bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Hydrogen Adsorption/Storage in Pure and Functionalized Single Wall Carbon Nanotubes
Authors: Wang Yubing , Iqbal Zafar 
Published: April 2011

AbstractSelf-assembled sheets of single wall carbon nanotubes (SWNTs) were used as the working electrode for electrochemical hydrogen adsorption/storage in a three-electrode cell in 6M aqueous KOH or HNO3 solution. Hydrogen adsorption studies on pristine SWNTs, as well as SWNTs functionalized with electrodeposited nanoparticles of magnesium (Mg) and cobalt (Co), have been performed. The adsorbed hydrogen (uncorrected for possible water uptake via nanocapillarity) was measured to be 2.5 weight percent by thermogravimetric analysis (TGA) on a Mg-functionalized sample and 3.2 weight percent by Prompt-Gamma Activation Analysis (PGAA) for a pristine sample charged for 20 hrs. Weight loss occurs in the 105° to 125°C temperature range for both sample types. Hydrogen in Co-functionalized SWNTs and 6M HNO3 electrolyte appears to be strongly chemisorbed as indicated by the appearance of a C-H stretching line in the Fourier-transform infrared spectrum (FTIR) and absence of a desorption peak in the TGA data in the 25° to 600°C temperature range. Thermopower measurements scale with the TGA data and suggest that hydrogen uptake is associated with partial charge transfer. Ex-situ Raman spectroscopy shows a reproducible downshift of the SWNT tangential stretching mode consistent with charge transfer or chemisorption on electrochemical charging, and a substantial decrease under some conditions in resonance-enhanced intensity with increasing charging time. A SWNT sheet electrochemically coated with the conducting polymer polyaniline and then charged in 6M KOH shows possible hydrogen uptake of 1.5 weight % that desorbs at 70°C.
TEM investigation of nucleation and initial growth of ZnSe nanowires
Authors: Cai Y. , Chan S. K. , Sou I. K. , Chan Y. F. , Su D. S. , Wang N. 
Published: April 2011

ABSTRACTSingle crystalline ZnSe nanowires were fabricated on GaAs substrates by molecular beam epitaxy technique via Au-catalyzed vapor-liquid-solid reaction. The nucleation and initial growth of the nanowires were investigated by high-resolution transmission electron microscopy. It was revealed that Au catalysts initially reacted with the substrate forming binary AuGa2 alloy droplets. The sizes of the catalysts determined the growth direction of ZnSe nanowires. A model based on the surface energies of the nanowire nuclei was proposed to explain the size dependence of growth direction for ZnSe nanowires.
Absolute measurement of three-dimensional polarization direction using scanning nonlinear dielectric Microscopy
Authors: Cho Yasuo , Sugihara Tomoyuki , Odagawa Hiroyuki 
Published: April 2011

ABSTRACTA technique for measuring the absolute value of the ferroelectric polarization angle using scanning nonlinear dielectric microscopy (SNDM) is proposed and demonstrated. Using the technique, periodically poled lithium niobate (PPLN) with three-dimensional domain structure is observed. The measured polarization angles agreed well with the actual polarization orientations, and allowed precise visualization of the microdomain structure in PPLN. Through this experiment, we confirmed that SNDM is a useful tool for the absolute evaluation of the three-dimensional polarization direction.
Tomographic Imaging of Nanocrystals by Aberration-Corrected Scanning Transmission Electron Microscopy
Authors: Benthem Klaus van , Peng Yiping , Pennycook Stephen J. 
Published: April 2011

ABSTRACTIn aberration corrected scanning transmission electron microscopy, the depth of focus is of the order of a few nanometers, so that the three-dimensional shape of nanocrystals could so far not be determined with atomic resolution. Here we show that with the assistance of image simulations it is possible to achieve atomic-scale information in the depth direction by analyzing a through-focal series where the number of atoms in most columns can be determined by Z-contrast simulations. The error in this analysis is about two atoms in the thickest regions, and less in thinner regions.
High-Resolution Interface Atomic Structure Analysis in Silicon Nitride Ceramics
Authors: Ziegler A. , Idrobo J. C. , Cinibulk M. K. , Kisielowski C. , Browning N. D. , Ritchie R. O. 
Published: April 2011

ABSTRACTIn this study we examine the immediate interface between matrix grains and the amorphous intergranular film in a Si3N4 ceramic doped with rare-earth oxides La2O3, Sm2O3, Er2O3, Yb2O3 and Lu2O3, extracting unique structural and atomic bonding information. In particular, we relate the structure of the interface to the ionic size and electronic structure of the rare-earth elements and the presence of oxygen in the intergranular film. We relate these results to the measured fracture toughness.
HREM imaging of screw dislocation core structures in bcc metals
Authors: Mendis B.G. , Mishin Y. , Hartley C.S. , Hemker K.J. 
Published: April 2011

ABSTRACTQuantitative High Resolution Electron Microscopy (HREM) is used to characterize the in-plane displacements of atoms around a screw dislocation core in bcc molybdenum. The in-plane displacements have an important effect on the bulk mechanical properties of bcc metals and alloys. However, the largest displacements are predicted to be less than 10 pm, requiring that the atom positions in an HREM image be determined to sub-pixel accuracy. In order to calculate the displacements the positions of the atom columns in the undistorted crystal must be determined precisely from the information available in the HREM image. An algorithm for such a task is briefly discussed and the technique applied to several HREM images. It is seen that the atomic displacements are predominantly due to surface relaxation (i.e. Eshelby twist) of a thin TEM foil, thereby masking the finer displacements of the dislocation core. Nye tensor plots, which map the resultant Burgers vector at each point of a distorted crystal, are also used to characterize the core structure. Although the large displacements from the Eshelby twist were completely removed, no signal from the dislocation core region was observed.
Towards 3D image-based nanocrystallography by means of transmission electron goniometry
Authors: Moeck Peter , Qin Wentao , Fraundorf Philip B. 
Published: April 2011

ABSTRACTIt is well known that the crystallographic phase and morphology of many materials changes with the crystal size in the tens of nanometer range and that many nanocrystals possess structural defects in excess of their equilibrium levels. A need to determine the ideal and real structure of individual nanoparticles, therefore, arises. High-resolution phase-contrast transmission electron microscopy (TEM) and atomic resolution Z-contrast scanning TEM (STEM) when combined with transmission electron goniometry offer the opportunity of develop dedicated methods for the crystallographic characterization of nanoparticles in three dimensions. This paper describes tilt strategies for taking data from individual nanocrystals “as found”, so as to provide information on their lattice structure and orientation, as well as on the structure and orientation of their surfaces and structural defects. Internet based java applets that facilitate the application of this technique for cubic crystals with calibrated tilt-rotation and double-tilt holders are mentioned briefly. The enhanced viability of image-based nanocrystallography in future aberration-corrected TEMs and STEMs is illustrated on a nanocrystal model system.
In situ HREM Study on the Thermal Stability of Atomic Layer Epitaxy Grown InAs/GaAs Quantum Dots
Authors: Kim H. S. , Suh J. H. , Park C. G. , Lee S. J. , Noh S. K. , Song J. D. , Park Y. J. , Choi W. J. , Lee J. I. 
Published: April 2011

ABSTRACTSelf-assembled InAs/GaAs quantum dots (QDs) were grown by the atomic layer epitaxy technique and the structure and the thermal stability of QDs have been studied by using high resolution electron microscopy with in-situ heating experiment capability. The QDs were found to form a hemispherical structure with {136} side facet in the early stage of growth. The average height and diameter of the QD were found to be ∼ 5.5 nm and ∼ 23 nm, respectively. Upon capping by GaAs layer, however, the apex structure of QD changed to a flat one. In-situ heating experiment within TEM revealed that the uncapped QD remained stable until 580°C. However, at temperature above 600°C, the QD structure became flat due to the fast decrease of QD height. After flattening, the atoms diffused from the InAs QD to the GaAs substrate, resulting in the total collapse. The density of the QD decreased abruptly by this collapse and most QDs disappeared at above 600°C.
In-Situ Electron Microscopy Studies of the Effect of Solute Segregation on Grain Boundary Anisotropy and Mobility in an Al-Zr Alloy
Authors: Taheri Mitra L. , Stach Eric , Radmilovic Velimir , Weiland Hasso , Rollett Anthony D. 
Published: April 2011

ABSTRACTThe presence of impurities in aluminum alloys is of great interest with respect to microstructural properties, specifically, the effect of solute on texture and anisotropy. This paper presents new evidence of the pronounced effect of solute drag based on in-situ annealing and Electron Backscatter Diffraction experiments of Zr-rich Al alloys subject to prior strain. A compensation effect was found for grain boundary mobility maxima for specific boundary types. Trends in activation energy as a function of boundary type support the observations of a compensation effect with respect to temperature. Evidence for irregular motion of boundaries from in-situ observations is discussed in reference to new theoretical results that suggest that boundaries migrating in the presence of solutes should move sporadically provided that the length scale at which observations are made is small enough. A study of both boundary motion and solute segregation to specific boundary types using Scanning Transmission Electron Microscopy and in-situ TEM is presented.
Structure and Dynamics of NaxCoO2 and the Hydrated Superconductor
Authors: Lynn J. W. , Huang Q. , Cava R. J. , Lee Y. S. 
Published: April 2011

ABSTRACTThe properties of the NaxCoO2 class of materials are of interest from a number of viewpoints. These compounds are based on a triangular lattice of spin-½ ions—prototype RVB system— where a high thermoelectric-power Curie-Weiss metallic paramagnet is found for Na0.7CoO2, a charge ordered insulator at x=0.5, and a paramagnetic metal where superconductivity is induced in Na0.3CoO2 when it is intercalated with water. Here we briefly review our neutron diffraction and inelastic scattering measurements characterizing the crystal structure and lattice dynamics, and relate these to the observed physical properties. The basic structure of NaxCoO2 is hexagonal and consists of robust layers of CoO2 interspersed by Na layers with two inequivalent sites. Two special cases are x=1 where one of these sites is fully occupied and the other empty, and x=½ where both sites have equal occupancies of ¼ and the system is a charge ordered insulator. For general × the site occupancies are inequivalent and vary systematically with x. In the regime of x=0.75 we find a first-order transition from a high symmetry Na site at low T to a three-fold split site (with lower symmetry) at high T. This transition is first order and varies with x. For the Na0.3CoO2. 1.4(H/D)2O superconductor, the water forms two additional layers between the Na and CoO2, increasing the c -axis lattice parameter of the hexagonal P 63/mmc space group from 11.16 Å to 19.5 Å. The Na ions are found to occupy a different configuration from the parent compound, while the water forms a structure that replicates the structure of ice to a good approximation. We find a strong inverse correlation between the CoO2 layer thickness and the superconducting transition temperature (TC increases with decreasing thickness). The phonon density-of-states for Na0.3CoO2 exhibits distinct acoustic and optic bands, with a high-energy cutoff of ∼100 meV. The lattice dynamical scattering for the superconductor is dominated by the hydrogen modes, with librational and bending modes that are quite similar to ice, supporting the structural model that the water intercalates and forms ice-like layers in the superconductor.
Structures of Optical Recording Materials Ge2Sb2+xTe5Studied by Pulsed Neutron Diffraction
Authors: Shamoto Shin-ichi , Taguchi Tomitsugu , Matsunaga Toshiyuki , Yamada Noboru , Ishii Kenji , Inami Toshiya 
Published: April 2011

ABSTRACTMetastable cubic Ge2Sb2+xTe5compounds, which can be prepared only as thin films, have been studied by both of neutron and x-ray powder diffraction measurements. Large displacement of germanium atoms in a crystalline cubic Ge2Sb2Te5phase is found by PDF analysis. By adding Sb, the crystalline cubic phases coexist with two types of amorphous phases, depending on the quenching temperature. One has a first sharp diffraction peak similar to the amorphous Sb atQ∼1.1 Å−1. Another has a new peak atQ∼0.74 Å−1. Based on our crystal structure analyses, the composition of the new amorphous phase was estimated to be about Ge7Sb8Te10. The composition of the crystalline solid was also found to be different from the matrix, resulting in the nucleation dominated crystal growth in this system.
In situ Neutron Diffraction Studies of Carbide-Matrix Interactions in HAYNES® 230® Nickel Based Superalloy
Authors: Saleh Tarik A. , Clausen Bjørn , Brown Donald W. , Choo Hahn , Liaw Peter K. , Bourke Mark A. M. , Vogel Sven C. , Buchanan Raymond A. , Klarstrom Dwaine L. 
Published: April 2011

ABSTRACTHAYNES 230 is a solid solution strengthened, face centered cubic (FCC), nickelbased superalloy, with a small amount (1–5 vol. %) of semi-coherent FCC carbides. Neutron diffraction experiments were performed to study the interaction of the carbides with the matrix during tensile and compressive loading. The behavior of the elastic lattice strains during in situ loading clearly showed a tension-compression asymmetry. Although the volume percentage is small, the interaction between the carbides and the matrix had a significant effect on the load sharing. In compression, the carbides began load sharing at the macroscopic yield point, while the tension test suggests no load sharing. Debonding at the carbide-matrix interface is proposed to explain the lack of load sharing during the tensile loading based on the disparities observed between the experimental results and the finite element models.
Asymmetric Lattice Response During Tensile and Compressive Deformation of a Uranium-Niobium Shape Memory Alloy
Authors: Brown D. W. , Bourke M. A. M. , Dunn P. S. , Field R. D. , Stout M. G. , Teter D. F. , Thoma D. J. , Vogel S. C. 
Published: April 2011

ABSTRACTThe deformation of polycrystalline uranium 6 wt. % niobium (U6Nb) was studied in-situ during uniaxial tensile and compressive deformation by time-of-flight neutron diffraction. Diffraction patterns were recorded at incremental strains to roughly 4% total deformation. The asymmetry in the crystallographic response of the lattice is discussed.
Evolution of Polar and Dipolar Dislocation Density from Polychromatic Microdiffraction
Authors: Ice G. E. , Barabash R. I. , Pang J. W. L. 
Published: April 2011

ABSTRACTPolychromatic X-ray microdiffraction (PXM) is sensitive to the density and organization of the dislocations, which occurs at several structural levels. At the lowest level statistically stored (dipolar) individual dislocations can exist within a crystal. At a higher structural level dislocations can organize into strongly correlated arrangements including walls and sub-boundaries. After plastic deformation geometrically necessary (polar) dislocations as well as geometrically necessary boundaries may be formed in a crystal. These dislocations cause not only random deformation, but also strongly correlated long range rotations within the crystal, grain, or subgrain. Non homogeneous plastic deformation is observed even in single crystals at smaller scale. Polar dislocations spread the conditions for x-ray (or neutron) diffraction transverse to the reciprocal space vector of each reflection. Diffracted intensity depends on the second rank dislocation density tensor. The polar dislocations density is related to the incompatibility of the plastic deformation and to the local lattice curvature. Laue patterns are therefore sensitive to the ratio between polar and dipolar dislocations density. Different slip systems of polar dislocations population cause distinctly different streaking in Laue patterns. Examination of streaked patterns enables one to determine statistically stored (dipolar) dislocations and geometrically necessary (polar) dislocations, GNDs, and to quantitativly determine the dislocation patterning parameters. The co-evolution of the statistically stored (dipolar) and geometrically necessary dislocations (polar) may be analyzed, and the ratio between the two densities may be obtained from the analysis of the Laue spots intensity distribution. The microbeam technique is applied to analyze a dislocation structure in a Ni bicrystal under uniaxial pulling.
Non-Destructive Measurement of the Density of Thin Coatings by a Combination of Instrumented (Nano) Indentation and Acoustical Techniques.
Authors: Jennett Nigel M. , Aldrich-Smith Giles , Maxwell Antony S. 
Published: April 2011

ABSTRACTNanoindentation is used to provide a measurement of coating plain strain modulus. The coating properties are then measured by surface acoustic wave spectroscopy (SAWS). It is shown that, by exploiting the relative insensitivity of the SAWS acoustical model to Poisson's ratio, it is possible to measure either the thickness or the density of a thin coating given the input of the other. Furthermore, the indentation and acoustical tests are non-destructive and the resulting value of thickness or density is of high precision. A case study is presented for the measurement of density for a 250 nm thick nano-crystalline Niobium coating on a Si (001) substrate. The density is found to be ρ = 8.4 ± 0.3 g cm−3, about 2 % below bulk values but the modulus is found to be only 85 GPa (for a Poisson's ratio of 0.4), which is 18 % below bulk.
Acoustic Emission Analysis of Nanoindentation-Induced Fracture Events
Authors: Dyjak Pawel , Singh Raman P. 
Published: April 2011

ABSTRACTMonitoring of acoustic emission (AE) activity was employed to characterize the initiation and progression of local failure processes during nanoindentation-induced fracture. Specimens of various brittle materials were loaded with a cube-corner indenter and AE activity was monitored during the entire loading and unloading event using an AE transducer mounted inside the specimen holder. As observed from the nanoindentation and AE response, there were fundamental differences in the fracture behavior of the various materials. Post-failure observations were used to identify particular features in the AE signal (amplitude, frequency, rise-time) that correspond to specific types of fracture events. Furthermore, analysis of the parametric and transient AE data was used to establish the crack-initiation threshold, crack-arrest threshold, and energy dissipation during failure. It was demonstrated that the monitoring of AE signals yields both qualitative and quantitative information regarding highly local failure events in brittle materials.
Initial Contact Behavior of Nanograined Ni-25at.%Al Film During Nanoindentation
Authors: Li Han. , Ngan Alfonso H. W. 
Published: April 2011

ABSTRACTCyclic indentation was performed on standard fused quartz, single crystal Ni3Al (111) and nanocrystalline Ni-25at. %Al alloy thin film with average grain size of a few nanometers. For the thin film sample, it is found the scattering of the effective Young's modulus at small depths goes far beyond the expectation from effects due to surface roughness alone. Three representative deformation mechanisms during initial contact stage were identified to be responsible for the scattering with the assistance of immediate pre and post indentation atomic force microscopy imaging. Furthermore, repeated loading was found to stiffen the thin film sample, but not the bulk ones.
Strengthening of iron aluminide alloys for high-temperature applications
Authors: Palm Martin , Schneider André , Stein Frank , Sauthoff Gerhard 
Published: April 2011

ABSTRACTAn overview is given on materials developments of ferritic and Fe3Al-based iron aluminium alloys with strengthening precipitate phases for high-temperature applications currently underway at the Max-Planck-Institut für Eisenforschung GmbH (MPIE). The development of high-temperature alloys for structural applications is to be focussed on optimisation of strength, creep and corrosion resistance at high temperatures and sufficient ductility at lower temperatures. This is discussed with respect to recent studies on Fe-Al-based alloys with strengthening precipitates, such as κ-phase Fe3AlCx, MC-carbides, Laves phase, and the B2-ordered intermetallic phase NiAl. The following alloy systems have been investigated: Fe-Al-X (X=C, Ti, Ta, Mo, Zr), Fe-Al-Ti-Nb, Fe-Al-Ni-Cr, and Fe-Al-M-C (M=Ti, V, Nb, Ta).The investigations have been focussed on the microstructure, constitution, mechanical properties, and high-temperature corrosion behaviour of Fe-Al-based alloys with Al contents ranging from 10 to 30 at. %.
Effect of Fe Alloying on the Vacancy Formation in Ni3Al
Authors: Partyka E. , Kozubski R. , Sprengel W. , Schaefer H.-E. 
Published: April 2011

ABSTRACTThe influence of Fe alloying on the formation of thermal vacancies in Ni75Al25-xFex has been specifically studied by high-temperature, positron lifetime spectroscopy (PLS). The results are consistent with a previously reported decrease of the activation energy for the vacancy formation upon alloying of Ni75Al25 with Fe derived from residual isochronal resistometry (REST): an indirect method for vacancy studies.
Effect of Microstructure and Zr Addition on the Crystallographic Orientation Relationships among Phases related to the Eutectoid Decomposition of Nb3Si in near Eutectic Nb-Si alloy
Authors: Miura Seiji , Ohkubo Kenji , Mohri Tetsuo 
Published: April 2011

ABSTRACTThe authors have reported in the previous study that the sluggish decomposition of Nb3Si phase is effectively accelerated by Zr addition [1]. This is obvious at lower temperature range than the nose temperature of the TTT curve. In the present study a eutectic alloy containing 1.5 % of Zr was investigated. The crystallographic orientation relationships among phases, such as eutectic Nb and product phases formed by eutectoid decomposition of Nb3Si (eutectoid Nb and Nb5Si3phases) in the Zr-containing sample which was heat treated at 1300°C were investigated by FESEM/EBSD for further understanding of the decomposition process in alloy with a different microstructure.
Solidification Processing and Fracture Behavior of RuAl-Based Alloys
Authors: Reynolds Todd , Johnson David 
Published: April 2011

ABSTRACTAlloys of RuAl-Ru were processed using various solidification methods, and the fracture behavior was examined. The fracture toughness values for RuAl-hcp(Ru, Mo) and RuAl-hcp(Ru, Cr) alloys ranged from 23 to 38 MPa√m, while the volume fraction of RuAl ranged from 22 to 56 percent. Increasing the volume fraction of RuAl resulted in a decrease in fracture toughness. The hcp solid solution was shown to be the more ductile phase with a fracture toughness approaching 68 MPa?m, while the B2 solid solution (RuAl) was found to have a fracture toughness less than 13 MPa√m. An alloy of Ru-7Al-38Cr (at.%) that consisted of a hcp matrix with RuAl precipitates had the highest room temperature toughness and the greatest hardness.