbon were 74, 30 and 65 emu/g, respectively. The coercive force of nickel ferrite-dispersed carbon was about 200 Oe.
Magnetic Properties of Mechanically Alloyed Nano-Crystalline Cu/Fe Composites
Authors: Reed C. P. , Axtell S. C. , De Angelis R. J. , Robertson B. W. , Munteanu V. V. , Liou S. H. 
Published: March 2011

AbstractMetal powders of the composition 70 at% Cu and 30 at% Fe were produced by high energy mechanical alloying of the elemental powders. The powders were processed in a Spex 8000 mixer/mill for various times to investigate the potential of the mechanical alloying process for producing nano-composite structures with modified magnetic properties. Optical microscopy revealed a layered structure of alternating copper and iron that developed upon milling. The spacing between the layers decreased with milling time, becoming optically unresolvable (< 1μm) after four hours of milling. A single profile x-ray diffraction profile shape analysis technique was used to determine the average diffracting particle size of the copper and iron phases. The diffracting particle size decreases with alloying time reaching values of 7.5 nm and 2 nm, for copper and iron respectively, after eight hours of alloying. The magnetic coercivity increased with milling time initially, reaching a maximum value above 300 Oe after six hours of milling. These results are discussed and compared to results obtained in Ag/Fe and Cu/Fe nano-composite films.
High Temperature Polymer Nanofoams
Authors: Hedrick J. , Labadie J. , Russell T. , Wakhiarkar V. , Hofer D. 
Published: March 2011

ABSTRACTA means of generating high temperature polymer foams which leads to pore sizes in the nanometer regime has been developed. Foams were prepared by casting block copolymers comprised of a thermally stable block and a thermally labile material, such that the morphology provides a matrix of the thermally stable material with the thermally labile material as the dispersed phase. Upon a thermal treatment, the thermally unstable block undergoes thermolysis leaving pores where the size and shape of the pores are dictated by the initial copolymer morphology. Nanopore foam formation is shown for triblock copolymers comprised of a poly(phenylquinoxaline) matrix with poly(propylene oxide) as the thermally labile block. Upon decomposition of this block, a 10–20% reduction in density was observed, consistent with the initial PO composition, and the resulting PPQ foam showed a dielectric constant of ∼ 2.4, substantially lower than PPQ (2.8). Small angle X-ray scattering and transmission electron microscopy show pore sizes of approximately 100Å.
Characterization of Thermotropic Liquid Crystalline Polymer Blends by Positron Annihilation Lifetime Spectroscopy
Authors: Naslund Robert A. , Jones Phillip L. , Crowson Andrew 
Published: March 2011

ABSTRACTPositron annihilation lifetime spectroscopy (PALS) is used to investigate polymer-based molecular composites of two separate thermotropic liquid crystalline polymers (TLCPs) and the thermoplastic matrix polyetherimide. Trends in PALS spectral components obtained isothermally at 20°C and 120°C as a function of TLCP content are discussed as a function of free volume and molecular structure. Differential scanning calorimetry was employed as a complementary technique to investigate the differences in miscibility of the two systems and possible effects on positron lifetime values.
Small Angle Neutron Scattering Studies of Single Phase IPNs
Authors: Bauer Barry J. , Briber Robert M. , Malone Shawn , Cohen Claude 
Published: March 2011

ABSTRACTInterpenetrating polymer networks (IPNs) have been synthesized from polymers that form miscible polymer blends. Full, semi-I and semi-II IPNs made from polystyrene-d8 and poly(vinylmethylether) can be made to phase separate by incorporating low levels of crosslinking. However, blends of these polymers have a negative Flory-Huggins interaction parameter, making them highly miscible. This indicates that formation of IPNs favors phase separation relative to blends.IPNs made from polystyrene-d8 and polystyrene-h8 show that increased crosslink density also destabilizes the mixture as shown by small angle neutron scattering.IPNs have also been made by crosslinking end functionalized polydimethylsiloxanes in the presence of nonfunctionalized, deuterated siloxanes. These IPNs are also destabilized by increasing crosslink density, suggesting that the destabilization is due to the network, and not to the particular type of network forming reaction.
Effect of Hydrogen on Dislocation Emission from a Crack Tip in Nickel
Authors: Hoagland Richard G. 
Published: March 2011

ABSTRACTA method for determining the intrinsic resistance to dislocation emission and glide in atomic models is presented and applied to EAM models of nickel containing a single-ended crack tip. The method is an adaptation of the Peierls approach in which the work done on the glide plane is computed as a function of dislocation position and its derivative is the intrinsic resistance to dislocation motion. The results indicate that there are two parts to the resistance dislocation glide from the crack tip: a distinct barrier to injection of the dislocation from the crack tip and a periodic resistance associated with the lattice. When a hydrogen interstitial is placed on the slip plane near the crack tip the barrier height is reduced but its width is increased.
A Study on First Principle Calculation of Alloy Phase Diagram by Monte Carlo Simulation
Authors: Sawada Hideaki , Nogami Atsushi , Yamada Wataru , Matsiuniya Tooru 
Published: March 2011

ABSTRACTA method of first principle calculation of alloy phase diagram was developed by the combination of first principle energy band calculation, cluster expansion method (CEM) and Monte Carlo (MC) simulation, where the effective multi-body potential energy for the flip test in MC simulation was obtained by the decomposition of the total energy by CEM. This method was applied to Cu-Au binary system. The calculated phase diagram agreed with that of CVM by introducing the dependence of the lattice constant on the concentration of the whole system. Furthermore an attempt of introducing the effect of local lattice relaxation was performed by the consideration of the local concentration. The order-disorder transition temperature became closer to the experimental value by adjustment of the local lattice constant depending on the concentration in the local region consisted of up to the second nearest neighbors of the atom tested for flipping.
Dynamics of a Metal Overlayer on Metallic Substrates – High Temperature Effects
Authors: Rahman Talat S. , Black John E. , Tian Zeng Ju 
Published: March 2011

ABSTRACTWe have explored the structure and the dynamics of a bimetallic system consisting of a hexagonal (almost) overlayer of Agon a square lattice (Ni(100) and Cu(100)), as a function of the surface temperature. In each case the structure is "nearly" incommensurate giving rise to a low frequency Goldstone mode. Also, the overlayer atoms slosh back and forth over the substrate in a corrugated fashion. The calculated dispersion of the Ag/metal vertical mode, at room temperature, is in excellent agreement with experimental data. At higher temperatures floater atoms appear on top of the overlayer displaying a variety of cluster formations and also exchanges with the substrate atoms leading to surface disordering, interdiffusion and melting.
Cooperative Pseudo Jahn-Teller Effect as Microscopic Mechanism of (OMT)-(LTT) Structural Phase Transition in La2−xBaxCuO4Superconductors
Authors: Kaplan Michael D. 
Published: March 2011

ABSTRACTA microscopic mechanism for the structural phase transition from the orthorhombic mediate temperature (OMT) phase into the low temperature tetragonal (LTT) one is suggested on the basis of the cooperative pseudo Jahn-Teller effect. The local distortions mixing the ground and the first excited electronic states are ordered antiferrodistortively and are connected in part, with the oxygen octahedra rotations around the [100] axis. The results are in agreement, with the neutron scattering experiments data.
Electronic Properties of Alumxna/Titania Mixed Oxides and Interfacial Surface Models: a Theoretical Analysis
Authors: Jansen S.A. , Grabania S.A. , Buecheler N.M. , Whitwell G. 
Published: March 2011

ABSTRACTAlumina is a common contaminate of titania, which is found in paints and food additives. Recently, thin films of rutile TiO2 grown on sapphire (α-Alumina) have received attention for possible use in electronic and optical devices.1−3 However, the alumina-titania interface has not been well characterized. In this work we report an extensive analysis of the alumina-titania interfacial relationship. Using existing structural data4, models of common alumina and titania surfaces have been constructed. The model used maximizes the commensurability between the two structures. Semi-empirical/tight binding calculations have been employed to examine the monolayer as well as the interfacial electronic properties in terms of chemical interaction potential and stability.
Ionic Overlayers on Corrugated Surfaces I: Structure
Authors: Çağin Tahir , Sen Surajit , Seong Hyangsuk , Mahanti S.D. 
Published: March 2011

ABSTRACTStructural and dynamic properties of a large class of intercalation compounds can be modelled by a collection of ions interacting via a screened Coulomb potential and subjected to the corrugation potential produced by the host atoms. In this paper we discuss the results of Molecular Dynamics simulation studies of the ground state structure of RbC24 and related systems focussing primarily on the micro-structure i.e.on the nature of the domains and domain walls.
Reactions and Segregation on α-Cristobalite (011) Surfaces by the Electronegativity Equalization Method
Authors: Mullins W. M. 
Published: March 2011

ABSTRACTThe electronegativity equalization method is used to calculate the atomic charges, framework electronegativity and framework energy of the α–cristobalite bulk and the relaxed (011) surface. The effect of surface hydration and fluoridation on the framework properties are then calculated and related to surface charge. The segregation of germanium, aluminum and phosphorus in the α-cristobalite structure are modelled using the same method. The framework electronegativity difference between surface and bulk is observed to be a driving force for reactions and segregation.
Ionic Overlayers on Corrugated Surfaces II: Melting
Authors: Seong Hyangsuk , Mahanti S.D. , Sen Surajit , Çağin Tahir 
Published: March 2011

ABSTRACTUsing molecular dynamics simulation we have investigated the melting properties of a 2-dimensional system of ions interacting through a screened Coulomb potential in the presence of a substrate. We focus on the role of the substrate potential in the melting transition. The physical system we study is the stage-2 graphite intercalation compound RbC24 and a related system RbC24,57 whose intercalant density differs from the former by a small amount. Our results reveal the nature of melting processes characteristic of periodic domain wall solids.
Elastic Modulus of the (GaA.s)m(A.l A.s)n Superlattices
Authors: Mirovitskii Vadim Yu. 
Published: March 2011

ABSTRACTThe ultrathin (GaAs)m (AlAs)n superlattices ( SL ) grown along [001] are formally considered as a result, of ordering-type phase transition from an initial hypothetical mixed crystal (Gax Al1-x)As with x = m/(m+n) . From this point of view changes of elastic modulus tensor (EMT) induced by ordering can he calculated nearly in a spirit of phenomenological Landau theory of second-order phase transitions. It .is shown that a change of EMT component. S66 is completely determined by symmetry properties of two translational (Dzyaloshinskji) invariants of m+n power .in the expansion of SL thermodynamic potential in a power series .in order parameter components. The changes of the other EMT components depend on the second power of order parameter .The expressions are found out to connect. EMT of a definite ordered phase (SL - family with m+n = 3) with that, of the initial one.
An Electrostatic Induction Model for Fluoroalkane Polymers
Authors: Carbeck Jeffrey D. , Rutledge Gregory C. 
Published: March 2011

ABSTRACTAn electrostatic induction model based on atom-centered partial charges is presented. In this representation, the local electric field is evaluated at each bond center. The bonds are treated as entities polarizable only in a direction parallel to the bond itself by means of a scalar bond polarization parameter. The resulting induced charge separation contributes to the local electric field experienced by neighboring bonds, resulting in a final set of charges which are calculated self-consistently. The model provides a reasonable approximation to dipole moment vectors and polarizabilities of small molecule fluoroalkanes. The results are discussed in comparison with other induction models. This model fits well into the framework of established atomistic potential energy calculations using an atom-centered partial charge representation.
Electronic Structure of LaBO3(B=Mn,Fe,Co,Ni,Cu) Perovskites and La2NiO4
Authors: De La Mora P. , De Teresa C. , Vicente L. 
Published: March 2011

ABSTRACTThe electronic structure ofLaBO3 perovskites and La2NiO4 perovskite- like materials (where B = Mn,Fe,Co,Ni,Cu) have been studied inside a tight binding scheme using the extended Hückel Method. An analysis of the metal- oxygen bond is presented as well as the electronic structure in order to establish a correlation between electronic properties and catalytic activity (oxidation) of these compounds.
Dynamical Structure Factor and Vibrational Normal Modes of SiO2 Glass
Authors: Jin Wei , Kalia Rajiv K. , Vashishta Priya 
Published: March 2011

ABSTRACTWe study the atomic vibrational dynamics in silica glass (a-SiO2) using molecular-dynamics (MD) simulations and classical lattice dynamics method. The SiO2 glasses were generated by molecular-dynamics and steepest-descent quench (SDQ) using an effective interatomic potential consisting of two-body and three-body interactions. The frequency and eigenvectors of vibrational normal modes are obtained by diagonalization of the dynamical matrix. The partial and total vibrational density of states (DOS), bond-projected DOS, participation ratio (PR), and neutron-weighted dynamic structure factor are calculated. The results are compared with inelastic neutron scattering experiments on SiO2 glass.
Calculations of the Electronic Structure of Vacancies in a-Si:H
Authors: Valladares Ariel A. , Sansores L. Enrique 
Published: March 2011

ABSTRACTThe electronic structure of random clusters has been used in the literature as representative of the electronic structure of random solids. In this work a calculation of the local density of states (LDOS) and charge density contours for clusters of the type XSi20H28 with X an Si atom, a vacancy or 4 hydrogen atoms, has been carried out. The method used was a pseudopotential SCF Hartree-Fock and the HONDO program. It is found that the generation of a vacancy in the center of the cluster (removal of the central Si atom), introduces p-like states in the energy gap of the LDOS for the region near the center of the cluster. The saturation of the dangling bonds of the vacancy with 4 hydrogen atoms removes the states within the gap. These results are also borne out by the charge density contours, thereby reinforcing the importance of amorphous cluster calculations in the understanding of the electronic structure of amorphous solids.
Monte Carlo Simulations of Surface Segregation in Cu Ni Alloys
Authors: Pasturel A. , Drchal V. , Kudrnovsky J. , Weinberger P. 
Published: March 2011

ABSTRACTA new method coupling electronic structure calculations with Monte Carlo simulations has been developed to determine surface compositions in Cu-Ni alloys. The calculations are based on an effective Ising model with parameters as defined within the framework of the Generalized Perturbation Method (GPM) and as calculated by means of the tight-binding version of the linear muffin-tin orbital method. The composition profiles are obtained for the fcc(OOl) surface for three bulk compositions, namely Cu75Ni25, Cu50Ni50, and Cu25Ni75 and compared with available experimental data.
Phase Transformations in Hexagonal-Close-Packed Alloys: Analysis with the Cluster Variation Method
Authors: Mccormack Ryan , Asta Mark , Ceder Gerbrand , Fontaine Didier de 
Published: March 2011

ABSTRACTWe present a study of the hexagonal close-packed (hcp) Ising model for binary alloys within the cluster variation approximation. Groundstates of order stabilized by nearest-neighbor (NN) pair, triplet, and tetrahedron interactions were determined using the cluster configuration polyhedron method; no previous hcp ground-state study has considered all of these interactions. We predict physically realizable groundstates with stoichiometries A, AB (3 distinct structures), A2B, A3B, and A4B3. The previously unpredicted A4B3 structure is stabilized by multiatom (i.e. triplet, tetrahedron) interactions, while the others are stabilized by the two NN pair interactions. The Cluster Variation Method (CVM) was used to calculate the finite-temperature phase-equilibria for prototypical binary alloys. We present the first ordering phase diagrams computed with the CVM which contain all relevant groundstates for both isotropic and anisotropic NN pair interactions.