bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure of Ca3Co4O9 Single Crystals and Thin Films
Authors: Hu Yufeng , Sutter Eli , Si Weidong , Li Qiang 
Published: April 2011

ABSTRACTWe present a comparative study of the microstructure of Ca3Co4O9 single crystals and c-axis oriented Ca3Co4O9 thin films grown on glass substrates. Though both crystals and films have similar values of Seekbeck coefficient and electric resistivity at room temperature, their microstructures are rather different. Extensive high resolution transmission electron microscopy (TEM) studies reveal that the films grown on glass substrates have abundant stacking faults, which is in contrast to the perfect crystalline structure found in the single crystal sample. The c-axis lattice constants derived from the x-ray diffraction (XRD) and TEM measurements for the single crystal sample and the thin film are virtually the same, suggesting that the thin film on the glass substrate was not strained.
Synthesis and Thermoelectric Properties of NaxCo2O4 Single Crystals
Authors: He Jian , Aaron Kelvin , Abbott Edward , Kolis Joseph , Tritt Terry M. 
Published: April 2011

ABSTRACTSingle crystal NaCo2O4 platelets with sizes up to 6mm were synthesized by the typical high temperature NaCl flux method. The in-plane thermopower α and in-plane resistivity ρ were measured to be ∼100µV/K and 0.3mΩ-cm at 300K, respectively. The in-plane thermal conductivity κ was measured by our custom-designed “PTC” system and found to be ∼5 W-m−1K−1 at 300K, which is 2-3 times larger than the polycrystalline NaCo2O4. The in-plane phonon mean free path lph was estimated to be ∼9.5Å, which is much smaller than the in-plane mean free path of conducting carriers (la∼51Å). A novel low temperature flux method where NaCl/NaOH was used as flux and metallic Co powders as Co source was developed to successfully synthesize Na-deficient NaxCo2O4 crystals with size up to 6mm at low temperature of 550°C. The different temperature dependence in resistivity reveals that two different types of crystals can exist, one is metallic and another is semiconducting. The temperature dependence of the measured k is like that of a disordered solid and the value is found to be ∼7 W-m−1K−1 at 300K.
Synthesis of (Bi2Te3)x(TiTe2)y and (Bi2Te3)x(TiTe2)3 Superlattices
Authors: Smeller Mary , Harris Fred R. , Johnson David C. 
Published: April 2011

ABSTRACTThe synthesis of (Bi2Te3)x(TiTe2)x and (Bi2Te3)x(TiTe2)3 superlattices using modulated elemental reactants was successfully accomplished. This required the calibration of the deposition parameters to achieve both the desired atomic compositions of the constituent layers and the deposition of the absolute amounts of each of the components to yield the title compounds. Proper annealing conditions were determined from an investigation of the x-ray diffraction patterns of a superlattice sample as a function of annealing temperature. The change in lattice parameters as a function of x showed the expected linear behavior with slopes consistent with values expected from the published lattice parameters of the binary components. Rietveld refinement showed that the characteristic structure of the binary components is maintained in the superlattices studied.
Evaluation of TiTe2 as a Diffusion Barrier in the Synthesis of (Bi2Te3)5(SnTe)5 Misfit Layer Compound
Authors: Li Sissi L. , Johnson David C. 
Published: April 2011

ABSTRACTThe evolution of modulated reactants designed to form (Bi2Te3)5(TiTe2)5(SnTe)5(TiTe2)5 and (Bi2Te3)5(SnTe)5 are compared and contrasted. The modulated reactant designed to form (Bi2Te3)5(SnTe)5 interdiffused at 220°C forming SnBi2Te4 rather than the desired superlattice structure. The second sample was designed to have TiTe2 as a potential diffusion barrier to prevent the formation of SnBi2Te4. This second sample remained layered after annealing at 220°C. SnTe crystals are observed in the high angle diffraction pattern after this annealing, but there is evidence for the beginning of SnBi2Te4 formation. Annealing this sample at 300°C results in the formation of SnBi2Te4. The interdiffusion of Sn and Bi appears to occur before the formation of the desired TiTe2 structure.
Growth and Characterization of 1D Bi2Te3 Nanowires
Authors: Craps M. , Gothard Nick , Rao Rahul , He Jian , Hudson JoAn , Tritt Terry M. , Rao Apparao M. 
Published: April 2011

ABSTRACTBulk bismuth telluride (Bi2Te3) is one of the best known thermoelectric materials with a figure of merit ZT ∼1 at room temperature. Theoretical studies have suggested that low-dimensional materials may exhibit ZT values that exceed 1. In this study, we used the pulsed laser vaporization (PLV) method to prepare Bi2Te3 nanowires on silicon and quartz substrates by ablating Bi2Te3 targets in an inert atmosphere. Nano-sized gold or iron catalyst particles were used to seed the growth of the Bi2Te3 nanowires. Results from electron microscopy and Raman spectroscopy are discussed.
Size-selective and High-yield Nanocrystal Growth of PbTe Compounds Using a Chemical Vapor Deposition Technique
Authors: Zhang B. , Gothard Nicholas , He Jian , Thompson Daniel , Tritt Terry M. 
Published: April 2011

ABSTRACTThe nanocrystals of PbTe and related compounds (Pb1−xSnxTe, PbTe1−xSex), differing by size and composition, have been synthesized using a chemical vapor transport (CVD) technique. The size–selective precipitation mechanism relying on the variation of heating temperatures, Ar flow rates and admixture with Au particles, enables a relatively good control of particle size distribution. In addition, the doping ratios of those nanocrystals are readily modified by changing the atomic ratio in the raw starting materials. Subsequently, a yield of hundreds of milligrams of nanocrystals which exhibit narrow size distributions at 100 nm, 300 nm and 600 nm and controllable composition have been obtained. XRD patterns taken on the PbTe samples show sharp, which indicate good crystallinity of samples. According to the shift of the Bragg reflections, the lattice constants of (Sn / Se) doped PbTe change with the variation of the doping ratios.
CVD Growth of Nanostructures from Bi2Te3
Authors: Gothard N. , Zhang Bo , He Jian , Tritt Terry 
Published: April 2011

ABSTRACTResearch into thermoelectric materials has recently undergone a push into lower dimensional materials in the hopes that quantum confinement effects will enhance the performance of these structures. It has already been demonstrated that 2D superlattice materials show enhanced properties. More recently, materials known to have good thermoelectric properties, such as Bi2Te3 or PbTe, have been grown in low dimensional morphologies. We investigate synthesis techniques for growing low dimensional structures of Bi-Te materials with the aim of incorporating them into a composite material alongside bulk Bi2Te3.
Solid-State and Vacuum Thermionic Energy Conversion
Authors: Shakouri Ali , Bian Z. , Singh R. , Zhang Y. , Vashaee D. , Humphrey T. E. , Schmidt H. , Zide J. M. , Zeng G. , Bahk J-H. , Gossard A. C. , Bowers J. E. , Rawat V. , Sands T. D. , Kim W. , Singer S. , Majumdar A. , Mayer P. M. , Ram R. J. , Russel K. J. , Narayanamurti V. , Koeck F. A. M. , Li X. , Park J.-S. , Smith J. R. , Bilbro G. L. , Davis R. F. , Sitar Z. , Nemanich R. J. 
Published: April 2011

ABSTRACTA brief overview of the research activities at the Thermionic Energy Conversion (TEC) Center is given. The goal is to achieve direct thermal to electric energy conversion with >20% efficiency and >1W/cm2power density at a hot side temperature of 300–650C. Thermionic emission in both vacuum and solid-state devices is investigated. In the case of solid-state devices, hot electron filtering using heterostructure barriers is used to increase the thermoelectric power factor. In order to study electron transport above the barriers and lateral momentum conservation in thermionic emission process, the current-voltage characteristic of ballistic transistor structures is investigated. Embedded ErAs nanoparticles and metal/semiconductor multilayers are used to reduce the lattice thermal conductivity. Cross-plane thermoelectric properties and the effective ZT of the thin film are analyzed using the transient Harman technique. Integrated circuit fabrication techniques are used to transfer the n- and p-type thin films on AlN substrates and make power generation modules with hundreds of thin film elements. For vacuum devices, nitrogen-doped diamond and carbon nanotubes are studied for emitters. Sb-doped highly oriented diamond and low electron affinity AlGaN are investigated for collectors. Work functions below 1.6eV and vacuum thermionic power generation at temperatures below 700C have been demonstrated.
On the optical properties of thermoelectric alkali metal chalcogenide compounds
Authors: Hatzikraniotis W. , Kyratsi Theodora , Zorba T. , Paraskevopoulos Kontantinos M. , Kanatzidis Mercouri G. 
Published: April 2011

ABSTRACTSolid solutions of K2Bi8−XSbXSe13 is an interesting series of complex bismuth-chalcogenide compounds, which are attractive for thermoelectric investigations. The highly anisotropic structure in these compounds results in needle-like morphology along the b- crystallographic axis, leaving structural tunnels where K+ ions reside. The complex electronic structure that arises from a large and low symmetry unit cell and the weakly bound K+ ions, lead to high Seebeck coefficient, highly anisotropic electrical properties and very low thermal conductivity.Reflectivity spectra in the FIR region are presented for several members in the Sb-rich (x≥6) side. Optical investigations are carried out on crystalline and pelletized samples. The received spectra are analyzed, examined comparatively and discussed. Results indicate that upon Bi/Sb substitution in the Sb-rich region, phonons develop a mixed-mode behavior in the FIR spectral region.
Electronic properties of CeOs4Sb12
Authors: Galvan Donald 
Published: April 2011

AbstractCeOs4Sb12 is a very interesting material due to the diversity of physical properties which could be dedicated to industrial applications. With this goal in mind, electronic structural calculations were performed in order to provide information regarding its properties. The energy bands yielded information regarding its semiconductor behavior as well as a mini gap of the order of 0.45 eV between the valence and conduction bands. Moreover, total and projected density of states yielded information of a possible hybridization between Ce f-, Os d- and p-, with Sb p-orbitals. Hence, this compound could be considered a likely candidate as a thermoelectic material
Thermoelectric Properties of Tl-X-Te (X=Pb, Sn, Ge) Systems
Authors: Kosuga Atsuko , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke 
Published: April 2011

ABSTRACTPolycrystalline-sintered samples of Tl2GeTe3, Tl4SnTe3, and Tl4PbTe3 were prepared by a solid-state reaction. Their thermoelectric properties were evaluated at temperatures ranging from room temperature to ca. 700 K by using the measured electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ). Despite their poor electrical properties, the dimensionless figure of merit ZT of all the compounds was relatively high, i.e., 0.74 at 673 K for Tl4SnTe3, 0.71 at 673 K for Tl4PbTe3, 0.29 at 473 K for Tl2GeTe3, due to the very low lattice thermal conductivity of the compounds.
Synthesis and Thermoelectric Properties of CeyRuxIr4−xSb12) Filled Skutterudite Compounds
Authors: Jewell April D. , Paik Jong-Ah , Caillat Thierry 
Published: April 2011

ABSTRACTRadioisotope Thermoelectric Generators (RTGs) have proved to be reliable, long-lived sources of electrical power that have enabled the conduct of a number of important NASA deep space missions since 1961. Past RTGs have used two types of thermoelectric materials: PbTe/TAGS and SiGe. In an effort to further improve both the thermoelectric efficiency and specific power of the next generation of RTGs, JPL is investigating a number of potential high-efficiency, high-temperature thermoelectric materials that could operate at a hot-side temperature of up to 1275 K. Among the materials being studied are the refractory CeyRu4−xIrxSb12 filled skutterudite compounds. We have synthesized polycrystalline samples for x ≤ 1.5 by a powder metallurgy technique. Dense samples have been hot-pressed from the pre-reacted powders and characterized by a variety of techniques including electron probe microanalysis, differential thermal analysis and thermogravimetic analysis. Seebeck coefficient, electrical resistivity, Hall coefficient, and thermal conductivity measurements have been conducted on the samples from room temperature to 1275 K. Results show that the samples are phase stable up to 1275 K. The results of the transport property measurements are presented and discussed.
Multi-scale Rule-of-Mixtures Model of Carbon Nanotube/Carbon Fiber/Epoxy Lamina
Authors: Frankland Sarah-Jane , Riddick J. C. , Gates T. S. 
Published: April 2011

ABSTRACTA unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes is modeled with a multi-scale method, the atomistically informed rule-of-mixtures. This multi-scale model is designed to include the effect of the carbon nanotubes on the constitutive properties of the lamina. It included concepts from the molecular dynamics/equivalent continuum methods, micromechanics, and the strength of materials. Within the model both the nanotube volume fraction and nanotube distribution were varied. It was found that for a lamina with 60% carbon fiber volume fraction, the Young’s modulus in the fiber direction varied with changes in the nanotube distribution, from 138.8 to 140 GPa with nanotube volume fractions ranging from 0.0001 to 0.0125. The presence of nanotube near the surface of the carbon fiber is therefore expected to have a small, but positive, effect on the constitutive properties of the lamina.
ESR Spin Resonance on Carbon Nanofibers
Authors: Chipara Mircea , Hauge Robert H. , Fan Hua , Booker Richard , Peng Haiqing , Hwang Wen Fang , Zaleski Jeffrey M. , Smalley Richard E. 
Published: April 2011

ABSTRACTElectron spin resonance investigations on the angular dependence of carbon nanotubes are reported. It is proved that the resonance line is a convolution of three lines one due to electron delocalized over carbon nanotubes, the second assigned either to amorphous carbon or to conducting electrons in interaction with metallic impurities, and the last one originating from catalyst residues.
Ion Desorption by Inner-shell Excitation and Photodegradation of Poly(vinylidene fluoride)
Authors: Okudaira Koji , Kobayashi Eiichi , Kera Satoshi , Mase Kazuhiko , Ueno Nobuo 
Published: April 2011

ABSTRACTAuger electron spectra (AES) and Auger electron photo-ion coincidence (AEPICO) spectra of poly(vinlylidene fluoride) (PVDF) were observed to study the mechanism of effective fluorine ion (F+) desorption by irradiation of photons corresponding to the transition from F 1s to s(C-F). In the AES at photon energy (hυ) = 690.3 eV (from F1s to |σ|(C-F)), the spectator-Auger shift is about 3 eV. At hn = 690.3 eV the contribution of spectator Auger electron to the observed Auger spectrum is large. In the F+ AEPICO spectra at hυ = 690.3 eV an intense peak appears. The peak positions of the F+ AEPICO spectra are in agreement with those of the Auger spectra. These results indicate that the mechanism for effective F+ ion desorption induced by the transition from F1s to σ(C-F) occurs through the spectator-Auger processes. The efficiency of ion desorption depends on the electronic structure of the spectator-Auger final state.
Fe-Core/Au-Shell Nanoparticles: Growth Mechanisms, Oxidation and Aging Effects
Authors: Liu Kai , Cho Sung-Jin , Kauzlarich Susan M. , Idrobo J. C. , Davies Joseph E. , Olamit Justin , Browning N. D. , Shahin Ahmed M. , Long Gary J. , Grandjean Fernande 
Published: April 2011

ABSTRACTWe report the chemical synthesis of Fe-core/Au-shell nanoparticles (Fe/Au) by a reverse micelle method, and the investigation of their growth mechanisms and oxidation-resistant characteristics. The core-shell structure and the presence of the Fe and Au phases have been confirmed by transmission electron microscopy, energy dispersive spectroscopy, x-ray diffraction, Mössbauer spectroscopy, and inductively coupled plasma techniques. Additionally, atomic-resolution Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope have been used to study details of the growth processes. The Au-shells grow by nucleating on the Fe-core surfaces before coalescing. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles have been measured as a function of time in order to investigate the evolution of their magnetic properties. The magnetic moments of such nanoparticles, in the loose powder form, decrease over time due to oxidation. The less than ideal oxidation-resistance of the Au shell may have been caused by the rough Au surfaces. In a small fraction of the particles, off-centered Fe cores have been observed, which are more susceptible to oxidation. However, in the pressed pellet form, electrical transport measurements show that the particles are fairly stable, as the resistance and magnetoresistance of the pellet do not change appreciably over time. Our results demonstrate the complexity involved in the synthesis and properties of these heterostructured nanoparticles.
Modeling of Coarsening Processes In Patterned Systems
Authors: Jhon Mark , Glaeser Andreas M , Chrzan Daryl C 
Published: April 2011

ABSTRACTAlthough particle coarsening has been studied for over a century, it remains an active area of materials science research. The current work presents a theoretical analysis of the degradation of regular arrays of spherical particles through diffusional interaction. In order to understand the onset of coarsening, a linear stability analysis is performed on a simple square lattice of particles. It is predicted that particles will dissolve in a spatially ordered manner. The active transport mechanism plays a strong role in the selection of the coherent growth modes.
Formation, evolution and degradation of nanostructured covalent thin films deposited by Low Energy Cluster Beam Deposition
Authors: Compagnini Giuseppe , D'Urso Luisa , Scalisi A. Alessandro , Altamore Corinna , Puglisi Orazio 
Published: April 2011

ABSTRACTLow Energy Cluster Beam Deposition (LECBD) is considered an intriguing technique to obtain thin layers with well defined structures at the nano- and meso-scale levels, allowing novel optical, electronic and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with “in situ” techniques in order to study their original composition and their evolution once exposed to reactive gases. In this work we present a general overview and some results on the formation evolution and deposition of silicon and carbon cluster beams produced using a laser vaporization source.
Large Area Coatings for Architectural Glass – Design, Manufacturing, Process Faults
Authors: Ridealgh John A 
Published: April 2011

ABSTRACTThe physical properties of architectural sputtered coatings are considered in the context of their design, manufacture, transport and processing. The design constraints of high optical and thermal performance lead to the use of thin metal layers in interference coating stacks. This, in turn, determines the chemical and mechanical property challenges. In-service examples of film failure are presented along with practical countermeasures. Laboratory methods for ranking development coating systems are also discussed.
Formation of coherent structures and mechanical properties of AlN/TiN multilayers
Authors: Allidi G. , Medjani Farida , Sanjines Rosendo , Karimi Ayat 
Published: April 2011

AbstractAlN/TiN multilayered thin films with layer thickness ranging from 1 nm to 50 nm were synthesized using rf magnetron sputtering at 400°C. Two series of samples were prepared at the substrate bias of Vb = −25 V and −100 V to modify growth texture of individual layers and verify its influence on the formation of coherent structures. XRD and TEM observations showed that in large period films (tc ≥ 30 nm) each constituent grows under its own kinetic, leading to the formation of nano-crysatlline film randomly oriented with no pronounced texture. Decreasing progressively the layer thickness favours the alignment of (0002) basal plane of w-AlN on (111) plane of TiN, and results in development of strong (111) texture, prerequisite for stabilisation of c-AlN and the formation of epitaxial coherent structures. The degree of crystallographic coherence was found to be higher in TiN(111) oriented films than for TiN(002) textured films. The increase of hardness coincides with the structure transition from a randomly oriented nanocrystalline films to a highly (111) textured multilayers, and the maximum hardness was obtained for epitaxially coherent nanolayers.
Plasma Surface Modification of Polymeric Materials
Authors: Razavi Ali 
Published: April 2011

ABSTRACTThis study was undertaken to improve the bonding of fluorinated and non-fluorinated polymers to acrylic and silicone based adhesives. The polymeric materials were exposed to plasma which is comprised of methane and a second gas selected from air, Oxygen and Nitrogen or a mixture thereof. By application of surface analysis (XPS), the optimized functionality can be incorporated in the surface of desired polymers to enhance the bond ability of prepared films for pressure sensitive tape applications. Perfluoroalkoxy-tetrafluoroethylene copolymer PFA, fluorinated ethylene-propylene FEP, Polytetrafluoroethylene PTFE, and Polyester materials were exposed to this plasma. The treated samples were coated with adhesives and the adhesion to steel, holding power and other properties associated with tapes performance were studied.