bluuebunny/crossref_metadata_2025 huggingface dataset:
SPEEK-based Composite Membranes for Direct Methanol Fuel Cells
Authors: D'Epifanio Alessandra , Mecheri Barbara , Weise Christoph F , Greenbaum Steve , Traversa E , Licoccia Silvia
Published: February 2009

Sulfonated polyether ether ketone (SPEEK)-based composite membranes doped with 23 and 50 wt% of hydrated tin oxide (SnO2·nH2O) were prepared and characterized for Direct Methanol Fuel Cell (DMFC) applications . The composite membranes were characterized in terms of ion exchange capacity (IEC), tensile tests, water uptake measurements, electrochemical impedance spectroscopy (EIS), and Pulsed-field-gradient spin-echo nuclear magnetic resonance (PFGSE NMR) spectroscopy. The body of results indicated the involvement of hydrated tin oxide in the proton conduction mechanism, the inorganic phase providing additional paths between the water clusters for proton transport. NMR measurements evidenced that SnO2·nH2O particles not only facilitate the proton transport but also hinder water diffusion. Therefore, due to the selectivity of SnO2·nH2O for proton diffusion, the filler effect was found to be also beneficial for the reduction of methanol crossover through the SPEEK membrane and for improving the performance of the SPEEK membrane when used as electrolyte in a DMFC test station.
Electrochemical preparation of nanostructured TiO2 as anode materials for Li ion batteries
Authors: Duan Huanan , Chen Xiangping , Gnanaraj Joe , Liang Jianyu
Published: February 2009

TiO2 is an attractive anode material for Li-ion batteries due to its high capacity, high mechanical stability during Li intercalation/deintercalation process, limited side reactions with the electrolyte, low cost, and environmental friendliness. In this study, titanium hydroxide gel films were prepared in acidic aqueous solutions of TiOSO4, H2O2 and KNO3 by potentiostatic cathodic electrosynthesis on various copper substrates, including planar Cu foil, mechanically polished planar Cu foil, and Cu nanorod arrays grown on Cu foil. Crystalline TiO2 films were obtained by heat treating the electrodeposited titanium hydroxide gel films at 500 oC in argon atmosphere. The morphology and microstructure of the TiO2 films were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). SEM results showed that after deposition, each Cu nanorod has been covered by a layer of TiO2 gel, forming a core-shell structure. The effects of Cu nanorod arrays on the morphology and the electrochemical property of the TiO2 deposits were discussed.
Reduction of bis(Oxalato)Borate on a High Surface Area Carbon Electrode
Authors: Flynn John , Schlaikjer Carl
Published: February 2009

Lithium bis(oxalato)borate (LiBOB) has gained widespread interest as an electrolyte salt for lithium ion batteries because of its high conductivity, low cost, thermal stability, and adequate solubility in many organic solvents [1]. Cyclic voltammetric data taken on platinum [2] and carbon [3] indicate electrochemical stability over a wide potential range.

We show that bis(oxalato)borate (BOB) can be reduced at about 1.75 volts anodic to lithium, by discharging electrolytes at low current density (0.1 mA/cm2) on high surface area carbon electrodes containing a mixture of acetylene and Ketjen carbon blacks. The evidence includes discharge profiles and 11B NMR data. The behavior of discharge plateaus indicates that BOB is reduced to a soluble species with electrolytic properties, and the appearance of a broad 11B NMR peak in the electrolyte indicates that the reduced species undergoes extensive exchange.
Development of Ultrahigh Surface Area Porous Electrodes using Simultaneous and Sequential Meso- and Micro-structuring Methods
Authors: Maddox Franchessa , Cook Catherine , McKenzie Leigh , O'Neil Brenda , Junkin Elizabeth A. , Redden Christopher , Basu Soumen , Bakker Martin G. , Småtts Jan-Henrik , Lindén Mika
Published: February 2009

Very high surface area nanostructured metal electrodes are of interest as efficient current collectors. For thin film devices, the nanostructured metal can be grown in place using electrodeposition or electroless deposition. For larger devices metal electrodes structured at more than one length scale are desirable. Self-assembling surfactant templates are a versatile method of generating a range of nanostructures. As we report here, electrodeposition of nickel, cobalt and copper from liquid crystalline solutions of Triton X-100 produces a number of nanostructures, with significant surface area increases. Electrodeposition into templates with microstructure has proven more demanding. Oil-in-water Microemulsions of Tween surfactants and soy oil, produce micrometer scale structures, however measured nickel surface area does not scale with sample thickness. The method is also not robust, and was found to give microstructures only for nickel and cobalt. Experiments show that under our conditions a combination of nickel metal, nickel acetate and nickel/detergent microstructures are formed.
Grain Refinement for Strengthening in Fe3Al-based Alloys Through Thermomechanical Processing
Authors: Kobayashi Satoru , Takei Akira , Takasugi Takayuki
Published: February 2009

A thermomechanical process (TMP) for grain refinement was performed in bulk Fe3Al-based alloys containing ˜10% volume fraction of κ-Fe3AlC precipitates. In the TMP, κ particles play an important role in reducing the inhomogeneity of recrystallization due to the matrix orientation. The grain size was refined to ˜20 μm by optimizing the κ particle size. A fine-grained and pancake/recovered microstructure fabricated by the TMP showed more than 1200 MPa tensile strength and 8% tensile ductility at room temperature in air. The tensile strength of this material was higher than those of conventional wrought Fe3Al alloys at temperatures between room temperature and 500 °C, and the specific tensile strength was as high as that of the Ti-6Al-4V alloy at temperatures above 400 °C.
Ab Initio Study of Elastic Properties in Fe3Al-based Alloys
Authors: Friák Martin , Deges Johannes , Stein Frank , Palm Martin , Frommeyer Georg , Neugebauer Jöerg
Published: February 2009

Fe3Al-based alloys constitute a very promising class of intermetallics with great potential for substituting austenitic- and martensitic steels at elevated temperatures. A wider use of these materials is partly hampered by their moderate ductility at ambient temperatures. Theoretical ab initio based calculations are becoming increasingly useful to materials scientists interested in designing new alloys. Such calculations are nowadays able to accurately predict basic material properties by needing only the atomic composition of the material. We have therefore employed this approach to explore (i) the relation between chemical composition and elastic constants, as well as (ii) the effect transition-metal substituents (Ti, W, V, Cr, Si) have on this relation. Using a scale-bridging approach we model the integral elastic response of Fe3Al-based polycrystals employing a combination of (i) single crystal elastic stiffness data determined by parameter-free first-principles calculations in combination with (ii) Hershey's homogenization model. The ab initio calculations employ density-functional theory (DFT) and the generalized gradient approximation (GGA). The thus determined elastic constants have been used to calculate the ratio between the bulk B and shear G moduli as an indication of brittle/ductile behavior. Based on this approach we have explored chemical trends in order to tailor mechanical properties. Using this information we have cast a selected set of Fe3Al-based ternary alloys, obtained for these the elastic constants by performing impulse excitation measurements at room as well as liquid nitrogen temperature and compared them with our theoretical results.
Ultrasonic Vacuum Chill Casting and Hot Rolling of FeAl-based Alloys
Authors: Šíma Vladimír , Málek Přemysl , Kozelský Petr , Schindler Ivo , Hána Petr
Published: February 2009

An ultrasonic device was designed to fabricate relatively small vacuum chill castings of FeAl-based alloys with improved microstructure. A special hot-rolling procedure preventing thermal shocks was used for the thermomechanical treatment of cast alloys.

The efficiency of ultrasonic vacuum casting is manifested by improved microstructure of hot-rolled iron aluminides Fe – 40 at.% Al with addition of C or Zr and B or Zr and B with 1 wt.% of Y2O3 particles.
Grain Refinement of γ-TiAl Based Alloys by Inoculation
Authors: Gosslar Daniel-Hendrik , Güenther Robert , Hartig Christian , Bormann Rüediger , Zollinger Julien , Steinbach Ingo
Published: February 2009

A significant grain refinement is achieved for a Ti-45Al (at.%) alloy via the addition of a novel Ti-Al-TiB2 master alloy. This refinement is attributed to a low lattice mismatch of TiB2 with the primary solidifying phase and its thermodynamic stability. Model calculations allow for the prediction of the grain size as a function of cooling rate, alloy constitution and particle size distribution and content. However, the model predictions are smaller than the experimentally observed grain size since the fraction of effective particles is overestimated.
Application of the Fluorine Effect to TiAl-Components
Authors: Donchev A. , Pflumm R. , Schütze M.
Published: February 2009

The oxidation resistance of TiAl-alloys can be improved by several orders of magnitude by fluorine doping of the surface zone of the material. The oxidation mechanism changes from the formation of a thick mixed oxide scale to a protective alumina layer. This fluorine treatment influences only the surface region of the components so that the bulk properties are not affected. Recent results achieved with TiAl-components showed the potential of a fluorine treatment for the use of TiAl in several high temperature applications. Turbine blades for aero engines made of TiAl were treated with fluorine by different methods and their performance during high temperature oxidation tests in air is shown. Further on by selective local fluorination a structured oxide scale develops on TiAl above 800°C. A simple high temperature activation cause the formation of areas covered by a thin alumina layer alternating with a thick mixed oxide scale where no fluorine was applied before oxidation. The aim is to reproduce a shark-skin pattern (tiny parallel ridges) on the surface in order to minimize the aero dynamic resistance of turbine blades rotating in a gas flow. Different methods used for this attempt and the corresponding results are also presented.
Processing, Microstructure, and Thermal Expansion Measurements for High Temperature Ru-Al-Cr B2 Alloys
Authors: Hashimoto Yutaka , Okamoto Norihiko L. , Acosta Manuel , Johnson David R , Inui Haruyuki
Published: February 2009

The B2 intermetallic compound RuAl has a melting temperature above 2000 °C and is a candidate for high temperature structural applications. A large extension of the B2 phase field is found in the Ru-Al-Cr system as was documented by the characterization of arc-melted and heat treated alloys. Two compositions consisting of Ru-35Al-19Cr and Ru-20Al-38Cr (at. %) were directionally solidified in an optical floating zone furnace. Depending upon the processing conditions, single phase, polycrystalline, B2 microstructures could be produced. The coefficient of thermal expansion (CTE) was measured from room temperature to 1250 °C for the Ru-20Al-38Cr alloy, and an average value of 11×10-6 K-1 was found. Additionally, the thermal conductivity was measured as 27 W/mK at room temperature for the Ru-20Al-38Cr B2 alloy and as 89 W/mK for binary RuAl.
Thermodynamic Re-Assessment of the Co-Nb System
Authors: He Cuiyun , Stein Frank , Palm M. , Raabe Dierk
Published: February 2009

A new thermodynamic assessment of the Co-Nb system is presented. All experimental phase diagram data available from the literature have been critically reviewed and assessed using thermodynamic models for the Gibbs energies of the individual phases (Thermo-Calc). Compared to previous assessments more elaborate models for the description of the C14 and C36 Laves phases and for the μ phase were employed. Thereby a calculated phase diagram is obtained which satisfactorily agrees with the experimental data.
Surface structure modification of Ni3Al foil catalysts by oxidation-reduction treatment
Authors: Jang Jun Hyuk , Xu Ya , Demura Masahiko , Wee Dang Moon , Hirano Toshiyuki
Published: February 2009

A two-step treatment, oxidation in air followed by reduction in hydrogen, was carried out to modify the smooth Ni3Al foil surface into Ni particles supported on the oxide structure. The surface structure significantly changed depending on the oxidation temperature. A layer of granular NiO formed on the outer surface and inner oxide zone (IOZ) over Ni3Al foil surface after oxidation at 973 K. The IOZ was a mixture of Al and Ni oxides. In contrast, a large amount of faceted NiO particles formed on the outer surface after oxidation at 1173 K. Beneath the NiO particles, NiAl2O4 thin layer formed on IOZ over Ni3Al foil surface. And then, these NiO was selectively reduced to Ni after reduction treatment, constituting an oxide supported Ni particles structure. These results suggest that it is possible to modify the surface structure of Ni3Al foils simply by oxidation-reduction treatment.
Direct Modeling of the Simultaneous Flow of Compressible Atomizing Gas Jets and a Weakly Compressible Liquid Intermetallic Stream During Gas Atomization
Authors: Tong Mingming , Browne David J.
Published: February 2009

The authors have developed a new atomization model enabling direct numerical simulation of the simultaneous flow of compressible atomizing gas jets and a weakly compressible liquid metal stream. It has been used to simulate the atomization of a Ni-50wt.%Al melt stream by argon gas jets in a closed-coupled atomizer. The 2D simulation results show that the presence of the liquid intermetallic stream significantly influences the field variables, particularly the aspiration pressure. At the gas plenum pressure used, the gas nozzles are choked and hence the gas flow upstream of the tip of the liquid delivery tube is not influenced by the presence of the liquid intermetallic stream, whereas the downstream gas flow is affected. Significant differences between model predictions assuming either incompressible or compressible gas are reported. Besides the atomization of liquid intermetallic stream by argon gas, this unified atomization model is available for use to simulate a variety of different twin-fluid atomization processes.
Physical and Mechanical Properties of Single Crystals of Co-Al-W Based Alloys with L12 Single-Phase and L12/fcc Two-Phase Microstructures
Authors: Inui Haruyuki , Tanaka Katsushi , Kishida Kyosuke , Okamoto Norihiko L. , Oohashi Takashi
Published: February 2009

Single-crystal elastic constants of Co3(Al,W) with the cubic L12 structure have been experimentally measured by resonance ultrasound spectroscopy at liquid helium temperature. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously reported. Two-phase microstructures with cuboidal L12 precipitates being well aligned parallel to <100> and well faceted parallel to {100} are expected to form very easily in Co-base superalloys because of the large value of E111/E100 and cij of Co3(Al,W). This is indeed confirmed by experiment. Values of yield stress obtained for both [001] and [¯123] orientations of L12/fcc two-phase single crystals moderately decrease with the increase in temperature up to 800°C and then decrease rapidly with temperature above 800°C without any anomaly in yield stress. Slip on {111} is observed to occur for both orientations in the whole temperature range investigated.
Microstructural Investigations of the Unusual Deformation Behavior of Nb2Co7
Authors: Stein Frank , Palm Martin , Frommeyer Georg , Jain Padam , Kumar Sharvan , Siggelkow Lisa , Grüner Daniel , Kreiner Guido , Leineweber Andreas
Published: February 2009

Usually, single-phase intermetallics in bulk form can easily be crushed into powder by hammering. It was therefore quite a surprise when we found that a bulk sample of the monoclinic intermetallic compound Nb2Co7 could be extensively deformed at room temperature without shattering or fracturing. In a previous paper, results of microhardness, compression, tensile and bending tests were provided and discussed [1]. In order to understand the observed unusual deformation behavior of this intermetallic phase, its hitherto unknown crystal structure has been studied and the microstructure of undeformed and deformed samples has been analyzed in the present investigation by light-optical, scanning electron and transmission electron microscopy.
Single-phase specimens deformed at very different strain rates (hammering and conventional compression testing) both show the occurrence of microcracks along grain boundaries which, in compression-deformed specimens, are strongly localized in extended shear bands oriented approximately 45° to the compression axis. The grains adjacent to the microcracks are heavily deformed whereas, away from the sheared regions, the samples remain free of any indication of plastic deformation.
Composition Dependence of the Hardness of Laves Phases in the Fe-Nb and Co-Nb Systems
Authors: Voß S. , Stein F. , Palm M. , Grüner D. , Kreiner G. , Frommeyer G. , Raabe D.
Published: February 2009

Single-phase Fe-Nb and Co-Nb Laves phase alloys were produced by arc melting and levitation melting. By casting the levitation melted alloys in a preheated mould and subsequent slow cooling to room temperature, solid rods of 15 mm in diameter and about 100 mm length of the brittle Laves phases were obtained. Within the extended homogeneity ranges of the NbFe2 and NbCo2 Laves phases, the Vickers hardness was measured in dependence on composition. The results show that the hardness has a maximum at the stoichiometric composition in both systems, indicating defect softening. Nanoindentation measurements on a Co-Nb diffusion couple confirm the dependence of the hardness on composition. In addition, these measurements indicate that the crystal structure of the Laves phase polytype – cubic or hexagonal – seems to have no effect on the hardness. Indentation fracture toughness KIC-IF data for the different polytypes of the Laves phases were evaluated from the Palmquist cracks originating from the edges of the Vickers indentations.
Controlled Assemble and Microfabrication of Zeolite Nanoparticles on SiO2 Substrates for Potential Biosensor Applications
Authors: Ozturk Seckin , Kamisoglu Kubra , Turan Rasit , Akata Burcu
Published: February 2009

Zeolite nanoparticles were organized into functional entities on SiO2 substrates and microfabrication technique was tested to form patterns of zeolite nanoparticles on SiO2 using the electron beam lithography (EBL). The effect of different techniques for efficient zeolite assembly on the SiO2 substrates was investigated. For this purpose, three different assembly techniques were tested. The first two methods are spin-coating (SC) and ultrasound aided strong agitation (US) methods, which were tested using bare and silanized zeolite nanoparticles. The third technique is the manual assembly method, which was also investigated using bare zeolites. All methods were facile in terms of experimental approach. Full coverage of the substrate was obtained after all three methods, however strong agitation (US) leads to better organization of zeolite nanoparticles. Among all techniques, manual assembly method lead to the most organized zeolite nanoparticles with full coverage. Although strong agitation (US) also results in organized zeolite entities, it was not found to be a suitable technique for EBL studies. Using the manual assembly method, it was possible to form monolayers of zeolite nanoparticles on SiO2 and to make patterns of zeolite nanoparticles by EBL, which offers a simple technique to engineer the surfaces for immobilization of biomolecules.
Multiple Phage-Based Magnetoelastic Biosensors System for the Detection of Salmonella typhimurium and Bacillus anthracis Spores
Authors: Huang S. , Li S. , Yang H. , Johnson M. L. , Lakshmanan Ramji S , Chen I.-H. , Petrenko V. A. , Barbaree J. M. , Chin B. A.
Published: February 2009

This paper presents a multiple magnetoelastic (ME) biosensor system for in-situ detection of S. typhimurium and B. anthracis spores in a flowing bacterial/spore suspension (5 x 101 - 5 x 108 cfu/ml). The ME biosensor was formed by immobilizing filamentous phage (specific to each detection target) on the ME platforms. An alternating magnetic field was used to resonate the ME biosensor to determine its resonance frequency. When cells/spores are bound to a ME biosensor surface, the additional mass of the cells/spores causes a decrease in the resonance frequency of the biosensor. The detection system was composed of a control sensor, an E2 phage-based biosensor (specific to S. typhimurium) and a JRB7 phage-based biosensor (specific to B. anthracis spores). The frequency response curves of the ME biosensors as a function of exposure time were then measured and the detection limit of the ME biosensor was observed to be 5 x 103 cfu/ml. The results show that phage-based ME biosensors can detect multiple pathogens simultaneously and offer good performance, including good sensitivity and rapid detection.
Metal Hydride Fluidic Artificial Muscle Actuation System
Authors: Vanderhoff Alexandra , Kim Kwang
Published: February 2009

The study determines the feasibility of a new actuation system that couples a fluidic artificial muscle designed by Festo [1] with a metal hydride hydrogen compressor to create a compact, lightweight, noiseless system capable of high forces and smooth actuation. An initial model for the complete system is developed. The analysis is restricted in some aspects concerning the complexity of the hydriding/dehydriding chemical process of the system and the three-dimensional geometry of the reactor, but it provides a useful comparison to other actuation devices and clearly reveals the parameters necessary for optimization of the actuation system in future work. The system shows comparable work output and has the benefits of biological muscle-like properties [2] for use in robotic systems. When compared to other previously developed metal hydride actuation systems the potential for increasing the reaction kinetics and improving the overall power output of the system is revealed. A comparison of the system to common actuation devices, including a biological muscle, shows similar stress and strain relations, but a lower power and frequency range due to the slow actuation time. Improving the reaction kinetics of the system will be the first approach to enhancing the system, along with optimization of the mass and type of metal hydride used in the reactor to produce a full actuation stoke of the fluidic muscle while minimizing system weight.
Finite Element Analysis of Aluminum Nitride Bimorph Actuators – The Influence of Contact Geometry and Position
Authors: Pagán V. R. , Korakakis D
Published: February 2009

In this work, the results of 3-dimensional finite element analysis (FEA) of Aluminum Nitride (AlN) homogeneous bimorphs (d31 mode) are shown. The coupled-field FEA simulations were performed using the commercially available software tool ANSYS. The effect of altering the contact geometry and position on the displacement, electric field, stress, and strain distributions for the static case is reported.

Piezoelectric beams are commonly used in microelectromechanical systems (MEMS) and also have many possible applications in smart sensor and actuator systems. For example, they have been used as the active element in microfluidic and microactuator MEMS devices. In the actuator mode, they employ the converse piezoelectric effect to couple electrical energy into mechanical deformation. Aluminum Nitride (AlN) based devices have attracted much interest because AlN is a piezoelectric material with high thermal stability, high dielectric strength, a reasonable electromechanical coupling coefficient, and a perfect compatibility with standard silicon processing techniques.
Sensing Shape Recovery using Conductivity Noise in Thin Films of NiTi Shape Memory Alloys
Authors: Chandni U. , Manjula M.V. , Ghosh Arindam , Vijaya H.S. , Mohan S.
Published: February 2009

Low frequency fluctuations in the electrical resistivity, or noise, have been used as a sensitive tool to probe into the temperature driven martensite transition in dc magnetron sputtered thin films of nickel titanium shape-memory alloys. Even in the equilibrium or static case, the noise magnitude was more than nine orders of magnitude larger than conventional metallic thin films and had a characteristic dependence on temperature. We observe that the noise while the temperature is being ramped is far larger as compared to the equilibrium noise indicating the sensitivity of electrical resistivity to the nucleation and propagation of domains during the shape recovery. Further, the higher order statistics suggests the existence of long range correlations during the transition. This new characterization is based on the kinetics of disorder in the system and separate from existing techniques and can be integrated to many device applications of shape memory alloys for in-situ shape recovery sensing.
Multiscale Modeling of Dislocation Mechanisms in Nanoscale Multilayered Composites
Authors: Akasheh Firas , Zbib Hussein M , Akarapu Sreekanth , Overman Cory , Bahr David
Published: February 2009

It is well known that the mechanical behavior of nanoscale multilayered composites is strongly governed by single dislocation mechanisms and dislocation-interface interactions. Such interactions are complex and multiscale in nature. In this work, two such significant effects are modeled within the dislocation dynamics-continuum plasticity framework: elastic properties mismatch (Koehler image forces) and interface shearing in the case of weak interfaces. The superposition principle is used to introduce the stress fields due to both effects solved for by finite elements. The validation of both methodologies is presented. Furthermore, it was found that the layer-confined threading stress of a dislocation in hair-pin configuration increases if the layer is surrounded by layers made of a stiffer material and that this strengthening effect grows more significant as the layer thickness decreases. The observation made through molecular dynamics, that weak interfaces act as dislocation sinks, was also captured with our approach. A dislocation is attracted to the interface independent of its sign or character. Also the force increases sharply as the dislocation approaches the interface. These findings agree with published molecular dynamics simulations and dislocation-based equilibrium models of this type of interaction.
Optical Interferometric Biosensor with PMMA as Functional Layer
Authors: Wang Wenhui , Ma Xiaodong , Clarizia Lisa-Jo , Wang Xingwei , McDonald Melisenda
Published: February 2009

Silica-on-silicon label-free biosensor with PMMA (Poly(methyl methacrylate), as the functional layer was designed, fabricated, and tested. The sensor is based on Fabry Perot (FP) interferometry. Specific binding was tested with Human IgG and anti-Human IgG. Non-specific binding was tested with Human IgG and Mouse IgG. The testing results show that the sensor has a nearly six-fold greater response upon specific binding than upon non specific binding. Thermal and long term stability experiments show that the sensor is insensitive to the environment fluctuation. The fabrication process is simple without special surface treatment. In addition, this biosensor is inexpensive and easy to use.
Investigation of Steady-State and Time-dependent Luminescence Properties of Colloidal InGaP Quantum Dots
Authors: Chatterjee Subhasish , Valappil Nikesh V. , Menon Vinod M.
Published: February 2009

Quantum dots play a promising role in the development of novel optical and biosensing devices. In this study, we investigated steady state and time-dependent luminescence properties of InGaP/ZnS core/shell colloidal quantum dots in a solution phase at room temperature. The steady state experiments exhibited an emission maximum at 650 nm with full width at half maximum of ~ 85 nm, and strong first-excitonic absorption peak at 600 nm. The time-resolved luminescence measurements depicted a bi-exponential decay profile with lifetimes of τ1 ~ 47 ns and τ2 ~ 142 ns at the emission maximum. Additionally, luminescence quenching and lifetime reduction due to resonance energy transfer between the quantum dot and an absorber are demonstrated. Our results support the plausibility of using these InGaP quantum dots as an effective alternative to highly toxic conventional Cd or Pb based colloidal quantum dots for biological applications.
Amplified Fluorescence Turn-on Assay for Mercury(II) Based on Conjugated Polyfluorene Derivatives and Nanospheres
Authors: Wang Yusong , Liu Bin
Published: February 2009

Detection of mercury with high sensitivity and selectivity constitutes a significant research concern. Here, we report an amplified fluorescence turn-on assay for mercury(II) with an improved performance. This sensing system takes advantage of optically amplifying fluorescent conjugated polyfluorene derivatives and DNA immobilized silica nanospheres (NSs) in addition to the specific thymine- mercury(II)-thymine(T- Hg2+-T) interaction. The employment of ion-specific T- Hg2+-T coordination increases the melting temperature (Tm) of the double-stranded DNA (dsDNA) on the hybridized NS surface. After thermal washing at 45 °C, the Hg2+ treated sample (dsDNA-NS) was effectively differentiated from that treated with nonspecific ions through monitoring fluorescence emission of fluorescein (Fl) labeled target DNA remained on the NS surface. Finally, a cationic conjugated polyfluorene derivative (CCP) was introduced to electrostatically associate with the DNA molecules on the NS surface, resulting in an amplified Fl signal via fluorescence resonance energy transfer (FRET) from the CCP to the dye molecule. In comparison with the use of Fl alone as a signal reporter, the presence of CCP significantly enhances the detection fluorescence intensity, reduces false-positive signal, and improves the detection selectivity for mercury(II). Further improvement in the probe design could yield more efficient metal ion sensors, which have the potential to be operated at room temperature and for the detection of other metal ions besides mercury(II).
Stochastic System Identification of the Compliance of Conducting Polymers
Authors: Pillai Priam Vasudevan , Hunter Ian W.
Published: February 2009

Conducting polymers such as polypyrrole, polythiophene and polyaniline are currently studied as novel biologically inspired actuators. The actuation mechanism of these materials depends upon the motion of ions in and out of the polymer film during electrochemical cycling. The diffusion of ions into the bulk of the film causes the dynamic mechanical compliance (or modulus) of the material to change during the actuation process. The mechanism of this change in compliance is not fully understood as it can depend on many different factors such as oxidation state, solvation of the film and the level of counter ion swelling. In-situ measurement of the dynamic compliance of polypyrrole as a function of charge is difficult since the compliance depends upon the excitation frequency as well as the electrochemical stimulus. Pytel et al [1] studied the effect of the changing elastic modulus in-situ at a fixed frequency. In this study we describe a technique to measure the compliance response of polypyrrole as a function of frequency and electrochemistry. A voltage input and a simultaneous stress input was applied to polypyrrole actuated in neat 1-butyl-3-methylimidazolium hexaflourophosphate. The stress input was a stochastic force with a bandwidth of 30 Hz and it allows us to compute the mechanical compliance transfer function of polypyrrole as function of the electrochemistry. Our studies show that the low frequency compliance changes by 50% as charge was injected into the polymer. The compliance changes reversibly as ions diffuse in and out of the film which indicates that the compliance depends upon the level of counter ion swelling.
Dielectric Response of Ceramic-Polymer Composite with High Permittivity
Authors: Shan Xiaobing , Zhang Lin , Wu Pei-xuan , Xu Canran , Cheng Zhong-Yang
Published: February 2009

Based on solution casting method, a ceramic [CaCu3Ti4O12 (CCTO)]-Polymer [P(VDF-TrFE)] composite with flexibility has been synthesized and its dielectric response has been studied. The CCTO ceramic powders were prepared by traditional sintering method and were milled with a relative uniform size. The dielectric properties of these films with micro-size and nano-size CCTO particle, as well as different polymer matrixes were determined. The process was optimized by hot pressing and surface modification to achieve high dielectric constant. A dielectric constant about 175 for one layer composite with high flexibility using silane coupling agent was obtained at 1 kHz at room temperature.
Strain Sensitivity in Ion-implanted Polymers
Authors: Di Girolamo Giovanni , Massaro Marcello , Piscopiello Emanuela , Pesce Emanuela , Esposito Ciro , Tapfer Leander , Vittori Antisari Marco
Published: February 2009

Ion implantation process was used to fabricate ultra-thin conducting films in inert polymers and to tailor the surface electrical properties for strain gauge applications. To this aim, polycarbonate substrates were irradiated at room temperature with low energy Cu+ ions of 60 keV at 1 μA/cm2 and with doses ranging from 1×1016 to 1×1017 ions/cm2. XRD and TEM measurements on the nanocomposite surfaces demonstrated the spontaneous precipitation of Cu nanocrystals at 1×1016 ions/cm2 fluence. These nanocrystals were located at about 50 nm - 80 nm below the polymer surface in accordance with TRIM calculations. Optical absorption spectra exhibited a surface plasmon resonance (SPR) at 2 eV, in accordance with the formation of Cu nanoparticles. For doses of 5×1016 ions/cm2 the formation of a continuous nanocrystalline Cu subsurface film occurred and a well pronounced SPR peak was observed. Otherwise, for higher doses (1×1017 ions/cm2) a damaged and structurally disordered film was obtained and the SPR peak was smeared out. Electrical conductivity measurements clearly indicated a reduced electrical resistance for the samples implanted with a doses up to 5×1016 ions/cm2, whereas higher doses (1×1017 ions/cm2) resulted detrimental for the electrical properties, probably due to the radiation induced damage. The dependence of electrical resistance from surface load was evaluated during compression tests up to 3 MPa. A significant linear variation of the electrical resistance with the surface load was found and could be related to the changes in the spatial distribution of nanoparticles inside the copper film.
Characterization of the Charging and Long Term Performance of Cytop Electret Layers for MEMS Applications
Authors: Bartsch Ulrich , Gaspar Joao , Paul Oliver
Published: February 2009

This paper reports on the characterization of the charge stability of an amorphous fluoropolymer electret called Cytop. Cytop is a dissolved polymer material, compatible with standard micromachining fabrication technologies. In this study, Cytop layers are deposited and patterned on Pyrex and silicon substrates, followed by the electrical poling of the material by corona discharge using a customized charging station. The long-term performance of Cytop as an electret material is evaluated as a function of several relevant charging parameters. The results reveal highly stable layers, able to keep at least 92% of the initial charge 143 days after the corona charging stored at 23°C.
Liquid Crystal Nanoparticles- LCNANOP: A SONSII Collaborative Research Project
Authors: Goodby John William , Bates Martin , Saez Isabel , Gorecka Ewa , Kitzerow Heinz , Guillon Daniel , Donnio Bertrand , Serrano Jose-Luis , Deschenaux Robert
Published: February 2009

LC-NANOP is an ESF EUROCORES SONS Collaborative Research Project that is addressing an innovative approach to self-organized nanostructures by combination of a variety of organic, inorganic and metal scaffolds with the unique self-organization properties of liquid crystals to obtain liquid crystal nano-particles. LC-NANOP is concerned with the synthesis, analysis, characterization, modeling and physico-chemical properties of super- and supra-molecular systems which are formed from a nano-particle as a central scaffold, surrounded by a layer of liquid crystal. The self-organization properties of the liquid crystal coating is the driving force leading to the self-assembly of the nano-particles into secondary or tertiary hierarchical structures, with emphasis on the systematic variation of nano-particle size, chirality, shape and functionality. This bottom-up approach to nano-structuring is very powerful as it combines the extraordinary variety of morphologies that liquid crystals present with the combination of functional entities, relevant for chemical, biological, optoelectronic, and photonic tasks, etc, to create ordered nano-structures that can be controlled by external stimuli.
Design and Fabrication of MEMS Piezoelectric Rotational Actuators
Authors: Gee Danny , Churaman Wayne , Currano Luke , Zakar Eugene
Published: February 2009

As Microelectromechanical Systems (MEMS) continue to mature and increase in design complexity, the need to exploit rotation in MEMS devices has become more apparent. An in-plane piezoelectric rotational actuator is proposed that provides free deflections on the order of 1.5° with applied biases of less than 35V and nanoampere currents. Moments up to 6×10−8 N·m, corresponding to forces of 125 μN, were measured using MEMS cantilever springs. The actuator utilizes the low-power, high-force characteristics of lead zirconate titanate and a coupled, dual offset-beam design to provide efficient rotational displacement. The resulting power consumption is three orders of magnitude less than current electrothermal rotational designs.
Fast and Controlled Integration of Carbon Nanotubes into Microstructures
Authors: Xu Wenjun , Ji Chang-Hyeon , Shafer Richard , Allen Mark
Published: February 2009

In this paper, we report the results of a rapid and room temperature integration approach for the selective and structured deposition of carbon nanotubes (CNTs) into three-dimensional microstructures. The approach exploits electrophoretic deposition (EPD) from an aqueous suspension of CNTs, together with suitably patterned and electrically-energized microstructure-bearing substrates. Uniform 2-D and 3-D micropatterns of CNTs on wafer scale have been achieved in less than 4 minutes with controllable thicknesses ranging from 133nm to several micrometers. Orientation of the deposited CNTs was observed in microstructures with certain dimensions. Surface hydrophobicity of the microstructures was found to be critical in achieving well-defined micropatterning of CNTs. A hydrophobic microstructure surface leads to the selective patterning profiles of CNTs, while a hydrophilic surface induces CNTs assembly over the entire microstructure, with resultant loss of selectivity. This approach can be further extended to fabricate 3-D micropatterns with multilayer materials on flexible substrate through the aid of transfer micromolding techniques.
A Novel Technique to Determine Elastic Constants of Thin Films
Authors: Martinschitz Klaus , Daniel Rostislav , Mitterer Christian , Jozef Keckes
Published: February 2009

A new X-ray diffraction technique to determine elastic moduli of polycrystalline thin films deposited on monocrystalline substrates is demonstrated. The technique is based on the combination of sin2ψ and X-ray diffraction wafer curvature techniques which are used to characterize X-ray elastic strains and macroscopic stress in thin film. The strain measurements must be performed for various hkl reflections. The stresses are determined from the substrate curvature applying the Stoney's equation. The stress and strain values are used to calculate hkl reflection dependent X-ray elastic moduli. The mechanical elastic moduli can be then extrapolated from X-ray elastic moduli considering film macroscopic elastic anisotropy. The derived approach shows for which reflection and corresponding value of the X-ray anisotropic factor Γ the X-ray elastic moduli are equal to their mechanical counterparts in the case of fibre textured cubic polycrystalline aggregates. The approach is independent of the crystal elastic anisotropy and depends on the fibre texture type, the texture sharpness, the amount of randomly oriented crystallites and on the supposed grain interaction model. The new method is demonstrated on a fiber textured Cu thin film deposited on monocrystalline Si(100) substrate. The advantage of the new technique remains in the fact that moduli are determined non-destructively, using a static diffraction experiment and represent volume averaged quantities.
Surface Treated PDMS by UV-Vis Light for Microfluidic Device
Authors: Kano Seisuke , Matsumoto Sohei , Ichikawa Naoki
Published: February 2009

Hydrophobic property of PDMS surface was improved by the 400 W UV-Vis lamp light irradiation in the atmospheric condition for several ten minutes. As a result of this surface treatment, the surface became to hydrophilic character for one month long. This surface treatment technique applied to PDMS micro-fluidic device and verified valve-less switching. The UV-Vis light irradiated to PDMS micro fluidic pattern with partly covered by aluminum foil. Finally inlet and outlets were connected 0.5 mm diameter tubes. The syringe pumps injected the distilled water into the inlet of the PDMS micro channel at the flow rates of 0.5, 5.0, and 50 μl/min for the both width channel. As results of water injection water flowed only the UV-Vis treated channel at the flow rates of 0.5 and 5.0 μl/min. On the other hand, the water flowed for all channels at the flow rate of 50 μl/min. This result was observed from 5.0 μl/min flow again for both width devices which dried by air. These results were occurred by the difference of the flow conductance and wettability. The mechanism of this hyrophilicity of PDMS was reported to form Si-O in the surface by means of glassy surface. From the IR spectra, the Si-O-Si peak shifted to higher wave number for UV-Vis irradiated PDMS than the untreated PDMS comparing with the other IR peaks. This result showed that the Si-O-Si network bonding of PDMS changed to the O-Si-O bonding around the surface.
Metal Wafer Bonding for MEMS Applications
Authors: Dragoi Viorel , Mittendorfer Gerald , Murauer Franz , Cakmak Erkan , Pabo Eric
Published: February 2009

Metal layers can be used as bonding layers at wafer-level in MEMS manufacturing processes for device assembly as well as just for electrical integration of different levels. One has to distinguish between two main types of processes: metal diffusion bonding and bonding with formation of an interface eutectic alloy layer or an intermetallic compound. The different process principles determine also the applications area for each. From electrical interconnections to wafer-level packaging (with emphasis on vacuum packaging) metal wafer bonding is a very important technology in MEMS manufacturing processes.
A Perturbation-Based Method for Extracting Elastic Properties during Spherical Indentation of an Elastic Film/Substrate Bilayer
Authors: Kim Jae Hun , Gouldstone Andrew , Korach Chad S.
Published: February 2009

Accurate mechanical property measurement of films on substrates by instrumented indentation requires a solution describing the effective modulus of the film/substrate system. Here, a first-order elastic perturbation solution for spherical punch indentation on a film/substrate system is presented. Finite element method (FEM) simulations were conducted for comparison with the analytic solution. FEM results indicate that the new solution is valid for a practical range of modulus mismatch, especially for a stiff film on a compliant substrate.
Microfabrication of Si/SiO2–Spherical Shells as a Path to Sub-mm3 Autonomous Robotic Systems
Authors: Vasilyev Vladimir , Reid James R. , Webster Richard T.
Published: February 2009

A process for forming thin (1-3 μm) stacks of Si/SiO2 or SiO2/Si/SiO2 layers into spherical shells 0.5-3.0 mm in diameter is demonstrated as the baseline for realizing sub-mm3 micro-robots. The fabrication process combines bulk and thin-film micromachining, design of novel masks, and multistage wet and dry etching to release the layers from the substrate. The released layers curl up, self assembling into a spherical shell. The radius of curvature of the released stack is a function of the type, thickness, and residual stresses in the layers. The diameter of the resulting shells is calculated using a mechanical model of the multi-layer stacks. This calculation is compared with measurements of fabricated spheres. The fabrication process is compatible with CMOS circuitry, and future work will focus on realizing spheres with embedded solar cell as a power source and a capacitor for energy storage, which will result in a functional micro-robot.