bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion Transport and Storage in Ionic Polymer Bending Actuators
Authors: Lin Jun-Hong , Liu Yang , Hatipoglu Gokhan , Zhang Qiming 
Published: April 2011

ABSTRACTThe actuation of ionic polymer actuators is mainly caused by the ion transport and excess ions storage in the membrane and electrodes. To quantify the charge transport behavior, a time domain method based on Poisson-Nernst-Planck equations was applied. The time domain transient current in response to a step voltage can provide insights on the charge transport and storage behaviors in the membranes. In this study, we investigate the charge transport behavior of Aquivion ionomer with different uptakes of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). A critical uptake and voltage independent of charge transport behavior were observed. The results also show that bending actuations of the Aquivion membrane with 40wt% EMI-Tf is much larger than that of Nafion, indicating that the shorter flexible side chain ionomer possesses a better electromechanical coupling between the excess ions and the membrane backbones, while not affect the actuation speed.
Thermo-switchable Polymer Dielectrics
Authors: Johnson Ross S. , Kholwadwala Fenil M. , Dirk Shawn M. 
Published: April 2011

ABSTRACTWe are interested in utilizing the thermo-switchable properties of precursor poly(p-phenylene vinylene) (PPV) polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material irreversibly switching from an insulator to a conducting polymer. By utilizing different leaving groups on the polymer main chain, the temperature at which the polymer transforms into a conductor can be varied over a range of temperatures. Electrical characterization of thin-film capacitors prepared from several precursor PPV polymers indicates that these materials have good dielectric properties until they reach elevated temperatures, at which point conjugation of the polymer backbone effectively disables the device. Here, we present the synthesis, dielectric processing, and electrical characterization of a new thermo-switchable polymer dielectric.
Modified Polyaniline Nanofibres for Ascorbic Acid Detection
Authors: Florea Larisa , Lahiff Emer , Diamond Dermot 
Published: April 2011

ABSTRACTPolyaniline nanofibres (PAni) can be surface modified to improve electroactivity over a broader pH range. The technique we describe here can be used to attach carboxylic acid terminated substituents. Modified nanofibres maintain their high surface area, and ability to switch between different redox states. These properties make the material suitable for sensing applications. Unlike unmodified PAni, the functionalised material is self-doping and hence more stable in higher pH solutions. Here we demonstrate how modified PAni fibres can be used for the detection of ascorbic acid.
Quantitative Studies of Long-term Stable, Top-down Fabricated Silicon Nanowire pH Sensor
Authors: Choi Sun , Pisano Albert P. 
Published: April 2011

ABSTRACTWe report simple and effective methods to develop long-term, stable silicon nanowire-based pH sensors and systematic studies of the performance of the developed sensors. In this work, we fabricate silicon nanowire pH sensors based on top-down fabrication processes such as E-beam lithography and conventional photolithography. In order to improve the stability of the sensor performance, the sensors are coated with a passivation layer (silicon nitride) for effective electrical insulation and ion-blocking. The stability, the pH sensitivity, and the repeatability of the sensor response are critically analyzed with regard to the physics of sensing interface between sample liquid and the sensing surface. The studies verify that the sensor with a passivation layer over critical thickness show long-term, stable sensor response without long-term drift. The studies also show the detection of pH level with silicon nanowire sensors is repeatable only after proper rinsing of sensor surfaces and there exists trade-off between the stability and the pH sensitivity of sensor response.
Effect of Non-equilibrium Pulsed Ejection of Si Species into Background Gas on the Formation of Si Nanocrystallite and Nanocrystal-film
Authors: Umezu Ikurou , Okubo Shunto , Sugimura Akira 
Published: April 2011

ABSTRACTThe Si nanocrystal-films are prepared by pulsed laser ablation of Si target in a mixture of helium and hydrogen gas. The total gas pressure and hydrogen partial gas pressure were varied to control structure of nanocrystal-film. The surface of Si nanocrystallite was hydrogenated and degree of hydrogenation increased with increasing hydrogen partial gas pressure. The aggregate structure of nanocrystal-film depended on both the total gas pressure and the hydrogen partial gas pressure. The former and the latter alter spatial confinement of Si species during deposition and the surface hydrogenation of individual nanocrystal, respectively. Spatial confinement increases probability of collision between nanocrystals in the plume. While, surface hydrogenation prevents coalescence of nanocrystals. The individual or aggregated nanocrystals formed in the plume reach the substrate and the nanocrystal-film is deposited on the substrate. The non-equilibrium growth processes during pulsed laser ablation are essential for the formation of the surface structure and the subsequent nanocrystal-film growth. Our results indicate that the structure of nanocrystal-film depends on the probabilities of collision and coalescence between nanocrystals in the plume. These probabilities can be varied by controlling the total gas pressure and the hydrogen partial gas pressure.
Mesoscale Simulation of Morphology in Hydrated Perfluorosulfonic Acid Membranes
Authors: Wescott James T. , Qi Yue , Subramanian Lalitha , Capehart T. Weston 
Published: April 2011

ABSTRACTCurrent fuel cell proton exchange membranes (PEM) rely on a random network of conducting hydrophilic domains to transport protons across the membrane. Despite extensive investigation, details of the structure of the hydrophilic domains in these membranes remain unresolved. In this study a dynamic self-consistent mean field theory has been applied to obtain the morphologies of hydrated Perfluorosulfonic Acid (PFSA) (equivalent weight of 1100) as a model for Nafion® at several water contents. A coarse-grained mesoscale model was developed by dividing the system into three components: backbone, side chain, and water. The interaction parameters for this model were generated using classical molecular dynamics. The simulated morphology shows phase separated micelles filled with water, surrounded by side chains containing sulfonic groups, and embedded in the fluorocarbon matrix. For λ<6 (λ gives the ratio of water molecules to sulfonic groups), the isolated domains obtained from simulation are nearly spherical with a domain size smaller than that fitted to experimental SANS data. For λ>8; the domains deform into elliptical and barbell shapes as they merge. The simulated morphology, hydrophilic domain size and shape are generally consistent with some experimental observations.
Application of Carbon Nanotube/Polymer Composites as Electrode for Polyelectrolyte Membrane Fuel Cells
Authors: Prehn Kirsten , Nunes Suzana Pereira , Schulte Karl 
Published: April 2011

ABSTRACTCarbon nanotubes (CNTs) possess remarkable mechanical and physical characteristics due to their unique structure. The high electrical conductivity of CNTs in combination with their structural and chemical properties make this material attractive for improvement of the performance of the electrodes in electrochemical devices, such as polyelectrolyte-membrane fuel cells. The requirements in particular for this application are manifold. Since the electrode is the reaction layer in a fuel cell, the electrolyte, being proton conductive, has to be combined with catalytic activity and electron conductivity, as well as chemical stability against the reactants. Employed as an electrode, CNTs offer feasibilities to enhance the efficiency of fuel cells due to an improved contact between electrolyte-membrane, electrode and catalyst. An other promising capacity is the large specific surface area of CNTs on which catalyst particles can be distributed in small clusters. This provides an increase of the catalyst efficiency on account of a higher reactive surface area which enables a reduction of the amount of catalyst required. In combination with a good electron conductivity, a CNT based electrode is a potential alternative fuel cell electrode. The presented work focuses on a membrane assembly, consisting of CNTs as electrode and sulfonated polyether ether ketone (SPEEK), which is used as polyelectrolyte in direct methanol fuel cells (DMFCs) and provides good proton conductivity. Nanocomposites were produced by a modified drop casting technique, leading to the formation of an asymmetric structure. Due to the process, the compounded membranes provided a single-sided electron conductivity on account of the CNTs. By using different 3D-structured CNT-carpets, varying in thickness, density and setup, the properties of the electrode membrane could be adjusted for its special application. In consideration of the insertion of platinum and ruthenium particles as catalyst in nano-sized clusters on the CNTs, carpets were modified and grown in a CVD-process at the TUHH. The evaluation of the assemblies comprised SEM-pictures in order to analyse the 3D-nano-structure, measurements of the surface conductivity as well as tests in a fuel cell.
Microstructural Control by a Rolling-Annealing Technique and Hydrogen Permeability in the Nb-Ti-Ni alloys
Authors: Tokui Sho , Ishikawa Kazuhiro , Aoki Kiyoshi 
Published: April 2011

ABSTRACTCold rolling reduction, microstructural changes induced by cold rolling and subsequent heat treatment, hydrogen permeability (Φ) of Nb-Ti-Ni duplex phase alloys have been investigated using a rolling machine, a scanning electron microscope (SEM), an X-ray diffractometer (XRD) and a gas flow technique. The Nb-Ti-Ni alloys on the line connecting the TiNi compound and the Nb90Ti10solid solution alloy show higher rolling reduction of 70 % or more at room temperature. The value of Φ for the Nb40Ti30Ni30alloy, which is higher than that of pure Pd at 673K, decreases with increasing rolling reduction and attains to one third of that of the original one by the 50 % rolling reduction. The eutectic microstructure consisting of {TiNi+(Nb, Ti)} phases disappears and is replaced by the (Nb, Ti) phase embedded in the TiNi matrix by heat treatment 1073 K or more and for 605ks in a vacuum. However, its Φ value remains as it was by annealing at 1273 K or less, while it increases with increasing annealing periods at 1373 K or more and recovers to the original value after annealing for 605ks. These experimental results indicate that rolling and annealing techniques are the useful method for the preparation of a hydrogen permeable Nb-Ti-Ni alloy membrane.
Thermoelectric properties of epitaxial and topotaxial NaxCoO2 thin films
Authors: Venimadhav Adyam , Ma Z , Li Qi , Soukiassian A , Xi X. X. , Schlom D. G. , Arroyave R. , Liu Z. K. , Lee Minhyea , Ong N. P. 
Published: April 2011

ABSTRACTWe report structural, electrical, and thermopower properties of epitaxial and topotaxial NaxCoO2 thin films on (0001) sapphire substrate. Topotaxial NaxCoO2 films were prepared by converting an epitaxial Co3O4 film to NaxCoO2 by annealing in Na vapor and epitaxial NaxCoO2 films were obtained by pulsed laser deposition. All the films are c-axis oriented. For topotaxial films, annealing in different Na vapor pressures resulted in films with different Na concentrations, which showed distinct transport properties. For directly deposited epitaxial films by pulsed laser deposition, deposition parameters are found to control the Na concentration and hence the film properties. The largest thermoelectric power of the samples made by different methods is found to be similar in the range of 70-100 μV/K at room temperature
Preparation of [(Bi2Te3)x(HfTe2)]y Superlattices
Authors: Schmid Benjamin Allen , Harris Fred R , Johnson David C 
Published: April 2011

ABSTRACTThe synthesis of a number of (Bi2Te3)x(HfTe2)y superlattices was accomplished using the modulated elemental reactants (MER) method. The samples were characterized using X-ray reflectivity and X-ray diffraction in the as deposited (amorphous) state and as a function of annealing temperature and time.
Preparation of (TiTe2)x(Sb2Te3)y(TiTe2)3(Bi2Te3)z Superlattices using the Modulated Elemental Reactants (MER) Technique
Authors: Mortensen Clay , Matelich Ben , Schmid Benjamin , Rostek Raimar , Johnson David C. 
Published: April 2011

AbstractDifficulty in preparing (Bi2Te3)x(Sb2Te3)y superlattices due to interdiffusion of Sb and Bi led to the study of interduffusion barriers. TiTe2 has been explored as an interdiffusion barrier to minimize the interdiffusion of Sb and Bi, as TiTe2 is not soluble in either Bi2Te3 or Sb2Te3. Preparation of (TiTe2)3(Sb2Te3)y(TiTe2)3(Bi2Te3)z superlattices has been achieved with varying x, y and z. The formation of the superlattices was studied as a function of annealing temperature and time. TOF-SIMS depth profiles were used to study the extent of interdiffusion in the samples. Unit cell control was achieved allowing for the preparation of an array of superlattices with varying periods with very good reproducibility.
Ab initiostudies of electronic structure of defects on the Te sites in PbTe
Authors: Ahmad Salameh , Mahanti S. D. , Kanatzidis M. G. 
Published: April 2011

ABSTRACTAb initioelectronic structure calculations have been carried out to understand the nature of anionic defect states in PbTe. We find that Te vacancies strongly perturb the electronic density of states (DOS) near the band gap region. New states of predominantly Pb p character appear in the band gap. Iodine is an ideal substitutional defect and a donor. Sulpher and Selenium do not affect the states near the conduction band minimum but suppress the DOS near the valence band maximum. These results have important implications on the thermoelectric properties of PbTe and PbTexM1−x(M=S, Se) ternary systems.
Thermoelectric Modeling of Si-Si1−xGex Ordered Nanowire Composites
Authors: Tang Ming Y. , Dresselhaus Mildred S. , Yang Ronggui , Chen Gang 
Published: April 2011

ABSTRACTThermoelectrics have always been attractive for power generation and cooling because of power reliability and environmentally friendly issues. However, this concept remains non-competitive due to the limitation in the efficiency of available thermoelectric materials and device designs [1]. In the 1990s, Hicks and Dresselhaus predicted the possibility of a dramatic enhancement in thermoelectric performance based on the special behavior of low dimensional materials [2, 3]. This enhancement is in part due to the increase in quantum confinement effects, the increase in electronic density of states at specified energies, and the increase in the phonon interface scattering for low dimensional structures.Nanowires and core-shell nanowires can be considered to be model systems to illustrate representative behavior in low dimensional thermoelectric materials. It is expected that a system made out of nanowires or core-shell nanowires would have a higher thermoelectric performance than its bulk counterpart due to an increase in the number of interfaces. The interfaces that are introduced must be such that phonons are scattered more strongly than are electrons. Theoretical studies have been carried out to better understand the transport properties of Si-Si1−xGex ordered nanowire composites. The composite is modeled as having Si wires embedded in a Si1−xGex host matrix. Thus, core-shell Si/Si1−xGex nanowires can be considered as a building block of the composite. The effect of the wire diameter and the shell alloy composition on ZT is presented.
Thermoelectric properties of icosahedral cluster solids – Metallic-Covalent Bonding Conversion and Weakly Bonded Rigid Heavy Clusters
Authors: Kimura Kaoru , Okada Junpei Tamura , Kim Hongki , Hamamatsu Takehito , Nagata Tomohiro , Kirihara Kazuhiro 
Published: April 2011

ABSTRACTBoron- or Aluminum-rich icosahedral cluster solids (ICS) consist mainly of B12 or Al12 icosahedral clusters. In the ICS, a slight change of the structure or environment of icosahedral cluster can cause metallic-covalent bonding conversion, which can cause that the electrical conductivity σ and the Seebeck coefficient S can be as high as those of metals and semiconductors, respectively. Five-fold symmetry of the icosahedral cluster does not match with the translational symmetry of a crystal, consequently makes lower thermal conductivity with complex structure. For these reasons, ICS are promising candidates for thermoelectric materials.Using MEM/Rietvelt method, we successfully obtained the clear image of the electron density distribution for alpha-AlReSi approximant crystal. The bond strength distributes widely from weak metallic to strong covalent bond, and the intra-cluster bonds are stronger than the inter-cluster ones. This means that alpha-AlReSi is located at the intermediate state of molecular, metallic- and covalent-bonded solids. Composition dependences of atomic density and quasi-lattice constant for AlPdRe icosahedral quasicrystals show the above situation is the same in the quasicrystals. The thermoelectric figure of merit Z and the effective mass m* of AlPdRe quasicrystals can be increased by strengthening the intra- and weakening the inter-cluster bonds. According to this scenario, Z was improved by a factor of 1.5 by substitution of Ru for Re.In β-rhombohedral boron, several interstitial sites, which have space large enough to accommodate foreign atoms, are known. For the V doped sample, in which V atoms mainly occupy A1 site, the metallic-covalent bonding conversion may occur, σ is increased very much, S is decreased even to negative value and kappa is decreased. The maximum and n-type ZT value is obtained and is approaching to that of B4C, which is considered to have the largest and p-type ZT value in boron-rich ICS.
Thermoelectric Properties of K2Bi8Se13−xSx Solid Solutions
Authors: Kyratsi Theodora , Lal Sangeeta , Hogan Tim , Kanatzidis Mercouri G. 
Published: April 2011

AbstractDerivatives of β-K2Bi8Se13 are an interesting series of materials for thermoelectric investigations due to their very low thermal conductivity and highly anisotropic electrical properties. Up to now substitutions on the Bi and alkali metal sites have been studied in order to tune the thermoelectric properties. In this work, the thermoelectric properties of the sulfur-substituted K2Bi8Se13−xSx (0<x<13) are presented with respect to Seebeck coefficient, the electrical and thermal conductivity as a function of temperature. Seebeck coefficient measurements showed the n-type character of all members while electrical conductivity shows higher values compare to the other solid solution series of the same type. The lattice thermal conductivity is affected due to the Se/S disorder. The temperature dependence of the figure-of-merit ZT shows that these materials have potential for high temperatures applications with promising thermoelectric performance.
High Temperature Thermoelectric Properies of LnPdX (Ln = lanthanide; X = Sb, Bi) Ternary Compounds
Authors: Sekimoto Takeyuki , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke 
Published: April 2011

ABSTRACTTernary compounds LnPdX (Ln = lanthanide elements of La, Gd, Er; X = Sb, Bi) were prepared by a spark plasma sintering (SPS) technique. The crystal structure of LaPdSb and GdPdSb was confirmed to be a hexagonal ZrBeSi-type structure and different from the other compounds with a MgAgAs-type structure. The electrical resistivities ρ of LaPdSb and GdPdSb indicate the metallic or semimetallic characteristics, while those of ErPdSb and LnPdBi indicate semiconductor characteristics. From the ln ρ − 1/T plot, the band gap energies Eg were estimated to be 0.28, 0.053, 0.081, and 0.049 eV for ErPdSb, LaPdBi, GdPdBi, and ErPdBi, respectively. All the samples have positive thermoelectric powers S above room temperature. The largest power factor S2/ρ was obtained as 49.5 μW/K2 cm at 327 K for LaPdSb. From the Hall effect measurements on ErPdX, the carrier concentration n of ErPdSb and ErPdBi were obtained as 5.9×1018 and 3.21×1019 cm−3 at room temperature, respectively. It is considered that the difference of n at room temperature is mainly due to the magnitude of the band gap energy.
Investigation of Low Resistance Contacts to Pb-Sb-Ag-Te (LAST) Materials for Module Fabrication
Authors: D'Angelo Jonathan , Short Jarrod L , Downey Adam D. , Pajor Michael A. , Hogan Timothy P. , Chung Duck-Young , Kanatzidis Mercouri G , Timm Ed , Schock Harold 
Published: April 2011

ABSTRACTLow electrical contact resistance is essential for the fabrication of high efficiency thermoelectric generators. These contacts must be stable to high temperatures and through thermal cycling. Here we present the fabrication procedure and characterization of several contacts to Pb-Sb-Ag-Te (LAST) compounds. Contact materials investigated include tungsten, antimony, tin, nickel, and bismuth antimony based solder. The contacts were typically deposited by an electron beam evaporation method after careful preparation of the sample surface. The resistances were measured by using the transmission line model, and ohmic behavior was verified through current vs. voltage measurements. The best contact resistivities of less than 20 µΩ·cm2 have been measured for annealed antimony to n-type LAST samples. We present these procedures for fabricating low resistance contacts and the use of these procedures towards the fabrication of high efficiency thermoelectric generator modules.
Development of Thermoelectric generating modules and system
Authors: Ota Toshinori , Tokunaga Chieko , Fujita Kouichi 
Published: April 2011

AbstractIshikawajima–Harima Heavy Industries Co., Ltd. (IHI) is currently investigating applications of thermoelectric conversion systems based on the usage of radiant heat for industrial furnaces. The thermoelectric module units, which have been connected to a water-cooled jacket wall inside an electric resistance-heating-type industrial furnace, receive the heat originating from the in-furnace heat insulator by means of radiation, and collect the electric power based on the temperature difference. In this work, experimental results are presented, concerning the mechanical characteristics of a two-step cascade connection type module based on the heat transmission and thermoelectric conversion characteristic.The module performance analytic result, which turned character of several physical properties of the thermal radiation receiver of the upper part of modules, heat transmission characteristic, and the result, which performed the foundation examination for industrial furnace application, is reported.
High-Performance of Half-Heusler MNiSn (M=Hf,Zr) Single-Phase Thermoelectric Alloys Fabricated using Optical Floating Zone Melting
Authors: Kimura Yoshisato , Kuji Tomoya , Zama Akihisa , Shibata Yasufumi , Mishima Yoshinao 
Published: April 2011

ABSTRACTWe have succeeded to grow almost single-phase of Half-Heusler intermetallic compounds MNiSn, where M = (Hfx,Zr1−x) and x varies from 0 to 1, for the first time by directional solidification using optical floating zone melting (OFZ). Thermoelectric power and electrical resistivity can be dramatically improved since OFZ process effectively reduces solidification defects such as micro-cracks and cavities as well as unfavorable coexisting phases. Dimensionless thermoelectric figure of merit, ZT, of OFZ (Hf,Zr)NiSn alloys can be improved effectively by lowering the lattice thermal conductivity through the solid solution effects due to the substitution of Hf and Zr with each other. The maximum ZT value of 0.9 is achieved in (Hf0.5Zr0.5)NiSn at 963 K.