bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved composite electrode and lithium battery performance From smart use of the polymers and their properties
Authors: Gaudefroy Vincent , Guy Delphine , Lestriez Bernard , Bouchet Renaud , Guyomard Dominique
Published: April 2011

To increase electrode cycling performance in batteries, most researchers generally focus their work on the active material optimisation. Here we show that the polymeric binder of the composite electrode may have an important role on the electrode performance. We describe a new tailored polymeric binder combination with controlled polymer-filler (carbon black) interactions that allows the preparation of new and more efficient electrode architecture. Using this polymeric binder, composite electrodes based on Li1.2V3O8 display a room-temperature cycling capacity of 280 mAh/g (C/5 rate, 3.3–2 V) instead of 150 mAh/g using a standard-type (PVdF-HFP binder) composite electrode. We have coupled SEM observations, galvanostatic cycling and electronic conductivity measurements in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance.
All Solid-State Batteries Using Super Ionic Conductor, Thio-Lisicon – Electrode/Electrolyte interfacial Design
Authors: Kobayashi Takesh , Inada Taro , Sonoyama Noriyuki , Yamada Atsuo , Kanno Ryoji
Published: April 2011

All solid-state ceramic lithium battery was studied using a composite anode, the thio-LISICON (Li3.25Ge0.25P0.75S4) solid electrolyte, and the Chevrel phase cathode. The nano-composite of cathode configuration reduced the interfacial resistance and provided fast-charge transfer at the interface. The self-assembled solid-electrolyte interfacial (SEI) phase was formed at the Li-Al/SE interface, while no formation was observed at the Li-In/SE interface. The SEI phase reduced the interfacial resistance and provided high charge-discharge characteristics. The all solid-state cell showed high current density of 1.3C rate and is a promising candidate for future lithium battery system.
Novel Non-aqueous Sol-Gel Synthesis of Carbon-Coated LiMPO4 (M = Fe, Mn, Co) for Lithium Ion Batteries
Authors: Yang Jingsi , Xu Jun John
Published: April 2011

A simple organic solvent based sol-gel method for synthesis of carbon-coated LiFePO4 is developed. Phase pure LiFePO4 with uniform size of 200–300 nm and no agglomeration is obtained, with 1.8 wt % surface carbon formed in-situ. Such a material gives specific discharge capacities of 150 mAh/g and 145 mAh/g at C/5 and 2C at room temperature, respectively, with desirable cycling stability. The dependence of particle size and morphology on precursor concentrations is opposite to conventional solution based methods. Other LiMPO4 (M = Mn, Co, Ni, etc) with favorable physical characteristics can be synthesized the same way.
Mesopore Size Dependence of Protonic and Lithium Ionic Conductivity of Porous Alumina
Authors: Maekawa Hideki , Shen HangYan , Fujimaki Yutaka , Kawata Kotaro , Shibata Kaoru , Kawai Masayosi , Yamamura Tsutomu
Published: April 2011

Ordered-mesoporous-Al2O3 was synthesized by the sol-gel route using neutral copolymer surfactants as templates. The pore size was controlled over the range of 3∼22 nm by using different surfactant copolymers under different synthetic conditions. Protonic conductivity of hydrated mesoporous alumina was examined for CIP treated mesoporous alumina pellet. The highest protonic conductivity was obtained as 0.004 S· cm−1 at 25 °C under 80% RH for the pellet with 15 nm averaged pores. The conductivity increased monotonically with increasing pore size under constant humidity. Quantitative determination of the concentration and the mobility of protons in hydrated mesoporous alumina was performed by 1H NMR, quasi-elastic neutron scattering (QENS) and TG/DTA measurements. Both the mobility and the concentration increased with increasing pore size. On the other hand, composites composed of synthesized mesoporous-Al2O3 and lithium iodide (LiI) was prepared. Dc electrical conductivity of 50LiI.50(mesoporous-Al2O3) was 2.6×10−4 S cm−1 at room temperature, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which the conductivity increased with decreasing the pore size except for pore size=3 nm. The 7Li diffusion constant of the composite was investigated by QENS as well as pulsed field gradient nuclear magnetic resonance (PFG-NMR). The dc conductivities showed reasonable agreement with an Einstein equation using measured diffusion constants.
Fabrication of Nanorod Arrays for Organic Solar Cell Applications
Authors: Huang Susan , Efstathiadis Harry , Haldar Pradeep , Lee Hee-Gyoun
Published: April 2011

We report on a novel use of nanorod arrays for organic based solar cell devices. A metal foil with copper nanorods attached to the surface was developed by electrodepositing copper from a copper sulfate solution into an anodic alumina oxide (AAO) template that had been coated with a metal on one side. The AAO membrane was dissolved in NaOH leaving behind an aligned array of copper nanorods. This nanorod array was evaluated to explore the possibility of increasing the power conversion efficiency of organic solar cells. Nanorod array characteristics were investigated by focus ion beam, scanning electron microscopy, and x-ray diffraction spectroscopy. A solar cell device was made by applying a polymer layer of poly(2-methoxy-5-(3', 7'-dimethyloctyloxy)-1, 4-phenylene-vinylene) (MDMO-PPV) mixed with 6, 6 phentl-C61-butyl acid-methylester (PCBM) onto the copper nanorod array and sandwiching it with a film of poly(3, 4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) applied onto a indium tin oxide coated glass substrate.
Temperature Effects on Photocurrent Generation in Polymer Hetero—Junction Photovoltaic Devices
Authors: Song Mi Yeon , Kim Kang-Jin , Kim Dong Yong
Published: April 2011

In a heterojunction photovoltaic device of ITO/TiO2/poly(3-alkylthiophene)/Au, the photocurrent was characterized with different temperature by using regio-random (P3HT), regular (RP3HT) poly(3-hexylthiophene) and regio-regular poly(3-dodecylthiophene)(RP3DT). The regio-regularity and alky chain length affected the photovoltaic characteristics due to the difference in the hole carrier transport. The drift charge mobility of those devices were analyzed by the space charge limited current (SCLC) theory using dark current versus bias relations. The photocurrent in the devices based on poly(3-alkylthiopene)s began to decrease rapidly below a temperature at which the drift charge mobility was 10−5 cm2/V.s.
Molecular Modeling Studies on a series of Metal-Organic Frameworks
Authors: Lee Tae-Bum , Kim Daejin , Choi Seung-Hoon , Lee Eungsung , Oh Youjin , Yoon Jihye , Kim Jaheon
Published: April 2011

In order to explore rational designs and synthetic strategies toward efficient hydrogen storage materials, quantum mechanical calculations and grand canonical Monte Carlo simulations have been carried out on a series of the Metal-Organic Frameworks containing various organic linkers. The calculations for specific surface areas and the shape of frontier orbitals for various frameworks indicate that the hydrogen storage capacity is largely dependent on the effective surface area of the material, rather than the free volume. Based on the iso-electrostatic potential surface from density functional calculations and the theoretical amount of adsorbed hydrogen from the grand canonical Monte Carlo calculations, it was also found that the electron localization around the organic linker plays an important role in the hydrogen storage capacity of Metal-Organic Frameworks. The prediction of the modeling study is supported by the hydrogen adsorption experiments with IRMOF-1 and -3, revealing the more enhanced hydrogen storage capacity of IRMOF-3 compared with that of IRMOF-1 at 77 K and H2 1 atm.
Generalized Kubas Complexes as a Novel Means for Room Temperature Molecular Hydrogen Storage
Authors: Kim Yong-Hyun , Zhao Yufeng , Heben M. J. , Zhang S. B.
Published: April 2011

We propose that generalized Kubas complexes of molecular hydrogen with light metal elements, such as B and Be embedded in carbon nanostructures, or related Be and B materials, could offer breakthrough performance in room temperature hydrogen storage. First-principles local-density functional calculations show that hydrogen bound to these materials are intact, in similarity to physisorbed H2, but with a greatly enhanced adsorption energy in the range of 0.2–0.7 eV. The metal-H2 binding is attributed to the Coulombic interaction between holes created at the metal sites and Σ electrons of the H2. Management of the hole density and electron-hole orbital overlap thus enables us to control the binding strength of H2 for optimal storage properties.
Decomposition Behavior of Ti-doped NaAlH4 Studied using X-ray Absorption Spectroscopy at the Titanium K-edge
Authors: Bruster E. , Dobbins T. A. , Tittsworth R. , Anton D.
Published: April 2011

The local bonding environment of Ti3+-dopant atoms in NaAlH4 after decomposition to release H2 has been studied using x-ray absorption fine structure (XAFS). The titanium K-edge spectra from doped hydride samples and the standard materials TiCl3 and TiO2 were collected in ambient atmosphere at the synchrotron source at the Center for Advanced Microstructures and Devices (CAMD). Titanium valence states present in the spectra collected from Ti-doped NaAlH4 after decomposition in air are Ti3+ and Ti4+. The Ti3+ is attributed to unreacted TiCl3. The Ti4+ present in the sample is attributed to TiO2 occurring after air oxidation. Coupled with studies of the kinetics of hydrogen desorption reactions, examination of dopant ion valence states after entry into the lattice may lead to better understanding of the interrelationship between lattice doping and desorption kinetics.
Electrochemical Hydrogen Adsorption/Storage in Pure and Functionalized Single Wall Carbon Nanotubes
Authors: Wang Yubing , Iqbal Zafar
Published: April 2011

Self-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

Single 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

A 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

In 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

In 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

Quantitative 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

It 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

Self-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

The 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

The 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

Metastable 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

HAYNES 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

The 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

Polychromatic 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

Nanoindentation 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

Monitoring 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

Cyclic 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

An 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

The 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

The 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

Alloys 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.
Evaluation of Deformation Mechanisms at Mineral-Protein Composite Interface Using Steered Molecular Dynamics Simulations
Authors: Katti Dinesh R. , Ghosh Pijush , Katti Kalpana
Published: April 2011

In the area of clay-polymer nanocomposites, recently montmorillonite is extensively used because of its unique characteristics of swelling. In this work, steered molecular dynamics is used to evaluate the mechanical behavior of a new class of nanocomposites, using amino acids to intercalate clay interlayers. Two positively charged amino acids, lysine and arginine, are used here. Our simulation indicates that both the amino acids have preferred orientation inside the clay interlayer. Our simulations also indicate that the clay-amino acid interlayer is about three times stiffer under tension as compared to under compression. On the other hand, dry montmorillonite shows similar stiffness under tension and compression. The fundamental mechanism of deformation during tension and compression is intrinsically different in the amino acid-clay composite. The stress-strain behavior of this clay-amino acid interlayer is predominantly linear until a stress of 1.5 GPa. This study is a first step towards the potential use of biomacromolecules as modifiers in clay nanocomposites.
Elastic modulus of dental enamel: effect of enamel prism orientation and mineral content
Authors: Ferguson V.L. , Boyde Alan , Bushby Andrew J.
Published: April 2011

Nanomechanical properties of mineralized tissues are determined by microstructural tissue organization and relative composition of organic, mineral, and water phases. We combine nanoindentation and quantitative backscattered electron (qBSE) imaging to understand how these factors influence material properties at the ultrastructural and tissue level. Developmental stages of equine tooth enamel provide a good situation for studying the effects of enamel prism orientation and mineralization. Equine cheek teeth continue to form new enamel whilst mature tissue is being worn away. Hence we can study graded mineral content that increases with enamel maturity. Hunter-Schreger bands (HSBs) containing enamel prisms of contrasting orientations allow investigation of the effect of orientation on modulus. An equine second mandibular molar (2-year-old) was embedded in poly-methylmethacrylate, sectioned longitudinally, polished, carbon coated, imaged in qBSE, and subjected to nanoindentation testing. Elastic modulus increases significantly during maturation as enamel protein matrix degradation makes space for increased mineral content with closer proximity of enamel crystals, finally reaching values exceeding 80 GPa for little further increase in mineral content. Indentations spanning HSBs in immature, poorly mineralized enamel yielded modulus values that varied with prism orientation in a sinusoidal pattern where modulus varies by as much as a factor of three. Nanoindentation helps to elucidate how the composition and ultrastructural organization of enamel contribute to mechanical properties.
Uniaxial and Biaxial Mechanical Behavior of Human Amnion
Authors: Oyen Michelle L. , Stylianopoulos Triantafyllos , Barocas Victor H. , Calvin Steven E. , Cook Robert F.
Published: April 2011

Chorioamnion, the membrane surrounding a fetus during gestation (the “amniotic sac”), is a structural soft tissue for which the mechanical behavior is poorly understood—despite its critical role in maintaining a successful pregnancy and delivery. Preterm rupture of the chorioamnion accounts for one third of all premature births. The structural component of chorioamnion is the amnion sublayer, which provides the membrane's mechanical integrity via a dense collagen network. Amnion uniaxial and planar equi-biaxial tension testing was performed using monotonic loading, cyclic loading and stress-relaxation. The prefailure material behavior was highly nonlinear, exhibiting an approximately quadratic response. Cyclic testing, both uniaxial and biaxial, exhibited dramatic energy dissipation in the first cycle followed by less hysteresis on subsequent cycles and an eventual stable hysteresis response with approximately 20% energy dissipation per cycle. Stress-relaxation testing, both uniaxial and biaxial, demonstrated a load dependent response and continued relaxation after long hold times. A nonlinear viscoelastic (separable) hereditary integral approach was used to model the amnion stress-strain-time response during relaxation. The mechanical results are discussed within the context of the in vivo clinical performance of amnion, and the potential for membrane repair.
Micro-Scale Physical and Chemical Heterogeneities in Biogenic Materials - A Combined Micro-Raman, Chemical Composition and Microhardness Investigation
Authors: Griesshaber E. , Job R. , Pettke T. , Schmahl W. W.
Published: April 2011

The ultrastructure and chemical composition of calcitic shells of the modern brachiopod specimen Magellania flavescens (Linnaeus) – order: Terebratulida – was investigated with μ-Raman spectroscopy, Vickers microhardness indentation and laser-ablation-inductively-coupled-plasma-mass-spectrometry. The shells contain a thin outer, nanocrystalline primary layer, which is followed by an inner, much softer, secondary layer composed of inorganic/organic fibre composite material. We observed significant chemical and structural inhomogeneities within the shells. The calcite A1g Raman mode was slightly reduced from 1084 cm-1 at the hinge (lock) down to 1083.5 cm-1 towards the tip. This is accompanied by a variation of some chemical impurity concentrations (e.g. Mg, Sr). A strong decrease in microhardness and distinct changes in chemical composition from the primary or the outermost part of the secondary layer towards the innermost portion of the secondary shell layer can be observed. Thus, our measurements show that chemical and structural inhomogeneities occur in modern brachiopods and not only between the primary and the secondary shell layer, but also within the secondary layer of the shell.
A Model for the Increased Elastic Compliance in Human Cancer Cells
Authors: Mohrdieck Camilla , Arzt Eduard
Published: April 2011

Human epithelial cancer cells are known to exhibit a reorganization of their keratin cytoskeleton and an attendant change in their elastic stiffness upon incubation with a natural lipid. The change in the keratin network was modeled and the model structures were computationally deformed using a Finite Element Method. The simulation results show a marked difference in the mechanical behavior of the cells for tensile and compressive loading conditions. In the former case, the elastic compliance increases in agreement with experimental findings. We interpret this increase by applying principles of structural engineering and suggest that cells may generally use these principles to regulate their cytoskeletal architecture.
A Novel Joint between Dissimilar Materials Inspired by the Mechanics of Trees
Authors: Roy Xu L. , Kuai Huacheng , Sengupta Sreeparna
Published: April 2011

An integrated experimental and numerical investigation was conducted for removing the free-edge stress concentrations in dissimilar material joints. A convex interface/joint design, inspired by the shape and mechanics of trees, allows for least stress concentrations at bi-material corners for most engineering material combinations. In-situ photoelasticity experiments on convex polycarbonate-aluminum joints showed that the free-edge stress concentration was successfully removed. As a result, the new design not only improves the static load transfer capacity of dissimilar material joints, but also yields more reasonable interfacial tensile strength evaluation. For convex polycarbonate-aluminum and PMMA-aluminum joint specimens, the ultimate tensile load increased up to 81% while the total material volume reduced by at least 15% over that of traditional butt-joint specimens with severe free-edge stress concentrations.
Mechanical Behavior of Ceramic/SAM Bilayer Coatings
Authors: Yang Quan , Zhang Guangneng , Chitre Kaustubh , Cho Junghyun
Published: April 2011

Ceramic/self-assembled monolayer (SAM) bilayer films can provide adequate protection and/or act as a multipurpose coating for microelectronics and MEMS applications, due to synergistic effects of the hybrid film structure. The organic SAM acts as a “template” for the growth of the ceramic film while the hard ceramic can provide protection from environmental and mechanical impact. To process the bilayer films, a low-temperature solution deposition technique (biomimetic process) is employed using phosphonate-based SAM and zirconium oxide precursors. A particulate zirconium oxide film is formed by enhanced hydrolysis of zirconium sulfate solutions in the presence of HCl at about 80°C, and its particle size and thickness effects are discussed. In addition, microstructure and micromechanics involved in the synthesis of both zirconia films and SAM are systematically assessed. Especially, mechanical properties such as Young's modulus and hardness are analyzed using a nanoindenter, as well as with the aid of theoretical models. Further, the substrate effects resulting from a large indentation depth relative to the film thickness are eliminated to obtain the “film-only” properties. This study also highlights the role of compliant SAM layer in forming a strain-tolerant bilayer film.
Surface Plasmon Excitations and Emission Light due to Molecular Luminescence on Metal Thin Film
Authors: Kaneko Futao , Toyoshima Susumu , Ohdaira Yasuo , Shinbo Kazunari , Kato Keizo
Published: April 2011

Emission light due to surface plasmon (SP) excitations has been investigated in Kretschmann configuration of prism/metal thin film/organic dye thin films by means of direct irradiation of a laser beam from air to the films. Emission light through the prism coincided with the resonant conditions of SP excitations in the configuration. It was thought that SPs on the metal surface were excited by luminescence of dye molecules close to the metal surface, and the SPs propagating along the metal surface were converted to the emission light according to the resonant conditions of SPs in the configuration. Intensities and spectra of the SP emission light through the prism strongly depended upon emission angles, nanostructures of dye films, the film thickness and mixture of two kinds of dyes.
Functionalized Guanidines for Electro-Optic Materials.
Authors: Buker Nicholas , Firestone Kimberly A. , Haller Marnie , Purvis Lafe , Lao David , Snoeberger Robert , Jen Alex K.-Y. , Dalton Larry R.
Published: April 2011

A family of nonlinear optical chromophores has been synthesized containing novel donor systems based on functionalized guanidines. Chromophores utilizing these donor systems display superior transparency and stability properties. The unusual and highly desirable characteristics of these chromophores make them very promising candidates for electro-optic applications. Systematic study of the molecular hyperpolarizabilities and bulk electro-optic properties of polymers containing these chromophores is being used to guide optimization of these systems.
New Light Emitting Polymers and High Energy Hosts for Triplet Emission
Authors: Mak Chris S. K. , Watkins Scott E. , Williams Charlotte K. , Evans Nicholas R. , Chan Khai Leok , Cho Sung Yong , Holmes Andrew B. , Boothby Clare E. , Friend Richard H. , Hayer Anna , Köhler Anna
Published: April 2011

This paper describes two aspects of research aimed at harnessing the triplet energy generated in electron-hole recombination in polymer electroluminescent devices. The purpose is to design solution-processible phosphorescent organometallic triplet emitters and to design high triplet energy polymer hosts that can transfer triplet energy to the phosphorescent guests. The method employed Suzuki cross coupling reactions to incorporate either phosphorescent cores or high energy triplet monomers covalently into polymer hosts to evaluate their optoelectronic properties. The results showed (i) efficient energy transfer from polyfluorene hosts to red phosphorescent guests and (ii) that pyridine and carbazole monomers could raise triplet energies of hosts. It is concluded that these approaches offer promise in the design of solution processible electrophosphorescent materials for red and green light emitting devices.
Magnetotransport Properties of Compression Molded CrO2-Polyimide Composite
Authors: Mishra Sanjay R. , Ghosh Kartik , Losby Joe , Kehl Ted , Viano Ann
Published: April 2011

The conductivity and magnetotransport properties of compression molded half-metallic CrO2/Polyimide composites over a range of different metallic concentrations have been studied. The conductivity measurements on these composites show negative slope of resistance versus temperature. The magnetoresistance measurement indicates obvious enhancement at low temperatures. The maximum in magnetoresistance (MR) is found to be temperature and metal volume fraction dependent. Significant differences in high and low temperature magnetoresistive behavior in the composite have been observed. The high field, 15 T MR measurements show 23% and 19% MR enhancement at 5K and 75 K, respectively. Thus, it is found that the polymer barrier can contribute to enhancing magnetoresistive properties of the composite.
Solution processable nanocomposites based on silsesquioxane cores for use in organic light emitting diodes (OLEDs)
Authors: Sellinger Alan , Tamaki Ryo , Laine Richard M. , Ueno Kazunori , Tanabe Hiroshi , Williams Evan , Jabbour Ghassan E.
Published: April 2011

A new family of materials that synergistically combine the attributes of both organic and inorganic properties for use in organic light emitting diodes (OLEDs) is presented. The hybrid materials are based on 3-D inorganic cores of octavinylsilsesquioxanes (OVS). The resultant materials have high Tg's (120–210°C), are formed from minimal step/high yield reactions and readily available starting reagents, are monodisperse (PDI<1.1), can be highly purified via common chroma-tographic techniques, and form defect-free amorphous films via spin-dip coating. For example TPD is known for its good hole injection/transport properties in OLED applications but suffers from a low Tg (65°C). TPD-OVS hybrid material has a Tg of 142°C while maintaining similar injection/transport properties to TPD. Photoluminescence analysis of the hybrid thin film reveals: 1) a 30 nm blue shift versus their dilute solution counterparts; and 2) 5 hour annealing cycles to within 10°C of their Tg show no indication of eximer formation (no red shift) that often causes reduced efficiencies in polymer LEDs.