bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short-Range-Ordering and Fe-Clustering in Au-Fe Alloys
Authors: Chou Chen-Chia , Chen F.-R. , Wayman C. M. 
Published: March 2011

AbstractAs an “archtypal” spin-glass system, the local atomic arrangement in Au-Fe alloys is still a controversial subject. In the present experiment, Au-Fe alloys with Fe content from 10.7 to 33% were studied as to microstructure evolution, through various transmission electron microscopic techniques. Information derived from aging experiments using real and reciprocal spaces appears to suggest the coexistence of short-range-order and Fe-clusters. At early stages of aging, lobe-like and/or rod-shaped strain contrast images, identified as clusters, were revealed after specimens were further cleaned by an ion-miller. The (1 1/2 0) special point diffuse reflections were prominent in the as-quenched condition and/or early stage aging, and the intensifies decrease gradually as aging proceeds. After a certain period, (1 1/2 0) diffuse reflections disappear but strain contrast images still remain similar. This suggests that the strain contrast images are not related to the (1 1/2 0) diffuse reflections. High resolution electron microscopy was also employed. The results are consistent with the arguments derived from aging experiments.
Small Angle Neutron Scattering Investigation of Paraffin Solid Solutions Undergoing Microphase Separation
Authors: Epperson J. E. , White J. W. , Wozniakt D. G. 
Published: March 2011

AbstractWe show that small angle neutron scattering can sensitively detect microphase separation in solid solutions of the C30H62:C36D74 mixed paraffins. By ramping the sample temperature at a constant rate of about 0.5°C per minute, information complementary to that from differential heat capacity measurements is obtained from the total small angle scattering signal and its first temperature derivative. Because neutron wavelengths in the range from 0.8 < λ (Å) < 14.0 are used, scattering functions over an extended range (0.005 < q (Å−1) < 0.35) are obtained at the Argonne pulsed neutron source in a single experiment. This is important inasmuch as there is significant scattering in the lowest q region accessible due to the presence of cracks and/or voids, in addition to that from the microphase separation. The specific interfacial area as a function of temperature is reported from time slicing experiments on the pure C36D74 compound. Weak superlattice reflections are identifiable in the scattering profiles of the mixed paraffins due to the microphase separation.
Time-Resolved Small-Angle X-ray Scattering Study of Reversion Kinetics of δ′ Precipitates in an Al - 12AT.% Li Alloy Utilizing Synchrotron Radiation
Authors: Chen Haydn , Yu M.S. , Okuda H. , Tanaka M. , Osamura K. 
Published: March 2011

AbstractStructure change during the reversion process in an Al−12at.%Li alloy above the metastable δ′ solvus was investigated using a time-resolved small-angle x-ray scattering technique with synchrotron radiation. Results showed that the reversion process started after a short incubation time and that the growth of the stable δ phase began before completion of the δ′ dissolution. The radius of gyration of the second phase particles showed little change in the initial stage of reversion, then increased with time, suggesting the presence of diffuse interfaces between the dissolving δ′ particles and the matrix. It is suggested that the undissolved δ′ particles serve as the nuclei of the more stable δ precipitates, which continue to grow with their radii of gyration showing a parabolic power law in the early stage of growth followed by the familiar coarsening kinetics.
Crystallization Behavior of Sputter Deposited Amorphous NixZr100-x, Films
Authors: Winters Gillian E. , Unruh K.M. , Swann C.P. 
Published: March 2011

AbstractSputter deposited films of amorphous NixZr100-x, have been prepared over a wide and continuous range of compositions between x=20 and x=90 atomic percent Ni on liquid nitrogen cooled and room temperature substrates. These films have been characterized by xray and electron diffraction, transmission electron microscopy, and Rutherford backscattering spectrometry. The crystallization behavior of these films has been systematically studied by differential scanning calorimetry and compared with earlier measurements on amorphous liquid quenched alloys. Systematic differences were found between the thermal stability of amorphous alloys of the same nominal composition prepared at different substrate temperatures. Larger differences exist between vapor deposited amorphous films and liquid quenched ribbons.
Kinetics of NiSi Formation by Solid State Diffusion in Pt/NiCr/Si Via Growth of an Amorphous Cr-Rich Barrier Layer
Authors: Patnaik B.K. , Lee Ju Hyeon , Adams D. , Rozgonyi G.A. , Parikh N.R. , Swanson M.L. , Salih A.S.M. , Balducci P. 
Published: March 2011

AbstractWe have used Rutherford backscattering spectroscopy (RBS) to study the kinetics of NiSi growth during low temperature annealing of a Ni(Cr) layer on Si. During the silicide growth, a Cr-rich amorphous layer was formed between the silicide and the Ni(Cr) layers. This amorphous layer produces a slow and uniform silicide growth rate; the NiSi thickness was 60 nm after a 2h anneal at 475°C. After prolonged annealing, the amorphous layer recrystallized, causing very rapid silicide growth. When a thin (0.5 nm) layer of Pt was deposited between the Si and Ni(Cr) layers, the amorphous layer was thinner, the silicide growth rate was correspondingly greater and the rapid growth stage occurred earlier. The RBS data agreed qualitatively with transmission electron microscopy results for the growth of both the amorphous layer and the silicide.
Crystal Face Dependent Melting of a Polycrystalline Iron Surface During 30 PS Laser Pulses
Authors: Vaterlaus A. , Guarisco D. , Meier F. 
Published: March 2011

AbstractThe melting of a polycrystalline iron surface with short laser pulses induces a surface structure with an orientation and a morphology depending on the crystal face of the surface. Different crystal planes irradiated with the same laser pulses show different degrees of disorder. This points to a crystal face dependent surface melting temperature.
Kinetics of Relaxation at the Liquid-Glass Transition
Authors: Lewis Laurent J. 
Published: March 2011

AbstractWe use molecular-dynamics simulations to investigate relaxation processes near the liquid-glass transition for a realistic model of the metal-metalloid system Ni80P20. We find that relaxation proceeds in two stages, excluding phonons: fast (or conformational) relaxation, related to local rearrangements of atoms, and slow relaxation, connected with atomic transport, i.e. diffusion. These processes are usually referred to as β and α, respectively. Our simulations show that diffusion exists even in the glass state, where it proceeds mostly by jumps, in contrast to the liquid phase where it is continuous. This relaxation mechanism is well described by a stretched exponential (Kohlrausch) law, in accord with recent modecoupling theories for supercooled liquids. The fast relaxation regime, on the other hand, does not appear to be well described by the theory.
The Time Lag in Transient Nucleation
Authors: Wu David T. 
Published: March 2011

AbstractThe time lag in transient nucleation was originally introduced to characterize the temporal evolution of the nucleation current in the simplest possible way. Previous attempts to calculate the time lag have relied mainly on either the approximate solution of the continuous Fokker-Planck equation or the numerical solution of the discrete rate equations. It is shown that the exact time lag can be calculated using a different method which requires knowledge only of the initial and the steady-state cluster populations.
Energy Barrier for ‘Magic-Strain’ Transformations in Crystals with Fcc Lattices
Authors: Boyer L.L. , Kaxiras E. , Mehl M.J. 
Published: March 2011

AbstractEnergy barriers for ‘magic’ strains, large pure shear strains which transform a lattice into itself, are computed for aluminum and iridium, using the linearized-augmented-plane-wave method, and for silicon, using the plane wave pseudopotential approach. The barrier energies are found to be of the order of the thermal energy available at the melting temperature. Volume changes associated with the barriers are consistent with the fact that the metals decrease in density while silicon increases in density upon melting.
Anomalous Solid Phase Epitaxy Near the Compensation Point in Amorphous Silicon with Boron and Phosphorus Impurity Profiles
Authors: Jeon Young-Jin , Becker M. F. , Walserd R. M. 
Published: March 2011

AbstractWe made high precision cw laser interferometric measurements of the variations of the rate of solid phase epitaxial regrowth (SPER) of amorphous layers on (100) silicon implanted with both boron and phosphorus. Depth profiles of SPER were correlated with the implanted boron and phosphorus distributions measured by secondary ion mass spectroscopy (SIMS). The results showed that: (1) the minimum (SPER) rate did not occur at the depth where the implanted impurity concentrations were equal; (2) the maximum activation energy for SPER (∼2.9 eV; ≈0.18 eV greater than for SPER in intrinsic Si) occurred at the depth where the regrowth rate was a minimum; (3) the regrowth rates in the dual implanted sample were different from those of the samples doped only with phosphorus at the same net phosphorusc concentration; and (4) the rate at the depth where the impurity concentrations were equal was different from the intrinsic rate. Further interpretation of the results suggests that the SPER rate in the dual implanted samples is equal to the value for intrinsic silicon at a depth where the net ionized impurity concentration is compensated. The SPER rate was a minimum at a depth where the net ionized impurity concentration was slightly p type.
Amorphous-to-Crystalline Transformation and Metal Induced Crystallization Phenomena in a-Si:F and a-Si:D:H Thin Films
Authors: Edelman F. , Cytermann C. , Brener R. , Eizenberg M. , Weil R. , Beyer W. 
Published: March 2011

AbstractThe structural stability of silicon in the amorphous state has been studied by TE1 on in-situ heat treated non-supported layers of a-Si:F, a-Si:D:H and double-layers of a-Si:F/Pd and a-Si:D:H/Pd structures. The a-Si:F and a-Si:D:H films, 500-800A thick, were evaporated by plasma decomposition of a(SiH4+D2)-mixture and SiF2, at 200-260°C onto cleaved rock salt. Pd film was deposited on a-Si by electron beam evaporation at room temperature. The amorphous-to-crystalline transition for the a-Si was quantitatively described by the delay time, t0, before the onset of crystallization. This parameter was found to decrease exponentially with the temperature. Influence of the Pd on t0 (metal induced crystallization) is discussed. This is the first report on the influence of F on the metal/a-Si system. It is also the first time a direct method is used to determine the temperature dependence of the fundamental parameter-delay time preceding a-Si crystallization.
Changing Segregation Coefficients During Ion Beam Induced Epitaxy of Amorphous Si
Authors: Custer J. S. , Thompson Michael O. , Jacobson D. C. , Poate J. M. 
Published: March 2011

AbstractIon beam induced epitaxial crystallization of Au and Ag doped amorphous Si results in segregation and trapping of the impurity. Combining the measured interface velocity and impurity profiles in segregation simulations provides a measure of the segregation coefficient k during growth. To adequately match the experimental profiles, k must increase during the early stage of growth until saturating at a temperature dependent value. This segregation process cannot be explained within standard models where k depends on the inteface velocity (kinetic trapping) or the interface impurity concentration (thermodynamic solubility). Instead the data suggests that the number of trapping sites at the interface increases during the initial stages of ion beam induced growth. We present several possible mechanisms for this trapping increase and discuss their significance in ion beam and thermal epitaxy models.
Picosecond Time-Resolved Amorphization Velocities in Silicon
Authors: Macdonald C.A. , Homan B.E. 
Published: March 2011

AbstractTransient time-resolved picosecond reflectivity measurements were performed on silicon melted by a 40 ps ultraviolet (308 nm) beam. These were compared to simulations of reflectivity versus amorphous and liquid layer depth and of amorphous interface velocity for various models including transition state theory and density limited growth, both with and without thermal activation.
Size Dependent Reactions of Boron and Carbon Cluster Ions
Authors: Hintz Paul A. , Ruatta Stephen A , Sowa Marianne B. , Anderson Scott L. 
Published: March 2011

ABSTRACTThe results of boron cluster ion reactions with SiH4 and N2O are presented. For N2O reactions, significant size effects were observed in the branching between the BnO+ and BnN+ product channels. Carbon cluster ion reactions with D2 reveal the effect of structural isomers on cluster reactivity.
Arrested Solid-Solid Phase Transition in Semiconductor Nanocrystals
Authors: Haase M. , Alivisatos A. P. 
Published: March 2011

ABSTRACTCdS crystallites of 40 and 45 Å average diameter have been studied under hydrostatic high pressure by optical absorption. The optical absorption onset is observed to shift to higher energy with pressure according toThis is exactly the same shift with pressure as is observed in the bulk. The solid-solid phase transition from the zincblende to the NaCl phase is observed as an abrupt change in the intensity, intercept, and functional form of the absorption onset. The phase transition, which occurs at 27Kbar in bulk CdS, is shifted to 85 Kbar in nanocrystals stabilized with polyphosphate, and to 60 Kbar in nanocrystals surface derivatized with EDTA. It thus appears possible to control the relative stability of the crystalline phases of a nanocrystal by chemical manipulation of the surface.
An Assessment of Electronic Exchange in Phosphomolybdates
Authors: Singh David J. , Jansen Susan A. , Mazurek Harry , Crocco Guy 
Published: March 2011

ABSTRACTIn the synthesis of polyacrylates, a necessary step involves the conversion of acroleins to acrylic acids- a process catalysed by Mo oxides. We have directed our work towards the elucidation of the electronic structure of the most stable structure of 12-heteromolybdate, ie. the α-keggin unit, using EPR spectroscopy, Cyclic Voltammetry, and molecular orbital calculations based on the extended Huckel theory. Metal ion substitution has been shown to have negligible effect on the electronic structure of the keggin unit thus rationalising previous arguments of structural rigidity. Electronic exchange has been shown to be facilitated through metal-metal interaction.
Effect of Borohydride Addition Rate on Chemically Prepared Amorphous Fe–B Particles
Authors: Koch C. Bender , Mørup S. , Linderoth S. 
Published: March 2011

ABSTRACTAmorphous Fe-B alloys can be prepared by reacting aqueous solutions of Fe salts and NaBH4. In this work the effect of the addition rate of the NaBH4 solution to the FeSO4 solution on the precipitate is investigated. The chemical composition of the amorphous alloys formed varies between Fe79B21 and Fe68B32. The hyperfine parameters of the alloys, derived from Mössbauer spectra, show a decrease from 29 to 25 T of the magnetic hyperfine field and an increase from 0.19 to 0.28 mms−1 of the isomer shift with increasing NaBH4 addition rate. The results suggest that alloys with different structures but identical composition may be produced by chemical reduction.
Soft-Landings, Hard Rebounds, and Fracture of Alkali-Halide Nanocrystals
Authors: Beck Rainer D. , St. John Pamela , Homer Margie L. , Whetten Robert L. 
Published: March 2011

Abstract:Collision phenomena involving the smallest solid objects and inert solid surfaces have been explored by the method of mass-selective time-of-flight and angular measurements of the surface-collision dynamics of ionized cluster beams. At lowest energy, both transient physisorption (soft-landing) and intact scattering have been observed. Impact of nanocrystalline sodium-fluoride clusters (NanFn-1+) against graphite at intermediate energy (0.2 - 1 eV per atom) leads efficiently to fracture-like processes. At higher energy, a featureless evaporative cascade dominates the fragment distribution. Energy- and angle-resolved scattering of mass-selected clusters from oriented graphite is shown to be a versatile method for investigation of cluster structure-energetics, cluster-surface interactions, and sticking phenomena.
Fabrication of Supported Catalytic Nickel Clusters of Controlled Size and Distribution Using Ionized Cluster Beam Deposition
Authors: Yoo M. C. , Kim K. 
Published: March 2011

ABSTRACTA novel technique for fabricating uniform, ultrafine metal clusters of controlled size and distribution is described. The technique employs conventional adiabatic expansion of an evaporated source material for controlled formation of the clusters, but additionally incorporates electron-impact ionization and acceleration for further control of the size and distribution of the deposited particles. The key control parameters investigated are the diameter of the adiabatic nozzle, the proportion and energy of the ionized particles in the cluster beam, the substrate temperature, and the deposition time. The use of electron irradiation and acceleration of the source beam has proven to be particularly effective in producing monodisperse clusters. Using this new approach, uniform Ni clusters as small as 10 Å were deposited on an amorphous carbon substrate. The size and structure of the deposited Ni clusters were analyzed using high-resolution TEM and STEM.
Studies of the Chemical Properties of Size Selected Metal Clusters: Kinetics and Saturation
Authors: Cox Donald M. , Brickman Robert O. , Creegan Kathleen , Kaldor Andrew 
Published: March 2011

ABSTRACTOur studies of small (n=2−40) gas phase transition metal clusters (cations, neutrals and anions) have revealed a number of size-dependent chemical and physical properties. This paper will discuss results involving activated dissociative molecular chemisorption of hydrogen (deuterium) and small alkanes on cationic, neutral and anionic platinum and gold clusters. For example, we have yet to find any size gold cluster anion to exhibit measurable reactivity towards di-deuterium, but reactivity is observed on small (n<15) gold cations and very small (n<9) neutral gold clusters. Methane or ethane chemisorption occurs most readily only on small Pt and Au cluster cations and least rapidly, if at all, on cluster anions. The larger Pt and Au clusters are found to be non-reactive towards the alkanes under our experimental conditions.At the other extreme, at steady state, small clusters of Pt, Rh, Ni, Pd, V, Nb, and Ta are hydrogen “rich” exhibiting H/M stoichiometrics >> 1. These results are consistent with a limited data base on supported clsutes obtained via EXAFS measurements and have important implications for catalytic reactions involving hydrogen and light hydrocarbons.
Nanometer-Sized Microstructures
Authors: Gleiter H. 
Published: March 2011

ABSTRACTMaterials with nanometer-sized microstructures are solids that contain such a high density of defects (point defects, dislocations, grain boundaries, interphase boundaries etc.) that the volume fraction of the defect cores becomes comparable to the residual, defect free volume. Since 1970, the interest of materials scientists focused on solids with nanometer-sized microstructures when it was recognized that specifically tailored nanometer-sized microstructures permit the generation of materials with new atomic and/or electronics structures. In the area of semiconductors, quantum well structures and superlattices consisting of thin coherent layers with different dopings or compositions have been studied extensively. In these structures quantum size effects prevail because the coherent boundaries structures between the layers act as electron confinements. Research activities aiming towards the synthesis of new atomic (and electronic) structures in metals, ceramics and semiconductors by means of three-dimensional nanometer-sized micro-structure were initiated by the proposal, to generate solids a large volume fraction of which consists of the cores of defects such as incoherent grain and/or interphase boundaries, such solids differ structurally and property-wise from crystals and glasses with the same chemical composition because the atomic arrangements formed in the cores of incoherent grain or interphase boundaries deviate from crystalline or glassy structures. Recent studies of nanometer-sized materials by x-ray/neutron diffraction, EXAFS, different spectroscopies as well as property measurements support this idea. The properties of materials with nanometer-sized microstructures are discussed on the basis of the knowledge available from the numerous studies that have been carried out in the last two decades about the structure and properties of grain and/or interphase boundaries.
Raman Scattering and Photoemission from Bi Clusters
Authors: Mitch M. G. , Chase S. J. , Yu R. Q. , Fortner J. , Lannin J. S. 
Published: March 2011

ABSTRACTRaman scattering measurements of Bi clusters formed on disordered C films at 110K exhibit a phase transformation from nanocrystalline rhombohedral structure to a suggested disordered phase. XPS measurements on this phase indicate core level shifts attributed to intrinsic, initial state effects on cluster electronic states.
Modelling Early Stages in the Formation of Cluster-Assembled Materials
Authors: Schön Christian , Salamon Peter 
Published: March 2011

ABSTRACTThe formation of cluster-assembled materials using the sintering process is investigated. We present a model that describes the initial stages exactly using information derived from ab initio calculations of cluster behavior. Surface area, effective cross section and density of the cluster-assembled material, are calculated as functions of time for several implementations of the model.
Issues in the Processing of Bulk Nanocrystalline Ceramics for Structural Applications
Authors: Mayo M. J. , Çiftçioglu M. 
Published: March 2011

ABSTRACTTiO2 has been fabricated using a modified alkoxide hydrolysis route; the process yields about 50 g/day of nanocrystalline powder on a laboratory scale, which can be used to make large (1–10 g) samples. Pore size distributions show the powder is non-agglomerated, and TEM and BET analyses confirm the nanocrystalline size of the particles at about 20 nm. The powder is extremely reactive, sintering at about half the temperatures required of commercial powders. The chemically produced powder compacts to only 62% of the density that can be achieved by compacting a gas phase condensation (GPC)-produced TiO2. Nevertheless, the reactivity of this less dense compact is such that it reaches final densities comparable to that of the GPC TiO2. The difficulties in compacting and sintering large nanocrystalline samples are discussed. It is hoped that an understanding of these problems will lead to more intelligent densification of ultrafine powders so that full densification can be accomplished while retaining a nanocrystalline grain size.