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Sample records for bi-in bi-mg bi-sb

  1. Lattice thermal conductivity of Bi, Sb, and Bi-Sb alloy from first principles

    NASA Astrophysics Data System (ADS)

    Lee, Sangyeop; Esfarjani, Keivan; Mendoza, Jonathan; Dresselhaus, Mildred S.; Chen, Gang

    2014-02-01

    Using first principles, we calculate the lattice thermal conductivity of Bi, Sb, and Bi-Sb alloys, which are of great importance for thermoelectric and thermomagnetic cooling applications. Our calculation reveals that the ninth-neighbor harmonic and anharmonic force constants are significant; accordingly, they largely affect the lattice thermal conductivity. Several features of the thermal transport in these materials are studied: (1) the relative contributions from phonons and electrons to the total thermal conductivity as a function of temperature are estimated by comparing the calculated lattice thermal conductivity to the measured total thermal conductivity, (2) the anisotropy of the lattice thermal conductivity is calculated and compared to that of the electronic contribution in Bi, and (3) the phonon mean free path distributions, which are useful for developing nanostructures to reduce the lattice thermal conductivity, are calculated. The phonon mean free paths are found to range from 10 to 100 nm for Bi at 100 K.

  2. Mechanical alloying of BiTe and BiSbTe thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Hasezaki, K.; Nishimura, M.; Umata, M.; Tsukuda, H.; Araoka, M.

    1994-06-01

    Two thermoelectric materials, BiTe and BiSbTe were prepared by mechanical attrition of elemental powders in a rare gas atmosphere. Nearly 20 min were required for the alloying of BiTe, while 10 h were required for BiSbTe. After attrition, the average powder diameter of the BiSbTe alloy was in 1.4 micron, and the impurity content, measured by Inductively Coupled Argon Plasma Emission Spectrophotometer, was less than 0.1 mass%. The MA powders were sintered by a hot pressing technique. Uniform elemental dispersions were measured by EPMA in BiSbTe alloys sintered at 623 K.

  3. BiSb and spin-related thermoelectric phenomena

    NASA Astrophysics Data System (ADS)

    Heremans, Joseph P.; Jin, Hyungyu; Zheng, Yuanhua; Watzman, Sarah J.; Prakash, Arati

    2016-05-01

    This article reviews the factors limiting the figure of merit zT of conventional thermoelectrics especially at cryogenic temperatures and then highlights modern approaches used to increase zT below 200 K. Two type of materials are discussed. The first are BiSb alloys, relatively conventional thermoelectrics in which the zT is enhanced by using resonant levels. The second is the spin- Seebeck effect (SSE), a new solid-state energy conversion technology. Classical thermoelectric and SSE physics are combined to provide new concepts, like magnon-drag, in which we hope to increase the performance of solid-state coolers by exploiting the spin degree of freedom.

  4. Optical properties and electronic band structure of BiMg2PO6, BiMg2VO6, BiMg2VO6:Pr3+ and BiMg2VO6:Eu3+

    NASA Astrophysics Data System (ADS)

    Barros, A.; Deloncle, R.; Deschamp, J.; Boutinaud, P.; Chadeyron, G.; Mahiou, R.; Cavalli, E.; Brik, M. G.

    2014-08-01

    The luminescence properties of the yellow pigment BiMg2VO6 are revisited and those of BiMg2PO6, BiMg2VO6:Pr3+ and BiMg2VO6:Eu3+ are described. It is shown that the undoped systems exhibit broad band emission in the green or orange spectral regions, but only upon UV or near UV excitation. In contradiction with a previous report, we found that the blue, host absorbed, photons are lost non-radiatively and do not contribute to the luminescence processes in BiMg2VO6. To understand these experimental results, the optical properties of BiMg2VO6 and BiMg2PO6 are theoretically analysed on the basis of electronic structure diagrams calculated by the DFT method. It is found that the optical transitions are mostly localised within [VO4]3- units or non-regular Bi3+ ions and occur in the UV or near UV regions. The luminescence of the trivalent lanthanide dopants is weak (Eu3+) or unobserved (Pr3+) in BiMg2VO6 which is explained by inefficient energy migration in the host lattice to the impurity sites.

  5. Crystal structure and dielectric properties of ordered perovskites Ba 2BiSbO 6 and BaSrBiSbO 6

    NASA Astrophysics Data System (ADS)

    Mangalam, R. V. K.; Suard, E.; Sundaresan, A.

    2009-01-01

    Neutron powder diffraction studies showed that the ordered perovskites Ba 2BiSbO 6 (BBS) and BaSrBiSbO 6 (BSBS) crystallize in a rhombohedral structure with the space group R3bar. The room-temperature lattice parameters are a=6.0351(2) Å; α=60.202(1)° and a=5.9809(2) Å; α=60.045(2)°, respectively. BBS exhibits a dielectric anomaly near room temperature which may be related to structural transition from the R3bar to low-temperature monoclinic I2/m symmetry. BSBS shows a dielectric anomaly near 723 K which coincides with a phase transition from the rhombohedral to cubic (Fm3barm) structure. In contrast to BBS, BSBS does not undergo structural transition below room temperature.

  6. High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.

    PubMed

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations. PMID:27128858

  7. Synthesis, Characterization and Photocatalytic Activity of New Photocatalyst ZnBiSbO4 under Visible Light Irradiation

    PubMed Central

    Luan, Jingfei; Chen, Mengjing; Hu, Wenhua

    2014-01-01

    In this paper, ZnBiSbO4 was synthesized by a solid-state reaction method for the first time. The structural and photocatalytic properties of ZnBiSbO4 had been characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscope and UV-visible spectrometer. ZnBiSbO4 crystallized with a pyrochlore-type structure and a tetragonal crystal system. The band gap of ZnBiSbO4 was estimated to be 2.49 eV. The photocatalytic degradation of indigo carmine was realized under visible light irradiation with ZnBiSbO4 as a catalyst compared with nitrogen-doped TiO2 (N-TiO2) and CdBiYO4. The results showed that ZnBiSbO4 owned higher photocatalytic activity compared with N-TiO2 or CdBiYO4 for the photocatalytic degradation of indigo carmine under visible light irradiation. The reduction of the total organic carbon, the formation of inorganic products, SO42− and NO3−, and the evolution of CO2 revealed the continuous mineralization of indigo carmine during the photocatalytic process. One possible photocatalytic degradation pathway of indigo carmine was obtained. The phytotoxicity of the photocatalytic-treated indigo carmine (IC) wastewater was detected by examining its effect on seed germination and growth. PMID:24879521

  8. Evidence for surface-generated photocurrent in (Bi,Sb)2Se3and(Bi,Sb)2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Pan, Yu; Richardella, Anthony; Yao, Bing; Lee, Joon Sue; Flanagan, Thomas; Kandala, Abhinav; Samarth, Nitin; Yeats, Andrew; Mintun, Peter; Awschalom, David

    2015-03-01

    Illumination with circularly polarized light is known produce a helicity-dependent photocurrent in topological insulators such as Bi2Se3 [e.g. Nature Nanotech. 7, 96 (2012)]. However, the exact origin of this effect is still unclear since it is observed with photons well above the bulk band gap. We report measurements of the polarization-dependent photocurrent in a series of (Bi,Sb)2Se3 thin films with different carrier concentrations and find that the photocurrent is enhanced as we increase the population of the surface states. This finding is supported by a study of helicity-dependent photocurrents in back-gated (Bi,Sb)2Te3 thin films, where the chemical potential is varied electrostatically. By illuminating our samples at different wavelengths, we show that the helicity-dependent photocurrent is enhanced when the photon energy approaches the energy difference between the lowest and first excited (unoccupied) topological surface states. This leads us to attribute the helicity-dependent photocurrent in topological insulators to optical excitations between these two spin-textured surface states. We will also discuss experiments imaging the spatial variation of these helicity-dependent photocurrents. This work is supported by ONR.

  9. Synthesis and Characterization of Bismuth Magnesium Phosphate and Arsenate: BiMg 2PO 6 and BiMg 2AsO 6

    NASA Astrophysics Data System (ADS)

    Huang, Jinfan; Gu, Qiuyi; Sleight, Arthur W.

    1993-08-01

    Two new compounds, BiMg 2PO 6 and BiMg 2AsO 6, have been synthesized and structurally characterized by single crystal and powder X-ray diffraction. Both compounds crystallize in the orthorhombic space group Cmcm (No. 63) with four formula units per unit cell. They are isostructural with bismuth magnesium vanadate, BiMg 2VO 6. The cell parameters for BiMg 2PO 6 are a = 7.801(2), b = 11.888(3), c = 5.273(2) Å, V = 489.0(2) Å 3 and for BiMg 2AsO 6 are a = 7.9142(5), b = 12.1637(8), c = 5.3898(4) Å, V = 518.9(2) Å 3. The formula for this series of compounds may be written as (BiO 2)Mg AO 4 to emphasize the (BiO 2) 1- chains and the (AO 4) 3- tetrahedral groups isolated from one another. Between these chains and tetrahedral groups sit Mg 2+ cations in an unusual fivefold coordination to oxygen. No emission bands were observed from BiMg 2PO 6 and BiMg 2AsO 6 under excitation with UV or visible radiation. The IR spectra of these compounds are compared to that of BiMg 2VO 6.

  10. Study of the circular photo-galvanic effect in electrically gated (Bi,Sb)2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Pan, Yu; Pillsbury, Timothy; Richardella, Anthony; Flanagan, Thomas; Samarth, Nitin

    Illumination with circularly polarized light is known to produce a helicity dependent photocurrent in topological insulators such as Bi2Se3 [Nature Nanotech. 7, 96 (2012)]. Symmetry considerations suggest that this ``circular photo-galvanic effect'' (CPGE) arises purely from the surface. However, whether or not the CPGE is directly related to optical excitations from the helical surface states is still under debate. To clarify the origin of the CPGE, we first compare the helicity dependent photocurrent in intrinsic (Bi,Sb)2Te3 to Cr doped (Bi,Sb)2Te3 thin films in which the Dirac surface states are perturbed by magnetic coupling. Secondly, we discuss the tunable CPGE in electrically gated (Bi,Sb)2Te3 thin films excited by optical excitations at different wavelengths. The dependence on the chemical potential and the photon energy of the excitation unveils the origin of the CPGE. Funded by ONR.

  11. Influence of Sedimentation of Atoms on Structural and Thermoelectric Properties of Bi-Sb Alloys

    NASA Astrophysics Data System (ADS)

    Januszko, Kamila; Stabrawa, Artur; Ogata, Yudai; Tokuda, Makoto; Khandaker, Jahirur Islam; Wojciechowski, Krzysztof; Mashimo, Tsutomu

    2016-03-01

    Functionally graded thermoelectric materials (FGTMs) have been prepared by sedimentation of atoms under a strong gravitational field. Starting samples of Bi x Sb1- x alloys with different composition x were synthesized by melting of metals and subsequent annealing of quenched samples. The thermoelectric properties (Seebeck coefficient, electrical conductivity) of the starting materials were characterized over the temperature range from 300 K to 525 K. Strong gravity experiments were performed in a unique ultracentrifuge apparatus under acceleration of over 0.5 × 106 G at temperatures of 538 K and 623 K. Changes of the microstructure and chemical composition were analyzed using scanning electron microscopy with energy-dispersive x-ray spectroscopy analysis. The distribution of the Seebeck coefficient of the Bi-Sb alloys was characterized by scanning thermoelectric microprobe. As a result of sedimentation, large changes in chemical composition ( x = 0.45 to 1) were obtained. It was found that the changes in chemical composition were correlated with alterations of the Seebeck coefficient. The obtained experimental data allowed the development of a semiempirical model for the selection of optimal processing parameters for preparation of Bi-Sb alloys with required thermoelectric properties.

  12. Homologous series of layered structures in binary and ternary Bi-Sb-Te-Se systems: Ab initio study

    NASA Astrophysics Data System (ADS)

    Govaerts, K.; Sluiter, M. H. F.; Partoens, B.; Lamoen, D.

    2014-02-01

    In order to account explicitly for the existence of long-periodic layered structures and the strong structural relaxations in the most common binary and ternary alloys of the Bi-Sb-Te-Se system, we have developed a one-dimensional cluster expansion (CE) based on first-principles electronic structure calculations, which accounts for the Bi and Sb bilayer formation. Excellent interlayer distances are obtained with a van der Waals density functional. It is shown that a CE solely based on pair interactions is sufficient to provide an accurate description of the ground-state energies of Bi-Sb-Te-Se binary and ternary systems without making the data set of ab initio calculated structures unreasonably large. For the binary alloys A1-xQx (A =Sb, Bi; Q =Te, Se), a ternary CE yields an almost continuous series of (meta)stable structures consisting of consecutive A bilayers next to consecutive A2Q3 for 00.6, the binary alloy segregates into pure Q and A2Q3. The Bi-Sb system is described by a quaternary CE and is found to be an ideal solid solution stabilized by entropic effects at T ≠0 K but with an ordered structure of alternating Bi and Sb layers for x =0.5 at T =0 K. A quintuple CE is used for the ternary Bi-Sb-Te system, where stable ternary layered compounds with an arbitrary stacking of Sb2Te3,Bi2Te3, and Te-Bi-Te-Sb-Te quintuple units are found, optionally separated by mixed Bi/Sb bilayers. Electronic properties of the stable compounds were studied taking spin-orbit coupling into account.

  13. The properties of BiSb nanoribbons from first-principles calculations.

    PubMed

    Lv, H Y; Liu, H J; Tan, X J; Pan, L; Wen, Y W; Shi, J; Tang, X F

    2012-01-21

    The structural, electronic and magnetic properties of BiSb nanoribbons (BSNRs) with different widths and edge configurations are investigated via the first-principles pseudopotential method. It is found that the pristine BSNRs with armchair edges (ABSNRs) are semiconductors and the band gaps exhibit a width dependent odd-even oscillation. In contrast, the pristine BSNRs with zigzag edges (ZBSNRs) are found to be metallic. When all the edge atoms are passivated by hydrogen, both the ABSNRs and ZBSNRs become semiconducting and the corresponding band gaps decrease monotonically with the increasing width. If, however, the edge atoms are partially passivated, the ABSNRs can be either semiconducting or metallic. Moreover, local magnetism appears when all the edge Sb atoms are passivated and there are one or more unsaturated Bi atoms. Using the nonequilibrium Green's function (NEGF) approach, we find that all the investigated odd-numbered ABSNRs have almost the same peak value of the power factor around the Fermi level. This is not the case for the even-numbered ABSNRs, where the peaks are twice that of when they are n-type doped. Our calculations indicate that BSNRs can have a very high room temperature figure of merit (ZT value), which makes them very promising candidates for thermoelectric applications. PMID:22101571

  14. Using anodic aluminum oxide templates and electrochemical method to deposit BiSbTe-based thermoelectric nanowires

    PubMed Central

    2014-01-01

    In this study, the cyclic voltammetry method was first used to find the reduced voltages and anodic peaks of Bi3+, Sb3+, and Te4+ ions as the judgments for the growth of the (Bi,Sb)2 - x Te3 + x-based materials. Ethylene glycol (C2H6O2) was used as a solvent, and 0.3 M potassium iodide (KI) was used to improve the conductivity of the solution. Two different electrolyte formulas were first used: (a) 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 and (b) 0.015 M Bi(NO3)3-5H2O, 0.005 M SbCl3, and 0.0075 M TeCl4. The potentiostatic deposition process was first used to find the effect of reduced voltage on the variation of compositions of the (Bi,Sb)2 - xTe3 + x-based materials. After finding the better reduced voltage, 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 were used as the electrolyte formula. The pulse deposition process was successfully used to control the composition of the (Bi,Sb)2 - xTe3 + x-based materials and grow the nanowires in anodic aluminum oxide (AAO) templates. PMID:24502697

  15. The microstructure network and thermoelectric properties of bulk (Bi,Sb){sub 2}Te{sub 3}

    SciTech Connect

    Xie Wenjie; Hitchcock, Dale A.; Kang, Hye J.; He Jian; Tang Xinfeng; Laver, Mark; Hammouda, Boualem

    2012-09-10

    We report small-angle neutron scattering studies on the microstructure network in bulk (Bi,Sb){sub 2}Te{sub 3} synthesized by the melt-spinning (MS) and the spark-plasma-sintering (SPS) process. We find that rough interfaces of multiscale microstructures generated by the MS are responsible for the large reduction of both lattice thermal conductivity and electrical conductivity. Our study also finds that subsequent SPS forms a microstructure network of {approx}10 nm thick lamellae and smooth interfaces between them. This nanoscale microstructure network with smooth interfaces increases electrical conductivity while keeping a low thermal conductivity, making it an ideal microstructure for high thermoelectric efficiency.

  16. AlO x /LiF composite protection layer for Cr-doped (Bi,Sb)2Te3 quantum anomalous Hall films

    NASA Astrophysics Data System (ADS)

    Ou, Yunbo; Feng, Yang; Feng, Xiao; Hao, Zhenqi; Zhang, Liguo; Liu, Chang; Wang, Yayu; He, Ke; Ma, Xucun; Xue, Qikun

    2016-08-01

    We have realized robust quantum anomalous Hall samples by protecting Cr-doped (Bi,Sb)2Te3 topological insulator films with a combination of LiF and AlO x capping layers. The AlO x /LiF composite capping layer well keeps the quantum anomalous Hall states of Cr-doped (Bi,Sb)2Te3 films and effectively prevent them from degradation induced by ambient conditions. The progress is a key step towards the realization of the quantum phenomena in heterostructures and devices based on quantum anomalous Hall system. Project supported by the National Natural Science Foundation of China (Grant No. 11325421).

  17. Switching of charge-current-induced spin polarization in the topological insulator BiSbTeSe2

    NASA Astrophysics Data System (ADS)

    Yang, Fan; Ghatak, Subhamoy; Taskin, A. A.; Segawa, Kouji; Ando, Yuichiro; Shiraishi, Masashi; Kanai, Yasushi; Matsumoto, Kazuhiko; Rosch, Achim; Ando, Yoichi

    2016-08-01

    The charge-current-induced spin polarization is a key property of topological insulators for their applications in spintronics. However, topological surface states are expected to give rise to only one type of spin polarization for a given current direction, which has been a limiting factor for spin manipulations. Here, we report that in devices based on the bulk-insulating topological insulator BiSbTeSe2, an unexpected switching of spin polarization was observed upon changing the chemical potential. The spin polarization expected from the topological surface states was detected in a heavily electron-doped device, whereas the opposite polarization was reproducibly observed in devices with low carrier densities. We propose that the latter type of spin polarization stems from topologically trivial two-dimensional states with a large Rashba spin splitting, which are caused by a strong band bending at the surface of BiSbTeSe2 beneath the ferromagnetic electrode used as a spin detector. This finding paves the way for realizing the "spin transistor" operation in future topological spintronic devices.

  18. First-principles study of homologous series of layered Bi-Sb-Te-Se and Sn-O structures

    NASA Astrophysics Data System (ADS)

    Govaerts, Kirsten

    In the first part of the thesis, we present a systematic study of the stable layered structures at T = 0 K for the Bi-Sb-Te-Se system by means of a combination of the Cluster Expansion (CE) method and first-principles electronic structure calculations. In order to account for the existence of long-periodic layered structures and the strong structural relaxations we have developed a one-dimensional CE with occupation variables explicitly accounting for the fact that Bi or Sb atoms are part of an even or odd number of layers. For the binary systems A1-xQx (A = Sb, Bi; Q = Te, Se) the resulting (meta)stable structures are the homologous series (A2) n(A2Q3)m built up from successive bilayers A 2 and quintuple units A2Q3. The Bi1-xSb x system is found to be an almost ideal solution. The CE for the ternary Bi-Sb-Te system not only reproduces the binary stable structures but also finds stable ternary layered compounds with an arbitrary stacking of Sb 2Te3, Bi2Te3 and Te-Bi-Te-Sb-Te quintuple units, optionally separated by mixed Bi/Sb bilayers. We also investigate the electronic properties of the newly found ground state structures, and in particular the effect of Bi bilayers on the electronic structure of the topological insulator Bi2Se3. Due to the charge transfer from the Bi bilayers to the quintuple layers, the top- and bottom-surface Dirac cones shift down in energy. Also the Rashba-split conduction band states shift down, resulting in a new Dirac cone. The bands of the additional Bi bilayer are just ordinary Rashba-split states originating from the dipole built up by the charge transfer. These results offer new insight in experimental results, where cones are not always correctly identified. In a second part of the thesis, we investigate the Sn-O system. First we show that a combination of current van der Waals-corrected functionals and many-body calculations within the GW approximation provide accurate values for both structural and electronic properties of Sn

  19. Terahertz Faraday Rotation in the Quantum Anomalous Hall System V-doped (Bi,Sb)2 Te3

    NASA Astrophysics Data System (ADS)

    Ozel, Ozge; Frenzel, Alex; Chang, Cui-Zu; Pilon, Daniel; Moodera, Jagadeesh; Gedik, Nuh; Gedik group Team; Moodera group Collaboration

    Time-reversal symmetry breaking in a topological insulator (TI) can be achieved by introducing ferromagnetism, which opens up a gap in the Dirac surface states. When the chemical potential is tuned to lie within the surface gap, the quantum anomalous Hall state emerges, which can be regarded as the quantum Hall state at zero external magnetic field. Recently, this state has been observed by static transport measurements in thin films of magnetically doped TIs. Time-domain terahertz spectroscopy has been demonstrated to be an effective probe of surface states and Hall effects in topological materials. Here, we use polarization modulation terahertz spectroscopy to study the intrinsic properties of massive Dirac electrons in V-doped (Bi,Sb)2Te3 via Faraday rotation measurements.

  20. Great enhancements in the thermoelectric power factor of BiSbTe nanostructured films with well-ordered interfaces.

    PubMed

    Chang, Hsiu-Cheng; Chen, Chun-Hua; Kuo, Yung-Kang

    2013-08-01

    An innovative concept of twin-enhanced thermoelectricity was proposed to fundamentally resolve the high electrical resistance while not degrading the phonon scattering of the thermoelectric nanoassemblies. Under this frame, a variety of highly oriented and twinned bismuth antimony telluride (BixSb2-xTe3) nanocrystals were successfully fabricated by a large-area pulsed-laser deposition (PLD) technique on insulated silicon substrates at various deposition temperatures. The significant presence of the nonbasal- and basal-plane twins across the hexagonal BiSbTe nanocrystals, which were experimentally and systematically observed for the first time, evidently contributes to the unusually high electrical conductivity of ~2700 S cm(-1) and the power factor of ~25 μW cm(-1) K(-2) as well as the relatively low thermal conductivity of ~1.1 W m(-1) K(-1) found in these nanostructured films. PMID:23803956

  1. Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film

    PubMed Central

    Li, W.; Claassen, M.; Chang, Cui-Zu; Moritz, B.; Jia, T.; Zhang, C.; Rebec, S.; Lee, J. J.; Hashimoto, M.; Lu, D.-H.; Moore, R. G.; Moodera, J. S.; Devereaux, T. P.; Shen, Z.-X.

    2016-01-01

    The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy. PMID:27599406

  2. Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film.

    PubMed

    Li, W; Claassen, M; Chang, Cui-Zu; Moritz, B; Jia, T; Zhang, C; Rebec, S; Lee, J J; Hashimoto, M; Lu, D-H; Moore, R G; Moodera, J S; Devereaux, T P; Shen, Z-X

    2016-01-01

    The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb)2Te3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb)2Te3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy. PMID:27599406

  3. Evolution of thermoelectric performance for (Bi,Sb)2Te3 alloys from cutting waste powders to bulks with high figure of merit

    NASA Astrophysics Data System (ADS)

    Fan, Xi‧an; Cai, Xin zhi; Han, Xue wu; Zhang, Cheng cheng; Rong, Zhen zhou; Yang, Fan; Li, Guang qiang

    2016-01-01

    Bi2Te3 based cutting waste powders from cutting wafers were firstly selected as raw materials to prepare p-type Bi2Te3 based thermoelectric (TE) materials. Through washing, reducing, composition correction, smelting and resistance pressing sintering (RPS) process, p-type (Bi,Sb)2Te3 alloy bulks with different nominal stoichiometries were successfully obtained. The evolution of microstructure and TE performance for (Bi,Sb)2Te3 alloys were investigated in detail. All evidences confirmed that most of contaminants from line cutting process such as cutting fluid and oxides of Bi, Sb or Te could be removed by washing, reducing and smelting process used in this work. The carrier content and corresponding TE properties could be adjusted effectively by appropriate composition correction treatment. At lastly, a bulk with a nominal stoichiometry of Bi0.44Sb1.56Te3 was obtained and its' dimensionless figure of merit (ZT) was about 1.16 at 90 °C. The ZT values of Bi0.36Sb1.64Te3 and Bi0.4Sb1.6Te3 alloy bulks could also reach 0.98 and 1.08, respectively. Different from the conventional recycling technology such as hydrometallurgy extraction methods, the separation and extraction of beneficial elements such as Bi, Sb and Te did not need to be performed and the Bi2Te3 based bulks with high TE properties could be directly obtained from the cutting waste powders. In addition, the recycling technology introduced here was green and more suitable for practical industrial application. It can improve material utilization and lower raw material costs of manufacturers.

  4. Transport studies on Cr-doped (Bi,Sb)2Te3 thin films with nearly quantized anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Liu, Minhao; Richardella, Anthony; Kandala, Abhinav; Wang, Wudi; Yazdani, Ali; Samarth, Nitin; Ong, N. Phuan

    2015-03-01

    We describe measurements of the quantum anomalous Hall effect in ferromagnetic Cr-doped (Bi,Sb)2Te3 thin films (6-8 QL thickness) grown on (111) SrTiO3 (STO) substrates by molecular beam epitaxy. The Fermi level is tuned close to the neutral point by tuning the growth flux ratios of Cr, Bi and Sb. Transport measurements were carried out in a dilution fridge at a base temperature of 20 mK. By tuning the chemical potential with a back gate on the STO substrate, we observed an anomalous Hall effect as high as 0.95h/e2, with a coercive field ~ 0.15 T and a narrow transition between positive/negative Hall plateaus. Transport measurements in a non-local configuration showed a Hall-effect-like non-local resistance with a systematic dependence on the back gate voltage and with pronounced peaks which resembled the non-local resistance of the quantum Hall effect. The non-local signal has a maximum that coincides with the maximum in Hall conductivity, indicating the edge channel as its origin. Our results show that the edge channel manifests itself in various transport properties even though the Hall resistance is not perfectly quantized. Supported by DARPA SPAWAR Grant No. N66001-11-1-4110 and MURI grant on Topological Insulators (ARO W911NF-12-1-0461).

  5. Magneto-optical Kerr effect in Cr-doped (Bi,Sb)2Te3 Thin Films

    NASA Astrophysics Data System (ADS)

    Pan, Yu; Yao, Bing; Richardella, Anthony; Kandala, Abhinav; Fraleigh, Robert; Lee, Joon Sue; Samarth, Nitin; Yeats, Andrew; Awschalom, David D.

    2014-03-01

    When a three-dimensional (3D) topological insulator (TI) is interfaced with magnetism, the breaking of time reversal symmetry results in new phenomena such as the recently observed quantum anomalous Hall effect [C.-Z. Zhang et al., Science340, 167 (2013)]. Thus motivated, we use the polar-mode magneto-optical Kerr effect (MOKE) to probe the temperature- and field-dependent magnetization in molecular beam epitaxy grown Cr-doped thin films of the 3D TI (Bi,Sb)2Te3. Square MOKE hysteresis loops observed at low temperatures indicate robust ferromagnetism with a perpendicular magnetic anisotropy and Curie temperature that varies from ~ 5 K to ~ 150 K, depending on sample details. A key question is the nature of the ferromagnetism: is it a carrier-mediated mechanism, Van Vleck mechanism or due to extrinsic clusters? We address this issue by varying the magnetic ion concentration and carrier density via sample composition as well as by varying the chemical potential by back gating. Finally, we use spatially-resolved MOKE to image the magnetization in these samples. Supported by ONR and DARPA.

  6. Synthesis, crystal structure and optical properties of BiMgVO 5

    NASA Astrophysics Data System (ADS)

    Benmokhtar, S.; El Jazouli, A.; Chaminade, J. P.; Gravereau, P.; Guillen, F.; de Waal, D.

    2004-11-01

    The new vanadate BiMgVO 5 has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P21/n, a=7.542(6) Å, b=11.615(5) Å, c=5.305(3) Å, β=107.38(5)°, wR2=0.0447, R=0.0255. The structure consists of [Mg 2O 10] and [Bi 2O 10] dimers sharing their corners with [VO 4] tetrahedra. The ranges of bond lengths are 2.129-2.814 Å for Bi-O; 2.035-2.167 Å for Mg-O and 1.684-1.745 Å for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 Å. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.

  7. Variable Temperature X-Ray Diffraction Study of Bismuth Magnesium Vanadate, BiMg 2VO 6

    NASA Astrophysics Data System (ADS)

    Radosavljevic, I.; Sleight, A. W.

    2000-01-01

    The space group for the structure of BiMg2VO6 at room temperature is shown to be Pmcn, rather than Amma as previously reported. However, when BiMg2VO6, is heated, its structure adopts the Amma space group at about 320 K. When the temperature is decreased through this transition, the (VO4)3- tetrahedron tilts, destroying one of the mirror planes in space group Amma. In space group Amma the (BiO2)1- chains have four equal Bi-O distances of 2.204 Å at 350 K. However, in the lower space group, there are two sets of Bi-O distances, 2.188 and 2.223 Å at 100 K. Unit cell edges in BiMg2VO6 increase with increasing temperature, giving an average linear thermal expansion of 5.2×10-6K-1 over the 100-350 K range.

  8. Synthesis, crystal structure and optical properties of BiMgVO{sub 5}

    SciTech Connect

    Benmokhtar, S.; El Jazouli, A. . E-mail: a.eljazouli@univh2m.ac.ma; Chaminade, J.P.; Gravereau, P.; Guillen, F.; Waal, D. de

    2004-11-01

    The new vanadate BiMgVO{sub 5} has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P21/n, a=7.542(6)A, b=11.615(5)A, c=5.305(3)A, {beta}=107.38(5){sup o}, wR2=0.0447, R=0.0255. The structure consists of [Mg{sub 2}O{sub 10}] and [Bi{sub 2}O{sub 10}] dimers sharing their corners with [VO{sub 4}] tetrahedra. The ranges of bond lengths are 2.129-2.814A for Bi-O; 2.035-2.167A for Mg-O and 1.684-1.745A for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747A. An emission band overlapping the entire visible region with a maximum around 650nm is observed.

  9. A New Bismuth Magnesium Vanadate with Reduced Vanadium: BiMg 2.5V 18.5O 38

    NASA Astrophysics Data System (ADS)

    Uma, S.; Sleight, A. W.

    2002-02-01

    A new oxide containing Bi, Mg, and V has been prepared, and its structure was determined from single-crystal X-ray diffraction data. The space group is Roverline3 with hexagonal cell dimensions of a=10.1985(9) and c=20.4875(14) Å. The formula may be written as BiMg2(MgV)V18O38 to indicate that one crystallographic site is occupied by a 1:1 mixture of Mg and V. The vanadium on that site appears to be in an oxidation state of 2. Thus, the average oxidation state of vanadium on the other three vanadium sites would be 3.72+. The site occupied exclusively by magnesium is in tetrahedral coordination to oxygen. All sites occupied by vanadium are octahedrally coordinated by oxygen. The low electrical resistivity of this compound suggests itinerant electron behavior.

  10. [Determination of Sb and Bi in 24 international geological reference materials by using pressurized acid digestion-ICP-MS].

    PubMed

    Hu, Zhao-chu; Gao, Shan; Liu, Xiao-ming; Yuan, Hong-lin; Liu, Ye; Diwu, Chun-rong

    2007-12-01

    The authors studied in detail the memory effect of Bi, Sb, As and Te in ICP-MS. The produced memory effects of these element were in the order of Bi>Sb>Te>As. Bi was seriously adsorbed by the polypropylene sample storing bottle and the sample introduction system in the low nitric acid medium (0.01%-1% HNO3). The washout effect of 0.1% HF was found to be better than those of 6% HNO3 and 0.1% HClO4. Under the given experiment conditions, the instrumental limit of detection was 0.001 and 0.0001 ng x mL(-1) for Sb and Bi, respectively. The authors report the determination of Sb and Bi in 24 international geological reference materials by using pressurized acid digestion-ICP-MS (including AGV-2, BHVO-2, BCR-2, etc.). Most of the results were found to be in reasonable agreement with the reported values in the literature. The authors' determined values of Sb for GSR-1 (granite; 0.30 microg x g(-1)) and JP-1 (peridotite; 0.045 microg x g(-1)) are obviously higher than those reported values. This is attributed to the efficient pressurized acid digestion, which is generally much more efficient than conventional wet digestions for insoluble minerals. PMID:18330312

  11. Synthesis, crystal structure, and optical properties of a new bismuth magnesium vanadate: BiMg 2VO 6

    NASA Astrophysics Data System (ADS)

    Huang, Jinfan; Sleight, Arthur W.

    1992-09-01

    A new bismuth magnesium vanadate, BiMg 2VO 6, has been synthesized and structurally characterized from single crystal X-ray diffraction data. It crystallizes in orthorhombic symmetry with a = 7.9136(6) Å, b = 12.246(2) Å, c = 5.444(2) Å, V = 527.6(2)Å 3, z = 4, and a space group of Cmcm (No. 63). An unusual fivefold coordination is found for Mg. The five O atoms bound to Mg form a square pyramidal coordination polyhedron with MgO bond lengths ranging from 1.973(7) to 2.066(3) Å. The Bi atom is coordinated by four O atoms with BiO bond lengths 2.213(2) Å forming a square pyramid. The V atom bonds to four O atoms with VO distances from 1.672(6) to 1.725(5) Å; all the OVO angles are very close to the value of an ideal VO 4 tetrahedron. The BiMg 2VO 6 structure may be viewed as connected chains of edge-shared BiO 4 units and corner-shared MgO 5 units extending along the c axis. These chains are then connected to each other through the VO 4 tetrahedra and edge sharing of the MgO 5 units. The absorption edge (about 450 nm) determined from the photothermal deflection technique is consistent with results from the excitation-emission spectrum. An emission band around 650 nm was observed. The IR spectrum of this compound is also reported.

  12. Utilisation de procedes de microfabrication pour la realisation de modules thermoelectriques a base d'alliages (Bi,Sb)2(Te,Se)3

    NASA Astrophysics Data System (ADS)

    Kashi, Siamak

    The production of thermoelectric devices uses nearly handmade techniques as an industry standard. These techniques are not suitable for the fabrication of smaller devices, where thermoelements are shorter than 1 millimetre. Researchers are focusing on how to decrease the height of thermoelements in a device, to the extent of depositing thermoelectric thin films. However, the best thermoelectric performances are obtained on modules fabricated from bulk material. Many tests were made to decrease the overall size of these devices, but until now, they would not permit to obtain the same range of performances as industrial devices. The aim of this project is to use microfabrication processes to obtain high power density thermoelectric devices. The precision obtained with the use of microfabrication techniques and automated methods has the potential to increase the performance and the industrial production of these devices. Fabrication steps were designed and tested in the facilities of the Ecole Polytechnique de Montreal to create hot extruded p-type and n-type (Bi,Sb)2(Te,Se)3 alloy based thermoelectric devices. These steps can be listed in three different categories, surface treatments, microfabrication methods and hot assembly. After cutting, p-type and n-type wafers were polished, underwent electropolishing and chemical etching before a diffusion barrier layer of nickel was deposited. Photolithography printed a pattern on the samples, where tin was then electroplated. A first assembly allowed soldering samples of each conduction type to alumina plates, before cutting the sample to free the thermoelements. A final assembly then created the finished devices by soldering of the two parts containing p-type and n-type thermoelements. The produced devices were functional, validating the designed steps. Electrical characterization of the best modules obtained indicate that the electromotive force is comparable to that of commercial modules under the same conditions

  13. Synthesis and characterization of (1-x)Bi(Mg2/3Sb1/3)O3-xPbTiO3 piezoceramics

    NASA Astrophysics Data System (ADS)

    Upadhyay, Ashutosh; Dwivedi, Saurabh; Pandey, Rishikesh; Singh, Akhilesh Kumar

    2016-05-01

    We present here the comprehensive x-ray diffraction and polarization-electric field hysteresis studies on (1-x)Bi(Mg2/3Sb1/3)O3-xPbTiO3 piezoceramics with x = 0.52, 0.56 and 0.60. The powder x-ray diffraction data reveals the presence of tetragonal phase for all the compositions. The saturation of hysteresis loop is observed for x ≤ 0.56.

  14. Preparation of Ag/AgCl/BiMg{sub 2}VO{sub 6} composite and its visible-light photocatalytic activity

    SciTech Connect

    Guo, Rui; Zhang, Gaoke; Liu, Jiu

    2013-05-15

    Graphical abstract: - Abstract: A novel composite photocatalyst Ag/AgCl/BiMg{sub 2}VO{sub 6} was synthesized by depositing Ag/AgCl nanoparticles on BiMg{sub 2}VO{sub 6} substrate via a precipitation–photoreduction method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDXA), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectrophotometer (UV–vis DRS). The photocatalyst showed high and stable photocatalytic activity for photocatalytic degradation of acid red G under visible-light irradiation (λ > 420 nm). In addition, the active ·O{sub 2}{sup −} and h{sup +}, as main reactive species, played the major roles during the reaction process. The high photocatalytic activity of the composite may be related to the efficient electron–hole pairs separation at the photocatalyst interfaces, as well as the surface plasmon resonance of Ag nanoparticles formed on AgCl particles in the degradation reaction.

  15. Comparison of crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te nanocrystalline thin films: Effects of homogeneous irradiation with an electron beam

    SciTech Connect

    Takashiri, Masayuki Imai, Kazuo; Uyama, Masato; Nishi, Yoshitake; Hagino, Harutoshi; Miyazaki, Koji; Tanaka, Saburo

    2014-06-07

    The effects of homogenous electron beam (EB) irradiation on the crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te thin films were investigated. Both types of thin films were prepared by flash evaporation, after which homogeneous EB irradiation was performed at an acceleration voltage of 0.17 MeV. For the n-type thin films, nanodots with a diameter of less than 10 nm were observed on the surface of rice-like nanostructures, and crystallization and crystal orientation were improved by EB irradiation. The resulting enhancement of mobility led to increased electrical conductivity and thermoelectric power factor for the n-type thin films. In contrast, the crystallization and crystal orientation of the p-type thin films were not influenced by EB irradiation. The carrier concentration increased and mobility decreased with increased EB irradiation dose, possibly because of the generation of defects. As a result, the thermoelectric power factor of p-type thin films was not improved by EB irradiation. The different crystallization behavior of the n-type and p-type thin films is attributed to atomic rearrangement during EB irradiation. Selenium in the n-type thin films is more likely to undergo atomic rearrangement than the other atoms present, so only the crystallinity of the n-type Bi-Se-Te thin films was enhanced.

  16. Electric field induced lattice strain in pseudocubic Bi(Mg1/2Ti1/2)O3-modified BaTiO3-BiFeO3 piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Fujii, Ichiro; Iizuka, Ryo; Nakahira, Yuki; Sunada, Yuya; Ueno, Shintaro; Nakashima, Kouichi; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Wada, Satoshi

    2016-04-01

    Contributions to the piezoelectric response in pseudocubic 0.3BaTiO3-0.1Bi(Mg1/2Ti1/2)O3-0.6BiFeO3 ceramics were investigated by synchrotron X-ray diffraction under electric fields. All of the lattice strain determined from the 110, 111, and 200 pseudocubic diffraction peaks showed similar lattice strain hysteresis that was comparable to the bulk butterfly-like strain curve. It was suggested that the hysteresis of the lattice strain and the lack of anisotropy were related to the complex domain structure and the phase boundary composition.

  17. Phase transition and chemical order in the ferroelectric perovskite (1-x)Bi(Mg3/4W1/4)O3-xPbTiO3 solid solution system

    NASA Astrophysics Data System (ADS)

    Stringer, C. J.; Eitel, R. E.; Shrout, T. R.; Randall, C. A.; Reaney, I. M.

    2005-01-01

    Building on the ferroelectric family based on the Bi(Me+3)O3-PbTiO3 solid solutions, the complex solid solution (1-x )Bi(Mg3/4W1/4)O3-xPbTiO3 [(1-x)BMW-xPT] was investigated. This system was found to exhibit a broad morphotropic phase boundary at x ˜0.48mol% PbTiO3 with a corresponding Curie temperature of 205°C separating pseudocubic and tetragonal ferroelectric phases. Based on dielectric, x-ray diffraction (XRD), and calorimetric data, a simple dielectric phase field diagram was established. On further structural analysis with diffraction contrast transmission electron microscopy along with XRD, evidence of B-site chemical ordering was found for the (1-x )Bi(Me'Me″)O3-xPbTiO3 perovskite family.

  18. Synthesis and structural studies on (1−x)Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}−xPbTiO{sub 3} piezoceramics

    SciTech Connect

    Upadhyay, Ashutosh Pandey, Rishikesh Anand, Shashwat Singh, Akhilesh K.

    2014-04-24

    We present here the structural studies on (1−x)Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}−xPbTiO{sub 3} (BMT-xPT) piezoceramics with x=0.28, 0.37 and 0.45 using powder x-ray diffraction data. Rietveld refinement of powder x-ray diffraction data reveals the tetragonal structure (space group P4mm) for the compositions with x>0.40 and rhombohedral (space group R3m) for the compositions with x<0.30 of BMT-xPT ceramics. The morphotropic phase boundary is found for the intermediate composition with 0.30

  19. Structural and dielectric properties of BaTiO3-Bi(Mg1/2Ti1/2)O3 thin films fabricated by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Moki, Shota; Kimura, Junichi; Kaneko, Noriyuki; Funakubo, Hiroshi; Uchida, Hiroshi

    2014-09-01

    Thin films of the BaTiO3-Bi(Mg1/2Ti1/2)O3 (BT-BMT) solid-solution system were fabricated with the aim of achieving a stable temperature coefficient of capacitance (TCC) favorable for high-temperature electronics. A single perovskite phase with pseudocubic symmetry was obtained for the films fabricated by chemical solution deposition on (111)Pt/TiO2/(100)Si substrates in the composition range of x = 0-0.80 for (1 - x)BT-xBMT. BMT added to the BaTiO3-based films enhanced the crystallinity of the perovskite phase and resulted in saturated P-E hysteresis behavior with remanent polarization of up to 13 µC/cm2. BMT addition led to gradual dielectric relaxation, which also resulted in stable TCC behavior with a relative dielectric constant of approximately 400 in the temperature range of RT - 400 °C, especially for the BT-BMT films with x = 0.20-0.40.

  20. Lead- and alkali-metal-free BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 solid-solution thin films with high dielectric constant prepared on Si substrates by solution-based method

    NASA Astrophysics Data System (ADS)

    Kimura, Junichi; Mohamed-Tahar, Chentir; Shimizu, Takao; Uchida, Hiroshi; Funakubo, Hiroshi

    2014-09-01

    Lead- and alkali-metal-free BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 solid-solution thin films were prepared on (111)cSrRuO3/(111)Pt/TiO2/SiO2/(100)Si substrates by chemical solution deposition (CSD) and their crystal structure and dielectric properties were investigated. The lattice spacing as a function of z/(x + z) in xBaTiO3-0.1Bi(Mg0.5Ti0.5)O3-zBiFeO3 indicated the existence of phase boundaries (pseudocubic/rhombohedral) in the range of z/(x + z) = 0.33-0.56, where the relatively high relative dielectric constant, ɛr, of above 800 was obtained. On the other hand, dielectric loss, tan δ, of below 0.2 was confirmed in the range z/(x + z) = 0-0.87, which rapidly increased toward z/(x + z) = 1.0. The relatively high ɛr values of these films deposited on Si substrates by a solution-based process suggest that they can be used as alternative to Pb(Zr,Ti)O3, KNbO3, and (Bi1/2Na1/2)TiO3-based films.

  1. Simultaneous achievement of high dielectric constant and low temperature dependence of capacitance in (111)-oriented BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 solid solution thin films

    NASA Astrophysics Data System (ADS)

    Kimura, Junichi; Chentir, Mohamed-Tahar; Shimizu, Takao; Uchida, Hiroshi; Funakubo, Hiroshi

    2016-01-01

    The temperature dependence of the capacitance of (111)c-oriented (0.90-x)BaTiO3-0.10Bi(Mg0.5Ti0.5)O3-xBiFeO3 solid solution films is investigated. These films are prepared on (111)cSrRuO3/(111)Pt/TiO2/SiO2/(100)Si substrates by the chemical solution deposition technique. All the films have perovskite structures and the crystal symmetry at room temperature varies with increasing x ratio, from pseudocubic when x = 0-0.30 to rhombohedral when x = 0.50-0.90. The pseudocubic phase shows a high relative dielectric constant (ɛr) (ranging between 400 and 560 at room temperature and an operating frequency of 100 kHz) and a low temperature dependence of capacitance up to 400°C, while maintaining a dielectric loss (tan δ) value of less than 0.2 at 100 kHz. In contrast, ɛr for the rhombohedral phase increases monotonically with increasing temperature up to 250°C, and increasingly high tan δ values are recorded at higher temperatures. These results indicate that pseudocubic (0.90-x)BaTiO3-0.10Bi(Mg0.5Ti0.5)O3-xBiFeO3 solid solution films with (111) orientation are suitable candidates for high-temperature capacitor applications.

  2. The motley family of polar compounds (MV)[M(X{sub 5-x}X Prime {sub x})] based on anionic chains of trans-connected M{sup (III)}(X,X Prime ){sub 6} octahedra (M=Bi, Sb; X, X Prime =Cl, Br, I) and methylviologen (MV) dications

    SciTech Connect

    Leblanc, Nicolas; Mercier, Nicolas; Allain, Magali; Toma, Oksana; Auban-Senzier, Pascale; Pasquier, Claude

    2012-11-15

    The search for hybrid organic-inorganic materials remains a great challenge in the field of ferroelectrics. Following the discovery of the room temperature ferroelectric material (MV)[BiI{sub 3}Cl{sub 2}] (MV{sup 2+}: methylviologen) exhibiting the highest polarization value in the field of hybrid ferroelectrics, we report here nine new hybrids with the general formulation (MV)[M{sup (III)}X{sub 5-x}X Prime {sub x}] (M=Bi, Sb; X, X Prime =Cl, Br, I): (MV)[BiCl{sub 3.3}Br{sub 1.7}] (1), (MV)[BiCl{sub 1.3}Br{sub 3.7}] (2), (MV)[BiBr{sub 3.2}I{sub 1.8}] (3), (MV)[SbCl{sub 5}] (4), (MV)[SbBr{sub 5}] (5), (MV)[SbCl{sub 3.8}Br{sub 1.2}] (6), (MV)[SbCl{sub 2.4}Br{sub 2.6}] (7), (MV)[SbI{sub 3}Cl{sub 2}] (8) and (MV)[SbBr{sub 3.8}I{sub 1.2}] (9). Depending on the presence of polar chains or not, and on the coupling of polar chains, two types of centrosymmetrical structures [C1] and [C2] and two types of polar structures [P1] and [P2] are defined. (2) undergoes a paraelectric-to-relaxor ferroelectric transition around 100-150 K depending of the frequency showing that the Curie temperature, T{sub C}, of (MV)[BiBr{sub 5}] (243 K) can be modulated by the substitution of Br by Cl. The most interesting family is the [P2] type because the syn coupling of polar chains is in favor of high polarization values, as in (MV)[BiI{sub 3}Cl{sub 2}]. Five of the nine new hybrids, (4), (6-9), which have the [P2] type structure are potential ferroelectrics. - Graphical abstract: The methylviologen haloantimonate (MV)[SbX{sub 5-x}X Prime {sub x}] families (X, X Prime =Cl, Br, I) - [P1] and [P2] are the two kinds of polar structures - and view of the (MV)[SbBr{sub 3.8}I{sub 1.2}] hybrid based on chiral polar chains which are in syn coupling. Highlights: Black-Right-Pointing-Pointer Nine hybrids based on methylviologen and halometalate chains have been discovered. Black-Right-Pointing-Pointer The polar nature of chains is due to the ns{sup 2} stereoactivity of Sb{sup (III)} or Bi{sup (III

  3. Bismuth-induced dielectric relaxation in the (1-x)La(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xBi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3} perovskite system

    SciTech Connect

    Salak, Andrei N.; Pullar, Robert C.; Alford, Neil McN.

    2008-07-01

    The temperature variation of the dielectric permittivity and loss of the solid solutions (1-x)La(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xBi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3} [(1-x)LMT-xBMT] (0{<=}x{<=}0.3) measured at radio, microwave, and far infrared frequency ranges has been analyzed in comparison with that observed in other bismuth-containing and bismuth-free perovskite ceramics based on LMT. It has been found that the low temperature dielectric response of the (1-x)LMT-xBMT compositions with x{>=}0 is frequency dependent over a wide range from radio to microwave frequencies. The considerable compositional growth of the dielectric permittivity and loss associated with the amount of bismuth in the system was revealed to be not contributed by the lattice polar phonon modes. The effect was suggested to be related to the low-temperature dielectric relaxation process due to a hopping movement of charge carriers in crystallographic A-sites of the perovskite lattice. Particular role of local lattice distortions caused by the anisotropic chemical bonds involving bismuth 6s{sup 2} electrons in a localization of hopping charge carriers in perovskites and other oxygen-octahedral compositions is considered. The characteristic features of the Bi-induced dielectric relaxation and those typical of the ferroelectric relaxors are compared and discussed.

  4. Role of point defects in bipolar fatigue behavior of Bi(Mg1/2Ti1/2)O3 modified (Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 relaxor ceramics

    NASA Astrophysics Data System (ADS)

    Kumar, Nitish; Ansell, Troy Y.; Cann, David P.

    2014-04-01

    Lead-free Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 106 cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.

  5. Ultraschall-Geschwindigkeit und-Absorption in Bi-In-Schmelzen /Ultrasonic Velocity and Absorption in Bi-In-melts

    NASA Astrophysics Data System (ADS)

    Bek, R.; Steeb, S.

    1981-02-01

    Using the pulse-echo method the ultrasonic velocity and absorption was measured with Bi-In-melts in the temperature range from liquidus up to more than 600 °C. The frequencies used reached from 10 MHz up to 130 MHz. Within the experimental accuracy no frequency dependence of the absorption coefficient α/f2 could be detected. An excess absorption can be observed, which for the molten elements can be explained by fluctuations of the packing density. For the molten alloys additionally concentration fluctuations play an important role. Thus an understanding of the temperature dependency of the ultrasonic velocity and absorption can be achieved.

  6. Role of point defects in bipolar fatigue behavior of Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3} modified (Bi{sub 1/2}K{sub 1/2})TiO{sub 3}-(Bi{sub 1/2}Na{sub 1/2})TiO{sub 3} relaxor ceramics

    SciTech Connect

    Kumar, Nitish Ansell, Troy Y.; Cann, David P.

    2014-04-21

    Lead-free Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-(Bi{sub 1/2}K{sub 1/2})TiO{sub 3}-(Bi{sub 1/2}Na{sub 1/2})TiO{sub 3} (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 10{sup 6} cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.

  7. Measurement of Activity of Indium in Liquid Bi-In-Sn Alloys by EMF Method

    NASA Astrophysics Data System (ADS)

    Kumar, M. R.; Mohan, S.; Behera, C. K.

    2016-05-01

    The electrochemical technique based on a molten salt electrolyte galvanic cell has been used to measure the activity of indium in liquid Bi-In-Sn alloys in the temperature range of 723 K to 855 K along three ternary sections. The activity of tin in Bi-Sn binary alloys has also been measured by the same technique in the above temperature range. The activity of indium in Bi-In-Sn alloys shows negative deviation from Raoult's law for most of the compositions and slight positive deviations for a few indium-rich compositions. The ternary excess molar free energies have been calculated by Darken's treatment. Isoactivity curves at 813 K in the ternary Bi-In-Sn alloys were derived by combining the activity data of In-Sn and Bi-In alloys. The values of excess molar free energy obtained in this study are compared with those calculated from the Muggianu model at 813 K.

  8. Measurement of Activity of Indium in Liquid Bi-In-Sn Alloys by EMF Method

    NASA Astrophysics Data System (ADS)

    Kumar, M. R.; Mohan, S.; Behera, C. K.

    2016-08-01

    The electrochemical technique based on a molten salt electrolyte galvanic cell has been used to measure the activity of indium in liquid Bi-In-Sn alloys in the temperature range of 723 K to 855 K along three ternary sections. The activity of tin in Bi-Sn binary alloys has also been measured by the same technique in the above temperature range. The activity of indium in Bi-In-Sn alloys shows negative deviation from Raoult's law for most of the compositions and slight positive deviations for a few indium-rich compositions. The ternary excess molar free energies have been calculated by Darken's treatment. Isoactivity curves at 813 K in the ternary Bi-In-Sn alloys were derived by combining the activity data of In-Sn and Bi-In alloys. The values of excess molar free energy obtained in this study are compared with those calculated from the Muggianu model at 813 K.

  9. Quantum-limit anisotropic magnetoresistance of semiconducting n-BiSb alloys

    NASA Astrophysics Data System (ADS)

    Redko, N. A.; Kagan, V. D.; Volkov, M. P.

    2009-12-01

    The magnetic-field dependences of resistivity and Hall coefficient of single crystals Bi 0.93Sb 0.07 alloys were investigated at low temperatures. For H∥ C3 and j∥ C1 orientation the cyclotron frequencies of all three ellipsoids are equal and the electron concentration raises with the magnetic field in quantum limit. For H∥ C2 and j∥ C1 the quantum oscillations of resistivity were observed connected with the electrons of two ellipsoids, at higher fields the transition to the quantum limit takes place. The magnetic field increase in the quantum limit leads to the increase of electron energy from secondary ellipsoids and to their migration to the main ellipsoid. For H∥ C1∥ j orientation the quantum oscillations of resistivity were connected with all three ellipsoids. The electron energy for main ellipsoid rises in quantum limit with magnetic field, leading to the migration of carriers from main ellipsoid to the secondary ellipsoids.

  10. Use of extruded alloys Bi-Sb in low temperature thermoelements

    NASA Astrophysics Data System (ADS)

    Banaga, M. P.; Buimistr, B. S.; Moloshnik, E. F.

    1988-10-01

    Values of thermoelectric factor of quality for extruded alloys Bi_88Sb_12 of n-type in the temperatures interval 200-100K and a magnetic field induction 0-0.3Tl has been given. Temperature dependencies of optimal ratios of crossections of frames of thermoelements, containing extruded n-frame for various values of the induction of the transversal magnetic field has been analysed. Temperature dependencies of the quality factors of the thermoelements has been given. Calculated and experimental temperature falls on thermoelements and their dependenices on the crossections frames ratios for various temperatures of the heat evacuation has been analysed. Thermoelements examined are designed for application in low-temperature coolers.

  11. Materials Data on Ba2BiSbO6 (SG:148) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  12. Single-crystal growth and thermoelectric properties of Ge(Bi,Sb)4Te7.

    PubMed

    von Rohr, Fabian; Schilling, Andreas; Cava, Robert J

    2013-02-20

    The thermoelectric properties between 10 and 300 K and the growth of single crystals of n-type and p-type GeBi(4)Te(7), GeSb(4)Te(7) and Ge(Bi(1-x)Sb(x))(4)Te(7) solid solution are reported. Single crystals were grown by the modified Bridgman method, and p-type behavior was achieved by the substitution of Bi by Sb in GeBi(4)Te(7). The thermopower in the Ge(Bi(1-x)Sb(x))(4)Te(7) solid solution ranges from -117 to +160 μV K(-1). The crossover from n-type to p-type is continuous with increasing Sb content and is observed at x ≈0.15. The highest thermoelectric efficiencies among the tested n-type and p-type samples are Z(n)T = 0.11 and Z(p)T = 0.20, respectively. For an optimal n-p couple in this alloy system the composite figure of merit is Z(np)T = 0.17 at room temperature. PMID:23343638

  13. Integrated measurements of 212Pb and 212Bi in the air by rotating filters.

    PubMed

    Pressyanov, D S

    1995-02-01

    A method for determining time integrated concentrations of 212Pb and 212Bi in the air is proposed. It employs solid state nuclear track detectors covered with an absorber and placed around a rotating filter. Results from experiments carried out in an artificial 220Rn atmosphere have been presented. They reveal that the method works within the range of integrated concentrations for indoor measurements. The experimental error was about 7% for 212Pb and 23% for 212Bi. Possibilities for improving the accuracy have been discussed. PMID:7814259

  14. Characterization of Low-Melting-Point Sn-Bi-In Lead-Free Solders

    NASA Astrophysics Data System (ADS)

    Li, Qin; Ma, Ninshu; Lei, YongPing; Lin, Jian; Fu, HanGuang; Gu, Jian

    2016-02-01

    Development of lead-free solders with low melting temperature is important for substitution of Pb-based solders to reduce direct risks to human health and the environment. In the present work, Sn-Bi-In solders were studied for different ratios of Bi and Sn to obtain solders with low melting temperature. The microstructure, thermal properties, wettability, mechanical properties, and reliability of joints with Cu have been investigated. The results show that the microstructures of the Sn-Bi-In solders were composed of β-Sn, Bi, and InBi phases. The intermetallic compound (IMC) layer was mainly composed of Cu6Sn5, and its thickness increased slightly as the Bi content was increased. The melting temperature of the solders was around 100°C to 104°C. However, when the Sn content exceeded 50 wt.%, the melting range became larger and the wettability became worse. The tensile strength of the solder alloys and solder joints declined with increasing Bi content. Two fracture modes (IMC layer fracture and solder/IMC mixed fracture) were found in solder joints. The fracture mechanism of solder joints was brittle fracture. In addition, cleavage steps on the fracture surface and coarse grains in the fracture structure were comparatively apparent for higher Bi content, resulting in decreased elongation for both solder alloys and solder joints.

  15. Surface Tomonaga-Luttinger-Liquid State on Bi/InSb(001).

    PubMed

    Ohtsubo, Yoshiyuki; Kishi, Jun-Ichiro; Hagiwara, Kenta; Le Fèvre, Patrick; Bertran, François; Taleb-Ibrahimi, Amina; Yamane, Hiroyuki; Ideta, Shin-Ichiro; Matsunami, Masaharu; Tanaka, Kiyohisa; Kimura, Shin-Ichi

    2015-12-18

    A 1D metallic surface state was created on an anisotropic InSb(001) surface covered with Bi. Angle-resolved photoelectron spectroscopy (ARPES) showed a 1D Fermi contour with almost no 2D distortion. Close to the Fermi level (E_{F}), the angle-integrated photoelectron spectra showed power-law scaling with the binding energy and temperature. The ARPES plot above E_{F}, obtained thanks to a thermally broadened Fermi edge at room temperature, showed a 1D state with continuous metallic dispersion across E_{F} and power-law intensity suppression around E_{F}. These results strongly suggest a Tomonaga-Luttinger liquid on the Bi/InSb(001) surface. PMID:26722934

  16. A comparative study of the microstructures observed in statically cast and continuously cast Bi-In-Sn ternary eutectic alloy

    SciTech Connect

    Sengupta, S.; Soda, H.; McLean, A.; Rutter, J.W.

    2000-01-01

    A ternary eutectic alloy with a composition of 57.2 pct Bi, 24.8 pct In, and 18 pct Sn was continuously cast into wire of 2 mm diameter with casting speeds of 14 and 79 mm/min using the Ohno Continuous Casting (OCC) process. The microstructures obtained were compared with those of statically cast specimens. Extensive segregation of massive Bi blocks, Bi complex structures, and tin-rich dendrites was found in specimens that were statically cast. Decomposition of {radical}Sn by a eutectoid reaction was confirmed based on microstructural evidence. Ternary eutectic alloy with a cooling rate of approximately 1 C/min formed a double binary eutectic. The double binary eutectic consisted of regions of BiIn and decomposed {radical}Sn in the form of a dendrite cell structure and regions of Bi and decomposed {radical}Sn in the form of a complex-regular cell. The Bi complex-regular cells, which are a ternary eutectic constituent, existed either along the boundaries of the BiIn-decomposed {radical}Sn dendrite cells or at the front of elongated dendrite cell structures. In the continuously cast wires, primary Sn dendrites coupled with a small Bi phase were uniformly distributed within the Bi-In alloy matrix. Neither massive Bi phase, Bi complex-regular cells, no BiIn eutectic dendrite cells were observed, resulting in a more uniform microstructure in contrast to the heavily segregated structures of the statically cast specimens.

  17. Growth and properties of chemical solution deposited BiInO3-PbTiO3 films

    NASA Astrophysics Data System (ADS)

    Ko, S. W.; Yeo, H. G.; Trolier-McKinstry, S.

    2009-10-01

    The dielectric, ferroelectric, and piezoelectric properties of chemical solution deposited xBiInO3-(1-x)PbTiO3 (0.10≤x ≤0.35) thin films on platinized silicon substrates were investigated. Using a PbTiO3 seed layer, phase pure xBiInO3-(1-x)PbTiO3 (0.10≤x ≤0.35) thin films were prepared. For a 470 nm thick 0.15BiInO3-0.85PbTiO3 film, the room temperature permittivity was 650, while the dielectric loss tangent was below 2%. The coercive field and remanent polarization were 73 kV/cm and 22 μC/cm2, respectively. The ferroelectric transition temperatures of the xBiInO3-(1-x)PbTiO3 (x =0.10-0.20) films were all in excess of 550 °C. For x=0.15, the e31,f piezoelectric coefficient was -2.7 C/m2.

  18. Enhanced power factor and high-pressure effects in (Bi,Sb){sub 2}(Te,Se){sub 3} thermoelectrics

    SciTech Connect

    Ovsyannikov, Sergey V. E-mail: sergey2503@gmail.com; Morozova, Natalia V.; Korobeinikov, Igor V.; Vokhmyanin, Alexander P.; Shchennikov, Vladimir V.; Lukyanova, Lidia N.; Usov, Oleg A.; Kutasov, Vsevolod A.; Manakov, Andrey Y.; Likhacheva, Anna Y.; Ancharov, Alexey I.; Berger, Ivan F.; Kulbachinskii, Vladimir A.; Okada, Taku

    2015-04-06

    We investigated the effects of applied high pressure on thermoelectric, electric, structural, and optical properties of single-crystalline thermoelectrics, Bi{sub 2}Te{sub 3}, Bi{sub x}Sb{sub 2−x}Te{sub 3} (x = 0.4, 0.5, 0.6), and Bi{sub 2}Te{sub 2.73}Se{sub 0.27} with the high thermoelectric performance. We established that moderate pressure of about 2–4 GPa can greatly enhance the thermoelectric power factor of all of them. X-ray diffraction and Raman studies on Bi{sub 2}Te{sub 3} and Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} found anomalies at similar pressures, indicating a link between crystal structure deformation and physical properties. We speculate about possible mechanisms of the power factor enhancement and suppose that pressure/stress tuning can be an effective tool for the optimization of the thermoelectric performance.

  19. Mechanical properties of (Bi,Sb)2Te3 solid solutions obtained by directional crystallization and spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Lavrent'ev, M. G.; Osvenskii, V. B.; Pivovarov, G. I.; Sorokin, A. I.; Bulat, L. P.; Bublik, V. T.; Tabachkova, N. Yu.

    2016-01-01

    We have studied the temperature dependence of the mechanical strength at uniaxial compression for solid solutions based on bismuth and antimony chalcogenides, which were prepared by three methods: (i) vertical zone melting (VZM), (ii) hot extrusion, and (iii) spark plasma sintering (SPS). In the samples of solid solutions obtained by VZM and extrusion, a brittle-ductile transition was observed in a wised temperature interval of 200-350°C. In nanostructured SPS samples, transition from brittle to plastic fracture was observed within 170-200°C. The room-temperature strength of nanostructured samples was eight to nine times as large as that of VZM samples, and the stress-strain curves of these materials were significantly different. At a temperature of about 300°C, the strength of nanostructured solid solutions decreases to nearly zero.

  20. Heavily Cr-doped (Bi,Sb)2Te3 as a ferromagnetic insulator with electrically tunable conductivity

    NASA Astrophysics Data System (ADS)

    Ou, Yunbo; Liu, Chang; Zhang, Liguo; Feng, Yang; Jiang, Gaoyuan; Zhao, Dongyang; Zang, Yunyi; Zhang, Qinghua; Gu, Lin; Wang, Yayu; He, Ke; Ma, Xucun; Xue, Qi-Kun

    2016-08-01

    With molecular beam epitaxy we have grown Cry(BixSb1-x)2-yTe3 thin films with homogeneous distribution of Cr dopants and Curie temperature up to 77 K. The films with Cr concentration y ≥ 0.39 are found to be topologically trivial, highly insulating ferromagnets, whose conductivity can be tuned over two orders of magnitude by gate voltage. The ferromagnetic insulators with electrically tunable conductivity can be used to realize the quantum anomalous Hall effect at higher temperature in topological insulator heterostructures and to develop field effect devices for spintronic applications.

  1. Mechanical robust BiSbTe alloys with superior thermoelectric performance: A case study of stable hierarchical nanostructured thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Su, Xianli; Zheng, Yun; Tang, Xinfeng; Uher, Ctirad; Tang's Group Team; Uher's Group Team

    2015-03-01

    Poor machinability and susceptibility to brittle fracture of commercial ingots often impose significant limitations on the manufacturing process and durability of thermoelectric devices. In this study, melt spinning combined with plasma activated sintering (MS-PAS) method is employed with commercial p-type zone-melted (ZM) ingots of Bi0.5Sb1.5Te3. This fast synthesis approach achieves hierarchical structures and in-situ nanoscale precipitates, resulting in the simultaneous improvement of thermoelectric performance and mechanical properties. Benefitting from a strong suppression of the lattice thermal conductivity, a peak ZT of 1.22 is achieved at 340 K in MS-PAS synthesized structures, representing about a 40% enhancement over that of ZM ingots. Moreover, MS-PAS specimens with hierarchical structures exhibit superior machinability and mechanical properties with an almost 30% enhancement in the fracture toughness, eightfold and a factor of six increase in the compressive and flexural strength respectively. We wish to acknowledge support from the National Basic Research Program of China (973 program) under Project 2013CB632502.

  2. Molecular Beam Epitaxy Growth of GaBi, InBi and InGaBi

    NASA Astrophysics Data System (ADS)

    Keen, B.; Makin, R.; Stampe, P. A.; Kennedy, R. J.; Piper, L. F. J.; McCombe, B.; McConville, C. F.; Durbin, S. M.

    2014-03-01

    Recent interest in bismuth alloys of III-V semiconductors for infrared and far-infrared device applications, specifically GaAsBi and InAsBi, has indicated that further study of the III-Bi family of binary compounds would be of great help in improving the quality of these material systems. While immiscibility issues have so far frustrated the growth of GaBi and AlBi, InBi is less problematic, and we have grown it by molecular beam epitaxy on (001) GaAs substrates. However, regions of varying composition exist across the substrate due to poor wetting of the surface. In an effort to improve film quality we have continued to refine the growth parameters by adjusting substrate temperature, beam flux ratio, and deposition rate. Characterization of these films has been performed by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Additionally, we have explored growth of GaBi and In1-xGaxBi at low Ga mole fractions, and modeled this using molecular dynamics simulations. This work is supported by the Research Foundation of the State University of New York Collaborations Fund.

  3. Metal-Silicate Partitioning of Bi, In, and Cd as a Function of Temperature and Melt Composition

    NASA Technical Reports Server (NTRS)

    Marin, Nicole; Righter, K.; Danielson, L.; Pando, K.; Lee, C.

    2013-01-01

    The origin of volatile elements in the Earth, Moon and Mars is not known; however, several theories have been proposed based on volatile elements such as In, As, Se, Te and Zn which are in lower concentration in the Earth, Moon, and Mars than in chondrites. Explanations for these low concentrations are based on two contrasting theories for the origin of Earth: equilibrium core formation versus late accretion. One idea is that the volatiles were added during growth of the planets and Moon, and some mobilized into the metallic core while others stayed in the mantle (e.g., [1]). The competing idea is that they were added to the mantles after core formation had completed (e.g., [2]). Testing these ideas involves quantitative modeling which can only be performed after data is obtained on the systematic metal-silicate partitioning behavior of volatile elements with temperature, pressure and melt composition. Until now, such data for Bi, In, and Cd has been lacking. After conducting a series of high pressure, high temperature experiments, the metal-silicate partition coefficients of Bi, In, and Cd as a function of temperature and melt composition can be used to evaluate potential conditions under which terrestrial planets differentiated into core and mantle, and how they acquired volatiles.

  4. Phase transitions in the liquid-vapor interface of dilute alloys of Bi in Ga: New experimental studies

    SciTech Connect

    Li, Dongxu; Jiang, Xu; Yang, Bin; Rice, Stuart A.

    2010-07-19

    We report the results of measurements of x-ray reflectivity and grazing incidence x-ray diffraction from the liquid-vapor interfaces of four dilute alloys of Bi in Ga with mole fractions x{sub Bi} = 0.0032, 0.0023, 0.00037, and 0.000037. The monolayer coverage of the alloys with x{sub Bi} = 0.0023, and x{sub Bi} = 0.00037 is about 0.85 and only very slightly temperature dependent. The monolayer coverage in the lowest-concentration alloy, with x{sub Bi} = 0.000037, ranged from 0.82 at 29 C to 0.58 at 110 C. In none of these alloys, down to the lowest temperature used, 29 C, can we find any evidence for crystallization of the Bi monolayer that segregates as the outermost stratum of the liquid-vapor interface. Drawing on theoretical arguments we propose that the transitions inferred from the second-harmonic generation and plasma generation studies of dilute Bi in Ga alloys are from the liquid state to the hexatic state of the Bi monolayer. The data for the alloy with x{sub Bi} = 0.000037 suggest that near 80 C there is a disordered phase-to-disordered phase transition.

  5. β -detected NMR of 8Li+ in Bi, Sb, and the topological insulator Bi0.9Sb0.1

    NASA Astrophysics Data System (ADS)

    MacFarlane, W. A.; Tschense, C. B. L.; Buck, T.; Chow, K. H.; Cortie, D. L.; Hariwal, A. N.; Kiefl, R. F.; Koumoulis, D.; Levy, C. D. P.; McKenzie, I.; McGee, F. H.; Morris, G. D.; Pearson, M. R.; Song, Q.; Wang, D.; Hor, Y. S.; Cava, R. J.

    2014-12-01

    We report the NMR Knight shift and spin-lattice relaxation of 8Li+ implanted ˜100 nm into single crystals of semimetallic Sb, Bi, and topologically insulating Bi0.9Sb0.1. We find small negative shifts (of order 100 ppm) in all three. In the insulator, the shift is nearly temperature independent, while in Bi and Sb it becomes more negative at low temperature without following the bulk susceptibility, suggesting two distinct temperature dependent contributions, possibly from the orbital and spin response. However, a simple model is unable to account for the observed shift. The spin-lattice relaxation differs in both scale and temperature dependence in all three. It is Korringa-like in Bi and remarkably is fastest in the insulating alloy and slowest in Sb with the highest bulk carrier density. These surprising results call for detailed calculations, but phenomenologically demonstrate that β -detected NMR of implanted 8Li+ is sensitive to the magnetic response of low-density carriers. The prospects for depth-resolved studies of conventional and topological surface states at lower implantation energies are good.

  6. In-situ Observation of Size and Irradiation Effects on Thermoelectric Properties of Bi-Sb-Te Nanowire in FIB Trimming

    PubMed Central

    Chien, Chia-Hua; Lee, Ping-Chung; Tsai, Wei-Han; Lin, Chien-Hung; Lee, Chih-Hao; Chen, Yang-Yuan

    2016-01-01

    In this report, the thermoelectric properties of a Bi0.8Sb1.2Te2.9 nanowire (NW) were in-situ studied as it was trimmed from 750 down to 490 and 285 nm in diameter by a focused ion beam. While electrical and thermal conductivities both indubitably decrease with the diameter reduction, the two physical properties clearly exhibit different diameter dependent behaviors. For 750 and 490 nm NWs, much lower thermal conductivities (0.72 and 0.69 W/m-K respectively) were observed as compared with the theoretical prediction of Callaway model. The consequence indicates that in addition to the size effect, extra phonon scattering of defects created by Ga ion irradiation was attributed to the reduction of thermal conductivities. As the NW was further trimmed down to 285 nm, both the electrical and thermal conductivities exhibited a dramatic reduction which was ascribed to the formation of amorphous structure due to Ga ion irradiation. The size dependence of Seebeck coefficient and figure of merit (ZT) show the maximum at 750 nm, then decrease linearly with size decrease. The study not only provides the thoroughly understanding of the size and defect effects on the thermoelectric properties but also proposes a possible method to manipulate the thermal conductivity of NWs via ion irradiation. PMID:27030206

  7. Slurry sampling flow injection chemical vapor generation inductively coupled plasma mass spectrometry for the determination of trace Ge, As, Cd, Sb, Hg and Bi in cosmetic lotions.

    PubMed

    Chen, Wei-Ni; Jiang, Shiuh-Jen; Chen, Yen-Ling; Sahayam, A C

    2015-02-20

    A slurry sampling inductively coupled plasma mass spectrometry (ICP-MS) method has been developed for the determination of Ge, As, Cd, Sb, Hg and Bi in cosmetic lotions using flow injection (FI) vapor generation (VG) as the sample introduction system. A slurry containing 2% m/v lotion, 2% m/v thiourea, 0.05% m/v L-cysteine, 0.5 μg mL(-1) Co(II), 0.1% m/v Triton X-100 and 1.2% v/v HCl was injected into a VG-ICP-MS system for the determination of Ge, As, Cd, Sb, Hg and Bi without dissolution and mineralization. Because the sensitivities of the analytes in the slurry and that of aqueous solution were quite different, an isotope dilution method and a standard addition method were used for the determination. This method has been validated by the determination of Ge, As, Cd, Sb, Hg and Bi in GBW09305 Cosmetic (Cream) reference material. The method was also applied for the determination of Ge, As, Cd, Sb, Hg and Bi in three cosmetic lotion samples obtained locally. The analysis results of the reference material agreed with the certified value and/or ETV-ICP-MS results. The detection limit estimated from the standard addition curve was 0.025, 0.1, 0.2, 0.1, 0.15, and 0.03 ng g(-1) for Ge, As, Cd, Sb, Hg and Bi, respectively, in original cosmetic lotion sample. PMID:25682241

  8. Defect studies in MBE grown GaSb{sub 1−x}Bi{sub x} layers

    SciTech Connect

    Segercrantz, N.; Kujala, J.; Tuomisto, F.; Slotte, J.; Song, Y.; Wang, S.

    2014-02-21

    Positron annihilation spectroscopy in Doppler broadening mode is used to study epitaxial layers of GaSb{sub 1−x}Bi{sub x} on undoped GaSb. The samples were grown by Molecular Beam Epitaxy at different temperatures and with different Bi/Sb beam equivalent pressure ratios resulting in Bi concentrations of 0–0.7 %. The results show a relationship between the growth parameters and Doppler broadening parameters. Incorporating Bi into GaSb decreases the vacancy concentration in the epitaxial layers compared to the sample with no Bi in the epitaxial layer.

  9. Difference in expression patterns of placental cholesterol transporters, ABCA1 and SR-BI, in Meishan and Yorkshire pigs with different placental efficiency

    PubMed Central

    Hong, Linjun; Xu, Xiangdong; Huang, Ji; Lei, Minggang; Xu, Dequan; Zhao, Shuhong; Yu, Mei

    2016-01-01

    Cholesterol is a key cell membrane component and precursor of steroid hormones. The maternal cholesterol is an important exogenous cholesterol source for the developing embryos and its transportation is mediated by ABCA1 and SR-BI. Here we reported that during the peri-implantation period in pigs, ABCA1 was expressed by uterine luminal epithelium (LE) and interestingly, its expression was more abundantly in LE on mesometrial side of uterus. However, SR-BI was expressed primarily by LE, glandular epithelial cells (GE) and trophoblast cells (Tr). During the placentation period, the expression levels of ABCA1 and SR-BI proteins at epithelial bilayer and placental areolae were significantly higher in Chinese Meishan pigs compared to Yorkshire pigs. Consisitently, mRNA levels of HMGCR, the rate-limiting enzyme for cholesterol synthesis, were significantly higher in Meishan placentas than in Yorkshire placentas. Our findings revealed the routes of transplacental cholesterol transport mediated by ABCA1 and SR-BI in pigs and indicated that ABCA1 related pathway may participate in anchoring the conceptus to the mesometrial side of uterus. Additionally, an ABCA1 dependent compensatory mechanism related to the placental efficiency in response to the smaller placenta size in Meishan pigs was suggested. PMID:26852751

  10. Refinement of the Microstructure of Sn-Ag-Bi-In Solder, by Addition of SiC Nanoparticles, to Reduce Electromigration Damage Under High Electric Current

    NASA Astrophysics Data System (ADS)

    Kim, Youngseok; Nagao, Shijo; Sugahara, Tohru; Suganuma, Katsuaki; Ueshima, Minoru; Albrecht, Hans-Juergen; Wilke, Klaus; Strogies, Joerg

    2014-12-01

    The trends of miniaturization, multi-functionality, and high performance in advanced electronic devices require higher densities of I/O gates and reduced area of soldering of interconnections. This increases the electric current density flowing through the interconnections, increasing the risk of interconnection failure caused by electromigration (EM). Accelerated directional atomic diffusion in solder materials under high current induces substantial growth of intermetallic compounds (IMCs) at the anode, and also void and crack formation at the cathode. In the work discussed in this paper, addition of SiC nanoparticles to Sn-Ag-Bi-In (SABI) lead-free solder refined its microstructure and improved its EM reliability under high current stress. Electron backscattering diffraction analysis revealed that the added SiC nanoparticles refined solder grain size after typical reflow. Under current stress, SABI joints with added nano-SiC had lifetimes almost twice as long as those without. Comparison of results from high-temperature aging revealed direct current affected evolution of the microstructure. Observations of IMC growth indicated that diffusion of Cu in the SiC composite solder may not have been reduced. During current flow, however, only narrow voids were formed in solder containing SiC, thus preventing the current crowding caused by bulky voids in the solder without SiC.

  11. Mn-doped 0.15BiInO3-0.85PbTiO3 piezoelectric films deposited by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Lee, Sun Young; Ko, Song Won; Lee, Soonil; Trolier-McKinstry, Susan

    2012-05-01

    Undoped, 0.5 and 1.0 mol. % Mn-doped 0.15BiInO3-0.85PbTiO3 films were grown on PbTiO3/Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Phase-pure perovskite films were obtained at a substrate temperature of 585 °C irrespective of Mn doping level. The 0.5 mol. % Mn-doped films showed a room temperature permittivity of 480 and a dielectric loss tangent of 0.015 at 100 kHz after 650 °C post-deposition annealing. The coercive field and remanent polarization were 80 kV/cm and 29 µC/cm2, respectively. The ferroelectric transition temperature of the films ranged from 535 to 585 °C. The e31,f piezoelectric coefficient was -7.1 C/m2. X-ray diffraction and phase transition temperature data showed that the Mn atoms substitute on the Ti-site as Mn3+; the resulting films have p-type conduction characteristics.

  12. Difference in expression patterns of placental cholesterol transporters, ABCA1 and SR-BI, in Meishan and Yorkshire pigs with different placental efficiency.

    PubMed

    Hong, Linjun; Xu, Xiangdong; Huang, Ji; Lei, Minggang; Xu, Dequan; Zhao, Shuhong; Yu, Mei

    2016-01-01

    Cholesterol is a key cell membrane component and precursor of steroid hormones. The maternal cholesterol is an important exogenous cholesterol source for the developing embryos and its transportation is mediated by ABCA1 and SR-BI. Here we reported that during the peri-implantation period in pigs, ABCA1 was expressed by uterine luminal epithelium (LE) and interestingly, its expression was more abundantly in LE on mesometrial side of uterus. However, SR-BI was expressed primarily by LE, glandular epithelial cells (GE) and trophoblast cells (Tr). During the placentation period, the expression levels of ABCA1 and SR-BI proteins at epithelial bilayer and placental areolae were significantly higher in Chinese Meishan pigs compared to Yorkshire pigs. Consisitently, mRNA levels of HMGCR, the rate-limiting enzyme for cholesterol synthesis, were significantly higher in Meishan placentas than in Yorkshire placentas. Our findings revealed the routes of transplacental cholesterol transport mediated by ABCA1 and SR-BI in pigs and indicated that ABCA1 related pathway may participate in anchoring the conceptus to the mesometrial side of uterus. Additionally, an ABCA1 dependent compensatory mechanism related to the placental efficiency in response to the smaller placenta size in Meishan pigs was suggested. PMID:26852751

  13. Pb-Bi-Ag-Cu-(Hg) chemistry of galena and some associated sulfosalts. A review and some new data from Colorado California and Pennsylvania

    USGS Publications Warehouse

    Foord, Eugene E.; Shawe, Daniel R.

    1989-01-01

    Galena, associated with Pb-Bi-Ag sulfosalts and simple sulfides, contains varied amounts of Ag and Bi in the Dandy vein system, Idarado mine, Ouray, Colorado; the Jackass mine, Darwin District, California; and the Leadville district, Colorado. Silver- and bismuth-bearing galena associated with minor amounts of pyrite, chalcopyrite and sphalerite occur at the Pequea mine, Lancaster County, Pennsylvania. Ag and Bi contents in the Dandy suite of galena range from about 1.4 to 3.4 and 2.5 to 6.5 wt.% respectively, and are comparable or lower in galena from the other localities. Exsolved matildite is present in galena from the Dandy, Jackass and Leadville localities. The presence in significant amounts of both Ag and Bi in a Pb-rich sulfide system is necessary for formation of PbSss (galena solid-solution). If Ag (especially) and Bi (to a lesser extent) are absent, the galena formed will be essentially pure PbS. Some minor Sb may substitute for Bi. Compositional data for all of the galena samples are in agreement with a previously proposed linear relationship between a and Ag-Bi(Sb) content. Matildite and seven additional Pb-Bi-Ag-Cu sulfosalts have been identified from the Dandy vein system, based on electron-microprobe analyses and some X-ray powder-diffraction data.

  14. Electronic band structure calculations of bismuth-antimony nanowires

    NASA Astrophysics Data System (ADS)

    Levin, Andrei; Dresselhaus, Mildred

    2012-02-01

    Alloys of bismuth and antimony received initial interest due to their unmatched low-temperature thermoelectric performance, and have drawn more recent attention as the first 3D topological insulators. One-dimensional bismuth-antimony (BiSb) nanowires display interesting quantum confinement effects, and are expected to exhibit even better thermoelectric properties than bulk BiSb. Due to the small, anisotropic carrier effective masses, the electronic properties of BiSb nanowires show great sensitivity to nanowire diameter, crystalline orientation, and alloy composition. We develop a theoretical model for calculating the band structure of BiSb nanowires. For a given crystalline orientation, BiSb nanowires can be in the semimetallic, direct semiconducting, or indirect semiconducting phase, depending on nanowire diameter and alloy composition. These ``phase diagrams'' turn out to be remarkably similar among the different orientations, which is surprising in light of the anisotropy of the bulk BiSb Fermi surface. We predict a novel direct semiconducting phase for nanowires with diameter less than ˜15 nm, over a narrow composition range. We also find that, in contrast to the bulk and thin film BiSb cases, a gapless state with Dirac dispersion cannot be realized in BiSb nanowires.

  15. Refinement of Mg{sub 2}Si reinforcement in a commercial Al–20%Mg{sub 2}Si in-situ composite with bismuth, antimony and strontium

    SciTech Connect

    Nordin, Nur Azmah; Farahany, Saeed Ourdjini, Ali; Abu Bakar, Tuty Asma; Hamzah, Esah

    2013-12-15

    Refinement by addition elements of Al–Mg{sub 2}Si alloys is known to result in a change of primary Mg{sub 2}Si morphology. In this paper, the effects of Bi, Sb and Sr on the characteristic parameters of Al–20%Mg{sub 2}Si in-situ composite have been investigated by computer aided cooling curve thermal analysis and microstructural inspection. Size, density and aspect ratio measurements showed that additions of 0.4 wt.% Bi, 0.8 wt.% Sb and 0.01 wt.% Sr refined the Mg{sub 2}Si reinforcement. Exceeding these concentrations, however, resulted in coarsening of Mg{sub 2}Si particles with no change in the morphology. The results also showed that addition elements caused a decrease in the nucleation and growth temperatures of Mg{sub 2}Si particles. The refining effect of Bi, Sb and Sr is likely to be related to the effect of oxide bifilms suspended in the composite melt as favored nucleation substrates for Mg{sub 2}Si particles. - Highlight: • 0.4 wt.%, 0.8 wt.% and 0.01 wt.% is the optimum content for Bi, Sb and Sr addition. • Exceeding optimum concentration resulted in the coarsening of reinforcements. • Nucleation and growth temperatures decrease with addition of Bi, Sb and Sr. • The refining effect of Bi, Sb and Sr is likely to be related to the oxide bifilms.

  16. Resistance noise in epitaxial thin films of ferromagnetic topological insulators

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Semonti; Kandala, Abhinav; Richardella, Anthony; Islam, Saurav; Samarth, Nitin; Ghosh, Arindam

    2016-02-01

    We report detailed temperature and gate-voltage dependence of 1/f resistance noise in magnetically doped topological insulators (TI) Crx(Bi,Sb)2-xTe3. The noise is remarkably sensitive to the gate voltage, increasing rapidly as the chemical potential is moved towards the charge neutrality point. Unlike in identically prepared (Bi,Sb)2Te3 films, where mobility-fluctuations in the surface states is the dominant mechanism, the noise in the magnetic Crx(Bi,Sb)2-xTe3 originates from transport in the localized band tail of the bulk valence band. A strong increase in noise with decreasing temperature supports this scenario. At higher temperature (≥10 K), we observed large noise peaks at gate voltage-dependent characteristic temperature scales. In line with similar observations in other non-magnetic TI systems, we attribute these peaks to generation-recombination in the Cr-impurity band.

  17. Optimizing proximity induced anomalous Hall effect in (BixSb1-x)2 Te3/YIG heterostructures

    NASA Astrophysics Data System (ADS)

    Jiang, Zilong; Tang, Chi; Shi, Jing; Chang, Cuizu; Wei, Peng; Moodera, Jagadeesh S.

    2015-03-01

    The spontaneously broken time reversal symmetry leads to an energy gap in the Dirac spectrum of the surface states of a topological insulator (TI) which gives rise to the quantized anomalous Hall effect (QAHE). QAHE has been observed in TI doped with Cr. Here we explore an alternative route by coupling the surface states of TI with yttrium iron garnet (YIG) ferrimagnetic insulator (FI). Just as in Cr-doped TI, a major challenge is to reduce the bulk conduction which overwhelms the surface state contribution. We have successfully grown 5 quintuple layer thick ternary TI (BixSb1-x)2 Te3 on atomically flat YIG films, in which the Fermi level of TI can be controlled by the Bi:Sb ratio. We have observed the anomalous Hall effect (AHE) in TI/YIG heterostructure over a wide range of carrier density and in both electron and hole types induced by varying the Bi:Sb ratio from 0:1 to 1:0. Both Rxx and RAH undergo systematic and dramatic changes as the Bi:Sb ratio is varied. The maximum RAH occurs near the p-n cross-over region at Bi:Sb ratio ~0.2:0.8, which is nearly two orders of magnitude greater than the minimum value at Bi:Sb ratio ~1:0. As the Bi:Sb ratio is varied, we find that RAH scales quadratically with Rxx, indicating the scattering rate independent AHE. The electric field effect study further demonstrates the existence of robust AHE while the Fermi level of TI is tuned. This research was supported by UC Lab fees program and a DOE/BES award at UCR, and by NSF/DMR at MIT.

  18. Corrosion behavior of Al-surface-treated steels in liquid Pb?Bi in a pot

    NASA Astrophysics Data System (ADS)

    Kurata, Y.; Futakawa, M.; Saito, S.

    2004-12-01

    Corrosion tests were performed in oxygen-saturated liquid Pb-Bi at 450 °C and 550 °C in a pot for 3000 h for Al-surface-treated steels containing various levels of Cr contents. The Al surface treatments were achieved using a gas diffusion method and a melt dipping method. Al2O3, FeAl2 and AlCr2 produced by the gas diffusion method exhibited corrosion resistance to liquid Pb-Bi, while the surface layer produced by the melt dipping method suffered a severe corrosion attack. Fe4Al13 and Fe2Al5 produced by the melt dipping method disappeared during the corrosion test at 550 °C and only FeAl remained.

  19. Bi atoms mobility-driven circular domains at the Bi/InAs(111) interface

    NASA Astrophysics Data System (ADS)

    Richter, M. C.; Mariot, J.-M.; Gafoor, M. A.; Nicolaï, L.; Heckmann, O.; Djukic, U.; Ndiaye, W.; Vobornik, I.; Fujii, J.; Barrett, N.; Feyer, V.; Schneider, C. M.; Hricovini, K.

    2016-09-01

    Bi films deposited on InAs(111) A and B sides have been studied by photoemission electron microscopy. A series of snapshots acquired during sequential annealing of the interfaces at temperatures below and above the melting temperature of Bi allowed obtaining a comprehensive image of the topographic and chemical evolutions of the Bi films that are found to be InAs side dependent. On the A side, a morphology of circular patterns controlled by Bi atoms mobility is observed. The patterns are formed on the pristine In-terminated InAs(111) surface covered by a weakly bonded Bi bilayer. On the B side, no particular morphology is observed due to a stronger chemical interaction between Bi and As atoms as evidenced by the spatially-resolved core-level photoelectron spectra.

  20. STM studies of topological phase transition in (Bi,In)2Se3

    NASA Astrophysics Data System (ADS)

    Zhang, Wenhan; Wang, Xueyun; Cheong, Sang-Wook; Wu, Weida; Weida Wu Team; Sang-Wook Cheong Collaboration

    Topological insulators (TI) are a class of materials with insulating bulk and metallic surface state, which is the result of band inversion induced by strong spin-orbit coupling (SOC). The transition from topological phase to non-topological phase is of great significance. In theory, topological phase transition is realized by tuning SOC strength. It is characterized by the process of gap closing and reopening. Experimentally it was observed in two systems: TlBi(S1-xSex)2 and (Bi1-xInx)2 Se3 where the transition is realized by varying isovalent elements doping concentration. However, none of the previous studies addressed the impact of disorder, which is inevitable in doped systems. Here, we present a systematic scanning tunneling microscopy/spectroscopy study on (Bi1-xInx)2 Se3 single crystals with different In concentrations across the transition. Our results reveal an electronic inhomogeneity due to the random distribution of In defects which locally suppress the topological surface states. Our study provides a new angle of understanding the topological transition in the presence of strong disorders. This work is supported by NSF DMR-1506618.

  1. Synthesis and Electronic Properties of Thermoelectric and Magnetic Nanoparticle Composite Materials

    NASA Astrophysics Data System (ADS)

    Koyano, Mikio; Kito, Daichi; Sakai, Kengo; Ariga, Tomoki

    2011-05-01

    Application of a magnetic field greatly enhances the thermoelectric efficiency of bismuth-antimony (Bi-Sb) alloys. We synthesized a hybrid of Bi-Sb alloy and magnetic nanoparticles, expecting improvement of the thermoelectric performance due to the magnetic field generated by the nanoparticles. Powder x-ray diffraction and magnetic measurements of the synthesized hybrid Bi0.88Sb0.12(FeSb)0.05 sample indicated that the ferromagnetic FeSb nanoparticles, with a size of about 30 nm, were distributed in the main phase of the Bi-Sb alloy. The FeSb nanoparticles act as soft ferromagnets in the diamagnetic host Bi-Sb alloy. The electrical resistivity ρ of the host Bi0.88Sb0.12 sample decreased concomitantly with decreasing temperature, showing a shoulder at 80 K. In contrast, ρ for the hybrid sample was enhanced below 100 K because of carrier scattering by the nanoparticles. The temperature dependence of the Seebeck coefficient S was also altered by the nanoparticle addition. In contrast, the addition of magnetic nanoparticles only slightly influenced the thermal conductivity κ. These results indicate that the addition of magnetic nanoparticles to thermoelectric materials modulates the electronic structures but does not influence the lattice system.

  2. Knockdown expression and hepatic deficiency reveal anatheroprotective role for SR-BI in liver and peripheral tissues

    SciTech Connect

    Huby, Thierry; Doucet, Chantal; Dachet, Christiane; Ouzilleau,Betty; Ueda, Yukihiko; Afzal, Veena; Rubin, Edward; Chapman, M. John; Lesnik, Philippe

    2006-07-18

    Scavenger receptor SR-BI has been implicated inHDL-dependent atheroprotective mechanisms. We report the generation of anSR-BI conditional knockout mouse model in which SR-BI gene targeting byloxP site insertion produced a hypomorphic allele (hypomSR-BI).Attenuated SR-BI expression in hypomSR-BI mice resulted in 2-foldelevation in plasma total cholesterol (TC) levels. Cre-mediated SR-BIgene inactivation of the hypomorphic SR-BI allele in hepatocytes(hypomSR-BI-KOliver) was associated with high plasma TC concentrations,increased plasma free cholesterol/TC (FC/TC) ratio, and alipoprotein-cholesterol profile typical of SR-BI-/- mice. Plasma TClevels were increased 2-fold in hypomSR-BI and control mice fed anatherogenic diet, whereas hypomSR-BI-KOliver and SR-BI-/- mice developedsevere hypercholesterolemia due to accumulation of FC-rich, VLDL-sizedparticles. Atherosclerosis in hypomSR-BI mice was enhanced (2.5-fold)compared with that in controls, but to a much lower degree than inhypomSR-BI-KOliver (32-fold) and SR-BI-/- (48-fold) mice. The lattermodels did not differ in either plasma lipid levels or in the capacity ofVLDL-sized lipoproteins to induce macrophage cholesterol loading.However, reduced atherosclerosis in hypomSR-BI-KOliver mice wasassociated with decreased lesional macrophage content as compared withthat in SR-BI-/- mice. These data imply that, in addition to its majoratheroprotective role in liver, SR-BI may exert an antiatherogenic rolein extrahepatic tissues.

  3. Knockdown expression and hepatic deficiency reveal an atheroprotective role for SR-BI in liver and peripheral tissues

    PubMed Central

    Huby, Thierry; Doucet, Chantal; Dachet, Christiane; Ouzilleau, Betty; Ueda, Yukihiko; Afzal, Veena; Rubin, Edward; Chapman, M. John; Lesnik, Philippe

    2006-01-01

    Scavenger receptor SR-BI has been implicated in HDL-dependent atheroprotective mechanisms. We report the generation of an SR-BI conditional knockout mouse model in which SR-BI gene targeting by loxP site insertion produced a hypomorphic allele (hypomSR-BI). Attenuated SR-BI expression in hypomSR-BI mice resulted in 2-fold elevation in plasma total cholesterol (TC) levels. Cre-mediated SR-BI gene inactivation of the hypomorphic SR-BI allele in hepatocytes (hypomSR-BI–KOliver) was associated with high plasma TC concentrations, increased plasma free cholesterol/TC (FC/TC) ratio, and a lipoprotein-cholesterol profile typical of SR-BI–/– mice. Plasma TC levels were increased 2-fold in hypomSR-BI and control mice fed an atherogenic diet, whereas hypomSR-BI–KOliver and SR-BI–/– mice developed severe hypercholesterolemia due to accumulation of FC-rich, VLDL-sized particles. Atherosclerosis in hypomSR-BI mice was enhanced (2.5-fold) compared with that in controls, but to a much lower degree than in hypomSR-BI–KOliver (32-fold) and SR-BI–/– (48-fold) mice. The latter models did not differ in either plasma lipid levels or in the capacity of VLDL-sized lipoproteins to induce macrophage cholesterol loading. However, reduced atherosclerosis in hypomSR-BI–KOliver mice was associated with decreased lesional macrophage content as compared with that in SR-BI–/– mice. These data imply that, in addition to its major atheroprotective role in liver, SR-BI may exert an antiatherogenic role in extrahepatic tissues. PMID:16964311

  4. Key Role for Scavenger Receptor B-I in the Integrative Physiology of Host Defense during Bacterial Pneumonia

    PubMed Central

    Gowdy, Kymberly M.; Madenspacher, Jennifer H.; Azzam, Kathleen M.; Gabor, Kristin A.; Janardhan, Kyathanahalli S.; Aloor, Jim J.; Fessler, Michael B.

    2014-01-01

    Scavenger receptor B-I (SR-BI) is a multirecognition receptor that regulates cholesterol trafficking and cardiovascular inflammation. Although it is expressed by neutrophils (PMNs) and lung-resident cells, no role for SR-BI has been defined in pulmonary immunity. Herein, we report that, compared to SR-BI+/+ counterparts, SR-BI−/− mice suffer markedly increased mortality during bacterial pneumonia associated with higher bacterial burden in lung and blood, deficient induction of the stress glucocorticoid corticosterone, higher serum cytokines, and increased organ injury. SR-BI−/− mice had significantly increased PMN recruitment and cytokine production in the infected airspace. This was associated with defective hematopoietic cell-dependent clearance of lipopolysaccharide from the airspace and increased cytokine production by SR-BI−/− macrophages. Corticosterone replacement normalized alveolar neutrophilia but not alveolar cytokines, bacterial burden, or mortality, suggesting that adrenal insufficiency derepresses PMN trafficking to the SR-BI−/− airway in a cytokine-independent manner. Despite enhanced alveolar neutrophilia, SR-BI−/− mice displayed impaired phagocytic killing. Bone marrow chimeras revealed this defect to be independent of the dyslipidemia and adrenal insufficiency of SR-BI−/− mice. During infection, SR-BI−/− PMNs displayed deficient oxidant production and CD11b externalization, and increased surface L-selectin, suggesting defective activation. Taken together, SR-BI coordinates several steps in the integrated neutrophilic host defense response to pneumonia. PMID:25336169

  5. Evaluation of the activity and molecular form of bi in cu smelting slags: Part I. ternary silicate slags

    NASA Astrophysics Data System (ADS)

    Marschman, S. C.; Lynch, D. C.

    1988-08-01

    The thermodynamic behavior of bismuth in the chemical systems associated with copper processing is not well understood. This study was designed to further the understanding of the physical chemistry of bismuth in slags that have similar compositions to those found in copper extractive metallurgical processing. The silicate system investigated was the FeO-Fe2O3-SiO2 ternary system in which bismuth was dissolved using an isopiestic experimental technique. Bismuth vapor pressures of 1 • 10-5 atm and 7.5 • 10-4 atm were used, and the silicates were equilibrated with this vapor at temperatures of 1458 K and 1523 K. In these experiments, the slag composition was varied such that P O 2 ranged from 10-12 to 10-8 atm. Bismuth was found to enter the silicate slag in both neutral and oxidic molecular forms. The oxidic form identified was that of BiO. The data suggest that the activity coefficient of neutral bismuth, γBi, is dependent on the solubility of that species in slag, even at the low concentrations observed in this study. It has been hypothesized, based on the large diameter of neutral Bi, that only a limited number of sites are available to accommodate neutral Bi, and that as the limit is approached γBi increases significantly. That hypothesis is shown to be consistent with the experimental results obtained in the present work as well as the results obtained by other investigators.

  6. Distribution of Be, Al, Se and Bi in the surface waters of the western North Atlantic and Caribbean

    NASA Astrophysics Data System (ADS)

    Measures, C. I.; Grant, B.; Khadem, M.; Lee, D. S.; Edmond, J. M.

    1984-11-01

    The mixed layer distributions of several trace elements have been determined along a detailed transect from Rhode Island to the Panama Canal. When taken together with a new and existing profile data from the North Atlantic and North Pacific, some general inferences emerge as to the processes controlling their concentrations in the surface waters. The large enrichments in Be observed in the upper waters of the North Atlantic relative to the North Pacific appear to be sustained mainly by fluvial inputs. Those of Se are derived from atmospheric transport. Aluminium and Bi also appear to have an aeolian source in the Sargasso Sea. However, in the tropical eastern Pacific, the Al input may be fluvial On this cruise, Be, Al and the Se species were analyzed on board ship within a few hours of collection. The demonstration that this is feasible opens up the prospect of the application of large-scale chemical hydrography to the study of the processes controlling the distribution and water column variability of trace elements in the oceans.

  7. Thickness Dependence of the Quantum Anomalous Hall Effect in Magnetic Topological Insulator Films.

    PubMed

    Feng, Xiao; Feng, Yang; Wang, Jing; Ou, Yunbo; Hao, Zhenqi; Liu, Chang; Zhang, Zuocheng; Zhang, Liguo; Lin, Chaojing; Liao, Jian; Li, Yongqing; Wang, Li-Li; Ji, Shuai-Hua; Chen, Xi; Ma, Xucun; Zhang, Shou-Cheng; Wang, Yayu; He, Ke; Xue, Qi-Kun

    2016-08-01

    The evolution of the quantum anomalous Hall effect with the thickness of Cr-doped (Bi,Sb)2 Te3 magnetic topological insulator films is studied, revealing how the effect is caused by the interplay of the surface states, band-bending, and ferromagnetic exchange energy. Homogeneity in ferromagnetism is found to be the key to high-temperature quantum anomalous Hall material. PMID:27166762

  8. Structure and transport of topological insulators on epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Kally, James; Reifsnyder Hickey, Danielle; Lin, Yu-Chuan; Richardella, Anthony; Lee, Joon Sue; Robinson, Joshua; Mkhoyan, K. Andre; Samarth, Nitin

    Recent advancements in spintronics have shown that a class of materials, topological insulators (TI), can be used as a spin-current generator or detector. Topological insulators have protected surface states with the electron's spin locked to its momentum. To access these surface states, (Bi, Sb)2Te3 can be grown by molecular beam epitaxy to have the Fermi energy near the Dirac point so that transport occurs only through the spin-dependent surface states. Graphene is another 2D material of great interest for spintronics because of its very long spin diffusion length. This is an ideal material to act as a spin channel in devices. The van der Waals nature of the growth exhibited by 2D materials such as (Bi, Sb)2Te3 and graphene allows heterostructures to be formed despite the large lattice mismatch. We explore the structure and transport of (Bi, Sb)2Te3 grown on epitaxial graphene on 6H-SiC substrates for spintronic applications. This work was supported in part by C-SPIN and LEAST, two of the six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  9. Magnetic modulation doping in topological insulators toward higher-temperature quantum anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Mogi, M.; Yoshimi, R.; Tsukazaki, A.; Yasuda, K.; Kozuka, Y.; Takahashi, K. S.; Kawasaki, M.; Tokura, Y.

    2015-11-01

    Quantum anomalous Hall effect (QAHE), which generates dissipation-less edge current without external magnetic field, is observed in magnetic-ion doped topological insulators (TIs) such as Cr- and V-doped (Bi,Sb)2Te3. The QAHE emerges when the Fermi level is inside the magnetically induced gap around the original Dirac point of the TI surface state. Although the size of gap is reported to be about 50 meV, the observable temperature of QAHE has been limited below 300 mK. We attempt magnetic-Cr modulation doping into topological insulator (Bi,Sb)2Te3 films to increase the observable temperature of QAHE. By introducing the rich-Cr-doped thin (1 nm) layers at the vicinity of both the surfaces based on non-Cr-doped (Bi,Sb)2Te3 films, we have succeeded in observing the QAHE up to 2 K. The improvement in the observable temperature achieved by this modulation-doping appears to be originating from the suppression of the disorder in the surface state interacting with the rich magnetic moments. Such a superlattice designing of the stabilized QAHE may pave a way to dissipation-less electronics based on the higher-temperature and zero magnetic-field quantum conduction.

  10. Magnetic modulation doping in topological insulators toward higher-temperature quantum anomalous Hall effect

    SciTech Connect

    Mogi, M. Yoshimi, R.; Yasuda, K.; Kozuka, Y.; Tsukazaki, A.; Takahashi, K. S.; Kawasaki, M.; Tokura, Y.

    2015-11-02

    Quantum anomalous Hall effect (QAHE), which generates dissipation-less edge current without external magnetic field, is observed in magnetic-ion doped topological insulators (TIs) such as Cr- and V-doped (Bi,Sb){sub 2}Te{sub 3}. The QAHE emerges when the Fermi level is inside the magnetically induced gap around the original Dirac point of the TI surface state. Although the size of gap is reported to be about 50 meV, the observable temperature of QAHE has been limited below 300 mK. We attempt magnetic-Cr modulation doping into topological insulator (Bi,Sb){sub 2}Te{sub 3} films to increase the observable temperature of QAHE. By introducing the rich-Cr-doped thin (1 nm) layers at the vicinity of both the surfaces based on non-Cr-doped (Bi,Sb){sub 2}Te{sub 3} films, we have succeeded in observing the QAHE up to 2 K. The improvement in the observable temperature achieved by this modulation-doping appears to be originating from the suppression of the disorder in the surface state interacting with the rich magnetic moments. Such a superlattice designing of the stabilized QAHE may pave a way to dissipation-less electronics based on the higher-temperature and zero magnetic-field quantum conduction.

  11. L{sub 3}-subshell alignment of Au and Bi in collisions with 12-55-MeV carbon ions

    SciTech Connect

    Kumar, Ajay; Choudhury, R. K.; Agnihotri, A. N.; Chatterjee, S.; Misra, D.; Tribedi, L. C.; Kasthurirangan, S.; Sarkadi, L.

    2010-06-15

    Angular distribution of the L x-ray intensities in Au and Bi induced by 12-55-MeV carbon ions has been measured. The L{sub {alpha}}, L{sub {beta}}, and L{sub {gamma}} x-ray intensities were found to be isotropic within experimental uncertainty. The alignment parameter A{sub 20} of the L{sub 3} (2p{sub 3/2}) subshell was deduced from the measured anisotropy parameter {beta} value of the well-resolved L{sub l} line, obtained from the angular distribution of the I{sub Ll}/I{sub L{alpha}}, I{sub Ll}/I{sub L{beta}}, and I{sub Ll}/I{sub L{gamma}} x-ray intensity ratios. The measured A{sub 20} values have been compared with those obtained using theoretical models that involve the plane-wave Born approximation; projectile's energy loss and its Coulomb deflection from the straight-line trajectory, perturbed-stationary-state, and relativistic effects (ECPSSR); and ECPSSR with the intrashell effect.

  12. Influence of Ce substitution for Bi in BiVO4 and the impact on the phase evolution and microwave dielectric properties.

    PubMed

    Zhou, Di; Pang, Li-Xia; Guo, Jing; Qi, Ze-Ming; Shao, Tao; Wang, Qiu-Ping; Xie, Hui-Dong; Yao, Xi; Randall, Clive A

    2014-01-21

    In the present work, the (Bi1-xCex)VO4 (x ≤ 0.6) ceramics were prepared via a solid-state reaction method and all the ceramic samples could be densified below 900 °C. From the X-ray diffraction analysis, it is found that a monoclinic scheelite solid solution can be formed in the range x ≤ 0.10. In the range 0.20 ≤ x ≤ 0.60, a composite region with both monoclinic scheelite and tetragonal zircon solid solutions was formed and the content of the zircon phase increased with the calcined or sintering temperature. The refined lattice parameters of (Bi0.9Ce0.1)VO4 are a = 5.1801(0) Å, b = 5.0992(1) Å, c = 11.6997(8) Å, and γ = 90.346(0)° with the space group I112/b(15). The VO4 tetrahedron contracts with the substitution of Ce for Bi at the A site, and this helps to keep the specific tetrahedron chain stable in the monoclinic structure. The microwave dielectric permittivity was found to decrease linearly from 68 to about 26.6; meanwhile, the quality factor (Qf) value increased from 8000 GHz to around 23900 GHz as the x value increased from 0 to 0.60. The best microwave dielectric properties were obtained in a (Bi0.75Ce0.25)VO4 ceramic with a permittivity of ∼47.9, a Qf value of ∼18000 GHz, and a near-zero temperature coefficient of ∼+15 ppm/°C at a resonant frequency of around 7.6 GHz at room temperature. Infrared spectral analysis supported that the dielectric contribution for this system at microwave region could be attributed to the absorptions of structural phonon oscillations. This work presents a novel method to modify the temperature coefficient of BiVO4-type materials. This system of microwave dielectric ceramic might be an interesting candidate for microwave dielectric resonator and low-temperature cofired ceramic technology applications. PMID:24392840

  13. Lead, Ba and Bi in Antarctic Law Dome ice corresponding to the 1815 AD Tambora eruption: an assessment of emission sources using Pb isotopes

    NASA Astrophysics Data System (ADS)

    Vallelonga, P.; Candelone, J.-P.; Van de Velde, K.; Curran, M. A. J.; Morgan, V. I.; Rosman, K. J. R.

    2003-06-01

    Lead, Ba and Bi concentrations and Pb isotopic compositions have been measured in Antarctic Law Dome (66.8°S, 112.4°E) ice dated from 1814 AD to 1819 AD by thermal ionisation mass spectrometry to investigate the possible deposition of heavy metals from the 1815 AD eruption of Tambora volcano (8.5°S, 117.4°E) in Indonesia. Although volcanic S emissions from Tambora (observed as SO 42-) are present in the Antarctic ice core record, there are grounds to question the origin of the Pb and Bi also deposited at Law Dome from late 1817, as the Pb isotope data suggest this Pb originated from Mount Erebus (77.5°S, 167.2°E) on Ross Island, Antarctica. It is shown that at least 97% of any Pb and Bi emitted from Tambora was removed from the atmosphere within the 1.6 year period required to transport aerosols from Indonesia to Antarctica. Consequently, increased Pb and Bi concentrations observed in Law Dome ice about 1818 AD are attributed to either increased heavy metal emissions from Mount Erebus, or increased fluxes of heavy metals to the Antarctic ice sheet resulting from climate and meteorological modifications following the Tambora eruption. Elevated Ba concentrations, observed from mid-1816 to mid-1818, indicate increased atmospheric loading of rock and soil dust also occurred at the time.

  14. Composites of Bi{sub 2-x}Sb{sub x}Te{sub 3} nanocrystals and fullerene molecules for thermoelectricity

    SciTech Connect

    Kulbachinskii, V.A.; Kytin, V.G.; Popov, M.Yu.; Buga, S.G.; Stepanov, P.B.; Blank, V.D.

    2012-09-15

    New nanocomposite thermoelectric material composed from nanocrystallites of Bi-Sb-Te alloys covered by C{sub 60} molecules has been synthesized and studied. An increase of fullerene content leads to the growth of hole concentration in p-type materials and reduction of electron concentration in n-type materials. The fullerene molecules provide additional scattering of phonons reducing lattice heat conductivity. Reduction of heat conductivity exceeds the reduction of electrical conductivity for fullerene content less than 0.5 volume % and essential enhances the thermoelectric figure of merit. The maximum value of thermoelectric figure of merit equals to 1.17 at 450 K was observed in Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} composite containing 0.5 volume % C{sub 60} molecules. The experimental results were analyzed in a frame of the model based on the Boltzmann equation. The analysis considers light and heavy electrons and holes and accounts the intervalley scattering of charge carriers. The calculations of the kinetic coefficients shows that the improvement of the thermoelectric figure of merit originates from the reduction of the lattice heat conductivity caused by fullerene molecules. The dependencies of the thermoelectric figure of merit on the acceptor concentration were calculated. - Graphical abstract: New nanocomposite thermoelectric material composed from nanocrystallites of Bi-Sb-Te alloys covered by C{sub 60} molecules has been synthesized and studied. An increase of fullerene content leads to the growth of hole concentration in p-type materials and reduction of electron concentration in n-type materials. The fullerene molecules provide additional scattering of phonons reducing lattice heat conductivity and enhances the thermoelectric figure of merit. The maximum value of thermoelectric figure of merit equal to 1.17 at 450 K was observed in Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} composite containing 0.5 volume % fullerene molecules. Simulations of thermoelectric

  15. Material compatibility and thermal aging of thermoelectric materials.

    SciTech Connect

    Gardea, Andrew D.; Nishimoto, Ryan; Yang, Nancy Y. C.; Morales, Alfredo Martin; Whalen, Scott A.; Chames, Jeffrey M.; Clift, W. Miles

    2009-09-01

    In order to design a thermoelectric (TE) module suitable for long-term elevated temperature use, the Department 8651 has conducted parametric experiments to study material compatibility and thermal aging of TE materials. In addition, a comprehensive material characterization has been preformed to examine thermal stability of P- and N-based alloys and their interaction with interconnect diffusion barrier(s) and solder. At present, we have completed the 7-days aging experiments for 36 tiles, from ambient to 250 C. The thermal behavior of P- and N-based alloys and their thermal interaction with both Ni and Co diffusion barriers and Au-Sn solder were examined. The preliminary results show the microstructure, texture, alloy composition, and hardness of P-(Bi,Sb){sub 2}Te{sub 3} and N-Bi{sub 2}(Te,Se){sub 3} alloys are thermally stable up to 7 days annealing at 250 C. However, metallurgical reactions between the Ni-phosphor barriers and P-type base alloy were evident at temperatures {ge} 175 C. At 250 C, the depth (or distance) of the metallurgical reaction and/or Ni diffusion into P-(Bi,Sb){sub 2}Te{sub 3} is approximately 10-15 {micro}m. This thermal instability makes the Ni-phosphor barrier unsuitable for use at temperatures {ge} 175 C. The Co barrier appeared to be thermally stable and compatible with P(Bi,Sb){sub 2}Te{sub 3} at all annealing temperatures, with the exception of a minor Co diffusion into Au-Sn solder at {ge} 175 C. The effects of Co diffusion on long-term system reliability and/or the thermal stability of the Co barrier are yet to be determined. Te evaporation and its subsequent reaction with Au-Sn solder and Ni and Co barriers on the ends of the tiles at temperatures {ge} 175 C were evident. The Te loss and its effect on the long-term required stoichiometry of P-(Bi, Sb){sub 2}Te{sub 3} are yet to be understood. The aging experiments of 90 days and 180 days are ongoing and scheduled to be completed in 30 days and 150 days, respectively. Material

  16. Selenium, tellurium and precious metal mineralogy in Uchalinsk copper-zinc-pyritic district, the Urals

    NASA Astrophysics Data System (ADS)

    Vikentev, I.

    2016-04-01

    During processing the most of Au, Ag, Se, Te, Pb, Bi, Sb, Hg as well as notable part of Cu, Zn and Cd fail for tailings and became heavy metal pollutants. Modes of occurrence of Au, Ag, Te and Se covers two giant VMS deposits: Uchaly (intensively deformed) and Uzelginsk (altered by late hydrothermal processes) as well as middle-sized Molodezn and West Ozern deposits (nondeformed) have been studied. Mineral forms of these elements as well as their presence in disperse mode in common ore minerals (pyrite, chalcopyrite, sphalerite) have been studied using SEM, EPMA, INAA, ICP-MS and LA-ICP-MS.

  17. Radioisotope space power generator. Annual report, October 1978-September 1979

    SciTech Connect

    Elsner, N.B.; Chin, J.; Staley, H.G.; Bass, J.C.; Morris, C.C.; Shearer, C.H.; Steeger, E.J.

    1982-03-01

    The emphasis of the Isotec Technology Program shifted from development of a Galileo generator to study of a segmented selenide element and couple technology. The goal of the FY 79 program was to determine the feasibility of fabricating segmented selenide P and N elements which exploit the high thermoelectric efficiency of (Cu,Ag)/sub 2/Se and Gd/sub 2/Se/sub 3/ materials. A preliminary evaluation of segmented element efficiencies, material compatibilities, and fabrication abilities was used to select (Cu,Ag)/sub 2/Se/Fe(Bi,Sb)/sub 2/Te/sub 3/ for the P element and Gd/sub 2/Se/sub 3//PbTe for the N element. The iron barrier between the (Cu,Ag)/sub 2/Se and (Bi,Sb)/sub 2/Te/sub 3/ prevented degradation of thermoelectric properties from copper contamination of the (Bi,Sb)/sub 2/Te/sub 3/. Fabrication processes for both elements were developed. Gd/sub 2/Se/sub 3/ was friable and difficult to fabricate crack-free. It also exhibited a phase transition from cubic to orthorhombic, which increased its susceptibility to microcracking and reduced its thermoelectric efficiency. Life testing of an all-bonded couple with unsegmented (Cu,Ag)/sub 2/Se P-type and Gd/sub 2/Se/sub 3/ N-type elements was stopped after 3300 h in a nominal 830/sup 0/C/390/sup 0/C thermal gradient. The Gd/sub 2/Se/sub 3/ leg did not show any significant degradation during the test. Examination of the hot end of the P element showed the need for a less reactive hot cap material and an improved vapor supression system. Module testing of a 1-W (Bi,Sb)/sub 2/(Se,Te)/sub 3/ generator was performed for 5000 h with no degradation in power. High-temperature Thermid 600 adhesive curing cycles were examined, 75-mW module loading tests were performed, and diagnostic examination of RTG-2A and RTG-201 was completed.

  18. New type of multijunction thermopile IR detector

    NASA Astrophysics Data System (ADS)

    Sun, Tietun; Guo, Lihui

    1996-09-01

    A newly designed thin-film thermopile infrared detector, which as an absorption layer and a sensitive area on two sides are fabricated using integrated-circuit technology. The device uses a series-connected thermocouples array whose `hot' junction are supported on a thin Myler film of 1 - 3 micrometers thickness. By a special method of fasting the shadow mask, the thermopile with 48 Bi-Sb couples for 2 X 2 mm(superscript 2) area produces a responsivity of 50 - 70 V/W and relaxation time of about 70 ms.

  19. Brittle thermoelectric semiconductors extrusion under high hydrostatic pressure

    SciTech Connect

    Sidorenko, N.A.

    1994-08-10

    Origins of strength increase of brittle materials like thermoelectric (TE) semiconductors during plastic deformation under high external pressure are analyzed. TE material stressed state in the process of extrusion is reviewed. Plastic deformation of monocrystalline TE material billet produced by extrusion under sufficiently high external hydrostatic pressure is more uniform than under ordinary ambient pressure and can lead to crack free extruded TE material structure, crystallographic symmetry of which coincides with original billet one. Experimental device realized the scheme of extrusion under high hydrostatic pressure is described. Here extrusion are carrying out in compressed liquid medium. The developed device ensures the value of hydrostatic pressure up to 2 GPa and extrusion temperature interval 300--600 K. Properties of extruded Bi-Sb and Bi-Sb-Te single crystals are also reviewed. Possible application of presented method of extrusion under high hydrostatic pressure to form TE branches with highly accurate cross section for miniature TE coolers or generators is discussed. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  20. Micromachined Thermoelectric Sensors and Arrays and Process for Producing

    NASA Technical Reports Server (NTRS)

    Foote, Marc C. (Inventor); Jones, Eric W. (Inventor); Caillat, Thierry (Inventor)

    2000-01-01

    Linear arrays with up to 63 micromachined thermopile infrared detectors on silicon substrates have been constructed and tested. Each detector consists of a suspended silicon nitride membrane with 11 thermocouples of sputtered Bi-Te and Bi-Sb-Te thermoelectric elements films. At room temperature and under vacuum these detectors exhibit response times of 99 ms, zero frequency D* values of 1.4 x 10(exp 9) cmHz(exp 1/2)/W and responsivity values of 1100 V/W when viewing a 1000 K blackbody source. The only measured source of noise above 20 mHz is Johnson noise from the detector resistance. These results represent the best performance reported to date for an array of thermopile detectors. The arrays are well suited for uncooled dispersive point spectrometers. In another embodiment, also with Bi-Te and Bi-Sb-Te thermoelectric materials on micromachined silicon nitride membranes, detector arrays have been produced with D* values as high as 2.2 x 10(exp 9) cm Hz(exp 1/2)/W for 83 ms response times.

  1. COEXISTING GALENA, PbS//S//S AND SULFOSALTS: EVIDENCE FOR MULTIPLE EPISODES OF MINERALIZATION IN THE ROUND MOUNTAIN AND MANHATTAN GOLD DISTRICTS, NEVADA.

    USGS Publications Warehouse

    Foord, Eugene E.; Shawe, Daniel R.; Conklin, Nancy M.

    1988-01-01

    Studies of galena and Pb-Bi-Ag-Cu(Hg) sulfosalts of varied compositions in the Round Mountain and Manhattan gold districts of Nevada corroborate the occurrence of several distinct mineralized systems characterized by different mineral compositions and assemblages. The different episodes of mineralization are related to different Cretaceous and Tertiary magmatic-hydrothermal events, although the assignment of specific mineral compositions and associations with dated mineralized systems is still incomplete. At the Fairview mine, galena associated with Pb-Bi-Ag sulfosalts and simple sulfides occurs as intergrowths of discretely different composition controlled by silver and bismuth content. A galena-type phase (Pbs//s//s) with solid solution toward matildite, AgBiS//2(composition Gal//6//0Mat//4//0) was found. If silver and, to a lasser extent, bismuth are absent, the galena formed will be almost pure PbS. Some minor antimony may substitute for bismuth. This study confirms a linear relationship between a cell edge and Ag-Bi(Sb) content for galena containing less than about 15 wt. percent Ag and Bi(Sb).

  2. Mechanisms of Si and Ge diffusion on surfactant terminated (111) silicon and germanium surfaces

    NASA Astrophysics Data System (ADS)

    Zhachuk, R.; Coutinho, J.

    2016-05-01

    Surfactant mediated growth of Ge layers and formation of small Ge clusters on Si(111) are promising assemblage processes with envisioned applications in areas such as nanoelectronics or photovoltaics. They critically depend on migration of Si and Ge adatoms on surfactant terminated Si(111) and Ge(111) surfaces. We address Si and Ge adsorption and migration on surfactant (Bi, Sb) terminated (111) surfaces of Si and strained Ge by comprehensively mapping potential energy surfaces using density functional calculations. The main migration paths are identified and corresponding energy barriers are reported. It is shown that the energy barrier for adatom migration through Bi or Sb surfactant trimers (by actually breaking the trimers) is virtually degenerate to the mechanism involving traveling of the adatom around the same surfactant structures. We also find a low-energy anchoring site that is suggested to act as a nucleation structure and to trigger the clustering process. These results suggest a fundamentally new picture for the whole Si(111)sbnd Bi(Sb) epitaxial process.

  3. Surface-State-Dominated Spin-Charge Current Conversion in Topological-Insulator-Ferromagnetic-Insulator Heterostructures

    NASA Astrophysics Data System (ADS)

    Wang, Hailong; Kally, James; Lee, Joon Sue; Liu, Tao; Chang, Houchen; Hickey, Danielle Reifsnyder; Mkhoyan, K. Andre; Wu, Mingzhong; Richardella, Anthony; Samarth, Nitin

    2016-08-01

    We report the observation of ferromagnetic resonance-driven spin pumping signals at room temperature in three-dimensional topological insulator thin films—Bi2Se3 and (Bi,Sb ) 2Te3 —deposited by molecular beam epitaxy on Y3 Fe5 O12 thin films. By systematically varying the Bi2 Se3 film thickness, we show that the spin-charge conversion efficiency, characterized by the inverse Rashba-Edelstein effect length (λIREE ), increases dramatically as the film thickness is increased from two quintuple layers, saturating above six quintuple layers. This suggests a dominant role of surface states in spin and charge interconversion in topological-insulator-ferromagnet heterostructures. Our conclusion is further corroborated by studying a series of Y3 Fe5 O12 /(Bi,Sb ) 2Te3 heterostructures. Finally, we use the ferromagnetic resonance linewidth broadening and the inverse Rashba-Edelstein signals to determine the effective interfacial spin mixing conductance and λIREE.

  4. Electrochemically deposited BiTe-based nanowires for thermoelectric applications

    SciTech Connect

    Ng, Inn-Khuan; Kok, Kuan-Ying; Rahman, Che Zuraini Che Ab; Saidin, Nur Ubaidah; Ilias, Suhaila Hani; Choo, Thye-Foo

    2014-02-12

    Nanostructured materials systems such as thin-films and nanowires (NWs) are promising for thermoelectric power generation and refrigeration compared to traditional counterparts in bulk, due to their enhanced thermoelectric figures-of-merit. BiTe and its derivative compounds, in particular, are well-known for their near-room temperature thermoelectric performance. In this work, both the binary and ternary BiTe-based nanowires namely, BiTe and BiSbTe, were synthesized using template-assisted electrodeposition. Diameters of the nanowires were controlled by the pore sizes of the anodised alumina (AAO) templates used. Systematic study on the compositional change as a function of applied potential was carried out via Linear Sweep Voltanmetry (LSV). Chemical compositions of the nanowires were studied using Energy Dispersive X-ray Spectrometry (EDXS) and their microstructures evaluated using diffraction and imaging techniques. Results from chemical analysis on the nanowires indicated that while the Sb content in BiSbTe nanowires increased with more negative deposition potentials, the formation of Te{sup 0} and Bi{sub 2}Te{sub 3} were favorable at more positive potentials.

  5. Mapping the chemical potential dependence of current-induced spin polarization in a topological insulator

    NASA Astrophysics Data System (ADS)

    Lee, Joon Sue; Richardella, Anthony; Hickey, Danielle Reifsnyder; Mkhoyan, K. Andre; Samarth, Nitin

    2015-10-01

    We report electrical measurements of the current-induced spin polarization of the surface current in topological insulator devices where contributions from bulk and surface conduction can be disentangled by electrical gating. The devices use a ferromagnetic tunnel junction (permalloy/Al 2O3 ) as a spin detector on a back-gated (Bi,Sb ) 2Te3 channel. We observe hysteretic voltage signals as the magnetization of the detector ferromagnet is switched parallel or antiparallel to the spin polarization of the surface current. The amplitude of the detected voltage change is linearly proportional to the applied dc bias current in the (Bi,Sb ) 2Te3 channel. As the chemical potential is tuned from the bulk bands into the surface state band, we observe an enhancement of the spin-dependent voltages up to 300% within the range of the electrostatic gating. Using a simple model, we extract the spin polarization near charge neutrality (i.e., the Dirac point).

  6. Surface-State-Dominated Spin-Charge Current Conversion in Topological-Insulator-Ferromagnetic-Insulator Heterostructures.

    PubMed

    Wang, Hailong; Kally, James; Lee, Joon Sue; Liu, Tao; Chang, Houchen; Hickey, Danielle Reifsnyder; Mkhoyan, K Andre; Wu, Mingzhong; Richardella, Anthony; Samarth, Nitin

    2016-08-12

    We report the observation of ferromagnetic resonance-driven spin pumping signals at room temperature in three-dimensional topological insulator thin films-Bi_{2}Se_{3} and (Bi,Sb)_{2}Te_{3}-deposited by molecular beam epitaxy on Y_{3}Fe_{5}O_{12} thin films. By systematically varying the Bi_{2}Se_{3} film thickness, we show that the spin-charge conversion efficiency, characterized by the inverse Rashba-Edelstein effect length (λ_{IREE}), increases dramatically as the film thickness is increased from two quintuple layers, saturating above six quintuple layers. This suggests a dominant role of surface states in spin and charge interconversion in topological-insulator-ferromagnet heterostructures. Our conclusion is further corroborated by studying a series of Y_{3}Fe_{5}O_{12}/(Bi,Sb)_{2}Te_{3} heterostructures. Finally, we use the ferromagnetic resonance linewidth broadening and the inverse Rashba-Edelstein signals to determine the effective interfacial spin mixing conductance and λ_{IREE}. PMID:27563980

  7. Magnetic ordering and quantum anomalous Hall phase of Cr-doped topological insulators: First principles studies

    NASA Astrophysics Data System (ADS)

    Kim, Jeongwoo; Jhi, Seung-Hoon; Wu, Ruqian

    Realization of transverse electric currents without external magnetic fields, so called the quantum anomalous Hall effect (QAHE), is achieved in Cr-doped topological insulating (Bi,Sb)2Te3 compounds. However, detailed mechanism of QAHE and magnetic ordering in topological insulators (TIs) is still unclear with several models in controversy. We study the origin of QAHE in magnetic impurity-doped TIs using first-principles calculations. We investigate a possibility of the quantum anomalous Hall phase in conventional three-dimensional topological insulators, such as Bi2Se3, Bi2Te3, and Sb2Te3. We find that Sb2Te3 is the most suitable compound for realizing QAHE, because it maintains insulating phase and relatively strong ferromagnetic ordering in a wide range of Cr doping while Bi2Se3 and Bi2Te3 become metallic even by a small amount of Cr doping. Contrary to previous predictions, the kinetic exchange is responsible for the magnetic phase of Cr-doped TIs and it induces spin-polarized valence and conduction bands in Sb2Te3. We also discuss the role of Bi doping in topological surfaces states of Cr-doped Sb2Te3, which leads to QAHE in (Bi,Sb)2Te3. Work was supported as part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. SC0012670.

  8. Characterization of La-doped xBiInO3(1 ‑ x)PbTiO3 Piezoelectric Films Deposited by the Radio-Frequency Magnetron Sputtering Method

    NASA Astrophysics Data System (ADS)

    Ke-Xue, Sun; Shu-Yi, Zhang; Kiyotaka, Wasa; Xiu-Ji, Shui

    2016-06-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11174142 and 11304160, the National Basic Research Program of China under Grant No 2012CB921504, and the Special Fund for Public Interest of China under Grant No 201510068.

  9. Hot Wall Epitaxy And Characterization Of Bismuth And Antimony Thin Films On Barium Fluoride Substrates

    NASA Astrophysics Data System (ADS)

    Collazo, Ramon; Dalmau, Rafael; Martinez, Antonio

    1998-03-01

    We have grown thin films of bismuth and antimony using hot wall epitaxy. The epitaxial films were grown on (111)-BaF2 substrates. The chemical integrity of the films was established using Auger electron spectroscopy and X ray Photoelectron Spectroscopy. The thickness of the films was measured using an atomic force microscope to establish their growth rate. The crystallographic properties of the films were assessed using x-ray diffraction techniques. Both bismuth and antimony thin films were found to be oriented with the [003] direction perpendicular to the plane of the films. Pole figures of both types of films indicate the epitaxial nature of the films. Bi/Sb multilayer structures were grown using the same growth technique. We will report on the results of the characterization of these films as well as on the growth apparatus and process. Work supported in part by EPSCoR-NSF Grant EHR-9108775 and NCRADA-NSWCDD-92-01.

  10. Determination of tungsten with iron(III) after reduction with mercury in thiocyanate medium.

    PubMed

    Yatirajam, V; Dhamija, S

    1976-01-01

    Tungsten(V) is formed by shaking for 2 min sodium tungstate solution in 0.4 M potassium thiocyanate-4M hydrochloric acid medium, with mercury. It is titrated with standard iron(III) solution. The thiocyanate present stabilizes W(V) to aerial oxidation and also acts as indicator. The W(V) can also be titrated potentiometrically in 7M hydrochloric acid, a tungsten wire electrode being used. Fe, Ni, Cr, Zr, Bi, Sb, Ce, Al, Pb, Ca and U do not interfere. Cu, V and As can be tolerated up to 5 mg. Co, Mo, Re, Nb and Mn interfere, but not in the potentiometric determination. The method is direct, simple, rapid, accurate and reproducible. PMID:18961802

  11. Thermoelectric microdevice fabricated by a MEMS-like electrochemical process

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey; Lim, James R.; Huang, Chen-Kuo; Fleurial, Jean-Pierre

    2003-01-01

    Microelectromechanical systems (MEMS) are the basis of many rapidly growing technologies, because they combine miniature sensors and actuators with communications and electronics at low cost. Commercial MEMS fabrication processes are limited to silicon-based materials or two-dimensional structures. Here we show an inexpensive, electrochemical technique to build MEMS-like structures that contain several different metals and semiconductors with three-dimensional bridging structures. We demonstrate this technique by building a working microthermoelectric device. Using repeated exposure and development of multiple photoresist layers, several different metals and thermoelectric materials are fabricated in a three-dimensional structure. A device containing 126 n-type and p-type (Bi, Sb)2Te3 thermoelectric elements, 20 microm tall and 60 microm in diameter with bridging metal interconnects, was fabricated and cooling demonstrated. Such a device should be of technological importance for precise thermal control when operating as a cooler, and for portable power when operating as a micro power generator.

  12. Topological Spintronics: Materials, Phenomena and Devices

    NASA Astrophysics Data System (ADS)

    Samarth, Nitin

    2015-03-01

    The two-dimensional surface states of three-dimensional topological insulators such as Bi2Se3and(Bi,Sb)2Te3 possess a spin texture that can potentially be exploited for spintronics applications. We provide a perspective on the emergence of ``topological spintronics,'' demonstrating how this spin texture can be engineered using either quantum tunneling between surfaces or by breaking time-reversal symmetry. We then discuss recent experiments that show striking spintronic phenomena useful for proof-of-concept devices, including a spin-orbit torque of record efficiency at room temperature and an electrically-gated ``giant anisotropic magnetoresistance'' at low temperature. This work was carried out in collaboration with A. Richardella, S.-Y. Xu, M. Neupane, A. Mellnik, A. Kandala, J. S. Lee, D. M. Zhang, M. Z. Hasan and D. C. Ralph. We acknowledge funding from the DARPA Meso program, ONR and C-SPIN (under sponsorship of MARCO and DARPA).

  13. Measurement of Local Peltier Constant at a Microcontact

    NASA Astrophysics Data System (ADS)

    Koyano, Mikio; Akashi, Naoya

    2009-07-01

    Our novel apparatus measures the local Peltier constant at a thermoelectric material microregion. A narrow metal needle probe contacts a sample mounted into a small adiabatic vacuum chamber with a pressure of about 10-4 Pa. A␣stepping-motor-type nano-actuator controls the probe’s contact pressure. We measured DC and AC I- V characteristics at the microcontact to determine thermoelectric properties. We measured I- V characteristics between the probe and a commercial (Bi,Sb)2Te3 surface. Measured values of local Peltier constants are of the same order as the bulk Peltier constant π: ca. 55 mV. They increase with increased contact resistance, suggesting that contact size affects thermoelectricity.

  14. Intrinsic Topological Insulator Bi1.5Sb0.5Te3-xSex Thin Crystals

    PubMed Central

    Wang, Wei; Li, Li; Zou, Wenqin; He, Liang; Song, Fengqi; Zhang, Rong; Wu, Xiaoshan; Zhang, Fengming

    2015-01-01

    The quaternary topological insulator (Bi,Sb)2(Te,Se)3 has demonstrated topological surface states with an insulating bulk. Scientists have identified an optimized composition of Bi1.5Sb0.5Te1.7Se1.3 with the highest resistivity reported. But the physics that drive to this composition remains unclear. Here we report the crystal structure and the magneto-transport properties of Bi1.5Sb0.5Te3-xSex (BSTS) series. A correlation between the structure and the physical properties has been revealed. We found out that within the rhombohedral structure, the composition with most Te substituting Se has the highest resistivity. On the other hand, segregation of other composition phases will introduce much higher bulk concentration. PMID:25604579

  15. Optical Probing of Ultrafast Electronic Decay in Bi and Sb with Slow Phonons

    NASA Astrophysics Data System (ADS)

    Li, J. J.; Chen, J.; Reis, D. A.; Fahy, S.; Merlin, R.

    2013-01-01

    Illumination with laser sources leads to the creation of excited electronic states of particular symmetries, which can drive isosymmetric vibrations. Here, we use a combination of ultrafast stimulated and cw spontaneous Raman scattering to determine the lifetime of A1g and Eg electronic coherences in Bi and Sb. Our results both shed new light on the mechanisms of coherent phonon generation and represent a novel way to probe extremely fast electron decoherence rates. The Eg state, resulting from an unequal distribution of carriers in three equivalent band regions, is extremely short lived. Consistent with theory, the lifetime of its associated driving force reaches values as small as 2 (6) fs for Bi (Sb) at 300 K.

  16. Liquidus of Silicon Binary Systems

    NASA Astrophysics Data System (ADS)

    Safarian, Jafar; Kolbeinsen, Leiv; Tangstad, Merete

    2011-08-01

    Thermodynamic knowledge about liquid silicon is crucial for the production of solar-grade silicon feedstock from molten silicon. In the current study, liquidus for silicon binary alloys is formulated using a previously developed method in which the liquidus curve is calculated using two constants. The liquidus measurements for the silicon portion of the silicon alloys with Al, Ca, Mg, Fe, Ti, Zn, Cu, Ag, Au, Pt, Sn, Pb, Bi, Sb, Ga, In, Ni, Pd, Mn, and Rh are reviewed, and the consistent data were used to determine the liquidus constants. The liquidus curves for silicon binary systems are calculated and plotted. It is indicated that the calculated liquidus curves fit well with the experimental data. A correlation between the determined liquidus constants is also observed, which can be used to gain a better understanding of the thermodynamics of the silicon binary melts.

  17. Cyclotene diaphragm for MEMS based IR detectors

    NASA Astrophysics Data System (ADS)

    Guo, Shuwen

    2003-01-01

    A novel structure employing Dow Chemical (Midland, MI) benzocyclobutene (BCB) Cyclotene as a diaphragm material is presented in this report. The main advantages of this BCB diaphragm are its low thermal conductivity, robustness, chemical inertness, low curing temperature and high structure yield. Moreover, a BCB film can be either photo-defined or plasma etched and is a suitable micromachining material for post IC processing. Micromachined IR thermopile single detectors and lineal detector arrays (1×16), using BiSeTeSb/BiSbTe sensing elements on BCB diaphragms, have been constructed and tested. Up to 100% structure yield has been obtained. The process used to realize this detector structure is compatible with the eventual inclusion of on-chip circuitry for signal amplification and conditioning.

  18. Investigating dissipation in the quantum anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Fox, Eli; Bestwick, Andrew; Goldhaber-Gordon, David; Feng, Yang; Ou, Yunbo; He, Ke; Wang, Yayu; Xue, Qi-Kun; Kou, Xufeng; Pan, Lei; Wang, Kang

    In the quantum anomalous Hall effect, a magnetic exchange gap in a 3D topological insulator gives rise to dissipationless chiral edge states. Though the effect has recently been realized in a family of ferromagnetically-doped (Bi,Sb)2Te3 topological insulator thin films, experiments to date have found non-vanishing longitudinal resistance, contrary to initial theoretical expectations. Proposed sources of this dissipation include extra gapless or activated quasi-helical edge states, thermally activated 2D conduction, and variable-range hopping. Here, we discuss transport measurements of Corbino disk and non-local geometries to identify the mechanism of non-ideal behavior. This work supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. 19-7503.

  19. Magnetic Coupling in FeBi2Se4 and FeSb2Se4 from first principles

    NASA Astrophysics Data System (ADS)

    Williams, Logan; Kioupakis, Emmanouil; Lopez, Juan; Poudeu, Pierre Ferdinand P.

    Spintronic devices offer benefits in power efficiency and size reduction over current electronics, but require the development of semiconductor materials with favorable magnetic properties. Specifically, a high ferromagnetic-to-paramagnetic Curie transition temperature is required for spintronics operation at room temperature. FeBi2Se4 and FeSb2Se4 are two n and p-type magnetic semiconductors, respectively, with Curie transition temperatures of 450K. We employ first-principles calculations based on density functional theory to examine the magnetic coupling mechanisms in these materials. Our results indicate that antisite defects of Fe upon the Bi/Sb sites are crucial to the ferromagnetic coupling of the Fe magnetic moments in the crystals. This research was supported by the National Science Foundation CAREER award through Grant No. DMR-1254314. Computational Resources were provided by the DOE NERSC facility.

  20. Experimental realization of quantized anomalous Hall effect

    NASA Astrophysics Data System (ADS)

    Xue, Qi-Kun

    2014-03-01

    Anomalous Hall effect was discovered by Edwin Hall in 1880. In this talk, we report the experimental observation of the quantized version of AHE, the quantum anomalous Hall effect (QAHE) in thin films of Cr-doped (Bi,Sb)2Te3 magnetic topological insulator. At zero magnetic field, the gate-tuned anomalous Hall resistance exhibits a quantized value of h /e2 accompanied by a significant drop of the longitudinal resistance. The longitudinal resistance vanishes under a strong magnetic field whereas the Hall resistance remains at the quantized value. The realization of QAHE paves a way for developing low-power-consumption electronics. Implications on observing Majorana fermions and other exotic phenomena in magnetic topological insulators will also be discussed. The work was collaborated with Ke He, Yayu Wang, Xucun Ma, Xi Chen, Li Lv, Dai Xi, Zhong Fang and Shoucheng Zhang.

  1. Thickness dependent band gap of Bi2-xSbxTe3 (x = 0, 0.05, 0.1) thin films

    NASA Astrophysics Data System (ADS)

    Patel, M. M.; Soni, P. H.; Desai, C. F.

    2016-05-01

    Thin films of Bi2Te3(Sb) were prepared on alkali halide crystal substrates. Sb content and the film thickness were varied. Bi2Te3 is a narrow gap semiconductor. Bi-Sb is a continuous solid solution of substitutional type and Sb therefore was used to test its effect on the band gap. The film thickness variation was also taken up. The infra-red absorption spectra were used in the wave number range 400 cm-1 to 4000 cm-1. The band gap obtained from the absorption data was found to increase with decreasing thickness since the thickness range used was from 30 nm to 170 nm. This is a range corresponding to nanostructures and hence quantum size effect was observed as expected. The band gap also exhibited Sb content dependence. The detail results are have been reported and explained.

  2. Fabrication of Thermoelectric Devices by Applying Microsystems Technology

    NASA Astrophysics Data System (ADS)

    Goncalves, L. M.; Alpuim, P.; Correia, J. H.

    2010-09-01

    Microsystems technologies were applied in the fabrication of thermoelectric (TE) microconverters. Common techniques used in microelectromechanical systems (MEMS) fabrication, namely wet etching, lift-off (with SU-8 photoresist), reactive ion etching (RIE), and lithography-electroplating-molding, were compared in the fabrication process of TE microsystems based on Bi, Sb, and Te thin-film compounds. Thin films of bismuth and antimony tellurides were deposited by co-evaporation, with figures of merit comparable to those of bulk materials. Test structures were fabricated using lithography and wet etching. The etching recipe was optimized by varying the etchant dilution and composition until higher etch rates and desired material selectivity were attained. Since the etching process is applied after deposition, this process allows prior deposition of TE materials by any deposition method; thus, films with high figure of merit can be fabricated. Moreover, wet etching does not require the use of expensive equipment.

  3. Effects of B-site chemistry on BiFeO[subscript 3]-containing enhanced tetragonality systems

    SciTech Connect

    Stein, David M.; Davies, Peter K.

    2012-02-06

    The ternary perovskite systems PbTiO{sub 3}-BiFeO{sub 3}-Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3} and PbTiO{sub 3}-BiFeO{sub 3}-BiScO{sub 3} were investigated to clarify the relationship between the observance of multiple dielectric transitions and B-site chemistry. Multiple dielectric transitions were observed for a range of compositions in the Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-containing system. A temperature-dependent diffraction study confirmed the existence of a cubic and tetragonal co-existence region at temperatures between the two transitions. No similar dielectric behavior was observed in the PbTiO{sub 3}-BiFeO{sub 3}-BiScO{sub 3} system.

  4. The simultaneous enhancement of photorefraction and optical damage resistance in MgO and Bi2O3 co-doped LiNbO3 crystals.

    PubMed

    Zheng, Dahuai; Kong, Yongfa; Liu, Shiguo; Chen, Muling; Chen, Shaolin; Zhang, Ling; Rupp, Romano; Xu, Jingjun

    2016-01-01

    For a long time that optical damage was renamed as photorefraction, here we find that the optical damage resistance and photorefraction can be simultaneously enhanced in MgO and Bi2O3 co-doped LiNbO3 (LN:Bi,Mg). The photorefractive response time of LN:Bi,Mg was shortened to 170 ms while the photorefractive sensitivity reached up to 21 cm(2)/J. Meanwhile, LN:Bi,Mg crystals could withstand a light intensity higher than 10(6)  W/cm(2) without apparent optical damage. Our experimental results indicate that photorefraction doesn't equal to optical damage. The underground mechanism was analyzed and attributed to that diffusion dominates the transport process of charge carriers, that is to say photorefraction causes only slight optical damage under diffusion mechanism, which is very important for the practical applications of photorefractive crystals, such as in holographic storage, integrated optics and 3D display. PMID:26837261

  5. The simultaneous enhancement of photorefraction and optical damage resistance in MgO and Bi2O3 co-doped LiNbO3 crystals

    PubMed Central

    Zheng, Dahuai; Kong, Yongfa; Liu, Shiguo; Chen, Muling; Chen, Shaolin; Zhang, Ling; Rupp, Romano; Xu, Jingjun

    2016-01-01

    For a long time that optical damage was renamed as photorefraction, here we find that the optical damage resistance and photorefraction can be simultaneously enhanced in MgO and Bi2O3 co-doped LiNbO3 (LN:Bi,Mg). The photorefractive response time of LN:Bi,Mg was shortened to 170 ms while the photorefractive sensitivity reached up to 21 cm2/J. Meanwhile, LN:Bi,Mg crystals could withstand a light intensity higher than 106  W/cm2 without apparent optical damage. Our experimental results indicate that photorefraction doesn’t equal to optical damage. The underground mechanism was analyzed and attributed to that diffusion dominates the transport process of charge carriers, that is to say photorefraction causes only slight optical damage under diffusion mechanism, which is very important for the practical applications of photorefractive crystals, such as in holographic storage, integrated optics and 3D display. PMID:26837261

  6. Metallurgy, thermal stability, and failure mode of the commercial Bi-Te-based thermoelectric modules.

    SciTech Connect

    Yang, Nancy Y. C.; Morales, Alfredo Martin

    2009-02-01

    Bi-Te-based thermoelectric (TE) alloys are excellent candidates for power generation modules. We are interested in reliable TE modules for long-term use at or below 200 C. It is known that the metallurgical characteristics of TE materials and of interconnect components affect the performance of TE modules. Thus, we have conducted an extensive scientific investigation of several commercial TE modules to determine whether they meet our technical requirements. Our main focus is on the metallurgy and thermal stability of (Bi,Sb){sup 2}(Te,Se){sup 3} TE compounds and of other materials used in TE modules in the temperature range between 25 C and 200 C. Our study confirms the material suite used in the construction of TE modules. The module consists of three major components: AlN cover plates; electrical interconnects; and the TE legs, P-doped (Bi{sub 8}Sb{sub 32})(Te{sub 60}) and N-doped (Bi{sub 37}Sb{sub 3})(Te{sub 56}Se{sub 4}). The interconnect assembly contains Sn (Sb {approx} 1wt%) solder, sandwiched between Cu conductor with Ni diffusion barriers on the outside. Potential failure modes of the TE modules in this temperature range were discovered and analyzed. The results show that the metallurgical characteristics of the alloys used in the P and N legs are stable up to 200 C. However, whole TE modules are thermally unstable at temperatures above 160 C, lower than the nominal melting point of the solder suggested by the manufacture. Two failure modes were observed when they were heated above 160 C: solder melting and flowing out of the interconnect assembly; and solder reacting with the TE leg, causing dimensional swelling of the TE legs. The reaction of the solder with the TE leg occurs as the lack of a nickel diffusion barrier on the side of the TE leg where the displaced solder and/or the preexisting solder beads is directly contact the TE material. This study concludes that the present TE modules are not suitable for long-term use at temperatures above 160 C due

  7. An experimental study on the geochemical behavior of highly siderophile elements (HSE) and metalloids (As, Se, Sb, Te, Bi) in a mss-iss-pyrite system at 650 °C: A possible magmatic origin for Co-HSE-bearing pyrite and the role of metalloid-rich phases in the fractionation of HSE

    NASA Astrophysics Data System (ADS)

    Cafagna, Fabio; Jugo, Pedro J.

    2016-04-01

    Pyrite, the most abundant sulfide in the Earth's crust, is an accessory mineral in several magmatic sulfide deposits. Although most pyrite is hydrothermal, previous experimental studies have shown that pyrite can also have a primary magmatic origin, by exsolving from monosulfide solid solution (mss) during cooling of a sulfide melt, if sulfur fugacity is sufficiently high. Pyrite from some localities has significant amounts of Co, and complex zonation in some low-melting-point chalcophile elements (LMCE), such as As, Se, Sb, Te, Bi (henceforth referred to as metalloids) and some platinum-group elements (PGE: Ru, Rh, Pd, Os, Ir, Pt). However, the origin of such pyrite and the causes of zonation are not clear. Because the distribution of some of these elements is heterogeneous and seems to be developed in concentric zones, the zonation has been interpreted to represent growth stages, some of them secondary and caused partly by hydrothermal fluids. Better constraints on the origin of Co-PGE-bearing pyrite could help unravel the geochemical processes affecting the sulfide assemblages in which it is found; thus, an experimental study was undertaken to characterize pyrite formation in magmatic sulfide environments and its relationship with metalloids and highly siderophile elements (HSE: PGE, Re, Au). Natural pyrrhotite, chalcopyrite, pentlandite and elemental S were mixed and doped with approximately 50 ppm of each HSE. A mixture of metalloids was added at 0.2 wt.% or 3 wt.% to aliquots of sulfide mixtures. Starting materials were sealed in evacuated silica tubes and fused at 1200 °C. The temperature was subsequently reduced to 750 °C (at 60 °C/h), then to 650 °C (at 0.5 °C/h) to produce relatively large euhedral pyrite crystals, then quenched. The experiments were analyzed using reflected light, SEM, EPMA and LA-ICP-MS. Experimental products contained euhedral pyrite, mss, intermediate solid solution (iss) and metalloid-rich phases, interpreted as quench product of an immiscible metalloid-rich liquid. The results show that Co-Ni-HSE-bearing pyrite with complex zonation in Ru, Rh, Os, Ir, and Pt can form by a subsolidus reaction involving both mss and iss, and does not require secondary (e.g. hydrothermal) processes. Because such pyrite results from the cooling of a sulfide melt (after mss and iss) it can be described as magmatic. Among the HSE, Ru, Rh, Os, Re and Ir have identical zonation patterns in pyrite, Pt is also zoned but differently, and Au and Pd are essentially excluded. Previously documented natural HSE-bearing pyrite also display identical zonation patterns in Ru, Rh, Os and Ir. The complex zoning is likely preserved due to the extremely slow diffusion rates for those elements in pyrite. Thus, the presence of pyrite with similar characteristic in natural sulfide assemblages is consistent with a magmatic origin and does not require hydrothermal processes. The results also show that if a metalloid-rich liquid is present it will significantly sequester Au, Pd and Pt, but will not affect Ru, Rh, Os, Re and Ir. In the absence of metalloid-rich phases, Au partitions strongly into iss and Pd partitions preferentially into mss.

  8. Quantum transport of two-species Dirac fermions in dual-gated three-dimensional topological insulators.

    PubMed

    Xu, Yang; Miotkowski, Ireneusz; Chen, Yong P

    2016-01-01

    Topological insulators are a novel class of quantum matter with a gapped insulating bulk, yet gapless spin-helical Dirac fermion conducting surface states. Here, we report local and non-local electrical and magneto transport measurements in dual-gated BiSbTeSe2 thin film topological insulator devices, with conduction dominated by the spatially separated top and bottom surfaces, each hosting a single species of Dirac fermions with independent gate control over the carrier type and density. We observe many intriguing quantum transport phenomena in such a fully tunable two-species topological Dirac gas, including a zero-magnetic-field minimum conductivity close to twice the conductance quantum at the double Dirac point, a series of ambipolar two-component half-integer Dirac quantum Hall states and an electron-hole total filling factor zero state (with a zero-Hall plateau), exhibiting dissipationless (chiral) and dissipative (non-chiral) edge conduction, respectively. Such a system paves the way to explore rich physics, ranging from topological magnetoelectric effects to exciton condensation. PMID:27142344

  9. Magnetic Cr doping of Bi2Se3: Evidence for divalent Cr from x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Figueroa, A. I.; van der Laan, G.; Collins-McIntyre, L. J.; Zhang, S.-L.; Baker, A. A.; Harrison, S. E.; Schönherr, P.; Cibin, G.; Hesjedal, T.

    2014-10-01

    Ferromagnetically doped topological insulators with broken time-reversal symmetry are a prerequisite for observing the quantum anomalous Hall effect. Cr-doped (Bi,Sb)2(Se,Te)3 is the most successful materials system so far, as it combines ferromagnetic ordering with acceptable levels of additional bulk doping. Here, we report a study of the local electronic structure of Cr dopants in epitaxially grown Bi2Se3 thin films. Contrary to the established view that the Cr dopant is trivalent because it substitutionally replaces Bi3+, we find instead that Cr is divalent. This is evidenced by the energy positions of the Cr K and L2,3 absorption edges relative to reference samples. The extended x-ray absorption fine structure at the K edge shows that the Cr dopants substitute on octahedral sites with the surrounding Se ions contracted by Δd =-0.36 Å, in agreement with recent band structure calculations. Comparison of the Cr L2,3 x-ray magnetic circular dichroism at T =5 K with multiplet calculations gives a spin moment of 3.64 μB/Crbulk, which is close to the saturation moment for Cr2+ d4. The reduced Cr oxidation state in doped Bi2Se3 is ascribed to the formation of a covalent bond between Cr d (eg) and Se p orbitals, which is favored by the contraction of the Cr-Se distances.

  10. Quantum transport of two-species Dirac fermions in dual-gated three-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Xu, Yang; Miotkowski, Ireneusz; Chen, Yong P.

    Topological insulators (TI) are a novel class of quantum matter with a gapped insulating bulk yet gapless spin helical Dirac fermion conducting surface states. Here, we report local and non-local electrical and magneto transport measurements in dual-gated BiSbTeSe2 thin film TI devices, with conduction dominated by the spatially separated top and bottom surfaces, each hosting a single species of Dirac fermions with independent gate control over the carrier type and density. We observe many intriguing quantum transport phenomena in such a fully-tunable two-species topological Dirac gas, including a zero-magnetic-field minimum conductivity of 4e2 / h at the double Dirac point, a series of ambipolar two-component ''half-integer'' Dirac quantum Hall states and an electron-hole total filling factor ν=0 state (with a zero-Hall plateau), exhibiting dissipationless (chiral) and dissipative (non-chiral) edge conduction respectively. Such a system paves the way to explore rich physics ranging from topological magnetoelectric effects to exciton condensation. DARPA MESO program.

  11. Manipulating edge transport in quantum anomalous Hall insulators

    NASA Astrophysics Data System (ADS)

    Kandala, Abhinav

    The quantum anomalous Hall (QAH) effect provides a path to obtain dissipation-less, one-dimensional (1D) edge states at zero magnetic field. It's recent experimental realization in magnetic topological insulator thin films lies at the overlap of several areas of condensed matter physics: dilute magnetic semiconductors, low dimensional electron transport and topologically non-trivial material systems. In this talk, we demonstrate how careful compositional and electrical tuning of epitaxial films of Cr-doped (Bi,Sb)2Te3 enables access to a robust zero-field quantized Hall effect, despite sample roughness and low carrier mobility. In samples that show near-dissipation-less transport, we manipulate the intermixing between edge states and dissipative channels via a tilted-field crossover from ballistic 1D edge transport to diffusive transport. This crossover manifests in a gate-tunable giant anisotropic magneto-resistance effect that we use as a quantitative probe of dissipation in our systems. Finally, we discuss experiments with mesoscopic channels of QAH insulator thin films, and discuss the effect of their modified magnetic anisotropy on edge transport. This work was carried out in collaboration with A. Richardella, C-X Liu, M. Liu, W. Wang, N. P. Ong, and N. Samarth. Funded by ARO/MURI, DARPA and ONR.

  12. Visualization of superparamagnetic dynamics in magnetic topological insulators.

    PubMed

    Lachman, Ella O; Young, Andrea F; Richardella, Anthony; Cuppens, Jo; Naren, H R; Anahory, Yonathan; Meltzer, Alexander Y; Kandala, Abhinav; Kempinger, Susan; Myasoedov, Yuri; Huber, Martin E; Samarth, Nitin; Zeldov, Eli

    2015-11-01

    Quantized Hall conductance is a generic feature of two-dimensional electronic systems with broken time reversal symmetry. In the quantum anomalous Hall state recently discovered in magnetic topological insulators, time reversal symmetry is believed to be broken by long-range ferromagnetic order, with quantized resistance observed even at zero external magnetic field. We use scanning nanoSQUID (nano-superconducting quantum interference device) magnetic imaging to provide a direct visualization of the dynamics of the quantum phase transition between the two anomalous Hall plateaus in a Cr-doped (Bi,Sb)2Te3 thin film. Contrary to naive expectations based on macroscopic magnetometry, our measurements reveal a superparamagnetic state formed by weakly interacting magnetic domains with a characteristic size of a few tens of nanometers. The magnetic phase transition occurs through random reversals of these local moments, which drive the electronic Hall plateau transition. Surprisingly, we find that the electronic system can, in turn, drive the dynamics of the magnetic system, revealing a subtle interplay between the two coupled quantum phase transitions. PMID:26601138

  13. Visualization of superparamagnetic dynamics in magnetic topological insulators

    PubMed Central

    Lachman, Ella O.; Young, Andrea F.; Richardella, Anthony; Cuppens, Jo; Naren, H. R.; Anahory, Yonathan; Meltzer, Alexander Y.; Kandala, Abhinav; Kempinger, Susan; Myasoedov, Yuri; Huber, Martin E.; Samarth, Nitin; Zeldov, Eli

    2015-01-01

    Quantized Hall conductance is a generic feature of two-dimensional electronic systems with broken time reversal symmetry. In the quantum anomalous Hall state recently discovered in magnetic topological insulators, time reversal symmetry is believed to be broken by long-range ferromagnetic order, with quantized resistance observed even at zero external magnetic field. We use scanning nanoSQUID (nano–superconducting quantum interference device) magnetic imaging to provide a direct visualization of the dynamics of the quantum phase transition between the two anomalous Hall plateaus in a Cr-doped (Bi,Sb)2Te3 thin film. Contrary to naive expectations based on macroscopic magnetometry, our measurements reveal a superparamagnetic state formed by weakly interacting magnetic domains with a characteristic size of a few tens of nanometers. The magnetic phase transition occurs through random reversals of these local moments, which drive the electronic Hall plateau transition. Surprisingly, we find that the electronic system can, in turn, drive the dynamics of the magnetic system, revealing a subtle interplay between the two coupled quantum phase transitions. PMID:26601138

  14. Modelling of segmented high-performance thermoelectric generators with effects of thermal radiation, electrical and thermal contact resistances

    PubMed Central

    Ouyang, Zhongliang; Li, Dawen

    2016-01-01

    In this study, segmented thermoelectric generators (TEGs) have been simulated with various state-of-the-art TE materials spanning a wide temperature range, from 300 K up to 1000 K. The results reveal that by combining the current best p-type TE materials, BiSbTe, MgAgSb, K-doped PbTeS and SnSe with the strongest n-type TE materials, Cu-Doped BiTeSe, AgPbSbTe and SiGe to build segmented legs, TE modules could achieve efficiencies of up to 17.0% and 20.9% at ΔT = 500 K and ΔT = 700 K, respectively, and a high output power densities of over 2.1 Watt cm−2 at the temperature difference of 700 K. Moreover, we demonstrate that successful segmentation requires a smooth change of compatibility factor s from one end of the TEG leg to the other, even if s values of two ends differ by more than a factor of 2. The influence of the thermal radiation, electrical and thermal contact effects have also been studied. Although considered potentially detrimental to the TEG performance, these effects, if well-regulated, do not prevent segmentation of the current best TE materials from being a prospective way to construct high performance TEGs with greatly enhanced efficiency and output power density. PMID:27052592

  15. High-mobility surface states and conductance fluctuations in Bismuth Telluro-Sulfide topological insulator devices

    NASA Astrophysics Data System (ADS)

    Trivedi, Tanuj; Sonde, Sushant; Movva, Hema C. P.; Banerjee, Sanjay K.

    Since the experimental discovery of three-dimensional topological insulators (TI), (Bi,Sb)2(Se,Te)3 binary compounds are the principal material systems to explore TI physics. However, transport experiments studying surface-states are complicated by parallel bulk conductivity contribution, which is expected to improve for ternary and quaternary chalcogenide compounds of Bi and Sb. A promising alternative is the Sulfur-based tetradymite with an ideal formula of Bi2Te2S, which has received little attention. We present van der Waals epitaxial growth and magnetotransport in Bismuth Telluro-Sulfide (BTS) crystalline nanosheets. Gating-enhanced Weak-antilocalization (WAL) and Universal Conductance Fluctuations (UCF) are observed in BTS devices. Empirical modeling of the data shows the existence of two-dimensional surface transport. A three-channel Hall conductivity model is proposed, which is utilized in conjunction with an extended-WAL analysis, showing the presence of a high-mobility surface component and indication for separation of transport channels in BTS devices. Our growth and comprehensive transport experiments demonstrate BTS as a promising candidate TI material.

  16. Controlled improvement in specific contact resistivity for thermoelectric materials by ion implantation

    NASA Astrophysics Data System (ADS)

    Taylor, Patrick J.; Maddux, Jay R.; Meissner, Greg; Venkatasubramanian, Rama; Bulman, Gary; Pierce, Jonathan; Gupta, Rahul; Bierschenk, Jim; Caylor, Chris; D'Angelo, Jonathan; Ren, Zhifeng

    2013-07-01

    To obtain reduced specific contact resistivity, iodine donors and silver acceptors were ion-implanted into n-type and p-type (Bi,Sb)2(Se,Te)3 materials, respectively, to achieve >10 times higher doping at the surface. Implantation into n-type materials caused the specific contact resistivity to decrease from 1.7 × 10-6 Ω cm2 to 4.5 × 10-7 Ω cm2. Implantation into p-type materials caused specific contact resistivity to decrease from 7.7 × 10-7 Ω cm2 to 2.7 × 10-7 Ω cm2. For implanted thin-film superlattices, the non-implanted values of 1.4 × 10-7 Ω cm2 and 5.3 × 10-8 Ω cm2 precipitously dropped below the detection limit after implantation, ≤10-8 Ω cm2. These reductions in specific contact resistivity are consistent with an increase in tunneling across the contact.

  17. Factors of the accumulation of heavy metals and metalloids at geochemical barriers in urban soils

    NASA Astrophysics Data System (ADS)

    Kosheleva, N. E.; Kasimov, N. S.; Vlasov, D. V.

    2015-05-01

    The bulk contents and concentrations of mobile (extracted by an ammonium acetate buffer with EDTA) Cd, Pb, Sb, As, Bi, Zn, and Cu were determined in the surface horizons of urban soils in the Eastern administrative okrug of Moscow. The regression analysis showed that the accumulation of these metals and metalloids in the soils is controlled by the physicochemical soil properties and by number of anthropogenic factors and landscape conditions (geochemical position, type of loose deposits, character of land use, dust load, vehicle emissions, building pattern, percent of green areas, and the extent of sealed soils). The precipitation of studied elements on the geochemical barriers had the following regularities: Cd, Cu, and Zn accumulated on the alkaline barriers; Bi, Sb, As, Cu, Pb, and Zn, on chemisorption barriers; Sb, As, and Pb, on organomineral barriers; and Cd and Cu, on the sorption-sedimentation barriers. Technogenic transformation of the physicochemical properties of urban soils resulted in the increase of the mean bulk contents of heavy metals and metalloids by 33-99%; the portion of elements fixed on the geochemical barriers increased by 26-50%.

  18. Observation of Pairing Correlations in Strongly Localized Amorphous Films

    NASA Astrophysics Data System (ADS)

    Stewart, M. D., Jr.; Valles, J. M., Jr.; Yin, Aijun; Xu, J. M.

    2007-03-01

    We have measured the Superconductor to Insulator Transition (SIT) as a function of thickness at dilution refrigerator temperatures in ultrathin Bi/Sb films perforated with a regular honeycomb array of holes separated by 100 nm. The presence of these perforations profoundly influences the character of the transition. In particular, on the insulating side of the SIT, the resistance as a function of temperature, R(T), rises monotonically and becomes activated below 1K. Closer to the SIT, a minimum develops in the R(T) suggestive of strong superconducting fluctuations and the onset of Cooper pairing. Simultaneously, the perpendicular field magnetoresistance begins to oscillate with a period that corresponds to the superconducting flux quantum. Yet thicker films exhibit a relatively broad R(T) transition toward a zero resistance state. This behavior constitutes direct evidence that the superconducting ground state of this amorphous film system emerges from an insulating state containing localized Cooper pairs. This work has been supported by the NSF through DMR-0203608, and DMR-0605797, AFRL, and ONR.

  19. Chern half metals: a new class of topological materials to realize the quantum anomalous Hall effect.

    PubMed

    Hu, Jun; Zhu, Zhenyue; Wu, Ruqian

    2015-03-11

    New topological insulators that demonstrate the quantum anomalous Hall effect (QAHE) are a cutting-edge research topic in condensed matter physics and materials science. So far, the QAHE has been observed only in Cr-doped (Bi,Sb)2Te3 at extremely low temperature. Therefore, it is important to find new materials with large topological band gap and high thermal stability for the realization of the QAHE. On the basis of first-principles and tight-binding model calculations, we discovered a new class of topological phase, Chern half metal, which manifests the QAHE in one spin channel while is metallic in the other spin channel, in Co or Rh deposited graphene. The QAHE is robust in these sytems for the adatom coverage ranging from 2% to 6%. Meanwhile, these systems have large perpendicular magnetic anisotropy energies of 5.3 and 11.5 meV, necessary for the observation of the QAHE at reasonably high temperature. PMID:25689149

  20. Enhanced thermoelectric performance of Cu2Se/Bi0.4Sb1.6Te3 nanocomposites at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Li, Y. Y.; Qin, X. Y.; Li, D.; Zhang, J.; Li, C.; Liu, Y. F.; Song, C. J.; Xin, H. X.; Guo, H. F.

    2016-02-01

    Bi2Te3-based thermoelectric materials with large thermoelectric figure of merit, ZT, at elevated temperatures are advantageous in power generation by using the low-grade waste heat. Here, we show that incorporation of small proportion (0.3 vol. %) of nanophase Cu2Se into BiSbTe matrix causes an enhanced high-temperature thermopower due to elevated energy filtering of carriers and inhibition of minority transport besides enhanced phonon blocking from scattering at interfaces, which concurrently result in an ˜20% increase in the power factor and an ˜60% reduction in the lattice thermal conductivity at 488 K. As a result, ZT = 1.6 is achieved at 488 K in the composite system with 0.3 vol. % of Cu2Se. Significantly, its ZT is larger than unit in broad high-temperature range (e.g., ZT = 1.3 at 400 K and ZT = 1.6 at 488 K), which makes this material to be attractive for applications in energy harvesting from the low-grade waste heat.

  1. Structural and proximity-induced ferromagnetic properties of topological insulator-magnetic insulator heterostructures

    NASA Astrophysics Data System (ADS)

    Jiang, Zilong; Chang, Cui-Zu; Tang, Chi; Zheng, Jian-Guo; Moodera, Jagadeesh S.; Shi, Jing

    2016-05-01

    The spontaneously broken time reversal symmetry can lead to the formation of an energy gap in the Dirac spectrum of the surface states of a topological insulator (TI) which can consequently give rise to a variety of interesting phenomena potentially useful for spintronics. In this work, we couple a non-magnetic TI to a high Curie temperature TC magnetic insulator to induce strong exchange interaction via the proximity effect. We have successfully grown 5 quintuple layer thick ternary TI (BixSb1-x)2Te3 films on atomically flat yttrium iron garnet (YIG) film with the combination of molecular beam epitaxy and pulsed laser deposition, in which the Fermi level position relative to the Dirac point is varied by controlling the Bi:Sb ratio. The anomalous Hall effect (AHE) and suppressed weak antilocalization (WAL) measured under out of plane magnetic fields reveal that the TI surface in contact with YIG is magnetized. Our high-quality (BixSb1-x)2Te3/Y IG heterostructure provides a tunable system for exploring the quantum anomalous Hall effect (QAHE) at higher temperatures in TI-based spintronic devices.

  2. Optical Control of Ferromagnetism in a Magnetically-Doped Topological Insulator

    NASA Astrophysics Data System (ADS)

    Yeats, Andrew L.; Mintun, Peter J.; Pan, Yu; Richardella, Anthony; Samarth, Nitin; Awschalom, David D.

    Many proposed experiments involving topological insulators (TIs) require spatial control over time-reversal symmetry and chemical potential. We demonstrate micron-scale optical control of both magnetization and chemical potential in thin films of Cr-doped (Bi,Sb)2Te3. By optically modulating the coercivity of the films, we write and erase arbitrary spatial configurations of their magnetization, which we then image with Kerr microscopy. Additionally, by optically manipulating a space charge layer in the underlying SrTiO3 substrates, we can control the local chemical potential of the films. This allows us to write and erase p- n junctions in the films, which we image with photocurrent microscopy. Both effects persist for > 16 hours. We will present systematic Kerr microscopy, photocurrent microscopy, and electrical transport studies of these materials and various electronic and magnetic structures patterned on them. We will discuss the prospects for using these optical phenomena to study and control the unique physics of TIs, such as edge-state transport in the quantum anomalous Hall regime. This work is supported by ONR, AFOSR-MURI, ARO, and NSF.

  3. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3.

    PubMed

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel; Feng, Xiao; Ou, Yunbo; He, Ke; Xue, Qi-Kun

    2015-01-01

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb)2Te3 (CBST) films grown on SrTiO3 (1 1 1) substrates with and without a Te capping layer. We find that both the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures. PMID:26123202

  4. Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators.

    PubMed

    Chang, Cui-Zu; Li, Mingda

    2016-03-31

    The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity σ(yx) = e2/h without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies. PMID:26934535

  5. Computational study of Met-Car analogue heterofullerenes

    NASA Astrophysics Data System (ADS)

    Domingos, H. S.

    2006-06-01

    Structural, chemical and electronic properties of a number of Met-Car analogue heterofullerenes were investigated using a combination of ab initio and semi-empirical quantum mechanical calculations.Met-Car clusters of known structure and chemistry were studied together with some new hypothetical configurations. In particular, the stability of clusters of the form Y8C12 (Y = Al, S, Si, Ti, As, Bi, Sb, P, N, B, Sn, Sc, Cr, V), XY7C12 (X, Y = B, N, Si) and Y8Z12 (Y, Z = N, B, Si) were investigated based on computed binding energies, Mulliken charges, bond orders and ionization potentials. The results indicate that some novel clusters are due for observation. Clusters of this type are known to form the building blocks of new polymerized solids and may exhibit some novel dielectric, magnetic and superconducting properties. Isomers of D3d symmetry, which are possible global energy minima for Cr, V and Sc carbide clusters, were also identified.

  6. Interdiffusion studies in Bi-based layered systems with nanosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Missana, T.; Afonso, C. N.; da Silva, M. F.

    1994-12-01

    Interdiffusion processes are induced by nanosecond laser pulses from an excimer laser. The Bi-based systems studied are formed by a Bi layer and a Sb or Ge layer. Configurations with Bi at the surface layer or at the innermost layer are both studied. Real-time reflectivity measurements are performed during the irradiation to determine the process kinetics and times and Rutherford backscattering spectrometry is used to obtain the concentration depth profiles. It will be shown that there is an interfacially initiated diffusion process in the Bi-Sb system and that the diffusion coefficients of this system within the liquid phase are in the 10-5 10-6 cm2/s range. The Bi-Ge system shows instead little mixing, the diffusion coefficients of the system within the liquid phase being at least two orders of magnitude lower. The differences observed when Bi is the surface layer or the innermost one are related to the different thermal responses of the system.

  7. Observation of topological surface state quantum Hall effect in an intrinsic three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Xu, Yang; Miotkowski, Ireneusz; Chen, Yong; Yong P. Chen's Group in Purdue Team; Chih-Kang Shih's Group in UT-Austin Collaboration; M. Zahid Hasan's Group in Princeton Collaboration

    2015-03-01

    A three-dimensional (3D) topological insulator (TI) is a novel quantum matter with a gapped insulating bulk yet a conducting surface hosting topologically-protected gapless surface states of Dirac fermions. One of the most distinct electronic transport signatures predicted for such topological surface states (TSS) is a half-integer quantum Hall effect (QHE) in a magnetic field. We have observed well-developed QHE arising from TSS in an intrinsic TI of BiSbTeSe2. Our samples can exhibit surface dominated conduction even close to room temperature, while the bulk conduction is negligible. At low temperatures and high perpendicular magnetic fields, the Hall conductance shows well quantized integer plateaux in exfoliated flake devices on SiO2 / Si substrates, where the top and bottom surface each contributing a half integer e2 / h Hall conductance, accompanied by vanishing longitudinal resistance. We have also studied dual-gated devices where both the top and bottom surfaces can be independently gated. Such intrinsic 3D TI materials exhibiting no measurable bulk conduction and well-developed surface state QHE pave the way for further applications of topological quantum electronics. DARPA MESO program (Grant N66001-11-1-4107).

  8. Quantum transport of two-species Dirac fermions in dual-gated three-dimensional topological insulators

    DOE PAGESBeta

    Xu, Yang; Miotkowski, Ireneusz; Chen, Yong P.

    2016-05-04

    Topological insulators are a novel class of quantum matter with a gapped insulating bulk, yet gapless spin-helical Dirac fermion conducting surface states. Here, we report local and non-local electrical and magneto transport measurements in dual-gated BiSbTeSe2 thin film topological insulator devices, with conduction dominated by the spatially separated top and bottom surfaces, each hosting a single species of Dirac fermions with independent gate control over the carrier type and density. We observe many intriguing quantum transport phenomena in such a fully tunable two-species topological Dirac gas, including a zero-magnetic-field minimum conductivity close to twice the conductance quantum at the doublemore » Dirac point, a series of ambipolar two-component half-integer Dirac quantum Hall states and an electron-hole total filling factor zero state (with a zero-Hall plateau), exhibiting dissipationless (chiral) and dissipative (non-chiral) edge conduction, respectively. As a result, such a system paves the way to explore rich physics, ranging from topological magnetoelectric effects to exciton condensation.« less

  9. Incommensurate host-guest structures in compressed elements: Hume—Rothery effects as origin

    NASA Astrophysics Data System (ADS)

    Degtyareva, V. F.

    2015-11-01

    Discovery of the incommensurate structure in the element Ba under pressure 15 years ago was followed by findings of a series of similar structures in other compressed elements. Incommensurately modulated structures of the host-guest type consist of a tetragonal host structure and a guest structure. The guest structure forms chains of atoms embedded in the channels of host atoms so that the axial ratio of these subcells along the c axis is not rational. Two types of the host-guest structures have been found so far: with the host cells containing 8 atoms and 16 atoms; in these both types the guest cells contain 2 atoms. These crystal structures contain a non-integer number of atoms in their unit cell: tI11* in Bi, Sb, As, Ba, Sr, Sc and tI19* in Na, K, Rb. We consider here a close structural relationship of these host-guest structures with the binary alloy phase Au3Cd5-tI32. This phase is related to the family of the Hume-Rothery phases that is stabilized by the Fermi sphere-Brillouin zone interaction. From similar considerations for alkali and alkaline-earth elements a necessary condition for structural stability emerges in which the valence electrons band overlaps with the upper core electrons and the valence electron count increases under compression.

  10. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3

    PubMed Central

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel; Feng, Xiao; Ou, Yunbo; He, Ke; Xue, Qi-Kun

    2015-01-01

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb)2Te3 (CBST) films grown on SrTiO3 (1 1 1) substrates with and without a Te capping layer. We find that both the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures. PMID:26123202

  11. Scalable Silicon Nanostructuring for Thermoelectric Applications

    NASA Astrophysics Data System (ADS)

    Koukharenko, E.; Boden, S. A.; Platzek, D.; Bagnall, D. M.; White, N. M.

    2013-07-01

    The current limitations of commercially available thermoelectric (TE) generators include their incompatibility with human body applications due to the toxicity of commonly used alloys and possible future shortage of raw materials (Bi-Sb-Te and Se). In this respect, exploiting silicon as an environmentally friendly candidate for thermoelectric applications is a promising alternative since it is an abundant, ecofriendly semiconductor for which there already exists an infrastructure for low-cost and high-yield processing. Contrary to the existing approaches, where n/ p-legs were either heavily doped to an optimal carrier concentration of 1019 cm-3 or morphologically modified by increasing their roughness, in this work improved thermoelectric performance was achieved in smooth silicon nanostructures with low doping concentration (1.5 × 1015 cm-3). Scalable, highly reproducible e-beam lithographies, which are compatible with nanoimprint and followed by deep reactive-ion etching (DRIE), were employed to produce arrays of regularly spaced nanopillars of 400 nm height with diameters varying from 140 nm to 300 nm. A potential Seebeck microprobe (PSM) was used to measure the Seebeck coefficients of such nanostructures. This resulted in values ranging from -75 μV/K to -120 μV/K for n-type and 100 μV/K to 140 μV/K for p-type, which are significant improvements over previously reported data.

  12. Quantum transport in topological insulator nanoribbon field effect and Josephson devices

    NASA Astrophysics Data System (ADS)

    Kayyalha, Morteza; Jauregui, Luis; Kazakov, Aleksander; Pettes, Michael; Miotkowski, Ireneusz; Shi, Li; Rokhinson, Leonid; Chen, Yong

    The spin-helical topological surface states (TSS) of topological insulators have attracted great attention in the past few years as an excellent platform to study topological transport and other exotic physics such as Majorana fermions. Here we present experiments studying quantum transport of TSS in topological insulator nanoribbon (TINR) field effect devices with normal as well as superconducting contacts. In Bi2Te3 NRs with normal contacts, we observe that the conductance vs. axial magnetic field exhibits Aharonov-Bohm (AB) oscillations with an alternating phase of zero and π, depending periodically on the Fermi momentum kF tuned by an applied back-gate voltage, consistent with the 1D sub-band structure formed by circumferentially quantized TSS. We also investigated the Josephson effects in BiSbTeSe2 TINRs with superconducting Nb contacts. We measured the gate voltage and temperature dependence of the supercurrent and multiple Andreev reflections (MAR), to probe phase coherent transport via TSS

  13. Development of a Measurement System for the Figure of Merit in the High-Temperature Region

    NASA Astrophysics Data System (ADS)

    Iwasaki, H.; Yamamoto, T.; Kim, H.; Nakamoto, G.

    2013-07-01

    New equipment has been developed for evaluating the figure of merit, ZT, on the basis of the Harman method in the temperature range between room temperature and 650 K. In this temperature range, the sample holder in the vacuum chamber has a different construction as compared with the sample holder constructed for the temperature range below room temperature. Several issues that need to be considered, such as compensation for the thermal radiation effect, suppression of heat leakage from the lead wires, and the setup method for the lead wires on the sample, are examined in the considered temperature region. Evaluations of ZT are successfully made for typical thermoelectric materials, (Bi,Sb)2Te3 and CeFe3CoSb12. We then demonstrate that the influence of thermal radiation between the high- and low-temperature edges of the sample induced by the Peltier effect on the estimated value of ZT is negligible at around 600 K. Furthermore, the change in the thermoelectric properties due to repetition of the thermal cycle is studied, and a typical hysteresis behavior is observed in the considered thermoelectric materials. It is revealed that heating the sample to a high temperature causes a change in its thermoelectric properties, which one must take into account for practical applications of thermoelectric materials.

  14. Role of trivalent antimony in the removal of As, Sb, and Bi impurities from copper electrolytes

    NASA Astrophysics Data System (ADS)

    Xiao, Fa-xin; Cao, Dao; Mao, Jian-wei; Shen, Xiao-ni; Ren, Feng-zhang

    2013-01-01

    The role of trivalent antimony was investigated in removing As, Sb, and Bi impurities from a copper electrolyte. Purification experiments were carried out by adding a various concentrations of Sb(III) ions in a synthetic electrolyte containing 185 g/L sulfuric acid, 45 g/L Cu2+, 10 g/L As, and 0.5 g/L Bi under stirring at 65°C for 2 h. The electrolyte was filtered, and the structure, morphology and composition of the precipitate were analyzed by means of chemical analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and IR spectroscopy. The precipitate is composed of irregular lumps which are agglomerated by fine dendritic and floccus particles, and it mainly consists of As, Sb, Bi, and O elements. Characteristic bands in the IR spectra of the precipitate are As-OX (X=As, Sb, Bi), Sb-OY (Y=Sb, Bi), O-As-O, As-OH, Sb-OH, and O-H. The precipitate is a mixture of microcrystalline SbAsO4, (Sb,As)2O3, and amorphous phases. As, Sb, and Bi impurities are effectively removed from the copper electrolyte by Sb(III) ions attributing to these precipitates.

  15. Modelling of segmented high-performance thermoelectric generators with effects of thermal radiation, electrical and thermal contact resistances

    NASA Astrophysics Data System (ADS)

    Ouyang, Zhongliang; Li, Dawen

    2016-04-01

    In this study, segmented thermoelectric generators (TEGs) have been simulated with various state-of-the-art TE materials spanning a wide temperature range, from 300 K up to 1000 K. The results reveal that by combining the current best p-type TE materials, BiSbTe, MgAgSb, K-doped PbTeS and SnSe with the strongest n-type TE materials, Cu-Doped BiTeSe, AgPbSbTe and SiGe to build segmented legs, TE modules could achieve efficiencies of up to 17.0% and 20.9% at ΔT = 500 K and ΔT = 700 K, respectively, and a high output power densities of over 2.1 Watt cm‑2 at the temperature difference of 700 K. Moreover, we demonstrate that successful segmentation requires a smooth change of compatibility factor s from one end of the TEG leg to the other, even if s values of two ends differ by more than a factor of 2. The influence of the thermal radiation, electrical and thermal contact effects have also been studied. Although considered potentially detrimental to the TEG performance, these effects, if well-regulated, do not prevent segmentation of the current best TE materials from being a prospective way to construct high performance TEGs with greatly enhanced efficiency and output power density.

  16. Thermoelectric microdevice fabricated by a MEMS-like electrochemical process.

    PubMed

    Snyder, G Jeffrey; Lim, James R; Huang, Chen-Kuo; Fleurial, Jean-Pierre

    2003-08-01

    Microelectromechanical systems (MEMS) are the basis of many rapidly growing technologies, because they combine miniature sensors and actuators with communications and electronics at low cost. Commercial MEMS fabrication processes are limited to silicon-based materials or two-dimensional structures. Here we show an inexpensive, electrochemical technique to build MEMS-like structures that contain several different metals and semiconductors with three-dimensional bridging structures. We demonstrate this technique by building a working microthermoelectric device. Using repeated exposure and development of multiple photoresist layers, several different metals and thermoelectric materials are fabricated in a three-dimensional structure. A device containing 126 n-type and p-type (Bi, Sb)2Te3 thermoelectric elements, 20 microm tall and 60 microm in diameter with bridging metal interconnects, was fabricated and cooling demonstrated. Such a device should be of technological importance for precise thermal control when operating as a cooler, and for portable power when operating as a micro power generator. PMID:12883550

  17. Nanotubes from Misfit Layered Compounds: A New Family of Materials with Low Dimensionality.

    PubMed

    Panchakarla, Leela S; Radovsky, Gal; Houben, Lothar; Popovitz-Biro, Ronit; Dunin-Borkowski, Rafal E; Tenne, Reshef

    2014-11-01

    Nanotubes that are formed from layered materials have emerged to be exciting one-dimensional materials in the last two decades due to their remarkable structures and properties. Misfit layered compounds (MLC) can be produced from alternating assemblies of two different molecular slabs with different periodicities with the general formula [(MX)1+x]m[TX2]n (or more simply MS-TS2), where M is Sn, Pb, Bi, Sb, rare earths, T is Sn, Nb, Ta, Ti, V, Cr, and so on, and X is S, Se. The presence of misfit stresses between adjacent layers in MLC provides a driving force for curling of the layers that acts in addition to the elimination of dangling bonds. The combination of these two independent forces leads to the synthesis of misfit layered nanotubes, which are newcomers to the broad field of one-dimensional nanostructures and nanotubes. The synthesis, characterization, and microscopic details of misfit layered nanotubes are discussed, and directions for future research are presented. PMID:26278742

  18. Visualization of superparamagnetic dynamics in magnetic topological insulators

    NASA Astrophysics Data System (ADS)

    Lachman, E.; Young, A. F.; Richardella, A.; Cuppens, J.; Hr, N.; Anahory, Y.; Meltzer, A. Y.; Kandala, A.; Kempinger, S.; Myasoedov, Y.; Huber, M. E.; Samarth, N.; Zeldov, E.

    Magnetically doped topological insulators have recently been shown to host a quantum anomalous Hall (QAH) state at low temperatures. Using scanning nanoSQUID magnetic imaging on a Cr-doped (Bi , Sb) 2 Te3 thin film[1], we reveal that the magnetic structure of magnetically doped topological insulators is not ferromagnetic as assumed so far. In fact it is superparamagnetic, formed by weakly interacting magnetic domains. These domains have a characteristic size of a few tens of nanometers, and undergo random reversals which drive the electronic state from one Hall plateau to the other. The superparamagnetic state is metastable, with small energy barriers to relaxation. We observe magnetic relaxation even at 300 mK, evident also in transport measurements. Unexpectedly, magnetic relaxation can also be induced by varying the gate voltage, and we propose a mechanism for the influence of the electronic phase on the magnetic relaxation. We speculate that the dynamic nature of magnetic disorder in QAH systems may contribute to the observed fragility of the QAH state at elevated temperatures.

  19. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3

    NASA Astrophysics Data System (ADS)

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel; Feng, Xiao; Ou, Yunbo; He, Ke; Xue, Qi-Kun

    2015-06-01

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb)2Te3 (CBST) films grown on SrTiO3 (1 1 1) substrates with and without a Te capping layer. We find that both the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures.

  20. Field induced gap infrared detector

    NASA Technical Reports Server (NTRS)

    Elliott, C. Thomas (Inventor)

    1990-01-01

    A tunable infrared detector which employs a vanishing band gap semimetal material provided with an induced band gap by a magnetic field to allow intrinsic semiconductor type infrared detection capabilities is disclosed. The semimetal material may thus operate as a semiconductor type detector with a wavelength sensitivity corresponding to the induced band gap in a preferred embodiment of a diode structure. Preferred semimetal materials include Hg(1-x)Cd(x)Te, x is less than 0.15, HgCdSe, BiSb, alpha-Sn, HgMgTe, HgMnTe, HgZnTe, HgMnSe, HgMgSe, and HgZnSe. The magnetic field induces a band gap in the semimetal material proportional to the strength of the magnetic field allowing tunable detection cutoff wavelengths. For an applied magnetic field from 5 to 10 tesla, the wavelength detection cutoff will be in the range of 20 to 50 micrometers for Hg(1-x)Cd(x)Te alloys with x about 0.15. A similar approach may also be employed to generate infrared energy in a desired band gap and then operating the structure in a light emitting diode or semiconductor laser type of configuration.

  1. Optimizing Thermoelectric Properties in Composites

    NASA Astrophysics Data System (ADS)

    Adams, Michael J.; Jin, Hyungyu; Heremans, Joseph P.

    Here we consider semiconductor composites as a way to yield high thermoelectric figure of merit. Effective medium theory limits the figure of merit of a composite made from two non-interacting materials, A and B, to the larger of the two. In previous work, we describe a mechanism that can lift this limitation by treating charge and heat flux separately. Silica beads coated with a conducting shell are inserted into a thermoelectric host. Thermal conductivity decreases with insulating material added, but electrical conductivity is maintained via locally conducting surfaces. We apply the theory to p-type (Bi,Sb)2Te3 host material. Several permutations are possible: Te-coated beads in Sb-rich material, or Sb-coated beads in Te-rich material. First, we review data for varying bead coatings and heat treatments, followed by varying stoichiometry in the host. New data considers an additional parameter of varying bead diameter, as well as optimizing these parameters simultaneously to enhance thermoelectric performance.

  2. Semiconductors for thermoelectric and spin-thermal solid-state energy conversion

    NASA Astrophysics Data System (ADS)

    Heremans, Joseph P.

    2013-03-01

    The recent decade has seen a doubling of the efficiency of thermoelectric converters through the use of nanotechnology. Here we first outline how specific doping impurities in semiconductors, called resonant levels, mimic the effects of nanostructures and give the same benefits in bulk semiconductors. Resonant impurities catalyse the formation of new bands in semiconductors, which can be engineered to tailor the thermopower. The result is an efficiency increase of 50% in BiSb and more in PbTe. Then, we describe a new solid-state heat-to-electricity conversion mechanism, the spin-Seebeck effect, which arises from driving spinpolarized particles out of thermal equilibrium. This generates a spin flux that is converted into a voltage in a non-polarized adjacent material; the effect can be as large as the highest thermoelectric voltages in semiconductors. Nanotechnologies and these new effects add new design variables to the old problem of optimizing the thermoelectric figure of merit, resulting in much improved thermal efficiencies.

  3. Thermoelectric power factor performance of Bi85Sb15/graphene composite

    NASA Astrophysics Data System (ADS)

    El-Asfoury, Mohamed S.; Nasr, Mohamed N. A.; Nakamura, Koichi; Abdel-Moneim, Ahmed

    2016-04-01

    Composite materials based on Bi85Sb15 with commercial graphene (Gr) nanoparticles have been synthesized by mechanical alloying and hot isostatic pressing. The effect of different amount of Gr nanoparticles (x = 0.02, 0.04, 0.06, and 0.08 wt %) on the thermoelectric properties of (Bi85Sb15)1- x Gr x composite was investigated. X-ray diffraction and scanning electron microscopy were carried out for the structure characterization of the composites. Transport properties, including electrical resistivity, Seebeck coefficient, and calculated power factor, were investigated and their variations were discussed with regard to microstructures in the temperature range of 173-373 K. Resistivity significantly declines in the sample with x = 0.04 wt % Gr, and the enhancement was 7% at 230 K and reached about 7.6% at room temperature. With 0.08 wt % Gr, a high absolute value of the Seebeck coefficient was observed. The power factor reaches its maximum of 3.7 × 10-3 W·m-1·K-2 with x = 0.08 wt % at 173 K. The results reflect that this synthesis process can be a powerful method of obtaining homogeneous Bi-Sb thermoelectric composite materials rapidly and at low cost. In addition, the demand for uniform coherent composites was significant because of their high-performance transport properties.

  4. Electrical Probing of Inherent Spin Polarization in a Topological Insulator with Electrical Gating

    NASA Astrophysics Data System (ADS)

    Lee, Joon Sue; Richardella, Anthony; Samarth, Nitin

    2015-03-01

    The hallmark of a time-reversal symmetry protected three-dimensional topological insulator is the helically spin-textured surface state. Although electrical detection of spin polarization in topological insulators has been demonstrated very recently, there have not been any electrical measurements to demonstrate the entire mapping of the spin polarization throughout the surface state. We report the electrical probing of the spin-polarized surface state using a magnetic tunnel junction as a spin detector while the chemical potential of a topological insulator (Bi,Sb)2Te3 is tuned by back gating. Hysteretic spin signals were observed as the magnetization of the detector ferromagnet (permalloy) switches with in-plane magnetic field. Changing the direction of bias current through the topological insulator channel flips the direction of the spin polarization, resulting in the reverse of sign of the detected spin signals. We demonstrate the control of the Fermi energy, which has importance not only in further understanding of the spin-momentum locking in the surface state but also in possible electrical tuning of the spin polarization for potential spin-based devices. Supported by C-SPIN & DARPA/SRC.

  5. Duo gating on a 3D topological insulator - independent tuning of both topological surface states

    NASA Astrophysics Data System (ADS)

    Li, Chuan; de Ronde, Bob; Snelder, Marieke; Stehno, Martin; Huang, Yingkai; Golden, Mark; Brinkman, Alexander; ICE Team; IOP Collaboration

    ABSTRACT: Topological insulators are associated with a trove of exciting physics, such as the ability to host robust anyons, Majorana Bound States, which can be used for quantum computation. For future Majorana devices it is desirable to have the Fermi energy tuned as close as possible to the Dirac point of the topological surface state. Based on previous work on gating BSTS, we report the experimental progress towards gate-tuning of the top and bottom topological surface states of BiSbTeSe2 crystal flakes. When the Fermi level is moved across the Dirac point conduction is shown to change from electron dominated transport to hole dominated transport independently for either surface. In the high magnetic field, one can tune the system precisely between the different landau levels of both surfaces, thus a full gating map of the possible landau levels combination is established. In addition, we provide a simple capacitance model to explain the general hysteresis behaviors in topological insulator systems.

  6. Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators

    NASA Astrophysics Data System (ADS)

    Chang, Cui-Zu; Li, Mingda

    2016-03-01

    The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to exhibit quantized Hall conductivity {σyx}=\\frac{{{e}2}}{h} without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. In this topical review, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies.

  7. Persistent optical gating of a topological insulator

    PubMed Central

    Yeats, Andrew L.; Pan, Yu; Richardella, Anthony; Mintun, Peter J.; Samarth, Nitin; Awschalom, David D.

    2015-01-01

    The spin-polarized surface states of topological insulators (TIs) are attractive for applications in spintronics and quantum computing. A central challenge with these materials is to reliably tune the chemical potential of their electrons with respect to the Dirac point and the bulk bands. We demonstrate persistent, bidirectional optical control of the chemical potential of (Bi,Sb)2Te3 thin films grown on SrTiO3. By optically modulating a space-charge layer in the SrTiO3 substrates, we induce a persistent field effect in the TI films comparable to electrostatic gating techniques but without additional materials or processing. This enables us to optically pattern arbitrarily shaped p- and n-type regions in a TI, which we subsequently image with scanning photocurrent microscopy. The ability to optically write and erase mesoscopic electronic structures in a TI may aid in the investigation of the unique properties of the topological insulating phase. The gating effect also generalizes to other thin-film materials, suggesting that these phenomena could provide optical control of chemical potential in a wide range of ultrathin electronic systems. PMID:26601300

  8. Memristive Switching in Bi(1-x)Sb(x) Nanowires.

    PubMed

    Han, Nalae; Park, Myung Uk; Yoo, Kyung-Hwa

    2016-04-13

    We investigated the memristive switching behavior in bismuth-antimony alloy (Bi(1-x)Sb(x)) single nanowire devices at 0.1 ≤ x ≤ 0.42. At 0.15 ≤ x ≤ 0.42, most Bi(1-x)Sb(x) single nanowire devices exhibited bipolar resistive switching (RS) behavior with on/off ratios of approximately 10(4) and narrow variations in switching parameters. Moreover, the resistance values in the low-resistance state (LRS) were insensitive to x. On the other hand, at 0.1 ≤ x ≤ 0.15, some Bi(1-x)Sb(x) single nanowire devices showed complementary RS-like behavior, which was ascribed to asymmetric contact properties. Transmission electron microscopy and elemental mapping images of Bi, Sb, and O obtained from the cross sections of the Bi(1-x)Sb(x) single nanowire devices, which were cut before and after RS, revealed that the mobile species was Sb ions, and the migration of the Sb ions to the nanowire surface brought the switch to LRS. In addition, we demonstrated that two types of synaptic plasticity, namely, short-term plasticity and long-term potentiation, could be implemented in Bi(1-x)Sb(x) nanowires by applying a sequence of voltage pulses with different repetition intervals. PMID:27042861

  9. Optimizing Spin Generation in 2D Materials: Topological Insulators and Graphene

    NASA Astrophysics Data System (ADS)

    Chen, Ching-Tzu

    Novel two-dimensional electronic systems with Dirac-like dispersion present unique opportunities for spintronic applications. In this seminar I will discuss two specific examples. First we examine the potential of topological insulators as spin-source materials. Using a new spin-polarized tunneling method, giant charge-spin conversion efficiency in topological insulators is revealed, well exceeding that in conventional magnetic tunnel junctions. Through a comparative study between Bi2Se3 and (Bi,Sb)2Te3, we verify the topological-surface-state origin of the observed giant spin signals and further extract the energy dependence of the effective spin polarization in Bi2Se3. Next we explore the potential of interfacial exchange interaction in 2D materials for spin control and spin generation. Using graphene as a prototype, we demonstrate that its coupling to a model magnetic insulator (EuS) produces a substantial magnetic exchange field (>14 T), which yields orders-of-magnitude enhancement in the spin signal originated from the Zeeman spin-Hall effect. Furthermore, the strong exchange field lifts the spin degeneracy of graphene in the quantum Hall regime, which may lead to interesting spin-polarized edge transport and thus open up new application space for classical and quantum information processing.

  10. Quantum transport of two-species Dirac fermions in dual-gated three-dimensional topological insulators

    PubMed Central

    Xu, Yang; Miotkowski, Ireneusz; Chen, Yong P.

    2016-01-01

    Topological insulators are a novel class of quantum matter with a gapped insulating bulk, yet gapless spin-helical Dirac fermion conducting surface states. Here, we report local and non-local electrical and magneto transport measurements in dual-gated BiSbTeSe2 thin film topological insulator devices, with conduction dominated by the spatially separated top and bottom surfaces, each hosting a single species of Dirac fermions with independent gate control over the carrier type and density. We observe many intriguing quantum transport phenomena in such a fully tunable two-species topological Dirac gas, including a zero-magnetic-field minimum conductivity close to twice the conductance quantum at the double Dirac point, a series of ambipolar two-component half-integer Dirac quantum Hall states and an electron-hole total filling factor zero state (with a zero-Hall plateau), exhibiting dissipationless (chiral) and dissipative (non-chiral) edge conduction, respectively. Such a system paves the way to explore rich physics, ranging from topological magnetoelectric effects to exciton condensation. PMID:27142344

  11. Magnetic-Field Dependence of Thermoelectric Properties of Sintered Bi90Sb10 Alloy

    NASA Astrophysics Data System (ADS)

    Murata, Masayuki; Yamamoto, Atsushi; Hasegawa, Yasuhiro; Komine, Takashi

    2016-03-01

    The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit ( ZT) of a sintered Bi90Sb10 alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered Bi90Sb10 alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77-300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the Bi90Sb10 alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L- and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model.

  12. Ion exchange defines the biological activity of titanate nanotubes.

    PubMed

    Rónavári, Andrea; Kovács, Dávid; Vágvölgyi, Csaba; Kónya, Zoltán; Kiricsi, Mónika; Pfeiffer, Ilona

    2016-05-01

    One-dimensional titanate nanotubes (TiONTs) were subjected to systematic ion exchange to determine the impact of these modifications on biological activities. Ion exchanged TiONTs (with Ag, Mg, Bi, Sb, Ca, K, Sr, Fe, and Cu ions) were successfully synthesized and the presence of the substituted ions was verified by energy dispersive X-ray spectroscopy (EDS). A complex screening was carried out to reveal differences in toxicity to human cells, as well as in antibacterial, antifungal, and antiviral activities between the various modified nanotubes. Our results demonstrated that Ag ion exchanged TiONTs exerted potent antibacterial and antifungal effects against all examined microbial species but were ineffective on viruses. Surprisingly, the antibacterial activity of Cu/TiONTs was restricted to Micrococcus luteus. Most ion exchanged TiONTs did not show antimicrobial activity against the tested bacterial and fungal species. Incorporation of various ions into nanotube architectures lead to mild, moderate, or even to a massive loss of human cell viability; therefore, this type of biological effect exerted by TiONTs can be greatly modulated by ion exchange. These findings further emphasize the contribution of ion exchange in determining not only the physical and chemical characteristics but also the bioactivity of TiONT against different types of living cells. PMID:26972521

  13. Surface-Micromachined Planar Arrays of Thermopiles

    NASA Technical Reports Server (NTRS)

    Foote, Marc C.

    2003-01-01

    Planar two-dimensional arrays of thermopiles intended for use as thermal-imaging detectors are to be fabricated by a process that includes surface micromachining. These thermopile arrays are designed to perform better than do prior two-dimensional thermopile arrays. The lower performance of prior two-dimensional thermopile arrays is attributed to the following causes: The thermopiles are made from low-performance thermoelectric materials. The devices contain dielectric supporting structures, the thermal conductances of which give rise to parasitic losses of heat from detectors to substrates. The bulk-micromachining processes sometimes used to remove substrate material under the pixels, making it difficult to incorporate low-noise readout electronic circuitry. The thermoelectric lines are on the same level as the infrared absorbers, thereby reducing fill factor. The improved pixel design of a thermopile array of the type under development is expected to afford enhanced performance by virtue of the following combination of features: Surface-micromachined detectors are thermally isolated through suspension above readout circuitry. The thermopiles are made of such high-performance thermoelectric materials as Bi-Te and Bi-Sb-Te alloys. Pixel structures are supported only by the thermoelectric materials: there are no supporting dielectric structures that could leak heat by conduction to the substrate.

  14. Transport studies of mesoscopic and magnetic topological insulators

    NASA Astrophysics Data System (ADS)

    Kandala, Abhinav

    integration of GdN with Bi2Se 3 thin films. Careful structural, magnetic and electrical characterization of the heterostructures is employed to confirm that the magnetic species is solely restricted to the surface, and that the ferromagnetic GdN layer to be insulating, ensuring current flow solely through the TI layer. We also devise a novel device geometry that enables direct comparison of the magneto-transport properties of TI films with and without proximate magnetism, all, in a single device. A comparative study of weak anti-localization suggested that the overlying GdN suppressed quantum interference in the top surface state. In our second generation heterostructure devices, GdN is interfaced with low-carrier density, gate-tunable thin films of (Bi,Sb)2Te3 grown on SrTiO 3 substrates. These devices enable us to map out the comparison of magneto-transport, as the chemical potential is tuned from the bulk conduction band into the bulk valence band. In a second approach to study the effects of magnetism on TI's, I shall present, in Chapter 5, our results from magnetic doping of (Bi,Sb) 2Te3 thin films with Cr -- a system that was recently demonstrated to be a Quantum Anomalous Hall (QAH) insulator. In a Cr-rich regime, a highly insulating, high Curie temperature ferromagnetic phase is achieved. However, a careful, iterative process of tuning the composition of this complex alloy enabled access to the QAHE regime, with the observation of near dissipation-less transport and perfect Hall quantization at zero external field. Furthermore, we demonstrate a field tilt driven crossover between a quantum anomalous Hall phase and a gapless, ferromagnetic TI phase. This crossover manifests itself in an electrically tunable, giant anisotropic magneto-resistance effect that we employ as a quantitative probe of edge transport in this system.

  15. Grain Refinement of Deoxidized Copper

    NASA Astrophysics Data System (ADS)

    Balart, María José; Patel, Jayesh B.; Gao, Feng; Fan, Zhongyun

    2016-08-01

    This study reports the current status of grain refinement of copper accompanied in particular by a critical appraisal of grain refinement of phosphorus-deoxidized, high residual P (DHP) copper microalloyed with 150 ppm Ag. Some deviations exist in terms of the growth restriction factor (Q) framework, on the basis of empirical evidence reported in the literature for grain size measurements of copper with individual additions of 0.05, 0.1, and 0.5 wt pct of Mo, In, Sn, Bi, Sb, Pb, and Se, cast under a protective atmosphere of pure Ar and water quenching. The columnar-to-equiaxed transition (CET) has been observed in copper, with an individual addition of 0.4B and with combined additions of 0.4Zr-0.04P and 0.4Zr-0.04P-0.015Ag and, in a previous study, with combined additions of 0.1Ag-0.069P (in wt pct). CETs in these B- and Zr-treated casts have been ascribed to changes in the morphology and chemistry of particles, concurrently in association with free solute type and availability. No further grain-refining action was observed due to microalloying additions of B, Mg, Ca, Zr, Ti, Mn, In, Fe, and Zn (~0.1 wt pct) with respect to DHP-Cu microalloyed with Ag, and therefore are no longer relevant for the casting conditions studied. The critical microalloying element for grain size control in deoxidized copper and in particular DHP-Cu is Ag.

  16. Experiments on a Cooper pair insulator

    NASA Astrophysics Data System (ADS)

    Nguyen, Hung Q.

    At temperatures below 1K, nm thick a-Bi/Sb films, patterned with a nanohoneycomb array of holes, exhibit a novel electronic state consisting of localized Cooper pairs[1]. The Superconductor Insulator Transition (SIT), a phenomenon where the ground state of electrons is tuned from a superconducting to an insulating state, on this patterned homogeneous system shows a clear bosonic nature with activated transport on the insulating side. To date, this homogeneous system is the only one that shows clear evidence for the localization of Cooper pairs. Experiments are described that were performed to further characterize the properties of the localized Cooper pair state and its superconductor to insulator transitions. We show that: (i) The shape of the magnetoresistance (MR) oscillations, which indicate the presence of Cooper pairs in these multiply connected systems, depends on the geometry of the underlying substrates, but not on parameters like the temperature or thickness of the films. The magnetic field tuned SITs of films that are just thick enough to superconduct at zero magnetic field exhibit a common critical sheet resistance separating the superconducting and insulating phases in the range of 3.5 to 5kO. We also report a new type of SIT, an incommensurability driven SIT, which occurs due to the interplay of magnetic field and disorder in the arrangement of the honeycomb array of holes. (ii) The Cooper pair insulator state exhibits a giant positive MR, which peaks at a field estimated to be sufficient to break the pairs. The electrical transport on the low field side of the peak is activated. At the highest fields, it resembles G ˜ log(T), which is consistent with the behavior expected for weakly localized electrons rather than strongly localized Cooper pairs. We discuss this MR peak, compare it to that observed in other amorphous systems and propose a zero temperature phase diagram for these films.

  17. Prospects of nanostructures Bi1-XSbx for thermoelectricity

    NASA Astrophysics Data System (ADS)

    Nikolaeva, Albina A.; Konopko, Leonid A.; Huber, Tito E.; Bodiul, Pavel P.; Popov, Ivan A.

    2012-06-01

    There is renewed focus on the thermoelectric properties of Bi-Sb. Reduced dimensionality samples of these alloys, such as nanowires, may exhibit exotic behavior that relate to the properties of the surfaces of topological insulators. It has been predicted that surface states of topological insulators have large thermopower and also ultrahigh mobilities. The authors report results of magneto-thermoelectric investigation of single crystal Bi1-xSbx nanowires in a glass cover with diameters ranging from 90 nm to 5 μm. The wide-ranging antimony concentration (0.01 < x < 0.2) enabled us to study the effect of nanowire dimensionality the (bulk) semimetal (x <0.05), semi-conductor 0.08

  18. Natural versus anthropogenic inhalable aerosol chemistry of transboundary East Asian atmospheric outflows into western Japan.

    PubMed

    Moreno, Teresa; Kojima, Tomoko; Querol, Xavier; Alastuey, Andrés; Amato, Fulvio; Gibbons, Wes

    2012-05-01

    The eastward transport of aerosols exported from mainland Asia strongly influences air quality in the Japanese archipelago. The bulk of the inhalable particulate matter (PM(10)) in these intrusions comprises either natural, desert-derived minerals (mostly supermicron silicates) or anthropogenic pollutants (mostly submicron sulphates), in various states of mixing. We analyse PM(10) collected in Kumamoto, SW Japan, during three contrasting types of aerosol intrusions, the first being dominated by desert PM which became increasingly mixed with anthropogenic components as time progressed, the second being a relatively minor event mixing fine, distal desert PM with anthropogenic materials, and the third being dominated by anthropogenic pollutants. Whereas the chemistry of the natural mineral component is characterised by "crustal" elements (Si, Al, Fe, Mg, K, Li, P, Sc, V, Rb, Sr, Zr, Th, lanthanoids), the anthropogenic component is rich in secondary inorganic compounds and more toxic metallic elements (NH(4)(+), SO(4)(2-), As, Pb, Cd, Cu, Zn, Sn, Bi, Sb, and Ge). Some desert-dust (Kosa) intrusions are more calcareous than others, implicating geologically different source areas, and contain enhanced levels of NO(3)(-), probably as supermicron Ca(NO(3))(2) particles produced by chemical reaction between NOx pollutants (mostly from industry and traffic) and carbonate during atmospheric transport. The overall trace element chemistry of aerosol intrusions into Kumamoto shows low V/Rb, low NO(3)(-)/SO(4)(2-), enhanced As levels, and unfractionated La/Ce values, which are all consistent with anthropogenic sources including coal emissions rather than those derived from the refining and combustion of oil fractionates. Geographically dispersed, residual sulphatic plumes of this nature mix with local traffic (revealed by OC and EC concentrations) and industrial emissions and dissipate only slowly, due to the dominance of submicron accumulation mode PM which is atmospherically

  19. The electronic structure and thermoelectric properties of BiTl{sub 9}Te{sub 6} and SbTl{sub 9}Te{sub 6}: First-principles calculations

    SciTech Connect

    Guo, Li Bin; Ye, Lingyun; Wang, Yuan Xu Yang, Jue Ming; Yan, Yu Li; Ren, Feng Zhu

    2015-12-21

    The electronic structure and thermoelectric properties of MTl{sub 9}Te{sub 6} (M = Bi, Sb) were studied using density functional theory and the semiclassical Boltzmann theory. It is found that the band gaps of BiTl{sub 9}Te{sub 6} and SbTl{sub 9}Te{sub 6} are equal to 0.59 eV and 0.72 eV, respectively. The relative large band gap and strong coupling between Sb s and Te p are helpful to the thermoelectric properties of SbTl{sub 9}Te{sub 6}. Near the bottom of the conduction bands, the number of band valleys of SbTl{sub 9}Te{sub 6} is four and is larger than that of BiTl{sub 9}Te{sub 6} (two band valleys), which will increase its Seebeck coefficient. Although BiTl{sub 9}Te{sub 6} has a larger electrical conductivity relative to relaxation time (σ/τ) along the z-direction than that of SbTl{sub 9}Te{sub 6}, the results show that the transport properties of SbTl{sub 9}Te{sub 6} are better than those of BiTl{sub 9}Te{sub 6} possibly due to its large Seebeck coefficient. The maximum value of power factor relative to relaxation time (S{sup 2}σ/τ) for SbTl{sub 9}Te{sub 6} reaches 4.30 × 10{sup 11 }W/K{sup 2} m s at 900 K, that is, originated from its relatively large Seebeck coefficient, suggesting its promising thermoelectric performance at high temperature.

  20. Selective oxidation of alkanes and/or alkenes to valuable oxygenates

    DOEpatents

    Lin, Manhua; Pillai, Krishnan S.

    2011-02-15

    A catalyst, its method of preparation and its use for producing at least one of methacrolein and methacrylic acid, for example, by subjecting isobutane or isobutylene or a mixture thereof to a vapor phase catalytic oxidation in the presence of air or oxygen. In the case where isobutane alone is subjected to a vapor phase catalytic oxidation in the presence of air or oxygen, the product is at least one of isobutylene, methacrolein and methacrylic acid. The catalyst comprises a compound having the formula A.sub.aB.sub.bX.sub.xY.sub.yZ.sub.zO.sub.o wherein A is one or more elements selected from the group of Mo, W and Zr, B is one or more elements selected from the group of Bi, Sb, Se, and Te, X is one or more elements selected from the group of Al, Bi, Ca, Ce, Co, Fe, Ga, Mg, Ni, Nb, Sn, W and Zn, Y is one or more elements selected from the group of Ag, Au, B, Cr, Cs, Cu, K, La, Li, Mg, Mn, Na, Nb, Ni, P, Pb, Rb, Re, Ru, Sn, Te, Ti, V and Zr, and Z is one or more element from the X or Y groups or from the following: As, Ba, Pd, Pt, Sr, or mixtures thereof, and wherein a=1, 0.05

  1. Geology, petrography, geochemistry, and genesis of sulfide-rich pods in the Lac des Iles palladium deposits, western Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Duran, Charley J.; Barnes, Sarah-Jane; Corkery, John T.

    2016-04-01

    The Lac des Iles Pd deposits are known for their Pd-rich sulfide-poor mineralization. However, previously undocumented sulfide-rich pods also occur within the intrusion that hosts the deposits. Given the complex magmatic and hydrothermal history of the mineralization at Lac des Iles, the sulfide-rich pods could have crystallized from magmatic sulfide liquids or precipitated from hydrothermal fluids. Sulfide-rich pods occur throughout the stratigraphy, in all rock types, and along comagmatic shear zones, and contain net-textured to massive sulfides. They can be divided into four main groups based on the variation in mineral assemblages: (1) pyrrhotite-pentlandite ± pyrite-chalcopyrite-magnetite-ilmenite; (2) chalcopyrite ± pyrrhotite-pentlandite-pyrite-magnetite-ilmenite; (3) pyrite ± pentlandite-chalcopyrite-pyrrhotite-magnetite-ilmenite; and (4) magnetite ± ilmenite-pyrrhotite-pentlandite-pyrite-chalcopyrite. Whole rock metal contents and S isotopic compositions do not change with the amount of pyrite present, except for slight enrichments in As and Bi. The presence of an essentially magmatic sulfide mineral assemblage (pyrrhotite-pentlandite ± chalcopyrite) with pentlandite exsolution flames in pyrrhotite in some pods suggests that the pods crystallized from magmatic sulfide liquids. The very low Cu contents of the pods suggests that they are mainly cumulates of monosulfide solid solution (MSS). We propose a model whereby sulfide liquids were concentrated into dilation zones prior to crystallizing cumulus MSS. Intermediate solid solution crystallized from the fractionated liquids at the edges of some pods leaving residual liquids enriched in Pt, Pd, Au, As, Bi, Sb, and Te. These residual liquids are no longer associated with the pods. During subsequent alteration, pyrite replaced MSS/pyrrhotite, but this did not affect the platinum-group element contents of the pods.

  2. Environmental assessment of the arsenic-rich, Rodalquilar gold-(copper-lead-zinc) mining district, SE Spain: data from soils and vegetation

    NASA Astrophysics Data System (ADS)

    Oyarzun, Roberto; Cubas, Paloma; Higueras, Pablo; Lillo, Javier; Llanos, Willians

    2009-08-01

    The Rodalquilar mineral deposits (SE Spain) were formed in Miocene time in relation to caldera volcanic episodes and dome emplacement phenomena. Two types of ore deposits are recognized: (1) the El Cinto epithermal, Au-As high sulphidation vein and breccia type; and (2) peripheral low sulphidation epithermal Pb-Zn-Cu-(Au) veins. The first metallurgical plants for gold extraction were set up in the 1920s and used amalgamation. Cyanide leaching began in the 1930s and the operations lasted until the mid 1960s. The latter left a huge pile of ~900,000-1,250,000 m3 of abandoned As-rich tailings adjacent to the town of Rodalquilar. A frustrated initiative to reactivate the El Cinto mines took place in the late 1980s and left a heap leaching pile of ~120,000 m3. Adverse mineralogical and structural conditions favoured metal and metalloid dispersion from the ore bodies into soils and sediments, whereas mining and metallurgical operations considerably aggravated contamination. We present geochemical data for soils, tailings and wild plant species. Compared to world and local baselines, both the tailings and soils of Rodalquilar are highly enriched in As (mean concentrations of 950 and 180 μg g-1, respectively). Regarding plants, only the concentrations of As, Bi and Sb in Asparagus horridus, Launaea arborescens, Salsola genistoides, and Stipa tenacissima are above the local baselines. Bioaccumulation factors in these species are generally lower in the tailings, which may be related to an exclusion strategy for metal tolerance. The statistical analysis of geochemical data from soils and plants allows recognition of two well-differentiated clusters of elements (As-Bi-Sb-Se-Sn-Te and Cd-Cu-Hg-Pb-Zn), which ultimately reflect the strong chemical influence of both El Cinto and peripheral deposits mineral assemblages.

  3. New Interest in Intermetallic Compound ZnSb

    NASA Astrophysics Data System (ADS)

    Fedorov, M. I.; Prokof'eva, L. V.; Pshenay-Severin, D. A.; Shabaldin, A. A.; Konstantinov, P. P.

    2014-06-01

    The intermetallic compound ZnSb has been known since the 1830s. It has semiconductor properties, but its mechanical, thermal, and chemical properties are very close to those of a metallic alloy. When thermoelectrics based on (BiSb)2(TeSe)3 solid solutions were created, interest in ZnSb subsided. However, the current situation is different, as tellurium has become expensive and rare. Moreover, its compounds are too toxic, and it is too difficult to produce such materials and devices from these solid solutions. Recently, n-type material based on Mg2(SnSi) solid solution was proposed in the Laboratory of Physics for Thermoelements of the Ioffe Physical-Technical Institute. This material together with ZnSb may form a promising couple for creating various thermoelectric modules. In this paper, various properties (Hall and Seebeck coefficients, electrical and thermal conductivities) are reported in the temperature range from 80 K to 797 K. Different acceptor impurities have been tested. The Hall concentration at room temperature varied from 1.5 × 1018 cm-3 to 2.7 × 1019 cm-3. Some features have been discovered in the behavior of the thermoelectric parameters of double-doped ZnSb samples at temperatures above 500 K. Their nature points to a temperature-dependent increase of the Hall concentration. The existence of two temperature ranges with additional doping is revealed by Hall coefficient and electrical conductivity measurements in the range from 80 K to 797 K. The experimental data are discussed based on a model of the energy spectrum with impurity and native defect states localized in the energy gap. It is shown that the dimensionless thermoelectric figure of merit of ZnSb: Cd, Ag, Sn is not less than 1.0 at 600 K.

  4. Modelling of Equilibrium Between Mantle and Core: Refractory, Volatile, and Highly Siderophile Elements

    NASA Technical Reports Server (NTRS)

    Righter, K.; Danielson, L.; Pando, K.; Shofner, G.; Lee, C. -T.

    2013-01-01

    Siderophile elements have been used to constrain conditions of core formation and differentiation for the Earth, Mars and other differentiated bodies [1]. Recent models for the Earth have concluded that the mantle and core did not fully equilibrate and the siderophile element contents of the mantle can only be explained under conditions where the oxygen fugacity changes from low to high during accretion and the mantle and core do not fully equilibrate [2,3]. However these conclusions go against several physical and chemical constraints. First, calculations suggest that even with the composition of accreting material changing from reduced to oxidized over time, the fO2 defined by metal-silicate equilibrium does not change substantially, only by approximately 1 logfO2 unit [4]. An increase of more than 2 logfO2 units in mantle oxidation are required in models of [2,3]. Secondly, calculations also show that metallic impacting material will become deformed and sheared during accretion to a large body, such that it becomes emulsified to a fine scale that allows equilibrium at nearly all conditions except for possibly the length scale for giant impacts [5] (contrary to conclusions of [6]). Using new data for D(Mo) metal/silicate at high pressures, together with updated partitioning expressions for many other elements, we will show that metal-silicate equilibrium across a long span of Earth s accretion history may explain the concentrations of many siderophile elements in Earth's mantle. The modeling includes refractory elements Ni, Co, Mo, and W, as well as highly siderophile elements Au, Pd and Pt, and volatile elements Cd, In, Bi, Sb, Ge and As.

  5. Self-organized charge puddles in a three-dimensional topological material

    NASA Astrophysics Data System (ADS)

    Borgwardt, N.; Lux, J.; Vergara, I.; Wang, Zhiwei; Taskin, A. A.; Segawa, Kouji; van Loosdrecht, P. H. M.; Ando, Yoichi; Rosch, A.; Grüninger, M.

    2016-06-01

    In three-dimensional (3D) topological materials, tuning of the bulk chemical potential is of crucial importance for observing their topological properties; for example, Weyl semimetals require chemical-potential tuning to the bulk Weyl nodes, while 3D topological insulators require tuning into the bulk band gap. Such tuning is often realized by compensation, i.e., by balancing the density of acceptors and donors. Here we show that in such a compensated 3D topological material, the possibility of local chemical-potential tuning is limited by the formation of self-organized charge puddles. The puddles arise from large fluctuations of the Coulomb potential of donors and acceptors. Their emergence is akin to the case of graphene, where charge puddles are already established as a key paradigm. However, there is an important difference: Puddles in graphene are simply dictated by the static distribution of defects in the substrate, whereas we find that puddles in 3D systems self-organize in a nontrivial way and show a strong temperature dependence. Such a self-organization is revealed by measurements of the optical conductivity of the bulk-insulating 3D topological insulator BiSbTeSe2, which pinpoints the presence of puddles at low temperatures as well as their surprising "evaporation" on a temperature scale of 30-40 K. The experimental observation is described semiquantitatively by Monte Carlo simulations. These show that the temperature scale is set by the Coulomb interaction between neighboring dopants and that puddles are destroyed by thermally activated carriers in a highly nonlinear screening process. This result indicates that understanding charge puddles is crucial for the control of the chemical potential in compensated 3D topological materials.

  6. Large strain under a low electric field in lead-free bismuth-based piezoelectrics

    NASA Astrophysics Data System (ADS)

    Ullah, Aman; Won Ahn, Chang; Ullah, Amir; Won Kim, Ill

    2013-07-01

    In this letter, the composition and electric field dependent strain behavior of (1 - x)Bi0.5(Na0.78K0.22)0.5TiO3-xBi(Mg0.5Ti0.5)O3 (BNKT-BMT) were investigated to develop lead-free piezoelectric materials with a large strain response at a low driving field for actuator applications. A large strain of 0.35% (Smax/Emax = 636 pm/V) at an applied field of 55 kV/cm was obtained with a composition of 4 mol. % BMT. In particular, the electric field required to deliver large strains was reduced to a level that revealed not only a large Smax/Emax of 542 pm/V at a driving field as low as 35 kV/cm, but also remarkably suppressed the large hysteresis.

  7. Seasonal distribution of metals in vertical and horizontal profiles of sheltered and exposed beaches on Polish coast.

    PubMed

    Bigus, Katarzyna; Astel, Aleksander; Niedzielski, Przemysław

    2016-05-15

    The distribution of alkali and heavy metals in coastal sediments of three Polish beaches was assessed. In all locations there are sandy beaches of different characteristics according to the anthropogenic impact and degree of sheltering. Core sediments collected in Czołpino and Ustka were characterized by the highest concentration of Cd, Ag, Ba, and Al, Cu, Cr, Bi, Na, respectively. Among the alkaline metals core sediments were the most abundant with Ca, Bi, Mg and Na, presenting almost stable decreasing order in all beaches. The majority of dredge material collected can be classified as light or trace contaminated by Cr, Cu, Zn, Cd and Hg. An abundance of mineralogical components in core sediments in Ustka increases in Summer and Autumn, while in Puck is stable throughout the year. The content of studied metals in core sediments collected in three Polish beaches changes both in the vertical and horizontal profiles of the beach. PMID:26975611

  8. Bulk Dirac Points in Distorted Spinels

    NASA Astrophysics Data System (ADS)

    Steinberg, Julia; Young, Steve; Zaheer, Saad; Kane, Charles; Mele, Eugene; Rappe, Andrew

    2014-03-01

    A Dirac point is characterized by four degenerate states that disperse linearly with momentum around a single point bk in the Brillouin zone. The resulting low energy theory is pseudorelativistic. A well-known example in two dimensions is graphene, which has a Fermi surface consisting exclusively of Dirac points that are responsible for many of its exotic properties. We report on an analogous Dirac-like Fermi surface in three-dimensional bulk materials in a distorted spinel structure on the basis of density functional theory (DFT) as well as tight-binding theory. The four examples we provide in this paper are BiZnSiO4, BiCaSiO4, BiMgSiO4, and BiAlInO4. A necessary characteristic of these structures is that they contain a Bi lattice which forms a hierarchy of chain-like substructures, with consequences for both fundamental understanding and materials design.

  9. Mineralogy of the Precambrian southern Kostomuksha gold prospect in Karelia

    NASA Astrophysics Data System (ADS)

    Kuleshevich, L. V.; Gor'kovets, V. Ya.

    2008-12-01

    The southern Kostomuksha gold-sulfide prospect with a grade of 0.2-30 g/t Au belongs to the gold-pyrrhotite-arsenopyrite mineral type and is localized in the metasomatically altered shear zone at the southern flank of the Kostomuksha iron deposit. The Au-bearing pyrite ore is commonly characterized by a low grade (0.02-1.0 g/t Au). The grade of Au-bearing mineralization composed of arsenopyrite, loellingite, and electrum (4.28-15.31 wt % Ag and up to 0.99-2.16 wt % Hg) is higher; pyrrhotite, chalcopyrite, galena, maldonite, aurostibite, and native bismuth are additional components of this mineral assemblage. The ore mineralization is hosted in the near-latitudinal shear zone close to the contact between the folded and metamorphosed banded iron formation (BIF) and hälleflinta. The early stage of collision-related HP-HT metamorphism resulted in the formation of a garnet-amphibole-biotite assemblage ( T = 680-750°C) and microcline. After an abrupt drop m pressure, metasomatic alteration and ore mineralization took place. The ore-forming process started at 510-440°C with deposition of arsenopyrite. Galena and electrum were formed at a lower temperature. The temperature continued to decline down to the stage of ore oxidation and deposition of colloform marcasite. Ore minerals precipitated from acid chloride aqueous solutions admixed with methane at the initial stage and from diluted aqueous solutions at the final stage. The character of wall-rock alteration and the gain of K, Rb, and B show that the ore-forming process postdated the emplacement of potassium granite. The occurrence of Cu, Zn, Pb, As, and Ni and other heterogeneous elements indicates a complex metamorphic-metasomatic source and an additional supply of Au, As, Bi, Sb, and Te under conditions of sulfur deficiency. The gold mineralization at the southern Kostomuksha prospect is classified as gold-sulfide (arsenopyrite) ore type related to shear zones in the BIF.

  10. Prospects of nanostructures Bi{sub 1-x}Sb{sub x} for thermoelectricity

    SciTech Connect

    Nikolaeva, Albina A.; Konopko, Leonid A.; Huber, Tito E.; Bodiul, Pavel P.; Popov, Ivan A.

    2012-09-15

    It has been predicted that surface states of topological insulators have large a thermopower and also ultrahigh mobilities. The authors report results of a magneto-thermoelectric investigation of single crystal Bi{sub 1-x}Sb{sub x} nanowires in a glass cover with diameters ranging from 90 nm to 5 {mu}m. The wide-ranging antimony concentration enabled us to study the effect of nanowire dimensionality in the semimetal, semi-conductor and gapless regimes. Quantum size effects in Bi-2 at%Sb nanowires, which are shown in temperature dependences of resistance R(T) and thermopower {alpha}(T) for the diameters significantly higher than the critical diameter for pure Bi-wires, are observed. The thermopower in weak magnetic fields, reaches values +400 {mu}V/K at T=20-40 K. Power factor {alpha}{sup 2}{sigma} depending on diameter of wires, structure, temperature and magnetic field is calculated. In connection with topological insulators, we will discuss the surface effect in the thermoelectric properties that we observe. - Graphical abstract: Temperature dependences of resistance R{sub T}/R{sub 300}(T) (a) for Bi-2 at%Sb wires various diameters d: 1-d=300 nm, 2-d=400 nm, 3-d=600 nm, 4-d=1600 nm. Inset (a) SEM cross sectional image of the 650 nm Bi-2 at%Sb wire (clear) in glass envelope (gray). The magnetic field dependences thermopower (H Double-Vertical-Line {Delta}T) (b) Bi-2 at%Sb wires, with different diameters: (1). d=300 nm, (2). d=400 nm, (3). d=600 nm, T=26 K. Highlights: Black-Right-Pointing-Pointer SMSC transition in semimetal Bi-Sb wires due to the quantum size effect is observed. Black-Right-Pointing-Pointer In Bi-6 at%Sb wires alloys has been realized the gapless (GL) state. Black-Right-Pointing-Pointer In the area GS state abnormal growth thermopower in magnetic fields is found out. Black-Right-Pointing-Pointer Semiconductor Bi{sub 1-x} Sb{sub x} nanowires manifest properties of the topological insulators.

  11. Grain refinement and texture development of cast bismuth-antimony alloy via severe plastic deformation

    NASA Astrophysics Data System (ADS)

    Im, Jae-Taek

    The purpose of this work was to study learn about grain refinement mechanisms and texture development in cast n-type Bi90Sb10 alloy caused by severe plastic deformation. The practical objective is to produce a fine grained and textured microstructure in Bi90Sb10 alloy with enhanced thermoelectric performance and mechanical strength. In the study, twelve millimeter diameter cast bars of Bi90Sb 10 alloy were encapsulated in square cross section aluminum 6061 alloy containers. The composite bars were equal channel angular (ECAE) extruded through a 90 degree angle die at high homologous temperature. Various extrusion conditions were studied including punch speed (0.1, 0.3 and 0.6 in/min), extrusion temperature (220, 235 and 250°C), number of extrusion passes (1, 2 and 4), route (A, BC and C), and exit channel area reduction ratio (half and quarter area of inlet channel). The affect of an intermediate long term heat treatment (for 100 hours at 250°C under 10-3 torr vacuum) was explored. Processed materials were characterized by optical microscopy, x-ray diffraction, energy dispersive spectroscopy, wavelength dispersive spectroscopy and scanning electron microscopy. Texture was analyzed using the {006} reflection plane to identify the orientation of the basal poles in processed materials. The cast grains were irregularly shaped, had a grain size of hundreds-of-microns to millimeters, and showed inhomogeneous chemical composition. Severe plastic deformation refines the cast grains through dynamic recrystallization and causes the development of a bimodal microstructure consisting of fine grains (5-30 micron) and coarse grains (50-300 micron). ECAE processing of homogenizied Bi-Sb alloy causes grain refinement and produces a more uniform microstructure. Texture results show that ECAE route C processing gives a similar or slightly stronger texture than ECAE route A processing. In both cases, the basal-plane poles become aligned with the shear direction. Reduction area exit

  12. Characterization of energy critical elements in ore resources and associated waste tailings: Implications for recovery and remediation

    NASA Astrophysics Data System (ADS)

    McClenaghan, Sean H.

    2015-04-01

    The occurrence of Energy Critical Elements (ECE) in primary ore minerals and their subsequent enrichment in waste tailings is of great metallurgical interest. Recovery of many ECEs, in particular In, Ge, and Ga have come chiefly as a by-product of base-metal production (smelting and refining); these elements are found only at very low levels in the Earth's crust and do not typically form economic deposits on their own. As the ECEs become more important for a growing number of technological applications, it is critical to map the distribution of these elements in ore and waste (gangue) minerals to optimize their recovery and remediation. The characterization and beneficiation of ECEs is best illustrated for Zn-rich ore systems, where a mineral such as sphalerite (ZnS) will concentrate a number of major (Fe, Mn) and important trace elements (Cd, Se, In, Ge, Te, Sn, Bi, Sb, Hg). Interestingly, the mineral chemistry of sphalerite will often differ between different styles of mineralization (i.e., granite-hosted veins versus volcanic-hosted massive sulfides) and can even exhibit considerable variability within a deposit in response to metal zonation across hydrothermal facies. This has significant metallurgical implications for the blending of ore resources, the efficient production of Zn concentrates, and their ultimate value during the smelting and refining stages. Gangue minerals transferred to waste tailings may also exhibit significant enrichment in ECEs and precious metals; including Au in pyrite-arsenopyrite, and rare earth elements in a range of carbonate and phosphate minerals. In situ micro-analytical techniques are ideal for the quantitative measurement of trace elements in ore minerals as well as associated gangue materials. Recent advances in ICP-MS and ICP-OES technology coupled with newer classes of UV Excimer lasers (native 193 nm light) have allowed for more discrete analyses, permitting micro-chemical mapping at small scales (<10 microns). Further

  13. Petrochemistry and hydrothermal alteration within the Tyrone Igneous Complex, Northern Ireland: implications for VMS mineralization in the British and Irish Caledonides

    NASA Astrophysics Data System (ADS)

    Hollis, Steven P.; Roberts, Stephen; Earls, Garth; Herrington, Richard; Cooper, Mark R.; Piercey, Stephen J.; Archibald, Sandy M.; Moloney, Martin

    2014-06-01

    Although volcanogenic massive sulfide (VMS) deposits can form within a wide variety of rift-related tectonic environments, most are preserved within suprasubduction affinity crust related to ocean closure. In stark contrast to the VMS-rich Appalachian sector of the Grampian-Taconic orogeny, VMS mineralization is rare in the peri-Laurentian British and Irish Caledonides. Economic peri-Gondwanan affinity deposits are limited to Avoca and Parys Mountain. The Tyrone Igneous Complex of Northern Ireland represents a ca. 484-464 Ma peri-Laurentian affinity arc-ophiolite complex and a possible broad correlative of the Buchans-Robert's Arm belt of Newfoundland, host to some of the most metal-rich VMS deposits globally. Stratigraphic horizons prospective for VMS mineralization in the Tyrone Igneous Complex are associated with rift-related magmatism, hydrothermal alteration, synvolcanic faults, and high-level subvolcanic intrusions (gabbro, diorite, and/or tonalite). Locally intense hydrothermal alteration is characterized by Na-depletion, elevated SiO2, MgO, Ba/Sr, Bi, Sb, chlorite-carbonate-pyrite alteration index (CCPI) and Hashimoto alteration index (AI) values. Rift-related mafic lavas typically occur in the hanging wall sequences to base and precious metal mineralization, closely associated with ironstones and/or argillaceous sedimentary rocks representing low temperature hydrothermal venting and volcanic quiescence. In the ca. 475 Ma pre-collisional, calc-alkaline lower Tyrone Volcanic Group rift-related magmatism is characterized by abundant non-arc type Fe-Ti-rich eMORB, island-arc tholeiite, and low-Zr tholeiitic rhyolite breccias. These petrochemical characteristics are typical of units associated with VMS mineralization in bimodal mafic, primitive post-Archean arc terranes. Following arc-accretion at ca. 470 Ma, late rifting in the ensialic upper Tyrone Volcanic Group is dominated by OIB-like, subalkaline to alkali basalt and A-type, high-Zr rhyolites. These units

  14. Enzyme leaching of surficial geochemical samples for detecting hydromorphic trace-element anomalies associated with precious-metal mineralized bedrock buried beneath glacial overburden in northern Minnesota

    USGS Publications Warehouse

    Clark, Robert J.; Meier, A.L.; Riddle, G.

    1990-01-01

    One objective of the International Falls and Roseau, Minnesota, CUSMAP projects was to develop a means of conducting regional-scale geochemical surveys in areas where bedrock is buried beneath complex glacially derived overburden. Partial analysis of B-horizon soils offered hope for detecting subtle hydromorphic trace-element dispersion patterns. An enzyme-based partial leach selectively removes metals from oxide coatings on the surfaces of soil materials without attacking their matrix. Most trace-element concentrations in the resulting solutions are in the part-per-trillion to low part-per-billion range, necessitating determinations by inductively coupled plasma/mass spectrometry. The resulting data show greater contrasts for many trace elements than with other techniques tested. Spatially, many trace metal anomalies are locally discontinuous, but anomalous trends within larger areas are apparent. In many instances, the source for an anomaly seems to be either basal till or bedrock. Ground water flow is probably the most important mechanism for transporting metals toward the surface, although ionic diffusion, electrochemical gradients, and capillary action may play a role in anomaly dispersal. Sample sites near the Rainy Lake-Seine River fault zone, a regional shear zone, often have anomalous concentrations of a variety of metals, commonly including Zn and/or one or more metals which substitute for Zn in sphalerite (Cd, Ge, Ga, and Sn). Shifts in background concentrations of Bi, Sb, and As show a trend across the area indicating a possible regional zoning of lode-Au mineralization. Soil anomalies of Ag, Co, and Tl parallel basement structures, suggesting areas that may have potential for Cobalt/Thunder Baytype silver viens. An area around Baudette, Minnesota, which is underlain by quartz-chlorite-carbonate-altered shear zones, is anomalous in Ag, As, Bi, Co, Mo, Te, Tl, and W. Anomalies of Ag, As, Bi, Te, and W tend to follow the fault zones, suggesting potential

  15. Studies of Flerovium and Element 115 Homologs with Macrocyclic Extractants

    SciTech Connect

    Despotopulos, John D.

    2015-03-12

    Study of the chemistry of the heaviest elements, Z ≥ 104, poses a unique challenge due to their low production cross-sections and short half-lives. Chemistry also must be studied on the one-atom-at-a-time scale, requiring automated, fast, and very efficient chemical schemes. Recent studies of the chemical behavior of copernicium (Cn, element 112) and flerovium (Fl, element 114) together with the discovery of isotopes of these elements with half-lives suitable for chemical studies have spurred a renewed interest in the development of rapid systems designed to study the chemical properties of elements with Z ≥ 114. This dissertation explores both extraction chromatography and solvent extraction as methods for development of a rapid chemical separation scheme for the homologs of flerovium (Pb, Sn, Hg) and element 115 (Bi, Sb), with the goal of developing a chemical scheme that, in the future, can be applied to on-line chemistry of both Fl and element 115. Carrier-free radionuclides, used in these studies, of the homologs of Fl and element 115 were obtained by proton activation of high-purity metal foils at the Lawrence Livermore National Laboratory (LLNL) Center for Accelerator Mass Spectrometry (CAMS): natIn(p,n)113Sn, natSn(p,n)124Sb, and Au(p,n)197m,gHg. The carrier-free activity was separated from the foils by novel separation schemes based on ion exchange and extraction chromatography techniques. Carrier-free Pb and Bi isotopes were obtained from development of a novel generator based on cation exchange chromatography using the 232U parent to generate 212Pb and 212Bi. Macrocyclic extractants, specifically crown ethers and their derivatives, were chosen for these studies; crown ethers show high selectivity for metal ions. Finally. a potential chemical system for Fl was established based on the Eichrom Pb resin, and insight to an improved system based on thiacrown ethers is

  16. The effects of nanoparticle inclusions upon the microstructure and thermoelectric transport properties of bismuth telluride-based composites

    NASA Astrophysics Data System (ADS)

    Gothard, Nicholas Wesley

    was adopted in order to consolidate the nanostructures into the bulk matrix. Nanocomposites were produced using both n-type and p-type bismuth telluride compounds as the matrix material, into which nanostructures of Bi2Te 3, BiSb, Bi2S3, as well as Au and Ag nanoparticles and C60 were incorporated. The preferred consolidation technique utilized a 3-axis mechanical mixer, followed first by cold and then hot pressing of the bulk-nano mixtures. The composites were studied with respect to their microstructure and elemental composition, as well as with regard to their thermal and electrical transport properties. The effects of the nanoparticle additions upon the efficiencies of the materials are presented, and the viability of improving the thermoelectric performance of this class of materials by this method is considered.

  17. Magnetic Topological Insulators and Quantum Anomalous Hall Effect

    NASA Astrophysics Data System (ADS)

    Kou, Xufeng

    The engineering of topological surface states is a key to realize applicable devices based on topological insulators (TIs). Among various proposals, introducing magnetic impurities into TIs has been proven to be an effective way to open a surface gap and integrate additional ferromagnetism with the original topological order. In this Dissertation, we study both the intrinsic electrical and magnetic properties of the magnetic TI thin films grown by molecular beam epitaxy. By doping transition element Cr into the host tetradymite-type V-VI semiconductors, we achieve robust ferromagnetic order with a strong perpendicular magnetic anisotropy. With additional top-gating capability, we realize the electric-field-controlled ferromagnetism in the magnetic TI systems, and demonstrate such magneto-electric effects can be effectively manipulated, depending on the interplays between the band topology, magnetic exchange coupling, and structural engineering. Most significantly, we report the observation of quantum anomalous Hall effect (QAHE) in the Cr-doped (BiSb)2Te3 samples where dissipationless chiral edge conduction is realized in the macroscopic millimeter-size devices without the presence of any external magnetic field, and the stability of the quantized Hall conductance of e2/h is well-maintained as the film thickness varies across the 2D hybridization limit. With additional quantum confinement, we discover the metal-to-insulator switching between two opposite QAHE states, and reveal the universal QAHE phase diagram in the thin magnetic TI samples. In addition to the uniform magnetic TIs, we further investigate the TI/Cr-doped TI bilayer structures prepared by the modulation-doped growth method. By controlling the magnetic interaction profile, we observe the Dirac hole-mediated ferromagnetism and develop an effective way to manipulate its strength. Besides, the giant spin-orbit torque in such magnetic TI-based heterostructures enables us to demonstrate the current

  18. Effects of simulated acid rain, EDTA, or their combination, on migration and chemical fraction distribution of extraneous metals in Ferrosol.

    PubMed

    Wen, Fang; Hou, Hong; Yao, Na; Yan, Zengguang; Bai, Liping; Li, Fasheng

    2013-01-01

    A laboratory repacked soil-leaching column experiment was conducted to study the effects of simulated acid rain or EDTA by themselves or in combination, on migration and chemical speciation distribution of Pb and its alternative rare metals including Ag, Bi, In, Sb, and Sn. Experimental results demonstrate that leaching with simulated acid rain promoted the migration of Bi, In and Pb, and their migration reached down to 8 cm in the soil profile, no enhancement of Sb, Ag or Sn migration was observed. Addition of EDTA significantly enhanced the migration of all six metals, especially Bi, In and Pb. The migration of metals was in the order Pb>Bi>In>Sb>Sn>Ag. The individual and combined effects of acid rain and EDTA increased the environmental risk of metals, by increasing the soluble content of metals in soil solutions and the relative distribution of the exchangeable fraction. Leaching risks of Bi, In and Pb were higher than other three metals. PMID:22921654

  19. Enhancement of Rashba interaction in GaAs/AlGaAs quantum wells due to the incorporation of bismuth

    SciTech Connect

    Simmons, R. A.; Jin, S. R.; Sweeney, S. J.; Clowes, S. K.

    2015-10-05

    This paper reports on the predicted increase in the Rashba interaction due to the incorporation of Bi in GaAs/AlGaAs heterostructures. Band structure parameters obtained from the band anti-crossing theory have been used in combination with self-consistent Schrödinger-Poisson calculations and k.p models to determine the electron spin-splitting caused by structural inversion asymmetry and increased spin-orbit interaction. A near linear seven fold increase in the strength of the Rashba interaction is predicted for a 10% concentration of Bi in a GaAsBi/AlGaAs quantum well heterostructure.

  20. Dielectric Properties and Complex Impedance Analysis of BT-BMT-BS Ceramics

    NASA Astrophysics Data System (ADS)

    Muhammad, Raz; Khesro, Amir; Uzair, Muhammad

    2016-08-01

    Polycrystalline (1- x)BaTiO3-0.5 xBi(Mg0.5Ti0.5)O3-0.5 xBiScO3 ( x = 0.4, 0.45, 0.5, and 0.55) samples have been prepared via a conventional mixed-oxide solid-state sintering route. Phase analysis of the samples with x ≥ 0.45 revealed formation of single-phase cubic structure, while at x = 0.4, a minor secondary phase formed. Complex impedance spectroscopy of the samples revealed more than one type of transport mechanism (grain/bulk, grain boundary, and electrode effect). At x = 0.4, the grain boundary was less conducting than the grain; however, grains dominated the total conductivity with further increase in x. At elevated temperatures, the higher conductivity values suggest semiconducting-like behavior with negative temperature coefficient of resistivity. The composition with x = 0.55 exhibited a temperature-stable relative permittivity ( ɛ r) of 1430 (±15% over 127°C to 500°C) and dielectric loss (tan δ) of <0.025 (over 150°C to 370°C).

  1. Interface stability of electrode/Bi-containing relaxor ferroelectric oxide for high-temperature operational capacitor

    NASA Astrophysics Data System (ADS)

    Nagata, Takahiro; Kumaragurubaran, Somu; Tsunekawa, Yoshifumi; Yamashita, Yoshiyuki; Ueda, Shigenori; Takahashi, Kenichiro; Ri, Sung-Gi; Suzuki, Setsu; Oh, Seungjun; Chikyow, Toyohiro

    2016-06-01

    The interface stability between electrodes (Pt, TaC, TiC, and RuO2) and a Bi-containing relaxor ferroelectric oxide, BaTiO3–Bi(Mg2/3Nb1/3)O3 (BT–BMN), applied to a high-temperature operational capacitor was investigated by hard X-ray photoelectron spectroscopy. All the electrodes showed electron filling at the Fermi level after annealing at 400 °C. However, Pt and TaC indicated electrical property degradations due to the thick intermediate layer formation and defect formation of the BT–BMN layer relating to the Bi diffusion into the electrodes. In contrast, TiC inhibited the Bi diffusion and did not show any change in the band alignment after annealing. Furthermore, RuO2 eliminated the defect formation in BT–BMN and showed no change in the band alignment although the Bi diffusion was also observed. These results suggest that the TiC/RuO2/BT–BMN stack structure is a potential candidate for the high-temperature operational capacitor.

  2. Lead-free ternary perovskite compounds with large electromechanical strains

    NASA Astrophysics Data System (ADS)

    Jarupoom, Parkpoom; Patterson, Eric; Gibbons, Brady; Rujijanagul, Gobwute; Yimnirun, Rattikorn; Cann, David

    2011-10-01

    Lead-free compounds based on perovskite solid solutions in the ternary system (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3-Bi(X1/2Ti1/2)O3, where X = Ni and Mg have been shown to exhibit large electromechanical strains. While the perovskite end members Bi(Mg1/2Ti1/2)O3 and Bi(Ni1/2Ti1/2)O3 display limited stability in their pure state, both compounds were found to have solid solubilities of at least 50 mol. % with (Bi1/2Na1/2)TiO3 and (Bi1/2K1/2)TiO3. Most importantly, under relatively large applied fields, these materials exhibited large hysteretic electromechanical strains characterized by a parabolic shape. With effective piezoelectric coefficients (d33*) greater than 500 pm/V, these systems have excellent potential as a Pb-free piezoelectric materials.

  3. Dielectric Properties and Complex Impedance Analysis of BT-BMT-BS Ceramics

    NASA Astrophysics Data System (ADS)

    Muhammad, Raz; Khesro, Amir; Uzair, Muhammad

    2016-05-01

    Polycrystalline (1-x)BaTiO3-0.5xBi(Mg0.5Ti0.5)O3-0.5xBiScO3 (x = 0.4, 0.45, 0.5, and 0.55) samples have been prepared via a conventional mixed-oxide solid-state sintering route. Phase analysis of the samples with x ≥ 0.45 revealed formation of single-phase cubic structure, while at x = 0.4, a minor secondary phase formed. Complex impedance spectroscopy of the samples revealed more than one type of transport mechanism (grain/bulk, grain boundary, and electrode effect). At x = 0.4, the grain boundary was less conducting than the grain; however, grains dominated the total conductivity with further increase in x. At elevated temperatures, the higher conductivity values suggest semiconducting-like behavior with negative temperature coefficient of resistivity. The composition with x = 0.55 exhibited a temperature-stable relative permittivity (ɛ r) of 1430 (±15% over 127°C to 500°C) and dielectric loss (tan δ) of <0.025 (over 150°C to 370°C).

  4. Thermally-Labile Trace Elements in Enstatite Meteorites

    NASA Technical Reports Server (NTRS)

    Wang, M.-S.; Lipschutz, M. E.

    2000-01-01

    RNAA data for Bi, In and Tl in 30 E3-6 chondrites accord well with trends for heated Abee (EH4) suggesting that all EH and EL samples reflect open-system, post-accretionary heating, independent of siderophile content or recovery location.

  5. Temperament and Family Environment in the Development of Anxiety Disorder: Two-Year Follow-Up

    ERIC Educational Resources Information Center

    Hudson, Jennifer L.; Dodd, Helen F.; Lyneham, Heidi J.; Bovopoulous, Nataly

    2011-01-01

    Objective: Behavioral inhibition (BI) in early childhood is associated with increased risk for anxiety. The present research examines BI alongside family environment factors, specifically maternal negativity and overinvolvement, maternal anxiety, and mother-child attachment, with a view to providing a broader understanding of the development of…

  6. Endothelial Expression of Scavenger Receptor Class B, Type I Protects against Development of Atherosclerosis in Mice

    PubMed Central

    Vaisman, Boris L.; Vishnyakova, Tatyana G.; Freeman, Lita A.; Amar, Marcelo J.; Demosky, Stephen J.; Liu, Chengyu; Stonik, John A.; Sampson, Maureen L.; Pryor, Milton; Bocharov, Alexander V.; Eggerman, Thomas L.; Patterson, Amy P.; Remaley, Alan T.

    2015-01-01

    The role of scavenger receptor class B, type I (SR-BI) in endothelial cells (EC) was examined in several novel transgenic mouse models expressing SR-BI in endothelium of mice with normal C57Bl6/N, apoE-KO, or Scarb1-KO backgrounds. Mice were also created expressing SR-BI exclusively in endothelium and liver. Endothelial expression of the Tie2-Scarb1 transgene had no significant effect on plasma lipoprotein levels in mice on a normal chow diet but on an atherogenic diet, significantly decreased plasma cholesterol levels, increased plasma HDL cholesterol (HDL-C) levels, and protected mice against atherosclerosis. In 8-month-old apoE-KO mice fed a normal chow diet, the Tie2-Scarb1 transgene decreased aortic lesions by 24%. Mice expressing SR-BI only in EC and liver had a 1.5 ± 0.1-fold increase in plasma cholesterol compared to mice synthesizing SR-BI only in liver. This elevation was due mostly to increased HDL-C. In EC culture studies, SR-BI was found to be present in both basolateral and apical membranes but greater cellular uptake of cholesterol from HDL was found in the basolateral compartment. In summary, enhanced expression of SR-BI in EC resulted in a less atherogenic lipoprotein profile and decreased atherosclerosis, suggesting a possible role for endothelial SR-BI in the flux of cholesterol across EC. PMID:26504816

  7. 12 CFR 218.700 - Defined terms relating to the networking exception from the definition of “broker.”

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    .... 78c(a)(4)(B)(i)) in the context of transactions with a customer, the following terms shall have the... be contingent on whether a customer: (1) Contacts or keeps an appointment with a broker or dealer as... by the bank or broker or dealer for customer referrals, including such criteria as minimum...

  8. 47 CFR 15.407 - General technical requirements.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... National Information Infrastructure Devices § 15.407 General technical requirements. (a) Power limits: (1... maximum conducted output power over the frequency band of operation shall not exceed 1 W provided the maximum antenna gain does not exceed 6 dBi. In addition, the maximum power spectral density shall...

  9. The COBRA Double Beta Decay Experiment

    NASA Astrophysics Data System (ADS)

    Dawson, J. V.

    2007-03-01

    The progress of the COBRA neutrinoless double beta decay experiment is discussed. Potential backgrounds are described. Estimates on the contamination levels of 214Bi in the detectors have been made using previously acquired low background data. New crystals with a different passivation material show an improved background count rate of approximately one order of magnitude.

  10. Bibliographic Instruction in Academic Libraries. A Review of the Literature and Selected Bibliography.

    ERIC Educational Resources Information Center

    Morris, Jacquelyn M.

    This overview of bibliographic instruction (B.I.) in college and university libraries provides a brief review of the literature, proposes an indexing language based on the special terminology of the field for more precise literature searches, and presents a 174-item bibliography of journal articles, books, and ERIC documents. The literature review…

  11. Impact of Behavioral Inhibition and Parenting Style on Internalizing and Externalizing Problems from Early Childhood through Adolescence

    ERIC Educational Resources Information Center

    Williams, Lela Rankin; Degnan, Kathryn A.; Perez-Edgar, Koraly E.; Henderson, Heather A.; Rubin, Kenneth H.; Pine, Daniel S.; Steinberg, Laurence; Fox, Nathan A.

    2009-01-01

    Behavioral inhibition (BI) is characterized by a pattern of extreme social reticence, risk for internalizing behavior problems, and possible protection against externalizing behavior problems. Parenting style may also contribute to these associations between BI and behavior problems (BP). A sample of 113 children was assessed for BI in the…

  12. The Potential Role of Business Intelligence in Church Organizations

    ERIC Educational Resources Information Center

    Felder, Charmaine

    2012-01-01

    Business intelligence (BI) involves transforming data into actionable information to make better business decisions that may help improve operations. Although businesses have experienced success with BI, how leaders of church organizations might be able to exploit the advantages of BI in church organizations remains largely unexplored. The purpose…

  13. 31 CFR 30.10 - Q-10: What actions are necessary for a TARP recipient to comply with section 111(b)(3)(D) of EESA...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... right to a bonus payment, see 26 CFR 1.409A-1(b)(i). In addition, the bonus payment must be made in... 31 Money and Finance: Treasury 1 2010-07-01 2010-07-01 false Q-10: What actions are necessary for....10 Section 30.10 Money and Finance: Treasury Office of the Secretary of the Treasury TARP...

  14. 3. VIEW OF WATER TANKS FROM ACCESS ROAD TO HATCH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. VIEW OF WATER TANKS FROM ACCESS ROAD TO HATCH ADIT. VIEW NORTH. LUCKY TIGER MILL OFFICE (FEATURE B-I) IN DISTANCE. (OCTOBER, 1995) - Nevada Lucky Tiger Mill & Mine, Water Tanks, East slope of Buckskin Mountain, Paradise Valley, Humboldt County, NV

  15. The COBRA Double Beta Decay Experiment

    SciTech Connect

    Dawson, J. V.

    2007-03-28

    The progress of the COBRA neutrinoless double beta decay experiment is discussed. Potential backgrounds are described. Estimates on the contamination levels of 214Bi in the detectors have been made using previously acquired low background data. New crystals with a different passivation material show an improved background count rate of approximately one order of magnitude.

  16. 31 CFR 30.10 - Q-10: What actions are necessary for a TARP recipient to comply with section 111(b)(3)(D) of EESA...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance: Treasury 1 2011-07-01 2011-07-01 false Q-10: What actions are necessary for... right to a bonus payment, see 26 CFR 1.409A-1(b)(i). In addition, the bonus payment must be made in....10 Section 30.10 Money and Finance: Treasury Office of the Secretary of the Treasury TARP...

  17. 31 CFR 30.10 - Q-10: What actions are necessary for a TARP recipient to comply with section 111(b)(3)(D) of EESA...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 31 Money and Finance: Treasury 1 2014-07-01 2014-07-01 false Q-10: What actions are necessary for... right to a bonus payment, see 26 CFR 1.409A-1(b)(i). In addition, the bonus payment must be made in....10 Section 30.10 Money and Finance: Treasury Office of the Secretary of the Treasury TARP...

  18. 31 CFR 30.10 - Q-10: What actions are necessary for a TARP recipient to comply with section 111(b)(3)(D) of EESA...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 31 Money and Finance: Treasury 1 2013-07-01 2013-07-01 false Q-10: What actions are necessary for... right to a bonus payment, see 26 CFR 1.409A-1(b)(i). In addition, the bonus payment must be made in....10 Section 30.10 Money and Finance: Treasury Office of the Secretary of the Treasury TARP...

  19. The Teaching of Critical Thinking Skills by Academic Librarians.

    ERIC Educational Resources Information Center

    Goetzfridt, Nicholas J.

    Teaching critical thinking is a relatively new dimension of bibliographic instruction (BI) in the academic environment. It marks a departure from the teaching of "user skills" in which the primary concern is enabling library patrons to determine the appropriateness of reference tools and to use those tools effectively. This report assembles a…

  20. Application of the superfine fraction analysis method in ore gold geochemical prospecting in the Shamanikha-Stolbovsky Area (Magadan Region)

    NASA Astrophysics Data System (ADS)

    Makarova, Yuliya; Sokolov, Sergey; Glukhov, Anton

    2014-05-01

    potential gold zones, and determine their formation affinity. Nadezhda Site. Contrast Au, Ag, Pb, Bi, Sb, As dispersion halos that form a linear anomalous geochemical field of ore body rank are identified. Predicted mineralization was related to the gold-sulfosalt mineral association according to the secondary dispersion halos chemical composition. Timsha Site. Contrast secondary Au, Ag, Sb, As, Hg, Pb, Bi dispersion halos are identified. These halos have rhythmically-banded structure, which can be caused by stringer morphological type of mineralization. Bands with anomalously high contents of elements have been interpreted by the authors as probable auriferous bodies. Four such bodies of 700 to 1500 m long were identified. Mineralization of the gold-sulfide formation similar to the "Carlin" type is predicted according to the secondary dispersion halos chemical composition as well as geological features. Temny Site. Contrast secondary Au, Ag, W, Sb dispersion halos are identified. A series of geochemical associations was identified based on factor analysis results. Au-Bi-W-Hg, and Pb-Sb-Ag-Zn associations, apparently related to the mineralization are of the greatest interest. Geochemical fields of these associations are closely spaced and overlapped in plan that may be caused by axial zoning of the subvertically dipping auriferous body. Three linear geochemical zones corresponding to potentially auriferous zones with pyrite type mineralization of the gold-quartz formation are identified within the anomalous geochemical field core zone. 3. In all these prospects, mining and drilling penetrated gold ore bodies within the identified potentially gold zones. The Nadezhda target now has the status of gold deposit.

  1. Geochemical features of the Osovey Area, perspective for the polymetallic mineralization revealing (Polar Urals)

    NASA Astrophysics Data System (ADS)

    Savicheva, Olga; Sholokhnev, Vladimir; Makarova, Yuliya

    2014-05-01

    Osovey prospective area (184 km2) is located in the north of the Polar Urals within the Verhnekarsk Eletsk metallogenic zone, specialized on the base metals, barium and bauxite. Three structural stages, namely Riphean-Early Cambrian, the Late Carboniferous, and Triassic-Cenozoic are identified in the geological structure of the area. They are divided by the stratigraphic and angular unconformity. Volcaniclastic rocks of the Oyuyahinskaay Formation such as basaltic andesite, apovolcanogenic shales, mediosilicic and basic composition tuffs, as well as black banded shales of carbon-clay-siliceous composition related to the Silurian-Early Devonian Harotskaay Formation are predominant. Area is characterized by complex landscape conditions for the prospecting. Increased thickness of loose sediments, transeluvial weakly dissected lowlands, superaqual landscapes in lower parts of the slopes are widespread. In 2012 at the 1:50 000 scale geochemical prospecting (sampling density 500×50 m), carried out in the Osovey Area, 6000 samples were picked out from unconsolidated sediments. The samples were analyzed by the ICP MS method. Principal typomorphic elements of the polymetallic mineralization (Zn, Pb, Cu, Ag) as well as elements-indicators such as Bi, Sb, Se, Mo, etc. were defined. In addition to the polymetallic mineralization the Osoveysky area is perspective on the identification of iron-manganese ores, barites with polymetals, phosphorites, and vanadium. Such elements as Mn, P, V, U, Ba were also defined for this reason. Contrast secondary dispersion halos of Cu (up to 2060 ppm), Ag (1,45 ppm), Sb (12,3 ppm), Mo (18,9 ppm), Mn (7, 6 %), P (1,05%), Ni (338 ppm), and medium-low contrast ones of Zn, Pb, Co, V, Se, Sr, Bi, Sn, Ba, Ti, U, Cr, Zr were identified according to the results of the geochemical prospecting. Five anomalous geochemical fields (AGF) of the ore deposit rank (n ×100 km2) were identified according to the results of geochemical data processing and their

  2. Theoretical study on transport properties of topological states of matter

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiu-Chuan

    larger conductance appears for half-integer magnetic flux, leading to magnetoconductance oscillations with a period equivalent to one magnetic flux quantum. Our numerical simulation of the magnetoconductance oscillations is supported by experimental observations in resistive Bi 2Te3 nanotubes. Another system that we study is the quantum anomalous Hall insulator. Similar to the quantum Hall effect, the Hall conductance is quantized and the longitudinal resistance drops to zero in the quantum anomalous Hall effect. However, the quantum anomalous Hall effect is realized in a magnetic system in absence of external magnetic fields and the associated Landau levels. The quantum anomalous Hall effect was first proposed in magnetically doped HgTe quantum wells. However, one obstacle is that this system is paramagnetic, and thus external magnetic fields are required to polarize magnetization and inevitably leads to Landau levels. In this study, we focus on the role of in-plane magnetic fields and find that the quantum anomalous Hall effect can be realized by a purely in-plane magnetic field when there is strain in the system. Symmetry analysis is adopted to provide more theoretical insight of the underlying physics. Without any strain, we explore how to extract the role of magnetization in the standard transport measurement of Hall resistance by rotating magnetic fields. Our results provide a guidance to the recent experiments in Mn doped HgTe quatnum wells with rotating magnetic fields. Besides these studies, we also investigate anisotropic magneto-conductance in magnetically doped (Bi,Sb)2Te3 films. The studies in the dissertation are in a close collaboration with transport measurements of experimental groups, including magneto-conductance oscillation observed by Qi's group at Penn State and the study of the Hall conductance in Mn doped HgTe quantum wells with rotating magnetic fields by Molenkamp's group at Wuerzburg University.

  3. Facile synthesis of bismuth(III) and antimony(III) complexes supported by silylated calix[5]arenes.

    PubMed

    Mendoza-Espinosa, Daniel; Hanna, Tracy A

    2009-11-01

    A series of bismuth(III) and antimony(III) complexes supported by silicon-containing calix[5]arene ligands were synthesized and fully characterized by NMR, X-ray, IR, mp, UV/vis, and elemental analysis. Reaction of the para-tert-butylcalix[5]arene [(t)BuC5(H)(5)] disodium salt, Na(2) x (t)BuC5(H)(3), with 1 equiv of R(2)SiCl(2) (R = Me, (i)Pr, Ph, CH=CH(2)) or treatment of the (t)BuC5(H)(5) lower rim monobenzyl ether [(t)BuC5(Bn)(H)(4)] in a 1:1 ratio with Me(2)Si(NMe(2))(2) yields the (t)BuC5(SiRR')(H)(3) (1-5) and (t)BuC5(Bn)(SiMe(2))(H)(2) (6) ligands, respectively. The (1)H NMR spectra of the (t)BuC5(SiRR')(H)(3) (1-5) ligands show three pairs of doublets and three singlets for the (t)Bu peaks, consistent with a C(s) symmetry. In the case of the (t)BuC5(Bn)(SiMe(2))(H)(2) (6) ligand, the presence of the monobenzyl group changes the (1)H NMR patterns to indicate a C(1) symmetry. Treatment of (t)BuC5(SiRR')(H)(3) (1-5) or (t)BuC5(Bn)(SiMe(2))(H)(2) (6) with 1 equiv of M(O(t)Bu)(3) (M = Bi, Sb) or Sb(NMe(2))(2) readily yields metalated products of the type [M{(t)BuC5(SiRR')}] (7-16) and [MX{(t)BuC5(Bn)(SiMe(2))}] (X = O(t)Bu, (NMe(2))(2)) (17-19), respectively. All monometallic complexes [M{(t)BuC5(SiRR')}] (7-19) display excellent solubility in organic solvents including pentane and hexane. The (1)H NMR patterns for complexes 7-16 are consistent with a 1,2- or 1,3-alternate conformation while complexes [MX{(t)BuC5(Bn)(SiMe(2))}] (17-19) display patterns for a C(1) symmetry. All crystals show monomeric structures. Ligand (t)BuC5(SiPh(2))(H)(3) (3) displays a distorted cone conformation while the presence of the monobenzyl ether in (t)BuC5(Bn)(SiMe(2))(H)(2) (6) forces a partial cone conformation. Complexes 7-19 all display a distorted 1,2-alternate conformation with the metal centers displaying coordination numbers of three, four or five. No Si...M interactions were observed. PMID:19785468

  4. A fluid inclusion and isotopic study of an intrusion-related gold deposit (IRGD) setting in the 380 Ma South Mountain Batholith, Nova Scotia, Canada: evidence for multiple fluid reservoirs

    NASA Astrophysics Data System (ADS)

    Kontak, Daniel J.; Kyser, Kurt

    2011-04-01

    A set of sheeted quartz veins cutting 380 Ma monzogranite at Sandwich Point, Nova Scotia, Canada, provide an opportunity to address issues regarding fluid reservoirs and genesis of intrusion-related gold deposits. The quartz veins, locally with arsenopyrite (≤5%) and elevated Au-(Bi-Sb-Cu-Zn), occur within the reduced South Mountain Batholith, which also has other zones of anomalous gold enrichment. The host granite intruded ( P = 3.5 kbars) Lower Paleozoic metaturbiditic rocks of the Meguma Supergroup, well known for orogenic vein gold mineralization. Relevant field observations include the following: (1) the granite contains pegmatite segregations and is cut by aplitic dykes and zones (≤1-2 m) of spaced fracture cleavage; (2) sheeted veins containing coarse, comb-textured quartz extend into a pegmatite zone; (3) arsenopyrite-bearing greisens dominated by F-rich muscovite occur adjacent the quartz veins; and (4) vein and greisen formation is consistent with Riedel shear geometry. Although these features suggest a magmatic origin for the vein-forming fluids, geochemical studies indicate a more complex origin. Vein quartz contains two types of aqueous fluid inclusion assemblages (FIA). Type 1 is a low-salinity (≤3 wt.% equivalent NaCl) with minor CO2 (≤2 mol%) and has T h = 280-340°C. In contrast, type 2 is a high-salinity (20-25 wt.% equivalent NaCl), Ca-rich fluid with T h = 160-200°C. Pressure-corrected fluid inclusion data reflect expulsion of a magmatic fluid near the granite solidus (650°C) that cooled and mixed with a lower temperature (400°C), wall rock equilibrated, Ca-rich fluid. Evidence for fluid unmixing, an important process in some intrusion-related gold deposit settings, is lacking. Stable isotopic (O, D, S) analyses for quartz, muscovite and arsenopyrite samples from vein and greisens indicate the following: (1) δ18Oqtz = +11.7‰ to 17.8‰ and δ18Omusc = +10.7‰ to +11.2‰; (2) δDmusc = -44‰ to-54‰; and (3) δ34Saspy = +7.8

  5. The origin of halide melt phases in layered intrusions, and their significance to platinum-group element mobility

    NASA Astrophysics Data System (ADS)

    Hanley, J. J.

    2007-12-01

    Fluid and melt inclusions are preserved within pegmatite bodies and cumulus minerals within mafic-ultramafic layered intrusions that host economic concentrations of the platinum-group elements (e.g., Bushveld Complex, South Africa; Stillwater Complex, Montana). The inclusions indicate that the earliest volatile phase to have exsolved from the crystallizing intrusions was a relatively anhydrous carbonic fluid (CO2-dominated). As crystallization proceeded, volatiles became increasingly water-rich and saline, consistent with the relative saturation limits of carbonic and aqueous fluids in mafic silicate liquids, and the partitioning behavior of Cl in fluid-melt systems. Previously unreported, the latest stage volatiles in the layered intrusions were halide melts (slightly hydrous molten salts) of relatively simply composition (NaCl with minor KCl or CaCl2) with salinities in excess of 90 wt% eq. NaCl or CaCl2. These volatiles were trapped at minimum temperatures of 760-800°C, near the eutectic temperature for water-saturated granitic liquid at moderate crustal pressures. Trace element analysis of the salt melt inclusions by laser ablation ICP-MS (ETH Zürich) show that they contain no detectable concentrations of ore and accessory metals. This is in contrast to the earlier, lower salinity volatiles which contain ppm-concentrations of Pt, Pd, As, Bi, Sb as well as abundant S and base metals. Heterogeneous entrapment of late-stage silicate melt and halide melt provides unambiguous evidence for the coexistence of both phases. However, experimental constraints on the nature of exsolved volatiles from mafic or felsic silicate liquids suggest that the halide melt phases cannot represent an exsolved phase from that coexisting silicate liquid, since this would require unrealistically high (initial) Cl:H2O ratios for the parental silicate liquid (> 9 for a granitic residue). Analysis of rhyodacitic silicate melt inclusions that coexist with the halide melt inclusions show

  6. EDITORIAL: Progress in topological insulators Progress in topological insulators

    NASA Astrophysics Data System (ADS)

    Morpurgo, Alberto; Trauzettel, Björn

    2012-12-01

    One of the most remarkable discoveries of the last few years in condensed matter physics is that the established distinction of crystalline solids in metals and insulators—which relies on the material band-structure—is incomplete. During the last several decades, the band structure of an uncountable variety of compounds of increasing complexity have been computed, and yet it has been overlooked that in the presence of sufficiently strong spin-orbit interaction, a new class of materials can be realized, that intrinsically behaves as insulators in their bulk and as metals at their surface. The discovery of this new class of materials was made only recently by Kane and Mele, during their theoretical studies of graphene in the presence of a sufficiently strong intrinsic spin-orbit interaction. Although the strength of the spin-orbit interaction in graphene is not sufficient to make the topological insulating state visible experimentally under currently reachable conditions, the validity and the originality of the concept were fully appreciated. Predictions for the occurrence of a two-dimensional topological insulating state in HgTe/CdTe heterostructures were made by Bernevig, Hughes and Zhang, and were followed by the experimental verification at Würzburg, in the Molenkamp group. Within a couple of years, this work brought the concept of topological insulator from an abstract theoretical discovery to an experimental reality, which stimulated further work. The concept of topological insulators was extended to the case of three-dimensional systems, for which an ideal experimental probe is angle-resolved photo-emission spectroscopy. Using this technique, specific theoretical predictions that had been made regarding the topological insulating character of different materials (e.g., for Bi-based compounds such as BiSb, Bi2Se3 or Bi2Te3), were verified experimentally through the direct observation of the Dirac surface fermions. This research was sufficient to put on

  7. An Improved Method to Determine {sup 210}Pb, {sup 210}Bi and {sup 210}Po in air Aerosol Filters

    SciTech Connect

    Miguel, E. G. San; Bolivar, J. P.; Teran, T.

    2008-08-07

    {sup 222}Rn daughters (e.g. {sup 210}Pb, {sup 210}Po, {sup 210}Bi) have been widely used to study a variety of atmospheric processes. Many works in literature about {sup 222}Rn daughters do not specify the way by the activities of these radionuclides are calculated. Besides, {sup 210}Po corrections due to the in-growth of {sup 210}Bi, if taken into account, are not indicated. In this work, the increase in uncertainties of radionuclides activities due to delay between air sampling and radionuclides determinations have been evaluated and the influence of neglecting the contribution of {sup 210}Bi in-growth to {sup 210}Po determination has been estimated. The results indicate that, in general, ignoring the {sup 210}Bi in-growth in {sup 210}Po determinations lead to significant differences (could reach until 100%) between the estimation of {sup 210}Po activity and its true value.

  8. A thermodynamic model of nickel smelting and direct high-grade nickel matte smelting processes: Part II. distribution behaviors of Ni, Cu, Co, Fe, As, Sb, and Bi

    NASA Astrophysics Data System (ADS)

    Tan, Pengfu; Neuschütz, Dieter

    2001-04-01

    A thermodynamic model has been developed to predict the distribution behavior of Ni, Cu, Co, Fe, S, As, Sb, and Bi in nickel smelting and direct high-grade nickel matte smelting processes. The model has been validated by numerous experimental data and industrial data with a wide range of operating conditions. The effect of operating conditions on the distributions of Ni, Cu, Co, As, Sb, and Bi among the gas, matte, and slag phases has been investigated. It was found that the distribution behavior of Ni, Co, Cu, As, Sb, and Bi in the nickel smelting furnace depends on process parameters such as the smelting temperature, matte grade, oxygen enrichment, Fe/SiO2 ratio in the slag, Cu/Ni ratio in charge, and oil/air ratio. The parameters also have an influence on the behavior of Fe3O4 in the slag.

  9. Internal switching and backward inhibition in depression and rumination.

    PubMed

    Chen, Xiao; Feng, Zhengzhi; Wang, Tao; Su, Hong; Zhang, Lihong

    2016-09-30

    Prior research has suggested that impairments of switching abilities are associated with depression as well as rumination. Backward inhibition (BI) refers to the ability to inhibit the processing of previously relevant information and is demonstrated to be one of the key mechanisms underlying switching abilities. However, the association between BI in internal switching and depression/rumination remains uninvestigated. To examine this association, a modified Internal Shifting Task (IST) was administered to a sample of dysphoric and healthy control undergraduates. Results showed that depressive symptoms were not associated with difficulties in switching among subjects held in working memory, while trait ruminators performed poorly in switching internally. Surprisingly, no association between BI in internal switching and rumination/depressive symptoms was found. These findings indicate that rumination is characterized by poor performance in internal switching, but this deficit is not associated with BI. PMID:27449002

  10. Calculation of the fractional interstitial component of boron diffusion and segregation coefficient of boron in Si0.8Ge0.2

    NASA Astrophysics Data System (ADS)

    Fang, Tilden T.; Fang, Wingra T. C.; Griffin, Peter B.; Plummer, James D.

    1996-02-01

    Investigation of boron diffusion in strained silicon germanium buried layers reveals a fractional interstitial component of boron diffusion (fBI) in Se0.8Ge0.2 approximately equal to the fBI value in silicon. In conjunction with computer-simulated boron profiles, the results yield an absolute lower-bound of fBI in Si0.8Ge0.2 of ˜0.8. In addition, the experimental methodology provides a unique vehicle for measuring the segregation coefficient; oxidation-enhanced diffusion is used instead of an extended, inert anneal to rapidly diffuse the dopant to equilibrium levels across the interface, allowing the segregation coefficient to be measured more quickly.

  11. Multi-Bit Nano-Electromechanical Nonvolatile Memory Cells (Zigzag T Cells) for the Suppression of Bit-to-Bit Interference.

    PubMed

    Choi, Woo Young; Han, Jae Hwan; Cha, Tae Min

    2016-05-01

    Multi-bit nano-electromechanical (NEM) nonvolatile memory cells such as T cells were proposed for higher memory density. However, they suffered from bit-to-bit interference (BI). In order to suppress BI without sacrificing cell size, this paper proposes zigzag T cell structures. The BI suppression of the proposed zigzag T cell is verified by finite-element modeling (FEM). Based on the FEM results, the design of zigzag T cells is optimized. PMID:27483893

  12. Temporal and spatial stability in translation invariant linear resistive networks.

    PubMed

    Solak, M K

    1997-01-01

    Simple algebraic methods are proposed to evaluate the temporal and spatial stability of translation invariant linear resistive networks. Temporal stability is discussed for a finite number of nodes n. The proposed method evaluates stability of a Toeplitz pencil A(n)(a)+muB(n)(b) in terms of parameters a(i ) and b(i). In many cases a simple method allows one to verify positive definition of B(n)(b) in terms of b(i) only. PMID:18255673

  13. Three dimensional Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Zaheer, Saad

    We extend the physics of graphene to three dimensional systems by showing that Dirac points can exist on the Fermi surface of realistic materials in three dimensions. Many of the exotic electronic properties of graphene can be ascribed to the pseudorelativistic behavior of its charge carriers due to two dimensional Dirac points on the Fermi surface. We show that certain nonsymmorphic spacegroups exhibit Dirac points among the irreducible representations of the appropriate little group at high symmetry points on the surface of the Brillouin zone. We provide a list of all Brillouin zone momenta in the 230 spacegroups that can host Dirac points. We describe microscopic considerations necessary to design materials in one of the candidate spacegroups such that the Dirac point appears at the Fermi energy without any additional non-Dirac-like Fermi pockets. We use density functional theory based methods to propose six new Dirac semimetals: BiO 2 and SbO2 in the beta-cristobalite lattice (spacegroup 227), and BiCaSiO4, BiMgSiO4, BiAlInO 4, and BiZnSiO4 in the distorted spinels lattice (spacegroup 74). Additionally we derive effective Dirac Hamiltonians given group representative operators as well as tight binding models incorporating spin-orbit coupling. Finally we study the Fermi surface of zincblende (spacegroup 216) HgTe which is effectively point-like at Gamma in the Brillouin zone and exhibits accidental degeneracies along a threefold rotation axis. Whereas compressive strain gaps the band structure into a topological insulator, tensile strain shifts the accidental degeneracies away from Gamma and enlarges the Fermi surface. States on the Fermi surface exhibit nontrivial spin texture marked by winding of spins around the threefold rotation axis and by spin vortices indicating a change in the winding number. This is confirmed by microscopic calculations performed in tensile strained HgTe and Hg0.5Zn 0.5 Te as well as k.p theory. We conclude with a summary of recent

  14. Emission factors and exposures from ground-level pyrotechnics

    NASA Astrophysics Data System (ADS)

    Croteau, Gerry; Dills, Russell; Beaudreau, Marc; Davis, Mac

    Potential exposures from ground-level pyrotechnics were assessed by air monitoring and developing emission factors. Total particulate matter, copper and SO 2 exposures exceeded occupational health guidelines at two outdoor performances using consumer pyrotechnics. Al, Ba, B, Bi, Mg, Sr, Zn, and aldehyde levels were elevated, but did not pose a health hazard based on occupational standards. Emission factors for total particulate matter, metals, inorganic ions, aldehydes, and polyaromatic hydrocarbons (PAHs) were determined for seven ground-supported pyrotechnics through air sampling in an airtight room after combustion. Particle generation ranged from 5 to 13% of the combusted mass. Emission factors (g Kg -1) for metals common to pyrotechnics were also high: K, 23-45; Mg, 1-7; Cu, 0.05-7; and Ba, 0.03-6. Pb emission rates of 1.6 and 2.7% of the combusted mass for two devices were noteworthy. A high correlation ( r2 ≥ 0.89) between metal concentrations in pyrotechnic compositions and emission factors were noted for Pb, Cr, Mg, Sb, and Bi, whereas low correlations ( r2 ≤ 0.1) were observed for Ba, Sr, Fe, and Zn. This may be due to the inherent heterogeneity of multi-effect pyrotechnics. The generation of inorganic nitrogen in both the particulate (NO 2-, NO 3-) and gaseous (NO, NO 2) forms varied widely (<0.1-1000 mg Kg -1). Aldehyde emission factors varied by two orders of magnitude even though the carbon source was carbohydrates and charcoal for all devices: formaldehyde (<7.0-82 mg Kg -1), acetaldehyde (43-210 mg Kg -1), and acrolein (1.9-12 mg Kg -1). Formation of lower molecular weight PAHs such as naphthalene and acenaphthylene were favored, with their emission factors being comparable to that from the combustion of household refuse and agricultural debris. Ba, Sr, Cu, and Pb had emission factors that could produce exposures exceeding occupational exposure guidelines. Sb and unalloyed Mg, which are banned from consumer fireworks in the US, were present in

  15. Studies of flerovium and element 115 homologs with macrocyclic extractants

    NASA Astrophysics Data System (ADS)

    Despotopulos, John Dustin

    Study of the chemistry of the heaviest elements, Z ? 104, poses a unique challenge due to their low production cross-sections and short half-lives. Chemistry also must be studied on the one-atom-at-a-time scale, requiring automated, fast, and very efficient chemical schemes. Recent studies of the chemical behavior of copernicium (Cn, element 112) and flerovium (Fl, element 114) together with the discovery of isotopes of these elements with half-lives suitable for chemical studies have spurred a renewed interest in the development of rapid systems designed to study the chemical properties of elements with Z ≥ 114. This dissertation explores both extraction chromatography and solvent extraction as methods for development of a rapid chemical separation scheme for the homologs of flerovium (Pb, Sn, Hg) and element 115 (Bi, Sb), with the goal of developing a chemical scheme that, in the future, can be applied to on-line chemistry of both Fl and element 115. Macrocyclic extractants, specifically crown ethers and their derivatives, were chosen for these studies. Carrier-free radionuclides, used in these studies, of the homologs of Fl and element 115 were obtained by proton activation of high purity metal foils at the Lawrence Livermore National Laboratory (LLNL) Center for Accelerator Mass Spectrometry (CAMS): natIn(p,n)113Sn, natSn(p,n)124Sb, and Au(p,n)197m,gHg. The carrier-free activity was separated from the foils by novel separation schemes based on ion exchange and extraction chromatography techniques. Carrier-free Pb and Bi isotopes were obtained from development of a novel generator based on cation exchange chromatography using the 232U parent to generate 212Pb and 212Bi. Crown ethers show high selectivity for metal ions based on their size compared to the negatively charged cavity of the ether. Extraction by crown ethers occur based on electrostatic ion-dipole interactions between the negatively charged ring atoms (oxygen, sulfur, etc.) and the positively

  16. Studies of flerovium and element 115 homologs with macrocyclic extractants

    NASA Astrophysics Data System (ADS)

    Despotopulos, John Dustin

    Study of the chemistry of the heaviest elements, Z ? 104, poses a unique challenge due to their low production cross-sections and short half-lives. Chemistry also must be studied on the one-atom-at-a-time scale, requiring automated, fast, and very efficient chemical schemes. Recent studies of the chemical behavior of copernicium (Cn, element 112) and flerovium (Fl, element 114) together with the discovery of isotopes of these elements with half-lives suitable for chemical studies have spurred a renewed interest in the development of rapid systems designed to study the chemical properties of elements with Z ≥ 114. This dissertation explores both extraction chromatography and solvent extraction as methods for development of a rapid chemical separation scheme for the homologs of flerovium (Pb, Sn, Hg) and element 115 (Bi, Sb), with the goal of developing a chemical scheme that, in the future, can be applied to on-line chemistry of both Fl and element 115. Macrocyclic extractants, specifically crown ethers and their derivatives, were chosen for these studies. Carrier-free radionuclides, used in these studies, of the homologs of Fl and element 115 were obtained by proton activation of high purity metal foils at the Lawrence Livermore National Laboratory (LLNL) Center for Accelerator Mass Spectrometry (CAMS): natIn(p,n)113Sn, natSn(p,n)124Sb, and Au(p,n)197m,gHg. The carrier-free activity was separated from the foils by novel separation schemes based on ion exchange and extraction chromatography techniques. Carrier-free Pb and Bi isotopes were obtained from development of a novel generator based on cation exchange chromatography using the 232U parent to generate 212Pb and 212Bi. Crown ethers show high selectivity for metal ions based on their size compared to the negatively charged cavity of the ether. Extraction by crown ethers occur based on electrostatic ion-dipole interactions between the negatively charged ring atoms (oxygen, sulfur, etc.) and the positively

  17. Predicted Growth of Two-Dimensional Topological Insulators Consisting of Hydrogenated III-V Thin films on Si(111) Substrate

    NASA Astrophysics Data System (ADS)

    Chuang, Feng-Chuan; Crisostomo, Christian; Yao, Liang-Zi; Yeh, Chun-Chen; Lai, Shu-Ming; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Lin, Hsin; Albao, Marvin; Bansil, Arun

    We have carried out systematic first-principles electronic structure calculations of growth of ultrathin films of compounds of group III (B, Al, In, Ga and Tl) with group V (N, P, As, Sb and Bi) elements on Si(111) substrate, including effects of hydrogenation. A total of six compounds (GaBi, InBi, TlBi, TlAs, TlSb and TlN) are identified to be nontrivial in unhydrogenated case; whereas for hydrogenated case, only four (GaBi, InBi, TlBi and TlSb) remains nontrivial. The band gap is found to be as large as 855 meV for the hydrogenated TlBi film, making this class of III-V materials suitable for room temperature applications. TlBi remains topologically nontrivial with a large band gap at various hydrogen coverages, indicating the robustness of its band topology against bonding effects of substrates. Two bilayers (BLs) of AlBi, InBi, GaBi, TlAs and TlSb are found to support a topological phase over a wide range of strains, in addition to BBi, TlN and TlBi which can be driven into the nontrivial phase via strain. One and two BL films of GaBi and 2 BL films of InBi and TlAs on Si(111) surface possess nontrivial phases with a band gap as large as 121 meV in the case of 2 BL film of GaBi. Persistence of the nontrivial phase upon hydrogenations in the III-V thin films suggests that these films are suitable for growing on various substrates.

  18. Laser-induced oxidation of Zn and Zn alloy films for direct-write grayscale photomasks

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Chang, Marian; Tu, Yuqiang; Poon, David K.; Chapman, Glenn H.; Choo, Chinheng; Peng, Jun

    2006-02-01

    Previous research showed that bimetallic Bi/In and Sn/In films exhibit good grayscale levels after laser exposure due to controlled film oxidation. While giving a large alteration in optical density (OD) from 3.0OD to 0.22OD at 365 nm, Bi/In and Sn/In films show a very nonlinear OD change with laser power, making fine control of grayscale writing difficult at some gray levels. This paper studies Zn and Zn alloy films as possible candidates for improved direct-write grayscale photomask applications. Zn and Zn alloys laser oxidation have been reported previously, but without grayscale optical measurements and applications. In this paper Zn films (50 nm ~ 240 nm), Sn/Zn (100 nm), Al/Zn (100 nm), Bi/Zn (100 nm) and In/Zn (100 nm) were DC- and RF-sputtered onto glass slides and then were scanned by argon ion CW laser (488 nm). Among these films, the highest OD change, 3OD (from 3.2OD before exposure to 0.2OD after laser exposure) at 365 nm, was found in the In/Zn (25/75 nm or 84at% Zn) film. The characterization of grayscale level to laser power modulation in Zn and Zn alloy films with various thickness or composition ratios were investigated. The Zn OD change versus laser power curve is more linear than those of Sn/In and Bi/In films. In/Zn films have better characterization of grayscale level versus laser writing power than pure Zn film. Among these four Zn alloy films, Zn/Al shows most linear relation of OD at 365 nm to laser power modulation.

  19. Does Brief Intervention Work For Heavy Episodic Drinking? A Comparison of Emergency Department Patients in Two Cultures

    PubMed Central

    Ye, Yu; Moskalewicz, Jacek; Swiatkiewicz, Grazyna

    2015-01-01

    Little has been reported on the efficacy of brief intervention (BI) among heavy episodic drinkers, although this drinking style is known to be especially harmful in relation to negative consequences including alcohol-related injuries. The comparative efficacy of BI is analyzed in two similar randomized controlled clinical trials of emergency department (ED) patients in two different cultures, both of which exhibit similar drinking styles of heavy episodic drinking: Poland and Mexican-Americans in the U.S. Improvements in drinking and problem outcomes are analyzed at 3-month and 12-month follow-up, using random effects modeling, among 446 Polish patients and 698 Mexican-American patients, randomized to screened only, assessment, and intervention conditions in each study. In Poland significant improvement was observed in all outcome measures for the assessed condition at 3-months compared to baseline, but only in the two problem variables at 12-months, while for the intervention condition, significant improvement was found in all outcome measures at both time periods; however, estimates of the interaction terms were not statistically significant. In the Mexica-American study, while significant improvement in nearly all outcome measures were observed at 3 months and 12 months for both conditions, estimates of the interaction terms suggest that for all drinking variables, but not problem variables, outcomes were significantly improved for the intervention condition over the assessed condition at 12 months, suggesting a 12-month intervention effect. Findings here are non-conclusive regarding a treatment effect of BI for heavy episodic drinking in ED patients. Given the mixed findings for BI in other ED studies, future studies need to explore the efficacy of BI in other populations and cultures exhibiting different drinking patterns to help identify what type of drinker would most benefit from BI in the ED setting. PMID:26688611

  20. Interaction of High-Energy Proton Beam with a Thin Target and Multiplicities of Neutron

    SciTech Connect

    Demirkol, I.; Tatar, M.; Safak, M. S.; Arasoglu, A.; Tel, E.

    2007-04-23

    An important ingredient in the performance of accelerator driven systems for energy production, waste transmutation and other applications are the number of spallation neutrons produced per incident proton. The neutron multiplicities, angular and energy distributions are usually calculated using simulation codes. We have presented multiplicities of the neutrons emitted in the interaction of a high-energy proton (1500 MeV) with a thin target Pb, Bi. In this study we have used the code ISABEL to calculate multiplicities of the neutron emitted. The results obtained have been compared with the available data.

  1. Theoretical investigations of optical properties of Ga(In)AsBi quantum well systems using 8-band and 14-band models

    NASA Astrophysics Data System (ADS)

    Gladysiewicz, M.; Ivashev, I.; Wartak, M. S.

    2016-03-01

    We report on possible consequences of alloying of GaAs with GaBi or InBi on band structure and material gain of quantum wells. Typical considered structure consists of 8nm wide GaAsBi quantum well on GaAs substrate. Our analysis is performed using 8-band and 14-band kp models. The obtained results indicate that for GaInAsBi/InP quantum well with 5% of Bi it might be possible to achieve emission wavelengths around 4 μm .

  2. Volatile/mobile trace elements in Karoonda /C4/ chondrite

    NASA Technical Reports Server (NTRS)

    Matza, S. D.; Lipschutz, M. E.

    1977-01-01

    Concentrations of ten volatile/mobile trace elements and of nonvolatile Co in the Karoonda (C4) meteorite were determined, and the atomic abundances relative to C1 are compared with values for the Murchison (C2) and Allende (C3) meteorites. Empirical Bi, In, and Tl data for Karoonda and heated Allende and Murchison are compared with theoretical curves for condensation from a gas of cosmic composition at low pressures. It is suggested that Karoonda might derive from low-temperature open-system metamorphism of pristine C3-like material.

  3. Cs5Sn9(OH)·4NH3

    PubMed Central

    Friedrich, Ute; Korber, Nikolaus

    2014-01-01

    The title compound, penta­caesium nona­stannide hydroxide tetra­ammonia, crystallized from a solution of CsSnBi in liquid ammonia. The Sn9 4− unit forms a monocapped quadratic anti­prism. The hydroxide ion is surrounded by five caesium cations, which form a distorted quadratic pyramidal polyhedron. A three-dimensional network is formed by Cs—Sn [3.8881 (7) Å to 4.5284 (7) Å] and Cs—NH3 [3.276 (7)–3.636 (7) Å] contacts. PMID:24940189

  4. First Measurement of Several β-Delayed Neutron Emitting Isotopes Beyond N=126.

    PubMed

    Caballero-Folch, R; Domingo-Pardo, C; Agramunt, J; Algora, A; Ameil, F; Arcones, A; Ayyad, Y; Benlliure, J; Borzov, I N; Bowry, M; Calviño, F; Cano-Ott, D; Cortés, G; Davinson, T; Dillmann, I; Estrade, A; Evdokimov, A; Faestermann, T; Farinon, F; Galaviz, D; García, A R; Geissel, H; Gelletly, W; Gernhäuser, R; Gómez-Hornillos, M B; Guerrero, C; Heil, M; Hinke, C; Knöbel, R; Kojouharov, I; Kurcewicz, J; Kurz, N; Litvinov, Yu A; Maier, L; Marganiec, J; Marketin, T; Marta, M; Martínez, T; Martínez-Pinedo, G; Montes, F; Mukha, I; Napoli, D R; Nociforo, C; Paradela, C; Pietri, S; Podolyák, Zs; Prochazka, A; Rice, S; Riego, A; Rubio, B; Schaffner, H; Scheidenberger, Ch; Smith, K; Sokol, E; Steiger, K; Sun, B; Taín, J L; Takechi, M; Testov, D; Weick, H; Wilson, E; Winfield, J S; Wood, R; Woods, P; Yeremin, A

    2016-07-01

    The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N≳126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis. PMID:27419564

  5. First Measurement of Several β -Delayed Neutron Emitting Isotopes Beyond N =126

    NASA Astrophysics Data System (ADS)

    Caballero-Folch, R.; Domingo-Pardo, C.; Agramunt, J.; Algora, A.; Ameil, F.; Arcones, A.; Ayyad, Y.; Benlliure, J.; Borzov, I. N.; Bowry, M.; Calviño, F.; Cano-Ott, D.; Cortés, G.; Davinson, T.; Dillmann, I.; Estrade, A.; Evdokimov, A.; Faestermann, T.; Farinon, F.; Galaviz, D.; García, A. R.; Geissel, H.; Gelletly, W.; Gernhäuser, R.; Gómez-Hornillos, M. B.; Guerrero, C.; Heil, M.; Hinke, C.; Knöbel, R.; Kojouharov, I.; Kurcewicz, J.; Kurz, N.; Litvinov, Yu. A.; Maier, L.; Marganiec, J.; Marketin, T.; Marta, M.; Martínez, T.; Martínez-Pinedo, G.; Montes, F.; Mukha, I.; Napoli, D. R.; Nociforo, C.; Paradela, C.; Pietri, S.; Podolyák, Zs.; Prochazka, A.; Rice, S.; Riego, A.; Rubio, B.; Schaffner, H.; Scheidenberger, Ch.; Smith, K.; Sokol, E.; Steiger, K.; Sun, B.; Taín, J. L.; Takechi, M.; Testov, D.; Weick, H.; Wilson, E.; Winfield, J. S.; Wood, R.; Woods, P.; Yeremin, A.

    2016-07-01

    The β -delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β -decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N ≳126 . These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β -decay strength distribution. This provides important constraints on global theoretical models currently used in r -process nucleosynthesis.

  6. Combinatorial pulsed laser deposition of doped yttrium iron garnet films on yttrium aluminium garnet

    SciTech Connect

    Sposito, A. Eason, R. W.; Gregory, S. A.; Groot, P. A. J. de

    2014-02-07

    We investigate the crystalline growth of yttrium iron garnet (YIG) films doped with bismuth (Bi) and cerium (Ce) by combinatorial pulsed laser deposition, co-ablating a YIG target and either a Bi{sub 2}O{sub 3} or a CeO{sub 2} target, for applications in microwave and optical communications. Substrate temperature is critical for crystalline growth of YIG with simultaneous inclusion of Bi in the garnet lattice, whereas Ce is not incorporated in the garnet structure, but forms a separate CeO{sub 2} phase.

  7. Robust Large Gap Two-Dimensional Topological Insulators in Hydrogenated III-V Buckled Honeycombs.

    PubMed

    Crisostomo, Christian P; Yao, Liang-Zi; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Lin, Hsin; Albao, Marvin A; Bansil, Arun

    2015-10-14

    A large gap two-dimensional (2D) topological insulator (TI), also known as a quantum spin Hall (QSH) insulator, is highly desirable for low-power-consuming electronic devices owing to its spin-polarized backscattering-free edge conducting channels. Although many freestanding films have been predicted to harbor the QSH phase, band topology of a film can be modified substantially when it is placed or grown on a substrate, making the materials realization of a 2D TI challenging. Here we report a first-principles study of possible QSH phases in 75 binary combinations of group III (B, Al, Ga, In, and Tl) and group V (N, P, As, Sb, and Bi) elements in the 2D buckled honeycomb structure, including hydrogenation on one or both sides of the films to simulate substrate effects. A total of six compounds (GaBi, InBi, TlBi, TlAs, TlSb, and TlN) are identified to be nontrivial in unhydrogenated case; whereas for hydrogenated case, only four (GaBi, InBi, TlBi, and TlSb) remains nontrivial. The band gap is found to be as large as 855 meV for the hydrogenated TlBi film, making this class of III-V materials suitable for room temperature applications. TlBi remains topologically nontrivial with a large band gap at various hydrogen coverages, indicating the robustness of its band topology against bonding effects of substrates. PMID:26390082

  8. Prediction of Large-Gap Two-Dimensional Topological Insulators Consisting of Hydrogenated Bilayers of Group III Elements with Bi

    NASA Astrophysics Data System (ADS)

    Crisostomo, Christian P.; Yao, Liang-Zi; Huang, Zhi-Quan; Hsu, Chia-Hsiu; Chuang, Feng-Chuan; Lin, Hsin; Albao, Marvin A.; Bansil, Arun

    2015-03-01

    We use first-principles electronic structure calculations to predict a new class of two-dimensional (2D) topological insulators (TIs) in hydrogenated binary compositions of group III elements (B, Al, Ga, In, and Tl) and bismuth (Bi). We identify band inversions in unhydrogenated pristine GaBi, InBi, and TlBi bilayers, with gaps as large as 556 meV for the TlBi case, making these materials suitable for room-temperature applications. Double-sided hydrogenation in which hydrogen was added on opposite sides also exhibited band inversions in the case of GaBi, InBi, and TlBi just as in the unhydrogenated pristine ones. Furthermore, we report the gap to be 885 meV for the hydrogenated TlBi case. Hydrogenation enhace the band gap without changing the band topology. Moreover, our study also aim to demonstrate the possibility of strain engineering in that the topological phase transition in systems whose phase was nontrivial could be driven by suitable strain. Finally, the effect of placing hydrogen to topological edges was also demonstrated. Our findings suggest that the buckled honeycomb structure is a versatile platform for hosting nontrivial topological states and spin-polarized Dirac fermions with the flexibility of chemical and mechanical tunability. The robustness of III-Bi upon hydrogenation shows that these materials are possible to synthesize by growing on substrates.

  9. Bioelectrical impedance changes in regional extracellular fluid alterations.

    PubMed

    Kim, C T; Findley, T W; Reisman, S R

    1997-08-01

    The purpose of this study was to determine whether changes in bioelectrical impedance (BI) can reveal regional extracellular fluid (ECF) alterations. ECF changes were induced by holding various arm positions for ten minutes, and they were evaluated through the measurement of BI in eight normal adult subjects. A low frequency current (100 Hz, 0.50 mA) was applied using an electromyography machine through two current electrodes, and the voltage signals were recorded by two amplitude electrodes. The corresponding BI was calculated by Ohm's law, resistance = voltage/current (R = V/I). There was no significant difference between BI and time interval, but between BI and arm position (two-way ANOVA with replicate, p = 0.954, p < 0.001). BI has a negative correlation with wrist circumference. These results show that this experimental method can be used as reflection of ECF changes and that both position and wrist circumference are major factors for BI in the upper extremity. PMID:9298342

  10. Anxiety-related behavioral inhibition in rats: a model to examine mechanisms underlying the risk to develop stress-related psychopathology.

    PubMed

    Qi, C; Roseboom, P H; Nanda, S A; Lane, J C; Speers, J M; Kalin, N H

    2010-11-01

    Behavioral inhibition (BI) is an adaptive defensive response to threat; however, children who display extreme BI as a stable trait are at risk for development of anxiety disorders and depression. The present study validates a rodent model of BI based on an ethologically relevant predator exposure paradigm. We show that individual differences in rat BI are stable and trait-like from adolescence into adulthood. Using in situ hybridization to quantify expression of the immediate early genes homer1a and fos as measures of neuronal activation, we show that individual differences in BI are correlated with the activation of various stress-responsive brain regions that include the paraventricular nucleus of the hypothalamus and CA3 region of the hippocampus. Further supporting the concept that threat-induced BI in rodents reflects levels of anxiety, we also show that BI is decreased by administration of the anxiolytic, diazepam. Finally, we developed criteria for identifying extreme BI animals that are stable in their expression of high levels of BI and also show that high BI (HBI) individuals exhibit maladaptive appetitive responses following stress exposure. These findings support the use of predator threat as a stimulus and HBI rats as a model to study mechanisms underlying extreme and stable BI in humans. PMID:20738409