bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Dependence of Cluster-cluster Coalescence in Monodispersed Co Cluster Assemblies
Authors: Peng D. L. , Hihara T. , Sumiyama K. 
Published: April 2011

ABSTRACTUsing a plasma-gas-condensation-type cluster beam deposition system, we deposited monodispersed Co clusters with mean diameter d = 8.5 nm on quartz and microgrid substrates. The cluster-cluster coalescence process of the Co cluster assemblies was investigated by in situ electrical conductivity measurements and ex situ transmission electron microscopy (TEM). The change of magnetic properties induced by the inter-cluster coalescence was also discussed. The electrical conductivity measurement indicated that, at temperatures T < 100°C, the Co clusters in the assemblies maintain their original size as deposited at room temperature, while the inter-cluster coalescence takes place at T > 100°C. The TEM observation showed that the size distribution and the interface morphology of the clusters do not change markedly at substrate temperatures Ts ≤ 200°C, while cluster-cluster coalescence starts at Ts > 200°C. Above Ts = 300°C, the interfacial area of coalesced clusters is crystalline, having its own orientation different from those of two connected cluster cores.
Synthesis and Sintering Characteristics of TiC – Ni – Ti – (Al) Nanocomposites
Authors: Vohwinkel Kai , Koc Rasit 
Published: April 2011

The sintering behavior of submicron / nanosize TiC powders was investigated. The TiC powders (31 wt.% carbon) are synthesized from a carbon coated precursor and have excess carbon content. Ti, Ni and Al powders were added to have in-situ intermetallic binders for sintering. The composition TiC-5 wt.% Ti (pellet 1) shows pure TiC in the XRD analysis after sintering. The composition TiC-30 wt.% Ni3Al (pellet 3) shows the formation of the liquid phase Ni3Al. No liquid phase can be clearly identified in the XRD pattern of pellet 2 (TiC-30 wt.% Ni3Ti). However the SEM micrograph of pellet 2 shows similarity to the SEM image of pellet 3 concerning the formation of liquid phase.Pellets 1 and 2 show densifications of 100 % TD (theoretical density), whereas pellet 3 is only 90 % TD. Pellet 3 has the highest hardness (2511 HV) and fracture toughness (12.08 MPa m1/2).
Peculiarity of Properties and Some Applications of Ultra Dispersed (Nano-) Materials
Authors: Petrunin Vadim F. 
Published: April 2011

ABSTRACTThree arguments are considered as main for peculiarity of nano-sized materials properties. An unusual and unique combination of properties can be feasible in ultra dispersed (nano-) materials, for examples, high hardness and superplasticity. Some examples of ultra dispersed materials applications working out by Atomic Energy Industry program are following.
Diffusion and Ionic Conduction in Nanocrystalline Ceramics
Authors: Heitjans Paul , Indris Sylvio 
Published: April 2011

ABSTRACTDiffusion and ionic conduction in nanocrystalline ceramics, both monophase and composite, was studied by NMR relaxation and NMR lineshape as well as impedance spectroscopy. Measurements were mainly done on Li ion conductors prepared by high-energy ball milling. It was possible to discriminate between mobile ions in the interfacial regions and immobile ions in the grains. In general the diffusivity and conductivity are enhanced in the nanocrystalline monophase system as compared to the microcrystalline one, e. g. by about four orders of magnitude in the case of CaF2. An exception is, e. g., Li2O where the nano- and microcrystalline forms have similar conductivities. However, when the nanocrystalline insulator B2O3 is added to nanocrystalline Li2O the conductivity of the composite increases whereas it decreases in the corresponding microcrystalline system.
Nanocrystalline Zirconia Ceramics and Films Prepared by Chemical Vapor Synthesis and Deposition
Authors: Seydel Johannes , Winterer Markus , Hahn Horst 
Published: April 2011

ABSTRACTWe have prepared thin yttria-stabilized zirconia (YSZ) electrolyte layers by chemical vapor deposition (CVD) on a pre-sintered NiO&sol;YSZ fuel cell anode substrate. Structural analysis by scanning electron microscopy (SEM) and x-ray-diffraction shows a homogeneous, nanocrystalline layer.Conventional electrolyte films reach desired electrical properties only at elevated temperatures, typically 1000°C to 1100°C. The YSZ films grown by CVD on rough anode substrates show better growth behavior and less defects at the anode&sol;electrolyte interface than films deposited by conventional methods (screen printing, sol-gel). Results of electrical properties at lower SOFC working temperatures are obtained by impedance spectroscopy on pressed nanocrystalline YSZ powder pellets produced by chemical vapor synthesis (CVS).
Structure and Giant Magneto-Resistive Properties of Co and CoFe nano-particles in a Au matrix
Authors: Kooi B. J. , Vystavel T. , De Hosson J. Th. M. 
Published: April 2011

ABSTRACTThis paper focuses on the relation between the microstructure and the Giant Magneto-Resistive (GMR) properties of Au80Co20 and Au80Co10Fe10 granular alloys. After annealing of quenched samples large differences in structure of Co and CoFe nano-particles arise: e.g. fcc Co versus bcc CoFe, spinodal decomposition of Co versus nucleation and growth of FeCo, truncated octahedrons for Co and plates for CoFe. Particularly the shape of the precipitates and the state of coherency at the interface between magnetic particle and non-magnetic matrix turned out to have important influences on the GMR behavior.
Substrate Based “Bricks-and-Mortar” Self-Assembly of Spherical Nanoparticle Aggregates
Authors: Boal Andrew K. , Ilhan Faysal , Rotello Vincent M. 
Published: April 2011

ABSTRACTTransmission Electron Microscope (TEM) sample girds were coated with recognition element functionalized polymer 2 and exposed to solutions of a Mixed Monolayer Protected Gold Cluster (MMPC) functionalized with a complimentarily recognition element. Interactions between the polymer and MMPC bound recognition elements provide a driving force for the formation of nanoparticle aggregates. Characterization of the resulting structures by TEM revealed that anisotropic growth of structures in the sub-micrometer size regime rapidly occurred. This process was shown to be the result of the specific hydrogen-bonding interactions between the two components. Casting films of polymer 2 from solutions of decreasing concentration achieved control over the process. This lead to the increased formation of regular, circular structuresand a decrease in random nanoparticle adsorption by the film. Analysis of the size of the circular structures revealed that a maximum diameter of approximately 1150 nm was achieved after 30 minutes exposure to MMPC 1 solutions. This size was independent of the concentration of polymer 2 solutions used to cast films.
Ab-initio modelling of atomic and molecular Hydrogen adsorption in graphite
Authors: Letardi Sara , Celino Massimo , Cleri Fabrizio , Rosato Vittorio , Volpe Manuela 
Published: April 2011

ABSTRACTAb-initio electronic structure calculations have been used to evaluate the binding energy of atomic and molecular hydrogen to graphite lattice defects. Results show that graphite defects (Stone- Wales, vacancy) are preferred binding sites with respect to regular lattice sites. We find that molecular hydrogen is physisorbed between the graphite planes, but cannot diffuse across a graphitic plane.
Impact Ionization and Auger Recombination in Semiconductors: Implementation Within the Flapw Code
Authors: Picozzi S. , Continenza A. , Asahi R. , Mannstadt W. , Geller C. B. , Freeman A. J. 
Published: April 2011

ABSTRACTWe present a method to calculate impact ionization and Auger recombination rates within density functional theory and a screened-exchange approach and implement it in the all- electron FLAPW method. We investigate the dependence of the overlap matrix elements as a function of the states involved along the main symmetry lines of the Brillouin zone. Our results for the final impact ionization rates along the main symmetry lines of the Brillouin zone. Our results for the final impact ionization rates along τ — X and τ —L directions for GaAs show a strong anisotropy imposed by energy and momentum conservation and related to the use of a realistic and accurate sX-LDA band structure.
Material Parameters for Analytical and Numerical Modeling of Si and Strained SiGe Heterostructure Devices
Authors: Jain S. C. , Mehra A. , Decoutere S. , Schoenmaker W. , Willander M. 
Published: April 2011

ABSTRACTWe present calculated values of effective masses, bandgap reduction, and Fermi energy of p-doped Si and strained p-doped SiGe layers. The calculations have been made for Ge concentrations in the range 0 to 30% and boron concentration in the range 1018 cm−3 to 3×1020 cm−3. Empirical expressions for the effective masses are given. These expressions and calculated values of the other parameters are convenient for use in computer codes for modeling device processing and performance. To validate the calculated values, we have compared them with the available experimental results. Good agreement between the calculated and the experimental values is found.
Modeling of Chlorine Related Defects and Complexes in ZnMgSe
Authors: Yang Yaxiang , Muratov Leonid , Cooper Bernard R. , Myers Thomas H. , Wills John M. 
Published: April 2011

ABSTRACTWe have used the ab-initio full potential LMTO method to model native defects and chlorine-impurity-related defects in ZnSe and ZnxMg1−xSe. Our results show that there is a strong tendency for formation of a defect complex between a chlorine impurity at the Se site and a vacancy at the neighboring Zn site. The formation energies of this complex and other chlorine related defects decrease in the presence of magnesium. However, the maximum achievable electron concentration in the presence of magnesium is lower because of the increase in the band gap.
Investigation of the Electron Energy Spectrum in a Three Dimensional Regimented Tetragonal Quantum Dot Superlattice
Authors: Lazarenkova Olga L. , Balandin Alexander A. 
Published: April 2011

ABSTRACTWe analyze the electron energy spectrum in three-dimensional regimented arrays of semiconductor quantum dots. The coupling among quantum dots results in formation of three- dimensional electron mini-bands. Changing the size of quantum dots, inter-dot distance, barrier height and regimentation, one can control the electronic band structure of this quantum dot superlattice, which can also be referred to as quantum dot crystal due to its structure and energy spectrum that resemble those of a real crystal. Results of computer simulations carried out for a tetragonal InAs/GaAs quantum dot superlattice show that the electron density of states, effective mass tensor and other properties are different from those of bulk and conventional quantum well superlattices.
Dual Scale Simulation of Grain Growth Using a Multi Phase Field Model
Authors: Steinbach Ingo , Apel Markus 
Published: April 2011

ABSTRACTThe kinetics of grain growth in multicrystalline materials is determined by the interplay of curvature driven grain boundary motion and interfacial stress balance at the vertices of the grain boundaries. A comprehensive way to treat both effects in one model is given by the time dependent Ginzburg Landau model or phase field model. The paper presents the application of a multi phase field model, recently developed for solidification processes to grain growth of a multicrystalline structure. The specific feature of this multi phase field model is its ability to treat each grain boundary with its individual characteristics dependent on the type of the grain boundary, its orientation or the local pinning at precipitates. The pinning effect is simulated on the nanometer scale resolving the interaction of an individual precipitate with a curved grain boundary. From these simulations an effective pinning force is deduced and a model of driving force dependent grain boundary mobility is formulated accounting for the pinning effect on the mesoscopic scale of the grain growth simulation. 2-D grain growth simulations are presented.
Particle Dynamic Simulation of Semi-Solid Metal Rheology
Authors: Mullis Andrew M. 
Published: April 2011

ABSTRACTModels of semi-solid processing currently utilise constitutive equations to describe slurry rheology. However, using the techniques of molecular dynamics it may be possible to go beyond this approach to obtain direct relationships between applied shear rates, the resultant microstructural changes and rheology.The results of a simple molecular dynamics simulation of semi-solid flow within a Couette rheometer are presented and compared with experimental data for the system Sn -15% Pb. We find that the model correctly predicts the apparent viscosity under steady state conditions, up to solid fractions of ≈ 40%.
Self-interstitial Diffusion in α-Zirconium
Authors: Zhu W.J. , Woo C.H. 
Published: April 2011

ABSTRACTSelf-interstitial Diffusion in α-Zirconium-Zr is studied using Molecular Dynamic (MD) and molecular static (MS) simulation using Ackland's many-body inter-atomic potential. The basal crowdion configuration is found to be the ground state. The diffusion process in Zr is complex. Four types of diffusion jumps can be identified, two in-plane and two out-of plane. The in-plane migration mechanism is dominated by one-dimensional crowdion motion along the [1120] directions, interrupted by occasional out-of-plane and on-line or off-line jumps. The mean lifetime before rotation of the crowdion is reported as a function of temperature. The activation energies for the diffusion processes are obtained. The diffusional anisotropy factor Dc/Da is also obtained, and compares well with experiment results.
Dislocation Nucleation and Propagation During Deposition of Cubic Metal Thin Films
Authors: Liu W. C. , Wang Y. X. , Woo C. H. , Huang Hanchen 
Published: April 2011

ABSTRACTIn this paper we present three-dimensional molecular dynamics simulations of dislocation nucleation and propagation during thin film deposition. Aiming to identify mechanisms of dislocation nucleation in polycrystalline thin films, we choose the film material to be the same as the substrate – which is stressed. Tungsten and aluminum are taken as representatives of BCC and FCC metals, respectively, in the molecular dynamics simulations. Our studies show that both glissile and sessile dislocations are nucleated during the deposition, and surface steps are preferential nucleation sites of dislocations. Further, the results indicate that dislocations nucleated on slip systems with large Schmid factors more likely survive and propagate into the film. When a glissile dislocation is nucleated, it propagates much faster horizontally than vertically into the film. The mechanisms and criteria of dislocation nucleation are essential to the implementation of the atomistic simulator ADEPT.
Characterization of the Activation-Relaxation Technique: Recent Results on Models of Amorphous Silicon
Authors: Malek Rachid , Mousseau Normand , Barkema G. T. 
Published: April 2011

ABSTRACTThe activation-relaxation technique (ART) is a method for finding saddle points in high-dimen- sional energy landscapes. ART has already been applied to a wide range of materials including amorphous semiconductors, Lennard-Jones glasses, and proteins. In spite of its successes, a number of fundamental questions remain to be answered regarding the biases associated with its sampling of the saddle points. We present here results of a detailed analysis of the biases in the simulation of amorphous silicon. We focus in particular on the biases of the method in sampling saddle points, the completeness of the sampling and the sensitivity of these quantities to variations of the different parameters.
A Synchrotron X-Ray Study of Texture Induced by Application of Magnetic Fields During Phase-Transformations in Shape-Memory Ni-Mn-Ga
Authors: Vaidyanathan R. , Yilmaz S. , O'Handley R.C. , Dunand D.C. 
Published: April 2011

AbstractNi-Mn-Ga alloys can exhibit a thermoelastic phase transformation near room temperature, which is associated with the shape-memory effect (i.e., temperature-induced strain recovery after twinning) or superelasticity (i.e., strain recovery after a stress-induced phase transformation). This work uses a synchrotron X-ray transmission technique to investigate texture induced by applying magnetic fields during the phase transformation in polycrystalline Ni2MnGa. Synchrotron X-ray radiation is ideally suited for such investigations since the measurements are representative of twinning in the bulk, in contrast with measurements from conventional X-ray sources that represent surface measurements affected by surface relaxation. Magnetic texturing of polycrystalline Ni2MnGa, by cooling through the phase-transformation in the presence of a magnetic field, has potential to lead to polycrystalline materials with more compatible field- induced strains and hence increased twin boundary mobility upon application of a magnetic and/or stress field.
The use of a variety of synchrotron techniques in the study of cementitious materials
Authors: Barnes P. , Colston S.L. , Jupe A.C. , Jacques S.D.M. , Attfield M. , Bailey S. P. , Pisula R. , Hall C. , Livesey P. 
Published: April 2011

The electron synchrotron ’revolution’ is barely twenty years old yet its impact on materials science is immeasurable. Fig.1 captures the essence of synchrotron radiation with the dipole magnet, which is associated with a highly collimated fan of radiation due to the centripetal acceleration of electron bunches responding to the inwardly acting Lorentz force; however dipole magnets often play a secondary role in current “third generation” synchrotrons which also utilize more advanced magnet configurations (wigglers and undulators) that are capable of producing even more brilliant sources of X-radiation. The five main attributes of synchrotron X-ray beams are:• The X-ray beam is intense, such that up to 1012 photons per second might be incident on a sample, thus enabling measurements with excellent counting statistics and/or short collection times.• The radiation is horizontally polarized in the plane of the electron orbit.• The X-ray beam is highly collimated, with a typical working divergence of ∼mrads, such that there is less wastage during its passage through the optical components and a superior angular resolution in the eventual measurement.• The radiation has a smooth continuous 'white' spectrum extending into the hard (penetrating) X-ray region, thus offering the choice of conducting experiments with white radiation or alternatively enabling a free choice of wavelength by use of a monochromator.• Since the electrons move in bunches the synchrotron X-ray source is actually pulsed, at a frequencies in the region of 3×108 s−1.
Study of TaSi2-Si Crystals with High Energy Synchrotron Radiation as Tunable Wide-bandpass Monochromator and Analyzer Optics
Authors: Rütt U. , Stock S.R. , Rek Z.U. 
Published: April 2011

AbstractSingle crystals of the in situ composite TaSi2-Si are candidates for wide bandpass monochromators and analyzers for x-ray experiments. Two large crystals (32 × 39 × 7 mm3 and 32 x 39 x 30 mm3) were studied in detail using 115 keV synchrotron radiation at the BESSRC beamline at the APS. For transmission geometry, the Si(111) reflection and 39 mm crystal thickness, rocking curve widths of 95 arc sec with reflectivities of 50% were measured over the entire crystal. Turning the crystal to an angle of 45° to the incident beam and translating it through the beam allowed investigation of the influence of crystal thickness on diffracted intensity. For sample thicknesses ranging between 5 mm and 12.5 mm, the full width at half maximum (FWHM) of the rocking curve increased linearly from 29 arc sec to 53 arc sec. The greatest gain in integrated intensity was obtained for 8-9 mm thickness where FWHM = 40 arc sec. If this crystal were used as a monochromator for synchrotron radiation, it would provide 40 times more intensity than a perfect silicon crystal and an energy bandwidth of 1 keV at 115 keV photon energy. With the increase of the rocking curve FWHM, a plateau across the peak maximum developed; its width increased from 5 arc sec to 25 arc sec when the crystal thickness increased from 5 mm to 12.5 mm, respectively. This plateau allows these crystals to be used as analyzer crystals in diffraction experiments, i.e., as very narrow slits to suppress background. A plateau width of about 5-20 arc sec for the analyzer crystal is needed to insure that the entire intensity scattered from a sample is delivered to the detector. The simple expedient of changing the crystal thickness alters the plateau width of the analyzer crystal and tunes its acceptance to the needs of the sample under study.
X-Ray Reflectivity and GISAXS Study of Derelaxation in Kr Implanted Si
Authors: Duč P. , Pivac B. , Milat O. , Bernstorff S. , Zulim I 
Published: April 2011

AbstractThe structural changes induced in single crystal silicon implanted with Krypton above the amorphisation threshold were studied by X-ray reflectivity together with Grazing Incidence Small Angle X-ray Scattering technique. Silicon samples were implanted with Krypton with two different ion energies. A well-defined layer, 220 nm thick of amorphous silicon, rich in Krypton, was formed below the top, undisturbed layer. A series of samples consist of as-implanted, relaxed, and a number of samples with increased level of defects induced by additional Kr implantation. Additional implantation caused changes in the films composition and thickness, which was well evidenced in reflectivity curve, while only minor changes of surface roughness and critical angle were detected in GISAXS spectra.
In Situ X-ray Absorption Spectroscopy in the Soft Energy Range: Novel Prospects for the Chemical Characterization of Solid State Surfaces at High Pressure And High Temperature
Authors: Schedel-Niedrig Th. , Hävecker M. , Knop-Gericke A. , Reinke P. , Schlögl R. , Lux-Steiner M. Ch. 
Published: April 2011

AbstractAn instrument equipped with total electron yield detectors was designed and constructed for in situ X-ray absorption spectroscopy (XAS) investigations in the soft X-ray range (100 eV ≤ hν ≤ 1000 eV) at elevated pressures (mbar range) and sample temperatures (T ≤ 1000 K) [1]. This allows, for the first time, XAS studies in a surface-sensitive mode of the light elements (Z = 3-15). Furthermore, the gas phase XAS and the surface-related XAS of the solid state phase can be collected simultaneously in order to correlate the gas/solid reaction rate with the surface electronic structure under working conditions in a flow-through mode.The novel experimental tool represents a contribution to the experimental overcoming of the “pressure gap” in material science. In this work examples are presented belonging to the field of heterogeneous catalysis [2-4] and to the reactivity of diamond surfaces [5]. Additionally, prospects for in situ studies in material science will be given.