bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of Microstructure of Grain Boundaries of ZnO Varistors using Backscattered-electron
Authors: Takada Masayuki , Sato Yuuki , Yoshikado Shinzo
Published: February 2009

The impurities segregated at the grain boundary of ZnO grains, such as Bi2O3, are important factor to obtain the nonlinear voltage-current (V-I ) characteristics of a Bi-added ZnO varistor. The deterioration of V-I characteristics progresses with voltage application. It has been reported that one of the reasons for this deterioration is the movement of oxide ions and interstitial Zn2+ ions across grain boundaries and around the neighborhood of grain boundaries. Thus, the mobility of ions and the pathway of the current formed by voltage application strongly correlate with the structure of grain boundary, such as the crystal orientation of ZnO grains, the phase of Bi2O3 at the grain boundary, and segregated grains. In the present studies, the structure of grain boundary for the ZnO varistor has been evaluated by composition images obtained from energy dispersive X-ray spectrometry (EDS) with scanning electron microscope (SEM) or with transmission electron microscope (TEM). However, the elemental mapping obtained from EDS with SEM is low resolution and the distribution of elements is obscure. Furthermore, the observation of varistor with TEM is difficult because the sample used for TEM needs precise processing. On the other hand, a composition image with high contrast of tone can be easily obtained using back-scattered electron (BSE) detector with SEM, although BSE detector is lack in the quantitative analysis. In this study, to clarify the microscopic distribution of impurities at the grain boundary with simple method, we observed the fractured surface of ZnO varistor using BSE detector with SEM. For the fractured surface, two types of fracture exist; grain boundary fracture and transcrystalline fracture. The microscopic distribution of impurities can be obtained by observing the surface of grain boundary fracture. The characteristics of ZnO varistor deeply correlate with the state of impurities at the grain boundary such as Bi2O3. To clarify the distribution of these impurities, the fractured surface of Bi-Mn-Co-Sb-added ZnO varistor was observed using SEM, EDS, and BSE detector. It was found that the deposit of Bi2O3 as additive had two types of shape on the surface of grain boundary fracture; spot-like and sheet-like, for Bi-Mn-Co-Sb-added ZnO varistor. With dissolving SiO2 in Bi2O3, the surface tension of Bi2O3 decreased and the sheet-like deposit of Bi2O3 increased, while the spot-like deposit of Bi2O3 decreased. Moreover, when the sample was annealed at 700°C, the surface free energy (surface tension) decreased because Zn2+ and Bi3+ were speculated to become the compound such as Bi7.65 Zn0.35 O11.83 and move to the triple point or line.
Excitation Pathways of Rare Earth Ions by Energetic Electrons
Authors: Penn Tafon Samson , Fleischman Zackary , Maurer Leon , Dierolf Volkmar
Published: February 2009

Using cathodoluminescence measurements, we studied the excitation of rare earth ions in LiNbO3and compare it with previously studied Eu ions in GaN. We find that in both hosts and all dopants the most efficient excitation pathways involves a defect traps that capture the energy from the electron-hole pairs created in the host by E-beam irradiation. Even then the excitation efficiency in LiNbO3is very low. Moreover, only a small fraction (<10-4) of the RE ions that are optically active can be excited through this pathway. We explain this behavior by a negligible direct excitation and a strong dependence of the excitation efficiency on the distance between the defect trap and the rare earth ion. The density of the defect traps is small such that many rare earth ions are far away from traps.
Optical and Luminescent Properties of Highly Oriented Nanocrystalline Gd2-xEuxO3 Thin Films
Authors: Jáuregui-Rosas Segundo , Perales-Pérez Oscar , Singh S. P. , Tomar M. S. , Jia Wei-Ji , Vásquez Omar
Published: February 2009

Highly crystalline and transparent Eu-doped Gd2O3 thin films were produced through a modified sol-gel method that did not require the use of any chelating agent. The effect of the atomic fraction of Eu3+ ions (‘x’ =0.05-0.30) on the structural, optical and luminescent properties has been studied. X-ray diffraction studies showed the preferential growth of Gd2-xEuxO3 thin films along the (400) plane corresponding to the cubic phase. UV-vis measurements revealed the high film transparency of the films in the visible region and a band gap value of 5.3eV. It has also been observed that the luminescence properties of the films were strongly dependent on both, the excitation wavelength and Eu concentration; the most efficient excitation conducive to red luminescence was achieved at the absorption band of Gd2O3 host (229nm). Under this condition all films exhibited strong red emission that is characteristic of Eu3+ ions. The emission intensity was also dependent on the doping level; the most intense luminescence was obtained at ‘x’=0.15. The drop in the luminescence intensity observed for ‘x’ values higher than 0.15 was attributed to quenching concentration effect.
First Eu3+@Organo-Si(HIPE) Hybrid Macro-Mesocellular Foams Generation and Associated Luminescent Properties
Authors: Brun Nicolas , Julian-Lopez Béatriz , Hesemann Peter , Laurent Guillaume , Deleuze Hervé , Sanchez Clément , Achard Marie-France , Babeau Annick , Backov Rénal
Published: February 2009

Using both β-diketone and malonamide organosilane derivatives and silica Si-HIPE macro-mesocellular foams (acronym refers to the High Internal Phase Emulsion process), organically modified silicates (ORMOSILs) with chelating functionality have been synthesized. The organic functionalities have been anchored to the silica porous networks by both a two-steps grafting method, relating to grafted gOrgano-Si(HIPE), and a one-step co-condensation process, relating to Organo-Si(HIPE). The loading of monoliths by lanthanides was performed by impregnation of an europium (III) salt in solution, leading to a new Eu3+@(g)Organo-Si(HIPE) hybrid foams series. The resulting materials have been thoroughly characterized via a large set of techniques such as SEM, TEM, SAXS, mercury intrusion porosimetry, nitrogen adsorption, FTIR and 29Si CP MAS NMR. Luminescence behavior of this Eu3+@Organo-Si(HIPE) series was also studied and the effects of environment and europium concentration will be discussed.
Solution Processed Self-Assembled Monolayer Gate Dielectrics for Low-Voltage Organic Transistors
Authors: Ball James , Wöbkenberg Paul H , Colléaux Florian , Kooistra Floris B , Hummelen Jan C , Bradley Donal D. C. , Anthopoulos Thomas D
Published: February 2009

Low-voltage organic transistors are sought for implementation in high volume low-power portable electronics of the future. Here we assess the suitability of three phosphonic acid based self-assembling molecules for use as ultra-thin gate dielectrics in low-voltage solution processable organic field-effect transistors. In particular, monolayers of phosphonohexadecanoic acid in metal-monolayer-metal type sandwich devices are shown to exhibit low leakage currents and high geometrical capacitance comparable to previously demonstrated self-assembled monolayer (SAM) type dielectrics but with a higher surface energy. The improved surface energy characteristics enable processing of a wider range of organic semiconductors from solution. Transistors based on a number of solution-processed organic semiconductors with operating voltages below 2 V are also demonstrated.
Flexible Audible Display using ITO on PVDF and Its Interface Analysis
Authors: Park Dong-Hee , Ie Sangyub , Bae Byeong-Taek , Choi Won-Kook
Published: February 2009

Flexible audible display (FAD) based on PVDF(Poly-vinylidene fluoride) film is researched to combine piezoelectric property with light emitting diode. Indium-Tin-Oxide (ITO) is deposited on PVDF film at low temperature condition with the vacuum web coating. Under the optimized working pressure and the oxygen/argon pressure ratio, ITO on PVDF shows good electrical property of sheet resistance about 120 ohm/sq at 160 nm thickness, good transmittance of 76%, and sound pressure level more than 70 dB. OLED device with Al/LIF/Alq3/ NPB/ 2T-NATA structure is fabricated on ITO/PVDF and shows the turn-on voltage of 3.5 V and the maximum luminescence of 1011.2 cd/cm2 at the driving voltage of 13 V. C-F chemical bondings are measured to decrease in the XPS spectrum of ITO/PVDF interface. This is originated from the bonding scission caused by incident energetic particles, such as sputtered atoms, backscattered Ar ions, and negative O ions during the sputtering and deposition process. These particles have energy, which is simulated by TRIM and is more than 5 eV, enough to cause the scission of C-F bondings with binding energy of 4 eV/atom.
In-situ Study of Electromigration-induced Grain Rotation in Pb-free Solder Joint by Synchrotron Microdiffraction
Authors: Chen Kai , Tamura Nobumichi , Tu King-Ning
Published: February 2009

The rotation of Sn grains in Pb-free flip chip solder joints hasn't been reported in literature so far although it has been observed in Sn strips. In this letter, we report the detailed study of the grain orientation evolution induced by electromigration by synchrotron based white beam X-ray microdiffraction. It is found that the grains in solder joint rotate more slowly than in Sn strip even under higher current density. On the other hand, based on our estimation, the reorientation of the grains in solder joints also results in the reduction of electric resistivity, similar to the case of Sn strip. We will also discuss the reason why the electric resistance decreases much more in strips than in the Sn-based solders, and the different driving force for the grain growth in solder joint and in thin film interconnect lines.
Evaluation of Adhesion Between UV-cured SiOC Film and Si Substrate by Nanoindentation Method
Authors: Takeda Masaaki , Matoba Nobuhiro , Oishi Manabu , Sakai Mototsugu
Published: February 2009

It is important to quantitatively measure the adhesion strength at the interface in a small area of electronics devices to ensure their reliability. In this study, a simple technique for measuring the adhesion using the nanoindentation method by considering the energy balance during the indentation process was proposed and applied to measure the adhesion of three kinds of UV-cured SiOC films with a thickness of 500 nm on a Si substrate.
The discontinuous points of approximately 300 nm in depth appeared in all the indentation curves with a high reproducibility, and it was confirmed that these points reflect the occurrence of an interfacial delamination. The total dissipated energies calculated from the load vs. indentation depth curves indicate a good correlation with the indentation load. The delamination energies can be estimated using this relationship. The energy release rates at the interface of the UV-cured SiOC films calculated from the energy balance increases with the increasing UV curing time.
From these result, we can confirm the technique proposed in this study is quite useful to simply and quantitatively measure the adhesion, especially against a thin film or the small area, even if the film is ductile.
Mechanical and Electrical Reliability of a Chronically Implanted Metal-Polyimide Electrode Array
Authors: Yeager John D. , Phillips Derrick J. , Rector David M. , Bahr David F.
Published: February 2009

A flexible electrode array consisting of a thin metal film on a polymer substrate has been developed for neural implantation in rats. The biocompatible arrays record cortical brain signals from awake and mobile rats in order to gather significant neurological data. Four point bend testing of the metal-Kapton system has been used to characterize the interfacial toughness, and therefore the mechanical durability, of the array. Several different adhesion layers on were evaluated using this method. Use of a titanium-tungsten interlayer increases the mixed-mode fracture toughness from approximately 1 J/m2 to approximately 2 J/m2, while a titanium interlayer provides a toughness of more than 4 J/m2. Gold-Kapton arrays were implanted in rats for periods exceeding 200 days, and neural recordings were taken frequently. The arrays exhibit excellent long-term reliability, with no decrease in signal recording capability over the course of the implantation.
Hydrogen Ordering and Metal-Semiconductor Transitions in Rare-Earth Hydrides
Authors: Vajda P.
Published: February 2009

After an introduction to the rare earth – hydrogen phase diagram, stressing the often broad existence range of the solid solution (α), dihydride (β) and trihydride (γ) phases, we are describing in detail the fluorite-type dihydride and its superstoichiometric composition, RH2+x, where the x atoms occupy the available octahedral interstitial sites. It is shown how these additional x atoms interact with each other to form ordered H superlattices (sometimes distorting the cubic CaF2structure) and how the latter influences the electronic structure of the systems modifying the magnetic properties and/or leading to metal-semiconductor transitions.
RBS and micro-PIXE study of I and Cs Heterogeneous Retention on Concrete
Authors: Alonso Ursula , Missana Tiziana , García-Gutiérrez Miguel , Patelli Alessandro , Ceccato Daniele , Rigato Valentino , Albarran Nairoby , Rojo Henar , Lopez Trinidad
Published: February 2009

A combination of two nuclear ion beam techniques, Rutherford Backscattering Spectrometry (RBS) and micro-Particle Induced X-Ray Emission (uPIXE) was tested to evaluate both diffusion profiles and radionuclide spatial distribution of radionuclides (RN) onto cement-based materials. The methodology was tested on a Spanish reference backfill concrete, used as engineering barrier in low-level radioactive waste repositories, using two elements (Cs and I) with different sorption behaviour onto the cement. The applicability and limitations of the selected methodology is discussed for both elements.
Conduction and Disorder in Y3NbO7 - Zr2Y2O7
Authors: Marrocchelli Dario , Madden Paul A. , Norberg Stefan T. , Hull Stephen
Published: February 2009

The construction of interaction potentials for the Y0.5+0.25xNb0.25xZr0.5–0.5xO1.75 system, on a purely ab-initio basis, is described. These potentials accurately reproduce experimental data on both the structure and the dynamics of these systems; the computer simulations also reproduce the experimental trend of the conductivity, which decreases as x increases, and of the level of static disorder within the O2− sublattice, which increases with x. A detailed analysis of these phenomena shows that the static disorder in Y3NbO7 is caused by the high Nb5+ charge and that in this material the conduction is heterogeneous, i.e. some anions are completely immobile while some others are very mobile. The role of the cation sublattice is explained in detail.
Structure and Electrochemistry of Carbon-Bromine Nanocomposite Electrodes for Electrochemical Energy Storage
Authors: Barpanda Prabeer , Amatucci Glenn G
Published: February 2009

Activated carbons have been mechanochemically modified by bromine incorporation through high-energy milling route. Varying the milling duration and bromine content, carbon-bromine nanocomposites of different compositions were fabricated. The highly reactive and electronegative bromine reacts with host carbon, which can modify its characteristic properties. We have examined the effect of bromination on the structure, chemistry, morphology and electrochemical properties of a mesoporous activated carbon. Bromination leads to possible charge transfer reaction, structural disordering with polybromide formation. Consequently, the non-faradaic capacitance improves and a faradaic pseudocapacitive reaction occurs at 3.1 V and a more traditional bromine reduction at 3.5V. The formation of carbon-bromine nanocomposites was found to deliver improved gravimetric and volumetric capacity. The effect of bromination on physical and electrochemical properties of activated carbons have been presented and contrasted to that of iodine incorporation.
PtRu Nanoparticle Catalytic Activity Enhanced by the Ligand Effect
Authors: Goto Shuji , Li Yuli , Nagasawa Naomi , Senoo Tadashi , Noda Kazuhiro , Kudo Yoshihiro , Maesaka Akihiro , Hatazawa Tsuyonobu
Published: February 2009

We synthesized a methanol electrocatalyst with high activity and low noble metal content. The electrocatalyst consists of carbon&supported PtRu nanoparticles, which have 1-2 Pt monoatomic layers on Ru nanocores. In spite of the pure Pt surface, the catalyst showed high catalytic activity when used in the anode of a direct methanol fuel cell. Clearly the underlying Ru atoms modified the property of the surface Pt atoms, bringing about the high catalytic activity.
Metallographic and numerical characterization of MgH2-Mg system
Authors: Aurora Annalisa , Celino Massimo , Cleri Fabrizio , Gattia Daniele Mirabile , Giusepponi Simone , Montone Amelia , Antisari Marco Vittori
Published: February 2009

The remarkable ability of magnesium to store significant quantities of hydrogen has fostered intense research efforts in the last years in view of its future applications where light and safe hydrogen-storage media are needed. Magnesium material, characterized by light weight and low cost of production, can reversibly store about 7.7 wt% hydrogen. However, further research is needed since Mg has a high operation temperature and slow absorption kinetics that prevent the use in practical applications. For these reasons a detailed study of the interface between Mg and MgH2 is needed. Further insights are gained by characterizing the Mg-MgH2 system from both the experimental and the numerical point of view.

The study of the MgH2-Mg phase transformation in powder samples has been performed to gain detailed metallographic information. A method for studying this phase transformation by cross sectional samples scanning electron microscopy observation of partially transformed material has been developed. This method exploits the peculiar features of this system where the MgH2 phase is insulating and the Mg is a metallic conducting phase. This difference can induce a contrast between the two phases owing to the different secondary emission yield. Further insights are gained by characterizing Mg-MgH2 interfaces by means of accurate first-principle molecular dynamics simulations based on the density-functional theory. Extensive electronic structure calculations are used to characterize the equilibrium properties and the behavior of the surfaces in terms of total energy considerations and atomic diffusion.
Phase Stability and Thermoelectric Properties of Half-Heusler (Ma, Mb)NiSn (Ma, Mb = Hf, Zr, Ti)
Authors: Kimura Yoshisato , Ueno Hazuki , Kenjo Takahiro , Asami Chihiro , Mishima Yoshinao
Published: February 2009

Aiming to improve thermoelectric properties of half-Heusler (Ma,Mb)NiSn alloys (Ma,Mb = Hf, Zr, Ti), phase equilibria in the (Ma,Mb)NiSn systems were investigated focusing on the phase separation of TiNiSn from ZrNiSn and HfNiSn while (Zr,Hf)NiSn forms all proportion miscible solid solution. Diffusion couples consisting of liquid Sn and solid (Ti,Zr)Ni were used to examine the partitioning behavior which is associated with T-rich and Ti-poor half-Heusler phase separation during the reaction at the interface. Thermal conductivity can be reduced in (Ma0.5,Mb0.5)NiSn and (Ti0.13,Zr0.87)NiSn alloys due to the solid solution effect of M-site substitution. (Ti0.13,Zr0.87)NiSn alloy has high potential as a ecological thermoelectric material.
Microstructure and Tensile Ductility of a Ti-43Al-4Nb-1Mo-0.1B Alloy
Authors: Droessler Laura M. , Schmoelzer Thomas , Wallgram Wilfried , Cha Limei , Das Gopal , Clemens Helmut
Published: February 2009

The microstructural development of a forged Ti-43Al-4Nb-1Mo-0.1B (in at%) alloy during two-step heat-treatments was investigated and its impact on the tensile ductility at room temperature was analyzed. The investigated material, a so-called TNM™gamma alloy, solidifies via the β-route, exhibits an adjustable β/B2-phase volume fraction and can be forged under near conventional conditions. Post-forging heat-treatments can be applied to achieve moderate to near zero volume fractions of β/B2-phase allowing for a controlled adjustment of the mechanical properties. The first step of the heat-treatment minimizes the β/B2-phase and adjusts the size of the α-grains, which are a precursor to the lamellar γ/α2-colonies. However, due to air cooling after the first annealing step, the resulting microstructure is far from thermodynamic equilibrium. Therefore, a second heat-treatment step is conducted below the eutectoid temperature which brings the microstructural constituents closer to thermodynamic equilibrium. It was found that temperature and duration of the second heat-treatment step critically affect the solid-state phase transformations and, thus, control the plastic fracture strain at room temperature. Scanning and transmission electron microscopy studies as well as hardness tests have been conducted to characterize the multi-phase microstructure and to study its correlation to the observed room temperature ductility.
Initial Stages of Lamellae Formation in High Nb Containing γ-TiAl Based Alloys
Authors: Cha Limei , Scheu Christina , Dehm Gerhard , Schnitzer Ronald , Clemens Helmut
Published: February 2009

In this study a two-step heat treatment was applied to high Nb containing γ-TiAl based alloys in order to investigate the initial stage of the lamellae formation in ordered α2-grains as well as in massively transformed γm-grains. The first heat treatment step, conducted in the single α-phase field followed by oil quenching, leads to a microstructure consisting of supersaturated α2-grains and a small volume fraction of γm-grains. The second step of the heat treatment was performed below the eutectoid temperature, i.e. within the (α2+γ)-phase field region and was again followed by oil quenching. There, the formation of ultra-fine γ-lamellae takes place in the α2-grains and (some) fine α2-lamellae are formed in the γm-grains. In both cases the lamellae show a Blackburn orientation relationship with the matrix grain. It was found that the precipitation of γ-laths in the supersaturated α2-grains is faster than the formation of α2-laths in γm-grains. The characteristics of the initial stage of formation were investigated by transmission electron microscopy.
The Role of Fundamental Material Parameters for the Fluorine Effect in the Oxidation Protection of Titanium Aluminides
Authors: Zschau Hans-Eberhard , Schütze Michael
Published: February 2009

To improve the insufficient oxidation resistance of Titanium Aluminides at temperatures above 750°C the fluorine effect offers an innovative way. The focus of this paper is to define the fundamental material variables for the fluorine effect related to the macroscopic behaviour (oxidation resistance) and its long time stability.
The thermodynamic model predicted the fluorine effect for the TiAl within a corridor of total fluorine amount in terms of partial pressures. To realize the fluorine effect the required F-concentration [in at.-%] within the near surface region had to be found. Using fluorine ion implantation several fluences within 5e15 and 5e17 F cm-2 were implanted with an energy of 20 keV. The implantation depth profiles were calculated by using the Monte Carlo simulation code T-DYN and verified experimentally by using the non-destructive PIGE - technique (Proton Induced Gamma-ray Emission). After oxidation tests at 800°C – 1000°C a value of 2e17 F cm-2 / 20 keV was determined as an optimal implantation parameter set. Following these results the maximal fluorine concentration was identified to be a fundamental material variable for starting the alumina formation with a required fluorine amount of about 40-45 at.-%. However this maximum fluorine concentration showed a rapid decrease to values less than 5 at.-% only after a few hours of oxidation (900°C and 1000°C) followed by a slow decrease. Therefore the maximum fluorine concentration Cmax – now located at the metal/oxide – interface – was identified to be a fundamental parameter for the long time stability. An exponential decay function containing a constant term of about 1 at.-% was found to describe the time behaviour of Cmax for isothermal and cyclic oxidation (900°C, 1000°C). Because the alumina scale on the surface acts as a diffusion barrier for fluorine, the stability of Cmax is strongly influenced by the F-diffusion into the metal. From the F-depth profiles the diffusion coefficient of fluorine into the TiAl at 900°C was determined as a fundamental parameter for the long-term stability of Cmax showing a value of 1.56e-15cm2/s.
Microstructure and Compression Behavior of Ti3Al Based Ti-Al-V Ternary Alloys
Authors: Takahashi Tohru , Kiyohara Ayumu , Masujima Daisuke , Nagakita Jun
Published: February 2009

The ordered alloy phase of Ti3Al shows a rather wide solid solution range in aluminum and also in vanadium. Several Ti-Al-V ternary alloys have been prepared to investigate the alloy composition effect upon microstructure, crystallography, and mechanical characteristics. The materials containing 75, 70, and 65 at.% titanium, and 0 or 5 at.% vanadium were prepared by arc melting. Metallographic observation has revealed that the binary Ti-Al alloys contained somewhat coarse grains with about 100 μm grain diameter. In contrast to this, ternary alloys containing 5 at.% vanadium showed smaller grained microstructures with grain diameters around 15 μm. The grain size could not be adjusted to a unified value in the present study. X-ray diffraction study and microanalysis showed that the alloys contained single phase α2. Not every possible diffraction peak of the D019 ordered structure has been observed in the XRD patterns. The lattice parameters, a and c, were observed to decrease as the aluminum content increased and also when vanadium was added. Compression tests have been performed at various temperature ranging from an ambient temperature up to 1300K on rectangular parallelepiped specimens with 2mm×2mm×3mm dimensions. Alloys containing more aluminum showed higher strength, and vanadium addition enhanced the strength of the alloys. In some alloys deformability and strength are both enhanced by vanadium addition in some alloys. Temperature dependence of strength showed a little variation upon chemical compositions.
Plasma-Assisted Surface Modification of Two-Phase Intermetallic Alloy Composed of Ni3X Type Structures
Authors: Kaneno Yasuyuki , Matsumoto Naoki , Tsuji Noriyoshi , Tanaka Shinichi , Takasugi Takayuki
Published: February 2009

A two-phase intermetallic alloy composed of Ni3Al (L12) and Ni3V (D022) was plasma-nitrided or -carburized in dependence of temperature and time. It was found that the hardness of the surface layer of the present intermetallic alloy was enhanced by both plasma-nitriding (PN) and -carburizing (PC), and primarily depended on treating temperature; the maximum surface hardness of the alloy was shown by nitriding at around 850 K and by carburizing at 1025 K. In addition, the hardened layers due to PN and PC effectively kept their hardness up to a high temperature. The XRD analysis revealed that vanadium nitride (VN) and vanadium carbide (VC) were formed in the surface of the nitrided and carburized alloy, respectively, suggesting that the enhanced surface hardness was attributed to the dispersion hardening due to the nitrides and carbides.
Surface modification of Ni/Ni3Al two-phase foils by electrochemically selective etching
Authors: Lee H.Y. , Demura M. , Xu Y. , Wee D.M. , Hirano T.
Published: February 2009

Surface morphology after the selective etching of the γ matrix was examined in Ni(γ)/Ni3Al(γ´) two-phase foils with various microstructures controlled by the 98 % cold rolling and subsequent heat treatment at 873, 1073 and 1273 K for 0.5 h. In the cold-rolled state, the elongated pancakeshape γ´ precipitates were distributed in the γ matrix, and this structure was almost the same after the heat treatment at 873 K though the recrystallization partly started. These γ´ pancakes were partitioned into the fine blocky particles of 10~100 nm in the edge after the heat treatment at 1073 K and the γ´ blocks significantly became larger at 1273 K. These foils were electrochemically etched in the electrolyte of distilled water with 1 wt.% (NH4)2SO4 and 1 wt.% citric acid at a constant potential of 1.75 V for 5 h. In this etching, the γ matrix was selectively dissolved and the γ´ precipitates were left behind, yielding rough and irregular surface. The surface morphologies corresponded to the γ/γ´ two-phase structures, thus demonstrating that the two-phase structure can be used as a template to make the surface area larger. The foil heattreated at 1073 K had a number of the fine γ´ particles with 10~100 nm in size densely dispersed on the surface. Such fine surface structure was expected to improve the catalytic activity of Ni3Al for the hydrogen production reaction.
Electron Irradiation Induced Crystal-to-Amorphous-to-Crystal (C-A-C) Transition in Intermetallic Compounds
Authors: Nagase Takeshi , Takizawa Kazuya , Nino Akihiro , Umakoshi Yukichi
Published: February 2009

Mechanical atomic displacement in intermetallic compounds can be introduced by var-ious processes such as severe plastic deformation, mechanical milling and electron irradiation, resulting in the crystal-to-amorphous (C-A) transition and amorphous-to-crystal (A-C) transition in some alloy systems. Recently, unique atomic displacement-induced-phase transitions contain-ing both amorphization and crystallization was found: a crystal-to-amorphous-to-crystal (C-A-C) transition under electron irradiation and a cyclic C-A transition during mechanical milling. The features and predicting factors of alloy systems which undergo C-A-C transition under MeV electron irradiation are discussed based upon the analysis of experimental data reported to date in intermetallic compounds irradiated by High voltage electron microscope (HVEM).
An Intermetallic Precipitate Strengthened Materials for Cryogenic Applications
Authors: Han Ke , Xin Yan , Walsh Robert P.
Published: February 2009

In high field magnets, most of the structural materials operate at very low temperatures (e.g. 1.8 K) and high magnetic fields (e.g. >20 T). Such an extreme environments ask for demanding properties from the materials. Austenite stainless steels have been used for such an application for decades and provide good combination of mechanical strength and toughness at cryogenic temperatures. In the National High Magnetic Field Laboratory, we have studied intermetallic precipitate strengthened alloys for high field magnet and cryogenic applications. An examination of the data from an intermetallic precipitate strengthened alloys shows that intermetallic precipitate strengthened alloys can be used at cryogenic temperatures and have some superior properties in extreme environments. Based on our experimental data, we developed a new alloy that has even better properties than the current intermetallic precipitate strengthened alloys.
Pseudo Fine Particle Effect on Unstable Phase Transition of Gd2Al
Authors: Yazdani A. , Kamali Sarvestani N. , Osaty Araghi R.
Published: February 2009

The unusual duality of magnetic phase transition (especially high transition temperature, remarkable shoulder) is thought to be due to second phase impurities of pure Gd or Gd3Al2 or even both. The temperature dependence and field dependence of magnetization have been studied in the temperature range of 4.2-350 K in three different strengths of magnetic field to investigate the cause or/and the source of metamagnetic character which is a puzzle on Gdintermetallic compounds, IMC, in order to find the critical field needed to overcome the fluctuation field, above which the magnetic behavior of the system is stabilized, and a critical turning field is defined.

However for the clearance of intrinsic instability behavior and the nature (and source) of anisotropy in the Gd2Al system, the following experimental works has been prepared.

The study of the effect of increasing the magnetic field up to the critical “threshold“ field which is exactly the same as decreasing the conduction electron concentration “c.e.c” from Gd2Al to Gd2Au; The contribution of short range order as well as thermal fluctuation of short range exchange “Jsh” through the long – range interaction “Jl” which can be induced by localized s-f (or d-f) exchange. This effect can be the cause (or the source) of internal magnetic field Hin= and fluctuation field Hf=Hin-Hext.
Stacking Faults and Dislocation Dissociation in MoSi2
Authors: Cak Miroslav , Sob Mojmir , Paidar Vaclav , Vitek Vaclav
Published: February 2009

The intermetallic compound MoSi2 crystallises in the body-centred-tetragonal C11b structure and while it is brittle when loaded in tension, it deforms plastically in compression even at and below the room temperature. The ductility of MoSi2 is controlled by the mobility of 1/2〈331] dislocations on {013) planes but the critical resolved shear stress for this slip system depends strongly on the orientation of loading and it is the highest for compression along the 〈001] axis. Such deformation behaviour suggests that the dislocation core is controlling the slip on the {013)〈331] system. Since the most important core effect is dissociation into partial dislocations connected by metastable stacking faults the first goal of this paper is to ascertain such faults. This is done by employing the concept of the γ-surface. The γ-surfaces have been calculated for the (013) and (110) planes using a method based on the density functional theory. While there is only one possible stacking fault on the (110) plane, three distinct stacking faults have been found on the (013) plane. This leads to a variety of possible dislocation splittings and the energetics of these dissociations has been studied by employing the anisotropic elastic theory of dislocations. The most important finding is the non-planar dissociation of the 1/2〈331] screw dislocation that is favoured over the planar splittings and may be responsible for the orientation dependence of the critical resolved shear stress for the {013)〈331] slip system.
Chemical Bonding in Laves Phases Revisited: Atom Volumina in Cs-K System
Authors: Grin Yuri , Simon Arndt , Ormeci Alim
Published: February 2009

Laves phases comprise a large group of intermetallic compounds with general composition AB2 and multi-component derivatives. The crystal structures of Laves phases are often regarded as closest packing of spheres. This observation, beginning with very early work on Laves phases, has led many researchers over the years, to emphasize the role of geometrical factors in the formation of Laves phases. In order to develop a firm understanding of chemical bonding in Laves phases and assess the importance of geometrical factors, we undertake a first-principles-electronic structure-based chemical bonding analysis for several representatives. As a first step towards this goal we concentrate on the K-Cs system which contains the Laves phase CsK2 and the hexagonal Cs6K7 compounds. In such alkali-metal-only compounds it is generally expected that chemical bonding effects are minimal. Atom volumina and charge transfer investigations reported here, however, suggest that even in alkali metal-alkali metal Laves phases chemical bonding plays a non-negligible role.
An In-situ Electron Microscopy Study of Microstructural Evolution in a Co-NbCo2Binary Alloy
Authors: Kumar Sharvan , Jain Padam , Kim Seong Woong , Stein Frank , Palm Martin
Published: February 2009

The microstructure in a Co-rich, Co-15 at.% Nb alloy was characterized in the as-cast condition. A predominantly lamellar eutectic morphology composed of a Co-Nb solid solution and the C15 Laves phase NbCo2was confirmed by transmission electron microscopy. The C15 phase was heavily twinned, with only one variant of twins being present in the individual lamella, while the Co solid solution had the face centered cubic structure. In-situ heating to 600°C in the microscope confirmed the decomposition of the metastable Laves phase into a fine equiaxed, ˜10-20 nm grain size microstructure, and the product phase is the monoclinic Nb2Co7. The individual grains appear faulted. The matrix solid solution retained the fcc structure and no change in structure was observed on cooling to room temperature. Heating to temperatures as high as 1130°C leads to rapid grain growth in the Nb2Co7phase, and the nucleation and growth of a few new grains within the original grains; however, the reverse peritectoid transformation previously reported, was not observed.
Lattice-Gas-Decomposition Model for Vacancy Formation Correlated with B2 Atomic Ordering in Intermetallics
Authors: Biborski A. , Zosiak L. , Kozubski R. , Pierron-Bohnes V.
Published: February 2009

Thermal vacancy formation correlated with atomic ordering was modelled in B2-ordering A-B binary intermetallics. Ising Hamiltonian was implemented with a specific thermodynamic formalism for thermal vacancy formation based on the phase equilibria in a lattice gas composed of atoms and vacancies. Extensive calculations within the Bragg-Williams approximation [1] were followed by Semi-Grand Canonical Monte Carlo (SGCMC) simulations. It has been demonstrated that for the atomic pair-interaction energies favouring vacancy formation on A-atom sublattice, equilibrium concentrations of vacancies and antisite defects result mutually proportional in well defined temperature ranges. The effect observed both in stoichiometric and non-stoichiometric (both A-rich and B-rich) binary alloys was interpreted as a tendency for triple defect formation. In B-rich alloys vacancy concentration did not extrapolate to zero at 0 K, which indicated the formation of constitutional vacancies. Energetic conditions for the occurrence of the effects were analysed in detail. The modelled temperature dependence of vacancy concentration in the B2-ordering A-B binaries with triple defects will be included in the Kinetic Monte Carlo (KMC) simulations of chemical ordering kinetics in these systems with reference to the experimental results obtained for NiAl [2].
Formation of Wrinkle Patterns on Porous Elastomeric Membrane and Their Fabrication of Hierarchical Architectures
Authors: Cui Yue , Yang Shu
Published: February 2009

We report the formation of wrinkle patterns on porous elastomeric membrane and their fabrication of hierarchical architectures through mechanical stretching and replica molding. The technique builds upon a buckling instability of a stiff layer supported by a porous elastomeric membrane which was induced by surface plasma oxidation of the pre-stretched porous elastomer followed by removal of the applied mechanical strain to form wrinkle patterns, and replica molding of the deformed features on the porous membrane into epoxy to form hierarchical architectures through casting the UV-curable epoxy prepolymer and UV curing. We find that due to the existence of micropores on the membrane, the formation of wrinkle patterns is different from that formed on a continuous elastomeric film, and by varying the applied mechanical stretching strain condition and plasma oxidation condition, the wrinkle patterns could be either confined by the micropores on the membrane to exhibit a wavelength equal to its pitch or form wrinkles with much large wavelength compared with that formed on a continuous elastomeric film. Therefore, the micropillar arrays fabricated by replica molding could stand on different types of wrinkle patterns to form different hierarchical architectures. The method we illustrate here offers a simple and cost-effective approach to fabricate various hierarchical structures, and provides possibilities for potential applications in various fields, such as microfluidics, micro- and nanofabrication of complex structures, crystal formation, cell attachment, superhydrophobicity and dry adhesion.
Cellulose Electroactive Paper (EAPap): The Potential for a Novel Electronic Material
Authors: Kim Joo-Hyung , Kang Kwangsun , Yun Sungryul , Yang Sangyeul , Lee Min-Hee , Kim Jung-Hwan , Kim Jaehwan
Published: February 2009

Cellulose electro-active paper (EAPap) has attracted much attention as a new smart electronic material to be utilized as mechanical sensors, bio compatible applications and wireless communications. The thin EAPap film has many advantages such as lightweight, flexible, dryness, biodegradable, easy to chemically modify, cheap and abundance. Also EAPap film has a good reversibility for mechanical performance, such as bending movement, under electric field. The main actuation mechanism governed by piezoelectric property can be modulated by material direction and stretching ratio during process. In this paper we present the overview as well as fabrication process of cellulose EAPap as a novel smart material. Also we propose the method to enhance the piezoelectricity, its mechanical and electromechanical properties. In addition, the fabrication of high quality metal patterns with Schottky diode on the cellulose surface is an initiating stage for the integration of the EAPap actuator and electronic components. The integration of flexible actuator and electronic elements has huge potential application including flying magic carpets, microwave driven flying insets and micro-robots and smart wall papers.
Shape Memory Actuation by Resistive Heating in Polyurethane Composites of Carbonaceous Conductive Fillers
Authors: Gunes I. Sedat , Jimenez Guillermo A , Jana Sadhan C
Published: February 2009

The dependence of electrical resistivity on specimen temperature and imposed tensile strains was determined for shape memory polyurethane (SMPU) composites of carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), and carbon black (CB). The SMPU composites with crystalline soft segments were synthesized from diphenylmethane diisocyanate, 1,4-butanediol, and poly(caprolactone)diol in a low-shear chaotic mixer and in an internal mixer. The materials synthesized in the chaotic mixer showed higher soft segment crystallinity and lower electrical percolation thresholds. The soft segment crystallinity reduced in the presence of CNF and ox-CNF; although the reduction was lower in the case of ox-CNF. The composites of CB showed pronounced positive temperature coefficient (PTC) effects which in turn showed a close relationship with non-linear thermal expansion behavior. The composites of CNF and ox-CNF did not exhibit PTC effects due to low levels of soft segment crystallinity. The resistivity of composites of CNF and ox-CNF showed weak dependence on strain, while that of composites of CB increased by several orders of magnitude with imposed tensile strain. A corollary of this study was that a high level of crystallinity may cause a PTC effect and prevent any actuation through resistive heating. However, a carefully tailored compound which has reduced crystallinity and which requires minimum amount of filler may prevent PTC phenomenon and could supply necessary electrical conductivity over the operating temperature range, while offering enough soft segment crystallinity and rubberlike properties for excellent shape memory function.
Knowledge-based Approach to Gas Sorption in Glassy Polymers by Combining Experimental and Molecular Simulation Techniques
Authors: Heuchel Matthias , Hölck Ole , Böhning Martin , Siegert Martin R. , Hofmann Dieter
Published: February 2009

We present a method which allows to calculate gas sorption in complex polymers where, as slow processes, gas induced plasticization and volume dilation are important factors. Since the relaxational swelling of the polymer matrix that is observed at elevated gas concentrations takes hours or days, the swelling process is orders of magnitudes too slow to simulate the respective molecular dynamics in reasonable time and effort. To address this apparent incompatibility of experiment and simulation, we use single representative reference states from experiment and construct atomistic packing models according to these specifications. Gas sorption of CO2 and CH4 was successfully calculated on polysulfone, a 6FDA-polyimide, and a polymer of intrinsic microporosity, PIM-1, at 308 K and pressures up to 50 bar.
Silicides for Infrared Surface Plasmon Resonance Biosensors
Authors: Cleary Justin , Peale Robert , Shelton David , Boreman Glenn , Soref Richard , Buchwald Walter
Published: February 2009

Pt-, Pd-, Ni-, and Ti-silicide films on silicon were evaluated as conducting hosts for surface plasmon polaritons (SPP) in proposed long-wave IR (LWIR) attenuated total reflection biosensors. Original LWIR complex permittivity data was collected, from which SPP properties were determined and compared with those for noble metals. LWIR SPPs on silicide films were found to offer enhanced sensitivity to thinner biological entities than when usual metal films are used.
Application of a Chemically Adsorbed Monolayer and Polypyrrole Thin Film for Increasing the Adhesion Force between the Resin Substrate and the Plated Copper Layer
Authors: Ohkubo Yuji , Onishi Shogo , Miyazawa Satoshi , Soejima Kazuhiro , Ogawa Kazufumi
Published: February 2009

A chemically adsorbed monolayer containing pyrrolyl group (Pyrrolyl-CAM) was prepared between a plated copper layer and a resin substrate for increasing the adhesion force without roughening a surface of the resin substrate. Although it was not enough to increase the adhesion force between the resin substrate and the copper layer by using only Pyrrolyl-CAM, the sufficient adhesion force was obtained by preparing a polypyrrole thin film between Pyrrolyl-CAM and the copper layer.

Pyrrolyl-CAM and the polypyrrole thin film on the substrate were evaluated by an automat-ic contact angle meter and auger electron spectroscopy in order to analyze the condition of the films between the resin substrate and the copper layer.

The peel strength test was carried out in order to evaluate the adhesion force. The best ad-hesion force was 0.98 [N/mm], and the target value of 0.60 [N/mm] was sufficiently achieved.
Synthesis of Poly(Methylmethacrylate) Latex with Enhanced Rigidity through Surfactant Control
Authors: Wu Alex , Cho Kwun Lun , Liaw Irving Ian , Zhang Hua , Lamb Robert
Published: February 2009

Water-based polymer latexes have attracted much attention since their invention in the early 1950s. Its advantages for both general health and the environment were recognized as they emit far less volatile organic compounds (VOCs) than their solvent-based counterparts.

The performance of latex paints and coatings is directly proportional to the ease of particle deformation. This is the main driving force for the paints and coatings industry to focus its research efforts towards understanding its mechanism.

In contrast, little has been published with respect to enhancing latex's resistance against deformation despite such needs in applications such as templating porous ceramics for catalysis and biomaterial engineering. Specifically, the latex's resistance to deformation is crucial to retain a network of uniform pores for applications relating to enzyme immobilization and materials reinforcement.

The current study reports increased heat-resistance observed in latexes when synthesized using a rigid surfactant, dimethyl siloxane – ethylene oxide block copolymer (PDMS-PEO). The film formation process for this latex was deduced using atomic force microscopy and subsequent roughness analysis. A comparative study using a non-ionic long-chain hydrocarbon surfactant, morpholine oleate, was also conducted.