bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Transformations During the Mechanical Alloying of Nickel and Ruthenium Elemental Powders
Authors: Neste A. Van , Kaliaguine S. , Trudeau M. , Schulz R. 
Published: March 2011

AbstractThe structural evolution of a mixture of elemental Ni and Ru powders during high energy ball milling has been studied as a function of milling time using X-ray diffraction and transmission electron microscopy. On the Ni-rich side of the phase diagram (Ni70Ru30) we observe, during the milling, the diffusion of Ru in the Ni and an expansion of the Ni fcc lattice. After about 20 hours of milling, all the Ru has diffused into the Ni and we are left with an oversaturated Ni(Ru) fcc structure with a lattice parameter about 3.6% larger than the one of pure Ni. The Ni does not seem to diffuse into Ru during the process. On the Ru-rich side (Ni43Ru57) we observe initially the same diffusion process taking place but more rapidly. After about 8 hours of milling, the incorporation of Ru in the Ni has driven the fcc Ni lattice to its limit of stability (about 3.9% expansion) and the fcc structure transforms, upon further milling, into a new hcp structure. In the later stage of the process the remaining Ru diffuses into this new phase.
A Study of the Diffusion of Phosphorus in Ni/amorphous NiPx and a-NiPx/a-NiPy. Multilayers
Authors: Ross C. A. , Goldman L. M. , Barnard J. A. , Spaepen F. 
Published: March 2011

AbstractAn x-ray technique has been used to measure the diffusion of phosphorus in crystalline Ni/amorphous NiPx and amorphous NiPx/NiPy multilayer thin films produced by electrodeposition. The films have repeat lengths in the range 30–80Å and P contents x, y < 25at.%. A value for the interdiffusivity in amorphous NiPx is derived from measurements on fully amorphous films. The behaviour of partially crystalline films is described in terms of phosphorus diffusion into the nickel grain boundaries.
Coherency Strain Energy in any Crystal System: Applications to in Situ Observations of Cigm in Calcite
Authors: May R.S. , Evans B. 
Published: March 2011

AbstractIn situ observations of CIGM in CaCO3 bicrystals with a SrCO3 solute source were made. The change in boundary orientation and migration rate were compared with solute concentration. The liquid film model for coherency strain Induced migration was generalized to any non-cubic system and applied to CaCO3-SrCO3. The coherent layer was modeled as a thin film on an infinite half-space. The strain energy was found from solution of the Hooke's law expressions transformed to the appropriate coordinate system. For triclinic or monoclinic films the strain tensor was found by an eigenvector decomposition of the transformation matrix that defined the lattice parameter change with composition. High anisotropy of Vegard's law constants for CaCO3-SrCO3 caused (111) to have the lowest coherency strain per unit solute. Surfaces perpendicular to (111) in coherent equilibria were predicted to have half the solute concentration and three times the migration driving force of those perpendicular to (111). However, no correlation between solute concentration and boundary orientation was observed. Ambiguous and contradictory evidence for a relationship between solute concentration, boundary orientation, and migration rate was found. The self-stress state of a grain boundary in a solute diffusion field may be better modelled as hydrostatic rather than plane stress. Hydrostatic compression may interact with the boundary excess volume and cause a PV driving force for migration. Predictions based on coherent equilibrium at a surface have not been tested for that geometry in calcite; they should be tested before they are applied to grain boundaries.
Raman Studies of Pressure and Temperature Induced Phase Transformations in Calcite
Authors: Exarhos Gregory J. , Hess Nancy J. 
Published: March 2011

AbstractPhase stability in the calcium carbonate system was investigated as a simultaneous function of pressure and temperature up to 40 kbar and several hundred degrees Kelvin using micro-Raman techniques to interrogate samples constrained within a resistively heated diamond anvil cell. Measured spectra allow unequivocal identification of crystalline phases and are used to refine the P, T phase diagram. Calcium carbonate was found to exhibit both reversible and irreversible transformation phenomena among the four known phases which exist under these conditions. Time-dependent Raman intensity variations as the material is perturbed from its equilibrium state allow real-time kinetics measurements to be performed. Evidence suggests that the order of certain observed transformations may be pressure dependent. The utility of Raman spectroscopy to follow transformation phenomena and to estimate fundamental thermophysical properties from the stress dependence of vibrational mode frequencies is demonstrated.
Crystallization Processes of Heterogeneous Systems Followed in Time Resolved X-ray Powder Diffraction
Authors: Christensen Axel NØrlund 
Published: March 2011

AbstractTime resolved X-ray powder diffraction was used to follow the crystallization processes in the systems MgO-MgCl2-H2O and MgO-H2O. A Stoe X-ray powder diffractometer with a position sensitive detector was used. The crystalline reaction products are [Mg2(OH)3(H2O)2]C1.H2O and Mg(OH)2 dependent upon the MgC12 concentrations in the heterogeneous systems. Mg(OH)2 was the product in a 1.50 M MgCl2 solution and [Mg2(OH)3(H2O)3]Cl.H2O was formed in 3.00 and 5.17 M MgCl2 solutions at 20°C.
Application of Solid Phase Epitaxy for Measuring Dangling Bond Densities and Impurity Ionization in Amorphous Silicon
Authors: Walser R. M. , Jeon Young-Jin 
Published: March 2011

AbstractAccording to a recent model [1], the enhancement in the rate of the solid phase epitaxial regrowth (SPER) of silicon produced by implanted impurities is determined by the superposition of reconstruction at sites that capture neutral, and ionized, three-fold coordinated dangling bond states. Considerable support for this model is derived from experiments on ionization-enhanced SPER in silicon. In this paper we discuss how this dangling bond model (DBM) could be used to determine the densities of neutral dangling bonds and ionized impurities in amorphous silicon from these experimental results. Both densities, determined by a self-consistent calculation, are in good agreement with those measured by other types of experiments. This result provides further support for the DBM and indicates that simultaneous SPER and ESR measurements could make it possible to depth profile low concentrations of ionized impurities in amorphous silicon.
New Insight into the Banded Microstructure of Rapidly Solidified Ag-Cu Alloys : Experiment and Theory
Authors: Yankov E. Y. , Copley S. M. , Todd J. A. , Yankova M. I. 
Published: March 2011

AbstractA transmission electron microscopy study has revealed that the banded microstructure produced in Cu-61.7 at. pct. Ag after surface laser melting and resolidification is not due to a cellular breakdown of the interface as previously thought, but consists of alternating regions of the extended metastable solid solution, y, and a coupled growth structure containing thin plates of y and the copper-rich phase β'. The spacing of this coupled growth structure is approximately 100 Å, which is less than half the minimum spacing yet observed for coupled growth from the melt in Ag-Cu.In order to explain the banded microstructure a theoretical model has been developed based on a finite elements solution of the diffusion equation in the melt, the interface response functions for continuous growth derived by Aziz and Kaplan and a recently developed theory for coupled growth that includes far-from-equilibrium regimes by Yankov et al..
The Planar to Cellular Transition and the Long Time Scale Dynamics of Pattern Formation During Thin-Film Directional Solidification
Authors: Lee John T.C. , Brown Robert A. 
Published: March 2011

AbstractExperimental observations of the melt/crystal interface in the directional solidification of a thin sample of a binary alloy are reported for conditions only slightly beyond those for the onset of morphological instability. Spectral analysis for long times shows dynamics leading to a band of most probable wavelengths with sharply selected peaks at wavelengths significantly below the most dangerous wavelength predicted by linear stability theory. These large-amplitude cells develop first in packets that spread to fill the interface.
Numerical Studies of Precipitate Coarsening Phenomena
Authors: Lavine James P. , Hawkins Gilbert A. 
Published: March 2011

AbstractA three-dimensional Monte Carlo computer program is used to study the time-dependent coarsening of a precipitate population in a solid. The emphasis is on the influence of the escape rate of solute atoms from a precipitate on the coarsening behavior. Three models for the escape attempt frequency are compared. The time when coarsening is observed and the extent of coarsening depend on the model as does the percentage of solute precipitated in a given time. The qualitative results of the present calculations are compared with earlier findings.
Kinetics of an Order-Disorder Transition in the Presence of Elastic Energies
Authors: Elder K. R. , Morin B. , Grant M. , Desai R. C. 
Published: March 2011

AbstractAn approximate late time solution to the dynamics of phase separation for a nonconserved ordering order parameter (ø) coupled to a stable conserved field (c) is presented. In the Halperin Hohenberg(1) classification scheme this model is known as Model C with a symmetric coupling between nonconserved and conserved fields. The different time dependences of long (i.e., domain size lengths ∼ power law in time) and short wavelength (i.e., interfacial lengths ∼ exponential decay in time) fluctuations imply a simple relationship between the two fields. In essence ø controls the growth of the long wavelength fluctuations, and c modifies the interfacial profile. Asymptotically the dynamic structure factor (Sø(k,t)≡<Ø(k,t)Ø*(k,t)>) for the nonconserved field is shown to scale in the form Sø(k,t) = tdnfø(ktn), with n = 1/2. Similarly the structure factor for the conserved field (Sc(k,t)) is shown to obey the scaling law Sc(k,t) = tdn−1fc(ktn), with n = 1/2. Explicit expressions for the scaling functions fc(z) and fø(z) are presented for arbitrary dimension. These predictions can be tested through scattering experiments.
Specific Heat and Melting Temperature of Relaxed and Unrelaxed Si Amorphous States
Authors: Grimaldi M.G. , Baeri P. , Malvezzi M.A. 
Published: March 2011

AbstractDirect picosecond laser measurements of the critical fluence for melting have been performed for the first time, giving unambiguously consistent differences in the energy required for surface melting of relaxed and unrelaxed amorphous silicon. The different optical coupling cannot account for this variation which can only be explained in term of different melting temperatures. Heating of unrelaxed amorphous silicon samples at temperatures close to the melting point may result in relaxation of the material even when the treatment occurs in the nanosecond time scale. However nanosecond UV irradiation of relaxed and unrelaxed amorphous silicon samples have provided informations on the specific heat of the two amorphous states. The melting temperature of unrelaxed amorphous silicon has been derived independently via both picosecond data and via free energy calculations.
Formation of Micro-Precipitates at the Melt-Solid Interface in Semiconductors
Authors: MÖller H.J. 
Published: March 2011

AbstractA theory is developed for the formation of precipitates in very dilute hypereutectic two phase systems during solidification. It is based on a mechanism for the growth of microdefects at the melt -interface. The model presents a solution of the diffusion problem for the solute atoms in the melt and provides an analysis of the factors which determine the particle size and their mean distance. The possibility of microdefect nucleation in front of the melt -interface, which can lead to very large precipitates, is discussed. The model is suitable to describe the formation of microdefects in semiconductors where impurity concentrations are generally low but may exceed the solubility limit in the melt. The results of the theory are compared with experimental investigations of the silicon carbide formation in carbon rich silicon crystals grown from the melt.
The Effect of Hydrogen on the Kinetics of Solid Phase Epitaxy in Amorphous Silicon
Authors: Roth J. A. , Olson G. L. , Jacobson D. C. , Poate J. M. , Kirschbaum C. 
Published: March 2011

AbstractThis paper discusses the intrusion of H into a-Si layers during solid phase epitaxy and the effect of this H on the growth kinetics. We show that during annealing in the presence of water vapor, H is continuously generated at the oxidizing a-Si surface and diffuses into the amorphous layer, where it causes a reduction in the epitaxial growth rate. The measured variation of growth rate with the depth of the amorphous/crystal interface is correlated with the concentration of H at the interface. The diffusion coefficient for H in a-Si is determined by comparing measured depth profiles with calculated values. Hydrogen intrusion is observed even in layers annealed in vacuum and in inert gas ambients. Thin (<;5000 Åthick) a-Si layers are especially susceptible to this effect, but we show that in spite of the presence of H the activation energy for SPE derived earlier from thin-layer data is in good agreement with the intrinsic value obtained from thick, hydrogen-free layers.
Numerical Simulation of Scanning Speed and Supercooling Effects During Zone-Melting-Recrystallization of Soi Wafers
Authors: Yoon Sharon M. , Miaoulis Loannis N. 
Published: March 2011

AbstractThe effects of scanning speed and supercooling were studied during zone-meltingrecrystallization (ZMR) of silicon-on-insulator (SOI) wafers. Using finite difference methods, a numerical simulation of the ZMR process was developed which captures all of the optical and thermal property changes during phase transformation. The effects of supercooling and scanning speed on the temperature profiles, the total width of the melt-zone and the width of ‘slush’ region were investigated. The melt-zone width increases for increasiongf thdee gfrreeeezsi nogf supercooling and decreases for increasing strip heater velocities. The combined effects on the melt-zone width were shown for various scanning speeds and degrees of supercooling. Supercooling also had a significant effect on the size of the freezing ‘slush’ region which was shown to decrease for increasing degrees of supercooling.
Effect of Low Level Photoionization in Solid Phase Epitaxial Regrowth of Amorphous Silicon
Authors: Jeon Young-Jin , Becker M. F. , Walser R. M. 
Published: March 2011

AbstractIn this work we searched for evidence of low level photoionization effects in the solid phase epitaxial regrowth (SPER) of intrinsic amorphous silicon on (100) silicon during isothermal furnace annealing. We used in situ cw laser interferometry to measure the changes in the rate at 500 °C as the laser power was varied from 20 mW-80 mW. Calculation showed that laser heating increased the sample temperature by a maximum of 6 °C at 80 mW. The measured change of the SPER rate with laser power in this range was always smaller than the change computed from an Arrhenius calculation using the measured activation energy, and the calculated value of the laser-produced increment in the sample temperature. The result indicates that there are negligible low level photoionization effects in silicon SPER.
Evolution of the Microstructure During Laser-Induced Amorphization of Si
Authors: Yater J.A. , Thompson Michael O. 
Published: March 2011

AbstractThe interface growth dynamics of Si leading to laser-induced amorphization have been studied as a function of incident energy density and crystallographic orientation using tran-smission electron microscopy (TEM). Using lithographic and dry etching techniques, cross sectional TEM specimens across the entire melt region were produced. These samples allowed observation of the evolution of the amorphous thickness and crystal defect structure from shallow anmorphous Si (a-Si) formation near the melt threshold energy density to crystallized material (c-Si) at higher energy densities. For surfaces near [111] orientations, marked differences in the solidification behavior were observed as compared to [001] or [110] orientations. The transition to a-Si growth at the moving liquid/crystal interface is discussed in terms of interface response function kinetics and crystallization models. A growth instability model, arising from the shape of the interface response function, is proposed to explain the observed nmicrostructure.
Electronic Structures of Icosahedral C60 and C60X (X=K, O and Cl) Clusters
Authors: Saito Susumu 
Published: March 2011

ABSTRACTI report the electronic structures of “buckminsterfullerene”, C60 cluster with truncated-icosahedron geometry, and C60X where X is a foreign atom trapped at the center of the C60 cage (X=K, O, and Cl). The local-density approximation with Xα exchange-correlation potential is used. The obtained electronic structure of C60 has a rather large energy gap between the completely occupied highest-occupied state and the lowest-unoccupied state, in accord with previous calculations. In the case of C60K, a valence electron of an alkali-metal atom is found to transfer to the outer C60 surface. On the other hand, in C60O and C60Cl, 2p state of O and 3p state of Cl appear inside the energy gap of the pure C60 cluster. Such variety of results indicates great possibilities of C60X as constructing units of new materials.
Quantum-Size Variation in Optical Transition Energies of CdTe Crystals in Glass
Authors: Potter B. G. , Simmons JH 
Published: March 2011

ABSTRACTWe examine the effects of finite crystallite size on the energies of optical transitions originating from states located at two different critical points of the semiconductor Brillouin zone. Using a versatile, dual source, R.F. sputtering technique, CdTe-glass composite thin films have been produced possessing average crystal sizes ranging from 24 to 125 Å in films containing up to 30 vol% semiconductor. Analysis of quantum-size induced transition energy shifts, monitored by optical absorption, indicates the persistence of significant Coulomb interactions between carriers at the gamma point of CdTe in crystallite sizes 0.3 times the size of the bulk exciton. L-point transition energy shifts support the existence of 2-D bound electron-hole pair states whose center-of-mass motion is confined in the semiconductor crystals.
Surface Melting and Surface Diffusion on Clusters
Authors: Cheng Hai-Ping , Stephen Berry R. 
Published: March 2011

ABSTRACTSurface melting on clusters is investigated by a combination of analytic modeling and computer simulation. Homogeneous, argon-like clusters bound by Lennard-Jones forces and Cu-like clusters bound by ‘embedded atom’ potentials are the systems considered. Molecular dynamics (MD) calculations have been carried out for clusters with 40–147 atoms. Well below the bulk melting temperature, the surfaces become very soft, exhibiting well-defined diffusion constants even while the cores remain nearly rigid and solid-like. The simulations, particularly animations, of atomic motion reveal that the surface melting is associated not with amorphous, random surface structures in constant, irregular motion, but rather in large-amplitude, organized, collective motion of most of the surface atoms accompanied by a few “floaters” and holes. At any time, a few of the surface atoms move out of the surface layer, leaving vacancies; these promoted particles wander diffusively, the holes also but less so, and occasionally exchange with atoms in the surface layer. This result is the basis for an analytic, statistical model. The caloric curves, particularly the latent heats, show that surface melting of clusters is a “phase change” different from the bulk melting of clusters.
Symmetry and High Magnetic Moment Clusters
Authors: Dunlap B. I. 
Published: March 2011

ABSTRACTHigh-spin 13-atom transition metal cluster are studied using the linear-combination-of-Gaussian-type-orbital, local-density-functional, all-electron method. The high degeneracy associated with high symmetry is exploited to find geometry optimized clusters that have the highest contribution by spin to the magnetic moment subject to a constraint. The constraint is that the cluster not distort by the Jahn-Teller mechanism and thus have the lowest possible orbital-angular-momentum component of the magnetic moment. Pure 13-atom nickel and iron clusters are approximately icosahedral because of increased symmetry-required orbital degeneracy for electrons of different spins in this largest point group. The central atom of the icosahedral iron cluster has been varied to optimize the spin of the cluster keeping the orbital contribution to the magnetic moment quenched. Varying the central atom under this constraint can alter the magnetic moment by 20%, relative to the pure iron cluster.
Molecular-Dynamics Simulations of Collisions of Buckminsterfullerene with Diamond Surfaces
Authors: Mowrey R.C. , Brenner D.W. , Dunlap B.I. , Mintmire J.W. , White C.T. 
Published: March 2011

ABSTRACTWe have performed molecular dynamics simulations using a recently developed empirical many-body potential energy function to study the collision of the C60 isomer buckmin-sterfullerene with a hydrogen-terminated diamond surface. The simulations indicate that the cluster can react with the surface and has a larger probability of gaining atoms from the surface than of losing atoms to the surface. We have investigated the dependence of the reaction probability on the initial center-of-mass translational velocity of the cluster. The structures and energy distributions of the product clusters have been determined. Both inelastically and reactively scattered clusters have large amounts of internal energy which suggests that gas-phase dissociation is likely.
Production of Ultra-Thin Metal Films Using Neutral Cluster Beams
Authors: Ramachandra A. , Vaziri M. , Andres R.P. 
Published: March 2011

ABSTRACTGold clusters (diam. = 1.0 ± .5 nm) are prepared in a gas aggregation source (MECS), expanded into a vacuum chamber to form a neutral cluster beam, and deposited at low impact velocity on room temperature substrates. When several monolayers of these clusters are deposited on clean substrates (nitrocellulose, glass, mica, NaCl), they form smooth ultra-thin films. These cluster-assembled films appear to be similar in quality to those produced by the Takagi-Yamada ion cluster beam process. They exhibit finite electrical conductivity at thicknesses much smaller than is the case with atomically evaporated films. They are extremely uniform and smooth with a surface height that typically varies less than 1 nm across the entire film.
In Situ Ellipsometry of Ge Clusters and Ultrathin Films
Authors: Yang B.-Y. , Gu T. , Yu R.Q. , Lannin J.S. , Collins R.W. 
Published: March 2011

ABSTRACTThe evolution of the nanostructure of a-Ge sputter-deposited onto naturally oxidized c-Si and disordered carbon substrates is characterized by in situ ellipsometry, with the focus of attention being on the initial stage when clusters are in evidence. The structural data deduced from ellipsometry are reproducible, are a sensitive function of the preparation parameters, and are also consistent with data deduced from less sensitive Auger electron spectroscopy. The information provided by ellipsometry is of critical importance in studying the effects of average size on the electronic and vibrational properties of clusters by ultraviolet photoelectron spectroscopy and Raman spectroscopy. Other structural probes of clusters for this system, including transmission electron microscopy, have failed to yield reliable results due to the small cluster size.