bluuebunny/crossref_metadata_2025 huggingface dataset:
The Surface Electronic Band Structure CoS2(001)
Authors: Wu Ning , Losovyj Ya. B. , Manno Michael , Leighton Chris , Dowben Peter
Published: February 2009

Angle-resolved photoemission was used to study the surface electronic band structure of ferromagnetic CoS2(below 120K) in high-quality single crystal samples. Strongly dispersing Co t2g bands are identified along the <100> k// direction. Fermi level crossings are identified along this Γ - X line (of the surface Brillouin zone) in higher resolution photoemission spectra, suggesting that the overall polarization may be controlled by the details of the band structure, particularly the surface band structure, rather than by exchange splitting on the Co atoms.
95Mo NMR Study of Crystallization in Model Nuclear Waste Glasses
Authors: Kroeker Scott , Farnan Ian , Schuller Sophie , Advocat Thierry
Published: February 2009

95Mo magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy is surprisingly sensitive to the local environment of tetrahedral molybdate species. A series of compounds related to expected crystallization products in nuclear waste glasses are probed to calibrate their spectral characteristics. Glasses formed with fast and slow quenching show a glassy peak corresponding to tetrahedral molybdate species. With slow quenching, a prominent sharp peak is observed, representing crystallinity. In sodium-borosilicate glasses with 2.5 mol% MoO3, the sharp peak corresponds to pure crystalline sodium molybdate. Cesium-sodium and lithium-sodium borosilicate glasses with Mo show crystalline peaks as well, and suggest that NMR may potentially be used to characterize mixed-cation molydates and more complex phase assemblages. While precise quantification of Mo in different phases is likely to be time-consuming, reasonable estimates can be obtained routinely, making 95Mo MAS NMR a useful tool for investigating phase separation and crystallization in model nuclear waste materials.
Experimental Work Conducted on MgO Characterization and Hydration
Authors: Deng Haoran , Xiong Yongliang , Nemer Martin , Johnsen Shelly
Published: February 2009

Magnesium oxide (MgO) is the only engineered barrier certified by the EPA for emplacement in the Waste Isolation Pilot Plant (WIPP), a U.S. Department of Energy repository for transuranic waste. MgO will reduce actinide solubilities by sequestering CO2 generated by the biodegradation of cellulosic, plastic, and rubber materials. Demonstration of the effectiveness of MgO is essential to meet the U.S Environmental Protection Agency's requirement for multiple natural and engineered barriers. In the past, a series of experiments was conducted at Sandia National Laboratories to verify the efficacy of Premier Chemicals LLC (Premier) MgO as a chemical-control agent in the WIPP. Since December 2004, Premier MgO is no longer available for emplacement in the WIPP. Martin Marietta Magnesia Specialties LLC is the new MgO supplier. MgO characterization, including chemical, mineralogic, and reactivity analysis, has been performed to address uncertainties concerning the amount of reactive constituents in Martin Marietta MgO. Characterization results of Premier MgO will be reported for comparison.
Particle size, solid-to-liquid ratio, and stir speed could affect the rate of carbonation of MgO slurries. Thus, it's reasonable to hypothesize that these factors will also affect the rate of hydration. Accelerated MgO hydration experiments were carried out at two or three levels for each of the above factors in deionized water at 70 °C. The Minitab statistical software package was used to design a fractional-factorial experimental matrix and analyze the test results. We also fitted the accelerated inundated hydration data to four different kinetic models and calculated the hydration rates. As a result of this study we have determined that different mechanisms may be important for different particle sizes, surface control for large particles and diffusion for small particles.
Investigation of Cathode Behavior of Model Thin Film SrTi1-xFexO3-δ Mixed Ionic-Electronic Conducting Electrodes
Authors: Tuller Harry L. , Jung WooChul , Haga Kengo
Published: February 2009

The defect structure, transport properties and band structure of the perovskite solid solution SrTi1-xFexO3-δ (STF) can be systematically controlled, over wide limits, by variation in the Fe fraction. In this paper, the authors review recent results which show that STF exhibits model mixed ionic-electronic conducting cathode behavior and extend the composition range investigated to include compositions from SrTiO3 rich values (x = 0.05) to SrFeO3-δ (x= 1). While the majority of the cathodes were prepared as dense films by pulsed layer deposition (PLD), selected compositions were also prepared by thermal inkjet printing. The cathodes were investigated by electrochemical impedance spectroscopy (EIS) as a function of electrode geometry, temperature and oxygen partial pressure. The electrode behavior was found to be controlled by surface exchange kinetics in almost all cases. Values for the surface exchange coefficient, k, were derived and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors such as (La,Sr)(Co,Fe)O3, thereby, confirming STF's suitability of as a model mixed conducting cathode material. Surprisingly, the magnitude of k was found to be only weakly dependent on the bulk electronic and ionic conductivities of STF which varied by many orders of magnitude (over nearly five orders of magnitude change in σel) over the x values examined in this study. The observed trends are discussed in relation to the known defect and transport properties of STF.
Sol-gel and PLD Preparation of Lanthanum Gallate-based Mixed Ionic-electronic Conducting Oxides
Authors: Golubko Natalia V , Kaleva Galina M , Roginskaya Yuliana E , Kabanov Sergey P , Avetisov Alexander A , Suchaneck Gunnar , Politova Ekaterina D
Published: February 2009

Ionic and mixed conducting oxides (La0.9Sr0.1)[(Ga1-xFex)0.8Mg0.2]O3-y (I) and (Sr1.8La0.2)(GaFe)O5.1 (II) with the perovskite and brownmillerite structures, respectively, have been prepared in forms of dense bulk ceramics and ceramic coatings by the sol-gel method. Thin films II have been grown by the pulsed laser deposition method on single crystal MgO (100) and Si (100), fused silica, and stainless steel substrates. The films grown under optimal process conditions were single-phase and homogeneous, with a high degree of preferential orientation. The structure and microstructure of the ceramic coatings have been studied by X-ray diffraction and scanning electron microscopy.
In situ Synchrotron X-ray Studies of Dense Thin-Film Strontium-Doped Lanthanum Manganite Solid Oxide Fuel Cell Cathodes
Authors: Chang Kee-Chul , Ingram Brian , Kavaipatti Balasubramaniam , Yildiz Bilge , Hennessy Daniel , Salvador Paul , Leyarovska Nadia , You Hoydoo
Published: February 2009

Using a model cathode-electrolyte system composed of epitaxial thin-films of La1-xSrxMnO3-δ (LSM) on single crystal yttria-stabilized zirconia (YSZ), we investigated changes in the cation concentration profile in the LSM during heating and under applied potential using grazing incidence x-rays. Pulsed laser deposition (PLD) was used to grow epitaxial LSM(011) on YSZ(111). At room temperature, we find that Sr segregates to form Sr enriched nanoparticles and upon heating the sample to 700°C, Sr is slowly reincorporated into the film. We also find different amounts of Sr segregation as the X-ray beam is moved across the sample. The variation in the amount of Sr segregation is greater on the sample that has been subject to 72 hours of applied potential, suggesting that the electrochemistry plays a role in the Sr segregation.
Doped Apatite Type Lanthanum Silicates: Structure and Property Characterization
Authors: Kharlamova Tamara , Pavlova Svetlana , Sadykov Vladislav A , Krieger Tamara , Batuev Lubsan , Muzykantov Vitalii , Lapina Olga , Khabibulin Dzalil , Chaikina Marina , Uvarov Nikolai , Pavlukhin Yurii , Petrov Sergei , Argirusis Christos
Published: February 2009

Structural features and transport properties of Fe- and Al-doped apatite-type lanthanum silicates were studied with relation to a role of the [SiO4] substructure. XRD, TEM, Mössbauer, UV-Vis electron, IR, 29Si and 27Al NMR spectroscopy were used for structural studies; impedance spectroscopy and oxygen isotope heteroexchange were used for transport properties characterization.
The Thickness Dependence of Oxygen Permeability in Sol-Gel Derived Ce0.8Gd0.2O2-δ-CoFe2O4Thin Films on Porous Ceramic Substrates: A Sputtered “Blocking Layer” for Thickness Control
Authors: Brinkman Kyle S. , Iijima Takashi , Takamura Hitoshi
Published: February 2009

Mixed conductive oxides are a topic of interest for applications in oxygen separation membranes as well as use in producing hydrogen fuel through the partial oxidation of methane. The oxygen flux through the membranes is governed both by the oxygen ionic conductivity as well as the material's electronic conductivity; composite membranes like Ce0.8Gd0.2O2-δ(CGO)-CoFe2O4 (CFO) use gadolinium doped ceria oxides as the ionic conducting material combined with cobalt iron spinel which serves as the electronic conductor. In this study we employ ˜ 50 nm sputtered CeO2layers on the surface of porous CGO ceramic substrates which serve as solution ‘blocking’ layers during the thin film fabrication process facilitating the control of film thickness. Films with thickness of ˜ 2 and 4 microns were prepared by depositing 40 and 95 separate sol-gel layers respectively. Oxygen flux measurements indicated that the permeation increased with decreasing membrane thickness; thin film membrane with thickness on the micron level showed flux values an order of magnitude greater (0.03μmol/cm2s) at 800oC as compared to 1mm thick bulk ceramic membranes (0.003 μmol/cm2).
Ink-jet printed carbon-based micro-supercapacitor for mobile self-powered modules
Authors: Brunet Magali , Taberna Pierre-Louis , Simon Patrice , Fabre Norbert , Conédéra Véronique , Mesnilgrente Fabien , Durou Hugo , Rossi Carole
Published: February 2009

Carbon-based micro-supercapacitors dedicated to energy storage in self-powered modules were fabricated with inkjet printing technology on silicon substrate. The ink containing activated carbon with particles size ranging from 1 μm to 10 μm, mixed with PTFE and glycol was stabilised with a surfactant, Triton X100. After functionalising the electrodes surroundings with octadecyltrichlorosilane (OTS), the ink was deposited by inkjet on the electrodes with the substrate heated at 140°C in order to assure a good homogeneity. The resulting structures have a resolution of 10 μm. Micro-supercapacitors with the carbon electrodes were tested in acetonitrile and Et4NBF4 dried salts: the capacitance density obtained was 50 μF.cm−2. The newly developed technology will allow the integration of the storage device as close as possible as the MEMS-based energy harvesting device, minimising power losses through connections.
Solidification of TiAl-based alloys
Authors: Hecht Ulrike , Daloz D. , Lapin J. , Drevermann A. , Witusiewicz V.T. , Zollinger J.
Published: February 2009

Titanium aluminides containing high niobium additions emerged as an attractive alloy family for automotive and aero-engine applications. Their processing by near net shape casting is rather demanding, not only due to easy contamination but also due to the fact that microstructure formation during solidification and subsequent solid state transformations sensitively depends on alloy composition and the applied processing conditions. The sequence of phase formation during solidification of the ternary alloy Ti-45Al-8Nb was analyzed based on non-equilibrium thermodynamic calculations and solidification experiments. This alloy solidifies completely via the β(Ti) phase, because the nucleation undercooling for the α(Ti) phase is high enough to prevent its formation. Thermodynamic calculations and experiments are shown to converge at last, with only minor improvements being necessary to correctly describe the metastable eutectic reaction “Liquid → β(Ti) + γ-TiAl” that occurs at the end of the solidification path.
Crystal Structure and Thermoelectric Properties of Mn-Substituted Ru2Si3 with the Chimney-Ladder Structure
Authors: Koyama Tatsuya , Okamoto Norihiko L. , Kishida Kyosuke , Tanaka Katsushi , Inui Haruyuki
Published: February 2009

Chimney-ladder compounds with the general chemical formula of Mn X2n-m (n, m: integers) possess tetragonal crystal structures which consist of two types of subcells; one composed of transition metal atoms (M) with the γÀ-Sn structure and the other composed of group 13 or 14 atoms (X) with a helical arrangement along the tetragonal c-axis. Since the chimney-ladder compounds generally exhibit very low thermal conductivity, presumably due to its long periodicity along the c-axis, they have been extensively investigated as promising thermoelectric materials. The high-temperature (HT) phase of Ru2Si3 is one of the chimney-ladder compounds with n=2 and m=1. Recently we have found that the HT-Ru2Si3 phase is stabilized by substituting Ru with Re so as to exist even at low temperatures in a wide compositional range of the Re content (Re: 14 to 73%), and that the thermoelectric power factor for alloys with high Re contents increases with the Re content and the highest value was obtained for the alloy with the highest Re content (73%), which is the solubility limit of Re in the chimney-ladder phase. In order to further enhance the thermoelectric properties, another ternary element which extends the solid solubility region of the HT-Ru2Si3 phase is favorable. We have chosen Mn as the ternary element because Mn4Si7 with the chimney-ladder structure exists as a counterpart of HT-Ru2Si3 in the Ru2Si3 -Mn4Si7 pseudo-binary system so that the solid solubility region of the chimney-ladder phase is anticipated to extend in a wider composition range than the Re case. Our study, in fact, shows that the Mn-substitution stabilizes the HT-Ru2Si3 phase in a wide compositional range of the Mn content; 12 to 100%. Compositional analyses indicate that the Si/M ratio gradually increases as the Mn content increases. This is considered to be due to the addition of Si atoms in the Si subcell in order to compensate the decrease in the valence electron concentrations (VEC) per M atom by the substitution of Ru (group 8) with Mn (group 7) with fewer valence electrons. The Seebeck coefficient and electrical resistivity of the Mn-substituted Ru2Si3 are explained in terms of the VEC deviation from the idealized value, 14, which is expected for intrinsic semiconductors with the chimney-ladder structure. The highest dimensionless thermoelectric figure of merit (ZT=0.76) is obtained for 90%Mn-substituted alloy. The relationships between the microstructure and thermoelectric properties will be discussed.
Consolidation and Mechanical Properties of Mechanically Alloyed Al-Mg Powders
Authors: Sakaliyska Mira , Scudino Sergio , Nguyen Hoang Viet , Surreddi Kumar Babu , Bartusch Birgit , Ali Fahad , Kim Ji Soon , Eckert Jürgen
Published: February 2009

Nanostructured Al-Mg bulk samples with compositions in the range of 10 – 40 at.% Mg have been produced by consolidation of mechanical alloyed powders. Powders with composition Al90Mg10and Al80Mg20were consolidated into highly dense specimens by hot extrusion. Room temperature compression tests for the Al90Mg10specimen reveal interesting mechanical properties, namely, a high strength of 630 MPa combined with a plastic strain of about 4 %. The increase of the Mg content to 20 at.% increases the strength by about 100 MPa but it suppresses plastic deformation. The Al60Mg40powder was consolidated at different temperatures by spark plasma sintering and the effect of the sintering temperature on microstructure, density and hardness have been studied. The results reveal that both density and hardness of the consolidated samples increase with increasing sintering temperature, while retaining a nanocrystalline structure. These results indicate that powder metallurgy is a suitable processing route for the production of nanocrystalline Al-Mg alloys with promising mechanical properties.
Role of the Microstructure on the Deformation Behavior in Mg12ZnY with a Long-Period Stacking Ordered Structure
Authors: Hagihara Koji , Yokotani Naoyuki , Kinoshita Akihito , Sugino Yuya , Yamamoto Hiroyuki , Yamasaki Michiaki , Kawamura Yoshihito , Umakoshi Yukichi
Published: February 2009

The influence of a heat-treatment on the plastic deformation behavior in Mg12ZnY with a long-period stacking ordered (LPSO) structure was investigated by using crystals grown by the Bridgman method. Annealing of the crystal at 798 K for 3 days induced the change in the crystal structure of Mg12ZnY from the 18-fold rhombohedral structure (18R) to the 14-fold hexagonal structure (14H). The plastic behavior of those LPSO crystals showed a large variation depending on the loading axis in both crystals, because of the limitation of operative deformation modes in them. The change in the stacking sequence in the LPSO crystals did not show a large influence on the plastic deformation behavior at room temperature.
Thin-Film Synthesis and Cyclic Oxidation Behavior of B2-RuAl
Authors: Woll Karsten , Chinnam Rama , Mücklich Frank
Published: February 2009

B2-RuAl as a potential intermetallic for thin-film applications at high temperatures is studied with respect to thin-film synthesis and cyclic oxidation behaviour. Using the multilayer approach, single phase RuAl thin films were fabricated. The phase sequence from the elements Ru and Al goes through RuAl6 to the final product RuAl. To understand the reaction mechanism calorimetric as well as kinetic experiments were performed. The cyclic oxidation behavior is characterized at 1200 °C up to 47 h. The morphology of the grown alumina shows no cracks or regions of spallation which indicates the good cyclic oxidation behavior. Compressive stresses in the oxidation scale of about 1.2 GPa at maximum were determined.
The European ULTMAT Project: Properties of New Mo- and Nb-Silicide Based Materials
Authors: Drawin Stefan
Published: February 2009

The development, in the frame of the European ULTMAT project, of alloys offering at least 150°C surface temperature increase above the Ni-based superalloys' capability is presented. The expected achievement of the project is a thorough evaluation of the capability of refractory metal (Nb and Mo) silicide based multiphase materials to withstand enhanced temperature turbine service conditions (up to 1300°C). This is based on microstructural, mechanical, physical and environmental investigations in close connection with industrial scale material processing and component fabrication technologies. The paper presents an overview of the project results. Base materials are the metal/intermetallic ductile/brittle composites in the Nb-Nb5Si3 and Mo-Si-B systems. Improvements in high temperature creep resistance (up to 1300°C) as well as oxidation resistance (700°C to 1300°C) have been obtained. Processing routes have been developed (ingot and powder metallurgy) that allowed the manufacture of complex shaped parts.
Metastable Hexagonal Modifications of the NbCr2 Laves Phase as Function of Cooling Rate
Authors: Aufrecht Jochen , Leineweber Andreas , Mittemeijer Eric Jan
Published: February 2009

In as-cast ingots produced by arc-melting, several metastable polytypic modifications of NbCr2 were found additional to the cubic C15 phase stable at room temperature: C14, C36 and 6H-type structures, often highly faulted and/or intergrown. Strikingly, these phases had formed at locations of the specimen which had experienced a relatively low cooling rate, whereas the C15 phase was formed preferentially in regions which had experienced the highest cooling rates.
Phase Equilibria in the Ternary Nb-Cr-Al System and Site Occupation in the Hexagonal C14 Laves Phase Nb(AlxCr1-x)2
Authors: Prymak Oleg , Stein Frank , Kerkau Alexander , Ormeci Alim , Kreiner Guido Michael , Frommeyer Georg , Raabe Dierk
Published: February 2009

The ternary Nb-Cr-Al phase diagram exhibits extended phase fields of the cubic C15 and the hexagonal C14 Laves phases Nb(AlxCr1-x)2. A number of Nb-Cr-Al alloys were prepared by levitation melting and annealed at temperatures between 1150 and 1450 °C for up to 1500 h. Isothermal sections of the ternary Nb-Cr-Al phase diagram at 1150, 1300 and 1450 °C were obtained from electron probe microanalysis, X-ray powder diffraction and metallographic investigations in order to study the effect of Al on the stability and structure of the Laves phases. The C14 Laves phase in the Nb-Cr-Al system can dissolve up to 45 at.% Al by substituting Cr with Al on the two different crystallographic B-sites 2a and 6h of the C14 AB2 unit cell. The site occupations of the Al and Cr atoms on these two B-sites were determined by Rietveld analysis using the program FullProf. The experimental site occupation factors were compared to site occupation factors computed by a statistical mechanics approach based on first-principles electronic structure calculations. The experimental as well as the calculated site occupation factors indicate a preferred occupation of the 2a site by Al.
Variable Thickness IPMC: Capacitance Effect on Energy Harvesting
Authors: Tiwari Rashi , Kim Sang-Mun , Kim Kwang
Published: February 2009

Ionic Polymer Metal Composites (IPMCs) are manufactured by electroless deposition of metal on Nafion. This deposition method results in the IPMCs with thickness between 0.17mm to 0.20mm with the electrode thickness of around a few m each. It is now generally accepted that on mechanical deformation IPMC produces charge thus making these materials potentially suitable for energy harvesting applications. Due to thin metal plating and inherited flexibility of the Nafion film the IPMCs suffer in stiffness that may be required for some energy harvesting applications. Also earlier works have shown that 0.20mm thick IPMC produce better battery charging than 0.17mm thick one. Hot pressing, using metal mold, Nafion films was employed to produce thicker and comparatively stiffer IPMCs electroded with Palladium metal. Palladium was used because of shorter manufacturing time. This IPMC shows improved energy harvesting. Due to the increased thickness these IPMCs also function as better capacitors than their conventional counterparts. On application of voltage, these IPMCs show charging and discharging effects of a capacitor. This property of IPMC may be useful for storing charge.
Electrical and Optical Properties of Gold-strontium Titanate Nano-composite Thin Films
Authors: Ganti S , Dhopade Y , Gupta R K , Ghosh K , Kahol P K
Published: February 2009

Thin films based on nano-composites have attracted considerable attention for their possible applications in devices and sensors. These nano-composite thin films are formed by embedding metal or semiconductor nano-particles in a host material and they exhibit interesting electrical transport properties. Using pulsed laser deposition technique, we have prepared nano-composite thin films of gold-strontium titanate on quartz substrate. Gold and strontium titanate were used as targets for pulsed laser deposition. Thin films having different compositions were grown. The effect of different composition on their electrical and optical properties has been studied in details. The structural characterizations of the films were done by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Transmission electron microscopy as well as atomic force microscopy shows the presence of gold nano-particles in these films. X-ray diffraction and energy dispersive x-ray spectroscopy shows the existence of strontium titanate and gold. Current-voltage characteristics and temperature dependent resistivity measurements were made to characterize electrical properties of these films. Electrical properties can be manipulated from metal to insulator through semiconductor by varying the composition. In addition, it is observed that the absorption of visible light increases with increase in gold percentage. This indicates that these nano-composites could also use as active materials for many electronic as well as optical sensors.
Thermal, Mechanical, and Electric Properties of Exfoliated Graphite Nanoplate Reinforced Poly(vinylidene fluoride) Nanocomposites
Authors: He Fuan , Fan Jintu
Published: February 2009

Poly(vinylidene fluoride) (PVDF)/exfoliated graphite nanoplate (xGnP) nanocomposites were prepared by a solution mixing method for the first time. The thermal, mechanical and electric properties of these nanocomposites were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and an impedance analyzer, respectively. The DSC results indicated that xGnP might act as the nucleating agents and accelerated the overall non-isothermal crystallization process of PVDF. Meanwhile, the incorporation of xGnP also significantly improved the storage modulus and conductivity of the PVDF/xGnP nanocomposites with an increment in the graphite nanoplate content, respectively.
Mechanical Characteristics of Al-Si-Cu Structural Films by Uniaxial Tensile Test with Elongation Measurement Image Analysis
Authors: Fujii Hiroki , Namazu Takahiro , Tomizawa Yasushi , Inoue Shozo
Published: February 2009

This paper presents mechanical characteristics of sputtered Al-Si-Cu film used as a structural material in microelectromechanical systems (MEMS). Novel tensile test technique with an elongation measurement image analysis system has been developed. Uniaxial tensile tests were conducted at temperatures ranging from room temperature (R.T.) to 358 K. No specimen-size effect on Young's modulus, yield stress, and fracture strength, was found, whereas the annealing and temperature effects were clearly observed. To study mechanical degradation mechanism, cyclic loading tests were conducted under constant stress- and strain-amplitude modes. In constant stress-amplitude mode, stain amplitude increased with an increase of loading cycles due to creep-like deformation. Almost of the specimens fractured during the tests. Meanwhile, in constant strain-amplitude mode, stress amplitude gradually decreased with increasing cycles due to stress-relaxation, but no fatigue failure was observed.
Optical Fiber Microarrays for Chemical and Biological Measurements
Authors: Walt David R , LaFratta Christopher , Webb Michael , Li Zhaohui , Gorris Hans-Heiner , Hayman Ryan
Published: February 2009

We have used coherent imaging fiber arrays as a platform for preparing chemical sensors and biosensors. Sensors can be made with spatially-discrete sensing sites for multi-analyte determinations. Micrometer sized sensors have been fabricated by etching the cores of an optical imaging fiber to create microwells and loading them with microspheres. These arrays possess both high sensitivity and reproducibility and can be used for making thousands of measurements simultaneously such as for genetic analysis or for the analysis of complex biological fluids. Both optical and optoelectrochemical arrays have been used for multiplexed sensing. In another scheme, the arrays can be used for single molecule detection. In this format, individual molecules, such as enzymes, can be trapped in the microwells by sealing each microwell with a silicone gasket. The enzyme molecules catalyze the formation of a fluorescent product that can be detected readily. The kinetic properties of hundreds to thousands of single enzyme molecules can be monitored simultaneously using this format. By observing the stochastic nature of the single molecule responses, new mechanistic insights into the fundamental nature of the enzymes can be obtained.
Photonic crystals: A platform for label-free and enhanced fluorescence biomolecular and cellular assays
Authors: Cunningham Brian T. , Chan Leo , Mathias Patrick C. , Ganesh Nikhil , George Sherine , Lidstone Erich , Heeres James , Hergenrother Paul J.
Published: February 2009

Photonic crystal surfaces represent a class of resonant optical structures that are capable of supporting high intensity electromagnetic standing waves with near-field and far-field properties that can be exploited for high sensitivity detection of biomolecules and cells. While modulation of the resonant wavelength of a photonic crystal by the dielectric permittivity of adsorbed biomaterials enables label-free detection, the resonance can also be tuned to coincide with the excitation wavelength of common fluorescent tags - including organic molecules and semiconductor quantum dots. Photonic crystals are also capable of efficiently channeling fluorescent emission into a preferred direction for enhanced extraction efficiency. Photonic crystals can be designed to support multiple resonant modes that can perform label free detection, enhanced fluorescence excitation, and enhanced fluorescence extraction simultaneously on the same device. Because photonic crystal surfaces may be inexpensively produced over large surface areas by nanoreplica molding processes, they can be incorporated into disposable labware for applications such as pharmaceutical high throughput screening. In this talk, the optical properties of surface photonic crystals will be reviewed and several applications will be described, including results from screening a 200,000-member chemical compound library for inhibitors of protein-DNA interactions, gene expression microarrays, and high sensitivity of protein biomarkers.
Surface Plasmon Enhanced Transmission with Self-assembled Hexagonal Nanohole Arrays
Authors: Lou Yi , Westcott Nathan , McGlade John , Muth John F. , Yousaf Muhammad
Published: February 2009

The optical properties of hexagonal nanohole arrays in gold films are investigated. Nanosphere lithography combined with reactive ion etching has been applied as a low cost method to fabricate nanohole arrays with hexagonal symmetry where the size and spacing of the holes can be independently controlled. In this study, the spacing between the nanoholes is 600 nm with the hole diameter varied between 450 and 250 nm. The transmission spectra of the surface patterns with different film thickness are collected with normally incident light. The color of the reflected light from the nanohole array was found to change from green to red as the diameter of the holes was reduced. One application of these films is to study cell adhesion to small areas with controlled size. We explore the possibility of making isolated cell adhesion dots by chemically modifying the nanohole area. Swiss 3T3 cells were adhered onto the patterned surface and imaged using environmental SEM and fluorescent microscopy.
Interplay Between Surface Chemistry and Optical Behavior of Semiconductor-biomolecule Functionalized Sensing Systems: An Optical Investigation by Spectroscopic Ellipsometry
Authors: Losurdo Maria , Wolters Scott D , Giangregorio Maria M , Lisco Fabiana , Angelo Michael , Lampert William , Bruno Giovanni , Brown April
Published: February 2009

Chemical functionalization of bio-molecules, including hemin (an iron porphyrin) and bovine albumin onto Si (100) and GaAs (100) surfaces is reported. Spectroscopic ellipsometry analysis on the optical response of functionalized surfaces provides information on molecular coverage and effective thickness as well as the kinetics of surface attachment. Topographic features of the chemically functionalized surfaces are investigated by atomic force microscopy
Molecular Adsorption and Fragmentation of Bromoform on Polyvinylidene Fluoride with Trifluoroethylene
Authors: Ilie Carolina C. , Xiao Jie , Dowben Peter
Published: February 2009

Bromoform absorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF-TrFE 70:30) was investigated by photoemission and inverse photoemission and found to be associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state.
High Frequency Length Mode PVDF Behavior over Temperature
Authors: Thompson Mitch , Toda Minoru , Ciccarone Melina
Published: February 2009

In an extension of earlier work, the temperature dependent parameters of PVDF operating in the length mode have been measured at frequencies useful in air ultrasound (20kHz to 100kHz) over a -45°C to +65°C temperature range. The length mode resonance of PVDF strips of different lengths was excited by mechanically clamping samples at the mid point during dielectric impedance testing conducted in a desiccated thermal chamber. Material properties were extracted from the impedance magnitude and phase angle data at temperature, and the various sample lengths allowed a range of resonant frequencies to be studied. Overall results generally confirm the visco-elastic behavior of PVDF. Testing was conducted on samples with both thin sputtered metal electrodes (∼60nm) and thicker elastomeric silver ink electrodes (∼8μm) to assess the performance difference. Silver ink is preferred in production as sputtered metal has current density an other limitations, but it causes a serious loss in performance at high frequencies.
Aromatic Polyurea for High Temperature High Energy Density Capacitors
Authors: Wang Yong , Zhou Xin , Lin Minren , Lu Sheng-Guo David , Lin Jun-Hong , Zhang Qiming
Published: February 2009

We investigate aromatic polyureas which can be fabricated in the form of thin films through CVD. It was found that the polymer possesses a flat dielectric response (k∼ 4.2 and loss <1%)) to more than 200°C. The frequency-independent dielectric properties in the investigated frequency range(1kHz∼1MHz), low conductance, low dissipation factor (∼0.005), high breakdown strength (>800MV/m), high energy density (>12J/cm3) and high efficiency suggest this polymer can be a good candidate material for high temperature energy storage capacitors. Breakdown strength was analyzed with Weibull model over a broad temperature range (25°C ∼180°C). Experimental results indicate that aromatic polyurea is more like a nonpolar linear dielectric material because of its highly cross-linked structures. The experiment results further show that this polymer maintains its high performance even at high temperatures.
A New Type of Display Device Based on Remote Swelling and Collapse of a pH Responsive Microgel
Authors: Cook Joseph Peter , Riley Jason
Published: February 2009

Microgel particles of poly(2-vinylpyridine) cross linked with 0.5 wt% divinylbenzene were synthesised. Due to differences in the scattering of light, a dispersion of the particles appears opaque milky white above pH 4.5 and transparent below pH 4.5. The pH of a 0.15 wt% dispersion was modified using a poly(aniline) film as a source/sink of protons and a Ag/AgCl electrode as a source/sink of chloride counterions. The absorption of the sample at 400 nm was typically reduced from c.a. 3.5 to c.a. 0.5 in less than 20 minutes and increased to c.a. 3.2 in less than 20 minutes. This system could form the basis for a new type of display device, but it is insufficiently fast or consistent in its current form.
The Melt Electrospinning of Polycaprolactone (PCL) Ultrafine Fibers
Authors: Subramanian Chitrabala , Ugbolue Samuel C. , Warner Steven B. , Patra Prabir K.
Published: February 2009

Electrospinning is a technique of producing nanofibers from polymer solution/melt solely under the influence of electrostatic forces. In this research, we investigated the formation of nanofibers by melt electrospinning polycaprolactone (PCL). The effect of process parameters such as molecular weight, applied voltage, and electrode separation on the fiber diameter was investigated. Controlling the process parameters could help increase the proportion of ultrafine fibers in the melt electrospun nonwoven mat. The velocity of the straight jets was in the range of 0.2-1 m/s. The melt electrospun fibers were characterized with respect to fiber diameter, distribution, mechanical properties and birefringence. Melt electrospun polycaprolactone fibers had a diameter distribution of the order of 5 -20 μm. The birefringence of the melt electrospun fibers increased with decrease in fiber diameter.
Commercial MEMS Case Studies: The Impact of Materials, Processes and Designs
Authors: Martin Jack
Published: February 2009

Minimizing risk is an important factor in new product planning because high volume breakthrough products require tens of millions of dollars to develop and bring to market. Sometimes risk can be minimized by following the IC model: build new devices on an existing process – just change the mask set. This approach obviously has limits. Adoption of new materials and processes greatly expands the horizon for “disruptive” products. This paper uses a case study approach to examine how changes in masks, materials and unit processes were used, and will continue to be used, to produce MEMS products for high volume applications.
BioMEMS Technologies for Regenerative Medicine
Authors: Borenstein Jeffrey T.
Published: February 2009

The emergence of BioMEMS fabrication technologies such as soft lithography, micromolding and assembly of 3D structures, and biodegradable microfluidics, are already making significant contributions to the field of regenerative medicine. Over the past decade, BioMEMS have evolved from early silicon laboratory devices to polymer-based structures and even biodegradable constructs suitable for a range ofex vivoandin vivoapplications. These systems are still in the early stages of development, but the long-term potential of the technology promises to enable breakthroughs in health care challenges ranging from the systemic toxicity of drugs to the organ shortage.Ex vivosystems for organ assist applications are emerging for the liver, kidney and lung, and the precision and scalability of BioMEMS fabrication techniques offer the promise of dramatic improvements in device performance and patient outcomes.

Ultimately, the greatest benefit from BioMEMS technologies will be realized in applications for implantable devices and systems. Principal advantages include the extreme levels of achievable miniaturization, integration of multiple functions such as delivery, sensing and closed loop control, and the ability of precision microscale and nanoscale features to reproduce the cellular microenvironment to sustain long-term functionality of engineered tissues. Drug delivery systems based on BioMEMS technologies are enabling local, programmable control over drug concentrations and pharmacokinetics for a broad spectrum of conditions and target organs. BioMEMS fabrication methods are also being applied to the development of engineered tissues for applications such as wound healing, microvascular networks and bioartificial organs. Here we review recent progress in BioMEMS-based drug delivery systems, engineered tissue constructs and organ assist devices for a range ofex vivoandin vivoapplications in regenerative medicine.
Fabrication and Hot Switching Behavior of Electroplated Gallium Spheres for MEMS
Authors: Kim Yoonkap , Bahr David
Published: February 2009

Liquid metal microscale switches, often using mercury, are sometimes used in place of solid-solid contact switches because of the ability to minimize damage from switching and the ability to make good contacts for electrical and thermal conductivity. However, mercury has potential health and safety problems, and is difficult to use at high frequency (kHz) operation due to poor adhesion between the liquid-solid contacts. One alternative to the mechanical and chemical problems of a liquid mercury switch is using soft metals, such as gallium or tin, as a solid metal sphere for switches that can melt at moderate temperatures. Ga micro-spheres for switching operations were deposited on a substrate consisting of photolithographically patterned W films on SiO2 and Si substrates by electroplating, and the applicability for use in a microscale switch was investigated by characterizing the macro structure, hardness, and electrical performance during switching. The resistivity of the electroplated Ga droplets was similar to the theoretical value for pure Ga, and suggests that the electrodeposited Ga will be suitable for a solid MEMS switch. The hardness of the Ga sphere was 5.7 MPa. This suggests a maximum of ∼40 micron-Newton can be applied to each 50 micron-meter radius Ga contact in the current configuration for switching applications. When the Ga spheres were investigated for electrical performance during hot switching, the resistance increased over six switching cycles, but the original lower resistivity was recovered after a 393 K thermal reflow process.
Transport of Charged Species Across Solid-State Nanopores
Authors: Fung Daisy , Akdemir Eyup , Vitarelli Michael , Sosnov Eugene , Prakash Shaurya
Published: February 2009

Nanofluidic devices are finding growing interest for a variety of applications. An initial report is presented here on a wide range of parameters influencing transport of ionic species as they translocate across solid-state nanopores. AC electrical bias at low ionic concentration with overlapping electric double layers provides an enhancement of ionic flux over pure DC bias. Furthermore, results also indicate that concentration and pH gradients can be maintained across solid-state nanopores for extended periods of time that can last for several hours in the absence of driving forces such as electric fields.
Growth of Epitaxial Potassium Niobate Film on (100)SrRuO3/(100)SrTiO3 by Hydrothermal Method and their Electromechanical Properties
Authors: Ishikawa Mutsuo , Yasui Shintaro , Utsugi Satoshi , Fujisawa Takashi , Yamada Tomoaki , Morita Takeshi , Kurosawa Minoru , Funakubo Hiroshi
Published: February 2009

Epitaxaially-grown KNbO3 thick films over 8 μm in thickness were successfully grown at 220 °C for 6 h on (100)cSrRuO3//SrTiO3 substrates by a hydrothermal method. Epitaxial SrRuO3 layers grown on (100)cSrTiO3 substrates by sputter method were used as bottom electrode layers. Relative dielectric constant and the dielectric loss were 530 and 0.11, respectively. Clear hysteresis loops originated to the ferreoelectricity were observed and a remanent polarization was 25 μC/cm2 at a maximum applied electric field of 540 kV/cm. In addition, the hydrothermal KNbO3 thick film was able to transmitting and receiving of ultrasonic waves over 50MHz.
Three-Dimensional Structure of Helical and Zigzagged Nanowires Using Electron Tomography
Authors: Kim Han Sung , Myung Yoon , Kim Chang Hyun , Bae Seung Yong , Ahn Jae-Pyoung , Park Jeunghee
Published: February 2009

Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique three-dimensional structures of helical or zigzagged GaN, ZnGa2O4 and Zn2SnO4 nanowires. The helical GaN nanowires adopt a helical structure that consists of six equivalent <0-111> growth directions with the axial [0001] direction. The ZnGa2O4 nanosprings have four equivalent <011> growth directions with the [001] axial direction. The zigzagged Zn2SnO4 nanowires consisted of linked rhombohedrons structure having the side edges matched to the <011> direction, and the [111] axial direction.
ZnO/Al2O3 Core-shell Nanorod Arrays: Processing, Structural Characterization, and Luminescent Property
Authors: Chen Cheng-Ying , Lin Chin-An , Chen Miin-Jang , Lin Gong-Ru , He Jr-Hau
Published: February 2009

We reported the aqueous chemical method to fabricate the well-aligned ZnO/Al2O3 core-shell nanorod arrays (NRAs). The shell is composed of α-Al2O3 nanocrystals in amorphous Al2O3 layers. The photoluminescence (PL) measurements showed that the enhancement of near-band-edge emission in ZnO NRAs arrays due to the addition of Al2O3 shell was observed. The Al2O3 shell layer resulting in flatband effect near ZnO surface leads to a stronger overlap of the wavefunctions of electrons and holes in the ZnO core, further enhancing the NBE emission.
Raman Spectroscopy of Group IV Nanostructured Semiconductors: Influence of Size and Temperature
Authors: Torres Alfredo , Martínez Oscar , Prieto Carmelo , Jimenez Juan , Rodríguez Andrés , Sangrador Jesús , Rodríguez Tomás
Published: February 2009

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. However, the Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation.
Size distribution of self assembled Ge nanocrystals determined by photoluminescence
Authors: Rowell Nelson , Lockwood David , Berbezier Isabelle , Szkutnik Pierre David , Ronda Antoine
Published: February 2009

Germanium nanocrystals (NCs) were formed by in-situ thermal annealing of an amorphous Ge layer deposited by molecular beam epitaxy on a thin SiO2 layer on Si(001). The Ge NCs were then capped in situ with a thin layer of amorphous Si to prevent oxidation. For the present range of particle sizes (2.5 to 60 nm), the NC photoluminescence (PL) appeared primarily as a wide near-infrared band peaked near 800 meV. The peak energy of the PL band reflects the average NC size and its shape depends on the NC size distribution. Using both the k·p and tight binding theoretical models, we have analyzed the PL spectrum in terms of the NC size distribution required to reproduce the observed asymmetric band shape, which includes, for the smaller diameter NCs, a band gap enlargement due to quantum confinement. The observed size distribution determined from transmission electron microscopy analysis allowed the determination of the nonlinear increase in the PL quantum efficiency with decreasing NC diameter. This implies that, given a good theoretical description of the system, it is possible to evaluate the size distribution of semiconductor NCs from their PL energy dependence.
Sol-gel Synthesis and Characterization of YAG:Ce3+ Phosphors by Various Pre-firing Temperatures
Authors: Hwang Kyu-Seog , Hwangbo Seung , Jeong Ju-Hyun , Lee Young-Hwan , Kim Jin-Tae
Published: February 2009

Ceria doped-yttrium aluminum garnet (Y3Al5O12:Ce3+, YAG:Ce), which is known as an efficient phosphor, have been widely used in optical display and lighting applications. Improved wet chemical method, sol-gel, has been studied, since conventional solid-state reaction requires a high-temperature and prolonged heating to obtain the pure phase. However, there has been little information, such as on pre-firing temperature, concerning high-quality powder formed by the wet chemical process. In this work, YAG:Ce was synthesized with a salted sol-gel process in which a water solution of inorganic salt with citric acid as additive. Transparent starting sol was pre-fired at 200 ˜ 300°C for 2 hrs in air and final annealing to obtain phase-pure YAG:Ce particles was performed at 1100°C for 2 hrs in argon. The effects of pre-firing temperatures on the crystal structure, morphology and luminescence were investigated. Effects of residual organics in the pre-fired gel on the properties of finally annealed phosphors will be fully discussed on the basis of the results of thermal analysis and chemical structure.