bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Temperature Superconductivity in Graphite-Sulfur Composites: Theoretical Analysis
Authors: Galvão D. S. , Laks B. , Silva R. R. da , Torres J. H. S. , Kopelevich Y. 
Published: April 2011

ABSTRACTRecently superconductivity in graphite-sulfur composites was experimentally observed. In this work we have analyzed the electronic structure changes associated with the presence of sulfur atoms in one and two dimensional graphite layers. We have considered ordered and disordered sulfur atoms distributions in many configurations. The density of states (DOS) of these structures were obtained using the negative factor counting (NFC) technique coupled to a tight-binding hamiltonian (Hückel type). Our results indicate that the incorporation of sulfur atoms at edge graphite layers (changing their global geometric curvature and increasing the DOS at the Fermi level) might be in the origin of the graphite superconductivity.
The Effect of Sheath Materials on the Superconductivity of MgB2
Authors: Zhu W. , Watson D. R. , Cave J. R. 
Published: April 2011

ABSTRACTInconel, tantalum and a silver-palladium alloy were used to fabricate MgB2tapes. The tapes, made by the Powder In Tube (PIT) method, were heat-treated at 800°C and 900°C in 1 atmosphere of flowing argon. The microstructure and phase composition of the tapes were examined by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). Critical temperatures (Tc) and magnetization-applied magnetic field (M-H) curves were measured by SQUID magnetometry. It is found that between 800–900°C inconel and tantalum sheaths have no effect on the Tc,inductive of the material. However, under certain processing conditions, the silver-palladium sheath can decrease the Tcor destroy the superconductivity completely. The inconel sheathed tape was found to have better superconducting properties than the tantalum and silver-palladium sheathed tapes. Consistency checks have been applied to verify the validity of the Bean Model in obtaining the critical current density (Jc) from magnetization data. The inconel sheathed tape is estimated to have a magnetization Jc(5K, ∼0.5 T) of 1.4 × 105A/cm2.
Pulsed Laser Deposition of Y1Ba2Cu3O7-δ?Thin Films in High Oxygen Partial Pressures
Authors: Haugan Timothy J. , Barnes Paul N. , Nekkanti Rama M. , Maartense Iman , Brunke Lyle B. , Murphy John P. 
Published: April 2011

ABSTRACTPulsed laser deposition of Yba2Cu3O7-δ?(YBCO) coated conductors was studied for the range of P(O2) from 120 mTorr to 1200 mTorr, higher than typically used oxygen partial pressures during deposition. The purpose of the investigation was to determine the sensitivity of YBCO film quality to varying P(O2) for scaled-up fabrication of long-length coated conductors. Deposition at high P(O2) (≥?400 mTorr) gave very high and more consistent critical temperatures (Tc ≈?92 ±?0.4 °K) than results obtained at lower oxygen partial pressures (≤?200 mTorr) as determined by magnetic susceptibility measurements. Typically, the lower partial pressures are used although the laser fluence used in this research (3.2 J/cm2) is higher than typical. Transport Jc's were consistantly high for a wide range of oxygen pressures, 5–8 ×?106 A/cm2 at 77 K, self-field for P(O2) = 200–1200 mTorr. These results indicate that pulsed laser deposition of YBCO is relatively insensitive to P(O2) at the higher pressures of oxygen considered.
Texture by the kilometer
Authors: Specht E. D. , List F. A. 
Published: April 2011

ABSTRACTA novel x-ray diffractometer has been used to characterize the texture of 2 km of textured tape in segments up to 20 m long. Techniques have been developed for the study of the uniformity of texture and for the detection of second phases, deviations from cube texture, and the sharpness of cube texture, in metal substrates, oxide buffer layers, and YBa2Cu3O7 (YBCO) superconductors.
Engineered Microstructures and Transport Properties in YBCO Coated Conductors
Authors: Holesinger T. G. , Gibbons B. J. , Coulter J. Y. , Foltyn S. R. , Groves J. R. , Arendt P. N. 
Published: April 2011

ABSTRACTEach process used to deposit or make the bi-axially textured template, buffer layer(s), and the superconductor in a coated conductor creates interfaces along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the superconducting film. Defects within the films and their corresponding transport properties have been correlated with the differences in the thickness of the underlying buffer layer material. This knowledge can be used to control and engineer the structure of the coated conductor to maximize critical current densities.
Overview of Various Strategies and Promising New Bulk Materials for Potential Thermoelectric Applications
Authors: Tritt Terry M. 
Published: April 2011

ABSTRACTRecently, there has been a renewed interest in thermoelectric material research. There are a number of different systems of potential thermoelectric (TE) materials that are under investigation by various research groups. Some of these research efforts focus on minimizing lattice thermal conductivity while other efforts focus on materials that exhibit large power factors. An overview of some of the requirements and strategies for the investigation and optimization of a new system of materials for potential thermoelectric applications will be discussed. Some of the newer concepts such as low-dimensional systems and Slack's phononglass, electron-crystal concept will be discussed. Current strategies for minimizing lattice thermal conductivity and also minimum requirements for thermopower will be presented. The emphasis of this paper will be to identify some of the more recent promising bulk materials and discuss the challenges and issues related to each. This paper is targeted more at “newcomers” to the field and does not discuss some of the very interesting results that are being reported in the thin film and superlattice materials. Some of the bulk materials which will be discussed include complex chalcogenides (e.g.CsBi4Te6 and pentatellurides such as the Zr1−XHfXTe5 system), half-Heusler alloys (e.g. TiNiSn1−XSbX), ceramic oxides (NaCo4O2), skutterudites (e.g. YbXCo4−XSb12 or EuXCo4−XSb12) and clathrates (e.g. Sr8Ga16Ge30). Each of these systems is distinctly different yet each exhibits some prospect as a potential thermoelectric material. Results will be presented and discussed on each system of materials.
Thermoelectric Transport Properties of Individual Bismuth Nanowires
Authors: Cronin Stephen B. , Lin Yu-Ming , Rabin Oded , Black Marcie R. , Dresselhaus Gene , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTWe developed a method for making 4-point contacts to Bi nanowires with a thick oxide coat using a combination of lithographic and focused ion beam (FIB) techniques. The resistivity of Bi nanowires with diameters in the range 70-200nm is found to increase with decreasing wire diameter. In contrast to bulk Bi, the temperature dependence of the resistivity is found to decrease monotonically with increasing temperature. The results are explained on the basis of increased scattering in the nanowire and the known temperature dependence of the electronic properties of bulk Bi. A large magneto-resistance was also measured, indicating a high crystalline quality of the nanowires. A large spread in the measured values of the resistivity indicates significant systematic error in the measurement technique. Possible sources for error are discussed.
Thermoelectric Module For Low Temperature Applications
Authors: Lal Sangeeta , Loo Sim , Chung Duck-Young , Kyratsi Theodora , Kanatzidis Mercouri G. , Cauchy Charles , Hogan Timothy P. 
Published: April 2011

ABSTRACTThe possibility of a prototype thermoelectric cooling device for operation near liquid nitrogen temperatures has been explored. In these devices, the figure of merit involves a combination of the properties of the two branches of the module. Here, we investigate the fabrication of a module with a new low temperature material, CsBi4Te6 (p-type), and the best known low temperature n-type materials Bi85Sb15. Transport measurements for each of these materials show high performance at low temperatures. Known values for the figure of merit Zmax of CsBi4Te6 is 3.5 × 10−3 K−1 at 225K and for Bi85Sb15 is 6.5 × 10−3 K−1 at 77K. At 100K these values drop to 2.0×10−3 K−1 for CsBi4Te6 and 6.0×10−3 K−1 for Bi85Sb15. Theoretical simulations based on these data show a cooling of δT = 12K at 100K, which is almost three times the efficiency of a Bi2Te3 module at that temperature. We present transport measurements of elements used in the fabrication of a low temperature thermoelectric module and properties of the resulting module.
Investigation of i-AlCuFe Quasicrystals and their ω and β Approximants as Thermoelectric Materials
Authors: Alboni P. N. , Pope A. L. , Tritt T. M. , Ross A. R. , Jenks C. , Sordelet D. 
Published: April 2011

ABSTRACTIn the search for new thermoelectric materials, quasicrystals have been investigated due to their inherently low thermal conductivity. Crystalline phases called approximants which are closely related to the quasicrystals, however, have largely been ignored. These approximants have similar structure, yet the periodicity of a crystal. In this paper, we have investigated an icosahedral i-AlCuFe quasicrystalline phase as well as two of its corresponding approximant phases (ω and β). Electrical and thermal transport properties of these materials are presented. The viability of the i-AlCuFe quasicrystalline system and the ω and β approximant phases as thermoelectric materials is discussed.
Thermoelectric Nanowires by Electrochemical Deposition
Authors: Rabin Oded , Lin Yu-Ming , Cronin Stephen B. , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTNanowires made of thermoelectric-relevant materials were grown by electrochemical deposition. Their diameter and ordering are dictated by the porous alumina template that is fabricated on the working electrode prior to the deposition. The composition of the nanowires is controlled by the composition of the electrolyte and the deposition potential. This technique offers unique opportunities regarding the range of geometries and materials that can be employed. The structural and transport properties of these wires will be presented, and comparison will be made to nanowires synthesized by other techniques.
Microstructure and Electrical Properties of PbTe Based Films Prepared by Pulsed Laser Deposition
Authors: Dauscher Anne , Lenoir Bertrand , Jacquot Alexandre , Bellouard Christine , Dinescu Maria 
Published: April 2011

ABSTRACTLead telluride thin films have been grown on BaF2(111) substrates by pulsed laser deposition from a Nd:YAG laser (λ = 532 nm) at very low temperature (150°C). The chemical composition, the morphology and the crystallographic structure of the layers depend strongly on the deposition conditions. Post-annealing treatments of the films also affect their microstructure. Preliminary electrical properties, conducted in the temperature range of 5 to 350 K, revealed that all the samples were n-type with Hall mobility values greater than 104 cm2/V.s at low temperatures.
Growth of PbTe films by magnetron sputtering
Authors: Jdanov A. , Pelleg J. , Dashevsky Z. , Shneck R. 
Published: April 2011

ABSTRACTThin films of PbTe were deposited on Si (111) wafers and glass substrates at a constant power for different times and at a constant time at various power levels. In some cases substrate heating to a temperature of ∼673K was performed during sputtering. Structural analysis by Xray diffraction (XRD) and high-resolution electron microscopy (HRTEM) were performed. The composition of the PbTe film was evaluated by Auger depth profile. At an appropriate combination of power and deposition time only (200) and its higher order peaks were observed in the PbTe film. It is expected that it is feasible to obtain epitaxial PbTe film by RF magnetron sputtering.
Characteristics of Polycrystalline Silicon thin Films Prepared by Pulsed Ion-Beam Evaporation
Authors: Yang Sung-Chae , Fazlat Ali , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi 
Published: April 2011

AbstractUsing intense pulsed ion-beam evaporation technique, we have succeeded in the preparation of polycrystalline silicon thin films on silicon substrate without impurities. Good crystallinity and high deposition rate have been achieved without heating the substrate. The crystallinity of poly-Si film has been improved with increasing the density of the ablation plasma. The intense diffraction peaks of poly-Si thin films can be obtained by using the substrate bias system. The crystallinity and the deposition rate of poly-Si thin films are increased by negative bias voltage for the substrate.
Diamond Coated WC Tools for Machining Wood and Particle Board
Authors: Makala Raghuveer S. , Yoganand S.N. , Jagannadham K. , Lemaster R.L. , Bailey J. 
Published: April 2011

AbstractDiamond coating was provided to improve the performance of WC-Co tools used in machining wood and particle board. Microwave plasma chemical vapor deposition was used to deposit diamond using a gas mixture with CH4: H2 in the ratio 0.5: 100 at a temperature of 900°C. The microwave energy was set at 900W and a pressure of 35Torr was maintained in the chamber. An essential factor that determines the life of polycrystalline diamond coated tools is poor film adhesion. To counter this problem, we have developed a process that includes etching away cobalt from surface regions, treatment with H2 plasma and use of TiN/ TiC intermediate and embedding layers. The TiN/ TiC layers were deposited by reactive magnetron sputtering. These layers embed diamond crystallites and improve adhesion, and in addition act as good diffusion barriers for Co. The diamond coated and uncoated tools have been characterized in the as deposited conditions and after prescribed wear by machining particle board using SEM and X-ray mapping. It was also found that the limited contact area with diamond on the cutting edge affects the adhesion of the coating. Improvement in contact area by providing a larger radius to the cutting edge is discussed.
Phase Analysis for Single Crystalline Silicon Scratched by Spherical Diamond TIP
Authors: Jeong Seong-Min , Oh Han-Seog , Park Sung-Eun , Kim Hyun-Ho , Lee Hong-Lim 
Published: April 2011

AbstractThe mechanical properties of silicon crystals are important from the viewpoint of wafer and device fabrication processes. It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using conventional high pressure devices, such as diamond anvils or hydrostatic pressure cells, or under indentation. Scratching on a silicon surface in the various conditions introduces various kinds of mechanical damage and stressed states. Micro-Raman spectroscopy was used to observe the phase transition of single crystal silicon. Several different phases were observed depending on scratching speed and scratched locations.
Plasma deposition of amorphous carbon films from methane atmospheres highly diluted in argon
Authors: Jacobsohn L. G. , Freire F. L. 
Published: April 2011

AbstractWe investigated the deposition, structure and mechanical properties of a-C:H films grown in Ar-CH4 mixtures with the Ar partial pressure ranging from 0 to 99 %. The deposition rate strongly decreased with progressive Ar dilution of the CH4 atmosphere. Films deposited in pure CH4 atmospheres have a hydrogen content of 20 at.% that showed a trend to decrease for lower CH4 partial pressures, while the density remained nearly constant at around 1.4x1023 at./cm3. Raman spectroscopy and x-ray diffraction revealed the amorphous character of the films. The compressive internal stress remained constant around 2.5 GPa and the hardness decreases for Ar rich precursor atmospheres.
Ionizing Radiation Effects on Interfaces in Carbon Nanotube-Polymer Composites
Authors: Harmon Julie P. , Muisener Patricia Anne O. , Clayton LaNetra , D'Angelo John , Sikder Arun K. , Kumar Ashok , Meyyappan Meyya , Cassell Alan M. 
Published: April 2011

AbstractThe purpose of this research was to probe nanotube-polymer composites for evidences of radiation induced chemistry at the interface of the host polymer and the nanotube structures. Single wall carbon nanotube (SWNT) / poly (methyl methacrylate) (PMMA) composites were fabricated and exposed to gamma radiation with a Co60 source at a dose rate of 1.28 X 106 rad/hour in an air environment for a total dose of 5.9 Mrads. Neat nanotube paper and neat PMMA were also exposed. Spun coat films of SWNT/PMMA were exposed to gamma radiation with a Ce157at a dose rate of 4.46 x 103 rad/hr for a total dose of 3.86 Mrads. Both irradiated and non-irradiated samples were compared. Glass transition temperatures were characterized by differential scanning calorimetry. Dynamic mechanical analysis and dielectric analysis evidenced changes in relaxations induced by irradiation. Irradiated composites exhibited radiation induced chemistry distinct from degradation effects noted in the pure polymer. Scanning electron microscopy provided images of the SWNTs and SWNT/PMMA interface before and after irradiation. This investigation imparts insight into the nature of radiation induced events in nanotubes and nanocomposites.
Self-Assembled Structures of Gas-Phase Prepared FePt Nanoparticles
Authors: Rellinghaus Bernd , Stappert Sonja , Acet Mehmet , Wassermann Eberhard F. 
Published: April 2011

AbstractWe report on a non-lithographic method for the preparation of self-assembled FePt nanoparticles via inert-gas condensation. Prior to deposition the particles can be sintered in flight at temperatures as high as TS = 1273 K. Whereas un-sintered particles have irregular shapes, particles sintered at elevated temperatures TS ≥ 793 K show a regular faceting. (High resolution) transmission electron microscopy ((HR)TEM) shows that these regularly faceted particles are of icosahedral structure. When being deposited onto amorphous carbon films, the gas-phase sintered particles are found to have a high mobility. In particular, for the high-temperature sintered FePt nanoparticles, we observe that this mobility leads to the formation of particle arrays with hexagonal close-packed arrangements. Within these ordered patches, the particles are separated from one another. Analytical investigations using energy filtered TEM (EFTEM) show that a carbon layer is formed between the particles. Magnetization analyses give results showing that the gas-phase sintered particles are superparamagnetic at room temperature with a blocking temperature of TB = 49K.
Nanofabrication at Biologically Important Length Scale: Etching of Dislocation Array in Twist-bonded Bicrystals
Authors: Mei Fang , Murtagh Martin J. , Sass Stephen L. , Wind Rikard A. , Wang Yu , Hines Melissa A. 
Published: April 2011

AbstractA process to fabricate a periodic surface structure at biologically important length scale is developed and nanostructured silicon surface with a periodicity of 38 nm has been obtained. The technique relies on controlled etching of a dislocation array in the twist boundaries formed by silicon bicrystals. The deviation from a perfect periodic structure and the method to improve the perfection have been investigated.
A photoemission spectroscopic study of the interface formation in organic thin film transistors
Authors: Watkins Neil J. , Zorba Serkan , Yan Li , Gao Yongli 
Published: April 2011

ABSTRACTPentacene is widely used in organic thin film transistors due to relatively large mobilities. It has been suggested that the functional behavior in these organic thin film transistors occurs within the first few molecular layers of the device at the interfaces between the organic and the metals and dielectrics used in fabrication of the thin film transistors. This makes understanding the electronic behavior of the interfaces involved in these devices critical. In order to better understand these interfaces we investigated the interface formation using photoemission spectroscopy to examine layer by layer growth of pentacene on Au and Ag and vice versa. We observed indications of dipole formation at the interfaces between the metals and organics for organic on metal deposition. On the other hand, more complex material intermixing takes place during metal on organic deposition and as a result, the electronic structure of the interface differs from that of organic on metal deposition.
Near-field photoconductivity imaging of a conjugated polymer blend
Authors: Riehn R. , Stevenson R. , Halls J.J.M. , Richards D.R. , Kang D.-J. , Blamire M. , Cacialli F. 
Published: April 2011

ABSTRACTWe report combined scanning near-field optical microscopy (SNOM) and near-field photocurrent (NPC) imaging of a binary conjugated polymer blend. We find phase separation on a scale of about 5 μm, with a good correspondence between topographic, fluorescence, and photocurrent images. We excited at 488 nm, a wavelength at which only one of the two polymers absorbs light. Under this illumination regions that are high in the topography image show high luminescence and photocurrent.The photoluminescence (PL) efficiencies in the different regions of the sample were determined by calculating the absorbed energy using the Bethe-Bouwkamp model, and knowledge about the chemical composition of the different phases of the polymer blend. The calculation also allowed us to conclude that the photocurrent generation efficiency (current/absorbed photons) of the different polymer phases is comparable within the limit of confidence of this experiment (±10 %).
Luminescent Polystyrene Composition Characteristics Stability Forecasting
Authors: Borisenko Artem Yu. , Senchishin Vitalij G. 
Published: April 2011

ABSTRACTThe stability of properties of luminescent polystyrene compositions depending on their material structure has been studied. The samples obtained by the methods of bulk polymerization and injection molding were used for the experiment. The influence of molecular mass distribution, supramolecular structure, plasticizer concentration and geometrical size of samples on the stability of their properties in severe conditions of natural and radiation aging has been investigated.
Evolution of Solution Chemistry through Interactions with Waste Package Internal Structural Components
Authors: Pan Y.-M. , Brossia C.S. , Cragnolino G.A. , Dunn D.S. , Jain V. , Sridhar N. 
Published: April 2011

ABSTRACTThe chemistry of the aqueous environment inside any breached waste packages is critical to the release of radionuclides from the waste packages for high-level waste disposal. A corrosion test cell that simulates some aspects of the internal geometry of the waste packages has been designed to investigate changes in the in-package solution chemistry. A series of tests was conducted to evaluate solution chemistry variations as a function of applied potential and temperature using a specimen of Type 316L stainless steel with a predrilled hole as a simulated pit. A micro-syringe was used to extract solutions from inside and outside the pit. The solutions were analyzed for cation concentrations using capillary electrophoresis, and the pH was measured using a micro-electrode. Preliminary measurements showed substantially high cation concentrations inside the pit due to anodic dissolution of Type 316L stainless steel. The solution pH became considerably acidic, reaching a value of 2.6. These results suggest that interactions of waste package internal structural components with incoming water may have significant influence on the evolution of water chemistry and the subsequent corrosion of waste forms such as spent nuclear fuel.