bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel approaches for the characterization of electromagnetic fields using electron holography
Authors: Kasama Takeshi , Antypas Yanna , Chong Ryan K.K. , Dunin-Borkowski Rafal E.
Published: April 2011

Two recent developments related to the application of off-axis electron holography to the characterization of magnetic and electrostatic fields in nanoscale materials and devices are described. The first is based on the design and implementation of a three-contact electrical biasing specimen holder that allows electron holograms to be recorded from samples as they are tilted to angles of up to ±70° with voltages applied to them in situ in the electron microscope. The second relates to the prospect of characterizing magnetic vector fields in materials in three dimensions using electron holography.
Suzuki Segregation to Stacking Faults in a Cu-Si alloy
Authors: Mendis B.G. , Jones I.P. , Smallman R.E.
Published: April 2011

Field Emission Gun Transmission Electron Microscopy (FEG TEM) is used to measure solute atom segregation to stacking faults in a Cu- 7.15 at% Si alloy annealed at temperatures of 275°C, 400°C and 550°C. A highly localised increase in the silicon concentration was detected at the stacking fault plane. Segregation of the higher valence silicon atoms increases the local electron to atom ratio in the crystal thereby lowering the stacking fault energy as expected for a Cu-Si alloy system. Measurements across low angle boundaries showed hardly any change in solute concentration, which suggests that the segregation observed at stacking faults is due to a genuine chemical interaction rather than an elastic interaction which can occur in for example high angle grain boundary segregation. The segregation was greatest for the 275°C annealed alloy, where the enrichment is more than 2 at% Si above matrix composition, and was found to decrease monotonically with increasing temperature. The binding energy, as determined from a McLean isotherm, was measured to be -0.021 eV/atom. This is significantly different to the theoretical estimate of -0.0022 eV/atom, as calculated by data on phase equilibria. This could be due to several reasons including experimental error, assigning thermodynamic data of a bulk phase to a stacking fault and inadequacies in the Suzuki segregation model itself.
Electron Holography as a Tool for Dopant Profile Characterization of Semiconductor Devices
Authors: Matsumoto Takao , Kouguchi Masanari
Published: April 2011

We used electron holography to analyze the dopant profile in a MOS transistor. The overall performance of the holography electron microscope at our laboratory has been confirmed by recording a maximum of 16, 000 numbers of electron interference fringes on a conventional electron microscope film. For thin film specimen preparation, we have developed an FIB system with a modified beam scanning scheme in which a high-frequency analog modulation signal is added to the digital signal of the beam deflector. This has enabled us to smooth the residual surface roughness presumably caused by the glitch-noise of D/A converter and we proved that a nearly atomically smooth surface was obtained as estimated with an AFM and TEM. We used this optimized system to characterize the dopant profile in MOS transistors, and comparisons with the calculated profiles from device simulator have proved that they are in good agreement.
Accurate determination of orientation relationships between ferroelastic domains: the tetragonal to monoclinic transition in LaNbO4 as an example.
Authors: Prytz Ø. , Taftø J.
Published: April 2011

LaNbO4 crystallizes in a tetragonal high-temperature phase with space group I41/a, which transforms to a monoclinic phase upon cooling below 500 °C. The low-temperature phase has space group I2/a (C2/c) with a monoclinic angle β=94.1°. This system serves as a useful model of a ferroelastic transition of the 4/mF2/m type using the notation of Aizu [1]. This transition produces ferroelastic domains, the boundaries between which are parallel to the monoclinic b-axis. The orientation of these boundaries relative to the monoclinic a- and c-axes has been predicted by Sapriel [2] for all 94 ferroelastic species, and calculations specifically for the LaNbO4 system have been presented by Jian and Wayman [3].

We present an accurate determination of the boundary orientation in LaNbO4 using selected area electron diffraction. The boundary planes are parallel to the (2 0 –5.10)/(5.10 0 2) planes of the two domains, as opposed to the predictions of Jian and Wayman which indicate that the domain boundaries should be oriented parallel to the (2 0 -4.04)/(4.04 0 2) planes. Our experimental results are in good agreement with the results of a previous study [4].

Furthermore, we present a simple geometric model for calculating the boundary orientation based only on the unit cell parameters of the monoclinic phase. This model gives a boundary orientation in excellent agreement with our experimental determination.
Synthesis and Microstructures of α-Fe2O3 Bicrystalline Nanowires
Authors: Wang R.M. , Chen Y.F. , Fu Y. Y. , Zhang H. , Kisielowski C.
Published: April 2011

Novel Fe2O3 nanowires have been successfully synthesized by a simple oxidation process of pure iron. The microstructure of the Fe2O3 nanowires have been systematically investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM). The investigated materials are found to be stoichiometric rhombohedral α-Fe2O3 with typical diameters of 20–80 nm and lengths up to 20 μm. In addition to known single crystal Fe2O3 nanowires, a great amount of novel bicrystalline nanowires were found with ellipsoidal heads. Investigations indicate that most of the bicrystalline nanowires are twins and their orientation relationship is obtained to be (−1, 1, 10)M//(−1, 1, 10)T, [110]M//[-1-10]T. High resolution TEM with numerical reconstruction of the electron exit wave was used to investigated the atomic structure of the micro-twins. Their growth mechanism is briefly discussed on the basis of solid phase growth process.
Electron Microscopy of the Operation of Nanoscale Devices
Authors: Cumings John , Goldhaber-Gordon David , Zettl A. , McCartney M.R. , Spence J. C. H.
Published: April 2011

A transmission electron microscope (TEM) is much more than just a tool for imaging the static state of materials. To demonstrate this, we present work on studying the mechanical and electrical properties of carbon nanotube devices. Multiwall carbon nanotubes are concentrically stacked tubular sheets of graphite, where the spacing between each cylinder is simply the natural spacing of graphite. Using a custom-built in-situ nanomanipulation probe, we have shown that it is possible to slide the nanotube layers in a telescopic extension mode that exhibits low friction, demonstrating the potential of nanotubes as the ultimate synthetic nanobearing. During this telescopic extension, the electrical resistance of the nanotube devices increases, opening the possibility that these devices can also be used as nanoscale rheostats. We also briefly describe work on using electron holography inside a TEM to study the electric field distribution in nanotube field-emission devices and on using a nanotube itself as a biprism for electron holography. These measurements together demonstrate the wealth of information that can be obtained and frontiers that can be opened by putting operational nanodevices inside an electron microscope.
Pair Distribution Function as a Probe for Zeolite Structures
Authors: Martínez-Iñesta María M. , Lobo Raúl F.
Published: April 2011

In this article we describe how we have used the pair distribution function of zeolites to solve complex structural problems. A first study was dedicated to refining the structure of disordered zeolite beta, a zeolite that is used in the alkylation of benzene. A second study is a work in progress geared toward the determination of the mechanism of negative thermal expansion of zeolite chabazite, which has been found to be one of the most contracting materials known. Preliminary results suggest that the individual Si-Ox distances and Ox-Si-Ox angles in the tetrahedral are deformed with temperature while the average tetrahedra dimensions stay constant.
Dynamic Responses in Polymer-Clay Gels
Authors: Loizou Elena , Porcar Lionel , Butler Paul , Malwitz Matthew , Schmidt Gudrun
Published: April 2011

The shear orientation of three polymer-clay gels has been investigated by means of small angle neutron scattering (SANS). The gels have the same polymer and clay concentrations but different polymer molecular weight. The polymer is adsorbed to the clay platelets. While long polymer chains can interconnect several platelets shorter polymer chains cannot. Although the polymer concentration is above c* the polymer chain length and cross linking between clay platelets strongly influence their shear orientation which leads to anisotropy in SANS. Our data suggest that the flow is strong enough to enhance and maintain a continuous increase in the shear orientation of the polymer clay gels only when the polymer chains are long enough to interconnect or strongly entangle between platelets.
X-Ray Diffraction as a Probe for Elastic Strain: Micro- and Nanoscale Investigation of Thin Metal Films
Authors: Spolenak R.
Published: April 2011

In the past years the concept of measuring strain by x-rays has changed significantly. The combination of 3rd generation synchrotron sources, advanced focusing techniques and large area detectors has made it possible to probe volumes smaller than a cubic micron. This devolopment has made it possible to probe microstrains directly without having to rely on highly sophisticated models to evaluate peak broadening effects. This paper will provide a review of the state of art of local strain measurements by x-rays, discuss their limitations, provide an outlook of where the field may be going within the next years and address the most important issues to be solved. Examples will be given for the current limits in terms of resolution in time, space, strain and intensity.
In-Situ Infrared (IR) Detection and Heating of the High Pressure Phase of Silicon during Scratching Test
Authors: Dong Lei , Patten John A. , Miller Jimmie A.
Published: April 2011

A novel method of in-situ detection of the high pressure phase transformation of silicon during dead-load scratching is described. The method is based on the simple fact that single crystal silicon is transparent to Infrared light while metallic materials are not. Infrared heating during scratching has been performed to thermally soften and deform the transformed metallic material and some promising results were obtained. The sample material used here is silicon, but the same approach can be applied to germanium and other materials, such as ceramics (SiC), which have appropriate optical properties.
An Investigation of Non-linear Stress-strain Behavior of Thin Metal Films
Authors: Huber N. , Dietz T. , Tyulyukovskiy E.
Published: April 2011

ABSTACT

Non-linear stress-strain curves of various films with thickness of one to four microns were determined from nanoindentation experiments with a Berkovich indenter. The measured load-depth data are analysed using a method based on neural networks. An inverse mapping of depth-dependent dimensionless hardness and stiffness data yields the material parameters describing a non-linear elastic-plastic stress-strain curve of the Armstrong-Frederick type. Suppositions for the application of this method are a sufficiently different hardness between film and substrate, and hardness and stiffness data available in a depth range of 10 to 200% of the film thickness. For all films considered a significant thickness dependence in strength has been observed. In addition, a remarkable influence of the substrate material on the strength of the film material was found and has been confirmed by focussed ion beam microscopy.
Nanoindentation of multilayer PZT/Pt/SiO2 thin film systems on silicon wafers for MEMS applications.
Authors: Chima-Okereke C. , Reece M. J. , Bushby A. J. , Whatmore R. W. , Zhang Q.
Published: April 2011

Nanoindentation is a promising tool for obtaining the elastic properties of thin films. However, no means exists to predict or extrapolate the elastic modulus of the top layer in multilayer systems from experimental data. The mechanical properties of PZT multilayer systems have become increasingly important in applications for MEMS devices. The indentation modulus vs. a/t behaviour of PZT on Pt/SiO2/Si wafer substrate was investigated and compared with a new analytical solution for Herztian indentation of multilayers. Five different PZT film thicknesses were indented (70, 140, 400, 700, 1500 nm), using a 10 μm radius indenter. Good agreement was found between analytical equations and experimental data. However the behaviour of the multilayer system was complex. This makes the deconvolution of film properties difficult for thicknesses less than about 1000 nm.
Effect of Fluoride on Mechanical Properties of Teeth Demineralized by Use of Orthodontic Appliances
Authors: Centeno Claudia , Ruiz Ulises , Contreras Oscar , Samano Enrique C.
Published: April 2011

The risk of dental caries increases with the use of orthodontic appliances, and it does not only depend on a patient's oral hygiene. Caries cause teeth enamel demineralization close to the orthodontic bracket. The hardness of the teeth consequently decreases, and they become brittle and loose. The type of adhesive used to fix brackets may or may not reduce enamel demineralization. Previous studies have shown that a resin-modified glass ionomer (RMGI) inhibits demineralization. The purpose of this work is to evaluate the effect of a fluoride-releasing bracket on mechanical properties of dentin and enamel on regions adjacent to orthodontic brackets bonded with RMGI and composite resin cements. The remineralization effect due to fluoride on teeth was assessed by measuring hardness and reduced elastic modulus on dentin, enamel and dentin-enamel junction (DEJ) around the bracket area by nanoindentation methods. Nanoindentation was performed using a TriboScope from Hysitron. For this purpose two sets of polished samples were prepared: one sample was a cut along a longitudinal section and the other one along a cross-section of a tooth with orthodontic treatment using RMGI. Anisotropy in the mechanical properties of the teeth is observed along each direction.
Displacement Modulation Based Dynamic Nanoindentation for Viscoelastic Material Characterization
Authors: Singh Sehaj P. , Singh Raman P. , Smith James F.
Published: April 2011

This paper demonstrates a new displacement modulation technique for using a depth sensing nanoindentation instrument to measure the dynamic mechanical properties of viscoelastic materials. For testing low modulus, high damping polymeric materials, dynamic nanoindentation offers several advantages over quasi-static testing. In this research, a model for the dynamic response of the system is proposed and shown to match well with experimental observations. A new calibration procedure, which involves the use of a variable cantilever spring, is employed to determine the damping characteristics of the testing frame as a function of excitation frequency. Using the proposed procedure dynamic nanoindentation tests are carried out on a viscoelastic material to determine the storage and loss moduli as functions of excitation frequency. Finally, a comparison with results from conventional testing (DMA) is provided.
On factors affecting the extraction of elastic modulus by nanoindentation of organic polymer films
Authors: Iacopi F. , Laknin M. , Mulloy A. , den Toonder J.M.J. , Vanhaeren D. , Brongersma S. H.
Published: April 2011

A detailed study of nanoindentation in Continuous Stiffness Mode (CSM) on a family of aromatic thermosetting polymers is carried out to identify the causes for the large variability in the extracted values of the elastic modulus of organic polymer films.

It is shown that the variation of parameters determining the dynamics of the force application such as the CSM frequency, the actual strain or load rate, and the duration of the waiting time segments can lead up to 20% difference in the estimated elastic modulus. The reason for this is related to creep, more specifically to viscoelastic behaviour, typical of organic films. On the other hand, pile-up is shown to have a negligible effect on the extraction of the elastic modulus from indentation depths below 50% of the film thickness, even for films with hardness as low as 0.13GPa. It is also concluded that neither pile-up nor creep phenomena can account for the overestimation of the elastic modulus with nanoindentation as compared to the values extracted with the surface acoustic waves technique.
Some Issues of Rough Surface Contact Plasticity at Micro- and Nano-Scales
Authors: Gao Y. F. , Bower A. F. , Kim K.-S.
Published: April 2011

Rough surface contact plasticity at microscale and nanoscale is of crucial importance in many new applications and technologies, such as nano-imprinting and nano-welding. This paper summarizes our recent progress in understanding contact plasticity from a multiscale point of view, and also presents our perspectives. We first discuss a contact model based on fractal roughness and continuum plasticity theory. Interestingly, our simple, elastic-plastic contact model of the Weierstrass-Archard type gives rise to many practical scaling relations of contact pressure, contact compliance etc. The usefulness of those predictions is discussed for experimental measurements of the thermal/electrical contact resistance. A material length scale can be introduced by a nonlocal plasticity theory, or implicitly by dislocation mechanics modeling. The recent work on micro-plasticity of surface steps gives a variety of surface yielding and hardening behaviors, depending on interface adhesion, roughness features and slip systems. As a consequence, a rough surface contact at mesoscale can lead to the formation of a boundary layer with sub-layer dislocation structures, which cannot be predicted by existing strain gradient plasticity theories. The micromechanical analysis of surface plasticity could serve as the connection between microscale bulk dislocation plasticity and nanoscale atomistic simulations.
Effect of Heat Treatments on Microstructure of Rapidly Solidified TiCo Ribbons
Authors: Yoshimi Kyosuke , Yamauchi Akira , Nakamura Ryusuke , Tsurekawa Sadahiro , Hanada Shuji
Published: April 2011

The effect of heat treatments (aging or annealing) on microstructure was investigated for rapidly solidified ribbons of near-stoichiometric TiCo. In as-spun ribbons, it was observed by TEM that an equiaxed grain structure was developed and its crystal structure had been already B2-ordered, while a small amount of a second phase, Ti2Co, finely disperses in grains and along grain boundaries. Some grains were dislocation-free but others contained curved or helical dislocations and prismatic loops having a Burgers vector parallel to <100> directions. By annealing the as-spun ribbons at 700°C for 24h, the dislocation density was obviously increased compared with that of the as-spun ribbons, while grain growth appears to occur slightly. The increase of the dislocation density in the annealed ribbons is believed to result from the condensation and/or absorption of supersaturated vacancies. Therefore, the TEM observation results indicate that a large amount of supersaturated thermal vacancies were retained in the TiCo ribbons by the rapid solidification.
Pseudoelasticity of D03 Ordered Monocrystalline Fe3Al
Authors: Kabra S. , Bei H. , Brown D. W. , Bourke M.A.M. , George E. P.
Published: April 2011

Pseudoelasticity in monocrystalline Fe3Al (23 at.% Al) was investigated by room-temperature mechanical testing along the <418> tensile and compressive axes. In tension, up to ∼10% strain is recoverable whereas only ∼5% strain is recoverable in compression. Straight, parallel, surface step lines were seen to appear/disappear as the specimens were pseudoelastically loaded/unloaded. In contrast, in the plastic region (ε >10%), wavy slip lines appeared on the specimen surfaces which did not disappear upon unloading. In-situ neutron diffraction was performed during compressive straining and the intensities of several diffraction peaks increase/decrease reversibly during loading/unloading. These changes are consistent with a deformation twin which produces large crystal rotations. They could also be indicative of a phase transformation. Unfortunately, we were able to sample only a limited range of 2θ in the present investigation and, within this range, none of the new peaks that appeared during the pseudoelastic deformation were disallowed peaks for the D03 crystal structure. Therefore we are unable at this time to distinguish between the two possible mechanisms, twinning and phase transformation.
Dislocation Structure, Phase Stability and Yield Stress Behavior of Ultra-High Temperature L12 Intermetallics: Combined First Principles-Peierls-Nabarro Approach
Authors: Kontsevoi Oleg Y. , Gornostyrev Yuri N. , Freeman Arthur J.
Published: April 2011

We present results of comparative studies of the dislocation properties and the mechanical behavior for a class of intermetallic alloys based on platinum group metals (PGM) which are being developed for ultra-high temperature applications: Ir3X and Rh3X (where X = Ti, Zr, Hf, V, Nb, Ta). For the analysis of dislocation structure and mobility, we employ a combined approach based on accurate first-principles calculations of the shear energetics and the modified semi-discrete 2D Peierls-Nabarro model with an ab-initio parametrization of the restoring forces. Based on our analysis of dislocation structure and mobility, we provide predictions of temperature yield stress behavior of PGM-based intermetallics, show that their dislocation properties are closely connected with features of the electronic structure and the L12 → D019 structural stability, and demonstrate the dramatic difference in dislocation structure and the mechanical behavior between PGM alloys with IVA and VA group elements.
Role of Microstructure in Promoting Fracture and Fatigue Resistance in Mo-Si-B Alloys
Authors: Kruzic J. J. , Schneibel J. H. , Ritchie R. O.
Published: April 2011

An investigation of how microstructural features affect the fracture and fatigue properties of a promising class of high temperature Mo-Si-B based alloys is presented. Fracture toughness and fatigue-crack growth properties are measured at 25° and 1300°C for five Mo-Mo3Si-Mo5SiB2 containing alloys produced by powder metallurgy with α-Mo matrices. Results are compared with previous studies on intermetallic-matrix microstructures in alloys with similar compositions. It is found that increasing the α-Mo phase volume fraction (17 – 49%) or ductility (by increasing the temperature) benefits the fracture resistance; in addition, α-Mo matrix materials show significant improvements over intermetallic-matrix alloys. Fatigue thresholds were also increased with increasing α-Mo phase content, until a transition to more ductile fatigue behavior occurred with large amounts of α-Mo phase (49%) and ductility (i.e., at 1300°C). The beneficial role of such microstructural variables are attributed to the promotion of the observed toughening mechanisms of crack trapping and bridging by the relatively ductile α-Mo phase.
Comparison of temperature driven ordering in bulk foil and thin film of L10ordered FePd
Authors: Issro Chaisak , Püschl Wolfgang , Pfeiler Wolfgang , Sepiol Bogdan , Rogl Peter F. , Soffa William A. , Acosta Manuel , Pierron-Bohnes Véronique
Published: April 2011

Changes in the degree of long-range order of 10 μm thick FePd foil are presented and compared with results on 50 nm thick FePd films. The films were produced by dc and rf magnetron co-sputtering on Si as well as by molecular beam epitaxy co-deposition on MgO substrates. Long-range order was studied by electrical resistivity measurement, X-ray diffraction and Möβbauer spectroscopy.
Shape Memory Effect through L10-fcc Order-Disorder Transition
Authors: Tanaka K.
Published: April 2011

Shape memory effect not associated with martensitic transformation but with order-disorder phase transformation is examined in the compounds of AuCu, CoPt and FePd. These exhibit the L10-fcc transition at 680K, 1060K and 950K, respectively, which is relatively high temperature. Under a uniaxial compressive stress, a reversible shape change (reduction and elongation in edge length) is observed by cooling and heating the specimen temperature. The elongation of the specimen associated with the disordering occurs at their equilibrium transition temperatures, and the reduction along the direction of a compressive stress associated with the ordering occurs at a certain supercooled temperature. A trial actuator constructed with FePd polycrystalline wire and a conventional inconel wire properly works by heating up and cooling down the temperature.
Directional Thermoelectric Performance of Ru2Si3
Authors: Simkin Benjamin A. , Hayashi Yoshinori , Inui Haruyuki
Published: April 2011

The orthorhombic compound Ru2Si3 is currently of interest as a high-temperature thermoelectric material. In order to clarify the effects of crystal orientation on the thermoelectric properties of Ru2Si3, we have examined the microstructure, Seebeck coefficient, electrical resistivity, and thermal conductivity of Ru2Si3 along the three principal axes, using these measured quantities to describe the relative thermoelectric performance as a property of crystal orientation. Ru2Si3 undergoes a high temperature (HT)→low temperature (LT) phase change and polycrystalline Si platelet precipitation during cooling, both of which are expected to effect the thermoelectric properties. The HT tetragonal→LT orthorhombic phase transformation results in a [010]//[010], [100]//[001] two-domain structure, while polycrystalline Si precipitation occurs on the (100)LT and (001)LT planes. The [010] orientation is found to posses superior thermoelectric properties (with the dimensionless figure of merit, ZT[010]/ZT[100]>4 at 650°C), due principally to the larger Seebeck coefficient along the [010] direction. The effect of the domain structure on the thermoelectric properties is discussed.
B2 Phases and their Defect Structures: Part I.I. Ab initio Vibrational and Electronic Free Energy in the Al-Ni-Pt-Ru System
Authors: Arroyave Raymundo , Prins Sara , Liu Zi-Kui
Published: April 2011

In this work, we calculate the finite temperature thermodynamic properties of the binary B2 phases in the Al-Ni-Pt-Ru system, particularly the B2 RuAl phase in the Pt-Al-Ru ternary, through the incorporation of the vibrational and electronic contributions to the total free energy. The harmonic approximation is used to consider the atomic vibrations, with the quasi-harmonic correction to account for volume expansion effects on the vibrational entropy as the temperature increases. The vibrational entropy calculations are incorporated through the supercell approach. The calculated phonon dispersion curves show that the B2 PtRu structure is mechanically unstable at low temperatures, while B2 PtAl is marginally stable. The thermal electronic contribution is added to the total free energy. Finally, the formation enthalpies and entropies of B2 RuAl are calculated as a function of temperature.
Microstructure and Mechanical Properties of Fe-Ni-Mn-Al Alloys
Authors: Wittmann M. W. , Baker I. , Hanna J. A.
Published: April 2011

In an attempt to produce a two-phase alloy consisting of a L21–structured (Fe, Ni)2MnAl-based phase in either a B2 or b.c.c. matrix, seven Fe-Ni-Mn-Al alloys were cast. Transmission electron microscopy (TEM) of the as-cast alloys revealed a range of microstructures including single phase L21, a f.c.c./B2 eutectic, and alternating, coherent 10–60 nm wide ordered and disordered b.c.c. rods aligned along <100>. A description of the phases, including chemical compositions and hardnesses is presented.
Crystal Structure, Phase Stability and Plastic Deformation Behavior of Ti-rich Ni3(Ti, Nb) Single Crystals with Various Long-Period Ordered Structures.
Authors: Hagihara Koji , Tanaka Tetsunori , Nakano Takayoshi , Umakoshi Yukichi
Published: April 2011

In Ni-Ti-Nb ternary system, there are some geometrically close-packed (GCP) phases with long-period stacking sequences of a close-packed plane (CPP). Among them, our focus is on the Ni3(Ti0.90Nb0.10) crystals with Pb3Ba-type rhombohedral structure with nine-fold stacking sequence. Compression tests were conducted using the single crystals and the temperature and orientation dependences of plastic deformation behavior were investigated in comparison with those of D024-Ni3Ti crystals with the four-fold stacking sequence. The K-W locking of screw dislocation was found to occur not only in the compounds such as Ni3Al and Ni3Ti with a relatively small unit cell, but also even in complex compounds with longer-period stacking structures by slip on the common CPP in the GCP structures.
Compressive Creep Behavior in Coarse Grained Polycrystals of Ti3Al and its Dependence on Binary Alloy Compositions
Authors: Takahashi Tohru , Sakaino Yuki , Song Shunzi
Published: April 2011

Compressive creep behavior has been investigated on coarse grained Ti3Al alloys with aluminum contents ranging from 15mol%Al to 42mol%Al, in order to obtain basic information concerning the chemical composition effect on creep of Ti3Al. Pure aluminum and titanium of 99.99% purity were arc-melted into small ingots weighing about 10grams under an argon atmosphere. The resulting microstructures after the hot deformation and vacuum annealing contained equiaxed grains whose average diameter ranged from 125 to 192 micrometers except alloys containing 40 and 42 mol% aluminum.

Compressive creep tests were performed in vacuum on parallelepiped specimens with dimensions of 2mm×2mm×3mm. The applied compressive stress was 159MPa, and the test temperature was around 1200K.

A very small primary transient and the minimum creep rate region followed by a gradual creep acceleration were observed in the materials containing aluminum up to 25mol%. In contrast to this, the materials containing more aluminum than 25mol% showed greater primary transient where creep deceleration continued up to about 0.1 true strain. Dual phase materials containing the γ phase showed small primary transient probably due to the constraint from the γ phase.
Formation of Defect Structures during Annealing of Cold-deformed L10-ordered equiatomic FePd Intermetallics
Authors: Deshpande Anirudha R. , Wiezorek Jörg M.K.
Published: April 2011

Planar defects produced in L10-ordered FePd during annealing after cold-deformation in the disordered cubic state have been characterized by transmission electron microscopy (TEM). The defects evolving during annealing include arrays of overlapping stacking faults (SF's), {111}-conjugated microtwins (μT's) and thermal antiphase boundaries (APB's). The defect formation mechanisms proposed here are similar to twinning mechanism reported for FCC-metals during annealing. Thus, SF arrays and faulted μT's in the L10-ordered FePd appear to form during the early stages of annealing by atomic attachment faulting on {111}-facets of the transformation interfaces. During later stages of annealing the reduced amount and the change in nature of the driving forces for the microstructural rearrangement result in changes in the predominant defect formation mechanism. The features of the defect genesis in L10-FePd are discussed with respect to solid-state transformations during processing of these ferromagnetic intermetallics.
On the Effects of Interstitial Elements on Microstructure and Properties of Ternary and Quaternary TiAl based alloys
Authors: Chevalier Jean-Pierre , Lamirand Mélanie , Bonnentien Jean-Louis
Published: April 2011

Ti-Al-Cr ternary and Ti-Al-Cr-Nb quaternary alloys have been studied as a function of initial purity and added interstitial content. Using strict clean processing together with either ultra high purity or commercial purity alloys, the effects of interstitial elements (essentially O, but also C and N) on microstructure and hardness, yield stress and fracture strain have been studied for both fully lamellar microstructures and duplex microstructures. The results are clear and similar trends are observed : as long as they do not precipitate, these stabilise the lamellar microstructure and affect the kinetics of the α-γ phase tranformation, leading to a higher than equilibrium value for the α2phase for continuous cooling. Both the lamellar spacing and the α2phase fraction correlate with increased hardness and yield stress, and also with decreasing fracture strain. The effects are significant.
Effect of B Addition on Thermal Stability of Lamellar Structure in Ti-47Al-2Cr-2Nb Alloys
Authors: Yamamoto Y. , Evans N. D. , Maziasz P. J. , Liu C. T.
Published: April 2011

Thermal stability of fully lamellar microstructures in Ti-47Al-2Cr-2Nb (at.%) alloys with and without B additions has been evaluated in the temperature range of 800 to 1200°C. The alloy with 0.15B exhibits an α2 + γ fully lamellar microstructure containing ribbon-like structures (TiB2+β) inside the lamellar colonies. During aging at 800 and 1000°C, β particles surrounded by γ grains form adjacent to the ribbon-like structures. The formation of these grains is attributed to the precipitation of thin plate-like β phase along {1100} within the TiB2 ribbon particles, resulting in the loss of α2 plates around the ribbon-like structure by scavenging Ti. This allows coarsening γ lamellar plates to form new γ grains, and then the ribbon-like structure completely dissolves to leave only β particles. At 1200°C, discontinuous coarsening (DC) of the lamellae becomes the dominant mode of microstructural change for all the alloys. However, the ribbon-like structures in the alloy with B additions play a role in pinning the DC cells, which leads to higher thermal stability of the lamellar microstructure in that alloy.
Structure/Property Relationships of Seashells
Authors: Scurr David J. , Eichhorn Stephen J.
Published: April 2011

This study uses various characterisation techniques on the razor shell (Ensis siliqua), to relate the shell's microstructure to its mechanical properties. Scanning electron microscopy (SEM) has shown that the outer and inner regions of the shell are composed of simple and complex crossed lamellar microstructures respectively. These layers are interspersed by prismatic layers of a completely different crystallographic orientation. Nanoindentation and microhardness measurements have shown that the structure is anisotropic, and Raman band shifts have been observed within these indented/deformed areas of shell, showing that the microstructure deforms rather than generating surface damage. The use of energy variable synchrotron X-ray diffraction has shown that the calcium carbonate crystals of the shell are preferentially orientated as a function of depth and that opposing residual stresses exist at the outer and inner regions of the shell. This study has analysed several microstructural features of the shell and provided an insight into how they prevent failure of the material.
Microstructure of Brachiopod Shells - An Inorganic/Organic Fibre Composite with Nanocrystalline Protective Layer
Authors: Griesshaber E. , Schmahl W. , Neuser R. , Job R. , Bluem M. , Brand U.
Published: April 2011

We investigated the ultrastructure of the modern calcitic brachiopods Megerlia truncata (Linnaeus) and Terebratalia transversa (Sowerby) with SEM, electron backscattering diffraction and microhardness indentation. The outer, primary shell layer can be regarded as a nanocrystalline thin film that forms a hard protective coating around the inner, much softer secondary layer that can be expressed as an inorganic/organic fibre composite. The fibrous, curved growth of the secondary shell layer crystals occurs in arbitrary directions perpendicular to the <0 0 0 1> triad symmetry direction of calcite and is most likely obtained by simple confinement to a protein sheath rather than by biomolecular adsorbates blocking growth of any specific crystal face. The curvature of the fibres is caused by rearrangements of the secreting cell array during growth, whereby the existing crystal lattice is not distorted. It serves as a substrate for continued crystal growth. Thus biologically mediated calcite crystallization is a purposeful process and seems to be significantly different to the inorganic crystallization of calcite.
Structure Property Characterization of Nonlinear Optical Materials
Authors: Rogers Joy E. , Slagle Jonathan E. , McLean Daniel G. , Hall Benjamin C. , Cooper Thomas M. , Fleitz Paul A.
Published: April 2011

This research is comprised of understanding the linear photophysical properties of various dyes to better understand the more complicated nonlinear optical properties. Determining structure property relationships of a series of structurally closely related chromophores is the key in understanding the drivers for the various photophysical properties. In this paper we survey the effect of physically changing the Pt poly-yne structure on the S0-S1 and T1-Tn absorption properties for each of the chromophores. A series of structurally modified platinum poly-ynes have been studied using experimental methods including UV/Vis absorption and nanosecond laser flash photolysis. We found that with extension of the ligand length both the ground and triplet excited state absorption shift to lower energies. Comparing the absorption properties of the ligands and butadiynes with the platinum containing versions reveal that the S1 and Tn exciton is localized on one portion of the ligand with extension and not conjugated through the whole molecule. Changing the phosphine R group results in little effect to the absorption properties except when the R group is conjugated in the case of phenyl. However, changing the R group results in varied materials properties.
Platinum-Functionalized Chiral Molecular Squares as Light-Emitting Materials
Authors: Zhang Lin , Niu Yu-Hua , Jen Alex K.-Y. , Lin Wenbin
Published: April 2011

A family of new chiral metallocycles based on Pt(II) diimine metallocornors and bis(acetylene) bridging ligands have been synthesized, and characterized by a variety of techniques including 1H and 13C NMR, UV-visible, luminescence, infrared, and circular dichroism (CD) spectroscopies, and mass spectrometry. All metallocycles exhibit very strong phosphorescence with quantum yields of 8.3 to 15.7%. Chiral Pt(II)-based molecular squares were used as the light-emitting layer in multiplayer devices, and a maximum brightness of 5470 cd/m2 with a maximum luminous efficiency of 0.93 cd/A was achieved.
Optical and Electronic Properties of Metal-containing Poly-ynes and their Organic Precursors
Authors: Jura Marek , Koentjoro Olivia F. , Raithby Paul R. , Sharp Emma L. , Wilson Paul J.
Published: April 2011

A series of platinum(II) di-yne complexes with the general formula [PhPt(PR3)2-C≡C-X-C≡C-Pt(PR3)2Ph] where R = Et, nBu and X = a range of extended hetero-aromatic spacer groups, have been prepared by the coupling reaction between two molar equivalents of [PhPt(PR3)2Cl] and one molar equivalent of the terminal dialkyne, HC≡C-X-C≡CH, in the presence of CuI catalyst. The complexes have been characterised by IR, NMR and optical spectroscopy. These materials, which are precursors to related platinum(II) poly-yne polymers, have been specifically designed to be incorporated into metal-molecule-metal junctions in nanoelectronic devices.
Percolation-Enhanced Supercontinuum and Second-Harmonic Generation from Metal Nanoshells
Authors: Rohde Charles , Hasegawa Keisuke , Chen Aiqing , Deutsch Miriam
Published: April 2011

We present results for linear and nonlinear light scattering experiments from percolative silver nanoshells on dielectric silica cores. Using ultrashort pulsed laser illumination we observe strong nonlinear optical (NLO) responses from single metallodielectric core-shell (MDSC) spheres and disordered MDSC sphere aggregates. Finally, combining scaling theory with core-shell Mie scattering formalism we obtain a new model for the observed linear extinction signals.
Ambipolar injection in a submicron channel light-emitting tetracene transistor with distinct source and drain contacts
Authors: Reynaert J. , Cheyns D. , Janssen D. , Arkhipov V. I. , Borghs G. , Genoe J. , Heremans P.
Published: April 2011

Over the last decade, organic semiconductor thin film transistors have been the focus of many research groups because of their potential application in low-cost integrated circuits. Recently, an organic light-emitting field-effect transistor (OLEFET) was reported. In an OLEFET structure, optimal injection of both holes and electrons into the light-emitting layer are required for maximum quantum efficiency, whereas the gate serves as a controlling electrode. In this work, we achieved an OLFET structure with interdigitated hole-injecting Au and electron-injecting Ca contacts within a submicrometer channel length. Both contacts are bottom contacts to the upper-lying tetracene organic semiconductor. The study of IV-characteristics and light emission from these devices shined light on the underlying physics of the OLEFETs.
Novel and Efficient electroluminescent organo-iridium phosphorescent OLED materials
Authors: Huang Heh-Lung , Shen Kou-Hui , Jhu Miao-Cai , Tseng Mei-Rurng , Liu Jia-Ming
Published: April 2011

We investigated and synthesized different orientation and substituted group of the thieno-pyridine framework organo-iridium complexes (PO-01, PO-02, PO-03). These materials exhibited yellow light. Fabrication of these emissive phosphorescent dopants with the device configuration of ITO/ NPB/ CBP: Ir-complex (4–6%) /BCP/Alq3/LiF/Al showed the EL emitting peak from 532nm to 564nm. The electroluminescent efficiencies of the devices were from 9.62 lm/W to 30.41 lm/W and maximum brightness was all above 7000 cd/m2. We demonstrated high-efficiency, high-brightness and saturated yellow Ir-complex phosphorescent materials for OLED.
Photo-induced Optical and Chemical Properties of Polysilane/Inorganic Nano-Hybrids
Authors: Matsukawa Kimihiro , Matsuura Yukihito
Published: April 2011

Polysilane/inorganic (silica, titania) nano-hybrids might be attractive materials for organic photonics. Polymethylphenylsilane (PMPS)/silica nano-hybrid thin films were prepared by a sol-gel reaction of PMPS block copolymers with alkoxysilanes. The refractive index of hybrid thin films could be controlled with the composition ratio of PMPS, and the value was changed by UV irradiation accompanying photodecomposition of PMPS. After development of the irradiated hybrid thin films, nano porous (ca. 20nm) silica thin films were generated by removing the decomposed PMPS segments and a high refractive index difference occurred between irradiated and non-irradiated part in the hybrid thin films. Furthermore, under photodecomposition of polysilane copolymers, polysilane functioned as a reducing agent of gold (III) ions to prepare the gold nanoparticles.
Crystallization of POSS in a PEG-Based Multiblock Polyurethane: Toward A Hybrid Hydrogel
Authors: Wu Jian , Ge Qing , Burke Kelly A. , Mather Patrick T.
Published: April 2011

Building upon earlier success in forming materials with crystalline ordering of POSS via the telechelic architecture with POSS end-capping polyethylene glycols, here we report similar ordering in PEG-POSS thermoplastic polyurethane applicable to a novel hybrid hydrogel. Thus, a unique series of hybrid thermoplastic polyurethanes (TPUs) were synthesized using poly(ethylene glycol) (PEG) as soft segment and incorporating an isobutyl-functionalized POSS diol (TMP POSS diol) in the hard segment. The molecular weight of PEG was systematically varied to include 10, 20, and 35 kDa while the mole ratio of PEG to POSS diol (as chain extender) was chosen as 8:1. The diisocyanate employed for TPU polymerization was 4, 4'-methylenebis(phenyl-isocyanate) (MDI). Wide-angle X-ray diffraction (WAXD) studies revealed that both the hydrophilic soft segments (PEG) and hydrophobic hard segments (POSS) can form crystalline structures driven by micro-phase separation, itself due to thermodynamic incompatibility. Differential scanning calorimetry (DSC) and rheological studies revealed that thermal history is important in controlling the crystallization of a POSS-rich nanophase. Increasing the cooling rate monotonically decreases the crystallinity of POSS-rich phase and results in a decrease in the ultimate dynamic storage modulus following POSS crystallization and an increase of the loss angle for temperatures above Tm of PEG and below Tm of POSS. We conclude that both composition and thermal history are key factors in determing the internal network built by the POSS nanophase, which will have a significant influence on the properties of the resulting hybrid hydrogels now being studied.
Bioactive organic-inorganic hybrid aerogels
Authors: Esquivias Luis , Morales-Flórez Víctor , Piñero Manuel , Rosa-Fox Nicolás de la , Ramírez Julio , González-Calbet José , Salinas Antonio , Vallet-Regí María
Published: April 2011

We have prepared organic-inorganic hybrid materials (OIHM), incorporating an organic phase in the inorganic precursor sol, using high power ultrasound for assistance with agitation. A sono-ormosil results after gelation. Colloidal silica particles have been added to these hybrids to enable network porous volume and pore radius to be tailored to specific requirements. Finally, in vitro bioactivity of this material has been promoted by adding calcium to the initial sol. The structure and bioactivity of these materials have been subjected to preliminary study, including their mechanical behaviour. These materials have a very fine structure especially after colloidal silica particles have been included. When immersed in a solution simulating blood plasma, they are bioactive, and the sample with colloid particles presents a better behaviour in vitro
Di-Urethane Cross-linked Poly(oxyethylene)/Siloxane Nanohybrids Doped With Eu(CF3SO3)3
Authors: Gonçalves M. C. , de Zea Bermudez V. , Sá Ferreira R. A. , Ostrovskii D. , Carlos L. D.
Published: April 2011

Attractive sol-gel derived di-urethane cross-linked poly(oxyethylene), POE/siloxane hybrids (di-urethanesils) doped with europium triflate, Eu(CF3SO3)3 were examined by Fourier Transform mid-infrared (FT-IR), Raman (FT-Raman) and Photoluminescence spectroscopies with the main goal of elucidating the chemical environment of the cations in these materials. In these hybrids the POE chains contain about 13 oxyethylene repeat units. Samples with compositions ∞ > n ≥ 5 (where n indicates the ratio of (OCH2CH2) moieties per Eu3+ion) were investigated. The FT-IR and FT-Raman data obtained provided unequivocal evidence that the ether oxygen atoms of the polymer chains start to interact with the Eu3+ ions at n = 20. The presence of a crystalline POE/Eu(CF3SO3)3 complex was detected at n ≥ 20. Photoluminescence results demonstrated that the doped di-urethanesils studied here are room temperature (RT) efficient full-color emitters. Two distinct cation local sites were unequivocally identified at n = 200 and 20. These Eu3+ local coordination sites involve the oxygen atoms of the urethane carbonyl groups and weakly coordinated Eu3+/CF3SO3 ionic species. For the most concentrated hybrid (n=5) evidences of a third local-environment probably involving the oxygen atoms of the polymer chains was observed.