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Sample records for nanochastitsy bi te

  1. Optical properties and electronic structure of BiTeCl and BiTeBr compounds

    Science.gov (United States)

    Makhnev, A. A.; Nomerovannaya, L. V.; Kuznetsova, T. V.; Tereshchenko, O. E.; Kokh, K. A.

    2016-09-01

    Optical properties of BiTeCl and BiTeBr compounds with a strong Rashba spin-orbit coupling are studied in the 0.08-5.0 eV range using the optical ellipsometry method. Fundamental characteristics of the electronic structure are obtained. Similarly to BiTeI, spectra of the imaginary part of dielectric permittivity constant ɛ2( E) in the energy interval between the plasma edge and the threshold of an intense interband absorption (0.7 eV in BiTeCl and 0.6 eV in BiTeBr) display a fine structure of electronic transitions at 0.25 and 0.55 eV in BiTeCl and 0.20 and 0.50 eV in BiTeBr. These features are assigned to electronic transitions between the bulk conduction zones split by the Rashba spin-orbit interaction. The parameters of the electronic structure of BiTeCl and BiTeBr are compared with the BiTeI compound that was studied earlier. In the BiTeCl-BiTeBr-BiTeI row, the absorption edge and main features of the fundamental absorption exhibit a shift to low energies.

  2. Electronic structures and stability of Ni/Bi2Te3 and Co/Bi2Te3 interfaces

    KAUST Repository

    Xiong, Ka

    2010-03-04

    We investigate the electronic structures and stability for Ni/Bi 2Te3, NiTe/Bi2Te3, Co/Bi 2Te3 and CoTe2/Bi2Te3 interfaces by first-principles calculations. It is found that the surface termination strongly affects the band alignment. Ni and Co are found to form Ohmic contacts to Bi2Te3. The interface formation energy for Co/Bi2Te3 interfaces is much lower than that of Ni/Bi2Te3 interfaces. Furthermore, we found that NiTe on Bi2Te3 is more stable than Ni, while the formation energies for Co and CoTe2 on Bi2Te3 are comparable. © 2010 IOP Publishing Ltd.

  3. Reduction in thermal conductivity of BiSbTe lump

    Science.gov (United States)

    Ahmad, Kaleem; Wan, C.; Al-Eshaikh, M. A.; Kadachi, A. N.

    2017-03-01

    In this work, systematic investigations on the thermal conductivities of BiSbTe lump, microstructured pristine BiSbTe bulk and single wall carbon nanotubes (SWCNTs)/BiSbTe bulk nanocomposites were performed. BiSbTe lumps were crushed to form a coarse powder (200 µm) and effect of particle size reduction on the effective thermal conductivity of BiSbTe (200 µm) bulk were analyzed. For further reduction in the conductivity, a two pronged strategy has been employed. First, additional refinement of BiSbTe (200 µm) were performed through ball milling in an inert environment. Second, SWCNTs in 0.75, and 1.0 vol% were distributed uniformly in the fine BiSbTe ball milled powder. The results showed that the effective thermal conductivities decrease with the reduction in the particle size from lump to BiSbTe (200 µm) bulk as well as with the addition of SWCNTs accompanied by further refinement of BiSbTe particles. The significant reduction in thermal conductivities of the lump was achieved for pure BiSbTe (200 µm) bulk and 0.75 vol% of SWCNTs/BiSbTe composite. This can be ascribed to the enhanced phonon scattering by the grain boundaries between the nanostructured BiSbTe particles as well as the interfaces between BiSbTe and the low dimensional carbon nanotubes.

  4. Reduction in thermal conductivity of BiSbTe lump

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, Kaleem [King Saud University, Sustainable Energy Technologies Center, College of Engineering, PO Box 800, Riyadh (Saudi Arabia); Wan, C. [Tsinghua University, State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Beijing (China); Al-Eshaikh, M.A.; Kadachi, A.N. [King Saud University, Research Center, College of Engineering, PO Box 800, Riyadh (Saudi Arabia)

    2017-03-15

    In this work, systematic investigations on the thermal conductivities of BiSbTe lump, microstructured pristine BiSbTe bulk and single wall carbon nanotubes (SWCNTs)/BiSbTe bulk nanocomposites were performed. BiSbTe lumps were crushed to form a coarse powder (200 μm) and effect of particle size reduction on the effective thermal conductivity of BiSbTe (200 μm) bulk were analyzed. For further reduction in the conductivity, a two pronged strategy has been employed. First, additional refinement of BiSbTe (200 μm) were performed through ball milling in an inert environment. Second, SWCNTs in 0.75, and 1.0 vol% were distributed uniformly in the fine BiSbTe ball milled powder. The results showed that the effective thermal conductivities decrease with the reduction in the particle size from lump to BiSbTe (200 μm) bulk as well as with the addition of SWCNTs accompanied by further refinement of BiSbTe particles. The significant reduction in thermal conductivities of the lump was achieved for pure BiSbTe (200 μm) bulk and 0.75 vol% of SWCNTs/BiSbTe composite. This can be ascribed to the enhanced phonon scattering by the grain boundaries between the nanostructured BiSbTe particles as well as the interfaces between BiSbTe and the low dimensional carbon nanotubes. (orig.)

  5. Radioisotope Thermoelectric Generators Based on Segmented BiTe/PbTe-BiTe/TAGS/PbSnTe

    Science.gov (United States)

    McAlonan, Malachy; Patel, Kalpesh; Cummer, Keith

    2006-01-01

    This paper reports on Phase 1 of a multifaceted effort to develop a more efficient radioisotope thermoelectric generator (RTG) for future NASA missions. The conversion efficiency goal is 10% or higher at a power level of 20 watt or higher. The thermoelectric (T/E) efficiency achievable with present T/E materials is about 8% for favorable temperatures. Thermoelectric converter designs, T/E material properties, and T/E couple thermal and electrical performance were investigated in Phase 1 of this program to find paths to improve conversion efficiency. T/E properties can be improved by optimizing the composition of the materials and by improving the micro structural characteristics such as homogeneity, grain size, and phases present. T/E couple performance can be improved by reducing the electrical and thermal contact resistances of the couple and within the segmented T/E elements. Performance and reliability improvements can be achieved by reducing the thermo-mechanical stresses, improving the quality of the bonds and interfaces, minimizing the number of required bonds, and reducing the degradation rates of both the T/E materials and the bonds. This paper focuses on one portion of the activity, i.e., the design of a small converter. In the converter design effort, a prototypic 20-watt device, suitable for use with a single general-purpose heat source (GPHS), was built using an optimized converter design of segmented thermoelectric elements of heritage composition. The 20-watt prototype achieved the power predicted for the test conditions. The chosen couple design used segmented BiTe/PbTe for the n-type element and BiTe/TAGS/PbSnTe, for the p-type T/E element. Use of the BiTe segment exploits the opportunity of the small RTG to operate at lower heat rejection temperatures and results in much higher conversion efficiency, the main objective of the NASA program. Long term data on similarly segmented couples at Teledyne together with the 20-watt module test results

  6. Ab initio calculation of the growth of Te nanorods and Bi2Te3 nanoplatelets

    Institute of Scientific and Technical Information of China (English)

    Tian Xiao-Qing; Du Shi-Xuan; Gao Hong-Jun

    2008-01-01

    In this paper the growth mechanism of a Te/Bi2Te3 novel structure is studied by ab-initio calculations.The results show that the growth of Te nanorods is determined by the adsorption energy of Te atoms on different crystalline Te surfaces.The adsorption energy of Te on the Te (001) surface is 3.29 eV,which is about 0.25 eV higher than that of Te on the Te (110).This energy difference makes the preferential growth direction along the < 001> direction.In addition,the higher surface energy of Bi2Te3 (110) and the lattice misfit between crystalline Bi2Te3 and Te along < 001> direction are considered to explain the growth of the Bi2Te3 nanoplatelets,in which Volmer-Weber model is used.The theoretical results axe in agreement with experimental observation.

  7. Orbital-dependent Rashba coupling in bulk BiTeCl and BiTeI

    KAUST Repository

    Zhu, Zhiyong

    2013-02-06

    By all-electron ab initio calculations, the layered polar semiconductor BiTeCl is shown to host giant bulk Rashba spin splitting, similar to the recently reported compound BiTeI. In both materials, the standard Rashba–Bychkov model is no longer applicable, because of huge band extrema shifts even in the absence of spin–orbit coupling and a strong momentum dependence of the Rashba coupling constant (αR). By assuming αR to be orbital dependent, a phenomenological extension of the Rashba–Bychkov model is proposed which explains the splitting behavior of states with small in-plane momentum.

  8. Extreme solid state refrigeration using nanostructured Bi-Te alloys.

    Energy Technology Data Exchange (ETDEWEB)

    Lima Sharma, Ana L. (San Jose State University, San Jose, CA); Spataru, Dan Catalin; Medlin, Douglas L.; Sharma, Peter Anand; Morales, Alfredo Martin

    2009-09-01

    Materials are desperately needed for cryogenic solid state refrigeration. We have investigated nanostructured Bi-Te alloys for their potential use in Ettingshausen refrigeration to liquid nitrogen temperatures. These alloys form alternating layers of Bi{sub 2} and Bi{sub 2}Te{sub 3} blocks in equilibrium. The composition Bi{sub 4}Te{sub 3} was identified as having the greatest potential for having a high Ettingshausen figure of merit. Both single crystal and polycrystalline forms of this material were synthesized. After evaluating the Ettingshausen figure of merit for a large, high quality polycrystal, we simulated the limits of practical refrigeration in this material from 200 to 77 K using a simple device model. The band structure was also computed and compared to experiments. We discuss the crystal growth, transport physics, and practical refrigeration potential of Bi-Te alloys.

  9. On the electronic structure and thermoelectric properties of BiTeBr and BiTeI single crystals and of BiTeI with the addition of BiI{sub 3} and CuI

    Energy Technology Data Exchange (ETDEWEB)

    Kulbachinskii, Vladimir A., E-mail: kulb@mig.phys.msu.ru [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Kytin, Vladimir G.; Kudryashov, Alexey A. [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Kuznetsov, Alexei N.; Shevelkov, Andrei V. [Chemistry Department, Lomonosov Moscow State University, Moscow 119991 (Russian Federation)

    2012-09-15

    The electronic structures were calculated for BiTeBr and BiTeI using the density-functional theory approach and accounting for the strong spin-orbital interaction. Qualitatively, the band structures for two compounds are similar, showing strong mixing of the p states of all elements in vicinity of the Fermi level, with the band gaps of 0.595 and 0.478 eV for BiTeBr and BiTeI, respectively. The optimized crystal structures show a tendency for the Bi-X (X=Br, I) bond elongation compared to the Bi-Te one. Both compounds are intrinsic n-type semiconductors but display a metallic-like conductivity coupled to rather large thermopower, which is rationalized within the frames of the acoustic phonons scattering model. Because of larger thermopower BiTeBr exhibits a twice higher thermoelectric figure-of-merit near room temperature, ZT=0.17, compared to BiTeI. The addition of 1 mass% of BiI{sub 3} or CuI to BiTeI decreases the mobility of electrons by two orders of magnitude, leading to significantly lower electrical conductivity, but at the same time effectively reduces the thermal conductivity. The prospects of further enhancing the thermoelectric efficiency are briefly discussed. - Graphical abstract: View of the crystal structure of BiTeBr is shown in the figure The optimized crystal structures show a tendency for the Bi-X (X=Br, I) bond elongation compared to the Bi-Te one. The electronic structures were calculated for BiTeBr and BiTeI using the density-functional theory approach and accounting for the strong spin-orbital interaction. Qualitatively, the band structures for two compounds are similar, showing strong mixing of the p states of all elements in vicinity of the Fermi level, with the band gaps of 0.595 and 0.478 eV for BiTeBr and BiTeI, respectively. Both compounds are intrinsic n-type semiconductors but display a metallic-like conductivity coupled to rather large thermopower, which is rationalized within the frames of the acoustic phonons scattering model. The

  10. Phase equilibria and the thermodynamic properties of saturated solid solutions of BiTeI, Bi2TeI, and Bi4TeI1.25 compounds of the AgI-Bi-Bi2Te3-BiTeI system

    Science.gov (United States)

    Moroz, M. V.; Prokhorenko, M. V.

    2016-07-01

    The phase equilibria of the Ag-Bi-Te-I system in the part AgI-Bi-Bi2Te3-BiTeI is studied in the interval of 500-540 K by means of physicochemical analysis. Thermodynamic properties of phases are determined via EMF. Potential-forming processes occur in electrochemical cells (ECCs) of the C|Ag|glass Ag3GeS3I|D|C structure (where C denotes inert (graphite) electrodes; Ag, D denotes ECC electrodes; D denotes four-phase alloys of the AgI-Bi-Bi2Te3-BiTeI system; and Ag3GeS3I glass is the selective Ag+ conducting membrane). Linear dependences of the EMFs of cells E(T) in the interval of 505-535 K are used to calculate the values of the thermodynamic functions of BiTeI, Bi2TeI, and Bi4TeI1.25 phases saturated over silver.

  11. Rational design and controlled synthesis of Te/Bi2Te3 heterostructure nanostring composites

    Science.gov (United States)

    Zhang, Yuzhuo; Chen, Hong; Li, Zhiliang; Huang, Ting; Zheng, Shuqi

    2015-07-01

    Te/Bi2Te3 heterostructure nanostring composites composed of several Bi2Te3 nanoplates, which were perpendicularly strung together by Te nanorod, were rationally designed and synthesized via a facile solvothermal method on a large scale. The X-ray diffraction (XRD) characterization demonstrated that the Bi2Te3 nanoplates were rhombohedral phase and the Te nanorods were trigonal phase. The uniform nanostring morphologies were well characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Detailed heterostructures were proved via energy dispersive spectrometer (EDS) and high-resolution transmission electron microscope (HRTEM). The morphology transformation from Bi2Te3 nanoplates to Te/Bi2Te3 heterostructure nanostrings could be controlled by adjusting the ratio of bismuth oxide to tellurium oxide. NaOH, serving as catalytic reduction agent and morphology controlling agent, played an important role in the synthesis of Te/Bi2Te3 heterostructure nanostrings. The reaction mechanism was also proposed to explain the formation process of the composites and the specific function of reagents in this reaction system.

  12. Lattice dynamics in Bi2Te3 and Sb2Te3: Te and Sb density of phonon states

    Science.gov (United States)

    Bessas, D.; Sergueev, I.; Wille, H.-C.; Perßon, J.; Ebling, D.; Hermann, R. P.

    2012-12-01

    The lattice dynamics in Bi2Te3 and Sb2Te3 were investigated both microscopically and macroscopically using 121Sb and 125Te nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements. In combination with earlier inelastic neutron scattering data, the element-specific density of phonon states was obtained for both compounds and phonon polarization analysis was carried out for Bi2Te3. A prominent peak in the Te specific density of phonon states at 13meV, that involves mainly in-plane vibrations, is mostly unaffected upon substitution of Sb with Bi revealing vibrations with essentially Te character. A significant softening is observed for the density of vibrational states of Bi with respect to Sb, consistently with the mass homology relation in the long-wavelength limit. In order to explain the energy mismatch in the optical phonon region, a ˜20% force constant softening of the Sb-Te bond with respect to the Bi-Te bond is required. The reduced average speed of sound at 20K in Bi2Te3, 1.75(1)km/s, compared to Sb2Te3, 1.85(4)km/s, is not only related to the larger mass density but also to a larger Debye level. The observed low lattice thermal conductivity at 295K, 2.4Wm-1K-1 for Sb2Te3 and 1.6Wm-1K-1 for Bi2Te3, cannot be explained by anharmonicity alone given the rather modest Grüneisen parameters, 1.7(1) for Sb2Te3 and 1.5(1) for Bi2Te3, without accounting for the reduced speed of sound and more importantly the low acoustic cutoff energy.

  13. Phonons in Bi2Te3 and Bi2Se3 Thin Films

    Science.gov (United States)

    Ren, Shang-Fen; Cheng, Wei

    2010-03-01

    Bi2Te3 and Bi2Se3 are topological insulators with interesting surface properties that have attracted great research attention in recent years. In this research, phonon dispersion curves and phonon density of states of Bi2Te3 and Bi2Se3 thin films with five atomic-layers are calculated by Medea-VASP program, and thermal dynamic functions are also analyzed. Phonon results of these two thin films are compared with each other and are also compared with available bulk measurements. Symmetry broken is found in the Brillouin zone center phonon modes.

  14. Low temperature magnetothermoelectric effect and magnetoresistance in Te vapor annealed Bi2Te3.

    Science.gov (United States)

    Hor, Y S; Qu, D; Ong, N P; Cava, R J

    2010-09-22

    The electrical properties of single crystals of p-type Bi(2)Te(3) are shown to be tuned by annealing as-grown crystals in elemental Te vapor at temperatures in the range of 400-420 °C. While as-grown nominally stoichiometric Bi(2)Te(3) has p-type conductivity below room temperature, Te vapor annealed Bi(2)Te(3) shows a cross over from p- to n-type behavior. The temperature dependent resistivity of the Te annealed crystals shows a characteristic broad peak near 100 K. Applied magnetic fields give rise to a large low temperature magnetothermoelectric effect in the Te annealed samples and enhance the low temperature peak in the resistivity. Further, Te annealed Bi(2)Te(3) shows a large positive magnetoresistance, ∼ 200% at 2 K, and ∼ 15% at room temperature. The annealing procedure described can be employed to optimize the properties of Bi(2)Te(3) for study as a topological insulator.

  15. Phonon spectroscopy in a Bi2Te3 nanowire array

    Science.gov (United States)

    Bessas, Dimitrios; Töllner, William; Aabdin, Zainul; Peranio, Nicola; Sergueev, Ilya; Wille, Hans-Christian; Eibl, Oliver; Nielsch, Kornelius; Hermann, Raphaël P.

    2013-10-01

    The lattice dynamics in an array of 56 nm diameter Bi2Te3 nanowires embedded in a self-ordered amorphous alumina membrane were investigated microscopically using 125Te nuclear inelastic scattering. The element specific density of phonon states is measured on nanowires in two perpendicular orientations and the speed of sound is extracted. Combined high energy synchrotron radiation diffraction and transmission electron microscopy was carried out on the same sample and the crystallinity was investigated. The nanowires grow almost perpendicular to the c-axis, partly with twinning. The average speed of sound in the 56 nm diameter Bi2Te3 nanowires is ~7% smaller with respect to bulk Bi2Te3 and a decrease in the macroscopic lattice thermal conductivity by ~13% due to nanostructuration and to the reduced speed of sound is predicted.

  16. Vibrational properties of epitaxial Bi4Te3 films as studied by Raman spectroscopy

    Directory of Open Access Journals (Sweden)

    Hao Xu

    2015-08-01

    Full Text Available Bi4Te3, as one of the phases of the binary Bi–Te system, shares many similarities with Bi2Te3, which is known as a topological insulator and thermoelectric material. We report the micro-Raman spectroscopy study of 50 nm Bi4Te3 films on Si substrates prepared by molecular beam epitaxy. Raman spectra of Bi4Te3 films completely resolve the six predicted Raman-active phonon modes for the first time. Structural features and Raman tensors of Bi4Te3 films are introduced. According to the wavenumbers and assignments of the six eigenpeaks in the Raman spectra of Bi4Te3 films, it is found that the Raman-active phonon oscillations in Bi4Te3 films exhibit the vibrational properties of those in both Bi and Bi2Te3 films.

  17. High thermoelectric potential of Bi2Te3 alloyed GeTe-rich phases

    Science.gov (United States)

    Madar, Naor; Givon, Tom; Mogilyansky, Dmitry; Gelbstein, Yaniv

    2016-07-01

    In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)1-x(Bi2Te3)x alloys, with x values of up to 20%. Higher solubility limit of Bi2Te3 in GeTe, than previously reported, was identified around ˜9%, extending the doping potential of GeTe by the Bi2Te3 donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ˜1.55 at ˜410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%-17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge8Bi2Te11 and Ge4Bi2Te7 phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi2Te3), was suggested for further electronic optimization of the thermoelectric properties.

  18. LaBiTe3: An unusual thermoelectric material

    KAUST Repository

    Singh, Nirpendra

    2014-06-18

    Using first-principles calculations and semi-classical Boltzmann transport theory, the thermoelectric properties of LaBiTe3 are studied. The band gap and, hence, the thermoelectric response are found to be easily tailored by application of strain. Independent of the temperature, the figure of merit turns out to be maximal at a doping of about 1.6 × 1021 cm-3. At room temperature we obtain values of 0.4 and 0.5 for unstrained and moderately strained LaBiTe3, which increases to 1.1 and 1.3 at 800 K. A large spin splitting is observed in the conduction band at the T point. Therefore, LaBiTe3 merges characteristics that are interesting for thermoelectric as well as spintronic devices.

  19. Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties

    Science.gov (United States)

    Liu, Dongmei; Li, Xinzhong; Borlido, Pedro Miguel De Castro; Botti, Silvana; Schmechel, Roland; Rettenmayr, Markus

    2017-03-01

    Layered (Bi1-xInx)2Te3-In2Te3 (x = 0.075) composites of pronounced anisotropy in structure and thermoelectric properties were produced by zone melting and subsequent coherent precipitation of In2Te3 from a (Bi1-xInx)2Te3 (x > 0.075) matrix. Employing solid state phase transformation, the Bi2Te3/In2Te3 interface density was tuned by modifying the driving force for In2Te3 precipitation. The structure-property relationship in this strongly anisotropic material is characterized thoroughly and systematically for the first time. Unexpectedly, with increasing Bi2Te3/In2Te3 interface density, an increase in electrical conductivity and a decrease in the absolute Seebeck coefficient were found. This is likely to be due to electron accumulation layers at the Bi2Te3/In2Te3 interfaces and the interplay of bipolar transport in Bi2Te3. Significantly improved thermoelectric properties of Bi2Te3-In2Te3 composites as compared to the single phase (Bi1-xInx)2Te3 solid solution are obtained.

  20. Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties

    Science.gov (United States)

    Liu, Dongmei; Li, Xinzhong; Borlido, Pedro Miguel de Castro; Botti, Silvana; Schmechel, Roland; Rettenmayr, Markus

    2017-01-01

    Layered (Bi1−xInx)2Te3-In2Te3 (x = 0.075) composites of pronounced anisotropy in structure and thermoelectric properties were produced by zone melting and subsequent coherent precipitation of In2Te3 from a (Bi1−xInx)2Te3 (x > 0.075) matrix. Employing solid state phase transformation, the Bi2Te3/In2Te3 interface density was tuned by modifying the driving force for In2Te3 precipitation. The structure-property relationship in this strongly anisotropic material is characterized thoroughly and systematically for the first time. Unexpectedly, with increasing Bi2Te3/In2Te3 interface density, an increase in electrical conductivity and a decrease in the absolute Seebeck coefficient were found. This is likely to be due to electron accumulation layers at the Bi2Te3/In2Te3 interfaces and the interplay of bipolar transport in Bi2Te3. Significantly improved thermoelectric properties of Bi2Te3-In2Te3 composites as compared to the single phase (Bi1−xInx)2Te3 solid solution are obtained. PMID:28272541

  1. Electrodeposition of Ni on Bi2Te3 and Interfacial Reaction Between Sn and Ni-Coated Bi2Te3

    Science.gov (United States)

    Tseng, Yu-Chen; Lee, Hsuan; Hau, Nga Yu; Feng, Shien-Ping; Chen, Chih-Ming

    2017-09-01

    Bismuth-telluride (Bi2Te3)-based compounds are common thermoelectric materials used for low-temperature applications, and nickel (Ni) is usually deposited on the Bi2Te3 substrates as a diffusion barrier. Deposition of Ni on the p-type (Sb-doped) and n-type (Se-doped) Bi2Te3 substrates using electroplating and interfacial reactions between Sn and Ni-coated Bi2Te3 substrates are investigated. Electrodeposition of Ni on different Bi2Te3 substrates is characterized based on cyclic voltammetry and Tafel measurements. Microstructural characterizations of the Ni deposition and the Sn/Ni/Bi2Te3 interfacial reactions are performed using scanning electron microscopy. A faster growth rate is observed for the Ni deposition on the n-type Bi2Te3 substrate which is attributed to a lower activation energy of reduction due to a higher density of free electrons in the n-type Bi2Te3 material. The common Ni3Sn4 phase is formed at the Sn/Ni interfaces on both the p-type and n-type Bi2Te3 substrates, while the NiTe phase is formed at a faster rate at the interface between Ni and n-type Bi2Te3 substrates.

  2. Polyol Synthesis of Nano-Bi2Te3

    Science.gov (United States)

    Kaspar, K.; Pelz, U.; Hillebrecht, H.

    2014-04-01

    In this work, a simple and easily scalable wet-chemical synthesis of nanoscale Bi2Te3 has been developed. Bi2Te3 nanoparticles were produced via a polyol method by reaction of Na2Te in solution with a selection of bismuth(III) salts in boiling ethylene glycol. Depending on the reaction temperature and time, particles with size ranging between 20 nm and 400 nm could be obtained in high yield. Phase-pure products could be obtained under refluxing conditions. We show the necessity of a certain reaction time or temperature for complete reaction of the compounds, and the dependence on the type of bismuth salt and the reactant quantity based on the tellurium contamination in the Bi2Te3 products. Nuclear magnetic resonance investigations suggest possible mechanisms for the formation of the Bi2Te3 particles. The composition, particle size, and morphology of the synthesized products were investigated by powder x-ray diffraction, energy-dispersive x-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. The resulting particles demonstrated high purity.

  3. Physical properties of Bi doped CdTe thin films grown by the CSVT method

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O.; Sastre-Hernandez, J.; Cruz-Gandarilla, F.; Aguilar-Hernandez, J.; Contreras-Puente, G.; Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico D. F. (Mexico); Marin, E. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada, Instituto Politecnico Nacional, 11500 Mexico, D. F. (Mexico); Saucedo, E.; Ruiz, C.M.; Bermudez, V. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain)

    2006-09-22

    A study of the physical properties of CdTe thin films doped with Bi is presented. CdTe:Bi thin films were deposited by the close space vapor transport (CSVT) technique using powdered CdTe:Bi crystals grown by the vertical Bridgman method. CdTe:Bi crystals were obtained with nominal Bi doping concentrations varying in the 1x10{sup 17}-8x10{sup 18}cm{sup -3} range. The physical properties of CdTe:Bi thin films were studied performing photoluminescence, X-ray, SEM, photoacoustic spectroscopy and resistivity measurements. We observed a decrease of the resistivity values of CdTe:Bi films with the Bi content as low as 6x10{sup 5}{omega}-cm for Bi concentrations of 8x10{sup 18}cm{sup -3}. These are meaningful results for CdTe-based solar cells. (author)

  4. Engineering topological surface states and giant Rashba spin splitting in BiTeI/Bi2Te3 heterostructures.

    Science.gov (United States)

    Zhou, Jin-Jian; Feng, Wanxiang; Zhang, Ying; Yang, Shengyuan A; Yao, Yugui

    2014-01-23

    The search for strongly inversion asymmetric topological insulators is an active research field because these materials possess distinct properties compared with the inversion symmetric ones. In particular, it is desirable to realize a large Rashba spin-splitting (RSS) in such materials, which combined with the topological surface states (TSS) could lead to useful spintronics applications. In this report, based on first principles calculations, we predict that the heterostructure of BiTeI/Bi2Te3 is a strong topological insulator with a giant RSS. The coexistence of TSS and RSS in the current system is native and stable. More importantly, we find that both the Z2 invariants and the Rashba energy can be controlled by engineering the layer geometries of the heterostructure, and the Rashba energy can be made even larger than that of bulk BiTeI. Our work opens a new route for designing topological spintronics devices based on inversion asymmetric heterostructures.

  5. High Thermoelectric Properties of PbTe Doped with Bi2Te3 and Sb2Te3

    Institute of Scientific and Technical Information of China (English)

    ZHU Pin-Wen; IMAI Yoshio; ISODA Yukihiro; SHINOHARA Yoshikazi; JIA Xiao-Peng; ZOU Guang-Tian

    2005-01-01

    @@ The composition-dependent thermoelectric properties of lead telluride (PbTe) doped with bismuth telluride(Bi2Te3), antimony telluride (Sb2Te3) and (BiSb)2Te3 have been studied at room temperature. All the samples exhibit small thermal conductivity. The figures of merit, 7.63, 1.03 and 8.97 × 10-4, have been obtained in PbTe with these dopants, respectively. These values are several times higher than those of PbTe containing other dopants with small grain sizes. The high thermoelectric performance is explained by electronic topological transition induced by alloying. The results indicate that these dopants are effective to enhance the thermoelectric performance of Pb Te.

  6. The Quantum Chemistry Calculation and Thermoelectrics of Bi-Sb-Te Series

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The density function theory and discrete variation method(DFT-DVM) was used to study correlation between composition, structure, chemical bond,and property of thermoelectrics of Bi-Sb-Te series.8 models of Bi20-xSbxTe32(x=0,2,6,8,12,14,18 and 20) were calculated.The results show that there is less difference in the ionic bonds between Te(Ⅰ)-Bi(Sb) and Te(Ⅱ)-Bi(Sb), but the covalent bond of Te(Ⅰ)-Bi(Sb) is stronger than that of Te(Ⅱ)-Bi(Sb).The interaction between Te(Ⅰ) and Te(Ⅰ) in different layers is the weakest and the interaction should be Van Der Waals power.The charge of Sb is lower than that of Bi,and the ionic bond of Te-Sb is weaker than that of Te-Bi.The covalent bond of Te-Sb is also weaker than that of Te-Bi.Therefore,the thermoelectric property may be improved by adjusting the electrical conductivity and thermal conductivity through changing the composition in the compounds of Bi-Sb-Te. The calculated results are consistent with the experiments.

  7. Formation of the bismuth-bilayer film at BiTeCl surface by atomic hydrogen deposition

    Science.gov (United States)

    Shvets, I. A.; Eremeev, S. V.; Chulkov, E. V.

    2017-07-01

    On the base of density functional theory calculations we investigate the atomic hydrogen adsorption on Cl- and Te-terminations of giant Rashba-split semiconductor BiTeCl and show that it leads to removal of the halogen and chalcogen top layer atoms by means of desorption of HCl and H2Te molecules. This mechanism accompanied by swapping of next Bi and deeper Te(Cl) layers with subsequent hydrogen-induced removal of Te(Cl) layer results in formation of Bi2 layer covering BiTeCl. The electronic structure of the formed Bi2@BiTeCl[Cl-term] and Bi2@BiTeCl[Te-term] interfaces shows a strong hybridization between Bi2-derived spin-split bands and BiTeCl interface states.

  8. Bulk band structure of Bi2Te3

    DEFF Research Database (Denmark)

    Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco

    2014-01-01

    The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all......-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...... distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators....

  9. Thermoelectric Response in Single Quintuple Layer Bi2Te3

    KAUST Repository

    Sharma, S.

    2016-10-05

    Because Bi2Te3 belongs to the most important thermoelectric materials, the successful exfoliation of a single quintuple layer has opened access to an interesting two-dimensional material. For this reason, we study the thermoelectric properties of single quintuple layer Bi2Te3 by considering both the electron and phonon transport. On the basis of first-principles density functional theory, the electronic and phononic contributions are calculated by solving Boltzmann transport equations. The dependence of the lattice thermal conductivity on the phonon mean free path is evaluated along with the contributions of the acoustic and optical branches. We find that the thermoelectric response is significantly better for p- than for n-doping. By optimizing the carrier concentration, at 300 K, a ZT value of 0.77 is achieved, which increases to 2.42 at 700 K.

  10. Corrosion Behavior of Bi2Te3-Based Thermoelectric Materials Fabricated by Melting Method

    Science.gov (United States)

    Kohri, Hitoshi; Yagasaki, Takayoshi

    2016-11-01

    Bi2Te3-based compounds are used practically as thermoelectric cooling materials. Bi2Te3-Sb2Te3 or Bi2Te3-Bi2Se3 pseudobinary system compounds are usually applied as p- or n-type material, respectively. Atmospheric water may condense on the surface of thermoelectric materials constituting Peltier modules, depending on their operating environment. Very few studies on the corrosion resistance of Bi2Te3-based compounds have been reported in literature. Moreover, the detailed corrosion behavior of Bi2Te3-based compounds remains unclear. In this study, the corrosion behavior of cleavage planes of Bi2Te3-based compounds fabricated by a melting method has been investigated. Bi2Te3, Sb2Te3, and Bi2Se3 were prepared by the vertical Bridgman method, respectively. Their electrochemical properties evaluated at room temperature by cyclic voltammetry in a standard three-electrode cell with naturally aerated 0.6 mass% or 3.0 mass% NaCl solution as working electrolyte. The c-planes of Bi2Te3 and Sb2Te3 exhibited similar corrosion potential. The corrosion potential of c-plane of Bi2Se3 was more cathodic compared with that of the telluride. The passive current density of the Bi2Te3-based compounds was single or double digit lower than that of stainless steel. X-ray photoelectron spectroscopy results for the electrolyte after testing indicated the possibility that a corrosion product diffuses to the environment including NaCl for Sb2Te3 and Bi2Se3.

  11. Phonons of single quintuple Bi2Te3 and Bi2Se3 films and bulk materials

    Science.gov (United States)

    Cheng, Wei; Ren, Shang-Fen

    2011-03-01

    Phonons of single quintuple films of Bi2Te3 and Bi2Se3 and corresponding bulk materials are calculated in detail by MedeA (a trademark of Materials Design) and Vienna ab initio simulation package (VASP). The calculated results with and without spin-orbit couplings are compared, and the important roles that the spin-orbit coupling plays in these materials are discussed. A symmetry breaking caused by the anharmonic potentials around Bi atoms in the single quintuple films is identified and discussed. The observed Raman intensity features in Bi2Te3 and Bi2Se3 quintuple films are explained.

  12. Phonons of single quintuple Bi 2 Te 3 and Bi 2 Se 3 films and bulk materials

    KAUST Repository

    Cheng, Wei

    2011-03-10

    Phonons of single quintuple films of Bi2Te3 and Bi2Se3 and corresponding bulk materials are calculated in detail by MedeA (a trademark of Materials Design) and Vienna ab initio simulation package (VASP). The calculated results with and without spin-orbit couplings are compared, and the important roles that the spin-orbit coupling plays in these materials are discussed. A symmetry breaking caused by the anharmonic potentials around Bi atoms in the single quintuple films is identified and discussed. The observed Raman intensity features in Bi 2Te3 and Bi2Se3 quintuple films are explained. © 2011 American Physical Society.

  13. [Bi]:[Te] Control, Structural and Thermoelectric Properties of Flexible Bi x Te y Thin Films Prepared by RF Magnetron Sputtering at Different Sputtering Pressures

    Science.gov (United States)

    Nuthongkum, Pilaipon; Sakdanuphab, Rachsak; Horprathum, Mati; Sakulkalavek, Aparporn

    2017-07-01

    In this work, flexible Bi x Te y thin films were prepared by radio frequency (RF) magnetron sputtering using a Bi2Te3 target on polyimide substrate. The effects of sputtering pressures, which ranged between 0.6 Pa and 1.6 Pa on the [Bi]:[Te] ratio, and structural and thermoelectric properties were investigated. The [Bi]:[Te] ratio of thin film was determined by energy-dispersive spectrometry (EDS). The EDS spectra show the variation of the [Bi]:[Te] ratio as the sputtering pressure is varied. The film deposited at 1.4 Pa almost has a stoichiometric composition. The selective films with different [Bi]:[Te] ratios and sputtering pressures were characterized by their surface morphologies, crystal and chemical structures by field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) and Raman spectroscopy, respectively. Electrical transport properties, including carrier concentration and mobility, were measured by Hall effect measurements. Seebeck coefficients and electrical conductivities were simultaneously measured by a direct current four-terminal method (ZEM-3). The XRD and Raman spectroscopy results show a difference in microstructure between BiTe and Bi2Te3 depending on the [Bi]:[Te] ratio. Electrical conductivity and Seebeck coefficient are related to the crystal and chemical structures. The maximum power factor of the Bi2Te3 thin film is 9.5 × 10-4 W/K2 m at room temperature, and it increases to 12.0 × 10-4 W/K2 m at 195°C.

  14. Interfacing 2D and 3D Topological Insulators: Bi(111) Bilayer on Bi2Te3

    Science.gov (United States)

    Hirahara, Toru; Bihlmayer, Gustav; Sakamoto, Yusuke; Yamada, Manabu; Miyazaki, Hidetoshi; Kimura, Shin-Ichi; Blügel, Stefan; Hasegawa, Shuji

    2012-02-01

    Topological insulators (TI) are insulating materials but have metallic edge states that carry spin currents and are robust against nonmagnetic impurities [1]. While there have been a large number of reports on three-dimensional (3D) TI, only few works have been done in terms of two-dimensional (2D) TI. In the present paper, we report the successful formation of bilayer Bi, which was theoretically predicted to be a 2D TI [2]. We deposited bilayer Bi on a 3D TI Bi2Te3, which the lattice mismatch is very small. From angle-resolved photoemission spectroscopy measurements and ab initio calculations, the electronic structure of the system can be understood as an overlap of the band dispersions of bilayer Bi and Bi2Te3. Our results show that the Dirac cone is actually robust against nonmagnetic perturbations and imply a unique situation where the topologically protected one- and two-dimensional edge states are coexisting at the surface [3]. [0pt] [1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).[0pt] [2] S. Murakami, Phys. Rev. Lett. 97, 236805 (2006).[0pt] [3] T. Hirahara et al., Phys. Rev. Lett. 107, 166801 (2011).

  15. Topological quantum phase transition and superconductivity induced by pressure in the bismuth tellurohalide BiTeI

    OpenAIRE

    Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G.; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, F. C.; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A.

    2016-01-01

    A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor BiTeI with giant Rashba spin splitting. In this work, the evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr while the resist...

  16. Physical properties of Bi doped CdTe thin films grown by CSVT and their influence on the CdS/CdTe solar cells PV-properties

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico)]. E-mail: osvaldo@esfm.ipn.mx; Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Ruiz, C.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Sastre-Hernandez, J. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Morales-Acevedo, A. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); CINVESTAV-IPN, Electrical Engineering Department, Av. IPN No2508, C. P. 07360, Mexico, D. F. (Mexico); Cruz-Gandarilla, F. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Aguilar-Hernandez, J. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Saucedo, E. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Bermudez, V. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain)

    2007-05-31

    The physical properties of Bi doped CdTe films, grown on glass substrates by the Closed Space Transport Vapour (CSVT) method, from different Bi doped CdTe powders are presented. The CdTe:Bi films were characterized using Photoluminescence, Hall effect, X-Ray diffraction, SEM and Photoconductivity measurements. Moreover, CdS/CdTe:Bi solar cells were made and their characteristics like short circuit current density (J {sub sc}), open circuit voltage (V {sub OC}), fill factor (FF) and efficiency ({eta}) were determined. These devices were fabricated from Bi doped CdTe layers deposited on CdS with the same growth conditions than those used for the single CdTe:Bi layers. A correlation between the CdS/CdTe:Bi solar cell characteristics and the physical properties of the Bi doped CdTe thin films are presented and discussed.

  17. Micro-Raman Spectroscopy of Mechanically Exfoliated Few-Quintuple Layers of Bi(2)Te(3), Bi(2)Se(3) and Sb(2)Te(3) Materials

    OpenAIRE

    2012-01-01

    Bismuth telluride - Bi(2)Te(3)- and related compounds have recently attracted strong interest owing to the discovery of the topological insulator properties in many members of this family of materials. The few-quintuple films of these materials are particularly interesting from the physics point of view. We report results of the micro-Raman spectroscopy study of the "graphene-like" exfoliated few-quintuple layers of Bi(2)Te(3), Bi(2)Se(3) and Sb(2)Te(3). It is found that crystal symmetry brea...

  18. Phase Equilibria in the Tl5Te3-Tl9BiTe6-Tl9TmTe6 Section of the Tl-Bi-Tm-Te Quaternary System

    OpenAIRE

    Imamaliyeva,Samira Zakir; Firudin,Mehdiyeva Ilaha; Gasymov,Vagif Akber; Babanly,Mahammad Baba

    2017-01-01

    Phase relations in the Tl5Te3-Tl9BiTe6-Tl9TmTe6 section of the Tl-Bi-Tm-Te quaternary system were studied by differential thermal analysis, powder X-ray diffraction technique and microhardness measurements applied to equilibria alloys. Some isopleth sections and isothermal section at 760 K, as well as projections of the liquidus and solidus surfaces, were constructed. The system is characterized by formation of continuous series of solid solutions at the solidus temperatures and below. Solid ...

  19. Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures.

    Science.gov (United States)

    Liu, Hong-Chao; Li, Hui; He, Qing Lin; Sou, Iam Keong; Goh, Swee K; Wang, Jiannong

    2016-05-17

    The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years' air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena.

  20. Superconductivity in Ba(Pb,Bi,Sb)O 3, Ba(Pb,Bi,Te)O 3 and (Ba,La) (Pb,Bi,Tl)O 3 systems

    Science.gov (United States)

    Nagarajan, R.; Vasanthacharya, N. Y.; Gopalakrishnan, J.; Rao, C. N. R.

    1991-02-01

    It is possible to substitute Bi in the superconducting BaPb 0.75Bi 0.25O 3 by Sb or Te without destroying the superconductivity. With Sb, a continuous series of solid solutions BaPb 0.75Bi 0.25-ySb yO 3 (0 ⩽ y ⩽ 0.25) exists, while with Te, perovskite BaPb 0.75Bi 0.25-yTe yO 3 exists only upto y = 0.15. With increasing substitution by Sb or Te, T c decreases continously in both the systems. Superconductivity with a maximum T c of 8K is found in Ba 0.9La 0.1Pb 0.9-yBi yTl 0.1O 3 for y = 0.25.

  1. Aggregation of BiTe monolayer on Bi2Te3 (111) induced by diffusion of intercalated atoms in the van der Waals gap

    Science.gov (United States)

    Wang, Zhi-Wen; Huang, Wen-Kai; Zhang, Kai-Wen; Shu, Da-Jun; Wang, Mu; Li, Shao-Chun

    2017-03-01

    We report a postgrowth aging mechanism of Bi2Te3 (111) films with scanning tunneling microscopy in combination with density functional theory calculation. It is found that a monolayered structure with a squared lattice symmetry gradually aggregates from the surface steps. Theoretical calculations indicate that the van der Waals (vdW) gap not only acts as a natural reservoir for self-intercalated Bi and Te atoms, but also provides them easy diffusion pathways. Once hopping out of the gap, these defective atoms prefer to develop into a two-dimensional BiTe superstructure on the Bi2Te3 (111) surface driven by positive energy gain. Considering the common nature of weak bonding between vdW layers, we expect such unusual diffusion and aggregation of the intercalated atoms may be of general importance for most kinds of vdW layered materials.

  2. Thermal Stability and Anisotropic Sublimation of Two-Dimensional Colloidal Bi2Te3 and Bi2Se3 Nanocrystals

    CERN Document Server

    Buha, Joka; Castillo, Antonio Esau Del Rio; Bonaccorso, Francesco; Manna, Liberato

    2016-01-01

    The structural and compositional stabilities of two dimensional 2D Bi2Te3 and Bi2Se3 nanocrystals, produced by both colloidal synthesis and by liquid phase exfoliation, were studied by in situ transmission electron microscopy TEM during annealing at temperatures between 350 and 500 C. The sublimation process induced by annealing is structurally and chemically anisotropic and takes place through the preferential dismantling of the prismatic 011-0 type planes, and through the preferential sublimation of Te or Se.

  3. Growth and atomic structure of tellurium thin films grown on Bi2Te3

    Science.gov (United States)

    Okuyama, Yuma; Sugiyama, Yuya; Ideta, Shin-ichiro; Tanaka, Kiyohisa; Hirahara, Toru

    2017-03-01

    We have grown tellurium (Te) thin films on Bi2Te3 and investigated the atomic structure. From low-energy electron diffraction (LEED) measurements, we found that the Te films are [10 1 bar0]-oriented with six domains. A detailed analysis of the reflection high-energy electron diffraction (RHEED) pattern revealed that the films are strained with the in-plane lattice constant compressed by ∼1.5% compared to the bulk value due to the epitaxy between Te and Bi2Te3. These films will be interesting systems to investigate the predicted topological phases that occur in strained Te.

  4. Transverse Peltier effect in tilted Pb -Bi2Te3 multilayer structures

    Science.gov (United States)

    Kyarad, A.; Lengfellner, H.

    2006-11-01

    A transverse Peltier effect has been observed in artificially created tilted Pb -Bi2Te3 multilayer structures. Multilayer stacks consisting of alternating layers of Pb and n-type Bi2Te3 have been prepared by a heating procedure and showed large thermoelectric anisotropy up to ΔS ≅200μV/K, depending on thickness ratio p =dBiTe/dPb, where dBiTe and dPb are the thicknesses of Bi2Te3 and Pb layers, respectively. Tilted samples were obtained by cutting stacks obliquely to the stack axis. Due to large ΔS and large electrical but small heat conductivity, samples showed temperature differences transverse to applied currents up to 22K.

  5. High thermoelectric potential of Bi{sub 2}Te{sub 3} alloyed GeTe-rich phases

    Energy Technology Data Exchange (ETDEWEB)

    Madar, Naor; Givon, Tom; Mogilyansky, Dmitry; Gelbstein, Yaniv [Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva (Israel)

    2016-07-21

    In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe){sub 1−x}(Bi{sub 2}Te{sub 3}){sub x} alloys, with x values of up to 20%. Higher solubility limit of Bi{sub 2}Te{sub 3} in GeTe, than previously reported, was identified around ∼9%, extending the doping potential of GeTe by the Bi{sub 2}Te{sub 3} donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ∼1.55 at ∼410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%–17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge{sub 8}Bi{sub 2}Te{sub 11} and Ge{sub 4}Bi{sub 2}Te{sub 7} phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi{sub 2}Te{sub 3}), was suggested for further electronic optimization of the thermoelectric properties.

  6. Physical properties of Bi-doped CdTe thin films deposited by cosputtering

    Energy Technology Data Exchange (ETDEWEB)

    Becerril, M.; Zelaya-Angel, O. [Departamento de Fisica, CINVESTAV-IPN, Apdo. Postal 14-740, 07000 Mexico D.F. (Mexico); Vigil-Galan, O.; Contreras-Puente, G.; Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico D.F. (Mexico)

    2007-03-15

    The structural, morphological, electrical, and optical properties of CdTe-Bi cosputtered thin films related with composition are presented. The films were grown on Corning glass substrates at room temperature from a CdTe-Bi target. The composition measurements show that the Bi content in the films ranges from x = 0.0 to x = 6.37 at%, depending on the area fraction covered by the Bi piece attached to the CdTe target. The structure of the annealed films was determined from X-ray diffraction measurements. Two kinds of structures were observed, depending on the Bi content: (1) CdTe polycrystalline films containing a small amount of Bi that is probably incorporated in the Cd and Te sites of the CdTe lattice. (2) Amorphization of the polycrystalline films, with higher Bi content. From the experimental results, we concluded that using this deposition method n/p-type Bi-doped CdTe polycrystalline films can be produced with electrical resistivity between 10{sup 2}-10{sup 3} {omega} cm and electron mobility between 10{sup 1} and 10{sup 2} cm{sup 2}V{sup -1}s{sup -1}. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Solvothermal preparation and thermoelectric properties of quasi-binary Sn(Pb)Te-Bi2Te3 compounds

    Institute of Scientific and Technical Information of China (English)

    周西松; 邓元; 韦国丹; 刘静; 南策文

    2003-01-01

    Bulk samples of quasi-binary compounds in the Sn(Pb)Te-Bi2Te3 system were prepared by solvothermal method followed by a sintering procedure of compacted pellets. The formation mechanism of the precursor powders, microstructure and thermoelectric properties of the final bulk samples were studied.

  8. Pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor.

    Science.gov (United States)

    He, M Q; Shen, J Y; Petrović, A P; He, Q L; Liu, H C; Zheng, Y; Wong, C H; Chen, Q H; Wang, J N; Law, K T; Sou, I K; Lortz, R

    2016-01-01

    In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.

  9. Preparation of Bi2-xSbxTe3 thermoelectric films by electrodeposition

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Bi2-xSbxTe3 thermoelectric films were electrochemically deposited from the solution containing Bi3+, HTeO2+and SbO+.ESEM (environmental scanning electron microscope) investigations indicated that the crystalline state of Bi2-xSbxTe3 films transformed from equiaxed crystal to dendritic crystal with the negative shift of deposition potential. XRD and EDS were used to characterize the structure and composition of the electrodeposited films. The Seebeck coefficient and the temperature dependence of the resistance of Bi2-xSbxTe3 films were measured. The results showed that the composition of the film electrodeposited at -0.5 V is Bi0.5Sb1.5Te3 with the largest Seebeck coefficient of 213 μV·K-1.

  10. Toward enhanced thermoelectric effects in Bi2Te3/Sb2Te3 heterostructures

    Science.gov (United States)

    Narendra, Namita; Kim, Ki Wook

    2017-03-01

    The possibility of enhanced thermoelectric properties through nanostructuring is investigated theoretically in a p-type Bi2Te3/Sb2Te3 heterostructure. A multi-scale modeling approach is adopted to account for the atomistic characteristics of the interface as well as the carrier/phonon transport properties in the larger scales. The calculations clearly illustrate the desired impact of carrier energy filtering at the potential barrier by locally boosting the power factor over a sizable distance in the well region. Further, the phonon transport analysis illustrates a considerable reduction in the thermal conductivity at the heterointerface. Both effects are expected to provide an effective means to engineer higher zT in this material system.

  11. Thermal Stability and Anisotropic Sublimation of Two-Dimensional Colloidal Bi2Te3 and Bi2Se3 Nanocrystals.

    Science.gov (United States)

    Buha, Joka; Gaspari, Roberto; Del Rio Castillo, Antonio Esau; Bonaccorso, Francesco; Manna, Liberato

    2016-07-13

    The structural and compositional stabilities of two-dimensional (2D) Bi2Te3 and Bi2Se3 nanocrystals, produced by both colloidal synthesis and by liquid phase exfoliation, were studied by in situ transmission electron microscopy (TEM) during annealing at temperatures between 350 and 500 °C. The sublimation process induced by annealing is structurally and chemically anisotropic and takes place through the preferential dismantling of the prismatic {011̅0} type planes, and through the preferential sublimation of Te (or Se). The observed anisotropic sublimation is independent of the method of nanocrystal's synthesis, their morphology, or the presence of surfactant molecules on the nanocrystals surface. A thickness-dependent depression in the sublimation point has been observed with nanocrystals thinner than about 15 nm. The Bi2Se3 nanocrystals were found to sublimate below 280 °C, while the Bi2Te3 ones sublimated at temperatures between 350 and 450 °C, depending on their thickness, under the vacuum conditions in the TEM column. Density functional theory calculations confirm that the sublimation of the prismatic {011̅0} facets is more energetically favorable. Within the level of modeling employed, the sublimation occurs at a rate about 700 times faster than the sublimation of the {0001} planes at the annealing temperatures used in this work. This supports the distinctly anisotropic mechanisms of both sublimation and growth of Bi2Te3 and Bi2Se3 nanocrystals, known to preferentially adopt a 2D morphology. The anisotropic sublimation behavior is in agreement with the intrinsic anisotropy in the surface free energy brought about by the crystal structure of Bi2Te3 or Bi2Se3.

  12. Pressure-induced superconductivity in the giant Rashba system BiTeI

    OpenAIRE

    VanGennep, D.; Linscheid, A.; Jackson, D E; Weir, S. T.; Vohra, Y. K.; Berger, H.; Stewart, G. R.; Hennig, R. G.; Hirschfeld, P. J.; Hamlin, J. J.

    2016-01-01

    At ambient pressure, BiTeI is the first material found to exhibit a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to ~40 GPa in an effort to characterize the properties of the high-pressure phases....

  13. The preparation process and feature of the topological insulator Bi2Te3

    Institute of Scientific and Technical Information of China (English)

    Peng Chen; Dajin Zhou; Pingyuan Li; Yajing Cui; Yongliang Chen

    2014-01-01

    Topological insulators are insulating in the bulk but have metallic surface states. Its unique physicochemi-cal properties can find numerous applications in electron-ics, spintronics, photonics, the energy sciences, and the signal control of transportation. We report an experimental approach to synthesize the high-quality single crystal of topological insulator Bi2Te3 by using self-flux method. We obtained the optimal preparation conditions by adjusting the parameters of heat treatment, and successfully prepared the single-crystal Bi2Te3 sample. The as-grown samples have a surface with bright metallic luster and are soft and fragile. Furthermore, Bi2Te3 has the obvious layer structure from SEM results. The data of X-ray diffraction and scanning electron microscope show that Bi2Te3 single crystal grows along the c-axis with the order of Te(1)-Bi-Te(2)-Bi-Te(1) and crystallizes in the hexagonal system with space group of R/3 m. The q-T curve shows that q decreases with temperature, showing metallic behavior over the whole temperature range.

  14. Pressure-induced superconductivity in the giant Rashba system BiTeI

    Science.gov (United States)

    VanGennep, D.; Linscheid, A.; Jackson, D. E.; Weir, S. T.; Vohra, Y. K.; Berger, H.; Stewart, G. R.; Hennig, R. G.; Hirschfeld, P. J.; Hamlin, J. J.

    2017-03-01

    At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to  ∼40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with T c values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute T c and find that our data is consistent with phonon-mediated superconductivity.

  15. Pressure dependence of the band-gap energy in BiTeI

    Science.gov (United States)

    Güler-Kılıç, Sümeyra; Kılıç, ćetin

    2016-10-01

    The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated, at which BiTeI becomes a topological insulator. Comparison of the critical pressure to the pressure at which BiTeI undergoes a structural phase transition indicates that the closure of the band gap would not be hindered by a structural transformation. Moreover, the band-gap pressure coefficients of BiTeI are computed, and an expression of the critical pressure is devised in terms of these coefficients. Our findings indicate that the semilocal and dispersion-corrected approaches are in conflict about the compressibility of BiTeI, which result in overestimation and underestimation, respectively. Nevertheless, the effect of pressure on the atomic structure of BiTeI is found to be manifested primarily as the reduction of the width of the van der Waals gap according to both approaches, which also yield consistent predictions concerning the interlayer metallic bonding in BiTeI under compression. It is consequently shown that the calculated band-gap energies follow qualitatively and quantitatively the same trend within the two approximations employed here, and the transition to the zero-gap state occurs at the same critical width of the van der Waals gap.

  16. Energy conversion efficiencies of thermoelectric pallets (Bi2Pb3,Bi2Te3 and Pb2Te3) under the influences of electric and magnetic fields

    Science.gov (United States)

    Singh, Jaspal; Verma, S. S.

    2013-06-01

    This paper aims to introduce the ability of thermo electric pallets to convert waste heat into electricity and also about the effect of electric or magnetic fields, which can exist already or applied in the conditions of their operation. Three thermo electric pallets (Bi2Pb3,Bi2Te3 and Pb2Te3) of cylindrical dimensions are prepared by 15mm mixture of different compositions. Thermo emf generations are carried out in the normal mode and then under the influence of applied electric and magnetic fields of different magnitudes in the temperature range of 460K.

  17. Theory of electron spin resonance in bulk topological insulators Bi2Se3, Bi2Te3 and Sb2Te3

    Science.gov (United States)

    Ly, O.; Basko, D. M.

    2016-04-01

    We report a theoretical study of electron spin resonance in bulk topological insulators, such as Bi2Se3, Bi2Te3 and Sb2Te3. Using the effective four-band model, we find the electron energy spectrum in a static magnetic field and determine the response to electric and magnetic dipole perturbations, represented by oscillating electric and magnetic fields perpendicular to the static field. We determine the associated selection rules and calculate the absorption spectra. This enables us to separate the effective orbital and spin degrees of freedom and to determine the effective g factors for electrons and holes.

  18. Phase equilibriums and thermodynamic properties of the system Bi-Te-I

    Energy Technology Data Exchange (ETDEWEB)

    Babanly, M.B. [Baku State University, Baku, AZ 1148, Z.Khalilov str, 23, BSU (Azerbaijan)], E-mail: Babanly_mb@rambler.ru; Tedenac, J.-C. [PMOF, ICGM UMR 5253 CNRS UM2, ENSCM, UM1, Place Eugene Bataillon, 34095 Montpellier (France)], E-mail: tedenac@univ-montp2.fr; Aliyev, Z.S. [Baku State University, Baku, AZ 1148, Z.Khalilov str, 23, BSU (Azerbaijan); Balitsky, D.V. [PMOF, ICGM UMR 5253 CNRS UM2, ENSCM, UM1, Place Eugene Bataillon, 34095 Montpellier (France)

    2009-07-29

    The system Bi-Te-I was studied by methods of differential thermal analysis and the X-ray diffraction, and also by measurements of electromotive forces (EMF) of concentration chains of type (-) Bi (s) | liquid electrolytic conductor, Bi{sup 3+} | (Bi-Te-I) (s) (+) in the temperatures range of 300-400 K. The series of polythermal sections and isothermal section of the phase diagram at 300 K, and a projection of the liquidus surface were constructed. Earlier indicated ternary compounds BiTeI, Bi{sub 2}TeI and Bi{sub 4}TeI{sub 1.25} were confirmed, the position of phase areas and their relationships was established. Areas of primary crystallization fields, types and coordinates of the non- and mono-variant equilibriums were determined. The measurements of EMF have allowed calculation of partial molar functions ({delta}G-bar,{delta}H-bar,{delta}S-bar) of bismuth in alloys, standard thermodynamic functions of formation and standard entropies of the indicated ternary compounds.

  19. Microstructural design of Bi{sub 2}Te{sub 3}-In{sub 2}Te{sub 3} thermoelectric composites; Gefuegedesign thermoelektrischer Bi{sub 2}Te{sub 3}- In{sub 2}Te{sub 3}-Verbundwerkstoffe

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Dongmei [Jena Univ. (Germany). Otto Schott Inst. of Materials Research; Rettenmayr, Markus [Center for Energy and Environmental Chemistry, Jena (Germany)

    2016-07-15

    Internal interfaces are known to play a key role for the performance of thermoelectric materials. In the present work, structures with high interface densities consisting of alternating Bi{sub 2}Te{sub 3} and In{sub 2}Te{sub 3} layers with varying thickness and distance have been generated by two processes. First In{sub 2}Te{sub 3} was precipitated from a supersaturated Bi{sub 2}Te{sub 3} matrix. Second, layered structures were generated by directional solidification of hypoeutectic and eutectic alloys, demonstrating the variability of structures with high interface densities and anisotropy that can be generated by up-to-date solidification and phase transformation techniques. The resulting microstructures have a high potential to reduce the thermal conductivity while retaining a high electric conductivity.

  20. Enhanced thermoelectric performance in the Rashba semiconductor BiTeI through band gap engineering

    Science.gov (United States)

    Wu, Lihua; Yang, Jiong; Zhang, Tiansong; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2016-03-01

    Rashba semiconductors are of great interest in spintronics, superconducting electronics and thermoelectrics. Bulk BiTeI is a new Rashba system with a giant spin-split band structure. 2D-like thermoelectric response has been found in BiTeI. However, as optimizing the carrier concentration, the bipolar effect occurs at elevated temperature and deteriorates the thermoelectric performance of BiTeI. In this paper, band gap engineering in Rashba semiconductor BiTeI through Br-substitution successfully reduces the bipolar effect and improves the thermoelectric properties. By utilizing the optical absorption and Burstein-Moss-effect analysis, we find that the band gap in Rashba semiconductor BiTeI increases upon bromine substitution, which is consistent with theoretical predictions. Bipolar transport is mitigated due to the larger band gap, as the thermally-activated minority carriers diminish. Consequently, the Seebeck coefficient keeps increasing with a corresponding rise in temperature, and thermoelectric performance can thus be enhanced with a ZT  =  0.5 at 570 K for BiTeI0.88Br0.12.

  1. Synthesis and Characterization of Polythiophene/Bi2Te3 Nanocomposite Thermoelectric Material

    Science.gov (United States)

    Ao, W. Q.; Wang, L.; Li, J. Q.; Pan, Fred; Wu, C. N.

    2011-09-01

    To achieve low thermal conductivity, polythiophene (PTh)/bismuth telluride (Bi2Te3) nanocomposite has been prepared by spark plasma sintering using a mixture of nanosized Bi2Te3 and PTh powders. Bi2Te3 powder with spherical-shaped particles of 30 nm diameter and PTh nanosheet powder were first prepared by hydrothermal synthesis and chemical oxidation, respectively. X-ray diffraction analysis and scanning electron microscopy observations revealed that the hybrid composite consists of PTh nanosheets and spherical Bi2Te3. The organic PTh acts as an adhesive in the composite. Transport measurements showed that the PTh in the Bi2Te3 matrix can reduce its thermal conductivity significantly, but also dramatically reduces its electrical conductivity. As a result, the figure of merit of the composite is lower than that of pure Bi2Te3 prepared under the same conditions. The maximum value of ZT for the sample with 5% PTh (by weight) was 0.18 at 473 K, which is rather high compared with other polymer/inorganic thermoelectric material composites.

  2. Enhanced thermoelectric performance in the Rashba semiconductor BiTeI through band gap engineering.

    Science.gov (United States)

    Wu, Lihua; Yang, Jiong; Zhang, Tiansong; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2016-03-01

    Rashba semiconductors are of great interest in spintronics, superconducting electronics and thermoelectrics. Bulk BiTeI is a new Rashba system with a giant spin-split band structure. 2D-like thermoelectric response has been found in BiTeI. However, as optimizing the carrier concentration, the bipolar effect occurs at elevated temperature and deteriorates the thermoelectric performance of BiTeI. In this paper, band gap engineering in Rashba semiconductor BiTeI through Br-substitution successfully reduces the bipolar effect and improves the thermoelectric properties. By utilizing the optical absorption and Burstein-Moss-effect analysis, we find that the band gap in Rashba semiconductor BiTeI increases upon bromine substitution, which is consistent with theoretical predictions. Bipolar transport is mitigated due to the larger band gap, as the thermally-activated minority carriers diminish. Consequently, the Seebeck coefficient keeps increasing with a corresponding rise in temperature, and thermoelectric performance can thus be enhanced with a ZT  =  0.5 at 570 K for BiTeI0.88Br0.12.

  3. Quantum Size Effects in Transport Properties of Bi2Te3 Topological Insulator Thin Films

    Science.gov (United States)

    Rogacheva, E. I.; Budnik, A. V.; Nashchekina, O. N.; Meriuts, A. V.; Dresselhaus, M. S.

    2017-07-01

    Bi2Te3 compound and Bi2Te3-based solid solutions have attracted much attention as promising thermoelectric materials for refrigerating devices. The possibility of enhancing the thermoelectric efficiency in low-dimensional structures has stimulated studies of Bi2Te3 thin films. Now, interest in studying the transport properties of Bi2Te3 has grown sharply due to the observation of special properties characteristic of three-dimensional (3D) topological insulators in Bi2Te3. One of the possible manifestations of quantum size effects in two-dimensional structures is an oscillatory behavior of the dependences of transport properties on film thickness, d. The goal of this work is to summarize our earlier experimental results on the d-dependences of transport properties of Bi2Te3 thin films obtained by thermal evaporation in a vacuum on glass substrates, and to present our new results of theoretical calculations of the oscillations periods within the framework of the model of an infinitely deep potential well, which takes into account the dependence of the Fermi energy on d and the contribution of all energy subbands below the Fermi level to the conductivity. On the basis of the data obtained, some general regularities and specificity of the quantum size effects manifestation in 3D topological insulators are established.

  4. Tight-binding theory of NMR shifts in topological insulators Bi2Se3 and Bi2Te3

    Science.gov (United States)

    Boutin, Samuel; Ramírez-Ruiz, Jorge; Garate, Ion

    2016-09-01

    Motivated by recent nuclear magnetic resonance (NMR) experiments, we present a microscopic s p3 tight-binding model calculation of the NMR shifts in bulk Bi2Se3 and Bi2Te3 . We compute the contact, dipolar, orbital and core polarization contributions to the carrier-density-dependent part of the NMR shifts in 209Bi,125Te, and 77Se. The spin-orbit coupling and the layered crystal structure result in a contact Knight shift with strong uniaxial anisotropy. Likewise, because of spin-orbit coupling, dipolar interactions make a significant contribution to the isotropic part of the NMR shift. The contact interaction dominates the isotropic Knight shift in 209Bi NMR, even though the electronic states at the Fermi level have a rather weak s -orbital character. In contrast, the contribution from the contact hyperfine interaction to the NMR shift of 77Se and 125Te is weak compared to the dipolar and orbital shifts therein. In all cases, the orbital shift is at least comparable to the contact and dipolar shifts, while the shift due to core polarization is subdominant (except for Te nuclei located at the inversion centers). By artificially varying the strength of spin-orbit coupling, we evaluate the evolution of the NMR shift across a band inversion but find no clear signature of the topological transition.

  5. GW quasiparticle energy study of ternary tetradymite Bi{sub 2}Te{sub 2}Se and Bi{sub 2}Te{sub 2}S thin films

    Energy Technology Data Exchange (ETDEWEB)

    Shuaibu, Alhassan [Department of Physics, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Department of Physics, Faculty of Science, Nigerian Defence Academy, P.M., 2109. Kaduna Nigeria (Nigeria); Rahman, Md. Mahmudur [Department of Physics, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Zainuddin, Hishamuddin [Department of Physics, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Institute for Mathematical Research, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Talib, Zainal Abidin [Institute for Mathematical Research, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Muhida, Rifki [Department of Physics, Surya College of Education (STKIP Surya), Gedung SURE, Jl. Scientia Boulevard Blok U/7, Gading Serpong, Tangerang 15810, Banten (Indonesia)

    2015-04-24

    In this work, we have evaluated the quasiparticle energies of ternary tetradymite Bi{sub 2}Te{sub 2}Se and Bi{sub 2}Te{sub 2}S using first-principles calculation within the G{sub 0}W{sub 0} methods. We have also performed a broad convergence tests in order to investigate the quasiparticle corrections to the structural parameters and to the semi core d electrons in both of the compounds. For each case, we have calculated the many-body corrections within a one-shot GW method of the compounds. Our results have shown that for Bi{sub 2}Te{sub 2}Se the GW corrections increase the band gap to almost 10%, and for specific atomic positions, the band structure shows a close value to the experimental one. For Bi{sub 2}Te{sub 2}S, despite increase in the band gap due to the GW corrections, possibility of bulk resistivity that can be significant for photovoltaic applications was observed.

  6. Bulk photovoltaic effect at infrared wavelength in strained Bi2Te3 films

    Science.gov (United States)

    Liu, Yucong; Chen, Jiadong; Wang, Chao; Deng, Huiyong; Zhu, Da-Ming; Hu, Gujin; Chen, Xiaoshuang; Dai, Ning

    2016-12-01

    As a prominent three-dimensional (3-D) topological insulator, traditional thermoelectric material Bi2Te3 has re-attracted greater interest in recent years. Herein, we demonstrate for the first time that c-axis oriented strained Bi2Te3 films exhibit the bulk photovoltaic effect (BPVE) at infrared wavelengths, which was only found in wide band-gap ferroelectric materials before. Moreover, further experiments show that the bulk photovoltaic effect probably comes from the flexoelectric effect which was induced by the stress gradient in strained Bi2Te3 films. And we anticipate that the results are generalizable to other layer-structured or two-dimensional (2-D) materials, e.g., Bi2Se3 and MoS2.

  7. Experimental and density functional study of Mn doped Bi2Te3 topological insulator

    Directory of Open Access Journals (Sweden)

    A. Ghasemi

    2016-12-01

    Full Text Available We present a nanoscale structural and density functional study of the Mn doped 3D topological insulator Bi2Te3. X-ray absorption near edge structure shows that Mn has valency of nominally 2+. Extended x-ray absorption fine structure spectroscopy in combination with electron energy loss spectroscopy (EELS shows that Mn is a substitutional dopant of Bi and Te and also resides in the van der Waals gap between the quintuple layers of Bi2Te3. Combination of aberration-corrected scanning transmission electron microscopy and EELS shows that Mn substitution of Te occurs in film regions with increased Mn concentration. First-principles calculations show that the Mn dopants favor octahedral sites and are ferromagnetically coupled.

  8. Fabrication and characterization of the -type (Bi2Te3)(Sb2Te3)1– thermoelectric crystals prepared via zone melting

    Indian Academy of Sciences (India)

    G Kavei; M A Karami

    2006-12-01

    In the present study, -type (Bi2Te3)(Sb2Te3)1– crystals with various chemical compositions ( = 0.2, 0.22, 0.235, 0.25, 0.265, 0.28 and 0.3) were fabricated through the zone melting method. Thermoelectric properties, including Seebeck coefficient (), electrical conductivity (), thermal conductivity () and Hall constants, were measured at room temperature, 300 K. The influence of the variations of Bi2Te3 content () on the thermoelectric properties was studied. The increase of Bi2Te3 content () caused a decrease in (carrier) hole concentration and thus a decrease of and an increase of . The maximum figure of merit ( = 2\\/) of 2.7 × 10-3 K-1 was obtained at about 300 K for the composition of 25% Bi2Te3–75% Sb2Te3 with 3wt% excess of Te.

  9. Properties and Structures of Bi2O3-B2O3-TeO2 Glass

    Institute of Scientific and Technical Information of China (English)

    Guoying Zhao; Ying Tian; Huiyan Fan; Junjie Zhang; Lili Hu

    2013-01-01

    Glass formation range of Bi2O3-B2O3-TeO2 system has been investigated (B2O3 ≤ 40 mol%).Four glasses with compositions xBi2O3-3OB2O3-(7O-x)TeO2 (x =40,50,60 and 70 mol%) have been prepared by using melt quenching technique.The effect of Bi2O3 content on thermal stability,optical properties and structures of these four Bi2O3-B2O3-TeO2 glasses is systematically investigated by inductive coupled plasma emission spectrometer (ICP),differential scanning calorimetry (DSC),Raman spectra and X-ray photoelectron spectroscopy (XPS).It is found that the density,refractive index and optical basicity increase with increasing Bi2O3.The Raman spectra and XPS spectra show that the glass network is mainly constituted by the [BiO6]octahedron,[TeO4] trigonal bipyramidal,[TeO3] trigonal pyramid,[BO3] trigonal pyramid and [BO4] tetrahedron structural units.With increasing Bi2O3,the coordination number around B atom changes from 3 to 4 and [TeO4] units are converted to [TeO3] units.Bi5+ ions may exist in Bi2O3-B2O3-TeO2 (BBT) system and their amount grows with increasing Bi2O3 content.

  10. Topological Quantum Phase Transition and Superconductivity Induced by Pressure in the Bismuth Tellurohalide BiTeI.

    Science.gov (United States)

    Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, Fang-Cheng; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A

    2017-03-06

    A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor bismuth tellurohalide BiTeI with giant Rashba spin splitting. In this work, evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted topological quantum phase transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr, while resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that superconductivity may develop from the multivalley semiconductor phase. The superconducting transition temperature, Tc , increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. The results demonstrate that BiTeX (X = I, Br) compounds with nontrivial topology of electronic states display new ground states upon compression.

  11. Vibrational properties of epitaxial Bi{sub 4}Te{sub 3} films as studied by Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Hao; Pan, Wenwu; Chen, Qimiao; Wu, Xiaoyan [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); University of Chinese Academy of Sciences, No.19A Yuquan Road, Beijing 100049 (China); Song, Yuxin, E-mail: songyuxin@mail.sim.ac.cn, E-mail: shumin@chalmers.se; Gong, Qian [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); Lu, Pengfei [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Wang, Shumin, E-mail: songyuxin@mail.sim.ac.cn, E-mail: shumin@chalmers.se [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg (Sweden)

    2015-08-15

    Bi{sub 4}Te{sub 3}, as one of the phases of the binary Bi–Te system, shares many similarities with Bi{sub 2}Te{sub 3}, which is known as a topological insulator and thermoelectric material. We report the micro-Raman spectroscopy study of 50 nm Bi{sub 4}Te{sub 3} films on Si substrates prepared by molecular beam epitaxy. Raman spectra of Bi{sub 4}Te{sub 3} films completely resolve the six predicted Raman-active phonon modes for the first time. Structural features and Raman tensors of Bi{sub 4}Te{sub 3} films are introduced. According to the wavenumbers and assignments of the six eigenpeaks in the Raman spectra of Bi{sub 4}Te{sub 3} films, it is found that the Raman-active phonon oscillations in Bi{sub 4}Te{sub 3} films exhibit the vibrational properties of those in both Bi and Bi{sub 2}Te{sub 3} films.

  12. Few-Layer Nanoplates of Bi 2 Se 3 and Bi 2 Te 3 with Highly Tunable Chemical Potential

    KAUST Repository

    Kong, Desheng

    2010-06-09

    A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V-VI materials Bi2Se3, Bi2Te3, and Sb2Te3 are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi2Te3 and Bi2Se3 nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO2/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface state effects in transport measurements. Low-temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential. © 2010 American Chemical Society.

  13. Thermoelectric properties of Cu-dispersed bi0.5sb1.5te3

    Science.gov (United States)

    Kim, Il-Ho; Choi, Soon-Mok; Seo, Won-Seon; Cheong, Dong-Ik

    2012-01-01

    A novel and simple approach was used to disperse Cu nanoparticles uniformly in the Bi0.5Sb1.5Te3 matrix, and the thermoelectric properties were evaluated for the Cu-dispersed Bi0.5Sb1.5Te3. Polycrystalline Bi0.5Sb1.5Te3 powder prepared by encapsulated melting and grinding was dry-mixed with Cu(OAc)2 powder. After Cu(OAc)2 decomposition, the Cu-dispersed Bi0.5Sb1.5Te3 was hot-pressed. Cu nanoparticles were well-dispersed in the Bi0.5Sb1.5Te3 matrix and acted as effective phonon scattering centers. The electrical conductivity increased systematically with increasing level of Cu nanoparticle dispersion. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K. PACS: 72.15.Jf: 72.20.Pa

  14. RSM Base Study of the Effect of Argon Gas Flow Rate and Annealing Temperature on the [Bi]:[Te] Ratio and Thermoelectric Properties of Flexible Bi-Te Thin Film

    Science.gov (United States)

    Nuthongkum, Pilaipon; Sakulkalavek, Aparporn; Sakdanuphab, Rachsak

    2016-10-01

    Bismuth telluride (Bi-Te) thin films coated on a flexible substrate were prepared by RF (radio frequency) magnetron sputtering technique. A response surface methodology based on a central composite design was used to optimize deposition parameters, including the amount of Ar gas flow rate (100.5-106.5 sccm) in the sputtering process and the annealing temperature (250-320°C) for stoichiometric Bi2Te3 thin films. The mathematical model was validated and proven to be statistically sufficient and accurate in predicting a response (Te content). The stoichiometric Bi2Te3 thin films can be prepared on terms appropriate to the Ar flow rate and annealing temperature under several conditions, such as at the Ar flow rate of 103.5 sccm followed by an annealing temperature of 285°C. The characterization of the crystal structure and surface morphology of selected samples with different [Bi]:[Te] content were analyzed by x-ray diffraction (XRD) and a field emission scanning electron microscope, respectively. The XRD spectra showed Bi-Te and Bi2Te3 structures that corresponded with the ratio of [Bi]:[Te]. The Seebeck coefficient and electrical conductivity were simultaneously measured at room temperature and up to 300°C by a direct current four-terminal method. The maximum power factor of the stoichiometric Bi2Te3 thin film was 61×10-5 W/K2m at 243°C.

  15. Study of the physical properties of Bi doped CdTe thin films deposited by close space vapour transport

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O.; Sanchez-Meza, E.; Sastre-Hernandez, J.; Cruz-Gandarilla, F. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico, D. F. (Mexico); Marin, E. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada, Instituto Politecnico Nacional, 11500 Mexico, D. F. (Mexico)], E-mail: emarin63@yahoo.es; Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico, D. F. (Mexico); Saucedo, E.; Ruiz, C.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico, D. F. (Mexico); Calderon, A. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada, Instituto Politecnico Nacional, 11500 Mexico, D. F. (Mexico)

    2008-04-30

    Bi doped cadmium telluride (CdTe:Bi) thin films were grown on glass-substrates by the close space vapour transport method. CdTe:Bi crystals grown by the vertical Bridgman method, varying the nominal Bi concentration in the range between 1 x 10{sup 17} and 8 x 10{sup 18} cm{sup -3}, were used in powder form for CdTe:Bi thin film deposition. Dark conductivity and photoconductivity measurements in the 90-300 K temperature range and determination by photoacoustic spectroscopy of the optical-absorption coefficient of the films in the 1.0 to 2.4 eV spectral region were carried out. The influence of Bi doping levels upon the intergrain barrier height and other associated grain boundary parameters of the polycrystalline CdTe:Bi thin films were determined from electrical, optical and morphological characterization.

  16. Soft chemistry synthesis route toward Bi{sub 2}Te{sub 3} hierarchical hollow spheres

    Energy Technology Data Exchange (ETDEWEB)

    Fouineau, J.; Peron, J., E-mail: jennifer.peron@univ-paris-diderot.fr; Nowak, S.; Giraud, M. [Univ Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086 CNRS (France); Sicard, M. [ONERA, The French Aerospace Lab (France); Ammar-Merah, S.; Sicard, L., E-mail: lorette.sicard@univ-paris-diderot.fr [Univ Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086 CNRS (France)

    2015-04-15

    Hollow spheres made of Bi{sub 2}Te{sub 3} nanoplatelets were successfully synthesized using a low temperature, wet chemical synthesis route. By using a one-pot synthesis, large quantities of microspheres, arranged in a gypsum flower manner, can be obtained in about 1 h. The mechanism leading to such a particular morphology has been deeply studied by both solid and solution characterization techniques (X-ray diffraction, scanning and transmission electron microscopy, X-ray fluorescence, {sup 1}H nuclear magnetic resonance spectroscopy) which were carried out at different stages of the synthesis. The key points are the generation of alcanethiol-in-polyol droplets and the subsequent in situ controlled interfacial reaction between Te and Bi precursors. The Te(IV) ions present in the alcanethiol phase are initially reduced into Te(0) by decanethiol. The Bi(III) ions initially dissolved in the polyol phase are then reduced at the decanethiol/polyol interface, resulting in the progressive growth of Bi{sub 2}Te{sub 3} hexagonal nanoplatelets at the outer surface of the pristine Te(0) sphere.

  17. Holographic performance of photorefractive Bi2TeO5 crystals

    Science.gov (United States)

    Foldvari, I.; Denz, C.; Berger, G.; Peter, A.

    Bismuth tellurite - Bi2TeO5 is a new photorefractive material recently available for optical memory investigations. Analogue volume holograms of a two-dimensional test pattern were recorded in undoped Bi2TeO5 crystals by using a cw Nd:YAG laser at 532 nm. The quality, dark decay and durability during permanent reading of the image were studied and compared to those of the reference LiNbO3 :Fe crystals. The holograms in the two crystals were of comparable quality, and they were less vulnerable for strong laser exposure in Bi2TeO5 than in the LiNbO3 :Fe crystals by a factor of 50.

  18. Structural, vibrational, and electrical study of compressed BiTeBr

    Science.gov (United States)

    Sans, J. A.; Manjón, F. J.; Pereira, A. L. J.; Vilaplana, R.; Gomis, O.; Segura, A.; Muñoz, A.; Rodríguez-Hernández, P.; Popescu, C.; Drasar, C.; Ruleova, P.

    2016-01-01

    Compresed BiTeBr has been studied from a joint experimental and theoretical perspective. Room-temperature x-ray diffraction, Raman scattering, and transport measurements at high pressures have been performed in this layered semiconductor and interpreted with the help of ab initio calculations. A reversible first-order phase transition has been observed above 6-7 GPa, but changes in structural, vibrational, and electrical properties have also been noted near 2 GPa. Structural and vibrational changes are likely due to the hardening of interlayer forces rather than to a second-order isostructural phase transition while electrical changes are mainly attributed to changes in the electron mobility. The possibility of a pressure-induced electronic topological transition and of a pressure-induced quantum topological phase transition in BiTeBr and other bismuth tellurohalides, like BiTeI, is also discussed.

  19. Observation of antiphase coherent phonons in the warped Dirac cone of Bi2Te3

    Science.gov (United States)

    Golias, E.; Sánchez-Barriga, J.

    2016-10-01

    In this Rapid Communication we investigate the coupling between excited electrons and phonons in the highly anisotropic electronic structure of the prototypical topological insulator Bi2Te3 . Using time- and angle-resolved photoemission spectroscopy we are able to identify the emergence and ultrafast temporal evolution of the longitudinal-optical A1 g coherent-phonon mode in Bi2Te3 . We observe an antiphase behavior in the onset of the coherent-phonon oscillations between the Γ K ¯ and the Γ M ¯ high-symmetry directions that is consistent with warping. The qualitative agreement between our density-functional theory calculations and the experimental results reveals the critical role of the anisotropic coupling between Dirac fermions and phonon modes in the topological insulator Bi2Te3 .

  20. Enhanced Thermoelectric Performance of Nanostructured Bi2Te3 through Significant Phonon Scattering.

    Science.gov (United States)

    Yang, Lei; Chen, Zhi-Gang; Hong, Min; Han, Guang; Zou, Jin

    2015-10-28

    N-type Bi2Te3 nanostructures were synthesized using a solvothermal method and in turn sintered using sparking plasma sintering. The sintered n-type Bi2Te3 pellets reserved nanosized grains and showed an ultralow lattice thermal conductivity (∼0.2 W m(-1) K(-1)), which benefits from high-density small-angle grain boundaries accommodated by dislocations. Such a high phonon scattering leads an enhanced ZT of 0.88 at 400 K. This study provides an efficient method to enhance thermoelectric performance of thermoelectric nanomaterials through nanostructure engineering, making the as-prepared n-type nanostructured Bi2Te3 as a promising candidate for room-temperature thermoelectric power generation and Peltier cooling.

  1. Thermoelectric properties of quaternary (Bi,Sb){sub 2}(Te,Se){sub 3} compound

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Pengfei, E-mail: photon.bupt@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Li, Yiluan; Wu, Chengjie; Yu, Zhongyuan; Cao, Huawei; Zhang, Xianlong; Cai, Ningning; Zhong, Xuxia [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 72, Beijing 100876 (China); Wang, Shumin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg (Sweden)

    2014-01-25

    Highlights: • Sb and Se spin–orbit coupling play a key role in the band structure. • Substituted Bi/Sb and Te/Se have a limited impact on the transport coefficients. • n-Type doping will be preferred for quaternary (Bi,Sb){sub 2}(Te,Se){sub 3} compound. -- Abstract: The quaternary (Bi,Sb){sub 2}(Te,Se){sub 3} compounds are investigated using first-principles study and Boltzmann transport theory. The energy band structure and density of states are studied in detail. The electronic transport coefficients are then calculated as a function of chemical potential. The figure of merit ZT is obtained assuming a constant relaxation time and an averaged thermal conductivity. Our theoretical result agrees well with previous experimental data.

  2. Unusual non saturating Giant Magneto-resistance in single crystalline Bi2Te3 topological insulator

    Science.gov (United States)

    Sultana, Rabia; Neha, P.; Goyal, R.; Patnaik, S.; Awana, V. P. S.

    2017-04-01

    We report synthesis, structural details and electrical transport properties of topological insulator Bi2Te3. The single crystalline specimens of Bi2Te3 are obtained from high temperature (950 °C) melt and slow cooling (2 °C/hour). The resultant crystals were shiny, one piece (few cm) and of bright silver color. The Bi2Te3 crystal is found to be perfect with clear [00l] alignment. The powder XRD pattern being carried out on crushed crystals showed that Bi2Te3 crystallized in R3̅m symmetry with a=b=4.3866(2) Å, c=30.4978(13) Å and γ=120°. The Bi position is refined to (0, 0, 0.4038 (9)) at Wyckoff position 6c and of Te are (0, 0, 0) at Wyckoff position 3a and at (0, 0, 0.2039(8)) at 6c. Ambient pressure and low temperature (down to 2 K) electrical transport measurements revealed metallic behavior. Magneto transport measurements under magnetic field showed huge non saturating magneto resistance (MR) reaching up to 250% at 2.5 K and under 50 kOe field. Summarily, the short communication clearly demonstrates that Bi2Te3 topological insulator exhibit non-saturating large positive MR at low temperature of say below 10 K. The non saturating MR is seen right up to room temperature albeit with much decreased magnitude. Worth mentioning is the fact that these crystals are bulk in nature and hence the anomalous MR is clearly an intrinsic property and not due to the size effect as reported for nano-wires or thin films of the same.

  3. Two-dimensional superconductivity at the interface of a Bi2Te3/FeTe heterostructure.

    Science.gov (United States)

    He, Qing Lin; Liu, Hongchao; He, Mingquan; Lai, Ying Hoi; He, Hongtao; Wang, Gan; Law, Kam Tuen; Lortz, Rolf; Wang, Jiannong; Sou, Iam Keong

    2014-06-23

    The realization of superconductivity at the interface between a topological insulator and an iron-chalcogenide compound is highly attractive for exploring several recent theoretical predictions involving these two new classes of materials. Here we report transport measurements on a Bi2Te3/FeTe heterostructure fabricated via van der Waals epitaxy, which demonstrate superconductivity at the interface, which is induced by the Bi2Te3 epilayer with thickness even down to one quintuple layer, though there is no clear-cut evidence that the observed superconductivity is induced by the topological surface states. The two-dimensional nature of the observed superconductivity with the highest transition temperature around 12 K was verified by the existence of a Berezinsky-Kosterlitz-Thouless transition and the diverging ratio of in-plane to out-plane upper critical field on approaching the superconducting transition temperature. With the combination of interface superconductivity and Dirac surface states of Bi2Te3, the heterostructure studied in this work provides a novel platform for realizing Majorana fermions.

  4. Preparation and structure of BiCrTeO{sub 6}: A new compound in Bi–Cr–Te–O system. Thermal expansion studies of Cr{sub 2}TeO{sub 6}, Bi{sub 2}TeO{sub 6} and BiCrTeO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Vats, Bal Govind; Phatak, Rohan; Krishnan, K.; Kannan, S., E-mail: skannan@barc.gov.in

    2013-09-01

    Graphical abstract: A new compound BiCrTeO{sub 6} in the Bi–Cr–Te–O system was prepared by solid state route and characterized by X-ray diffraction method. The crystal structure of BiCrTeO{sub 6} shows that there is one distinct site for bismuth (Bi) atom (pink color), one chromium rich (Cr/Te = 68/32) (blue/green color), one tellurium rich (Te/Cr = 68/32) sites (green/blue color), and one distinct site for oxygen (O) atom (red color) in the unit cell. All cations in this structure show an octahedral coordination with oxygen atoms at the corners. The thermogram (TG) of the compound in air shows that it is stable up to 1103 K and decomposes thereafter. The thermal expansion behaviour of BiCrTeO{sub 6} was studied using high temperature X-ray diffraction method from room temperature to 923 K under vacuum of 10{sup −8} atmosphere and showed positive thermal expansion with the average volume thermal expansion coefficients of 16.0 × 10{sup −6}/K. - Highlights: • A new compound BiCrTeO{sub 6} in Bi–Cr–Te–O system was prepared and characterized. • The crystal structure of BiCrTeO{sub 6} was determined by Rietveld refinement method. • The structure of BiCrTeO{sub 6} shows an octahedral coordination for all the metal ions. • The thermal expansion behavior of BiCrTeO{sub 6} from room temperature to 923 K showed a positive thermal expansion. • The average volume thermal expansion coefficient for BiCrTeO{sub 6} is 16.0 × 10{sup −6}/K. - Abstract: A new compound BiCrTeO{sub 6} in Bi–Cr–Te–O system was prepared by solid state reaction of Bi{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} and H{sub 6}TeO{sub 6} in oxygen and characterized by X-ray diffraction (XRD) method. It could be indexed on a trigonal lattice, with the space group P-31c, unit cell parameters a = 5.16268(7) Å and c = 9.91861(17) Å. The crystal structure of BiCrTeO{sub 6} was determined by Rietveld refinement method using the powder XRD data. Structure shows that there is one distinct

  5. Shubnikov-de Haas Oscillations in the Bulk Rashba Semiconductor BiTeI

    Energy Technology Data Exchange (ETDEWEB)

    Bell, C.; Bahramy, M.S.; Murakawa, H.; Checkelsky, J.G.; Arita, R.; Kaneko, Y.; Onose, Y.; Nagaosa, N.; Tokura, Y.; Hwang, H.Y.

    2012-07-11

    Bulk magnetoresistance quantum oscillations are observed in high quality single crystal samples of BiTeI. This compound shows an extremely large internal spin-orbit coupling, associated with the polarity of the alternating Bi, Te, and I layers perpendicular to the c-axis. The corresponding areas of the inner and outer Fermi surfaces around the A-point show good agreement with theoretical calculations, demonstrating that the intrinsic bulk Rashba-type splitting is nearly 360 meV, comparable to the largest spin-orbit coupling generated in heterostructures and at surfaces.

  6. Pressure dependence of the band-gap energy in BiTeI

    OpenAIRE

    Güler-Kılıç, Sümeyra; Kılıç, Çetin

    2016-01-01

    The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated,...

  7. Evolution of the Fermi surface of BiTeCl with pressure

    OpenAIRE

    Vangennep, D; Jackson, D E; Graf, D.; Berger, H.; Hamlin, J. J.

    2017-01-01

    We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeCl under applied pressures up to ~2.5 GPa. We observe two distinct oscillation frequencies, corresponding to the Rashba-split inner and outer Fermi surfaces. BiTeCl has a conduction band bottom that is split into two sub-bands due to the strong Rashba coupling, resulting in two spin-polarized conduction bands as well as a Dirac point. Our results suggest that the chemical potential lies above this D...

  8. Crystal growth and physical property of Bi-Sb-Te-Se topological insulator materials, and Cu-Bi-Se and Sn-In-Te topological superconductors

    Science.gov (United States)

    Gu, Genda; Yang, Alina; Schneeloch, J.; Zhong, R. D.; Xu, Z. J.; Tranquada, J. M.; Pan, Z. H.; Si, W. D.; Shi, X. Y.; Li, Q.; Valla, T.

    2013-03-01

    The discovery of 3D topological insulator materials and topological superconductor opens up a new research field in the condensed matter physics. We have grown a number of Bi-Sb-Te-Se topological insulator, and Cu-Bi-Se and Sn-In-Te topological superconductor single crystals. We have measured the physical properties on these single crystals. We have studied the effect of growth condition and impurity on the bulk electrical conductivity of these single crystals. We try to answer two questions for the topological insulator materials if it is possible to grow the bulk-insulating topological insulator single crystals and Which maximum resistivity of these topological insulator single crystals we can grow. For the topological superconductor, we have got the bulk superconducting single crystals with a maximum Tc =4.5K. DOE under Contract No. DE-AC02-98CH10886 and the DOE Center for Emergent Superconductivity.

  9. Gate-tunable transport properties of in situ capped Bi2Te3 topological insulator thin films

    NARCIS (Netherlands)

    Ngabonziza, Prosper; Stehno, Martin P.; Myoren, Hiroaki; Neumann, Viola A.; Koster, Gertjan; Brinkman, Alexander

    2016-01-01

    Combining of the ability to prepare high-quality, intrinsic Bi2Te3 topological insulator thin films of low carrier density with in situ protective capping, a pronounced, gate-tunable change in transport properties of Bi2Te3 thin films is demonstrated. Using a back gate, the carrier density is tuned

  10. Electron-phonon coupling and surface Debye temperature of Bi2Te3(111) from helium atom scattering

    DEFF Research Database (Denmark)

    Tamtogl, Anton; Kraus, Patrick; Avidor, Nadav

    2017-01-01

    We have studied the topological insulator Bi2Te3(111) by means of helium atom scattering. The average electron-phonon coupling lambda of Bi2Te3(111) is determined by adapting a recently developed quantum-theoretical derivation of the helium scattering probabilities to the case of degenerate...

  11. Effect of Initial Bulk Material Composition on Thermoelectric Properties of Bi2Te3 Thin Films

    Science.gov (United States)

    Budnik, A. V.; Rogacheva, E. I.; Pinegin, V. I.; Sipatov, A. Yu.; Fedorov, A. G.

    2013-07-01

    V2VI3 compounds and solid solutions based on them are known to be the best low-temperature thermoelectric (TE) materials. The predicted possibility of enhancement of the TE figure of merit in two-dimensional (2D) structures has stimulated studies of the properties of these materials in the thin-film state. The goal of the present work is to study the dependences of the Seebeck coefficient S, electrical conductivity σ, Hall coefficient R H, charge carrier mobility μ H, and TE power factor P = S 2 σ of Bi2Te3 thin films on the composition of the initial bulk material used for preparing them. Thin films with thickness d = 200 nm to 250 nm were grown by thermal evaporation in vacuum of stoichiometric Bi2Te3 crystals (60.0 at.% Te) and of crystals with 62.8 at.% Te onto glass substrates at temperatures T S of 320 K to 500 K. It was established that the conductivity type of the initial material is reproduced in films fairly well. For both materials, an increase in T S leads to an increase in the thin-film structural perfection, better correspondence between the film composition and that of the initial material, and increase in S, R H, μ H, σ, and P. The room-temperature maximum values of P for the films grown from crystals with 60.0 at.% and 62.8 at.% Te are P = 7.5 × 10-4 W/K2 m and 35 × 10-4 W/K2 m, respectively. Thus, by using Bi2Te3 crystals with different stoichiometry as initial materials, one can control the conductivity type and TE parameters of the films, applying a simple and low-cost method of thermal evaporation from a single source.

  12. Growth and characterization of molecular beam epitaxy-grown Bi2Te3-xSex topological insulator alloys

    Science.gov (United States)

    Tung, Y.; Chiang, Y. F.; Chong, C. W.; Deng, Z. X.; Chen, Y. C.; Huang, J. C. A.; Cheng, C.-M.; Pi, T.-W.; Tsuei, K.-D.; Li, Z.; Qiu, H.

    2016-02-01

    We report a systematic study on the structural and electronic properties of Bi2Te3-xSex topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3-xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3-xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi2Te3-xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.

  13. Real-space characterization of reactivity towards water at Bi2Te3(111) surface

    CERN Document Server

    Zhang, Kai-Wen; Yang, Chao-Long; Gan, Yuan; Li, Shichao; Huang, Wen-Kai; Song, Ye-Heng; Jia, Zhen-Yu; Li, Xiang-Bing; Zhu, Zihua; Wen, Jinsheng; Chen, Mingshu; Li, Shao-Chun

    2016-01-01

    Surface reactivity is important in modifying the physical and chemical properties of surface sensitive materials, such as the topological insulators (TIs). Even though many studies addressing the reactivity of TIs towards external gases have been reported, it is still under heavy debate whether and how the topological insulators react with H$_2$O. Here, we employ scanning tunneling microscopy (STM) to directly probe the surface reaction of Bi$_2$Te$_3$ towards H$_2$O. Surprisingly, it is found that only the top quintuple layer is reactive to H$_2$O, resulting in a hydrated Bi bilayer as well as some Bi islands, which passivate the surface and prevent from the subsequent reaction. A reaction mechanism is proposed with H$_2$Te and hydrated Bi as the products. Unexpectedly, our study indicates the reaction with water is intrinsic and not dependent on any surface defects. Since water inevitably exists, these findings provide key information when considering the reactions of Bi$_2$Te$_3$ with residual gases or atm...

  14. Enhanced thermoelectric performance of Bi2Te3 through uniform dispersion of single wall carbon nanotubes

    Science.gov (United States)

    Ahmad, Kaleem; Wan, Chunlei

    2017-10-01

    The advancement in nanostructured powder processing has attracted great interest as a cost effective and scalable strategy for high performance thermoelectric bulk materials. However, the level of technical breakthrough realized in quantum dot supperlattices/wires has not yet been demonstrated in these materials. Here, we report the first ever study on the uniform dispersion of single wall carbon nanotubes (SWCNTs) in nanostructured Bi2Te3 bulk, and their effect on thermoelectric parameters above room temperature. The Bi2Te3 based SWCNT composites were prepared through controlled powder processing, and their thermoelectric properties were finely tuned at the nanoscale by regulating various (0.5, 0.75, 1.0 and 1.5) vol% of SWCNTs in the matrix. The flexible ropes of SWCNT, making an interconnected network through the inter/trans granular positions of Bi2Te3, thus substantially change the transport properties of the composites. The perfect one-dimensional (1D) conducting structure of SWCNTs acts as a source of electrical transport through a percolating network, with significantly suppressed lattice thermal conductivity, via intensified boundary scattering. The remarkable increase in power factor is ascribed to energy filtering effects and excellent electrical transport of 1D SWCNTs in the composites. Consequently, with a considerable reduction in thermal conductivity, the figure of merit culminates in a several-fold improvement, at 0.5 vol% of SWCNTs, over pristine bulk Bi2Te3.

  15. Effects of Heat Treatment on Thermoelectric and Infrared Properties of Bi2Te3 Films

    Institute of Scientific and Technical Information of China (English)

    Shi-Feng Zou; Pei-Heng Zhou; Xin Wang; Jian-Liang Xie; Long-Jiang Deng

    2016-01-01

    In this work, Bi2Te3 films (250nm) are fabricated on SiO2/Si substrates by radio frequency (RF) magnetron sputtering at room temperature, and the prepared films are annealed over the temperature range of 200 °C to 400 °C. Crystallinity and electrical properties of the films can be tuned correspondingly. The power factors of Bi2Te3 films of 0.85μW/K2cm to 11.43μW/K2cm were achieved after annealing. The infrared reflectance measurements from 2.5µm to 5.0 µm demonstrate that there is also a slight red-shift of the plasma oscillation frequency in the Bi2Te3 films. By means of plasmonic calculations, we attribute the red-shift of absorption peaks to the reduction of carrier concentration and the change of effective mass of Bi2Te3 films with the increased annealing temperature.

  16. Effects of Mass Fluctuation on Thermal Transport Properties in Bulk Bi2Te3

    Science.gov (United States)

    Huang, Ben; Zhai, Pengcheng; Yang, Xuqiu; Li, Guodong

    2016-10-01

    In this paper, we applied large-scale molecular dynamics and lattice dynamics to study the influence of mass fluctuation on thermal transport properties in bulk Bi2Te3, namely thermal conductivity (K), phonon density of state (PDOS), group velocity (v g), and mean free path (l). The results show that total atomic mass change can affect the relevant vibrational frequency on the micro level and heat transfer rate in the macro statistic, hence leading to the strength variation of the anharmonic phonon processes (Umklapp scattering) in the defect-free Bi2Te3 bulk. Moreover, it is interesting to find that the anharmonicity of Bi2Te3 can be also influenced by atomic differences of the structure such as the mass distribution in the primitive cell. Considering the asymmetry of the crystal structure and interatomic forces, it can be concluded by phonon frequency, lifetime, and velocity calculation that acoustic-optical phonon scattering shows the structure-sensitivity to the mass distribution and complicates the heat transfer mechanism, hence resulting in the low lattice thermal conductivity of Bi2Te3. This study is helpful for designing the material with tailored thermal conductivity via atomic substitution.

  17. Bi2Te3 thin hexagonal nanoplatelets: Synthesis and its characterization studies

    Science.gov (United States)

    Vinoth, S.; Balaganapathi, T.; KaniAmuthan, B.; Arun, T.; Muthuselvam, I. Panneer; Chou, Fang-Cheng; Thilakan, P.

    2017-08-01

    Solvothermal synthesis and optimization of pure Bismuth telluride (Bi2Te3) hexagonal nanoplatelets was carried out from Bismuth Oxide (Bi2O3) and Tellurium dioxide (TeO2). XRD measurements revealed a sensitive change in crystallization behaviour in correlation with variation in Te/Bi stoichiometry identified through the exchange in intensities between (10 10 ̅) and (110) peaks. Further, Energy Dispersive X-ray (EDAX) analysis revealed the variation in Te/Bi ratio with respect to autoclave temperature. Field emission scanning electron Microscope (FESEM) and the high resolution transmission electron Microscope (HRTEM) studies show the complete growth of hexagonal nanoplatelets at 200 °C. Confocal Micro-Raman measurements revealed the occurrence of symmetry breaking in the synthesized hexagonal nanoplatelets. The electrical conductivity and the activation energy were recorded as 6.01×10-3 S/m and 0.042 eV respectively. Highest maximum absolute value of Seebeck coefficient of -355 μV/K was obtained for the hexagonal nanoplatelets.

  18. In situ Raman spectroscopy of topological insulator BiTe films with varying thickness

    DEFF Research Database (Denmark)

    Wang, C.; Zhu, X.; Nilsson, Louis;

    2013-01-01

    Topological insulators (TIs) are a new state of quantum matter with a band gap in bulk and conducting surface states. In this work, the Raman spectra of topological insulator Bi2Te3 films prepared by molecular beam epitaxy (MBE) have been measured by an in situ ultrahigh vacuum (UHV...

  19. Transverse peltier effect in Pb-Bi{sub 2}Te{sub 3} multilayer structures

    Energy Technology Data Exchange (ETDEWEB)

    Reitmaier, Christina; Walther, Franziska; Kyarad, Amir; Lengfellner, Hans [University of Regensburg (Germany)

    2009-07-01

    Metal-semiconductor multilayer structures show, according to model calculations, large anisotropy in their electrical and thermal transport properties. Multilayer stacks consisting of alternating layers of Pb and n-type Bi{sub 2}Te{sub 3} and prepared by a heating procedure displayed large thermoelectric anisotropy up to {delta}S{approx}200 {mu} V/K, depending on the thickness ratio p=d{sub BiTe}/d{sub Pb}, where d{sub BiTe} and d{sub Pb} are the thicknesses of Bi{sub 2}Te{sub 3} and Pb layers, respectively. From multilayer stacks, tilted samples with layers inclined with respect to the sample surface where obtained by cutting stacks obliquely to the stack axis. Non-zero off-diagonal elements in the Seebeck-tensor describing the thermopower of tilted samples allow for the occurance of a transverse Peltier effect. Experimental results demonstrate cooling by the transverse Peltier effect and are compared to model calculations.

  20. Thermoelectric properties of Bi0.5Sb1.5Te3/C60 nanocomposites

    NARCIS (Netherlands)

    Blank, V.D.; Buga, S.G.; Kulbachinskii, V.A.; Kytin, V.G.; Medvedev, V.V.; Popov, Y.M.; Stepanov, P.B.; Skok, V.F.

    2012-01-01

    A thermoelectric nanocomposite of Bi0.5Sb1.5Te3 with the C60 fullerene molecules has been synthesized and studied. The fullerene molecules provide the phonons blocking, reducing the lattice thermal conductivity. The reduction of the electrical conductivity is much less than the heat conductivity red

  1. The microstructure network and thermoelectric properties of bulk (Bi,Sb)2Te3

    DEFF Research Database (Denmark)

    Xie, Wenjie; Hitchcock, Dale A.; Kang, Hye J.

    2012-01-01

    We report small-angle neutron scattering studies on the microstructure network in bulk (Bi,Sb)(2)Te-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...

  2. Formation of Dense Pore Structure by Te Addition in Bi0.5Sb1.5Te3: An Approach to Minimize Lattice Thermal Conductivity

    Directory of Open Access Journals (Sweden)

    Syed Waqar Hasan

    2013-01-01

    Full Text Available We herein report the electronic and thermal transport properties of p-type Bi0.5Sb1.5Te3 polycrystalline bulks with dense pore structure. Dense pore structure was fabricated by vaporization of residual Te during the pressureless annealing of spark plasma sintered bulks of Te coated Bi0.5Sb1.5Te3 powders. The lattice thermal conductivity was effectively reduced to the value of 0.35 W m−1 K−1 at 300 K mainly due to the phonon scattering by pores, while the power factor was not significantly affected. An enhanced ZT of 1.24 at 300 K was obtained in spark plasma sintered and annealed bulks of 3 wt.% Te coated Bi0.5Sb1.5Te3 by these synergetic effects.

  3. Development of Low-Cost Remote-Control Generators Based on BiTe Thermoelectric Modules

    Science.gov (United States)

    Juanicó, Luis E.; Rinalde, Fabián; Taglialavore, Eduardo; Molina, Marcelo

    2013-07-01

    This paper presents a new thermogenerator based on moderate-temperature (up to 175°C) BiTe modules available on the open market. Despite this handicap relative to commercial thermogenerators based on high-temperature proprietary-technology PbBi modules (up to 560°C), this new design may become economically competitive due to its innovative thermal sink. Our thermal sink is based on a free-convection water loop built with standard tubing and household hot-water radiators, leading to a more practical, modular design. So, the specific cost of about 55,000 USD/kW obtained for this 120-W prototype is improved to 33,000 USD/kW for a 1-kW unit, which represents about half the price of commercial thermogenerators. Moreover, considering recently launched BiTe modules (that withstand up to 320°C), our proposition could have an even more favorable outlook.

  4. Selective area growth of Bi2Te3 and Sb2Te3 topological insulator thin films

    Science.gov (United States)

    Kampmeier, Jörn; Weyrich, Christian; Lanius, Martin; Schall, Melissa; Neumann, Elmar; Mussler, Gregor; Schäpers, Thomas; Grützmacher, Detlev

    2016-06-01

    The intrinsic bulk behavior of topological insulators (TI) is a key issue for their employment in future device applications. State of the art TIs predominantly suffer from large bulk charge carrier concentrations that mask their extraordinary surface states. In this paper we present the selective area growth of Bi2Te3 and Sb2Te3 TI thin films on prestructured Si(111) Si on insulator (SOI) substrates, paving the way to high quality TI nanostructures in which access to surface states is enhanced. Therefore high quality Bi2Te3 and Sb2Te3 thin films were deposited by means of solid source molecular beam epitaxy (MBE) and subsequently investigated by energy dispersive x-ray spectroscopy (EDX). To investigate the transport properties of the selectively grown thin films, magnetotransport measurements were performed at low temperatures. Nucleation in the SiO2 valleys next to the prepatterned Si(111) mesa structures was not observed. The structural and morphological qualities of crystals deposited on untreated Si(111) SOI wafers are completely preserved by employing the selective area growth on prepatterned substrates. The transport characteristics of the selectively-grown TI systems are comparable to those of the analogous postpatterned films.

  5. Weak Antilocalization in Bi 2 (Se x Te 1– x ) 3 Nanoribbons and Nanoplates

    KAUST Repository

    Cha, Judy J.

    2012-02-08

    Studying the surface states of Bi 2Se 3 and Bi 2Te 3 topological insulators has proven challenging due to the high bulk carrier density that masks the surface states. Ternary compound Bi 2(Se xTe 1-x) 3 may present a solution to the current materials challenge by lowering the bulk carrier mobility significantly. Here, we synthesized Bi 2(Se xTe 1-x) 3 nanoribbons and nanoplates via vapor-liquid-solid and vapor-solid growth methods where the atomic ratio x was controlled by the molecular ratio of Bi 2Se 3 to Bi 2Te 3 in the source mixture and ranged between 0 and 1. For the whole range of x, the ternary nanostructures are single crystalline without phase segregation, and their carrier densities decrease with x. However, the lowest electron density is still high (∼10 19 cm -3) and the mobility low, suggesting that the majority of these carriers may come from impurity states. Despite the high carrier density, weak antilocalization (WAL) is clearly observed. Angle-dependent magnetoconductance study shows that an appropriate magnetic field range is critical to capture a true, two-dimensional (2D) WAL effect, and a fit to the 2D localization theory gives α of -0.97, suggesting its origin may be the topological surface states. The power law dependence of the dephasing length on temperature is ∼T -0.49 within the appropriate field range (∼0.3 T), again reflecting the 2D nature of the WAL. Careful analysis on WAL shows how the surface states and the bulk/impurity states may interact with each other. © 2012 American Chemical Society.

  6. Enhanced Thermoelectric Performance in Cu-Intercalated BiTeI by Compensation Weakening Induced Mobility Improvement.

    Science.gov (United States)

    Wu, Lihua; Yang, Jiong; Chi, Miaofang; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2015-09-23

    The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization.

  7. Optical and thermoelectric properties of nano-particles based Bi2(Te1-xSex)3 thin films

    Science.gov (United States)

    Adam, A. M.; Lilov, E.; Petkov, P.

    2017-01-01

    Nano-particles of Bi2Te3 and Bi2(Te1-xSex)3 films were deposited using vacuum thermal evaporation technique from previously prepared bulk alloys synthesized by melting method. Optical and thermoelectric properties were studied in the temperature range of 300-473K. The formation of none- and Se-doped Bi2Te3 nano-particles was verified by EDX and XRD analysis. TEM, SEM and AFM analysis showed the prepared films are polycrystalline in nature. The measurements of electrical conductivity and Seebeck coefficient, alongside with thermal conductivity calculations, resulted in the highest values of thermoelectric power at high temperature to be reported. The maximum value of power factor was calculated at 62.82917 μWK-2cm-1 for (Bi2Se0.3Te1.7) sample at 463 K. On the addition of Se to Bi2Te3 film, a significant decrease of the electronic thermal conductivity (Kel) from 2.181 × 10-2 to 0.598 × 10-2 (μW/cm.K) could be achieved. Figure of merit (ZT) calculations showed a maximum value of 0.85 at room temperature, for Bi2Te3. Besides the increase of ZT value for all samples at higher temperature, surprisingly, a value of 2.75 for (Bi2Se1.2Te1.8) was obtained. We believe our results could open avenues for new applications.

  8. Systematic control of surface Dirac fermion density on topological insulator Bi2Te3

    Science.gov (United States)

    Xu, Suyang; Xia, Yuqi; Grauer, David; Hor, Yewsan; Cava, Robert; Hasan, Zahid

    2010-03-01

    Three dimensional (3D) topological insulators are quantum materials with a spin-orbit induced bulk insulating gap that exhibit quantum-Hall-like phenomena in the absence of applied magnetic fields. They feature surface states that are topologically protected against scattering by time reversal symmetry. The proposed applications of topological insulators in device geometries rely on the ability to tune the chemical potential on their surfaces in the vicinity of the Dirac node. Here, we demonstrate a suite of surface control methods based on a combination of photo-doping and molecular-doping to tune the Dirac fermion density on the topological (111) surface of Bi2Te3. Their efficacy is demonstrated via direct electronic structure measurements using high resolution angle-resolved photoemission spectroscopy. These results open up new opportunities for probing topological behavior of Dirac electrons in Bi2Te3. At least one of the methods demonstrated here can be successfully applied to other topological insulators (Bi1-xSbx, Sb2Te3 and Bi2Se3). More importantly, our methods of topological surface state manipulation demonstrated here are highly suitable for future spectroscopic studies of topological phenomena which will complement the transport results gained from the traditional electrical gating techniques.

  9. Topological insulator thin films of Bi{sub 2}Te{sub 3} with controlled electronic structure

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Guang; Zhu, Xie-Gang; Li, Yao-Yi; Wen, Jing; Chen, Xi; Jia, Jin-Feng [State Key Lab of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Sun, Yi-Yang; Zhang, Shengbai B. [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Zhang, Tong; He, Ke; Wang, Li-Li; Ma, Xu-Cun [Institute of Physics, The Chinese Academy of Sciences, Beijing 100190 (China); Xue, Qi-Kun [State Key Lab of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Institute of Physics, The Chinese Academy of Sciences, Beijing 100190 (China)

    2011-07-12

    Topological insulator thin films of Bi{sub 2}Te{sub 3} with controlled electronic structure can be grown by regulating the molecular beam epitaxy (MBE) growth kinetics without any extrinsic doping. N- to p-type conversion results from the change in the concentrations of Te{sub Bi} donors and Bi{sub Te} acceptors. This represents a step toward controlling topological surface states, with potential applications in devices. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Bismuth telluride (Bi2Te3) nanowires: synthesis by cyclic electrodeposition/stripping, thinning by electrooxidation, and electrical power generation.

    Science.gov (United States)

    Menke, E J; Brown, M A; Li, Q; Hemminger, J C; Penner, R M

    2006-12-01

    Nanowires composed of the thermoelectric material Bi2Te3 were synthesized on highly oriented pyrolytic graphite (HOPG) electrodes using the electrochemical step edge decoration (ESED) method. Nanowire synthesis was initiated by applying a voltage pulse of -0.75 V versus SCE for 5 ms to an HOPG electrode in an aqueous solution containing both Bi3+ and TeO22-, thereby producing nuclei at the step edges. Bi2Te3 was electrodeposited onto these nuclei using a cyclic electrodeposition-stripping scheme that involved the electrodeposition of bismuth-rich Bi2Te3 on a negative-going voltammetric scan (to -0.05 V) and the subsequent anodic stripping of excess bismuth from these nanowires during a positive-going scan (to +0.35 V). When this cycle was repeated 10-50 times, Bi2Te3 nanowires in the 100-300-nm-diameter range were obtained. These nanowires were narrowly dispersed in diameter (RSDdia = 10-20%), were more than 100 microm in length, and were organized into parallel arrays containing hundreds of wires. Smaller nanowires, with diameters down to 30 nm, were obtained by electrooxidizing 150-nm-diameter Bi2Te3 nanowires at +0.37 V under conditions of kinetic control. This oxidation process unexpectedly improved the uniformity of Bi2Te3 nanowires, and X-ray photoelectron spectroscopy (XPS) shows that these nanowires retain a Bi2Te3 core but also have a thin surface layer composed of Bi and Te oxides. The ability of Bi2Te3 nanowires to generate electrical power was assessed by transferring ensembles of these nanowires onto cyanoacrylate-coated glass surfaces and evaporating 4-point nickel contacts. A dimensionless figure of merit, ZT, ranging from 0 to 0.85 was measured for fresh samples that were less than 1 day old. XPS reveals that Bi2Te3 nanowires are oxidized within a week to Bi2O3 and TeO2. These oxides may interfere with the application by evaporation of electrical contacts to these nanowires.

  11. Characterization of Bulk Nanostructural Bi2Te3-based Material Prepared by Microwave-solvothermal Synthesis and Hot Isostatic Pressure

    Directory of Open Access Journals (Sweden)

    O.N. Ivanov

    2014-07-01

    Full Text Available The bulk nanostructural Bi2Te3-based material was prepared by microwave assisted solvothermal method and hot isostatic pressure. Optimal synthesis conditions of the Bi2Te3 nanopowder were found. It was established that hot isostatic pressing of the nanopowders at the temperature of 400 С and the pressures of 2, 4, 6 and 8 GPa allowed us to prepare the homogeneous and dense Bi2Te3-based material with the mean grain size of  50 nm. It is found that an electrical resistivity increases as the mean grain size of the material under study decreases.

  12. Transport Phenomena in the Vapor-phase PbTe-Bi2Te3 Condensates on Sital

    Directory of Open Access Journals (Sweden)

    D.M. Freik

    2013-10-01

    Full Text Available Dependences of the structural characteristics and electrical properties of thin films of PbTe-Bi2Te3 solid solutions with compositions of 1,3,5 ml. % of Bi2Te3 deposited in an open vacuum on the sital substrates on their thickness d  (0,2-2 microns were studied. The effective mean free path  of charge carriers is defined and the dominant mechanism of scattering is found. The values of thermoelectric parameters of the near-surface layers are estimated within the two-layer Petritz model. It is stablished that condensate is characterized by a stable n-type conductivity, and there is a diffuse scattering on the surface that conditions a significant decrease in the magnitude of mobility (s, conductivity (s, and increase in the Seebeck coefficient (Ss with respect to the film volume. The obtained results are explained by acceptor influence of atmospheric oxygen and throttling of charge carriers on potential barriers of the interfaces.

  13. Optical Properties of Bi Doped Amorphous Se-Te Thin Films

    Science.gov (United States)

    Kumar, Anup; Heera, Pawan; Barman, P. B.; Sharma, Raman

    2011-12-01

    Effect of Bismuth (Bi) doping on the optical constants of Se-Te thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index decreases with wavelength, for all compositions and the absorption coefficient increases with increase in optical energy. On the other hand the optical band gap is found to decreases with increase in Bi content.

  14. Crystal and electronic structure of BiTeI, AuTeI, and PdTeI compounds: A dispersion-corrected density-functional study

    OpenAIRE

    Güler-Kılıç, Sümeyra; Kılıç, Çetin

    2015-01-01

    Semilocal and dispersion-corrected density-functional calculations have been performed to study the crystal structure, equation of state, and electronic structure of metal tellurohalides with chemical formula MeTeI where Me=Bi, Au, or Pd. A comparative investigation of the results of these calculations is conducted which reveals the role of van der Waals attraction. It is shown that the prediction of crystal structure of metal tellurohalides is systematically improved thanks to the inclusion ...

  15. Ion beam synthesis of Te and Bi nanoclusters in silicon: The effect of post-implantation high frequency electromagnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Kalitzova, M. [Institute of Solid State Physics - BAS, Boulevard Tzarigradsko Chaussee 72, BG-1784 Sofia (Bulgaria)]. E-mail: markaliz@issp.bas.bg; Peeva, A. [Institute of Solid State Physics - BAS, Boulevard Tzarigradsko Chaussee 72, BG-1784 Sofia (Bulgaria); Ignatova, V. [SCK.CEN, Reactor Materials Research, Boeretang 200, 2400 Mol (Belgium); Lebedev, O.I. [EMAT, RUCA, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp (Belgium); Zollo, G. [Dipartimento di Enerdetica, Univ. La Sapienza, Via A. Scarpa 14, 00161 Rome (Italy); Vitali, G. [Dipartimento di Enerdetica, Univ. La Sapienza, Via A. Scarpa 14, 00161 Rome (Italy)

    2006-01-15

    The post-implantation effect of high frequency electromagnetic field (HFEMF) on the microstructure and electrical properties of high dose Te{sup +} and Bi{sup +} implanted (1 0 0) Si was investigated by cross-sectional high resolution transmission electron microscopy and four-point probe electrical measurements. Te and Bi nanoclusters (NCs) embedded in amorphized Si have been formed by ion implantation. Post-implantation treatment with HFEMF reorganizes the cluster shape and distribution by stimulation of spinodal decomposition and ordering of Te NCs to a percolation system. The effect of HFEMF on Bi NCs is assumed to be connected with the formation of electrical microcurrents causing local heating of their interfaces with the a-Si matrix. The results of electrical measurements show that the HFEMF application reduces the sheet resistance by a factor of about 6 for Te{sup +} and about 3 for Bi{sup +} irradiation.

  16. Polarization of Bi{sub 2}Te{sub 3} thin film in a floating-gate capacitor structure

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Hui, E-mail: hyuan@gmu.edu, E-mail: qli6@gmu.edu; Li, Haitao; Zhu, Hao [Department of Electrical and Computer Engineering, George Mason University, Fairfax, Virginia 22030 (United States); Semiconductor and Dimensional Metrology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8120 (United States); Zhang, Kai; Baumgart, Helmut [Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529 (United States); Bonevich, John E. [Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Richter, Curt A. [Semiconductor and Dimensional Metrology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8120 (United States); Li, Qiliang, E-mail: hyuan@gmu.edu, E-mail: qli6@gmu.edu [Department of Electrical and Computer Engineering, George Mason University, Fairfax, Virginia 22030 (United States)

    2014-12-08

    Metal-Oxide-Semiconductor (MOS) capacitors with Bi{sub 2}Te{sub 3} thin film sandwiched and embedded inside the oxide layer have been fabricated and studied. The capacitors exhibit ferroelectric-like hysteresis which is a result of the robust, reversible polarization of the Bi{sub 2}Te{sub 3} thin film while the gate voltage sweeps. The temperature-dependent capacitance measurement indicates that the activation energy is about 0.33 eV for separating the electron and hole pairs in the bulk of Bi{sub 2}Te{sub 3}, and driving them to either the top or bottom surface of the thin film. Because of the fast polarization speed, potentially excellent endurance, and the complementary metal–oxide–semiconductor compatibility, the Bi{sub 2}Te{sub 3} embedded MOS structures are very interesting for memory application.

  17. Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface

    Science.gov (United States)

    Pang, Yuan; Wang, Junhua; Lyu, Zhaozheng; Yang, Guang; Fan, Jie; Liu, Guangtong; Ji, Zhongqing; Jing, Xiunian; Yang, Changli; Lu, Li

    2016-11-01

    Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface. In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi2Te3 surface. Project supported by the National Basic Research Program of China (Grant Nos. 2009CB929101 and 2011CB921702), the National Natural Science Foundation of China (Grant Nos. 91221203, 11174340, 11174357, 91421303, and 11527806), and the Strategic Priority Research Program B of the Chinese Academy of Sciences (Grant No. XDB07010100).

  18. Structural stability and phase transition of Bi 2 Te 3 under high pressure and low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, J. L.; Zhang, S. J.; Zhu, J. L.; Liu, Q. Q.; Wang, X. C.; Jin, C. Q.; Yu, J. C.

    2017-09-01

    Structural stability and phase transition of topological insulator Bi2Te3 were studied via angle-dispersive synchrotron radiation X-ray diffraction under high pressure and low temperature condition. The results manifest that the R-3m phase (phase I) is stable at 8 K over the pressure range up to 10 GPa and phase transition occurs between 8 K and 45 K at 8 GPa. According to the Birch-Murnaghan equation of state, the bulk modulus at ambient pressure B0 was estimated to be 45 ± 3 GPa with the assumption of B0' = 4. The structural robustness of phase I at 8 K suggests that the superconductivity below 10 GPa is related to phase I. Topological properties of superconducting Bi2Te3 phase under pressure were discussed.

  19. Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI.

    Science.gov (United States)

    Butler, Christopher John; Yang, Hung-Hsiang; Hong, Jhen-Yong; Hsu, Shih-Hao; Sankar, Raman; Lu, Chun-I; Lu, Hsin-Yu; Yang, Kui-Hon Ou; Shiu, Hung-Wei; Chen, Chia-Hao; Kaun, Chao-Cheng; Shu, Guo-Jiun; Chou, Fang-Cheng; Lin, Minn-Tsong

    2014-06-05

    Surfaces of semiconductors with strong spin-orbit coupling are of great interest for use in spintronic devices exploiting the Rashba effect. BiTeI features large Rashba-type spin splitting in both valence and conduction bands. Either can be shifted towards the Fermi level by surface band bending induced by the two possible polar terminations, making Rashba spin-split electron or hole bands electronically accessible. Here we demonstrate the first real-space microscopic identification of each termination with a multi-technique experimental approach. Using spatially resolved tunnelling spectroscopy across the lateral boundary between the two terminations, a previously speculated on p-n junction-like discontinuity in electronic structure at the lateral boundary is confirmed experimentally. These findings realize an important step towards the exploitation of the unique behaviour of the Rashba semiconductor BiTeI for new device concepts in spintronics.

  20. Signatures of a pressure-induced topological quantum phase transition in BiTeI.

    Science.gov (United States)

    Xi, Xiaoxiang; Ma, Chunli; Liu, Zhenxian; Chen, Zhiqiang; Ku, Wei; Berger, H; Martin, C; Tanner, D B; Carr, G L

    2013-10-11

    We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through p(z) band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition and are consistent with a recent theoretical proposal.

  1. Optical response of relativistic electrons in the polar BiTeI semiconductor.

    Science.gov (United States)

    Lee, J S; Schober, G A H; Bahramy, M S; Murakawa, H; Onose, Y; Arita, R; Nagaosa, N; Tokura, Y

    2011-09-09

    The transitions between the spin-split bands by spin-orbit interaction are relevant to many novel phenomena such as the resonant dynamical magnetoelectric effect and the spin Hall effect. We perform optical spectroscopy measurements combined with first-principles calculations to study these transitions in the recently discovered giant bulk Rashba spin-splitting system BiTeI. Several novel features are observed in the optical spectra of the material including a sharp edge singularity due to the reduced dimensionality of the joint density of states and a systematic doping dependence of the intraband transitions between the Rashba-split branches. These confirm the bulk nature of the Rashba-type splitting in BiTeI and manifest the relativistic nature of the electron dynamics in a solid.

  2. Spin dynamics and magnetic interactions of Mn dopants in the topological insulator Bi2Te3

    Science.gov (United States)

    Zimmermann, S.; Steckel, F.; Hess, C.; Ji, H. W.; Hor, Y. S.; Cava, R. J.; Büchner, B.; Kataev, V.

    2016-09-01

    The magnetic and electronic properties of the magnetically doped topological insulator Bi2 -xMnxTe3 were studied using electron-spin resonance (ESR) and measurements of static magnetization and electrical transport. The investigated high-quality single crystals of Bi2 -xMnxTe3 show a ferromagnetic phase transition for x ≥0.04 at TC≈12 K. The Hall measurements reveal a p -type finite charge-carrier density. Measurements of the temperature dependence of the ESR signal of Mn dopants for different orientations of the external magnetic field give evidence that the localized Mn moments interact with the mobile charge carriers leading to Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a low-dimensional character of magnetic correlations that persist far above the ferromagnetic ordering temperature.

  3. Crystal growth of Bi{sub 2}Te{sub 3} and noble cleaved (0001) surface properties

    Energy Technology Data Exchange (ETDEWEB)

    Atuchin, V.V., E-mail: atuchin@thermo.isp.nsc.ru [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Functional Electronics Laboratory, Tomsk State University, Tomsk 634050 (Russian Federation); Golyashov, V.A. [Laboratory of Molecular Beam Epitaxy of III-V Semiconductors, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Kokh, K.A. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 630090 (Russian Federation); Laboratory of Nanostructured Surfaces, Tomsk State University, Tomsk 634050 (Russian Federation); Spintronics Laboratory, Saint Petersburg State University, Saint Petersburg 198504 (Russian Federation); Korolkov, I.V. [Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Laboratory of Crystal Chemistry, Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090 (Russian Federation); Kozhukhov, A.S. [Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Laboratory of Nanodiagnostics and Nanolithography, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Kruchinin, V.N. [Laboratory for Ellipsometry of Semiconductor Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Loshkarev, I.D. [Laboratory of Molecular Beam Epitaxy of Elementary Semiconductors and A3B5 Compounds, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Pokrovsky, L.D. [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Prosvirin, I.P. [Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Boreskov Institute of Catalysis, SB RAS, Novosibirsk 630090 (Russian Federation); and others

    2016-04-15

    A high quality Bi{sub 2}Te{sub 3} crystal has been grown by Bridgman method with the use of rotating heat field. The phase purity and bulk structural quality of the crystal have been verified by XRD analysis and rocking curve observation. The atomically smooth Bi{sub 2}Te{sub 3}(0001) surface with an excellent crystallographic quality is formed by cleavage in the air. The chemical and microstructural properties of the surface have been evaluated with RHEED, AFM, STM, SE and XPS. The Bi{sub 2}Te{sub 3}(0001) cleaved surface is formed by atomically smooth terraces with the height of the elemental step of ~1.04±0.1 nm, as estimated by AFM. There is no surface oxidation process detected over a month keeping in the air at normal conditions, as shown by comparative core level photoelectron spectroscopy. - Graphical abstract: A high quality Bi{sub 2}Te{sub 3} crystal has been grown by Bridgman method with the use of rotating heat field and the Bi{sub 2}Te{sub 3}(0001) cleaved surface has been evaluated with RHEED, AFM, STM, SE and XPS. - Highlights: • High-quality Bi{sub 2}Te{sub 3} crystal of 10 mm in diameter and 50 mm long have been grown. • The high-purity cleaved Bi{sub 2}Te{sub 3}(0001) surface has been evaluated by RHEED, AFM, STM and XPS methods. • The Bi{sub 2}Te{sub 3} surface covered by atomically smooth (0001) terraces is chemically stable for a long time.

  4. Circular Dichroism and Superdiffusive Transport at the Surface of BiTeI

    OpenAIRE

    Mauchain, J; Kokh, K. A.; Tereshchenko, O. E.; Eremeev, S. V.; Chulkov, Eugene V.; Perfetti, L

    2013-01-01

    International audience; We investigate the electronic states of BiTeI after the optical pumping with circularly polarized photons. Our data show that photoexcited electrons reach an internal thermalization within 300 fs from the arrival of the pump pulse. Instead, the dichroic contrast generated by the circularly polarized light relaxes on a timescale shorter than 80 fs. This result implies that orbital and spin polarization created by the circular pump pulse rapidly decays via manybody inter...

  5. High electrical conductivity in out of plane direction of electrodeposited Bi2Te3 films

    Directory of Open Access Journals (Sweden)

    Miguel Muñoz Rojo

    2015-08-01

    Full Text Available The out of plane electrical conductivity of highly anisotropic Bi2Te3 films grown via electro-deposition process was determined using four probe current-voltage measurements performed on 4.6 - 7.2 μm thickness Bi2Te3 mesa structures with 80 - 120 μm diameters sandwiched between metallic film electrodes. A three-dimensional finite element model was used to predict the electric field distribution in the measured structures and take into account the non-uniform distribution of the current in the electrodes in the vicinity of the probes. The finite-element modeling shows that significant errors could arise in the measured film electrical conductivity if simpler one-dimensional models are employed. A high electrical conductivity of (3.2 ± 0.4 ⋅ 105 S/m is reported along the out of plane direction for Bi2Te3 films highly oriented in the [1 1 0] direction.

  6. Preparation and Characterization of Bi2Te3/Graphite/Polythiophene Thermoelectric Composites

    Science.gov (United States)

    Lai, Chunhua; Li, Junjie; Pan, Chengjun; Wang, Lei; Bai, Xiaojun

    2016-10-01

    The Bi2Te3/graphite/polythiophene composites were prepared by solution mixing, mechanical ball milling, cold pressing and spark plasma sintering (SPS) in order to utilize and integrate the high Seebeck coefficient of Bi2Te3, high electrical conductivity of graphite (G) and low thermal conductivity of polythiophene (PTh). The structures and properties of the composites were characterized by scanning electron microscope, thermo gravimetric analyzer, x-ray diffraction and ULVAC ZEM-2 Seebeck coefficient measurement. The results showed that the related components were uniformly dispersed in the composites, and the electrical conductivity of the composites increased significantly with increasing G content. A small addition of Bi2Te3 to the matrix contributed to an increase in Seebeck coefficient and the thermal conductivity of the composites stayed at a low level owing to the low thermal conductivity of PTh. These composites prepared by SPS show an increase in Seebeck coefficient but a decrease in electrical conductivity as compared to corresponding composites prepared by cold pressing.

  7. Crystal growth and physical property of Bi-Sb-Te-Se topological insulator and CuxBi2Se3 topological superconductor materials

    Science.gov (United States)

    Gu, Genda; Yang, Alina; Schneeloch, John; Xu, Zhijun; Tranquada, John; Zhoa, J. G.; Pan, Z. H.; Yang, H. B.; Si, W. D.; Valla, T.

    2012-02-01

    The discovery of 3D topological insulator and topological superconductor materials opens up a new research field in the condensed matter physics. In order to exploit the novel surface properties of these topological insulators, it is crucial to achieve a bulk-insulating state in these topological insulator crystals. Unfortunately, all available topological insulator crystals are not bulk-insulating. We have grown a number of Bi-Se, Bi-Te, Sb-Te-Se, Bi-Sb-Se, Bi-Sb-Te-Se and Bi-Sb-Te-Se-S topological insulator single crystals by using 5N and 6N pure elements. We have measured the physical properties on these single crystals. We have studied the effect of growth condition and impurity on the bulk electrical conductivity of these single crystals. We try to answer two questions if it is possible to grow the bulk-insulating topological insulator single crystals and which maximum resistivity of these topological insulator single crystals we can grow. We have also grown a number of CuxBi2Se3 topological superconductor single crystals.

  8. Band Structure of Topological Insulator BiSbTe1.25Se1.75.

    Science.gov (United States)

    Lohani, H; Mishra, P; Banerjee, A; Majhi, K; Ganesan, R; Manju, U; Topwal, D; Kumar, P S Anil; Sekhar, B R

    2017-07-04

    We present our angle resolved photoelectron spectroscopy (ARPES) and density functional theory results on quaternary topological insulator (TI) BiSbTe1.25Se1.75 (BSTS) confirming the non-trivial topology of the surface state bands (SSBs) in this compound. We find that the SSBs, which are are sensitive to the atomic composition of the terminating surface have a partial 3D character. Our detailed study of the band bending (BB) effects shows that in BSTS the Dirac point (DP) shifts by more than two times compared to that in Bi2Se3 to reach the saturation. The stronger BB in BSTS could be due to the difference in screening of the surface charges. From momentum density curves (MDCs) of the ARPES data we obtained an energy dispersion relation showing the warping strength of the Fermi surface in BSTS to be intermediate between those found in Bi2Se3 and Bi2Te3 and also to be tunable by controlling the ratio of chalcogen/pnictogen atoms. Our experiments also reveal that the nature of the BB effects are highly sensitive to the exposure of the fresh surface to various gas species. These findings have important implications in the tuning of DP in TIs for technological applications.

  9. Separation of top and bottom surface conduction in Bi2Te3 thin films.

    Science.gov (United States)

    Yu, Xinxin; He, Liang; Lang, Murong; Jiang, Wanjun; Xiu, Faxian; Liao, Zhiming; Wang, Yong; Kou, Xufeng; Zhang, Peng; Tang, Jianshi; Huang, Guan; Zou, Jin; Wang, Kang L

    2013-01-11

    Quantum spin Hall (QSH) systems are insulating in the bulk with gapless edges or surfaces that are topologically protected and immune to nonmagnetic impurities or geometric perturbations. Although the QSH effect has been realized in the HgTe/CdTe system, it has not been accomplished in normal 3D topological insulators. In this work, we demonstrate a separation of two surface conductions (top/bottom) in epitaxially grown Bi(2)Te(3) thin films through gate dependent Shubnikov-de Haas (SdH) oscillations. By sweeping the gate voltage, only the Fermi level of the top surface is tuned while that of the bottom surface remains unchanged due to strong electric field screening effects arising from the high dielectric constant of Bi(2)Te(3). In addition, the bulk conduction can be modulated from n- to p-type with a varying gate bias. Our results on the surface control hence pave a way for the realization of QSH effect in topological insulators which requires a selective control of spin transports on the top/bottom surfaces.

  10. Solid state transformations and electrophysical properties of GeTe-rich solid solutions in the GeTe-Ag sub 2 Te-Bi sub 2 Te sub 3 system

    Energy Technology Data Exchange (ETDEWEB)

    Plachkova, S.K. (Faculty of Physics, Univ. of Sofia (Bulgaria)); Georgieva, O.G. (Inst. for Foreign Students, Sofia (Bulgaria)); Odin, I.N. (Faculty of Chemistry, M.V. Lomonosov State Univ., Moscow (USSR))

    1991-12-16

    Equilibrium polycrystalline samples of GeTe-rich (GeTe){sub 1-x}((Ag{sub 2}Te){sub 1-y}(Bi{sub 2}Te{sub 3}){sub y}){sub x} (y=0.4667, 0.5000, and 0.5333) SS are prepared. On the base of different experimental investigations the T-x projection of the phase equilibrium diagram of SS with y=0.4667 is drawn. The GeTe-rich SS keep the crystal structure of GeTe. The phase transition temperature Tc decreases with increasing amount of the ternary compound and reaches 300 K at x of about 0.23. From a comparison of the power coefficient S{sup 2}{sigma} of SS with different y at 300 K it is found that a deviation in stoichiometry of the ternary compound towards Ag{sub 2}Te (y=0.4667) or Bi{sub 2}Te{sub 3} (y=0.5333) influences unfavorably the thermoelectric parameters. (orig.).

  11. Enhanced Thermoelectric Performance in Cu-Intercalated BiTeI by Compensation Weakening Induced Mobility Improvement

    OpenAIRE

    Lihua Wu; Jiong Yang; Miaofang Chi; Shanyu Wang; Ping Wei; Wenqing Zhang; Lidong Chen; Jihui Yang

    2015-01-01

    The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor co...

  12. Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

    DEFF Research Database (Denmark)

    Manna, S; Kamlapure, A; Cornils, L;

    2017-01-01

    on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to Tc∼6 K for one unit cell FeTe grown on Bi2Te3, in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens...... perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators....

  13. High Current Density Effect on In-situ Atomic Migration Characteristics of a BiTe Thin Film System

    Science.gov (United States)

    Kim, Seunghyun; Park, Yong-Jin; Joo, Young-Chang; Park, Young-Bae

    2013-10-01

    Understanding fundamental atomic migration characteristics of multicomponent chalcogenide materials such as GeSbTe (GST) and BiTe are important in order to investigate the failure mechanism related to the electrical reliability of thermoelectric materials under high current density. In this work, high current density effect on the in-situ atomic migration characteristics of the BiTe thermoelectric thin films was conducted by real-time observation inside an scanning electron microscope chamber. Under the high current density conditions ranging from 0.83×106 to 1.0×106 A/cm2 at 100 °C, Te migrated toward the cathode, and Bi migrated toward the anode because the electrostatic force was dominant by very high Joule heating effect.

  14. Glass formation and properties of Ge-Te-BiI3 far infrared transmitting chalcohalide glasses.

    Science.gov (United States)

    Sun, Jie; Nie, Qiuhua; Wang, Xunsi; Dai, Shixun; Xu, Tiefeng; Wang, Guoxiang

    2011-09-01

    A novel series of Ge-Te-BiI(3) chalcogenide glasses were prepared by traditional melt-quenching method and the glass-forming region was determined. Properties measurements including density, Vis-NIR and infrared (IR) transmission spectra with FTIR, XRD, DSC were adopted to analyze the composition, structure and performance of the Ge-Te-BiI3 glass system. Based on the metallization criterion and band gap energy theory, the relationships between energy gap, metallization criterion and glass composition was investigated. The results show that with the addition of BiI3, the glasses-forming ability and thermal stability are improved. The values of energy band gap and metallization criterion are within the range of 0.627-0.343 eV and 0.177-0.131, respectively. These series of glasses have wide optical transmission window from 2.2 to 25 μm and can offer an alternative solution for far infrared transmitting applications.

  15. Intrinsic conduction through topological surface states of insulating Bi2Te3 epitaxial thin films.

    Science.gov (United States)

    Hoefer, Katharina; Becker, Christoph; Rata, Diana; Swanson, Jesse; Thalmeier, Peter; Tjeng, L H

    2014-10-21

    Topological insulators represent a novel state of matter with surface charge carriers having a massless Dirac dispersion and locked helical spin polarization. Many exciting experiments have been proposed by theory, yet their execution has been hampered by the extrinsic conductivity associated with the unavoidable presence of defects in Bi2Te3 and Bi2Se3 bulk single crystals, as well as impurities on their surfaces. Here we present the preparation of Bi2Te3 thin films that are insulating in the bulk and the four-point probe measurement of the conductivity of the Dirac states on surfaces that are intrinsically clean. The total amount of charge carriers in the experiment is of the order of 10(12) cm(-2) only, and mobilities up to 4,600 cm(2)/Vs have been observed. These values are achieved by carrying out the preparation, structural characterization, angle-resolved and X-ray photoemission analysis, and temperature-dependent four-point probe conductivity measurement all in situ under ultra-high-vacuum conditions. This experimental approach opens the way to prepare devices that can exploit the intrinsic topological properties of the Dirac surface states.

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

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Xi' an, E-mail: groupfxa@163.com [The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081 (China); Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081 (China); School of Materials and Metallurgy, Wuhan University of Science and Technology, 947 Heping Road, Qingshan District, Wuhan 430081 (China); Cai, Xin zhi, E-mail: xzcwust@163.com [The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081 (China); Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081 (China); School of Materials and Metallurgy, Wuhan University of Science and Technology, 947 Heping Road, Qingshan District, Wuhan 430081 (China); Han, Xue wu, E-mail: hanxuewu1990@163.com [The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081 (China); Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081 (China); School of Materials and Metallurgy, Wuhan University of Science and Technology, 947 Heping Road, Qingshan District, Wuhan 430081 (China); Zhang, Cheng cheng, E-mail: zcc516990418@live.com [The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081 (China); Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081 (China); School of Materials and Metallurgy, Wuhan University of Science and Technology, 947 Heping Road, Qingshan District, Wuhan 430081 (China); and others

    2016-01-15

    Bi{sub 2}Te{sub 3} based cutting waste powders from cutting wafers were firstly selected as raw materials to prepare p-type Bi{sub 2}Te{sub 3} based thermoelectric (TE) materials. Through washing, reducing, composition correction, smelting and resistance pressing sintering (RPS) process, p-type (Bi,Sb){sub 2}Te{sub 3} alloy bulks with different nominal stoichiometries were successfully obtained. The evolution of microstructure and TE performance for (Bi,Sb){sub 2}Te{sub 3} 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 Bi{sub 0.44}Sb{sub 1.56}Te{sub 3} was obtained and its' dimensionless figure of merit (ZT) was about 1.16 at 90 °C. The ZT values of Bi{sub 0.36}Sb{sub 1.64}Te{sub 3} and Bi{sub 0.4}Sb{sub 1.6}Te{sub 3} 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 Bi{sub 2}Te{sub 3} 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. - Graphical abstract: Three kinds of typical morphologies for the fractographs: typical lamellar structure, agglomerated submicron-sized granules and dispersed cubic particles from the initial cutting waste powders. - Highlights: • Bi{sub 2}Te{sub 3} based wastes were directly selected as raw materials

  17. Distinct superconducting states in the pressure-induced metallic structures of the nominal semimetal Bi[subscript 4]Te[subscript 3

    Energy Technology Data Exchange (ETDEWEB)

    Jeffries, J.R.; Sharma, A.L. Lima; Sharma, P.A.; Spataru, C.D.; McCall, S.K.; Sugar, J.D.; Weir, S.T.; Vohra, Y.K. (Sandia); (LLNL); (UAB)

    2011-11-07

    The end members, Bi and Bi{sub 2}Te{sub 3}, of the infinitely adaptive (Bi{sub 2})m(Bi{sub 2}Te{sub 3}){sub n} series of compounds have not only been revealed to be topological insulators under the appropriate conditions, but have also been shown to be superconductors under pressure, suggesting the potential for bulk superconductor-topological-insulator interfaces and associated quantum computing applications. Herein, we report the pressure-dependent evolution of the structure and electrical transport of the nominal semimetal Bi4Te{sub 3}, a member of the (Bi{sub 2})m(Bi{sub 2}Te{sub 3}){sub n} series. Under pressure, Bi4Te{sub 3} undergoes several structural phase transformations, ultimately yielding a metallic body-centered-cubic structure exhibiting superconductivity with a maximum T{sub c} = 8.4 K at 16.2 GPa. The occurrence of structure-dependent superconductivity in Bi{sub 4}Te{sub 3} is remarkably similar to the end members of the (Bi{sub 2})m(Bi{sub 2}Te{sub 3}){sub n} series, intimating a convergence to high-pressure universal behavior that may expose the subtle variations that lead to the topological insulating and superconducting states in these systems.

  18. Electronic spectrum of non-tetrahedral acceptors in CdTe:Cl and CdTe:Bi,Cl single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Krivobok, V. S., E-mail: krivobok@lebedev.ru [P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation); Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region (Russian Federation); Nikolaev, S. N.; Bagaev, V. S.; Pruchkina, A. A.; Onishchenko, E. E.; Kolosov, S. A.; Klevkov, Yu. V.; Skorikov, M. L. [P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2016-02-07

    The electronic spectra of complex acceptors in compensated CdTe:Cl, CdTe:Ag,Cl, and CdTe:Bi,Cl single crystals are studied using low-temperature photoluminescence (PL) measurements under both nonresonant and resonant excitation of distant donor–acceptor pairs (DAP). The wavelength modulation of the excitation source combined with the analysis of the differential PL signal is used to enhance narrow spectral features obscured because of inhomogeneous line broadening and/or excitation transfer for selectively excited DAPs. For the well-known tetrahedral (T{sub D}) Ag{sub Cd} acceptor, the energies of four excited states are measured, and the values obtained are shown to be in perfect agreement with the previous data. Moreover, splitting between the 2P{sub 3/2} (Γ{sub 8}) and 2S{sub 3/2} (Γ{sub 8}) states is clearly observed for Ag{sub Cd} centers located at a short distance (5–7 nm) from a hydrogen-like donor (Cl{sub Te}). This splitting results from the reduction of the T{sub D} symmetry taking place when the acceptor is a member of a donor–acceptor pair. For the Cl-related complex acceptor with an activation energy of ∼121 meV (A-center), the energies of eight excited states are measured. It is shown that this defect produces low-symmetry central-cell correction responsible for the strong splitting of S-like T{sub D} shells. The energy spectrum of the Bi-related shallow acceptor with an activation energy of ∼36 meV is measured as well. The spectrum obtained differs drastically from the hydrogen-like set of levels, which indicates the existence of repulsive low-symmetry perturbation of the hydrogen-like Coulomb potential. It is also shown that the spectra of selectively excited PL recorded for a macroscopic ensemble of distant donor–acceptor pairs allow one to detect the low symmetry of acceptors of a given type caused by their complex nature or by the Jahn–Teller distortion. This method does not require any additional (external) field and is

  19. Study of optical nonlinearities in Se-Te-Bi thin films

    Science.gov (United States)

    Sharma, Ambika; Yadav, Preeti; Kumari, Anshu

    2014-04-01

    The present work reports the nonlinear refractive index of Se85-xTe15Bix thin films calculated by Ticha and Tichy relation. The nonlinear refractive index of Chalcogenide amorphous semiconductor is well correlated with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system. The density of the system is calculated theoretical as well as experimentally by using Archimedes principle. The linear refractive index and WDD parameters are calculated using single transmission spectra in the spectral range of 400-1500 nm. It is observed that linear as well as nonlinear refractive index increases with Bi content. The results are analyzed on the basis of increasing polarizability due to larger radii of Bi.

  20. Growth of Anodic Aluminum Oxide Templates and the Application in Fabrication of the BiSbTe-Based Thermoelectric Nanowires

    Directory of Open Access Journals (Sweden)

    Chin-Guo Kuo

    2014-01-01

    Full Text Available A two-step electrochemical anodization was used to form the anodic aluminum oxide (AAO thin films with nanotube arrays of self-organized honeycomb structure. Al foil was anodized in 10% sulfuric acid (H2SO4 and 3% oxalic acid (H2C2O4 at 25°C at constant voltage of 40 V for 60 min for two times. Ethylene glycol (C2H6O2 was used as a solution and 0.3 M potassium iodide (KI was used to improve the solution’s conductivity. Different electrolyte concentrations of Bi(NO33-5H2O, SbCl3, and TeCl4 were added into KI-C2H6O2 solution and the cyclic voltammetry experiment was used to find the reduced voltages of Bi3+, Sb3+, and Te4+ ions. The potentiostatic deposition and pulse electrodeposition (PED processes were used to deposit the (Bi,Sb2−xTe3+x-based materials. Field-emission scanning electron microscope and energy dispersive spectrometers were used to analyze the compositions of the deposited (Bi,Sb2−xTe3+x-based materials. After finding the optimal deposition parameter of the PED process the AAO nanotube arrays were used as the templates to deposit the (Bi,Sb2−xTe3+x-based thermoelectric nanowires.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ovsyannikov, Sergey V., E-mail: sergey.ovsyannikov@uni-bayreuth.de, E-mail: sergey2503@gmail.com [Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstrasse 30, D-95447 Bayreuth (Germany); Institute for Solid State Chemistry of Ural Branch of Russian Academy of Sciences, Yekaterinburg 620219 (Russian Federation); Morozova, Natalia V.; Korobeinikov, Igor V.; Vokhmyanin, Alexander P.; Shchennikov, Vladimir V. [M. N. Miheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, 18 S. Kovalevskaya Str., Yekaterinburg 620137 (Russian Federation); Lukyanova, Lidia N.; Usov, Oleg A.; Kutasov, Vsevolod A. [Ioffe Institute, St Petersburg 194021 (Russian Federation); Manakov, Andrey Y. [A. V. Nikolaev Institute of Inorganic Chemistry of Russian Academy of Sciences, Siberian Division, Novosibirsk 630090 (Russian Federation); Likhacheva, Anna Y. [Institute of Mineralogy and Petrography of Russian Academy of Sciences, Siberian Division, Novosibirsk 630090 (Russian Federation); Ancharov, Alexey I. [Budker Institute of Nuclear Physics of Russian Academy of Sciences, Siberian Division, 630090 Novosibirsk (Russian Federation); Institute for Solid State Chemistry and Mechanochemistry of Sibirian Branch of Russian Academy of Sciences, Novosibirsk 630128 (Russian Federation); Berger, Ivan F. [Institute for Solid State Chemistry of Ural Branch of Russian Academy of Sciences, Yekaterinburg 620219 (Russian Federation); Kulbachinskii, Vladimir A. [M. V. Lomonosov Moscow State University, Physics Department, 119991 GSP1, Moscow (Russian Federation); Okada, Taku [Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581 Chiba (Japan)

    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.

  2. Pressure evolution of electrical transport in the 3D topological insulator (Bi,Sb)2(Se,Te)3

    Science.gov (United States)

    Jeffries, J. R.; Butch, N. P.; Vohra, Y. K.; Weir, S. T.

    2015-03-01

    The group V-VI compounds—like Bi2Se3, Sb2Te3, or Bi2Te3—have been widely studied in recent years for their bulk topological properties. The high-Z members of this series form with the same crystal structure, and are therefore amenable to isostructural substitution studies. It is possible to tune the Bi-Sb and Te-Se ratios such that the material exhibits insulating behavior, thus providing an excellent platform for understanding how a topological insulator evolves with applied pressure. We report our observations of the pressure-dependent electrical transport and crystal structure of a pseudobinary (Bi,Sb)2(Te,Se)3 compound. Similar to some of its sister compounds, the (Bi,Sb)2(Te,Se)3 pseudobinary compound undergoes multiple, pressure-induced phase transformations that result in metallization, the onset of a close-packed crystal structure, and the development of distinct superconducting phases.

  3. Rational design, high-yield synthesis, and low thermal conductivity of Te/Bi{sub 2}Te{sub 3} core/shell heterostructure nanotube composites

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhiliang; Zheng, Shuqi, E-mail: zhengsq09@163.com; Huang, Ting; Zhang, Yuzhuo; Teng, Renyuan; Lu, Guiwu

    2014-12-25

    Graphical abstract: The Te/Bi{sub 2}Te{sub 3} core/shell heterostructure nanotubes with serrate interface and enhanced phonon scattering were synthesized by an in-situ growth method. - Highlights: • Te/Bi{sub 2}Te{sub 3} core/shell heterostructure nanotubes were rationally designed and synthesized. • Mass products were obtained by the high-yield two-step solution phase method. • The rough serrated interfaces were in favor of increasing phonon scatterings. • The composites own ultralow thermal conductivities at near room temperatures. • The design, method and structure may be instructive to other materials. - Abstract: Te/Bi{sub 2}Te{sub 3} core/shell heterostructure nanotube (NT) composites with rough serrated interfaces, and hollow structures were designed and synthesized to enhance phonon scattering. A conventional two-step solution phase method was used to synthesize the mass products in high-yield. The external diameter and wall thickness of the NTs measured approximately 250 nm and 60 nm, and their lengths ranged from 7 μm to 9 μm. The hexagonal phase Te core, rhombohedral phase Bi{sub 2}Te{sub 3} shell, hollow structure, and saw-toothed interface were accurately determined through X-ray diffraction, scanning electron microscopy and transmission emission microscopy. Relatively stable and low thermal conductivities (from 0.43 Wm{sup −1} K{sup −1} to 0.46 Wm{sup −1} K{sup −1}) were obtained when the temperatures increased from 300 K to 400 K (near room temperatures). Finally, this research systematically examined the formation mechanisms based on the in situ growth method and the phonon scattering occurring in both the hollow structures and on the saw-toothed interface.

  4. Flexible Micro Thermoelectric Generator based on Electroplated Bi2Te3

    CERN Document Server

    Schwyter, E; Durrer, L; Hierold, Ch

    2008-01-01

    We present and discuss the fabrication process and the performance of a flexible micro thermoelectric generator with electroplated Bi2Te3 thermocouples in a SU-8 mold. Demonstrator devices generate 278uWcm-2 at dTmeas=40K across the experimental set up. Based on model calculations, a temperature difference of dTG=21.4K across the generator is assumed. Due to the flexible design and the chosen generator materials, the performance stays high even for curved contact surfaces. The measurement results correlate well with the model based design optimization predictions.

  5. Giant ambipolar Rashba effect in the semiconductor BiTeI.

    Science.gov (United States)

    Crepaldi, A; Moreschini, L; Autès, G; Tournier-Colletta, C; Moser, S; Virk, N; Berger, H; Bugnon, Ph; Chang, Y J; Kern, K; Bostwick, A; Rotenberg, E; Yazyev, O V; Grioni, M

    2012-08-31

    We observe a giant spin-orbit splitting in the bulk and surface states of the noncentrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases, it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics-a large, robust spin splitting and ambipolar conduction-are present in this material.

  6. Circular dichroism and superdiffusive transport at the surface of BiTeI.

    Science.gov (United States)

    Mauchain, J; Ohtsubo, Y; Hajlaoui, M; Papalazarou, E; Marsi, M; Taleb-Ibrahimi, A; Faure, J; Kokh, K A; Tereshchenko, O E; Eremeev, S V; Chulkov, E V; Perfetti, L

    2013-09-20

    We investigate the electronic states of BiTeI after the optical pumping with circularly polarized photons. Our data show that photoexcited electrons reach an internal thermalization within 300 fs of the arrival of the pump pulse. Instead, the dichroic contrast generated by the circularly polarized light relaxes on a time scale shorter than 80 fs. This result implies that orbital and spin polarization created by the circular pump pulse rapidly decays via manybody interaction. The persistent dichroism at longer delay times is due to the helicity dependence of superdiffussive transport. We ascribe it to the lack of inversion symmetry in an electronic system far from equilibrium conditions.

  7. Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI

    OpenAIRE

    Joonbum Park; Kyung-Hwan Jin; Jo, Y. J.; Choi, E. S.; Kang, W.; Kampert, E.; J.-S. Rhyee; Seung-Hoon Jhi; Jun Sung Kim

    2015-01-01

    We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for t...

  8. Electrical Resistivity Peculiarities of the Nanograined Bi2Te3 Material

    Directory of Open Access Journals (Sweden)

    O.N. Ivanov

    2015-12-01

    Full Text Available The hot quasiisostaic pressure method was applied to sinter the nanograined Bi2Te3 material. The samples with various mean grain size of 64, 61, 56 and 51 nm were prepared by changing the pressure of sintering. It was found that the specific electrical resistivity of the material under study increases when the mean grain size decreases. The Hall effect was measured to extract the concentration and mobility values of the charge carries. It was found that the electron concentration decreases as the mean grain size decreases while the electron mobility has extreme dependence on the grain size.

  9. Optical band gap of Sn0.2Bi1.8Te3 thin films

    Indian Academy of Sciences (India)

    P H Soni; M V Hathi; C F Desai

    2003-12-01

    Sn0.2Bi1.8Te3 thin films were grown using the thermal evaporation technique on a (001) face of NaCl crystal as a substrate at room temperature. The optical absorption was measured in the wave number range 500–4000 cm-1. From the optical absorption data the band gap was evaluated and studied as a function of film thickness and deposition temperature. The data indicate absorption through direct interband transition with a band gap of around 0.216 eV. The detailed results are reported here.

  10. Enhancement in thermoelectric figure of merit in nanostructured Bi{sub 2}Te{sub 3} with semimetal nanoinclusions

    Energy Technology Data Exchange (ETDEWEB)

    Sumithra, S.; Nolting, Westly M.; Stokes, Kevin L. [Dept. of Physics and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA (United States); Takas, Nathan J.; Misra, Dinesh K.; Poudeu, P.F.P. [Dept. of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA (United States)

    2011-11-15

    The effect of Bi (semimetal) nanoinclusions in nanostructured Bi{sub 2}Te{sub 3} matrices is investigated. Bismuth nanoparticles synthesized by a low temperature solvothermal method are incorporated into Bi{sub 2}Te{sub 3} matrix phases, synthesized by planetary ball milling. High density pellets of the Bi nanoparticle/Bi{sub 2}Te{sub 3} nanocomposites are created by hot pressing the powders at 200 C and 100 MPa. The effect of different volume fractions (0-7%) of Bi semimetal nanoparticles on the Seebeck coefficient, electrical conductivity, thermal conductivity and carrier concentration is reported. Our results show that the incorporation of semimetal nanoparticles results in a reduction in the lattice thermal conductivity in all the samples. A significant enhancement in power factor is observed for Bi nanoparticle volume fraction of 5% and 7%. We show that it is possible to reduce the lattice thermal conductivity and increase the power factor resulting in an increase in figure of merit by a factor of 2 (from ZT = 0.2 to 0.4). Seebeck coefficient and electrical conductivity as a function of carrier concentration data are consistent with the electron filtering effect, where low-energy electrons are preferentially scattered by the barrier potentials set up at the semimetal nanoparticle/semiconductor interfaces. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Fabrication of Bi-Te based thermoelectric semiconductors by using hybrid powders

    Energy Technology Data Exchange (ETDEWEB)

    Lim, C.H.; Cho, D.C.; Lee, Y.S.; Lee, C.H. [School of Materials Science and Engineering, Inha Univ., Inchon (Korea, Republic of); Kim, K.T.; Kim, Y.H. [Korea Inst. of Industrial Technology, Chonan (Korea, Republic of)

    2005-07-01

    P-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds doped with 3wt% Te were fabricated by spark plasma sintering and their mechanical and thermoelectric properties were investigated. The sintered compounds with the bending strength of more than 50 MPa and the figure-of-merit 2.9 x 10{sup -3}/K were obtained by controlling the mixing ratio of large powders (P{sub L}) and small powders (P{sub S}). Compared with the conventionally prepared single crystal thermoelectric materials, the bending strength was increased up to more than three times and the figure-of-merit Z was similar those of single crystals. It is expected that the mechanical properties could be improved by using hybrid powders without degradation of thermoelectric properties. (orig.)

  12. Electronic structure of antimonene grown on Sb{sub 2}Te{sub 3} (111) and Bi{sub 2}Te{sub 3} substrates

    Energy Technology Data Exchange (ETDEWEB)

    Lei, Tao; Liu, Chen; Zhao, Jia-Li; Li, Jin-Mei; Wang, Jia-Ou; Wu, Rui; Qian, Hai-Jie; Ibrahim, Kurash, E-mail: kurash@ihep.ac.cn [Institute of High Energy of Physics, Chinese Academy of Sciences, Beijing 100049 (China); Li, Ya-Ping; Wang, Hui-Qiong [Department of Physics, Xiamen University, Xiamen 361995, Fujian (China)

    2016-01-07

    We explore the formation of single bilayer Sb(111) ultrathin film (Antimonene) on Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} substrates for the first time, which is theoretically predicated to be a robust trivial semiconductor but can be tuned to a 2D TI by reducing the buckling height. From angle-resolved photoemission spectroscopy measurements, the antimonene can be well grown on the two surfaces and shows clear band dispersion. The electronic structure of the antimonene shows similar character on the two surfaces, but due to the interfacial strain effect, the bands of antimonene on Bi{sub 2}Te{sub 3} are flatter than on Sb{sub 2}Te{sub 3}, which attributes to Bi{sub 2}Te{sub 3} substrate lattice constants lager than Sb{sub 2}Te{sub 3}. At the same time, the charge transfer effect is also observed through core level shift, which influences the band dispersion simultaneously.

  13. Synthesis, Crystal Structure, and Properties of Bi3 TeBO9 or Bi3 (TeO6 )(BO3 ): A Non-Centrosymmetric Borate-Tellurate(VI) of Bismuth.

    Science.gov (United States)

    Daub, Michael; Krummer, Michael; Hoffmann, Anke; Bayarjargal, Lkhamsuren; Hillebrecht, Harald

    2017-01-26

    Pale-yellow single crystals of the new borate tellurate(VI) Bi3 TeBO9 were obtained by reaction of stoichiometric amounts of Bi2 O3 , B2 O3 , and Te(OH)6 at 780 °C. The non-centrosymmetric crystal structure (P63 , Z=2, a=8.7454(16), c=5.8911(11) Å, 738 refl., 43 param, R1=0.037, wR2=0.093) contains isolated trigonal-planar BO3 units and nearly undistorted TeO6 octahedra. The Bi(3+) cations are located in between in octahedral voids. The BiO6 octahedra are significantly distorted to a [3+3] pattern (2.25/2.50 Å) due to the ns(2) configuration. According to the structural features, the formula can be written as Bi3 (TeO6 )(BO3 ). Alternatively, the structure can also be described as hcp of oxygen with Te(VI) and Bi(III) in octahedral voids and B(III) in trigonal- planar voids. The vibrational spectra show the typical features of BO3 and TeO6 units with a significant (10) B/(11) B isotopic splitting of the IR-active B-O valence mode (1248 and 1282 cm(-1) ). The UV/Vis spectrum shows an optical band edge with an onset around 480 nm (2.6 eV). MAS-NMR spectra of (11) B show an anisotropic signal with a quadrupole coupling constant of CQ =2.55 MHz. and a very small deviation from rotational symmetry (η=0.2). The isotropic chemical shift is 20.1 ppm. The second harmonic generation (SHG) test was positive with an activity comparable to potassium dihydrogen phosphate (KDP). Bi3 TeBO9 decomposes in air at 825 °C to Bi2 TeO5 .

  14. Crystal growth and electronic properties of a 3D Rashba material, BiTeI, with adjusted carrier concentrations.

    Science.gov (United States)

    Kanou, Manabu; Sasagawa, Takao

    2013-04-03

    3D Rashba materials can be a leading player in spin-related novel phenomena, ranging from the metallic extreme (unconventional superconductivity) to the transport intermediate (spin Hall effects) to the novel insulating variant (3D topological insulating states). As the essential backbone for both fundamental and applied research of such a 3D Rashba material, this study established the growth of sizeable single crystals of a candidate compound BiTeI with adjusted carrier concentrations. Three techniques (standard vertical Bridgman, modified horizontal Bridgman, and vapour transport) were employed, and BiTeI crystals (>1 × 1 × 0.2 mm(3)) with fundamentally different electronic states from metallic to insulating were successfully grown by the chosen technique. The 3D Rashba electronic states, including the Fermi surface topology, for the corresponding carrier concentrations of the obtained BiTeI crystals were revealed by relativistic first-principles calculations.

  15. Observation of large nonlinear responses in a graphene-Bi2Te3 heterostructure at a telecommunication wavelength

    Science.gov (United States)

    Wang, Yingwei; Mu, Haoran; Li, Xiaohong; Yuan, Jian; Chen, Jiazhang; Xiao, Si; Bao, Qiaoliang; Gao, Yongli; He, Jun

    2016-05-01

    We report the large nonlinear response and ultrafast carrier relaxation dynamics of a graphene-Bi2Te3 heterostructure produced by two-step chemical vapour deposition. The nonlinear refractive index reaches n2 = 0.2 × 10-7 cm2/W at the telecommunication wavelength of 1550 nm, which is almost seven orders of magnitude larger than that of the bulk Si material. Additionally, a pump-probe experiment is performed to investigate the ultrafast dynamic process (intraband relaxation time τ1 = 270 ± 20 fs; interband relaxation time τ2 = 3.6 ± 0.2 ps) of the graphene-Bi2Te3 heterostructure. Then, based on the donor-acceptor structure model, we propose a theoretical model to explain the dynamic relaxation process. Our results show that the graphene-Bi2Te3 heterostructure is a promising saturable absorber for ultrafast pulse laser applications at telecommunication wavelengths.

  16. Pressure evolution of electrical transport in the 3D topological insulator (Bi,Sb)2(Te,Se)3

    Science.gov (United States)

    Jeffries, Jason; Butch, N. P.; Vohra, Y. K.; Weir, S. T.

    2014-03-01

    The group V-VI compounds--like Bi2Se3, Sb2Te3, or Bi2Te3--have been widely studied in recent years for their bulk topological properties. The high-Z members of this series form with the same crystal structure, and are therefore amenable to isostructural substitution studies. It is possible to tune the Bi-Sb and Te-Se ratios such that the material exhibits insulating behavior, thus providing an excellent platform for understanding how a topological insulator evolves with applied pressure. We report our observations of the pressure-dependent electrical transport and compare that behavior with other binary V-VI compounds under pressure. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

  17. Effect of molecular length on the electrical conductance across metal-alkanedithiol-Bi2Te3 interfaces

    Science.gov (United States)

    Cardinal, Thomas; Kwan, Matthew; Borca-Tasciuc, Theodorian; Ramanath, Ganpati

    2016-10-01

    Controlling electronic transport across metal-thermoelectric interfaces is important for realizing high-efficiency solid-state refrigeration and waste-heat harvesting devices. We report up to 34-fold increase in electrical contact conductivity Σc across Cu-alkanedithiol-Bi2Te3 interfaces. Longer chain dithiols are more effective in curtailing Cu diffusion, telluride formation, and reducing interfacial oxides of Bi and Te, leading to higher Σc. In contrast, Σc is insensitive to the alkanedithiol chain length at Ni-alkanedithiol-Bi2Te3 interfaces due to weak Ni-S bonding. These results indicate that interfacial bonding and phase formation are primary determinants of Σc rather than charge transport through the alkanedithiol molecules. Our findings provide insights for tuning electronic transport across metal-thermoelectric interfaces using an interfacial nanolayer comprising molecules with suitably chosen chemical termini and molecular length.

  18. Design of Ball-Milling Experiments on Bi2Te3 Thermoelectric Material

    Science.gov (United States)

    Kanatzia, A.; Papageorgiou, Ch.; Lioutas, Ch.; Kyratsi, Th.

    2013-07-01

    In this work, factorial ball-milling experiments have been applied to Bi2Te3 material, for the first time, aiming to investigate the effect of the main process parameters on the structural features and thermoelectric properties of the ball-milled materials. The selected main parameters were the duration of milling, the speed, and the ball-to-material ratio. Analysis suggests a strong effect of the speed and duration of processing, whereas the ball-to-material ratio is of minor importance. This approach is advantageous for better understanding of the milling mechanism and the importance of the role of each independent parameter as well as their interaction. All experiments led to nanocrystalline Bi2Te3, whose structural features were studied. The nanocrystalline size was estimated based on x-ray diffraction analysis, while transmission electron microscopy (TEM) studies were also performed to confirm the presence of nanoscale crystals. A mathematical model was developed based on statistical analysis for prediction of the crystalline size and the Seebeck coefficient of the nanopowders. The thermoelectric properties were also investigated on selected, highly dense pellets fabricated via hot-pressing of the nanopowders.

  19. Free-electron creation at the 60° twin boundary in Bi2Te3

    Science.gov (United States)

    Kim, Kwang-Chon; Lee, Joohwi; Kim, Byung Kyu; Choi, Won Young; Chang, Hye Jung; Won, Sung Ok; Kwon, Beomjin; Kim, Seong Keun; Hyun, Dow-Bin; Kim, Hyun Jae; Koo, Hyun Cheol; Choi, Jung-Hae; Kim, Dong-Ik; Kim, Jin-Sang; Baek, Seung-Hyub

    2016-08-01

    Interfaces, such as grain boundaries in a solid material, are excellent regions to explore novel properties that emerge as the result of local symmetry-breaking. For instance, at the interface of a layered-chalcogenide material, the potential reconfiguration of the atoms at the boundaries can lead to a significant modification of the electronic properties because of their complex atomic bonding structure. Here, we report the experimental observation of an electron source at 60° twin boundaries in Bi2Te3, a representative layered-chalcogenide material. First-principles calculations reveal that the modification of the interatomic distance at the 60° twin boundary to accommodate structural misfits can alter the electronic structure of Bi2Te3. The change in the electronic structure generates occupied states within the original bandgap in a favourable condition to create carriers and enlarges the density-of-states near the conduction band minimum. The present work provides insight into the various transport behaviours of thermoelectrics and topological insulators.

  20. Spin-texture inversion in the giant Rashba semiconductor BiTeI

    Science.gov (United States)

    Maaß, Henriette; Bentmann, Hendrik; Seibel, Christoph; Tusche, Christian; Eremeev, Sergey V.; Peixoto, Thiago R. F.; Tereshchenko, Oleg E.; Kokh, Konstantin A.; Chulkov, Evgueni V.; Kirschner, Jürgen; Reinert, Friedrich

    2016-05-01

    Semiconductors with strong spin-orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices. Unveiling the full spin texture in momentum space for such materials and its relation to the microscopic structure of the electronic wave functions is experimentally challenging and yet essential for exploiting spin-orbit effects for spin manipulation. Here we employ a state-of-the-art photoelectron momentum microscope with a multichannel spin filter to directly image the spin texture of the layered polar semiconductor BiTeI within the full two-dimensional momentum plane. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the valence and conduction band electrons in BiTeI have spin textures of opposite chirality and of pronounced orbital dependence beyond the standard Rashba model, the latter giving rise to strong optical selection-rule effects on the photoelectron spin polarization. These observations open avenues for spin-texture manipulation by atomic-layer and charge carrier control in polar semiconductors.

  1. Giant Rashba-type spin splitting in bulk BiTeI.

    Science.gov (United States)

    Ishizaka, K; Bahramy, M S; Murakawa, H; Sakano, M; Shimojima, T; Sonobe, T; Koizumi, K; Shin, S; Miyahara, H; Kimura, A; Miyamoto, K; Okuda, T; Namatame, H; Taniguchi, M; Arita, R; Nagaosa, N; Kobayashi, K; Murakami, Y; Kumai, R; Kaneko, Y; Onose, Y; Tokura, Y

    2011-06-19

    There has been increasing interest in phenomena emerging from relativistic electrons in a solid, which have a potential impact on spintronics and magnetoelectrics. One example is the Rashba effect, which lifts the electron-spin degeneracy as a consequence of spin-orbit interaction under broken inversion symmetry. A high-energy-scale Rashba spin splitting is highly desirable for enhancing the coupling between electron spins and electricity relevant for spintronic functions. Here we describe the finding of a huge spin-orbit interaction effect in a polar semiconductor composed of heavy elements, BiTeI, where the bulk carriers are ruled by large Rashba-like spin splitting. The band splitting and its spin polarization obtained by spin- and angle-resolved photoemission spectroscopy are well in accord with relativistic first-principles calculations, confirming that the spin splitting is indeed derived from bulk atomic configurations. Together with the feasibility of carrier-doping control, the giant-Rashba semiconductor BiTeI possesses excellent potential for application to various spin-dependent electronic functions.

  2. Interesting pressure dependence of power factor in BiTeI

    Science.gov (United States)

    Guo, San-Dong; Wang, Jian-Li

    2016-06-01

    We investigate pressure dependence of electronic structures and thermoelectric properties in BiTeI by using a modified Becke and Johnson exchange potential. Spin-orbit coupling (SOC) effects are also included due to giant Rashba splitting. Thermoelectric properties are illuminated through solving Boltzmann transport equations within the constant scattering time approximation. The calculated energy band gap of 0.36 eV agrees well with the experimental value of 0.38 eV. As the pressure increases, the energy band gap first decreases, and then increases. The Rashba energy has the opposite trend with the energy band gap. SOC has obvious detrimental influence on the power factor in both n-type and p-type doping. For low doping concentration, the power factor has the same trend with the energy band gap with increasing pressure, but shows a monotonic changing trend in high doping. It is found that the pressure can induce a significantly enhanced power factor in high n-type doping, which can be understood as pressure leading to two-dimensional-like density of states in the conduction bands. These results suggest that BiTeI may be a potential candidate for efficient thermoelectricity in n-type doping by pressure, turning an ordinary insulator into a topological insulator.

  3. Free-electron creation at the 60° twin boundary in Bi2Te3

    Science.gov (United States)

    Kim, Kwang-Chon; Lee, Joohwi; Kim, Byung Kyu; Choi, Won Young; Chang, Hye Jung; Won, Sung Ok; Kwon, Beomjin; Kim, Seong Keun; Hyun, Dow-Bin; Kim, Hyun Jae; Koo, Hyun Cheol; Choi, Jung-Hae; Kim, Dong-Ik; Kim, Jin-Sang; Baek, Seung-Hyub

    2016-01-01

    Interfaces, such as grain boundaries in a solid material, are excellent regions to explore novel properties that emerge as the result of local symmetry-breaking. For instance, at the interface of a layered-chalcogenide material, the potential reconfiguration of the atoms at the boundaries can lead to a significant modification of the electronic properties because of their complex atomic bonding structure. Here, we report the experimental observation of an electron source at 60° twin boundaries in Bi2Te3, a representative layered-chalcogenide material. First-principles calculations reveal that the modification of the interatomic distance at the 60° twin boundary to accommodate structural misfits can alter the electronic structure of Bi2Te3. The change in the electronic structure generates occupied states within the original bandgap in a favourable condition to create carriers and enlarges the density-of-states near the conduction band minimum. The present work provides insight into the various transport behaviours of thermoelectrics and topological insulators. PMID:27527268

  4. Nanostructured Bi2Te3 Prepared by a Straightforward Arc-Melting Method

    Science.gov (United States)

    Gharsallah, M.; Serrano-Sánchez, F.; Bermúdez, J.; Nemes, N. M.; Martínez, J. L.; Elhalouani, F.; Alonso, J. A.

    2016-03-01

    Thermoelectric materials constitute an alternative source of sustainable energy, harvested from waste heat. Bi2Te3 is the most utilized thermoelectric alloy. We show that it can be readily prepared in nanostructured form by arc-melting synthesis, yielding mechanically robust pellets of highly oriented polycrystals. This material has been characterized by neutron powder diffraction (NPD), scanning electron microscopy (SEM), and electronic and thermal transport measurements. A microscopic analysis from NPD data demonstrates a near-perfect stoichiometry of Bi2Te3 and a fair amount of anharmonicity of the chemical bonds. The as-grown material presents a metallic behavior, showing a record-low resistivity at 320 K of 2 μΩ m, which is advantageous for its performance as a thermoelectric material. SEM analysis shows a stacking of nanosized sheets, each of them presumably single-crystalline, with large surfaces perpendicular to the c crystallographic axis. This nanostructuration notably affects the thermoelectric properties, involving many surface boundaries that are responsible for large phonon scattering factors, yielding a thermal conductivity as low as 1.2 W m-1 K-1 around room temperature.

  5. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements

    Science.gov (United States)

    Hada, Masaki; Norimatsu, Katsura; Tanaka, Sei'ichi; Keskin, Sercan; Tsuruta, Tetsuya; Igarashi, Kyushiro; Ishikawa, Tadahiko; Kayanuma, Yosuke; Miller, R. J. Dwayne; Onda, Ken; Sasagawa, Takao; Koshihara, Shin-ya; Nakamura, Kazutaka G.

    2016-07-01

    The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

  6. Gate Tunable Infrared Optical Response of (Bi1-xSbx)2 Te3 Topological Insulators

    Science.gov (United States)

    Whitney, William; Brar, Victor; Ou, Yunbo; He, Ke; Xue, Qi-Kun; Atwater, Harry

    The electronic properties of topological insulators - narrow band-gap semiconductors that exhibit insulating bulk and semimetallic Dirac surface states - have been the subject of intense study over the past several years. The optical and optoelectronic behavior of these materials, however, remain widely uncharacterized. It has previously been shown that electrostatic gating can be used to tune the Fermi level in the Dirac semimetal graphene, modifying interband transitions and free carrier absorption. We report here experiments that demonstrate electronic control of the optical properties of 5-20 nm thick (Bi1-xSbx)2 Te3 films grown by Van der Waals epitaxy and transferred to silicon dioxide on silicon via an epitaxial lift off process. We find that infrared transmission and reflection from 3 to 10 microns are consistent with modulation of free-carrier absorption and bulk interband transitions in (Bi1-xSbx)2 Te3. We discuss transport results as well as the contributions that bulk and topological surface electronic transitions make to the optical response of these materials.

  7. Electronic structures of topological insulator Bi2Te3 surfaces with non-conventional terminations

    Science.gov (United States)

    Zhu, Xie-Gang; Zhang, Yun; Feng, Wei; Yuan, Bing-Kai; Liu, Qin; Qiu, Rui-Zhi; Xie, Dong-Hua; Tan, Shi-Yong; Duan, Yu; Fang, Yun; Zhang, Wen; Lai, Xin-Chun

    2016-09-01

    Topological insulators (TIs) are theoretically believed to possess robust surface states (SSs) for any surface terminations. In reality, for TIs with non-conventional terminations, the directly experimental demonstration of this argument is somehow hindered, due to the difficulties in sample preparation and lack of efficient electronic structure characterization method. Here, by using the state-of-the-art molecular beam epitaxy, we manage to prepare TI Bi2Te3 thin film with non-conventional fractional quintuple layer (FQL) termination. Scanning tunneling microscopy reveals that the as-grown Bi2Te3 thin film may not necessarily terminate at the van der Waals gap between two adjacent quintuple layers. The electronic structures of the FQL termination are studied in combination with quasi-particle interference pattern by scanning tunneling spectroscopy and SS calculations by tight binding method. Our results suggest that the topological nature of SSs be preserved on various terminations. Possible ways of achieving exotic topological SSs are also discussed.

  8. Nanostructured Bi2Te3 Prepared by a Straightforward Arc-Melting Method.

    Science.gov (United States)

    Gharsallah, M; Serrano-Sánchez, F; Bermúdez, J; Nemes, N M; Martínez, J L; Elhalouani, F; Alonso, J A

    2016-12-01

    Thermoelectric materials constitute an alternative source of sustainable energy, harvested from waste heat. Bi2Te3 is the most utilized thermoelectric alloy. We show that it can be readily prepared in nanostructured form by arc-melting synthesis, yielding mechanically robust pellets of highly oriented polycrystals. This material has been characterized by neutron powder diffraction (NPD), scanning electron microscopy (SEM), and electronic and thermal transport measurements. A microscopic analysis from NPD data demonstrates a near-perfect stoichiometry of Bi2Te3 and a fair amount of anharmonicity of the chemical bonds. The as-grown material presents a metallic behavior, showing a record-low resistivity at 320 K of 2 μΩ m, which is advantageous for its performance as a thermoelectric material. SEM analysis shows a stacking of nanosized sheets, each of them presumably single-crystalline, with large surfaces perpendicular to the c crystallographic axis. This nanostructuration notably affects the thermoelectric properties, involving many surface boundaries that are responsible for large phonon scattering factors, yielding a thermal conductivity as low as 1.2 W m(-1) K(-1) around room temperature.

  9. Effects of hot pressing on electric performances of Bi0.5Sb1.5Te3

    Institute of Scientific and Technical Information of China (English)

    XIAO Bo; CHEN Hui; WU Borong; ZHU Lei; LIU Mingyi; JIAN Xuyu; LI Lin

    2006-01-01

    The effects of hot pressing on electric performance and mechanical strength of Bi0.5Sb1.5Te3 thermoelectric material prepared through vacuum melting and milling were studied. The phase constituent and microstructure were analyzed by X-ray Diffraction and cold field emission Scanning Electric Microscope. Aeolotropisms of the material on microstructure and electric performances are approved. With the rise of hot pressing temperature (from 300-500 ℃) and pressure (30-70 Mpa), electric conductivity and power factor are improved. Moreover, Bi0.5Sb1.5Te3 material can gain ideal thermoelectric performances and increased mechanical strength by hot pressing.

  10. Thermoelectric characterization and fabrication of nanostructured p-type Bi0.5Sb1.5Te3 and n-type Bi2Te3 thin film thermoelectric energy generator with an in-plane planar structure

    Directory of Open Access Journals (Sweden)

    No-Won Park

    2016-06-01

    Full Text Available This paper presents in-plane bismuth-telluride-based thermoelectric (TE energy generators fabricated using metal-shadow and radio-frequency sputtering methods at room temperature. The TE energy generators consist of four couples of 300-nm-thick nanostructured Bi2Te3 (n-BT and Bi0.5Sb1.5Te3 (p-BST thin films used as n-type and p-type materials, respectively, on a Si substrate for the p/n junctions of the TE energy generators. Furthermore, the effect of annealing treatment of both n-BT and p-BST thin films on the electrical and TE properties as well as the TE performance of the TE energy generators is discussed. By varying the temperature between the hot and cold junction legs of the n-BT/p-BST in-plane TE energy generators annealed at 200 °C, the maximum output voltage and power are determined to be ∼3.6 mV and ∼1.1 nW, respectively, at a temperature difference of 50 K. The output powers increased by ∼590% compared to that of the as-grown TE generator at a temperature difference of 90 K. This improvement in the TE performance is attributed to the enhancement of the electrical conductivity after heat treatment. From a numerical simulation conducted using a commercial software (COMSOL, we are confident that it plays a crucial role in determining the dimension (i.e., thickness of each leg and material properties of both n-BT and p-BST materials of the in-plane TE energy generators.

  11. Thermoelectric characterization and fabrication of nanostructured p-type Bi0.5Sb1.5Te3 and n-type Bi2Te3 thin film thermoelectric energy generator with an in-plane planar structure

    Science.gov (United States)

    Park, No-Won; Park, Tae-Hyun; Ahn, Jay-Young; Kang, So-Hyeon; Lee, Won-Yong; Yoon, Young-Gui; Yoon, Soon-Gil; Lee, Sang-Kwon

    2016-06-01

    This paper presents in-plane bismuth-telluride-based thermoelectric (TE) energy generators fabricated using metal-shadow and radio-frequency sputtering methods at room temperature. The TE energy generators consist of four couples of 300-nm-thick nanostructured Bi2Te3 (n-BT) and Bi0.5Sb1.5Te3 (p-BST) thin films used as n-type and p-type materials, respectively, on a Si substrate for the p/n junctions of the TE energy generators. Furthermore, the effect of annealing treatment of both n-BT and p-BST thin films on the electrical and TE properties as well as the TE performance of the TE energy generators is discussed. By varying the temperature between the hot and cold junction legs of the n-BT/p-BST in-plane TE energy generators annealed at 200 °C, the maximum output voltage and power are determined to be ˜3.6 mV and ˜1.1 nW, respectively, at a temperature difference of 50 K. The output powers increased by ˜590% compared to that of the as-grown TE generator at a temperature difference of 90 K. This improvement in the TE performance is attributed to the enhancement of the electrical conductivity after heat treatment. From a numerical simulation conducted using a commercial software (COMSOL), we are confident that it plays a crucial role in determining the dimension (i.e., thickness of each leg) and material properties of both n-BT and p-BST materials of the in-plane TE energy generators.

  12. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy.

    Science.gov (United States)

    Schreyeck, S; Brunner, K; Kirchner, A; Bass, U; Grauer, S; Schumacher, C; Gould, C; Karczewski, G; Geurts, J; Molenkamp, L W

    2016-04-13

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x = 0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only ≈ 75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films.

  13. Structural characterization of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} as a function of temperature using neutron powder diffraction and extended X-ray absorption fine structure techniques

    Energy Technology Data Exchange (ETDEWEB)

    Mansour, A. N. [Naval Surface Warfare Center, Carderock Division, West Bethesda, Maryland 20817 (United States); Wong-Ng, W. [Materials Measurement Science Division National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Huang, Q. [Center for Neutron Research National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Tang, W. [Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018 (China); Thompson, A.; Sharp, J. [Marlow Industries, Inc Dallas, Texas 75238 (United States)

    2014-08-28

    The structure of Bi{sub 2}Te{sub 3} (Seebeck coefficient Standard Reference Material (SRM™ 3451)) and the related phase Sb{sub 2}Te{sub 3} have been characterized as a function of temperature using the neutron powder diffraction (NPD) and the extended X-ray absorption fine structure (EXAFS) techniques. The neutron structural studies were carried out from 20 K to 300 K for Bi{sub 2}Te{sub 3} and from 10 K to 298 K for Sb{sub 2}Te{sub 3}. The EXAFS technique for studying the local structure of the two compounds was conducted from 19 K to 298 K. Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} are isostructural, with a space group of R3{sup ¯}m. The structure consists of repeated quintuple layers of atoms, Te2-M-Te1-M-Te2 (where M = Bi or Sb) stacking along the c-axis of the unit cell. EXAFS was used to examine the bond distances and static and thermal disorders for the first three shells of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} as a function of temperature. The temperature dependencies of thermal disorders were analyzed using the Debye and Einstein models for lattice vibrations. The Debye and Einstein temperatures for the first two shells of Bi{sub 2}Te{sub 3} are similar to those of Sb{sub 2}Te{sub 3} within the uncertainty in the data. However, the Debye and Einstein temperatures for the third shell of Bi-Bi are significantly lower than those of the third shell of Sb-Sb. The Einstein temperature for the third shell is consistent with a soft phonon mode in both Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3}. The lower Einstein temperature of Bi-Bi relative to Sb-Sb is consistent with the lower value of thermal conductivity of Bi{sub 2}Te{sub 3} relative to Sb{sub 2}Te{sub 3}.

  14. Investigation of the Microstructural and Thermoelectric Properties of the (GeTe0.95(Bi2Te30.05 Composition for Thermoelectric Power Generation Applications

    Directory of Open Access Journals (Sweden)

    Lior Weintraub

    2014-01-01

    Full Text Available In the frame of the current research, the p-type Bi2Te3 doped (GeTe0.95(Bi2Te30.05 alloy composed of hot pressed consolidated submicron structured powder was investigated. The influence of the process parameters (i.e., powder particles size and hot pressing conditions on both reduction of the lattice thermal conductivity and electronic optimization is described in detail. Very high maximal ZT values of up to ∼1.6 were obtained and correlated to the microstructural characteristics. Based on the various involved mechanisms, a potential route for further enhancement of the ZT values of the investigated composition is proposed.

  15. Intrinsic Rashba-like splitting in asymmetric Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} heterogeneous topological insulator films

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiaofei; Guo, Wanlin, E-mail: wlguo@nuaa.edu.cn [State Key Laboratory of Mechanics and Control for Mechanical Structures and Key Laboratory for Intelligent Nano Materials and Devices (MOE), Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2014-08-25

    We show by density functional theory calculations that asymmetric hetero-stacking of Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} films can modulate the topological surface states. Due to the structure inversion asymmetry, an intrinsic Rashba-like splitting of the conical surface bands is aroused. While such splitting in homogeneous Bi{sub 2}Te{sub 3}-class topological insulators can be realized in films with more than three quintuple layers under external electric fields, the hetero-stacking breaks the limit of thickness for preserving the topological nature into the thinnest two quintuple layers. These results indicate that the hetero-stacking can serve as an efficient strategy for spin-resolved band engineering of topological insulators.

  16. Atomic and electronic structure of a Rashba p-n junction at the BiTeI surface

    OpenAIRE

    Tournier-Colletta, C.; Autes, G.; Kierren, B.; Bugnon, Ph.; Berger, H.; Fagot-Revurat, Y.; Yazyev, O. V.; Grioni, M.; Malterre, D.

    2014-01-01

    The non-centrosymmetric semiconductor BiTeI exhibits two distinct surface terminations that support spin-split Rashba surface states. Their ambipolarity can be exploited for creating spin-polarized $p$-$n$ junctions at the boundaries between domains with different surface terminations. We use scanning tunneling microscopy/spectroscopy (STM/STS) to locate such junctions and investigate their atomic and electronic properties. The Te- and I-terminated surfaces are identified owing to their disti...

  17. Ferromagnetism and topological surface states of manganese doped Bi{sub 2}Te{sub 3}: Insights from density-functional calculations

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yuanchang [National Center for Nanoscience and Technology, Beijing 100190 (China); Zou, Xiaolong [Department of Materials Science and Nanoengineering, Rice University, Houston, Texas 77005 (United States); Li, Jia, E-mail: lijia@phys.tsinghua.edu.cn [Key Laboratory of Thermal Management Engineering and Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055 (China); Zhou, Gang [Department of Physics, Tsinghua University, Beijing 100084 (China)

    2014-03-28

    Based on first-principles calculations, the electronic, magnetic, and topological characters of manganese (Mn) doped topological insulator Bi{sub 2}Te{sub 3} were investigated. The Mn substitutionally doped Bi{sub 2}Te{sub 3}, where Mn atoms tend to be uniformly distributed, was shown to be p-type ferromagnetic, arising from hole-mediated Ruderman-Kittel-Kasuya-Yosida interaction. Mn doping leads to an intrinsic band splitting at Γ point, which is substantially different from that of nonmagnetic dopant. The topological surface state of Bi{sub 2}Te{sub 3} is indeed gapped by Mn doping; however, the bulk conductance limits the appearance of an insulating state. Moreover, the n-type doping behavior of Bi{sub 2}Te{sub 3} is derived from Mn entering into the van der Waals gap of Bi{sub 2}Te{sub 3}.

  18. Electric and mechanical performances of Bi0.5Sb1.5Te3 prepared by spark plasma sintering

    Institute of Scientific and Technical Information of China (English)

    XIAO Bo; CHEN Hui; WU Borong; ZHU Lei; LIU Mingyi; JIAN Xuyu; LI Lin

    2006-01-01

    Thermoelectric (TE) materials are a kind of functional materials which can be used to convert directly heat energy to electricity or reversely.The thermoelectric effects hold great potential for application in power generation and refrigeration.Bi2Te3 and its alloys are well known as best TE materials currently available near room temperature.This paper studies respectively the effects of spark plasma sintering (SPS) on electric performance of Bi0.5Sb1.5Te3 thermoelectric materials that are prepared through vacuum melting and ball milling.Through X-ray Diffraction and cold field emission scanning electric microscope s4800, the phase constituent and microstructure of the TE materials samples were analyzed.Electric conductivity and power factor can be improved with the rise of Spark Plasma Sintering temperature (from 300 to 500 ℃) and pressure(from 30 to 60 MPa), and the density and mechanical strength of Bi0.5Sb1.5Te3 thermoelectric material increase, too.

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

    Science.gov (United States)

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

    2013-07-01

    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.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. Electronic supplementary information (ESI) available: Morphologies, XRD patterns, SEM compositions and room-temperature thermoelectric properties of the series of (015) oriented Bi0.4Sb1.6Te3 nanocolumns (Fig. S1-S3), (00l) oriented

  20. Compositional effects on the low-temperature transport properties of non-stoichiometric Bi2Te x Se y -based crystals

    Science.gov (United States)

    Ramachandran, B.; Wu, K. K.; Kuo, Y. K.; Guo, L. S.; Wang, L. M.

    2017-01-01

    We grew a series of non-stoichiometric crystals of the ternary alloy Bi2Te x Se y via a direct solidification route. The temperature-dependent electrical and thermal transport properties, such as electrical resistivity (ρ), Seebeck coefficient (S), Hall coefficient (R H), and thermal conductivity (κ), of six selected crystals of Bi2Te x Se y with x  +  y ~ 3 were studied. We found that the physical properties of the Bi2Te x Se y -based crystals varied significantly with the Te/Se (x/y) content. This is essentially due to the modification of the electronic band structure of the crystals with the change in sample composition, which ultimately leads to the formation of a p-type material (Bi2Te2.10Se0.66) from an n-type Bi2Te1.89Se0.98. Most importantly, the feature associated with surface-state conduction at low temperatures was also observed in some of these crystals, including Bi2Te1.89Se0.98, Bi2Te2.16Se0.71, and Bi2Te2.10Se0.66. In particular, two highly resistive compounds, Bi2Te2.16Se0.71 and Bi2Te2.10Se0.66 with low carrier densities were identified as potential materials for topological applications. The observed complex transport behavior was realized in connection with the formation of impurity bands (multiband effects) in the Bi2Te x Se y -based systems. Analysis of the lattice thermal conductivity of the Bi2Te x Se y -based crystals indicates that the sample composition has a major effect on low-temperature heat conduction via phonon-boundary and phonon-point-defect scattering. Finally, the highest room temperature thermoelectric figure of merit, a ZT of about 0.46, was achieved for n-type Bi2Te1.63Se1.23.

  1. The mechanism of formation of the interlayer quantum wires in zinc-doped Bi2Te3

    Directory of Open Access Journals (Sweden)

    Alieva A. P.

    2012-06-01

    Full Text Available Nanowires formation process on a (0001 surface of Bi2Te3 is studied. It has been established that on interlayer surface Te(1—Te(1 there is a process of migration of atoms, moving and coagulation of clusters on the basis of Zn atoms. As a result of diffusion-limited aggregation the structures with quantum dots are formed, from which nanowires are self-organized. Such superficial structures play regulating role in working out the topological insulators based on A2VB3VI and increase thermoelectric efficiency of a composite.

  2. Growth and characterization of molecular beam epitaxy-grown Bi{sub 2}Te{sub 3−x}Se{sub x} topological insulator alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tung, Y.; Chiang, Y. F.; Chong, C. W., E-mail: cheongwei2000@yahoo.com, E-mail: jcahuang@mail.ncku.edu.tw, E-mail: makalu@nsrrc.org.tw; Deng, Z. X.; Chen, Y. C. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Huang, J. C. A., E-mail: cheongwei2000@yahoo.com, E-mail: jcahuang@mail.ncku.edu.tw, E-mail: makalu@nsrrc.org.tw [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Advanced Optoelectronic Technology Center (AOTC), National Cheng Kung University, Tainan 70101, Taiwan (China); Taiwan Consortium of Emergent Crystalline Materials (TCECM), Ministry of Science and Technology, Taipei 10622, Taiwan (China); Cheng, C.-M., E-mail: cheongwei2000@yahoo.com, E-mail: jcahuang@mail.ncku.edu.tw, E-mail: makalu@nsrrc.org.tw; Pi, T.-W.; Tsuei, K.-D. [National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Li, Z.; Qiu, H. [School of Electronic Science and Applied Physics, HeFei University of Technology, Anhui (China)

    2016-02-07

    We report a systematic study on the structural and electronic properties of Bi{sub 2}Te{sub 3−x}Se{sub x} topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi{sub 2}Se{sub 3} to Bi{sub 2}Te{sub 3} was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi{sub 2}Te{sub 3−x}Se{sub x} films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi{sub 2}Te{sub 3−x}Se{sub x} with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi{sub 2}Te{sub 3−x}Se{sub x} thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.

  3. Transport properties of thermoelectric Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} and Bi{sub 2}Te{sub 2.7}Se{sub 0.3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Bourgault, D., E-mail: daniel.bourgault@grenoble.cnrs.fr [Institut Néel/Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France); Schaechner, B. [Institut Néel/Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France); Giroud Garampon, C. [Institut Néel/Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France); Schneider-Electric France, 38TEC/T1, 37 Quai Paul Louis Merlin, 38050 Grenoble Cedex 9 (France); Crozes, T. [Institut Néel/Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France); Caillault, N.; Carbone, L. [Schneider-Electric France, 38TEC/T1, 37 Quai Paul Louis Merlin, 38050 Grenoble Cedex 9 (France)

    2014-06-15

    Highlights: • Transport properties of as-deposited and annealed Bi–Te thin films have been studied. • Temperature dependences of the transport properties are described. • The role of crystallization and defects on the transport properties was studied. - Abstract: Transport properties of as-deposited and annealed Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} (p-type) and Bi{sub 2}Te{sub 2.7}Se{sub 0.3} (n-type) thin films have been studied. The p-type and n-type thin films were annealed between 150 and 300 °C. Temperature dependence of the transport properties and effect of annealing are described for both types. The role of the crystallization and the defects in relation with the atomic composition are studied for the different annealed thin films.

  4. Thermal conductivity of Bi{sub 2}Te{sub 3} tilted nanowires, a molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shen, E-mail: shen.li@univ-lorraine.fr; Lacroix, David; Termentzidis, Konstantinos, E-mail: konstantinos.termentzidis@univ-lorraine.fr [Université de Lorraine, LEMTA UMR 7563, CNRS F-54506 Vandoeuvre Les Nancy (France); Chaput, Laurent [Université de Lorraine, IJL-P2M, UMR-7198, CNRS F-54506 Vandoeuvre les Nancy (France); Stein, Nicolas [Université de Lorraine, IJL-CP2S, UMR-7198, CNRS Metz (France); Frantz, Cedric [Université de Lorraine, IJL-P2M, UMR-7198, CNRS Metz (France)

    2015-06-08

    Evidence for an excellent compromise between structural stability and low thermal conductivity has been achieved with tilted Bi{sub 2}Te{sub 3} nanowires. The latter ones were recently fabricated and there is a need in modeling and characterization. The structural stability and the thermal conductivity of Bi{sub 2}Te{sub 3} nanowires along the tilted [015]* direction and along the [010] direction have been explored. For the two configurations of nanowires, the effect of the length and the cross section on the thermal conductivity is discussed. The thermal conductivity of infinite size tilted nanowire is 0.34 W/m K, significantly reduced compared to nanowire along the [010] direction (0.59 W/m K). This reveals that in Bi{sub 2}Te{sub 3} nanowires the structural anisotropy can be as important as size effects to reduce the thermal conductivity. The main reason is the reduction of the phonon mean free path which is found to be 1.7 nm in the tilted nanowires, compared to 5.3 nm for the nanowires along the [010] direction. The fact that tilted Bi{sub 2}Te{sub 3} nanowire is mechanically stable and it has extremely low thermal conductivity suggests these nanowires as a promising material for future thermoelectric generation application.

  5. Thermoelectric properties of rare earth-doped -type Bi2Se0.3Te2.7 nanocomposites

    Indian Academy of Sciences (India)

    Fang Wu; Hongzhang Song; Jianfeng Jia; Xing Hu

    2014-08-01

    -Type R0.2Bi1.8Se0.3Te2.7 (R = Ce, Y and Sm) nanopowders were synthesized by hydrothermal method and the thermoelectric properties of the bulk samples made by hot-pressing these nanopowders were investigated. The Ce, Y and Sm doping have significant effects on the morphologies of the synthesized nanopowders. The thermoelectric property results show that Ce, Y and Sm doping not only help to decrease the electrical resistivity, but also help to reduce the thermal conductivity. Among rare earth elements–doped samples, it seems that the Y0.2Bi1.8Se0.3Te2.7 bulk has a suitable microstructure, which scatters phonons effectively but does not scatter electronic carriers as much. As a result, the ZT values of Y0.2Bi1.8Se0.3Te2.7 can reach 1.21 at 413 K, which is higher than those of Bi2Se0.3Te2.7 ingots made by zone-melting method.

  6. Morphological evolution in single-crystalline Bi2Te3 nanoparticles, nanosheets and nanotubes with different synthesis temperatures

    Indian Academy of Sciences (India)

    Punita Srivastava; Kedar Singh

    2013-10-01

    A general surfactant-assisted wet chemical route has been developed for the synthesis of a variety of bismuth telluride (Bi2Te3) single-crystalline nanostructures with varied morphologies at different temperatures in which hydrazine hydrate plays as an important solvent. Bi2Te3 sheet grown nanoparticles, nanosheets and nanotubes have been synthesized by a simplest wet chemical route at 50, 70 and 100 °C within 4 h. Bi2Te3 sheet grown nanoparticles are obtained in agglomerate state and they are found with many wrinkles. Various types of Bi2Te3 nanotubes are also found which are tapered with one end open and the other closed. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern and energy dispersive X-ray (EDX) spectroscopy were employed to characterize the powder product. It is found that all nanoparticles, nanosheets and nanotubes are well-crystallized nanocrystals and morphologies of the powder products are greatly affected by different synthesis temperatures. The formation mechanisms of bismuth telluride nanostructures are also discussed.

  7. Biomolecule-Assisted Hydrothermal Synthesis and Self-Assembly of Bi2Te3 Nanostring-Cluster Hierarchical Structure

    DEFF Research Database (Denmark)

    Mi, Jianli; Lock, Nina; Sun, Ting;

    2010-01-01

    A simple biomolecule-assisted hydrothermal approach has been developed for the fabrication of Bi2Te3 thermoelectric nanomaterials. The product has a nanostring-cluster hierarchical structure which is composed of ordered and aligned platelet-like crystals. The platelets are100 nm in diameter...

  8. Fabrication and Optimization of Brush-Printed n-type Bi2Te3 Thick Films for Thermoelectric Cooling Devices

    Science.gov (United States)

    Liu, Xing; Zhao, Wen-yu; Zhou, Hong-yu; Mu, Xin; He, Dan-qi; Zhu, Wan-ting; Wei, Ping; Wu, Han; Zhang, Qing-jie

    2016-03-01

    A simple, efficient and rapid brush-printing method has been developed for preparation of n-type Bi2Te2.7Se0.3 films approximately 100-150 μm thick. X-ray diffraction, scanning electron microscopy, electron probe microanalysis, and four-point probe measurements were used to characterize the crystal structure, composition, microstructure, and electrical properties of the films. The results showed that all the n-type Bi2Te2.7Se0.3 thick films were composed of single-phase Bi2Te2.7Se0.3; the grains in the films were randomly distributed in the low-temperature-annealed samples and predominantly oriented along the (00 l) plane in samples annealed at temperatures >673 K. σ and the absolute value of α first increased substantially with increasing the annealing temperature in the range 573-673 K then decreased when the annealing temperature was increased further. The dependence of σ and α on annealing temperature may be reasonably explained on the basis of the change in the microstructure induced by annealing. The performance of a prototype cooling device containing n-type Bi2Te2.7Se0.3 thick films was evaluated for temperature differences produced by use of different DC currents.

  9. Enhancement in Figure of Merit ( ZT) by Annealing of BiTe Nanostructures Synthesized by Microwave-Assisted Flash Combustion

    Science.gov (United States)

    Kaur, Harjeet; Sharma, Lalit; Singh, Simrjit; Sivaiah, Bathula; Reddy, G. B.; Senguttuvan, T. D.

    2014-06-01

    Uniform polycrystalline bismuth telluride (BiTe) nanowires of diameter 100 nm to 150 nm and hexagonal nanoplates with thickness of 50 nm to 100 nm have been successfully synthesized by the microwave-assisted flash combustion technique. The formation of BiTe nanostructures depends on the type of fuel and the oxidant-to-fuel ratio, which in turn affect the reaction time and reaction temperature. Spark plasma sintering has been employed for compaction and sintering of both as-synthesized as well as annealed BiTe powders. Increasing the sintering temperature while using faster sintering cycles reduced the porosity, resulting in high densification while preserving the nanostructures. The dimensionless figure of merit ( ZT) was evaluated from the Seebeck coefficient, electrical resistivity, and thermal conductivity values over the range from 300 K to 600 K. The effect of annealing on the enhancement of ZT is discussed. These evaluations suggest that the rarely studied BiTe is a potential candidate for thermoelectric applications at low temperatures.

  10. Electronic structure and transport in the low-temperature thermoelectric CsBi4Te6: Semiclassical transport equations

    DEFF Research Database (Denmark)

    Lykke, Lars; Iversen, Bo Brummerstedt; Madsen, Georg

    2006-01-01

    The band structure of the low-temperature thermoelectric material, CsBi4Te6, is calculated and analyzed using the semiclassic transport equations. It is shown that to obtain a quantitative agreement with measured transport properties, a band gap of 0.08 eV must be enforced. A gap in reasonable...

  11. Low Resistance Ohmic Contacts to Bi[sub 2]Te[sub 3] Using Ni and Co Metallization

    KAUST Repository

    Gupta, Rahul P.

    2010-04-27

    A detailed study of the impact of surface preparation and postdeposition annealing on contact resistivity for sputtered Ni and Co contacts to thin-film Bi2 Te3 is presented. The specific contact resistivity is obtained using the transfer length method. It is observed that in situ sputter cleaning using Ar bombardment before metal deposition gives a surface free of oxides and other contaminants. This surface treatment reduces the contact resistivity by more than 10 times for both Ni and Co contacts. Postdeposition annealing at 100°C on samples that were sputter-cleaned further reduces the contact resistivity to < 10-7 cm2 for both Ni and Co contacts to Bi2 Te3. Co as a suitable contact metal to Bi2 Te3 is reported. Co provided similar contact resistance values as Ni, but had better adhesion and less diffusion into the thermoelectric material, making it a suitable candidate for contact metallization to Bi2 Te3 based devices. © 2010 The Electrochemical Society.

  12. Giant magneto-optical response in non-magnetic semiconductor BiTeI driven by bulk Rashba spin splitting

    OpenAIRE

    Demkó, L.; Schober, G. A. H.; Kocsis, V.; Bahramy, M.S.; Murakawa, H.; Lee, J. S.; Kézsmárki, I.; Arita, R.; Nagaosa, N.; Tokura, Y.

    2012-01-01

    We study the magneto-optical (MO) response of polar semiconductor BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being non-magnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (

  13. Synthesis and investigation of BiSbTeSe single crystal doped with Zr produced using Bridgman method

    Directory of Open Access Journals (Sweden)

    Emina Požega

    2017-09-01

    Full Text Available Single crystal ingot of BiSbTeSe doped with Zr was synthesized using Bridgman method. Energy dispersive spectrometry (EDS analysis was used to determine chemical composition of studied samples as well as to check and confirm samples homogeneity. X-ray diffraction (XRD measurements proved that obtained crystal ingot is a single cristal and confirms Bi2Te3-type compound with orientation (00l of single crystal. Melting point was determined by dilatometrically measured shrinkage during heating. Mobility, concentration, resistivity/conductivity and Hall coefficient of BiSbTeSe doped with Zr samples were determined using a Hall Effect measurement system based on the Van der Pauw method. The Hall Effect was measured at room temperature with an applied magnetic field strength of 0.37 T at different current intensities. The measured ingot samples were cut and cleaved from different regions. Calculated results obtained using a Hall Effect measurement system (Ecopia, HMS-3000 were mutually compared for cleaved and cut samples. Changing of transport and electrical parameters with the increase of the current intensity was also monitored.The results confirmed that electrical and transport properties of single crystal depend on crystal growth direction and mobility was also significantly improved in comparison with theoretical value of Bi2Te3 and available literature data.

  14. The role of Te(IV) and Bi(III) chloride complexes in hydrothermal mass transfer: An X-ray absorption spectroscopic study

    Energy Technology Data Exchange (ETDEWEB)

    Etschmann, Barbara E.; Liu, Weihua; Pring, Allan; Grundler, Pascal V.; Tooth, Blake; Borg, Stacey; Testemale, Denis; Brewe, Dale; Brugger, Joël

    2016-05-01

    Tellurium (Te) and bismuth (Bi) are two metal(loid)s often enriched together with gold (Au) in hydrothermal deposits; however the speciation and transport properties for these two metals in hydrothermal systems are poorly understood. We investigated the effect of chloride on the speciation of Te(IV) and Bi(III) in hydrothermal solutions using in-situ XAS spectroscopy. At ambient temperature, oxy-hydroxide complexes containing the [TeO3] moiety (e.g., H3TeO3+ under highly acidic conditions) predominate in salty solutions over a wide range in pH and salt concentrations. Te(IV)-Cl complexes only appear at pH(25 degrees C) <= 2 and high Cl- activity (>= 10). The highest order Te(IV) chloride complex detected is TeCl4(aq), and contains the [TeCl4] moiety. Upon heating to 199 degrees C, the Te(IV)-Cl complexes become more stable; however they still required highly acidic conditions which are likely to exist only in very limited environments in nature. At ambient temperature, Bi(III) is coordinated to 5.5(5) Cl atoms in high salinity, acidic (HCl >= 0.5 m) chloride solutions. This, combined with large EXAFS-derived structural disorder parameters, suggests that the Bi(III) complex is most likely present as both BiCl52- and BiCl63-. The number of Cl atoms coordinated to Bi(III) decreases with increasing temperature; at around 200 degrees C and above, Bi(III) is coordinated to three Cl atoms. Overall the data show that Te(IV) chloride complexes can be ignored in predicting Te mobility under oxidizing conditions in most geological environments, but that Bi(III) chloride complexes are expected to account for Bi mobility in acidic brines. New thermodynamic properties for Bi(III) chloride complexes are provided to improve reactive transport modeling of Bi up to 500 degrees C. Although higher order complexes such as BiCl52- and BiCl63- exist at ambient temperature, the BiCl3(aq) complex becomes the predominant chloride complex in saline solutions at T >= 200 degrees C.

  15. Influence of Bi, Se and Te additions on the formation temperature of MgB2

    DEFF Research Database (Denmark)

    Grivel, Jean-Claude; Andersen, Niels Hessel; Pallewatta, P. G. Asanka Pramod;

    2012-01-01

    The formation of the MgB2 superconducting compound from a mixture of Mg and amorphous B powders with various low melting point metals (Bi, Se and Te) was studied in situ by means of high-energy (synchrotron) x-ray diffraction in wires with a composite Cu/Nb sheath. In comparison with an undoped...... sample, it was found that the addition of Bi results in a clear lowering of the formation temperature of MgB2, whereas Se and Te have no significant influence. Tc is slightly higher in the Bi-doped sample than in the others but the jc in this case is lower than in the pure MgB2 sample, probably due...

  16. Ab initio lattice dynamics and thermochemistry of layered bismuth telluride (Bi2Te3)

    Science.gov (United States)

    Zurhelle, Alexander F.; Deringer, Volker L.; Stoffel, Ralf P.; Dronskowski, Richard

    2016-03-01

    We present density-functional theory calculations of the lattice dynamics of bismuth telluride, yielding force constants, mean-square displacements and partial densities of phonon states which corroborate and complement previous nuclear inelastic scattering experiments. From these data, we derive an element- and energy-resolved view of the vibrational anharmonicity, quantified by the macroscopic Grüneisen parameter γ which results in 1.56. Finally, we calculate thermochemical properties in the quasiharmonic approximation, especially the heat capacity at constant pressure and the enthalpy of formation for bismuth telluride; the latter arrives at ▵H f (Bi2Te3)  =  -102 kJ mol-1 at 298 K.

  17. Mechanisms of enhanced orbital dia- and paramagnetism: application to the Rashba semiconductor BiTeI.

    Science.gov (United States)

    Schober, G A H; Murakawa, H; Bahramy, M S; Arita, R; Kaneko, Y; Tokura, Y; Nagaosa, N

    2012-06-15

    We study the magnetic susceptibility of a layered semiconductor BiTeI with giant Rashba spin splitting both theoretically and experimentally to explore its orbital magnetism. Apart from the core contributions, a large temperature-dependent diamagnetic susceptibility is observed when the Fermi energy E(F) is near the crossing point of the Rashba spin-split conduction bands at the time-reversal symmetry point A. On the other hand, when E(F) is below this band crossing, the susceptibility turns to be paramagnetic. These features are consistent with first-principles calculations, which also predict an enhanced orbital magnetic susceptibility with both positive and negative signs as a function of E(F) due to band (anti)crossings. Based on these observations, we propose two mechanisms for the enhanced paramagnetic orbital susceptibility.

  18. Disentanglement of surface and bulk Rashba spin splittings in noncentrosymmetric BiTeI.

    Science.gov (United States)

    Landolt, Gabriel; Eremeev, Sergey V; Koroteev, Yury M; Slomski, Bartosz; Muff, Stefan; Neupert, Titus; Kobayashi, Masaki; Strocov, Vladimir N; Schmitt, Thorsten; Aliev, Ziya S; Babanly, Mahammad B; Amiraslanov, Imamaddin R; Chulkov, Evgueni V; Osterwalder, Jürg; Dil, J Hugo

    2012-09-14

    BiTeI has a layered and noncentrosymmetric structure where strong spin-orbit interaction leads to a giant Rashba spin splitting in the bulk bands. We present direct measurements of the bulk band structure obtained with soft x-ray angle-resolved photoemission (ARPES), revealing the three-dimensional Fermi surface. The observed spindle torus shape bears the potential for a topological transition in the bulk by hole doping. Moreover, the bulk electronic structure is clearly disentangled from the two-dimensional surface electronic structure by means of high-resolution and spin-resolved ARPES measurements in the ultraviolet regime. All findings are supported by ab initio calculations.

  19. Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI.

    Science.gov (United States)

    Park, Joonbum; Jin, Kyung-Hwan; Jo, Y J; Choi, E S; Kang, W; Kampert, E; Rhyee, J-S; Jhi, Seung-Hoon; Kim, Jun Sung

    2015-11-02

    We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for the outer Fermi surface shows an abrupt phase shift. In comparison with band structure calculations, we find that these unusual behaviors originate from the Fermi surface shape change due to pressure-induced band inversion. These results clearly demonstrate that the topological quantum phase transition is intimately tied to the shape of bulk Fermi surfaces enclosing the time-reversal invariant momenta with band inversion.

  20. Surface oxidation effect on the electrical behaviour of Bi2Te2Se nanoplatelets

    Science.gov (United States)

    Gehring, Pascal; Reusch, Frieder B.; Mashhadi, Soudabeh S.; Burghard, Marko; Kern, Klaus

    2016-07-01

    Charge transport in topological insulators is notably influenced by moisture and air in the surrounding environment. At present, however, little is known about the detailed composition of the oxidized surface and its impact on the electrical characteristics of these materials. Here, we investigate the surface oxide formation on the topological insulator Bi2Te2Se (BTS) and how this affects its electrical behavior. While ambient exposure of BTS nanoplatelets predominantly creates surface hydroxyl groups, oxygen plasma treatment yields a compact, few-nanometer thick surface oxide layer. The plasma causes p-type doping, accompanied by a decrease of the effective platelet thickness, the interplay of which is manifested in a resistance maximum as a function of plasma treatment time. It is furthermore demonstrated that the structural integrity of the plasma-derived surface oxide is sufficient to enable its use as a gate insulator layer in combination with a top gate.

  1. Substrate Temperature Effect on Structural Properties Of Bi2Te3 Thin Films

    Directory of Open Access Journals (Sweden)

    B.S. Jariwala

    2011-01-01

    Full Text Available Structural properties of Bi2Te3 thin films, thermally evaporated on well-cleaned glass substrate at different substrate temperature, are reported here. X-ray diffraction was carried out for the structural characterization. XRD pattern of the films exhibits preferential orientation along the [0 1 5] direction for the films of all the substrate temperature together with other supported planes [2 0 5] & [1 1 0]. All deposition conditions like thickness, deposition rate and pressure were maintained throughout the experiment. X-ray diffraction lines confirm that, the grown films are polycrystalline in nature with the hexagonal crystal structure. The effect of substrate temperature on these parameters have been investigated and reported in this paper. Various structural parameters such as lattice constants, grain size, micro strain, number of crystallites, stacking fault and dislocation density were calculated using X-ray diffraction analysis.

  2. Role of oxidation on surface conductance of the topological insulator Bi2Te2Se

    Science.gov (United States)

    Hwang, Jin Heui; Park, Joonbum; Kwon, Sangku; Kim, Jun Sung; Park, Jeong Young

    2014-12-01

    We investigated the effect of surface oxides on charge transport properties in a topological insulator (Bi2Te2Se) using conductive probe atomic force microscopy in an ultrahigh vacuum environment. Uniform distribution of the measured friction and current were observed over a single quintuple layer terrace after exposure to the ambient environment, which is an indication of uniform surface oxide coverage. An oxide-free topological insulator surface was exposed using tip-induced etching. By comparing surface conduction on a fresh surface versus a surface exposed to air, we observed a minor change in resistance when surface oxide was present. The current density varied with applied load on the oxidized surface, which implies that the topological surface states respond to tip-induced pressure even though surface oxide is present. From these results, we conclude that surface oxidation in air has a negligible effect on surface conductance in topological insulators.

  3. Room temperature giant and linear magnetoresistance in topological insulator Bi2Te3 nanosheets.

    Science.gov (United States)

    Wang, Xiaolin; Du, Yi; Dou, Shixue; Zhang, Chao

    2012-06-29

    Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi(2)Te(3) topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

  4. Photovoltaic effect in Bi{sub 2}TeO{sub 5} photorefractive crystal

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Ivan de, E-mail: ivan@ft.unicamp.brg; Capovilla, Danilo Augusto [GOMNI-Faculdade de Tecnologia/UNICAMP, Limeira (Brazil); Carvalho, Jesiel F.; Montenegro, Renata; Fabris, Zanine V. [Instituto de Física/Universidade Federal de Goiás, Goiânia (Brazil); Frejlich, Jaime [Instituto de Física “Gleb Wataghin”/UNICAMP, Campinas (Brazil)

    2015-10-12

    We report on the presence of a strong photovoltaic effect on nominally undoped photorefractive Bi{sub 2}TeO{sub 5} crystals and estimated their Glass photovoltaic constant and photovoltaic field for λ = 532 nm illumination. We directly measured the photovoltaic-based photocurrent in this material under λ = 532 nm wavelength laser light illumination and compared its behavior with that of a well known photovoltaic Fe-doped Lithium Niobate crystal. We also show the photovoltaic current to strongly depend on the polarization direction of light. Holographic diffraction efficiency oscillation during recording and the behavior of fringe-locked running holograms in self-stabilized experiments are also demonstrated here as additional indirect proofs of the photovoltaic nature of this material.

  5. Oscillatory thermopower waves based on Bi{sub 2}Te{sub 3} films

    Energy Technology Data Exchange (ETDEWEB)

    Walia, Sumeet; Kalantar-zadeh, Kourosh [School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC 3000 (Australia); Weber, Rodney [School of Physical, Environmental and Mathematical Sciences, University of New South Wales at Australian Defence Force Academy, Canberra, ACT 2600 (Australia); Latham, Kay [School of Applied Sciences, Applied Chemistry, RMIT University, Melbourne, VIC 3000 (Australia); Petersen, Phred [School of Media and Communications, RMIT University, Melbourne, VIC 3000 (Australia); Abrahamson, Joel T.; Strano, Michael S. [Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

    2011-06-07

    Exothermic chemical reactions that are coupled to Bi{sub 2}Te{sub 3} porous layers, which are deposited onto terracotta or alumina (Al{sub 2}O{sub 3}) substrates, are used to produce self-propagating thermal waves that are guided along the surface. Nitrocellulose is used as the highly reactive chemical. Bi{sub 2}Te{sub 3} is employed because of its large Seebeck coefficient and high electrical conductivity. For the Al{sub 2}O{sub 3} based structures, the thermal conduction of the substrate results in strong oscillations of the output signals. Such thermopower waves produce a power as large as 10 mW and voltages as high as 150 mV. The power per mass ratio of the developed system is quite remarkable, namely, on the order of 1 kW kg{sup -1}. Depending on the thermal conductivity of the substrate used, the wave front average propagation velocity is either slow (ca. 0.009 m s{sup -1} for terracotta) or much faster (on the order of 0.4 m s{sup -1} for Al{sub 2}O{sub 3}). We have used a mathematical model based on two coupled heat transport equations, in conjunction with the chemical reaction equation, to predict the behavior of the system, which describes the average propagation velocity and the time between oscillation peaks. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Measurements of current-induced spin polarizations in topological insulators Bi2Te2Se and Bi2Se3 thin flakes

    Science.gov (United States)

    Tian, Jifa; Miotkowski, Ireneusz; Hong, Seokmin; Datta, Supriyo; Chen, Yong

    Topological insulators (TIs) possess nontrivial spin-momentum-locked topological surface states (TSS). Real TI can also host trivial surface 2DEG with strong Rashba spin-orbit coupling derived from the bulk states. Both TSS and Rashba 2DEG can generate current induced spin polarization, although the dominant helicities of their spin-momentum locking (SML) are expected to be opposite. Here, we report spin potentiometric measurements in exfoliated bulk-insulating Bi2Te2Se and bulk-metallic Bi2Se3 thin flakes. In both materials, the voltage measured by a FM electrode shows a hysteretic step-like change when the FM magnetization is switched by an in-plane magnetic field. The trend of the voltage change can be reversed by reversing the direction of the dc current, and the amplitude of the spin signal increases linearly with increasing bias current. Such a spin signal is consistent with a current induced spin polarization arising from a helical SML. However, the observed trend of the voltage change is opposite between Bi2Te2Se and Bi2Se3, suggesting opposite signs of dominant spin helicity that we attribute to TSS and Rashba 2DEG respectively.

  7. Current driven vortex-antivortex pair breaking and vortex explosion in the Bi2Te3/FeTe interfacial superconductor

    Science.gov (United States)

    Dean, C. L.; Kunchur, M. N.; He, Q. L.; Liu, H.; Wang, J.; Lortz, R.; Sou, I. K.

    2016-08-01

    We investigated the dissipative regime of the Bi2Te3/FeTe topological insulator-chalcogenide interface superconductor at temperatures well below the Berezinski-Kosterlitz-Thouless transition. We observe a transition in the current-resistance and temperature-resistance curves that quantitatively agrees with the Likharev vortex-explosion phenomenon. In the limit of low temperatures and high current densities, we were able to demonstrate the regime of complete vortex-antivortex dissociation arising from current driven vortex-antivortex pair breaking.

  8. Current driven vortex-antivortex pair breaking and vortex explosion in the Bi{sub 2}Te{sub 3}/FeTe interfacial superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Dean, C.L. [Department of Physics and Astronomy, University of South Carolina, Columbia, SC, 29208 (United States); Kunchur, M.N., E-mail: kunchur@sc.edu [Department of Physics and Astronomy, University of South Carolina, Columbia, SC, 29208 (United States); He, Q.L.; Liu, H.; Wang, J.; Lortz, R.; Sou, I.K. [William Mong Institute of Nano Science and Technology, the Hong Kong University of Science and Technology, Hong Kong (China)

    2016-08-15

    We investigated the dissipative regime of the Bi{sub 2}Te{sub 3}/FeTe topological insulator-chalcogenide interface superconductor at temperatures well below the Berezinski-Kosterlitz-Thouless transition. We observe a transition in the current-resistance and temperature-resistance curves that quantitatively agrees with the Likharev vortex-explosion phenomenon. In the limit of low temperatures and high current densities, we were able to demonstrate the regime of complete vortex-antivortex dissociation arising from current driven vortex-antivortex pair breaking.

  9. Deposition of n-Type Bi2Te3 Thin Films on Polyimide by Using RF Magnetron Co-Sputtering Method.

    Science.gov (United States)

    Joo, Sung-Jae; Kim, Bong Seo; Min, Bok-Ki; Oh, Min Wook; Lee, Ji-Eun; Ryu, Byung Ki; Lee, Hee Woong; Park, Su Dong

    2015-10-01

    Bi2Te3 thermoelectric thin films were deposited on the flexible polyimide substrates by RF magnetron co-sputtering of a Bi and a Te targets. The influence of the substrate temperature and RF power on the microstructure, chemical composition, and the thermoelectric properties of the sputtered films was investigated by using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and in-plane resistivity/Seebeck coefficient measurement. It was shown that the thermoelectric properties of the films depend sensitively on the Bi/Te chemical composition ratio and the substrate temperature, and the layered structure was clearly observed from the cross section of the (00L)-oriented, nearly stoichiometric Bi2Te3 films when the substrate temperature is higher than 250 °C. As-deposited Bi2Te3 films deposited at 300 °C show the highest power factor of 0.97 mW/K(2)m and the Seebeck coefficient of -193 μV/K at 32 °C, which also have (00L) preferred orientation and the layered structure. The durability of the Bi2Te3 films on polyimide against repeated bending was also tested by monitoring the film resistance, and it was concluded that the Bi2Te3 films are applicable reliably on the curved surfaces with the radius of curvature larger than 5 mm.

  10. Effect of Uniform Dispersion of Single-Wall Carbon Nanotubes on the Thermoelectric Properties of BiSbTe-Based Nanocomposites

    Science.gov (United States)

    Ahmad, Kaleem; Wan, Chunlei; Al-Eshaikh, Mohammad A.

    2017-02-01

    Thermoelectric properties of BiSbTe-based bulk nanocomposites by incorporation of single-wall carbon nanotubes (SWCNTs) in different (0.0, 0.5, 1.0 and 1.5) vol.% were investigated from 300 K to 500 K. SWCNTs were uniformly dispersed in BiSbTe via a combination of ultra-sonication, magnetic stirring and mild ball milling. Fine BiSbTe powder was formed by crushing and ball milling the lumps in an inert environment. The composites demonstrate grain boundary structures exhibiting a three-dimensional network of one-dimensional flexible SWCNTs in BiSbTe bulks. The homogenous distribution of SWCNTs in BiSbTe drastically changes the transport properties of the composites. At 0.5 vol.% of SWCNTs, the effective thermal conductivity decreases suggesting the increased phonon scattering. Meanwhile, at 1.0 vol.% and 1.5 vol.%, the conductivities of the composites somehow increases attributed to homogenous distribution of SWCNTs in the BiSbTe matrix. The increased electrical resistivity with the addition of SWCNTs implies the enhanced scattering of carriers at the grain boundaries and SWCNTs/BiSbTe interfaces. The dimensionless figure of merit somewhat decreases with the addition of 0.5 vol.% SWCNTs. The results suggest that the figure of merit can be improved by optimizing the SWCNT composition below 0.5 vol.% by adequately tailoring the thermoelectric transport.

  11. Nuclear magnetic resonance study of a Bi2Te3 topological insulator

    Science.gov (United States)

    Podorozhkin, D. Yu.; Charnaya, E. V.; Antonenko, A.; Mukhamad'yarov, R.; Marchenkov, V. V.; Naumov, S. V.; Huang, J. C. A.; Weber, H. W.; Bugaev, A. S.

    2015-09-01

    The results of the nuclear magnetic resonance (NMR) study of a grown high-quality Bi2Te3 semiconductor single crystal have been presented. Signals from the 125Te isotope were detected by the spin echo method in the range from 10 K to room temperature. It was found that the NMR spectrum consists of two lines. The line with a positive shift of the resonance frequency corresponded to the bulk of the sample. The line with a negative shift was interpreted as a signal from the surface of the single crystal. The temperature and orientational dependences of the positions of the NMR line of nuclei in the bulk of the crystal were studied. It was shown that the shifts are mainly determined by the Knight shift due to the interaction with mobile charge carriers. The thermoactivation character of the concentration of mobile charges in the crystal under study, which corresponds to the intrinsic conductance, was proved, and the energy parameters of the thermoactivation processes were calculated.

  12. Comparison of space- and ground-grown Bi 2Se 0.21Te 2.79 thermoelectric crystals

    Science.gov (United States)

    Zhou, Yanfei; Li, Xiaoya; Bai, Shengqiang; Chen, Lidong

    2010-03-01

    Two crystals of Bi 2Se 0.21Te 2.79 doped with 0.08 wt% TeI 4 were grown by zone melting on the Foton-M3 spacecraft of Russia and the ground in 2007, respectively. The chemical composition, structure and thermoelectric properties of the space and ground crystals grown were evaluated by EPMA, XRD and thermoelectric measurements including Seebeck coefficient, electrical conductivity and thermal conductivity. The compositions of the space crystal grown along growth direction were more homogeneous than that of the ground crystal grown. The crystallization of space crystal grown was obviously improved. The maximum ZT value of space crystal reached 1.14 at 300 K, which was higher about 29% than that of ground crystal at room temperature. These results imply that the composition homogeneity and crystallization of Bi 2Se 0.21Te 2.79 crystal can be improved under microgravity conditions, which is helpful for enhancing thermoelectric figure of merit of Bi 2Te 3-base materials.

  13. Thermal Stability of P-Type BiSbTe Alloys Prepared by Melt Spinning and Rapid Sintering

    Directory of Open Access Journals (Sweden)

    Yun Zheng

    2017-06-01

    Full Text Available P-type BiSbTe alloys have been widely implemented in waste heat recovery from low-grade heat sources below 600 K, which may involve assorted environments and conditions, such as long-term service, high-temperature exposure (generally 473–573 K and mechanical forces. It is important to evaluate the service performance of these materials in order to prevent possible failures in advance and extend the life cycle. In this study, p-type Bi0.5Sb1.5Te3 commercial zone-melting (ZM ingots were processed by melt spinning and subsequent plasma-activated sintering (MS-PAS, and were then subjected to vacuum-annealing at 473 and 573 K, respectively, for one week. The results show that MS-PAS samples exhibit excellent thermal stability when annealed at 473 K. However, thermal annealing at 573 K for MS-PAS specimens leads to the distinct sublimation of the element Te, which degrades the hole concentration remarkably and results in inferior thermoelectric performance. Furthermore, MS-PAS samples annealed at 473 K demonstrate a slight enhancement in flexural and compressive strengths, probably due to the reduction of residual stress induced during the sintering process. The current work guides the reliable application of p-type Bi0.5Sb1.5Te3 compounds prepared by the MS-PAS technique.

  14. First principles study of electronic structure dependent optical properties of oxychalcogenides BiOCu Ch ( Ch = S, Se, Te)

    Science.gov (United States)

    Ul Islam, A. K. M. Farid; Helal, M. A.; Liton, M. N. H.; Kamruzzaman, M.; Islam, H. M. Tariqul

    2017-04-01

    The optical properties of BiOCu Ch and their dependency on the electronic structures are investigated using first principles study. Modified Perdew-Burke-Ernzerhof generalized gradient approximation functional for solids are used to optimize lattice parameters. These optimized lattice parameters are used to calculate the electronic energy band, density of state and optical properties. It is observed that the optical constants are dependent on the energy band gap and also on the contribution of Copper and Chalcogen atoms in the formation of electronic band structure. The obtained results reveal that the optical constants are dominated by the inter-band transitions. In the case of higher incident photon energy these materials behave like metal, where optical constants are dominated by the free carriers. The obtained optical band gaps 0.60, 0.56 and 0.55 eV for BiOCuS, BiOCuSe and BiOCuTe, respectively are consistent with available theoretical results. We also calculate the carrier concentration, electrical conductivity, effective mass of the carrier and their temperature dependency using semi-classical BoltzTraP package. Among these three materials BiOCuTe shows higher electrical conductivity. Analyzing their optical properties, we conclude that these materials are useful in the optoelectronic devices such as coating materials, high frequency reflector, infrared radiation detector and emitter and also important to design quantum devices.

  15. First principles study of electronic structure dependent optical properties of oxychalcogenides BiOCuCh (Ch = S, Se, Te)

    Science.gov (United States)

    Ul Islam, A. K. M. Farid; Helal, M. A.; Liton, M. N. H.; Kamruzzaman, M.; Islam, H. M. Tariqul

    2016-11-01

    The optical properties of BiOCuCh and their dependency on the electronic structures are investigated using first principles study. Modified Perdew-Burke-Ernzerhof generalized gradient approximation functional for solids are used to optimize lattice parameters. These optimized lattice parameters are used to calculate the electronic energy band, density of state and optical properties. It is observed that the optical constants are dependent on the energy band gap and also on the contribution of Copper and Chalcogen atoms in the formation of electronic band structure. The obtained results reveal that the optical constants are dominated by the inter-band transitions. In the case of higher incident photon energy these materials behave like metal, where optical constants are dominated by the free carriers. The obtained optical band gaps 0.60, 0.56 and 0.55 eV for BiOCuS, BiOCuSe and BiOCuTe, respectively are consistent with available theoretical results. We also calculate the carrier concentration, electrical conductivity, effective mass of the carrier and their temperature dependency using semi-classical BoltzTraP package. Among these three materials BiOCuTe shows higher electrical conductivity. Analyzing their optical properties, we conclude that these materials are useful in the optoelectronic devices such as coating materials, high frequency reflector, infrared radiation detector and emitter and also important to design quantum devices.

  16. Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111 substrates: a potential route to fabricate topological insulator p-n junction

    Directory of Open Access Journals (Sweden)

    Zhaoquan Zeng

    2013-07-01

    Full Text Available High quality Bi2Te3 and Sb2Te3 topological insulators films were epitaxially grown on GaAs (111 substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111 substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111 substrate is better than a vicinal substrate to provide high quality Bi2Te3 and Sb2Te3 films. Hall and magnetoresistance measurements indicate that p type Sb2Te3 and n type Bi2Te3 topological insulator films can be directly grown on a GaAs (111 substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

  17. Mechanical and thermoelectric properties of Bi2-xSbxTe3 prepared by using encapsulated melting and hot pressing

    Science.gov (United States)

    Jung, Woo-Jin; Kim, Il-Ho

    2016-10-01

    Bi2-xSbxTe3 ( x = 1.4 - 1.7) solid solutions were synthesized by using encapsulated melting (EM) and were consolidated by using hot pressing (HP). The lattice constants decreased with increasing Sb content, which indicated that solid solutions were successfully synthesized. The relative densities of all the hot-pressed specimens were higher than 97.9 %. X-ray diffraction patterns, pole figures and electron backscattered diffraction spectra of all the hot-pressed specimens indicated randomly oriented textures. Very low values of the orientation factor (F) were obtained, Fmin = 0.008 for Bi0.4Sb1.6Te3 hot-pressed at 673 K and Fmax = 0.115 for Bi0.4Sb1.6Te3 hot-pressed at 723 K, which implied that the microstructures were highly isotropic. A bending strength of 46 MPa and a Vickers hardness of 94 Hv were attained for Bi0.4Sb1.6Te3 hot-pressed at 648 K. However, the mechanical properties were degraded with increasing HP temperature owing to grain growth. An increased HP temperature did not affect the electrical properties significanctly. The carrier concentration increased with increasing Sb content, and the specimen with x = 1.4 showed nondegenerate semiconductor behavior whereas those with x ≥ 1.5 behaved as degenerate semiconductors. All specimens showed p-type conduction, which was confirmed from the positive signs of the Seebeck coefficient and the Hall coefficient. The increased Sb content caused a shift in the peak values of the Seebeck coefficient to higher temperatures and an enhancement of the power factor. The electronic thermal conductivity decreased, but the lattice thermal conductivity increased, with increasing Sb content. The lowest theraml conductivity of 0.83 Wm -1K -1 was obtained at 373 K for Bi0.4Sb1.6Te3. The maximum dimensionless figure of merit, ZT max = 1.1, was achieved at 323 K for Bi0.4Sb1.6Te3.

  18. Thermoelectric properties of p-type (Bi0.15Sb0.85)2Te3-PbTe graded thermoelectric materials with different barriers

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The p-type (Bi0.15Sb0.85)2Te3 and PbTe are typical thermoelectric materials used for low and middle temperature range and functional graded materials (FGM) is an inevitable way to widen the working temperature range. Here two segments graded thermoelectric materials (GTM) consisting of (Bi0.15Sb0.85)2Te3, PbTe and different barriers were fabricated by the common hot pressure method. Metals Fe, Mg and Ni were used as barriers between the two segments. The diffusion of different barriers between the barriers and bases were analyzed by electron microprobe analysis (EMA). The phase and crystal structures were determined by X-ray diffraction analysis (XRD). The thermoelectric properties were measured at 303 K along the direction parallel to the pressing direction.The results show that the compositional diffusion occurs when there is no barrier at the interface of the two segments, and the diffusion of Pb is most obvious; as the barrier material, the diffusion of metals Fe, Mg and Ni between different bases is not very obvious,and the thermoelectric properties of GTM is much better than that of the original segment.

  19. Positive dependence of thermal conductivity on temperature in GeTe/Bi2Te3 superlattices: the contribution of electronic and particle wave lattice thermal conductivity

    Science.gov (United States)

    Tong, H.; Lan, F.; Liu, Y. J.; Zhou, L. J.; Wang, X. J.; He, Q.; Wang, K. Z.; Miao, X. S.

    2017-09-01

    Temperature-dependent thermal conductivity of phase-change material, GeTe/Bi2Te3 superlattices, has been investigated in the temperature range of 40-300 K. We have found that thermal conductivity increases with increasing temperature, which is contrary to the common results indicated by other works. In this paper, two possible mechanisms are suggested for this result. One is that the thermal conductivity is affected by the thermal boundary resistance at the interfaces between layers, and the other considers the factor of electronic thermal conductivity in the partially coherent regime which is based on the very wave-particle duality of phonons. Finally, the periodic thickness dependence of the thermal conductivity in GeTe/Bi2Te3 superlattices have been measured at room temperature, and the results indicate the main contribution of electron in the total thermal conductivity and the partially coherent regime of phonon. Thus we believe that the second explanation is more reasonable. The work here deepens the understanding of basic mechanisms of thermal transport in phase-change superlattices, and is instructive in modeling and simulation of phase change memories.

  20. Mechanical properties of bismuth telluride (Bi{sub 2}Te{sub 3}) processed by high pressure torsion (HPT); Propiedades mecanicas del telururo de bismuto (Bi{sub 2}Te{sub 3}) procesado mediante torsion bajo alta presion (HPT)

    Energy Technology Data Exchange (ETDEWEB)

    Santamaria, J. A.; Alkorta, J.; Gil Sevillano, J.

    2013-06-01

    Bismuth telluride, Bi{sub 2}Te{sub 3}, is the main thermoelectric material currently in use for commercial cooling devices or for energy harvesting near room temperature. Because of its highly anisotropic layered structure, Bi{sub 2}Te{sub 3} is very brittle, failing by cleavage along its basal plane. Refining its grain size is expected to increase its toughness with the advantage that, simultaneously, its thermoelectric figure of merit results increased. In this work, powders of the compound have been compacted by conventional methods as well as by severe plastic deformation under high pressure (3 GPa) using high pressure torsion (HPT, one turn at room temperature). Near-theoretical density has been achieved. The hardness and toughness of the compacts have been assessed by micro and nano-indentation. (Author) 11 refs.

  1. Fe-Doping Effect on Thermoelectric Properties of p-Type Bi0.48Sb1.52Te3

    Directory of Open Access Journals (Sweden)

    Hyeona Mun

    2015-03-01

    Full Text Available The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb and dopants (Fe. An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects.

  2. Stabilization of Thermoelectric Properties of the Cu/Bi0.48Sb1.52Te3 Composite for Advantageous Power Generation

    Science.gov (United States)

    Xie, Dewen; Xu, Jingtao; Liu, Zhu; Liu, Guoqiang; Shao, Hezhu; Tan, Xiaojian; Jiang, Haochuan; Jiang, Jun

    2016-09-01

    Bi2Te3 thermoelectric materials have been developed for refrigeration around room temperature. But the ZT values decrease quickly above 400 K, which need to be improved for applications in power generation. In the present work, P-type Cu/BiSbTe alloys have been prepared via a zone melting method followed by spark plasma sintering. Due to the effects of Cu powders, the as-prepared materials exhibit a shift of the peak Seebeck coefficient value towards higher temperature and suppressed lattice thermal conductivity with increasing Cu powders. A peak ZT value as high as 0.87 has been obtained around 500 K in the BiSbTe alloy with 1 wt.% Cu powder addition, and the ZT values stabilize above 0.8 from 375 K to 550 K. This high and stable value for BiSbTe alloys at such a high temperature is very attractive for its application in power generation devices.

  3. Enhanced infrared magneto-optical response of the nonmagnetic semiconductor BiTeI driven by bulk Rashba splitting.

    Science.gov (United States)

    Demkó, L; Schober, G A H; Kocsis, V; Bahramy, M S; Murakawa, H; Lee, J S; Kézsmárki, I; Arita, R; Nagaosa, N; Tokura, Y

    2012-10-19

    We study the magneto-optical (MO) response of the polar semiconductor BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being nonmagnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (up to 3 T). Our first-principles calculations show that the enhanced MO response of BiTeI comes mainly from the intraband transitions between the Rashba-split bulk conduction bands. These transitions connecting electronic states with opposite spin directions become active due to the presence of strong spin-orbit interaction and give rise to distinct features in the MO spectra with a systematic doping dependence. We predict an even more pronounced enhancement in the low-energy MO response and dc Hall effect near the crossing (Dirac) point of the conduction bands.

  4. Enhanced infrared magneto-optical response of the nonmagnetic semiconductor BiTeI driven by bulk Rashba splitting

    Energy Technology Data Exchange (ETDEWEB)

    Demko, L.; Tokura, Y. [Multiferroics Project, ERATO, JST, c/o Department of Applied Physics, University of Tokyo (Japan); Schober, G.A.H. [Institute for Theoretical Physics, University of Heidelberg (Germany); Kocsis, V.; Kezsmarki, I. [Department of Physics, Budapest University of Technology and Economics and Condensed Matter Research Group of the Hungarian Academy of Sciences (Hungary); Bahramy, M.S.; Murakawa, H. [CMRG and CERG, RIKEN ASI (Japan); Lee, J.S.; Arita, R.; Nagaosa, N. [Department of Applied Physics, University of Tokyo (Japan)

    2013-07-01

    We study the magneto-optical (MO) response of the polar semiconducting BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being nonmagnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (up to 3 T). Our first-principles calculations show that the enhanced MO response of BiTeI comes mainly from the intraband transitions between the Rashba-split bulk conduction bands. These transitions connecting electronic states with opposite spin directions become active due to the presence of strong spin-orbit interaction and give rise to distinct features in the MO spectra with a systematic doping dependence. We predict an even more pronounced enhancement in the low-energy MO response and dc Hall effect near the crossing (Dirac) point of the conduction bands.

  5. Work function of bulk-insulating topological insulator Bi2-xSbxTe3-ySey

    Science.gov (United States)

    Takane, Daichi; Souma, Seigo; Sato, Takafumi; Takahashi, Takashi; Segawa, Kouji; Ando, Yoichi

    2016-08-01

    Recent discovery of bulk insulating topological insulator (TI) Bi2-xSbxTe3-ySey paved a pathway toward practical device application of TIs. For realizing TI-based devices, it is necessary to contact TIs with a metal. Since the band-bending at the interface dominates the character of devices, knowledge of TIs' work function is of essential importance. We have determined the compositional dependence of the work function in Bi2-xSbxTe3-ySey by high-resolution photoemission spectroscopy. The obtained work-function values (4.95-5.20 eV) track the energy shift of the surface chemical potential seen by angle-resolved photoemission spectroscopy. The present result serves as a useful guide for developing TI-based electronic devices.

  6. Improved mechanical properties of thermoelectric (Bi0.2Sb0.8)2Te3 by nanostructuring

    Science.gov (United States)

    Lavrentev, M. G.; Osvenskii, V. B.; Parkhomenko, Yu. N.; Pivovarov, G. I.; Sorokin, A. I.; Bulat, L. P.; Kim, H.-S.; Witting, I. T.; Snyder, G. J.; Bublik, V. T.; Tabachkova, N. Yu.

    2016-10-01

    Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.

  7. Synthesis of diluted magnetic semiconductor Bi{sub 2−x}Mn{sub x}Te{sub 3} nanocrystals in a host glass matrix

    Energy Technology Data Exchange (ETDEWEB)

    Silva, R.S. [Instituto de Ciências Exatas, Naturais e Educação (ICENE), Departamento de Física, Universidade Federal do Triângulo Mineiro, 38025-180 Uberaba, Minas Gerais (Brazil); Mikhail, H.D., E-mail: ricardosilva@fisica.uftm.edu.br [Instituto de Ciências Tecnológicas e Exatas (ICTE), Departamento de Engenharia Mecânica, Universidade Federal do Triângulo Mineiro, 38064-200 Uberaba, Minas Gerais (Brazil); Pavani, R. [Instituto de Ciências Exatas, Naturais e Educação (ICENE), Departamento de Física, Universidade Federal do Triângulo Mineiro, 38025-180 Uberaba, Minas Gerais (Brazil); Cano, N.F. [Departamento de Ciências do Mar, Universidade Federal de São Paulo, 11030-400 Santos, São Paulo (Brazil); Silva, A.C.A.; Dantas, N.O. [Instituto de Física, Laboratório de Novos Materiais Isolantes e Semicondutores (LNMIS), Universidade Federal de Uberlândia, 38400-902 Uberlândia, Minas Gerais (Brazil)

    2015-11-05

    Diluted magnetic semiconductors of manganese doped in bismuth-telluride nanocrystals (Bi{sub 2−x}Mn{sub x}Te{sub 3} NCs) were grown in a glass matrix and investigated by Transmission Electron Microscopy, X-Ray Diffraction, Atomic Force Microscopy/Magnetic Force Microscopy, and Electron Paramagnetic Resonance. TEM images showed that the nanocrystals formed within the glass matrix were nearly spherical, with average sizes between 4 and 5 nm, and d{sub 015}-spacing of approximately 0.322 nm, which corresponds to the (015) interplanar distance in Bi{sub 2}Te{sub 3} bulk. The diffraction patterns showed that the diffraction peak associated with the (015) plane of the Bi{sub 2−x}Mn{sub x}Te{sub 3} nanocrystals shifts to larger diffraction angles as manganese (Mn) concentration increases, suggesting that the Mn{sup 2+} ions are substitutional defects occupying Bi sites (Mn{sub Bi}). AFM and MFM measurements showed magnetic phase contrast patterns, providing further evidence of Mn{sup 2+} ion incorporation in the nanocrystal structure. EPR signal of manganese ion incorporation and valence states in the crystalline structure of the Bi{sub 2}Te{sub 3} nanocrystals confirmed the presence of the Mn{sup 2+} state. - Highlights: • Bi{sub 2−x}Mn{sub x}Te{sub 3} NCs were synthesized in a glass matrix by fusion method. • Transmission Electronic Microscopy shows the formation of Bi{sub 2−x}Mn{sub x}Te{sub 3} NCs. • The sp-d exchange interaction in DMS NCs can be evidenced by X Ray-Diffraction and Magnetic Force Microscopy. • Electron Paramagnetic Resonance spectra confirmed that Mn{sup 2+} ions are located in two distinct Bi{sub 2}Te{sub 3} NCs sites.

  8. Power generation by the transverse Seebeck effect in Pb-Bi{sub 2}Te{sub 3} multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Reitmaier, C.; Walther, F.; Lengfellner, H. [Universitaet Regensburg, Institut fuer Experimentelle und Angewandte Physik, Regensburg (Germany)

    2011-11-15

    The transverse Seebeck effect in tilted metal-semiconductor multilayer structures has been exploited for electric power generation. In tilted Pb-Bi{sub 2}Te{sub 3} multilayer samples, coefficients of performance for transverse thermoelectric power generation have been determined, in dependence of temperature difference between hot and cold sample surfaces. The results can be described well by modeling calculations of transverse thermoelectric power generation. (orig.)

  9. Influence of Te doping on the dielectric and optical properties of InBi crystals grown by directional freezing

    Institute of Scientific and Technical Information of China (English)

    C.J. Ajayakumar; A.G. Kunjomana

    2014-01-01

    Stoichiometric pure and tellurium (Te) doped indium bismuthide (InBi) were grown using the directional freezing technique in a fabricated furnace. The X-ray diffraction profiles identified the crystallinity and phase composition. The surface topographical features were observed by scanning electron microscopy and atomic force microscopy. The energy dispersive analysis by X-rays was performed to identify the atomic proportion of elements. Studies on the temperature dependence of dielectric constant (ε), loss tangent (tanδ), and AC conductivity (σac) reveal the existence of a ferroelectric phase transition in the doped material at 403 K. When InBi is doped with tellurium (4.04 at%), a band gap of 0.20 eV can be achieved, and this is confirmed using Fourier transform infrared studies. The results thus show the conversion of semimetallic InBi to a semiconductor with the optical properties suitable for use in infrared detectors.

  10. Annealing Effect on the Thermoelectric Properties of Bi2Te3 Thin Films Prepared by Thermal Evaporation Method

    Directory of Open Access Journals (Sweden)

    Jyun-Min Lin

    2013-01-01

    Full Text Available Bismuth telluride-based compounds are known to be the best thermoelectric materials within room temperature region, which exhibit potential applications in cooler or power generation. In this paper, thermal evaporation processes were adopted to fabricate the n-type Bi2Te3 thin films on SiO2/Si substrates. The influence of thermal annealing on the microstructures and thermoelectric properties of Bi2Te3 thin films was investigated in temperature range 100–250°C. The crystalline structures and morphologies were characterized by X-ray diffraction and field emission scanning electron microscope analyses. The Seebeck coefficients, electrical conductivity, and power factor were measured at room temperature. The experimental results showed that both the Seebeck coefficient and power factor were enhanced as the annealing temperature increased. When the annealing temperature increased to 250°C for 30 min, the Seebeck coefficient and power factor of n-type Bi2Te3-based thin films were found to be about −132.02 μV/K and 6.05 μW/cm·K2, respectively.

  11. Quantum spin Hall insulators in centrosymmetric thin films composed from topologically trivial BiTeI trilayers

    Science.gov (United States)

    Nechaev, I. A.; Eremeev, S. V.; Krasovskii, E. E.; Echenique, P. M.; Chulkov, E. V.

    2017-03-01

    The quantum spin Hall insulators predicted ten years ago and now experimentally observed are instrumental for a break- through in nanoelectronics due to non-dissipative spin-polarized electron transport through their edges. For this transport to persist at normal conditions, the insulators should possess a sufficiently large band gap in a stable topological phase. Here, we theoretically show that quantum spin Hall insulators can be realized in ultra-thin films constructed from a trivial band insulator with strong spin-orbit coupling. The thinnest film with an inverted gap large enough for practical applications is a centrosymmetric sextuple layer built out of two inversely stacked non-centrosymmetric BiTeI trilayers. This nontrivial sextuple layer turns out to be the structure element of an artificially designed strong three-dimensional topological insulator Bi2Te2I2. We reveal general principles of how a topological insulator can be composed from the structure elements of the BiTeX family (X = I, Br, Cl), which opens new perspectives towards engineering of topological phases.

  12. Constructing nanoporous carbon nanotubes/Bi2Te3 composite for synchronous regulation of the electrical and thermal performances

    Science.gov (United States)

    Zhang, Qihao; Xu, Leilei; Zhou, Zhenxing; Wang, Lianjun; Jiang, Wan; Chen, Lidong

    2017-02-01

    Porous nanograined thermoelectric materials exhibit low thermal conductivity due to scattering of phonons by pores, which are favorable for thermoelectric applications. However, the benefit is not large enough to overcome the deficiency in the electrical performance. Herein, an approach is presented to reduce the thermal conductivity and synchronously enhance the electrical conductivity through constructing a nanoporous thermoelectric composite. Carbon nanotubes (CNTs) are truncated and homogeneously dispersed within the Bi2Te3 matrix by a cryogenic grinding (CG) technique for the first time, which efficiently suppress the Bi2Te3 grain growth and create nanopores with the size ranging from dozens to hundreds of nanometers. The lattice thermal conductivity is substantially decreased by broad wavelength phonon scattering resulting from nanopores, increased grain boundaries, and newly formed interfaces. Meanwhile, the electrical conductivity is improved due to the enhanced carrier mobility, which may originate from the bridging effect between the Bi2Te3 grains and CNTs. The maximum ZT is improved by almost a factor of 2 due to the simultaneous optimization of electrical and thermal performances. Our study demonstrates the superiority of constructing a bulk thermoelectric composite with nanopores by the uniform dispersion of CNTs through a CG technique for enhanced thermoelectric properties, which provides a wider approach to thermoelectric nanostructure engineering.

  13. Quantum spin Hall insulators in centrosymmetric thin films composed from topologically trivial BiTeI trilayers

    Science.gov (United States)

    Nechaev, I. A.; Eremeev, S. V.; Krasovskii, E. E.; Echenique, P. M.; Chulkov, E. V.

    2017-01-01

    The quantum spin Hall insulators predicted ten years ago and now experimentally observed are instrumental for a break- through in nanoelectronics due to non-dissipative spin-polarized electron transport through their edges. For this transport to persist at normal conditions, the insulators should possess a sufficiently large band gap in a stable topological phase. Here, we theoretically show that quantum spin Hall insulators can be realized in ultra-thin films constructed from a trivial band insulator with strong spin-orbit coupling. The thinnest film with an inverted gap large enough for practical applications is a centrosymmetric sextuple layer built out of two inversely stacked non-centrosymmetric BiTeI trilayers. This nontrivial sextuple layer turns out to be the structure element of an artificially designed strong three-dimensional topological insulator Bi2Te2I2. We reveal general principles of how a topological insulator can be composed from the structure elements of the BiTeX family (X = I, Br, Cl), which opens new perspectives towards engineering of topological phases. PMID:28252656

  14. Determination of Te, Bi, Ni, Sb and Au by X-ray fluorescence spectrometry following electroenrichment on a copper cathode

    Science.gov (United States)

    Zawisza, Beata; Sitko, Rafał

    2007-10-01

    The electrodepositons of Te, Bi, Ni, Sb and Au from aqueous solution of pH = 1 on the cathode surface have been studied for X-ray fluorescence analysis (XRF). A special holder for a copper electrode has been constructed to perform the electrodeposition process on only one side of the electrode. After electrolysis, the copper electrode can be easily removed from the holder; after rinsing it with water and drying it can be analyzed by XRF. The proposed method of sample preparation and preconcentration of Te, Bi, Ni, Sb, Au provides suitable samples which are devoid of the negative and undesirable effects of XRF analysis, such as particle size and matrix effects. The influence of time on the deposition yield has been examined. The method of preconcentration is efficient. The inhomogeneity of the prepared specimens has been studied using internal standard method. The calibration is based on using synthetic standards, certified reference materials and standard addition method. The best results are achieved by the standard addition method. The agreement between results obtained with XRF analysis and certified values is satisfactory and indicates the usefulness of the proposed method for determination of Te, Bi, Ni, Sb and Au in anode slime.

  15. Orientation-controlled synthesis and characterization of Bi{sub 2}Te{sub 3} nanofilms, and nanowires via electrochemical co-deposition

    Energy Technology Data Exchange (ETDEWEB)

    Erdogan, Ibrahim Y., E-mail: ibrahimyerdogan@gmail.co [Bingol University, Faculty of Sciences and Arts, Department of Chemistry, 12000 Bingol (Turkey); Demir, Umit [Atatuerk University, Faculty of Sciences, Department of Chemistry, 25240 Erzurum (Turkey)

    2011-02-01

    An electrochemical deposition technique based on co-deposition was used to deposit preferentially oriented Bi{sub 2}Te{sub 3} nanostructures (nanofilm, and nanowire). The shared underpotential deposition (UPD) potentials for both Bi and Te co-deposition were determined by cyclic voltammetric measurements. The scanning probe microscopy (scanning tunneling microscopy (STM) and atomic force microscopy (AFM)) and the X-ray diffraction (XRD) data indicated that the electrodeposition of Bi{sub 2}Te{sub 3} results in nanofilm-structured deposits with a preferential orientation at (0 1 5) and nanowired-structured deposits with a preferential orientation at (1 1 0) in acidic and basic (in the presence of ethylenediaminetetraacetic acid (EDTA)) medium, respectively. The results show that the nucleation and growth mechanism follows 3D mode in acidic solutions and 2D mode in basic solution containing EDTA additive. The optical characterization performed by reflection absorption Fourier transform infrared (RA-FTIR) spectroscopy showed that the band gap energy of Bi{sub 2}Te{sub 3} nanostructures depends on the thickness, size, and shape of the nanostructures and the band gap increases as the deposition time decreases. Moreover, the quantum confinement is strengthened in the wire-like deposits relative to the film-like deposits. Energy dispersive X-ray spectroscopy (EDS) analysis demonstrated that Bi{sub 2}Te{sub 3} nanostructures were always in 2:3 stoichiometry, and they were made up of only pure Bi and Te.

  16. Emergence of non-centrosymmetric topological insulating phase in BiTeI under pressure.

    Science.gov (United States)

    Bahramy, M S; Yang, B-J; Arita, R; Nagaosa, N

    2012-02-14

    The spin-orbit interaction affects the electronic structure of solids in various ways. Topological insulators are one example in which the spin-orbit interaction leads the bulk bands to have a non-trivial topology, observable as gapless surface or edge states. Another example is the Rashba effect, which lifts the electron-spin degeneracy as a consequence of the spin-orbit interaction under broken inversion symmetry. It is of particular importance to know how these two effects, that is, the non-trivial topology of electronic states and the Rashba spin splitting, interplay with each other. Here we show through sophisticated first-principles calculations that BiTeI, a giant bulk Rashba semiconductor, turns into a topological insulator under a reasonable pressure. This material is shown to exhibit several unique features, such as a highly pressure-tunable giant Rashba spin splitting, an unusual pressure-induced quantum phase transition, and more importantly, the formation of strikingly different Dirac surface states at opposite sides of the material.

  17. Investigation of Optical Nonlinearities in Bi-Doped Se-Te Chalcogenide Thin Films

    Science.gov (United States)

    Yadav, Preeti; Sharma, Ambika

    2015-03-01

    The present paper reports the nonlinear optical properties of chalcogenide Se85- x Te15Bi x (0 ≤ x ≤ 5) thin films. The formulation proposed by Boling, Fournier, and Snitzer and Tichy and Ticha has been used to compute the nonlinear refractive index n 2. The two-photon absorption coefficient β 2, and first- and third-order susceptibilities [ χ (1) and χ (3)] are also reported. The nonlinear refractive index n 2 is well correlated with the linear refractive index n and Wemple-DiDomenico (WDD) parameters, in turn depending on the density ρ and molar volume V m of the system. The density of the system is calculated experimentally by using Archimedes' principle. The linear optical parameters, viz. n, WDD parameters, and optical bandgap E g, are measured experimentally using ellipsometric curves obtained by spectrophotometry. The composition-dependent behavior of n 2 is analyzed on the basis of various parameters, viz. density, bond distribution, cohesive energy (CE), and optical bandgap E g, of the system. The variation of n 2 and β 2 with changing bandgap E g is also reported. The values of n 2 and χ (3) of the investigated chalcogenides are compared with those of pure silica, oxide, and other Se-based glasses.

  18. Magnetic ordering in Ho-doped Bi{sub 2}Te{sub 3} topological insulator

    Energy Technology Data Exchange (ETDEWEB)

    Figueroa, A.I.; Van der Laan, G.; Hesjedal, T. [Magnetic Spectroscopy Group, Diamond Light Source, Didcot (United Kingdom); Harrison, S.E. [Department of Physics, Clarendon Laboratory, University of Oxford (United Kingdom); Department of Electrical Engineering, Stanford University, Stanford, CA (United States); Collins-McIntyre, L.J. [Department of Physics, Clarendon Laboratory, University of Oxford (United Kingdom)

    2016-06-15

    We investigate the magnetic properties of Ho-doped Bi{sub 2}Te{sub 3} thin films grown by molecular beam epitaxy. Analysis of the polarized X-ray absorption spectra at the Ho M{sub 5} absorption edge gives an effective 4f magnetic moment which is ∝45% of the Hund's rule ground state value. X-ray magnetic circular dichroism (XMCD) shows no significant anisotropy, which suggests that the reduced spin moment is not due to the crystal field effects, but rather the presence of non-magnetic or antiferromagnetic Ho sites. Extrapolating the temperature dependence of the XMCD measured in total electron yield and fluorescence yield mode in a field of 7 T gives a Curie-Weiss temperature of and vartheta;{sub CW} ∼ -30 K, which suggests antiferromagnetic ordering, in contrast to the paramagnetic behavior observed with SQUID magnetometry. From the anomaly of the XMCD signal at low temperatures, a Neel temperature T{sub N} between 10 K and 25 K is estimated. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Effect of compositional variation on the electrical properties of Se-Te-Bi-Ag glassy alloy

    Science.gov (United States)

    Kumar, Anup; Heera, Pawan; Sharma, Raman

    2015-05-01

    In this paper we have studied the effect of Ag addition on electrical properties of Se80.5Bi1.5Te18-yAgy (y = 1.0, 1.5 and 2.0 at. %) glassy system by using digital picometer (Keithley, model 6487) in the voltage range 0-300V. I-V study reveals that the glassy alloys under study exhibit ohmic behavior at low voltage and non-ohmic at high voltage. The field dependence studies for pellets reveal the ohmic nature of current for voltage less than 60V and non-ohmic nature of current for voltage greater than 60V. At higher voltage, greater than 60V, thermal effects come into plays which result in an increase in electrical conductivity. The d.c. conductivity is found to increase with an increase in Ag content. The conduction mechanism is discussed in terms of Poole-Frenkel conduction mechanism. The linearity of the plots between ln(I) and V1/2 shows that the conduction mechanism in the higher voltage range is of Poole-Frenkel type.

  20. Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

    Science.gov (United States)

    Manna, S.; Kamlapure, A.; Cornils, L.; Hänke, T.; Hedegaard, E. M. J.; Bremholm, M.; Iversen, B. B.; Hofmann, Ph.; Wiebe, J.; Wiesendanger, R.

    2017-01-01

    The discovery of high-temperature superconductivity in Fe-based compounds triggered numerous investigations on the interplay between superconductivity and magnetism, and on the enhancement of transition temperatures through interface effects. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture remains elusive because of the lack of atomically resolved data. Here we present spin-polarized scanning tunnelling spectroscopy of ultrathin FeTe1-xSex (x=0, 0.5) films on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to Tc~6 K for one unit cell FeTe grown on Bi2Te3, in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators.

  1. Process controllability of thermoelectric properties of (Bi2Te3)(0.2)(Sb2Te3)(0.8) on the root of bulk mechanical alloying; Bulk MA ni yori soseisareru (Bi2Te3)(0.2)(Sb2Te3)0.8 netsuden zairyo tokusei no process izonsei

    Energy Technology Data Exchange (ETDEWEB)

    Iwaisako, Y.; Aizawa, T. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering; Yamamoto, A.; Ota, T. [Electrotechnical Laboratory, Tsukuba (Japan)

    1998-10-15

    Bulk Mechanical Alloying (BMA) is proposed to produce p-type Bi2Te3-Sb2Te3 thermoelectric materials with large yield and without any contamination. Because of the solid-state alloyment through this process, no melting nor solidification process is necessary to yield the targeting composition of this type of thermoelectric materials. Furthermore, hot pressing is applied for densification by varying both the pressure and the holding temperature. Process parameter dependency of thermoelectric properties is investigated for three different BMA samples. 6 refs., 9 figs.

  2. Growth and characterization of large weak topological insulator Bi2TeI single crystal by Bismuth self-flux method

    Science.gov (United States)

    Ryu, Gihun; Son, Kwanghyo; Schütz, Gisela

    2016-04-01

    Two dimensional (2D) topological insulators (TIs) with a quantum spin Hall (QSH) effect feature edge states (ESs) that are topologically protected from backscattering. Bi2TeI with 2D Bismuth bilayer is one of the representative compounds of weak topological insulator. However, nobody has prepared a high quality single crystal with a millimeter size so far. Here, we have successfully synthesized a large single crystal sized up to "millimeter (~5×5 mm2)" using the Bismuth self-flux method. And we also found its giant anisotropy transport behavior in Bi2TeI of a 2D TI constructed from nontrivial Bi bilayers (Quantum Spin Hall phase) capped by a trivial Te-Bi-I layer.

  3. Ion beam irradiation effect on thermoelectric properties of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Gaosheng [Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY 11794 (United States); Zuo, Lei, E-mail: leizuo@vt.edu [Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY 11794 (United States); Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061 (United States); Lian, Jie [Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Wang, Yongqiang [Materials Science & Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87544 (United States); Chen, Jie [Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061 (United States); Longtin, Jon [Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY 11794 (United States); Xiao, Zhigang [Department of Electrical Engineering, Alabama A& M University, Normal, AL 35762 (United States)

    2015-09-01

    Thermoelectric energy harvesting is a very promising application in nuclear power plants for self-maintained wireless sensors. However, the effects of intensive radiation on the performance of thermoelectric materials under relevant reactor environments such as energetic neutrons are not fully understood. In this work, radiation effects of bismuth telluride (Bi{sub 2}Te{sub 3}) and antimony telluride (Sb{sub 2}Te{sub 3}) thermoelectric thin film samples prepared by E-beam evaporation are investigated using Ne{sup 2+} ion irradiations at different fluences of 5 × 10{sup 14}, 10{sup 15}, 5 × 10{sup 15} and 10{sup 16} ions/cm{sup 2} with the focus on the transport and structural properties. Electrical conductivities, Seebeck coefficients and power factors are characterized as ion fluence changes. X-ray diffraction (XRD) and transmission electron microscopy (TEM) of the samples are obtained to assess how phase and microstructure influence the transport properties. Carrier concentration and Hall mobility are obtained from Hall effect measurements, which provide further insight into the electrical conductivity and Seebeck coefficient mechanisms. Positive effects of ion irradiations from Ne{sup 2+} on thermoelectric material property are observed to increase the power factor to 208% for Bi{sub 2}Te{sub 3} and 337% for Sb{sub 2}Te{sub 3} materials between fluence of 1 and 5 × 10{sup 15} cm{sup 2}, due to the increasing of the electrical conductivity as a result of ionization radiation-enhanced crystallinity. However, under a higher fluence, 5 × 10{sup 15} cm{sup 2} in this case{sub ,} the power factor starts to decrease accordingly, limiting the enhancements of thermoelectric materials properties under intensive radiation environment.

  4. Thermoelectric properties of I-doped n-type Bi2Te3-based material prepared by hydrothermal and subsequent hot pressing

    Directory of Open Access Journals (Sweden)

    Fang Wu

    2017-04-01

    Full Text Available I-doped Bi2Te3−xIx (x=0, 0.05, 0.1, 0.2 flower-like nanoparticles were synthesized by a hydrothermal method through a careful adjustment of the amount of ethylenediamine tetraacetic acid surfactant. The nanopowders of flower-like nanoparticles were hot-pressed into bulk pellets and the thermoelectric properties of the pellets were investigated. The results showed that I-doping decreased the electrical resistivity effectively, and the thermal conductivitives of the Bi2Te3−xIx bulk samples was lower because of the closer atomic mass of I compared to Te. As a result, a ZT value of 1.1 was attained at 448 K for the Bi2Te2.9I0.1 sample.

  5. Thermal Stability of P-Type BiSbTe Alloys Prepared by Melt Spinning and Rapid Sintering.

    Science.gov (United States)

    Zheng, Yun; Tan, Gangjian; Luo, Yubo; Su, Xianli; Yan, Yonggao; Tang, Xinfeng

    2017-06-06

    P-type BiSbTe alloys have been widely implemented in waste heat recovery from low-grade heat sources below 600 K, which may involve assorted environments and conditions, such as long-term service, high-temperature exposure (generally 473-573 K) and mechanical forces. It is important to evaluate the service performance of these materials in order to prevent possible failures in advance and extend the life cycle. In this study, p-type Bi0.5Sb1.5Te₃ commercial zone-melting (ZM) ingots were processed by melt spinning and subsequent plasma-activated sintering (MS-PAS), and were then subjected to vacuum-annealing at 473 and 573 K, respectively, for one week. The results show that MS-PAS samples exhibit excellent thermal stability when annealed at 473 K. However, thermal annealing at 573 K for MS-PAS specimens leads to the distinct sublimation of the element Te, which degrades the hole concentration remarkably and results in inferior thermoelectric performance. Furthermore, MS-PAS samples annealed at 473 K demonstrate a slight enhancement in flexural and compressive strengths, probably due to the reduction of residual stress induced during the sintering process. The current work guides the reliable application of p-type Bi0.5Sb1.5Te₃ compounds prepared by the MS-PAS technique.

  6. Thermoelectric Properties of Alumina-Doped Bi0.4Sb1.6Te3 Nanocomposites Prepared through Mechanical Alloying and Vacuum Hot Pressing

    Directory of Open Access Journals (Sweden)

    Chung-Kwei Lin

    2015-11-01

    Full Text Available In this study, γ-Al2O3 particles were dispersed in p-type Bi0.4Sb1.6Te3 through mechanical alloying to form γ-Al2O3/Bi0.4Sb1.6Te3 composite powders. The composite powders were consolidated using vacuum hot pressing to produce nano- and microstructured composites. Thermoelectric (TE measurements indicated that adding an optimal amount of γ-Al2O3 nanoparticles improves the TE performance of the fabricated composites. High TE performances with figure of merit (ZT values as high as 1.22 and 1.21 were achieved at 373 and 398 K for samples containing 1 and 3 wt % γ-Al2O3 nanoparticles, respectively. These ZT values are higher than those of monolithic Bi0.4Sb1.6Te3 samples. The ZT values of the fabricated samples at 298–423 K are 1.0–1.22; these ZT characteristics make γ-Al2O3/Bi0.4Sb1.6Te3 composites suitable for power generation applications because no other material with a similarly high ZT value has been reported at this temperature range. The achieved high ZT value may be attributable to the unique nano- and microstructures in which γ-Al2O3 nanoparticles are dispersed among the grain boundary or in the matrix grain, as revealed by high-resolution transmission electron microscopy. The dispersed γ-Al2O3 nanoparticles thus increase phonon scattering sites and reduce thermal conductivity. The results indicated that the nano- and microstructured γ-Al2O3/Bi0.4Sb1.6Te3 alloy can serve as a high-performance material for application in TE devices.

  7. An optical study of vacuum evaporated Se 85-xTe 15Bi x chalcogenide thin films

    Science.gov (United States)

    Ambika; Barman, P. B.

    2010-02-01

    Thin films of Se 85-xTe 15Bi x ( x=0, 1, 2, 3, 4, 5) glassy alloys prepared by melt quenching technique, are deposited on glass substrate using thermal evaporation technique under vacuum. The analysis of transmission spectra, measured at normal incidence, in the spectral range 400-1500 nm helphelps us in the optical characterization of thin films under study. Well -known Swanepoel's method is employed to determine the refractive index ( n) and film thickness ( d). The increase in n with increasing Bi content over the entire spectral range is related to the increased polarizability of the larger Bi atom (atomic radius 1.46 Å) compared with the Se atom (atomic radius 1.16 Å). Dispersion energy ( E d), average energy gap ( E0) and static refractive index ( n0) isare calculated using Wemple-DiDomenico model (WDD). The value of absorption coefficient ( α) and hence extinction coefficient ( k) hashave been determined from transmission spectra. Optical band gap ( E g) is estimated using Tauc's extrapolation and is found to decrease from 1.46 to 1.24 eV with the Bi addition. This behavior of optical band gap is interpreted in terms of electronegativity difference of the atoms involved and cohesive energy of the system.

  8. Preparation of P-type Bi2Te3 based thermoelectric material by hot pressing%热压法制备P型Bi2Te3基温差电材料研究

    Institute of Scientific and Technical Information of China (English)

    葛晓丽; 杨文昭; 张丽丽

    2012-01-01

    In this article,with the p-type pseudo-binary thermoelectric material Bi2Te3-Sb2Te3 as the precursor,the samples were prepared with vacuum hot pressing technology,and their properties were measured before and after the hot pressing.The results indicate that the hot pressing samples have higher density and mechanical strength,which improves the phenomenon of splitting along the cleavage plane.Meanwhile,the hot pressing method changes the crystal structure and carrier concentration in the materials,which lead to the decrease of electric conductivity and the change of Seebeck coefficient,and then results in the decrease of thermal conductivity.For comprehensive consideration,the thermoelectric figure of merit of the hot pressing material is basically equivalent to that of zone-melting samples,but the mechanical properties of the former are much better than the later,which will provide a great advantage in practical application.%以P型赝二元Bi2Te3-Sb2Te3体系温差电材料区熔晶棒为前驱体,采用真空热压烧结法制备材料样品.测试热压前后材料样品性能,测试结果表明:热压样品较区熔材料具有更高的致密度和机械强度,改善了Bi2Te3基温差电材料易沿解理面发生劈裂的现象;同时,热压工艺促使了材料内部晶体结构和载流子浓度的变化,引起材料电导率的降低和塞贝克系数的改变,导致材料热导率显著降低.综合考虑材料各项性能参数,热压材料的热电优值基本与区熔材料相当,但前者的力学强度明显优于后者,在实际使用中将占有明显的优势.

  9. Electrodeposition of textured Bi{sub 27}Sb{sub 28}Te{sub 45} nanowires with enhanced electrical conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Hasan, Maksudul, E-mail: maksudul.hasan@tyndall.ie [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland); Gautam, Devendraprakash [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland); Enright, Ryan [Thermal Management Research Group, Efficient Energy Transfer Department, Bell Labs Ireland, Alcatel-Lucent Ireland Ltd., Dublin (Ireland)

    2016-04-15

    This work presents the template based pulsed potential electrodeposition technique of highly textured single crystalline bismuth antimony telluride (Bi{sub 1-x}Sb{sub x}){sub 2}Te{sub 3} nanowires from a single aqueous electrolyte. Cyclic voltammetry was used as an electroanalytical tool to assess the effect of the precursor concentrations on the composition of the deposits and to determine the deposition potential for each element. Pulsed potential electrodeposition was then applied on a gold-coated anodised alumina template to examine the effect of the pulse parameters on the composition and texture of Bi{sub 27}Sb{sub 28}Te{sub 45} nanowires. The nanowires are cylindrical in shape formed during the deposition inside the porous template and highly textured as they are decorated with sparse distribution of small crystal domains. The electrical conductivity (24.1 × 10{sup 4} S m{sup −1}) of a single nanowire was measured using a four-point probe technique implemented on a custom fabricated test chip. In this work, we demonstrated that crystal orientation with respect to the transport direction controlled by tuning the pulsed electrodeposition parameters. This allowed us to realise electrical conductivities ∼2.5 times larger than Sb doped bismuth-tellurium based ternary material systems and similar to what is typically seen in binary systems. - Highlights: • Pulsed electrodeposition is described towards fabrication of (Bi{sub 1-x}Sb{sub x}){sub 2}Te{sub 3} nanowires. • The adopted method is compatible with existing CMOS process. • The nanowires were fabricated as highly textured to enhance phonon scattering. • The electrical conductivity is ∼2.5 times larger than the current ternary materials.

  10. Hydrothermal Synthesis Au-Bi2Te3 Nanocomposite Thermoelectric Film with a Hierarchical Sub-Micron Antireflection Quasi-Periodic Structure

    Directory of Open Access Journals (Sweden)

    Junlong Tian

    2015-06-01

    Full Text Available In this work, Au-Bi2Te3 nanocomposite thermoelectric film with a hierarchical sub-micron antireflection quasi-periodic structure was synthesized via a low-temperature chemical route using Troides helena (Linnaeus forewing (T_FW as the biomimetic template. This method combines chemosynthesis with biomimetic techniques, without the requirement of expensive equipment and energy intensive processes. The microstructure and the morphology of the Au-Bi2Te3 nanocomposite thermoelectric film was analyzed by X-ray diffraction (XRD, field-emission scanning-electron microscopy (FESEM, and transmission electron microscopy (TEM. Coupled the plasmon resonances of the Au nanoparticles with the hierarchical sub-micron antireflection quasi-periodic structure, the Au-Bi2Te3 nanocomposite thermoelectric film possesses an effective infrared absorption and infrared photothermal conversion performance. Based on the finite difference time domain method and the Joule effect, the heat generation and the heat source density distribution of the Au-Bi2Te3 nanocomposite thermoelectric film were studied. The heterogeneity of heat source density distribution of the Au-Bi2Te3 nanocomposite thermoelectric film opens up a novel promising technique for generating thermoelectric power under illumination.

  11. Tuning the Dirac cone of the topological insulator Bi{sub 2}Te{sub 3} thin films by substitutional nonmagnetic atoms

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wenliang; Zhang, Zhen [Hunan Key Laboratory of Micro-Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Laboratory for Quantum Engineering and Micro-Nano Energy Technology and Faculty of Materials and Optoelectronic Physics, Xiangtan University, Xiangtan 411105, Hunan (China); Peng, Xiangyang, E-mail: xiangyang_peng@xtu.edu.cn [Hunan Key Laboratory of Micro-Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Laboratory for Quantum Engineering and Micro-Nano Energy Technology and Faculty of Materials and Optoelectronic Physics, Xiangtan University, Xiangtan 411105, Hunan (China); Zhong, Jianxin, E-mail: jxzhong@xtu.edu.cn [Hunan Key Laboratory of Micro-Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Laboratory for Quantum Engineering and Micro-Nano Energy Technology and Faculty of Materials and Optoelectronic Physics, Xiangtan University, Xiangtan 411105, Hunan (China)

    2015-01-01

    Based on first‐principles calculations, it is found that the Dirac cone of Bi{sub 2}Te{sub 3} film, which is buried in the bulk valence bands, can be tuned by the substitutional nonmagnetic atoms. It is found that substituting the Bi layer at the two ends of Bi{sub 2}Te{sub 3} films with group III atoms Al, Ga, In and Tl, which have lower electronegativity than Bi atoms, can lead to an isolated Dirac cone with the Dirac point shifted into the bulk band gap and located on the Fermi level. Substituting the more electronegative Se, S and O atoms for Te atoms at the top and bottom layers of Bi{sub 2}Te{sub 3} film, only the most electronegative O atoms give rise to a nearly ideal Dirac cone. The charge distribution of the resulting isolated Dirac point state is concentrated at the Te layers facing the van der Waals layers and vanishes in the middle of the quintuple layers.

  12. Experimental and first-principles study of the electronic transport properties of strained Bi2Te3 thin films on a flexible substrate

    Science.gov (United States)

    Inamoto, Takuya; Takashiri, Masayuki

    2016-09-01

    On the basis of an experimental and first-principles study, strain effects on the thermoelectric properties of bismuth telluride (Bi2Te3) thin films were investigated. Bi2Te3 thin films were deposited on flexible polyimide substrates using a radio frequency magnetron sputtering method at a substrate temperature of 200 °C. Prior to deposition, various compressive and tensile bending strains were applied to the films by changing the bending radii of the flexible substrates. The structural and thermoelectric properties of the completed samples were analyzed. It was found that the lattice parameters of all samples exhibited smaller values compared to that of standard data for Bi2Te3 (JCPDS 15-0863) because the substrates might have shrunk during the film deposition, indicated by the fact that all the samples presented various compressive lattice strains. A theoretical analysis was performed using the first-principles study based on density functional theory. We calculated the electronic band structures for Bi2Te3 with the different lattice strains and predicted the thermoelectric properties based on the semi-classical Boltzmann transport equation in the rigid band approximation. The lowest conduction band edge in the Bi2Te3 band structure narrowed as the compressive lattice strain increased, indicating that the effective mass became smaller. Finally, the experimentally measured thermoelectric properties were compared with those obtained by the calculation. It was found that the calculated results were in good agreement with the experimental results.

  13. Thermoelectric properties of p-type Bi-Sb-Te compositionally graded thermoelectric materials with different barriers

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    In order to find more suitable materials as barriers and to improve the thermoelectric properties, p-type (BiSb)2Te3 (0.85, 0.9) two segments compositionally graded thermoelectric materials (CGTM) with different barriers were fabricated by conventional hot pressure method. Metals Fe, Co, Cu and Al were used as barriers between two segments. The effects of different barriers on thermoelectric properties of CGTM were investigated. The results show that metal Fe is more stable and suitable as the barrier.

  14. Effects of Sb Content (x) on (Bi(1-x)Sb(x))2Te3 Thermoelectric Thin Film Deposited by Effusion Cell Evaporator.

    Science.gov (United States)

    Yong, Ho; Na, Sekwon; Gang, Jun-Gu; Jeon, Seong-Jae; Hyun, Seungmin; Lee, Hoo-Jeong

    2015-10-01

    This paper investigates the effects of the Sb content (x) on (Bi(1-x)Sb(x))2Te3 thermoelectric films with x changing widely from 0 (Sb2Te3) to 1 (Bi2Te3). First, the XRD analysis discloses that with the Sb content (x) increasing, the phase changed gradually from Bi2Te3 to Sb2Te3 as Sb atoms replaced substitutionally Bi atoms. Further microstructure analysis reveals that an extensive grain growth occurred during post-annealing for the samples with high Sb contents. According to the measurement of electrical and thermoelectric properties, the polarity of the charge carrier and Seebeck coefficient switched n-type to p-type in the range of x = 0.45~0.63. For the n-type samples, the power factor is highest when x = 0.18 around 46.01 μW/K(2) whereas Sb2Te3, for the p-type samples, shows the highest value, 62.48 μW/K(2)cm.

  15. From thermoelectric bulk to nanomaterials: Current progress for Bi{sub 2}Te{sub 3} and CoSb{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Peranio, N.; Eibl, O. [Institute of Applied Physics, Eberhard Karls University of Tuebingen (Germany); Baessler, S.; Nielsch, K. [Institute of Nanostructure and Solid State Physics, University of Hamburg (Germany); Klobes, B. [Juelich Centre for Neutron Science JCNS and Peter Gruenberg Institute PGI, JARA-FIT, Forschungszentrum Juelich GmbH (Germany); Hermann, R.P. [Juelich Centre for Neutron Science JCNS and Peter Gruenberg Institute PGI, JARA-FIT, Forschungszentrum Juelich GmbH (Germany); Faculte des Sciences, Universite de Liege (Belgium); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Daniel, M. [Institute of Physics, Technische Universitaet Chemnitz (Germany); Albrecht, M. [Institute of Physics, Technische Universitaet Chemnitz (Germany); Institute of Physics, University of Augsburg (Germany); Goerlitz, H.; Pacheco, V. [Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Dresden (Germany); Bedoya-Martinez, N.; Hashibon, A.; Elsaesser, C. [Fraunhofer-Institut fuer Werkstoffmechanik IWM, Freiburg (Germany)

    2016-03-15

    Bi{sub 2}Te{sub 3} and CoSb{sub 3} based nanomaterials were synthesized and their thermoelectric, structural, and vibrational properties analyzed to assess and reduce ZT-limiting mechanisms. The same preparation and/or characterization methods were applied in the different materials systems. Single-crystalline, ternary p-type Bi{sub 15}Sb{sub 29}Te{sub 56}, and n-type Bi{sub 38}Te{sub 55}Se{sub 7} nanowires with power factors comparable to nanostructured bulk materials were prepared by potential-pulsed electrochemical deposition in a nanostructured Al{sub 2}O{sub 3} matrix. p-type Sb{sub 2}Te{sub 3}, n-type Bi{sub 2}Te{sub 3}, and n-type CoSb{sub 3} thin films were grown at room temperature using molecular beam epitaxy and were subsequently annealed at elevated temperatures. This yielded polycrystalline, single phase thin films with optimized charge carrier densities. In CoSb{sub 3} thin films the speed of sound could be reduced by filling the cage structure with Yb and alloying with Fe yielded p-type material. Bi{sub 2}(Te{sub 0.91}Se{sub 0.09}){sub 3}/SiC and (Bi{sub 0.26}Sb{sub 0.74}){sub 2}Te{sub 3}/SiC nanocomposites with low thermal conductivities and ZT values larger than 1 were prepared by spark plasma sintering. Nanostructure, texture, chemical composition, as well as electronic and phononic excitations were investigated by X-ray diffraction, nuclear resonance scattering, inelastic neutron scattering, Moessbauer spectroscopy, and transmission electron microscopy. For Bi{sub 2}Te{sub 3} materials, ab-initio calculations together with equilibrium and non-equilibrium molecular dynamics simulations for point defects yielded their formation energies and their effect on lattice thermal conductivity, respectively. Current advances in thermoelectric Bi{sub 2}Te{sub 3} and CoSb{sub 3} based nanomaterials are summarized. Advanced synthesis and characterization methods and theoretical modeling were combined to assess and reduce ZT-limiting mechanisms in these

  16. Effect of annealing temperature on photoelectrochemical properties of nanocrystalline MoBi2(Se0.5Te0.5)5 thin films

    Science.gov (United States)

    Salunkhe, Manauti; Pawar, Nita; Patil, P. S.; Bhosale, P. N.

    2014-10-01

    Nanocrystalline MoBi2(Se0.5Te0.5)5 thermoelectric thin films have been deposited on ultrasonically cleaned glass and FTO-coated glass substrates by Arrested Precipitation Technique. The change in properties of MoBi2(Se0.5Te0.5)5 thin films were examined after annealing at the temperature 473 K for 3 h. The structural, morphological, compositional and electrical properties of thin films were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, etc. Thermoelectric properties of the thin films have been evaluated by measurements of electrical conductivity and Seebeck coefficient in the temperature range 300-500 K. Our aim is to investigate the effect of annealing on behaviour of MoBi2(Se0.5Te0.5)5 thin films along with photoelectrochemical properties.

  17. The energy spectrum of PbBi4Te7 on evidence derived from light reflection and absorption coefficients

    Directory of Open Access Journals (Sweden)

    Alexander N. Veis

    2015-10-01

    The compound under study was established to exhibit a narrow direct forbidden gap. It was found that its optical band gap Egopt=0.31eV, an energy gap parameter Eg0 between absolute extremums of the valence and conduction bands in the sample with the Hall electron concentration of 5.45 × 1020 cm–3 was equal to 0.08–0.12 eV, and a mdn/mdp ratio (effective masses of electron and hole states densities was equal to about unity. No other subbands located near the absolute extremum of conduction band were revealed in PbBi4Te7. The electron dispersion law was also found to be non-parabolic in this matter. The law involved can be described in the context of Kane non-parabolisity model taking into account an exchange interaction of free electrons. It was shown that the most probable value of the Eg0 parameter fell within the range from 0.16 to 0.24 eV for PbBi4Te7 with nondegenerate free electron gas.

  18. Effect of nanocrystallinity on lattice dynamics in Bi{sub 2}Te{sub 3} based thermoelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Klobes, B. [Juelich Centre for Neutron Science JCNS and Peter Gruenberg Institute PGI, JARA-FIT, Forschungszentrum Juelich GmbH, Juelich (Germany); Bessas, D. [European Synchrotron Radiation Facility, Grenoble (France); Juranyi, F. [Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen (Switzerland); Goerlitz, H.; Pacheco, V. [Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM-DD), Dresden (Germany); Hermann, R.P. [Juelich Centre for Neutron Science JCNS and Peter Gruenberg Institute PGI, JARA-FIT, Forschungszentrum Juelich GmbH, Juelich (Germany); Faculte des Sciences, Universite de Liege (Belgium)

    2015-01-01

    The lattice dynamics in as-cast and nanocrystalline thermoelectric Bi{sub 2}Te{sub 3} based p-type and n-type material were investigated using inelastic neutron scattering. Generalized densities of phonon states show substantial agreement between the lattice dynamics in as-cast samples and previous studies. The lattice dynamics in the nanocrystalline materials differ significantly from its as-cast counterparts in the acoustic phonon regime. In nanocrystalline p-type and n-type compounds, the average acoustic phonon group velocity was found to be reduced to 80(5)% and 95(2)% of the value in as-cast material. It is argued that point-defect and strain contrast scattering may play an important role for the understanding of lattice thermal conductivity in (nanocrystalline) Bi{sub 2}Te{sub 3} based thermoelectrics beside the observed decrease of sound velocity. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Thermoelectric Properties of Bi2Te3-y Se y :I m Prepared by Mechanical Alloying and Hot Pressing

    Science.gov (United States)

    Eum, A.-Young; Choi, Soon-Mok; Lee, Soonil; Seo, Won-Seon; Park, Jae-Soung; Yang, Seung-Ho; Kim, Il-Ho

    2016-08-01

    Bi2Te3-y Se y :I m (y = 0.15-0.6 and m = 0.0025-0.01) solid solutions were prepared by mechanical alloying and hot pressing. The lattice constants that were measured from x-ray diffraction patterns decreased linearly with increasing Se content, but they were not changed remarkably by I doping. The average relative densities of the hot-pressed specimens are higher than 97%. All of the specimens exhibited n-type conductions in the measured temperature range from 323 K to 523 K, and their electrical conductivity decreased slightly with increasing temperature, indicating degenerate semiconductor behaviors. The electrical conductivity decreased with increasing Se content, whereas it was increased by I doping, and this is in contrast with the Seebeck coefficient; this resulted from the changes of the electron concentrations due to the Se substitution and the I doping. The thermal conductivity decreased with increasing Se content, and this is the result of both the decreased electronic thermal conductivity due to the decreased carrier concentration and the decreased lattice thermal conductivity due to the increased alloy scattering. The maximum dimensionless figure of merit for Bi2Te2.4Se0.6, ZT max = 0.84 at 473 K, is due to its low thermal conductivity and high Seebeck coefficient.

  20. Pressure tuning the Fermi level through the Dirac point of giant Rashba semiconductor BiTeI.

    Science.gov (United States)

    VanGennep, D; Maiti, S; Graf, D; Tozer, S W; Martin, C; Berger, H; Maslov, D L; Hamlin, J J

    2014-08-27

    We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeI under applied pressures up to ∼2 GPa. We observe one high frequency oscillation at all pressures and one low frequency oscillation that emerges between ∼0.3-0.7 GPa indicating the appearance of a second small Fermi surface. BiTeI has a conduction band bottom that is split into two sub-bands due to the strong Rashba coupling, resulting in a 'Dirac point'. Our results suggest that the chemical potential starts below the Dirac point in the conduction band at ambient pressure and moves upward, crossing it as pressure is increased. The presence of the chemical potential above this Dirac point results in two Fermi surfaces. We present a simple model that captures this effect and can be used to understand the pressure dependence of our sample parameters. These extracted parameters are in quantitative agreement with first-principles calculations and other experiments. The parameters extracted via our model support the notion that pressure brings the system closer to the predicted topological quantum phase transition.

  1. Growth, characterization, and transport properties of ternary (Bi1-x Sb x )2Te3 topological insulator layers.

    Science.gov (United States)

    Weyrich, C; Drögeler, M; Kampmeier, J; Eschbach, M; Mussler, G; Merzenich, T; Stoica, T; Batov, I E; Schubert, J; Plucinski, L; Beschoten, B; Schneider, C M; Stampfer, C; Grützmacher, D; Schäpers, Th

    2016-12-14

    Ternary (Bi1-x Sb x )2Te3 films with an Sb content between 0 and 100% were deposited on a Si(1 1 1) substrate by means of molecular beam epitaxy. X-ray diffraction measurements confirm single crystal growth in all cases. The Sb content is determined by x-ray photoelectron spectroscopy. Consistent values of the Sb content are obtained from Raman spectroscopy. Scanning Raman spectroscopy reveals that the (Bi1-x Sb x )2Te3 layers with an intermediate Sb content show spatial composition inhomogeneities. The observed spectra broadening in angular-resolved photoemission spectroscopy (ARPES) is also attributed to this phenomena. Upon increasing the Sb content from x  =  0 to 1 the ARPES measurements show a shift of the Fermi level from the conduction band to the valence band. This shift is also confirmed by corresponding magnetotransport measurements where the conductance changes from n- to p-type. In this transition region, an increase of the resistivity is found, indicating a location of the Fermi level within the band gap region. More detailed measurements in the transition region reveals that the transport takes place in two independent channels. By means of a gate electrode the transport can be changed from n- to p-type, thus allowing a tuning of the Fermi level within the topologically protected surface states.

  2. Effect of annealing on the optical properties of amorphous Se79Te10Sb4Bi7 thin films

    Science.gov (United States)

    Nyakotyo, H.; Sathiaraj, T. S.; Muchuweni, E.

    2017-07-01

    Thin films of Se79Te10Sb4Bi7, were prepared by Electron beam deposition technique. The structure of the as-prepared and annealed films has been studied by X-ray diffraction and the surface morphology by the scanning electron microscope (SEM). These studies show that there is a gradual change in structure and the formation of some polycrystalline structures in the amorphous phases is observed when the Se79Te10Sb4Bi7 film is annealed in the temperature range of 333-393 K. The optical transmission of these films has been studied as a function of photon wavelength in the range 300-2500 nm. It has been found that the optical band gap Egopt decreased with increasing annealing temperature in the range 333-393 K. The Urbach energy (Eu), optical conductivity (σopt), imaginary (εi), and real (εr) parts of the complex dielectric constant (ε) and lattice dielectric constant (εL) were also determined. The changes noticed in optical parameters with increasing annealing temperature were explained on the basis of structural relaxation as well as change in defect states and density of localized states due to amorphous-crystalline transformation.

  3. Influence of point defects on the phonon thermal conductivity and phonon density of states of Bi{sub 2}Te{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Bedoya-Martinez, O.N.; Hashibon, A.; Elsaesser, C. [Fraunhofer IWM, Freiburg (Germany)

    2016-03-15

    The influence of point defects on the lattice thermal conductivity and vibrational properties of Bi{sub 2}Te{sub 3} were studied by using equilibrium and non-equilibrium molecular-dynamics simulations. Three types of point defects at various concentrations were considered, namely Bi and Te vacancies and Bi anti-sites. It is shown that point defects can result in a reduction of up to 80% of the bulk thermal conductivity. A detailed analysis of the phonon density of states (PDOS) of the studied systems is provided. Element (Bi or Te) and orientation (in-plane or cross-plane) resolved PDOS were calculated. In agreement with experimental observations and other simulations, features in the PDOS were identified with specific atomic and orientation contributions. Systems containing point defects exhibit a broadening of the PDOS peaks as the defect concentration increases, which is due to the disorder induced by the defects. Such disorder leads to a higher phonon scattering and thus to a lower lattice thermal conductivity. Tuning the point defect type and concentrations during growth may, therefore, provide a route for optimizing Bi{sub 2}Te{sub 3} based thermoelectric devices. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Optimization of p-type Segmented Bi2Te3/CoSb3 Thermoelectric Material Prepared by Spark Plasma Sintering

    Institute of Scientific and Technical Information of China (English)

    WANG Jun; TANG Xinfeng; LIU Haiqiang; YANG Xiuli; ZHANG Qingjie

    2006-01-01

    A kind of p- type segmented Bi2 Te3/ CoSb3 thermoelectric material was prepared by spark plasma sintering( SPS ). When the segmented materials were used at the temperature ranging from 300 K to 800 K, the junction temperature was optimized, which is about 500 K, and the corresponding length ratio of CoSb3 to Bi2 Te3 is about 15:2. The measured maximum power output of segmented materials is about 320 W·m-2, which is about 1.8 times as high as that of monolithic material CoSb3 under the same measuring conditions.

  5. Self-Assembly of Bi2Te3-Nanoplate/Graphene-Nanosheet Hybrid by One-Pot Route and Its Improved Li-Storage Properties

    Directory of Open Access Journals (Sweden)

    Xinbing Zhao

    2012-07-01

    Full Text Available A sandwich structured Bi2Te3-nanoplates/graphene-nanosheet (Bi2Te3/G hybrid has been synthesized by a facile in situ solvothermal route and has been investigated as a potential anode material for Li-ion batteries. Bi2Te3 grows during the solvothermal process with the simultaneous reduction of graphite oxide into graphene. The in situ formation process of the hybrid has been investigated by X-ray diffraction and X-ray photoelectron spectra. The Li-storage mechanism and performance of Bi2Te3/G and bare Bi2Te3 have been studied by galvanostatic cycling and cyclic voltammetry. The Bi2Te3/G sandwich exhibits an obviously improved cycling stability compared to bare Bi2Te3. The enhancement in electrochemical performance can be attributed to the combined conducting, confining and dispersing effects of graphene for Bi2Te3 nanoplates and to the self-assembled sandwich structure.

  6. Effect of heat treatment on the structure and the thermoelectric properties of Sb0.9Bi1.1Te2.9Se0.1 thin films and composites based on them

    Science.gov (United States)

    Kalinin, Yu. E.; Kashirin, M. A.; Makagonov, V. A.; Pankov, S. Yu.; Sitnikov, A. V.

    2017-01-01

    This work considers the effect of vacuum annealing on the thermoelectric properties of Sb0.9Bi1.1Te2.9Se0.1 thin film and Sb0.9Bi1.1Te2.9Se0.1-C composites with various carbon contents produced by ion-beam deposition in an argon atmosphere. The electrical resistivity and the thermopower of Sb0.9Bi1.1Te2.9Se0.1-C nanocomposites are found to be dependent on not only the carbon concentration but also the type and the concentration of intrinsic point defects of the Sb0.9Bi1.1Te2.9Se0.1 solid solution, which determine the type of conductivity of Sb0.9Bi1.1Te2.9Se0.1 granules. The power factors are estimated for films of Sb0.9Bi1.1Te2.9Se0.1 solid solution and films of Sb0.9Bi1.1Te2.9Se0.1-C composites and found to have values comparable with the values for nanostructured materials on the basis of (Bi,Sb)2(Te,Se)3 solid solutions.

  7. Growth behavior of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} thin films on graphene substrate grown by plasma-enhanced chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chang Wan [Thin Film Materials Research Group, Korea Research Institute of Chemical Technology, Daejeon (Korea, Republic of); School of Electrical and Electronic Engineering, Yonsei University, Seoul (Korea, Republic of); Kim, Gun Hwan; Kang, Min A.; An, Ki-Seok; Lee, Young Kuk [Thin Film Materials Research Group, Korea Research Institute of Chemical Technology, Daejeon (Korea, Republic of); Kang, Seong Gu [School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of); Kim, Hyungjun [School of Electrical and Electronic Engineering, Yonsei University, Seoul (Korea, Republic of)

    2017-03-15

    A comparative study of the substrate effect on the growth mechanism of chalcogenide Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} thin films was carried out. Obvious microstructural discrepancy in both the as-deposited Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} thin films was observed when grown on graphene or SiO{sub 2}/Si substrate. Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} thin films deposited on the graphene substrate were observed to be grown epitaxially along c-axis and show very smooth surface compared to that on SiO{sub 2}/Si substrate. Based on the experimental results of this study, the initial adsorption sites on graphene substrate during deposition process, which had been discussed theoretically, could be demonstrated empirically. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Na和Al双掺杂P型Bi0.5Sb1.5Te3热电材料的制备及性能研究%Preparation and Thermoelectric Properties of Na and Al Dual Doped P-Type Bi0.5Sb1.5Te3

    Institute of Scientific and Technical Information of China (English)

    段兴凯; 胡孔刚; 满达虎; 丁时锋; 江跃珍; 郭书超

    2013-01-01

    采用真空熔炼及热压烧结技术制备了Na和Al双掺杂P型Bi0.5Sb1.5Te3热电材料.利用X射线衍射(XRD)、扫描电子显微镜(SEM)对样品的物相结构和表面形貌进行了表征.XRD分析结果表明,Na0.04Bi0.5Sbl.46-xAlxTe3块体材料的XRD图谱与块体材料Bi0.5Sb1.5Te3的图谱完全对应,所有块体材料的衍射峰均与衍射卡JCPDS 49-1713对应,这表明Na和Al元素已经完全固溶到Bi0.5Sb1.5Te3晶体结构中,形成了单相固溶体合金.SEM形貌表明材料组织致密且有层状结构特征.Na和Al双掺杂提高了Bi0.5Sb1.5Te3在室温附近的Seebeck系数.在Na掺杂量为0.04时,同时Al掺杂量由x=0.04增加至0.12,电导率逐渐降低,在实验掺杂浓度范围内,Na和Al双掺杂会使P型Bi0.5Sb1.5Te3材料的电导率受到较大的损失.在300~500K时,通过Na和Al部分替代Sb,Na0.04Bi0.5Sb1.42Al0.04Te3和Na0.04Bi0.5 Sbl.38Al0.08Te3样品的热导率均有不同程度地减小,在300K时双掺杂样品Na0.04Bi0.5Sb1.42Al0.04Te3的最大Zr值达到1.45.

  9. Fabrication and Characterization of Brush-Printed p-Type Bi0.5Sb1.5Te3 Thick Films for Thermoelectric Cooling Devices

    Science.gov (United States)

    Wu, Han; Liu, Xing; Wei, Ping; Zhou, Hong-Yu; Mu, Xin; He, Dan-Qi; Zhu, Wan-Ting; Nie, Xiao-Lei; Zhao, Wen-Yu; Zhang, Qing-Jie

    2016-11-01

    Bismuth telluride alloys are promising thermoelectric materials used for portable and wearable cooling devices due to their excellent thermoelectric properties near the ambient temperature. Here, a simple and cost-effective brush-printing technique, together with a subsequent annealing treatment, has been used to prepare Bi2Te3-based thick films and prototype devices. The composition, microstructure, and electrical properties of the brush-printed p-type Bi0.5Sb1.5Te3 thick films at different annealing temperatures are investigated. It is found that annealing temperature plays an important role in promoting densification and preventing the film from cracking, hence improving the electrical transport properties. The maximum power factor of the brush-printed thick films is 0.15 mW K-2 m-1 when annealed at 673 K for 4 h. A prototype thermoelectric device is manufactured by connecting the brush-printed p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 thick films with Cu thick-film electrodes on an Al2O3 substrate. The cooling performance of the thermoelectric device is evaluated by measuring the temperature difference produced under applied currents.

  10. Distribution of lanthanoids, Be, Bi, Ga, Te, Tl, Th and U on the territory of Bulgaria using Populus nigra 'Italica' as an indicator

    Energy Technology Data Exchange (ETDEWEB)

    Djingova, R.; Ivanova, Ju. [Department of Analytical Chemistry, Faculty of Chemistry, University of Sofia, 1, J. Bouchier Blvd, 1126 Sofia (Bulgaria); Wagner, G. [University of Saarland, Center of Environmental Research, Institute of Biogeography, D-66041 Saarbruecken (Germany); Korhammer, S.; Markert, B. [International Graduate school IHI-Zittau, Chair of Environmental High Technology, Markt 23, D-02763 Zittau (Germany)

    2001-12-03

    The concentrations of lanthanoids, Be, Bi, Ga, Te, Tl, Th and U have been determined using ICP-MS for 100 standardized samples of poplar leaves collected from the territory of Bulgaria. The investigated elements are log-normally distributed on the territory. Using cluster analysis of the analytical data the samples were grouped according soil type on which the plants are growing.

  11. Sensitive elements of pressure transducers made of layered intercalated InSe, GaSe, and Bi2Te3 crystals

    Science.gov (United States)

    Kudrynskyi, Z. R.; Kovalyuk, Z. D.

    2013-12-01

    It is shown that layered InSe, GaSe, and Bi2Te3 semiconductors are promising for sensitive elements of pressure transducers. Two ways for measuring pressure with layered crystals are suggested: from the pressure dependence of the intercalation parameter (current) and from the pressure dependence of the intercalate electromotive force.

  12. Influence of Ga-doping on the thermoelectric properties of Bi(2−xGaxTe2.7Se0.3 alloy

    Directory of Open Access Journals (Sweden)

    Xingkai Duan

    2015-02-01

    Full Text Available Bi(2−xGaxTe2.7Se0.3 (x=0, 0.04, 0.08, 0.12 alloys were fabricated by vacuum melting and hot pressing technique. The structure of the samples was evaluated by means of X-ray diffraction. The peak shift toward higher angle can be observed by Ga-doping. The effects of Ga substitution for Bi on the electrical and thermal transport properties were investigated in the temperature range of 300–500 K. The power factor values of the Ga-doped samples are obviously improved in the temperature range of 300–440 K. Among all the samples, the Bi(2−xGaxTe2.7Se0.3 (x=0.04 sample showed the lowest thermal conductivity near room temperature and the maximum ZT value reached 0.82 at 400 K.

  13. Thermoelectric Transport Properties of Cu Nanoprecipitates Embedded Bi2Te2.7Se0.3

    Directory of Open Access Journals (Sweden)

    Eunsil Lee

    2015-01-01

    Full Text Available We suggest a simple and scalable synthesis to prepare Cu-Bi2Te2.7Se0.3 (Cu-BTS nanocomposites. By precipitating Cu nanoparticle (NP in colloidal suspension of as-exfoliated BTS, homogeneous mixtures of Cu NP and BTS nanosheet were readily achieved, and then the sintered nanocomposites were fabricated by spark plasma sintering technique using the mixed powder as a raw material. The precipitated Cu NPs in the BTS matrix effectively generated nanograin (BTS and heterointerface (Cu/BTS structures. The maximum ZT of 0.90 at 400 K, which is 15% higher compared to that of pristine BTS, was obtained in 3 vol% Cu-BTS nanocomposite. The enhancement of ZT resulted from improved power factor by carrier filtering effect due to the Cu nanoprecipitates in the BTS matrix.

  14. Intrinsic conduction through topological surface states of insulating Bi{sub 2}Te{sub 3} epitaxial thin films

    Energy Technology Data Exchange (ETDEWEB)

    Hoefer, Katharina; Becker, Christoph; Rata, Diana; Thalmeier, Peter; Tjeng, Liu Hao [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Swanson, Jesse [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); University of British Columbia, Vancouver (Canada)

    2015-07-01

    Topological insulators represent a new state of matter that open up new opportunities to create unique quantum particles. Many exciting experiments have been proposed by theory, yet, the main obstacle for their execution is material quality and cleanliness of the experimental conditions. The presence of tiny amounts of defects in the bulk or contaminants at the surface already mask these phenomena. We present the preparation, structural and spectroscopic characterisation of MBE-grown Bi{sub 2}Te{sub 3} thin films that are insulating in the bulk. Moreover, temperature dependent four-point-probe resistivity measurements of the Dirac states on surfaces that are intrinsically clean were conducted. The total amount of surface charge carries is in the order of 10{sup 12} cm{sup -2} and mobilities up to 4600 cm{sup 2}/Vs are observed. Importantly, these results are achieved by carrying out the preparation and characterisation all in-situ under ultra-high-vacuum conditions.

  15. Production of the Volume Composite Based on Bi2Te3-SiO2 Nanoparticles and its Electroconductivity

    Directory of Open Access Journals (Sweden)

    M.N. Yapryntsev

    2015-12-01

    Full Text Available The nanoparticles of Bi2Te3-SiO2 were synthesized by microwave solvotermal recovery of oxide precursors of bismuth and tellurium with simultaneous hydrolysis of tetraethylorthosilicate (TEOS. The compacting was carried out by method of cold isostatic pressing with the following sintering. The resulting system can be regarded as a thermoelectric semiconductor material containing structural inhomogeneities in the form of inclusions with a low thermal conductivity – SiO2. It was proved that composite is a single-phase bismuth telluride uniformly distributed in the bulk of amorphous silicon dioxide. It was also found that the tunnel type of conductivity is realized in the obtained material at temperatures from about 50 to 180 K.

  16. Study of Ho-doped Bi{sub 2}Te{sub 3} topological insulator thin films

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, S. E. [Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Collins-McIntyre, L. J.; Zhang, S. L.; Chen, Y. L.; Hesjedal, T., E-mail: Thorsten.Hesjedal@physics.ox.ac.uk [Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Baker, A. A. [Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Figueroa, A. I.; Laan, G. van der [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Kellock, A. J.; Pushp, A.; Parkin, S. S. P. [IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States); Harris, J. S. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)

    2015-11-02

    Breaking time-reversal symmetry through magnetic doping of topological insulators has been identified as a key strategy for unlocking exotic physical states. Here, we report the growth of Bi{sub 2}Te{sub 3} thin films doped with the highest magnetic moment element Ho. Diffraction studies demonstrate high quality films for up to 21% Ho incorporation. Superconducting quantum interference device magnetometry reveals paramagnetism down to 2 K with an effective magnetic moment of ∼5 μ{sub B}/Ho. Angle-resolved photoemission spectroscopy shows that the topological surface state remains intact with Ho doping, consistent with the material's paramagnetic state. The large saturation moment achieved makes these films useful for incorporation into heterostructures, whereby magnetic order can be introduced via interfacial coupling.

  17. Local phonon mode in thermoelectric Bi{sub 2}Te{sub 2}Se from charge neutral antisites

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Yao [Department of Physics and Institute of Optical Sciences, University of Toronto, Toronto, Ontario M5S 1A7 (Canada); Osterhoudt, Gavin B.; Burch, Kenneth S., E-mail: ks.burch@bc.edu [Department of Physics, Boston College, 140 Commonwealth Ave., Chestnut Hill, Massachusetts 02467-3804 (United States); Jia, Shuang; Cava, R. J. [Department of Chemistry, Princeton University, Princeton, New Jersey 08540 (United States)

    2016-01-25

    Local modes caused by defects play a significant role in the thermal transport properties of thermoelectrics. Of particular interest are charge-neutral defects that suppress thermal conductivity, without significantly reducing electrical transport. Here, we report a temperature dependent Raman study that identifies such a mode in a standard thermoelectric material, Bi{sub 2}Te{sub 2}Se. One of the modes observed, whose origin has been debated for decades, was shown most likely to be an antisite defect induced local mode. The anomalous temperature independent broadening of the local mode is ascribed to the random arrangement of Se atoms. The temperature renormalization of all modes is well explained by an anharmonic model–Klemens's model.

  18. Faraday Rotation Due to Surface States in the Topological Insulator (Bi1-xSbx)2Te3.

    Science.gov (United States)

    Shao, Yinming; Post, Kirk W; Wu, Jhih-Sheng; Dai, Siyuan; Frenzel, Alex J; Richardella, Anthony R; Lee, Joon Sue; Samarth, Nitin; Fogler, Michael M; Balatsky, Alexander V; Kharzeev, Dmitri E; Basov, D N

    2017-02-08

    Using magneto-infrared spectroscopy, we have explored the charge dynamics of (Bi,Sb)2Te3 thin films on InP substrates. From the magneto-transmission data we extracted three distinct cyclotron resonance (CR) energies that are all apparent in the broad band Faraday rotation (FR) spectra. This comprehensive FR-CR data set has allowed us to isolate the response of the bulk states from the intrinsic surface states associated with both the top and bottom surfaces of the film. The FR data uncovered that electron- and hole-type Dirac Fermions reside on opposite surfaces of our films, which paves the way for observing many exotic quantum phenomena in topological insulators.

  19. Cathodic Deposition of Components in BiSbTe Ternary Compounds as Thermoelectric Films Using Choline-Chloride-Based Ionic Liquids

    Science.gov (United States)

    Golgovici, Florentina; Cojocaru, Anca; Nedelcu, Marin; Visan, Teodor

    2010-09-01

    This paper reports electrodeposition of BiTe, SbTe, and BiSbTe films using ionic liquids based on choline chloride (ChCl) and malonic acid mixtures (1:1 moles) at 80°C to 85°C. The electrolyte contained bismuth and/or antinomy species and tellurium species with 1.5 mM to 50 mM concentrations; Pt sheet, Pt mesh, and Pt wire were used for working, auxiliary, and quasireference electrodes, respectively. Cyclic voltammograms revealed the beginning and cathodic peak of pure Te deposition; at more negative potentials simultaneous codeposition of binary or ternary compounds as limiting currents or a series of peaks were observed. Correspondingly, two or three dissolution (stripping) anodic peaks were observed. Nyquist and Bode impedance spectra show differences in Pt behavior due to its polarization at various cathodic potentials. Equivalent-circuit components providing the best fit to the data were calculated. Deposition of BiSbTe films on copper plates was also performed by electrolysis at controlled potentials or current pulses. Some measurements of Seebeck coefficients of the obtained films were carried out.

  20. Redirected lysis of human melanoma cells by a MCSP/CD3-bispecific BiTE antibody that engages patient-derived T cells.

    Science.gov (United States)

    Torisu-Itakura, Hitoe; Schoellhammer, Hans F; Sim, Myung-Shin; Irie, Reiko F; Hausmann, Susanne; Raum, Tobias; Baeuerle, Patrick A; Morton, Donald L

    2011-10-01

    Melanoma-associated chondroitin sulfate proteoglycan (MCSP; also called HMW-MAA, CSPG4, NG2, MSK16, MCSPG, MEL-CSPG, or gp240) is a well characterized melanoma cell-surface antigen. In this study, a new bispecific T-cell engaging (BiTE) antibody that binds to MCSP and human CD3 (MCSP-BiTE) was tested for its cytotoxic activity against human melanoma cell lines. When unstimulated peripheral mononuclear blood cells (PBMCs) derived from healthy donors were cocultured with melanoma cells at effector:target ratios of 1:1, 1:5, or 1:10, and treated with MCSP-BiTE antibody at doses of 10, 100, or 1000 ng/mL, all MCSP-expressing melanoma cell lines (n=23) were lysed in a dose-dependent and effector:target ratio-dependent manner, whereas there was no cytotoxic activity against MCSP-negative melanoma cell lines (n=2). To investigate whether T cells from melanoma patients could act as effector cells, we cocultured unstimulated PBMCs with allogeneic melanoma cells from 13 patients (4 stage I/II, 3 stage III, and 6 stage IV) or with autologous melanoma cells from 2 patients (stage IV). Although cytotoxic activity varied, all 15 PBMC samples mediated significant redirected lysis by the BiTE antibody. When PBMC or CD8 T cells were prestimulated by anti-CD3 antibody OKT-3 and interleukin-2, the MCSP-BiTE concentrations needed for melanoma cell lysis decreased up to 1000-fold. As MCSP is expressed on most human melanomas, immunotherapy with MCSP/CD3-bispecific antibodies merits clinical investigation.

  1. Point Defects in Pb-, Bi-, and In-Doped CdZnTe Detectors: Deep-Level Transient Spectroscopy (DLTS) Measurements

    Science.gov (United States)

    Gul, R.; Keeter, K.; Rodriguez, R.; Bolotnikov, A. E.; Hossain, A.; Camarda, G. S.; Kim, K. H.; Yang, G.; Cui, Y.; Carcelen, V.; Franc, J.; Li, Z.; James, R. B.

    2012-03-01

    We studied, by current deep-level transient spectroscopy (I-DLTS), point defects induced in CdZnTe detectors by three dopants: Pb, Bi, and In. Pb-doped CdZnTe detectors have a new acceptor trap at around 0.48 eV. The absence of a VCd trap suggests that all Cd vacancies are compensated by Pb interstitials after they form a deep-acceptor complex [[PbCd]+-V{Cd/2-}]-. Bi-doped CdZnTe detectors had two distinct traps: a shallow trap at around 36 meV and a deep donor trap at around 0.82 eV. In detectors doped with In, we noted three well-known traps: two acceptor levels at around 0.18 eV (A-centers) and 0.31 eV (VCd), and a deep trap at around 1.1 eV.

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

    Science.gov (United States)

    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).

  3. Orientation distribution in Bi{sub 2}Te{sub 3}-based compound prepared by spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K.T.; Kim, Y.H. [System Engineering Team, Korea Inst. of Industrial Technology, Ibjang-Myun, Chonan, ChungNam (Korea); Lim, C.H.; Cho, D.C.; Lee, Y.S.; Lee, C.H. [Dept. of Metallurgical Engineering, Coll. of Engineering, Inha Univ., Nam-Gu, Inchon (Korea)

    2005-07-01

    P-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds doped with 3wt.% Te were fabricated by spark plasma sintering after mixing large powders(P{sub L}) and small powders(P{sub S}). We could obtained the highest figure of merit(Z{sub C}) of 2.89 x 10{sup -3}/K in sintered compound mixed to P{sub L}:P{sub S}=80:20. This resulted from the increase of orientation by large powders(P{sub S}) and the reduce of pores by small powders. The figure of merit(Z{sub C}) of the sintered compound using only small powders(P{sub S}) showed lower value of 2.67 x 10{sup -3}/K compared with that of sintered compound mixed to P{sub L}:P{sub S}=80:20 due to the increase of electrical resistivity. (orig.)

  4. Effect of ionic liquid amount (C{sub 8}H{sub 15}BrN{sub 2}) on the morphology of Bi{sub 2}Te{sub 3} nanoplates synthesized via a microwave-assisted heating approach

    Energy Technology Data Exchange (ETDEWEB)

    Ji Guangbin [Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, College of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Shi Yi, E-mail: yshi@nju.edu.cn [Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, College of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Pan Lijia; Zheng Youdou [Jiangsu Provincial Key Laboratory of Photonic and Electronic Materials Sciences and Technology, College of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China)

    2011-05-19

    Highlights: > Rapidly synthesis Bi{sub 2}Te{sub 3} nanoplates via a microwave-assisted ionic liquid method. > Ionic liquid plays a key role on the morphologies of the samples. > Single-crystal in nature with the growth direction of <112-bar 0>. > Power factor gets a maximum at about 450 K. - Abstract: Bi{sub 2}Te{sub 3} crystals with plate-like morphology have been successfully synthesized via a microwave-assisted heating approach in room temperature ionic liquid (RTIL) of 1-butyl-3-methylimidazolium bromide (C{sub 8}H{sub 15}BrN{sub 2}). Scanning electronic microscopy (SEM) observation of as-synthesized Bi{sub 2}Te{sub 3} confirmed their morphology of the hexagonal plates. It was observed that the edge and thickness values of as-synthesized Bi{sub 2}Te{sub 3} were in the size of 0.5-2 {mu}m and less than 100 nm, respectively. High-resolution transmission electronic microscopy (HR-TEM) and selected area electron diffraction (SAED) results revealed that the Bi{sub 2}Te{sub 3} plates are of single-crystal in nature with the growth direction of <112-bar 0>. In addition, as increasing the amount of ionic liquid, SEM results showed a novel evolution process of Bi{sub 2}Te{sub 3} morphologies from mixture of Bi{sub 2}Te{sub 3} nanorods and nanoplates to regular hexagonal plates, and then nanoplates with many small flecks. Furthermore, a possible mechanism regarding the formation of Bi{sub 2}Te{sub 3} plates was proposed as well on the basis of the experimental results. The power factor of Bi{sub 2}Te{sub 3} nanoplates is examined to evaluate its thermoelectric property.

  5. Evolution of MoTeO x/SiO 2 and MoBiTeO x/SiO 2 catalysts in the partial oxidation of propane to acrolein

    Science.gov (United States)

    He, Yiming; Wu, Ying

    2010-04-01

    A thorough investigation of the catalysts Mo 1Te 1O x/SiO 2 and Mo 1Bi 0.05Te 1O x/SiO 2 in the partial oxidation of propane is presented in this paper, in order to elucidate the nature and behavior of the active surface. The catalysts' structures and redox properties were investigated by means of X-ray powder diffraction, Raman spectroscopy, in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and H 2-TPR techniques. The results indicate that Te-polymolybdate is the main active phase on fresh catalysts. During reaction, the catalysts underwent a progressive reduction, resulting in the reconstruction of the active surface and the formation of a MoO 3 phase. The synergistic effect between Te-polymolybdate and MoO 3 was assumed to promote catalytic performance. The different stabilities of Mo 1Te 1O x/SiO 2 and Mo 1Bi 0.05Te 1O x/SiO 2 catalysts are also discussed.

  6. Физико-химическое исследование подсистемы Tl-Tl2Te-Tl9BiTe6-Bi

    OpenAIRE

    Джафаров, Я.; Имамалиева, С.; Бабанлы, М.

    2014-01-01

    Методами ДТА, РФА, измерением микротвердости и ЭДС концентрационных элементов исследованы фазовые равновесия в системе Tl-Bi-Te в области составов Tl-Tl2Te-Tl9BiTe6-Bi. Построены политермические сечения Tl9BiTe6-Bi(Tl2Bi3) и Tl-[TlBiTe0,667], изотермическое сечение при 300К фазовой диаграммы и проекция поверхности ликвидуса подсистемы Tl-Tl2Te-Tl9BiTe6-Bi. Установлены типы и координаты нонвариантных равновесий. Показано наличие широкой области расслаивания....

  7. Quantum Hall effect on top and bottom surface states of topological insulator (Bi1-xSbx)2Te3 films.

    Science.gov (United States)

    Yoshimi, R; Tsukazaki, A; Kozuka, Y; Falson, J; Takahashi, K S; Checkelsky, J G; Nagaosa, N; Kawasaki, M; Tokura, Y

    2015-04-14

    The three-dimensional topological insulator is a novel state of matter characterized by two-dimensional metallic Dirac states on its surface. To verify the topological nature of the surface states, Bi-based chalcogenides such as Bi2Se3, Bi2Te3, Sb2Te3 and their combined/mixed compounds have been intensively studied. Here, we report the realization of the quantum Hall effect on the surface Dirac states in (Bi1-xSbx)2Te3 films. With electrostatic gate-tuning of the Fermi level in the bulk band gap under magnetic fields, the quantum Hall states with filling factor ±1 are resolved. Furthermore, the appearance of a quantum Hall plateau at filling factor zero reflects a pseudo-spin Hall insulator state when the Fermi level is tuned in between the energy levels of the non-degenerate top and bottom surface Dirac points. The observation of the quantum Hall effect in three-dimensional topological insulator films may pave a way toward topological insulator-based electronics.

  8. Influence of NaOH on the formation and morphology of Bi{sub 2}Te{sub 3} nanostructures in a solvothermal process: From hexagonal nanoplates to nanorings

    Energy Technology Data Exchange (ETDEWEB)

    Liang Yujie [School of Science, Minzu University of China, Beijing 100081 (China); Wang, Wenzhong, E-mail: wzhwang@aphy.iphy.ac.cn [School of Science, Minzu University of China, Beijing 100081 (China); School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Zeng Baoqing [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Zhang Guling [School of Science, Minzu University of China, Beijing 100081 (China); He Qingyu [Institute of Electronic Information Material and Apparatus, Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Fu Junli [School of Science, Minzu University of China, Beijing 100081 (China)

    2011-09-15

    Highlights: {yields} Bi{sub 2}Te{sub 3} nanoplates and nanorings were synthesized by a simple solvothermal process. {yields} NaOH is not necessary for Bi{sub 2}Te{sub 3} nanostructure growth in a solvothermal process. {yields} Hexagonal Bi{sub 2}Te{sub 3} nanoplates were achieved with NaOH concentrations of 5-7 M. {yields} Hexagonal Bi{sub 2}Te{sub 3} nanorings were fabricated with NaOH concentrations of 9-11 M. {yields} Bi{sub 2}Te{sub 3} nanorings were fabricated by dissolving the inner part of the nanoplates with NaOH. - Abstarct: Hexagonal bismuth telluride (Bi{sub 2}Te{sub 3}) nanoplates and nanorings were synthesized by a simple solvothermal process. The composition, morphology and size of the as-prepared products were investigated by X-ray diffraction and transmission electron microscopy in detail. The systemically experiments have been performed to investigate the effect of alkaline additive NaOH on composition and morphology of Bi{sub 2}Te{sub 3} nanostructures. The results indicate that alkaline additive NaOH is not necessary for the formation of Bi{sub 2}Te{sub 3} nanostructures in a solvothermal process. However, NaOH plays an important role in determining the morphology and size of Bi{sub 2}Te{sub 3} nanostructures. When the experiment was carried out with NaOH concentration ranging from 5 to 7 M, hexagonal Bi{sub 2}Te{sub 3} nanoplates with edge length of 140-280 nm were synthesized. When the experiment was carried out at higher NaOH concentration of 9-11 M, hexagonal Bi{sub 2}Te{sub 3} nanorings were fabricated by dissolving the inner part of the hexagonal nanoplates with NaOH for the first time. A possible formation mechanism has been proposed based on the experimental results and analysis. This work may open a new rational route for the synthesis of hexagonal Bi{sub 2}Te{sub 3} nanorings which may have some scientific and technological applications in various functional devices.

  9. Crystallization kinetics of amorphous Te(Bi2Se3)1– glasses

    Indian Academy of Sciences (India)

    Manish Saxena

    2004-12-01

    The activation energy plays a dominant role in deciding the utility of the material for the specific purpose—here storage. The dependence of the peak temperature of crystallization (p) on the composition and heating rate () has been studied here. From the heating rate dependence, p, the activation energy for crystallization (c) has been evaluated. The activation energy, c, calculated using three different approaches is found to decrease with the increase in Bi content. This analysis helps in finding the suitability of an alloy to be used in phase transition optical memories/switches. The results have been analysed using Kissinger’s equation for non-isothermal crystallization of materials.

  10. Structural, chemical, and thermoelectric properties of Bi{sub 2}Te{sub 3} Peltier materials. Bulk, thin films, and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Peranio, Nicola

    2008-07-01

    In this work, the nature of the natural nanostructure (nns) was analysed and the correlations to the transport coefficients, particularly the lattice thermal conductivity, is discussed. Experimental methods are presented for the first time, yielding an accurate quantitative analysis of the chemical composition and of stress fields in Bi{sub 2}Te{sub 3} and in compounds with similar structural and chemical microstructures. This work can be subdivided as follows: (I) N-type Bi{sub 2}(Te{sub 0.91}Se{sub 0.09}){sub 3} and p-type (Bi{sub 0.26}Sb{sub 0.74}){sub 1.98}(Te{sub 0.99}Se{sub 0.01}){sub 3.02} bulk materials synthesised by the Bridgman technique. (II) Bi{sub 2}Te{sub 3} thin films and Bi{sub 2}Te{sub 3}/Bi{sub 2}(Te{sub 0.88}Se{sub 0.12}){sub 3} superlattices epitaxially grown by molecular beam epitaxy (MBE) on BaF{sub 2} substrates with periods of {delta}-12 nm at the Fraunhofer-Institut fuer Physikalische Messtechnik (IPM). (III) Experimental methods, i.e., TEM specimen preparation, high-accuracy quantitative chemical analysis by EDX in the TEM, and image simulations of dislocations and the nns according to the two-beam dynamical diffraction theory. The nns was analysed in detail by stereomicroscopy and by image simulation and was found to be a pure sinusoidal displacement field with (i) a displacement vector parallel to <5,-5,1> and an amplitude of about 10 pm and (ii) a wave vector parallel to {l_brace}1,0,10{r_brace} and a wavelength of 10 nm. The results obtained here showed a significant amount of stress in the samples, induced by the nns which was still not noticed and identified. Both kinds of nanostructures, artificial (ans) and natural (nns) nanostructures, yielded in thermoelectric materials a low lattice thermal conductivity which was beneficial for the thermoelectric figure of merit ZT. (orig.)

  11. Effects of Ni and carbon-coated Ni addition on the thermoelectric properties of 25Bi{sub 2}Te{sub 3}+75Sb{sub 2}Te{sub 3} base composites

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Sang Min; Dharmaiah, Peyala; Femi, Olu Emmanuel; Lee, Chul Hee; Hong, Soon-Jik, E-mail: hongsj@kongju.ac.kr

    2017-07-01

    In this paper, we report the effect of nickel (Ni) and carbon coated nickel (C-Ni) on the thermoelectric and mechanical properties of 25Bi{sub 2}Te{sub 3}+75Sb{sub 2}Te{sub 3} (GA) base composites. Ni and C-Ni powders were synthesized using pulse wire evaporation and mixed with 25Bi{sub 2}Te{sub 3}+75Sb{sub 2}Te{sub 3} in a planetary ball mill. The morphology of the Ni and C-Ni powders and GA + x (x = none, Ni, or C-Ni) composites were examined using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The thermoelectric properties of the GA + x (x = none, Ni, or C-Ni) composites shows that the addition of Ni increases the carrier concentration while the presence of C-Ni reduces the carrier concentration to a level comparable to the bare sample (x = 0). Subsequently, the Seebeck coefficient of the GA + C-Ni sample increases by about 18% more than in the bare sample. The thermal conductivity of the GA + Ni and GA + C-Ni samples was considerably lower at room temperature compared to the bare sample. The mechanical properties of the GA + Ni and GA + C-Ni composite samples show a three-fold improvement compared to the bare sample. - Highlights: • Ni and carbon-coated Ni nanoparticles were incorporated into 25Bi{sub 2}Te{sub 3}+75Sb{sub 2}Te{sub 3} (BST) matrix. • Seebeck coefficient increased by 18% for BST/carbon coated Ni composites. • BST/carbon coated Ni composite reduces the thermal conductivity (21%). • The Vickers hardness of the BST/C-Ni composite samples significantly improved.

  12. Temperature-induced liquid state change and its effects on solidiifcation of thermoelectric alloy Bi0.3Sb1.7Te3

    Institute of Scientific and Technical Information of China (English)

    Zhang Wenjin; Wu Zhan; Yu Yuan; Zu Fangqiu

    2014-01-01

    The behaviors of electrical resistivityvs temperature (ρ-T) of the molten p-type thermoelectric aloy Bi0.3Sb1.7Te3 (at.%) were explored in heating and cooling processes. An obvious hump appeared on theρ-T curve from 932℃ to 1,020℃ at the heating process, while the curve became smooth in the folowing cooling, which suggests an irreversible temperature-induced liquid-liquid structure transition (TI-LLST) occurred in the liquid aloy. Based on this judgment, solidiifcation experiments were carried out to ifnd out the effects of the different liquid states. It was veriifed that, for the melt experiencing the presumed TI-LLST, both the nucleation and growth undercooling degrees were elevated and the solidiifcation time was remarkably prolonged. On the other hand, the conifguration of Bi0.3Sb1.7Te3 phase was reifned, and its preferential orientation was weakened.

  13. Facile fabrication of core-shell ZnO/Bi0.5Sb1.5Te3 nanorods: Enhanced photoluminescence through electron charge

    Science.gov (United States)

    Shen, Shengfei; Gao, Hongli; Deng, Yuan; Wang, Yao; Qu, Shengchun

    2016-01-01

    Surface decoration techniques are emerging as promising strategy to improve the optical properties of the ZnO based materials. The core-shell ZnO/Bi0.5Sb1.5Te3 nanorods were grown on a FTO substrate through a facile hydrothermal and magnetron sputtering combined approach. The microstructure of the core-shell nanorod arrays were investigated by the X-ray diffraction (XRD), a field emission Scanning electron microscopy (SEM) and high resolution transmission electron microscope (HTEM). The optical properties of the core-shell nanorod arrays were investigated through the diffuse reflectance absorption spectra and photoluminescence emission. The visible light absorption and especially the photoluminescence emission of the ZnO nanorods are enhanced markedly with the Bi0.5Sb1.5Te3 grains coating the ZnO nanorods through the electron charge.

  14. Infrared- and Raman-spectroscopy measurements of a transition in the crystal structure and a closing of the energy gap of BiTeI under pressure.

    Science.gov (United States)

    Tran, M K; Levallois, J; Lerch, P; Teyssier, J; Kuzmenko, A B; Autès, G; Yazyev, O V; Ubaldini, A; Giannini, E; van der Marel, D; Akrap, A

    2014-01-31

    BiTeI is a giant Rashba spin splitting system, in which a noncentrosymmetric topological phase has recently been suggested to appear under high pressure. We investigated the optical properties of this compound, reflectivity and transmission, under pressures up to 15 GPa. The gap feature in the optical conductivity vanishes above p∼9  GPa and does not reappear up to at least 15 GPa. The plasma edge, associated with intrinsically doped charge carriers, is smeared out through a phase transition at 9 GPa. Using high-pressure Raman spectroscopy, we follow the vibrational modes of BiTeI, providing additional clear evidence that the transition at 9 GPa involves a change of crystal structure. This change of crystal structure possibly inhibits the high-pressure topological phase from occurring.

  15. Tunable thermoelectric transport properties of Cu0.008Bi2Te2.7Se0.3 via control of the spark plasma sintering conditions

    Science.gov (United States)

    Moon, Seung Pil; Ahn, Yeon Sik; Kim, Tae Wan; Choi, Soon-Mok; Park, Hee Jung; Kim, Sung Wng; Lee, Kyu Hyoung

    2016-09-01

    Polycrystalline bulks of n-type Cu0.008Bi2Te2.7Se0.3 were prepared to investigate the controllability of its thermoelectric transport properties by using the compaction conditions of spark plasma sintering (SPS). The 00 l crystal orientation to the press direction of the SPSed bulks was easily improved by increasing the applied pressure at 500 °C. The thermoelectric figure of merit, ZT values (0.72 - 0.75 at 300 K), of all samples were almost the same, however, both the electronic and the thermal transport properties could be tuned significantly by adjusting the sintering pressure. This result highlights the feasibility of using pressure-induced sintering as a fabrication technology for Bi2Te3-based polycrystalline bulks with high mechanical reliability, which is an effective means of optimizing the electrical and the thermal conductivities for maximizing the efficiencies of the thermoelectric cooling and the power generation modules.

  16. Propiedades mecánicas del telururo de bismuto (Bi2Te3 procesado mediante torsión bajo alta presión (HPT

    Directory of Open Access Journals (Sweden)

    Santamaría, Jon Ander

    2013-06-01

    Full Text Available Bismuth telluride, Bi2Te3, is the main thermoelectric material currently in use for commercial cooling devices or for energy harvesting near room temperature. Because of its highly anisotropic layered structure, Bi2Te3 is very brittle, failing by cleavage along its basal plane. Refining its grain size is expected to increase its toughness with the advantage that, simultaneously, its thermoelectric “figure of merit” results increased. In this work, powders of the compound have been compacted by conventional methods as well as by severe plastic deformation under high pressure (3 GPa using high pressure torsion (HPT, one turn at room temperature. Near-theoretical density has been achieved. The hardness and toughness of the compacts have been assessed by micro and nano-indentation.Actualmente el telururo de bismuto (Bi2Te3 es el material termoeléctrico más ampliamente usado en sistemas de refrigeración comerciales o en la conversión de energía en torno a temperatura ambiente. Debido a su estructura laminar altamente anisótropa, el Bi2Te3 es muy frágil y suele agrietarse fácilmente a lo largo de su plano basal. Se espera que el afino del tamaño de grano incremente su tenacidad, con la ventaja de que al mismo tiempo la figura de mérito termoeléctrica se vea incrementada. En este trabajo, polvos del compuesto Bi2Te3 se han compactado mediante dos métodos convencionales y mediante deformación plástica severa bajo alta presión (3 GPa usando la técnica HPT (torsión a alta presión, 1 giro de deformación. Se ha conseguido una densidad cercana a la teórica. La dureza y tenacidad de los compuestos se han ensayado mediante micro- y nano- indentación.

  17. Possible phase transitions probed by infrared spectroscopy under high pressure: BiTeI and Li0.9Mo6O17

    OpenAIRE

    Tran, Michaël

    2014-01-01

    Ce travail de thèse porte sur la spectroscopie optique dans le cas où l’échantillon se trouve dans une cellule de haute pression et à basse température. La mise en place de ce dispositif expérimental a permis l’étude de deux composés : BiTeI et Li0.9Mo6O17.

  18. Extremely large non-saturating magnetoresistance and ultrahigh mobility due to topological surface states in metallic Bi2Te3 topological insulator

    OpenAIRE

    Shrestha, K; Chou, M; Graf, D.; Yang, H. D.; Lorenz, B.; Chu, C. W.

    2017-01-01

    Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been investigated at high and low bulk charge carrier concentrations. At low charge carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. At high charge carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. WAL due to topolog...

  19. Low-Temperature Bonding of Bi0.5Sb1.5Te3 Thermoelectric Material with Cu Electrodes Using a Thin-Film In Interlayer

    Science.gov (United States)

    Lin, Yan-Cheng; Yang, Chung-Lin; Huang, Jing-Yi; Jain, Chao-Chi; Hwang, Jen-Dong; Chu, Hsu-Shen; Chen, Sheng-Chi; Chuang, Tung-Han

    2016-09-01

    A Bi0.5Sb1.5Te3 thermoelectric material electroplated with a Ni barrier layer and a Ag reaction layer was bonded with a Ag-coated Cu electrode at low temperatures of 448 K (175 °C) to 523 K (250 °C) using a 4- μm-thick In interlayer under an external pressure of 3 MPa. During the bonding process, the In thin film reacted with the Ag layer to form a double layer of Ag3In and Ag2In intermetallic compounds. No reaction occurred at the Bi0.5Sb1.5Te3/Ni interface, which resulted in low bonding strengths of about 3.2 MPa. The adhesion of the Bi0.5Sb1.5Te3/Ni interface was improved by precoating a 1- μm Sn film on the surface of the thermoelectric element and preheating it at 523 K (250 °C) for 3 minutes. In this case, the bonding strengths increased to a range of 9.1 to 11.5 MPa after bonding at 473 K (200 °C) for 5 to 60 minutes, and the shear-tested specimens fractured with cleavage characteristics in the interior of the thermoelectric material. The bonding at 448 K (175 °C) led to shear strengths ranging from 7.1 to 8.5 MPa for various bonding times between 5 and 60 minutes, which were further increased to the values of 10.4 to 11.7 MPa by increasing the bonding pressure to 9.8 MPa. The shear strengths of Bi0.5Sb1.5Te3/Cu joints bonded with the optimized conditions of the modified solid-liquid interdiffusion bonding process changed only slightly after long-term exposure at 473 K (200 °C) for 1000 hours.

  20. Self-supporting (Bi0.11Sb0.29 )(Te0.25,Se0.41) nanowire arrays for thermoelectric microdevices

    Science.gov (United States)

    El Matbouly, Hatem; Sands, Timothy; Biswas, Kalapi

    2009-03-01

    Nanostructuring of thermoelectric material can lead to improved performance through suppression of the lattice contribution to thermal conductivity and enhancement of the power factor by quantum confinement or thermionic energy filtering. To take advantage of these effects in a Peltier microcooler or Seebeck generator, it is necessary to prepare nanostructure materials with leg lengths ranging from tens of microns to millimeters. We have developed a process for fabrication of thick, self-supporting (Bi0.11,Sb0.29)(Te0.25,Se0.41) nanowire arrays using a novel branched porous anodic alumina template that can be removed completely by selective etching following electrodeposition of the thermoelectric material, resulting in 100-micron-thick nanostructured thermoelectric material without the parasitic thermal shunt that is associated with the template. The electrodeposition process allows composition modulation and grading, effects that are difficult to achieve by bulk synthesis. Bandgaps of the electrodeposited material range from 0.13 eV for Bi2Te3 to an optical gap of 0.52 eV measured for a (Bi,Sb)2(Te,Se)3 alloy, suggesting an operating tempurature range from below room temperature to ˜300 C.

  1. First-principles investigations of electron-hole inclusion effects on optoelectronic properties of Bi2Te3, a topological insulator for broadband photodetector

    Science.gov (United States)

    Lawal, Abdullahi; Shaari, A.; Ahmed, R.; Jarkoni, Norshila

    2017-09-01

    Bismuth telluride (Bi2Te3), a layered compound with narrow band gap has been potentially reported for thermoelectric. However, strong light interaction of Bi2Te3 is an exciting feature to emerge it as a promising candidate for optoelectronic applications within broadband wavelengths. In this study, we investigate structural, electronic and optical properties of Bi2Te3 topological insulator using combination of density functional theory (DFT) and many-body perturbation theory (MBPT) approach. With the inclusion of van der Waals (vdW) correction in addition to PBE, the lattice parameters and interlayer distance are in good agreement with experimental results. Furthermore, for the precise prediction of fundamental band gap, we go beyond DFT and calculated band structure using one-shot GW approach. Interestingly, our calculated quasiparticle (QP) band gap, Eg of 0.169 eV, is in good agreement with experimental measurements. Taken into account the effects of electron-hole interaction by solving Bethe-Salpeter equation, the calculated optical properties, namely, imaginary and real parts of complex dielectric function, absorption coefficient, refractive index, reflectivity, extinction coefficient, electron energy loss function and optical conductivity all are in better agreement with available experimental results. Consistencies of our findings with experimental data validate the effectiveness of electron-hole interaction for theoretical investigation of optical properties.

  2. High mobility, large linear magnetoresistance, and quantum transport phenomena in Bi2Te3 films grown by metallo-organic chemical vapor deposition (MOCVD).

    Science.gov (United States)

    Jin, Hyunwoo; Kim, Kwang-Chon; Seo, Juhee; Kim, Seong Keun; Cheong, Byung-Ki; Kim, Jin-Sang; Lee, Suyoun

    2015-11-07

    We investigated the magnetotransport properties of Bi2Te3 films grown on GaAs (001) substrate by a cost-effective metallo-organic chemical vapor deposition (MOCVD). We observed the remarkably high carrier mobility and the giant linear magnetoresistance (carrier mobility ∼ 22 000 cm(2) V(-1) s(-1), magnetoresistance ∼ 750% at 1.8 K and 9 T for a 100 nm thick film) that depends on the film thickness. In addition, the Shubnikov-de Haas oscillation was observed, from which the effective mass was calculated to be consistent with the known value. From the thickness dependence of the Shubnikov-de Haas oscillation, it was found that a two dimensional electron gas with the conventional electron nature coexists with the topological Dirac fermion states and dominates the carrier transport in the Bi2Te3 film with thickness higher than 300 nm. These results are attributed to the intrinsic nature of Bi2Te3 in the high-mobility transport regime obtained by a deliberate choice of the substrate and the growth conditions.

  3. Investigation of Thermoelectric Properties with Dispersion of Fe2O3 and Fe-85Ni Nanospheres in Bi0.5Sb1.5Te3 Matrix

    Science.gov (United States)

    Yoon, Sang Min; Dharmaiah, Peyala; Kim, Hyo-Seob; Lee, Chul Hee; Hong, Soon-Jik; Koo, Jar Myung

    2016-09-01

    In this work, we fabricated Bi0.5Sb1.5Te3 thermoelectric alloys using the mass-production technique, and subsequently Fe2O3 and Fe-85Ni alloy nanoparticles were dispersed in the matrix by high energy ball milling and consolidated using spark plasma sintering technique. The influence of Fe2O3 and Fe-85Ni alloy spherical nanoparticles in Bi0.5Sb1.5Te3 (BST) matrix on thermoelectric transport properties has been investigated. The x-ray diffraction and scanning electron microscopy results show that the nanoparticles were dispersed in the matrix. The spark plasma sintered bulk BST/Fe2O3 composite sample exhibited high Seebeck coefficient which was 39% higher than the bare BST due to low carrier concentration and a significant reduction in the thermal conductivity (38%) owing to enhanced carrier scattering by the dispersed nanoparticles compared to that of the bare BST sample. As a result, the maximum ZT values for the BST, BST/Fe2O3, and BST/Fe-85Ni samples were found as 1.17, 0.98, and 0.88 at 375 K, respectively. Micro Vickers hardness of BST/Fe2O3 and BST/Fe-85Ni composite samples was significantly enhanced compared to bare Bi0.5Sb1.5Te3 sample.

  4. Magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 driven by the Stark effect.

    Science.gov (United States)

    Zhang, Zuocheng; Feng, Xiao; Wang, Jing; Lian, Biao; Zhang, Jinsong; Chang, Cuizu; Guo, Minghua; Ou, Yunbo; Feng, Yang; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Yayu

    2017-08-07

    The recent experimental observation of the quantum anomalous Hall effect has cast significant attention on magnetic topological insulators. In these magnetic counterparts of conventional topological insulators such as Bi2Te3, a long-range ferromagnetic state can be established by chemical doping with transition-metal elements. However, a much richer electronic phase diagram can emerge and, in the specific case of Cr-doped Bi2(SexTe1-x)3, a magnetic quantum phase transition tuned by the actual chemical composition has been reported. From an application-oriented perspective, the relevance of these results hinges on the possibility to manipulate magnetism and electronic band topology by external perturbations such as an electric field generated by gate electrodes-similar to what has been achieved in conventional diluted magnetic semiconductors. Here, we investigate the magneto-transport properties of Cr-doped Bi2(SexTe1-x)3 with different compositions under the effect of a gate voltage. The electric field has a negligible effect on magnetic order for all investigated compositions, with the remarkable exception of the sample close to the topological quantum critical point, where the gate voltage reversibly drives a ferromagnetic-to-paramagnetic phase transition. Theoretical calculations show that a perpendicular electric field causes a shift in the electronic energy levels due to the Stark effect, which induces a topological quantum phase transition and, in turn, a magnetic phase transition.

  5. Helical mode and supercurrent measured on the topological surface states of Bi2Te3 nanoribbon field effect devices

    Science.gov (United States)

    Jauregui, Luis A.; Pettes, Michael T.; Shi, Li; Rokhinson, Leonid P.; Chen, Yong P.

    2014-03-01

    Topological superconductivity can be proximity induced by coupling s-wave superconductors with spin-helical electron systems, such as the surface of 3D topological insulators (TIs), where the energy bands follow Dirac dispersion and the electronic states possess helical spin-momentum locking. We have grown Bi2Te3 nanoribbons (NRs) by vapor liquid solid method and characterized their crystalline structure by TEM and Raman spectroscopy. We fabricate backgated field effect devices where the chemical potential (μ) can be tuned from bulk bands to surface states and ambipolar field effect has been observed. The temperature dependence of the resistance and Shubnikov de Haas oscillations show suppressed bulk conduction with surface conduction dominating and a pi-Berry's phase. The Aharonov-Bohm oscillations (ABO), measured with a magnetic field parallel to the NR axis, have a period equal to one flux quanta with conductance maxima at half flux quanta (pi-ABO), for μ close to the charge neutrality point. Such pi-ABO is a direct evidence of the existence of 1D helical modes at half flux quanta. We have also fabricated Josephson junctions on our TI NR devices with inter-electrode separations up to 200 nm, and measured supercurrent with a proximity induced gap of 0.5meV at 0.25K.

  6. Effect of Sn doping on nonlinear optical properties of quaternary Se-Sn-(Bi,Te) chalcogenide thin films

    Science.gov (United States)

    Yadav, Preeti; Sharma, Ambika

    2015-08-01

    The aim of this work is to report the effect of Sn doping on the third order nonlinear optical properties of chalcogenide Se84-xTe15Bi1.0Snx thin films. Melt quenching technique has been used for the preparation of bulk chalcogenide glasses. Thin films of the studied composition are deposited on cleaned glass substrate by thermal evaporation technique. Optical band gap (Eg) is calculated by using Tauc extrapolation method and is found to increase from 1.27 eV to 1.64 eV with the incorporation of Sn content. Stryland approach is utilized for the calculation of two photon absorption coefficient (β2). The nonlinear refractive index (n2) and third order susceptibility (χ(3) are calculated using Tichy and Ticha approach. The result shows that nonlinear refractive index (n2) follows the same trend as that of linear refractive index (n). The values of n2 of studied composition as compared to pure silica are 1000-5000 times higher.

  7. Hot pressing effect on (Bi0.25Sb0.75)2Te3 mechanical and thermoelectric properties

    Indian Academy of Sciences (India)

    G Kavei; K Ahmadi; A Seyyedi

    2011-12-01

    (Bi0.25Sb0.75)2Te3 thermoelectric material is a well known type of compound that has higher figure of merit than other stoichiometries. The crystal of this compound was prepared, pulverized in a particle size ratio of 64% with a mesh of 80 (200 m2) and 36% with a mesh of 60 (250 m2). The powder was sintered in a heat up to 350–500°C under pressure of 500 MPa (hot pressing). To find out the temperature effects on thermal conductivity of the sample it was systematically investigated in nano-scale intrinsic structures by systems of X-ray diffraction, scanning electron microscopy and, for only once successful attempt, atomic force microscopy. The acquired images ensured to show homogeneous structures for hot pressed samples. In terms of thermal conductivity and with regard to the figure of merit (), optimum sintering temperature hovers at around 500°C, which leads to a maximum value of around 1.53 K-1.

  8. Recovery of the bulk-like electronic structure of manganese phthalocyanine beyond the first monolayer on Bi2Te3

    Science.gov (United States)

    Hewitt, A. S.; Boltersdorf, J.; Maggard, P. A.; Dougherty, D. B.

    2017-08-01

    The evolution of electronic structure of manganese phthalocyanine on Bi2Te3 shows a transition to a bulk-like aspect abruptly after completion of the first layer. This allows the inference that, in the first layer, there is charge transfer and electronic hybridization involving the occupied Mn-derived d orbitals of the molecule into the conduction band of the substrate. The charge transfer coupling is seen using angle-resolved ultraviolet photoelectron spectroscopy by monitoring the evolution of work function and band structure with increasing molecular film thickness. The electronic structure in the second layer is more bulk-like as indicated by the reappearance of well-known low energy d orbitals that were depopulated in the first layer. Scanning tunneling microscopy shows that the transition to bulk like behavior is also reflected in film structure as a transition from a unique disordered monolayer to a locally ordered and dense second layer. These observations are relevant to ongoing efforts to control topological insulator interfaces especially for spintronics applications.

  9. Linear and nonlinear optical properties of new Se-based quaternary Se-Sn-(Bi,Te) chalcogenide thin films

    Science.gov (United States)

    Yadav, Preeti; Sharma, Ambika

    2015-02-01

    We are reporting the linear and nonlinear optical properties of Se-based quaternary chalcogenide Se-Sn-(Bi,Te) thin films. Thin films of bulk chalcogenide glasses, prepared by melt quenching method are deposited on glass substrate using thermal evaporation technique. The optical behavior of studied chalcogenide glass systems is investigated using transmission spectra in the spectral range of 400-2500 nm. The glasses exhibit considerable optical nonlinearities which are estimated using linear optical parameters. Linear refractive index has been calculated using well-known Swanepoel method. Wemple-DiDomenico (WDD) parameters are also reported for the investigated glasses. Optical band gap is determined using Tauc extrapolation method and is observed to increase with Sn content. The formulation proposed by Fournier and Snitzer is used to determine the nonlinear behavior of the refractive index. It is observed that n2 increases linearly with increasing n. The values of n2 are compared with pure silica and the results are 100-600 orders higher. The third-order susceptibility χ(3) is also reported in this paper. Two-photon absorption coefficient β2 is determined using optical band gap data. A strong dependence of β2 and n2 is observed on normalized photon energy (?) for a fixed excitation wavelength (1064 nm).

  10. Mirror-symmetry protected non-TRIM surface state in the weak topological insulator Bi2TeI

    Science.gov (United States)

    Rusinov, I. P.; Menshchikova, T. V.; Isaeva, A.; Eremeev, S. V.; Koroteev, Yu. M.; Vergniory, M. G.; Echenique, P. M.; Chulkov, E. V.

    2016-01-01

    Strong topological insulators (TIs) support topological surfaces states on any crystal surface. In contrast, a weak, time-reversal-symmetry-driven TI with at least one non-zero v1, v2, v3 ℤ2 index should host spin-locked topological surface states on the surfaces that are not parallel to the crystal plane with Miller indices (v1 v2 v3). On the other hand, mirror symmetry can protect an even number of topological states on the surfaces that are perpendicular to a mirror plane. Various symmetries in a bulk material with a band inversion can independently preordain distinct crystal planes for realization of topological states. Here we demonstrate the first instance of coexistence of both phenomena in the weak 3D TI Bi2TeI which (v1 v2 v3) surface hosts a gapless spin-split surface state protected by the crystal mirror-symmetry. The observed topological state has an even number of crossing points in the directions of the 2D Brillouin zone due to a non-TRIM bulk-band inversion. Our findings shed light on hitherto uncharted features of the electronic structure of weak topological insulators and open up new vistas for applications of these materials in spintronics. PMID:26864814

  11. Quantum coherence phenomenon in disordered Bi2SeTe2 topological single crystal: effect of annealing.

    Science.gov (United States)

    Amaladass, E P; Devidas, T R; Sharma, Shilpam; Mani, Awadhesh

    2017-05-04

    We report a comparative magnetotransport study on pristine and annealed Bi2SeTe2 single crystals. The pristine sample shows a metallic trend from 300 to 180 K, and an insulating behavior for T    2.5 T. Further, the quantum MR behaviours seen at low temperature gradually transform to classical B (2) dependent upon increasing the temperatures. In contrast, the annealed sample shows a WAL at small field superimposed on a parabolic feature for B  >  ±4 T at low temperatures (T    100 K. Hall measurements on both samples exhibit a nonlinear behavior at 4.2 K pointing to the existence of two types of carriers with different mobility. The annealed sample also shows a drastic decrease in mobility by one order of magnitude and a reduction in Ioffe-Regel parameter (k F l) by a factor of ~3. Disorder-induced localization of bulk carriers and its coexistence with localization-immune surface carriers at low T leads to WAL and WL. MR observed in the annealed sample can be attributed to the presence of both quantum-classical contribution and has been analysed using the Hikami-Larkin-Nagaoka (HLN) equation.

  12. Mirror-symmetry protected non-TRIM surface state in the weak topological insulator Bi2TeI

    Science.gov (United States)

    Rusinov, I. P.; Menshchikova, T. V.; Isaeva, A.; Eremeev, S. V.; Koroteev, Yu. M.; Vergniory, M. G.; Echenique, P. M.; Chulkov, E. V.

    2016-02-01

    Strong topological insulators (TIs) support topological surfaces states on any crystal surface. In contrast, a weak, time-reversal-symmetry-driven TI with at least one non-zero v1, v2, v3 ℤ2 index should host spin-locked topological surface states on the surfaces that are not parallel to the crystal plane with Miller indices (v1 v2 v3). On the other hand, mirror symmetry can protect an even number of topological states on the surfaces that are perpendicular to a mirror plane. Various symmetries in a bulk material with a band inversion can independently preordain distinct crystal planes for realization of topological states. Here we demonstrate the first instance of coexistence of both phenomena in the weak 3D TI Bi2TeI which (v1 v2 v3) surface hosts a gapless spin-split surface state protected by the crystal mirror-symmetry. The observed topological state has an even number of crossing points in the directions of the 2D Brillouin zone due to a non-TRIM bulk-band inversion. Our findings shed light on hitherto uncharted features of the electronic structure of weak topological insulators and open up new vistas for applications of these materials in spintronics.

  13. PENGEMBANGAN APLIKASI BERBASIS MATLAB UNTUK MENGANALISIS SIFAT LASING KACA Te-Zn-Bi YANG TERDADAH ION Er3+

    Directory of Open Access Journals (Sweden)

    Rudi Susanto

    2016-06-01

    Full Text Available Tujuan penelitian ini adalah mengembangkan  aplikasi untuk menganalis sifat lasing kaca bahan penguat optik dengan parameter Judd-Ofelt. Pengembangan aplikasi menggunakan kaidah Software Development Life Cycle (SDLC yang terdiri dari analisis, perancangan, pembangunan dan pengujian. Perancangan aplikasi mengunakan flowchart yang sesuai dengan kebutuhan dan pembangunan aplikasi mengunakan GUI matlab. Pengujian aplikasi mengunakan metode black box serta perbandingan hasil aplikasi dan perhitungan manual. Hasil pengujian menunjukan bahwa aplikasi mampu bekerja sesuai fungsionalitasnya yaitu digunakan untuk menganalisis sifat lasing kaca Te-Zn-Bi dengan doping Er3+ yang ditunjukan dengan output aplikasi berupa  (1 Parameter , (2 Probabilitas Transisi, (3 Branching Ratio, (4 Life Time, (5 Omega4/ Omega6 serta(6 Aem/AESA. Output aplikasi tersebut merupakan parameter yang digunakan untuk menganalis sifat lasing sesuai parameter Judd Ofelt. Hasil perbandingan perhitungan manual dan aplikasi dapat diketahui bahwa rata-rata kesalahan relative adalah 1.2476%. Dari hasil pengujian dapat disimpulkan bahwa aplikasi dapat digunakan untuk menganalisis sifat lasing.

  14. X-ray magnetic circular dichroism study of Dy-doped Bi2Te3 topological insulator thin films

    Science.gov (United States)

    Figueroa, A. I.; Baker, A. A.; Harrison, S. E.; Kummer, K.; van der Laan, G.; Hesjedal, T.

    2017-01-01

    Magnetic doping of topological insulators (TIs) is crucial for unlocking novel quantum phenomena, paving the way for spintronics applications. Recently, we have shown that doping with rare earth ions introduces large magnetic moments and allows for high doping concentrations without the loss of crystal quality, however no long range magnetic order was observed. In Dy-doped Bi2Te3 we found a band gap opening above a critical doping concentration, despite the paramagnetic bulk behavior. Here, we present a surface-sensitive x-ray magnetic circular dichroism (XMCD) study of an in situ cleaved film in the cleanest possible environment. The Dy M4,5 absorption spectra measured with circularly polarized x-rays are fitted using multiplet calculations to obtain the effective magnetic moment. Arrott-Noakes plots, measured by the Dy M5 XMCD as a function of field at low temperatures, give a negative transition temperature. The evaporation of a ferromagnetic Co thin film did not introduce ferromagnetic ordering of the Dy dopants either; instead a lowering of the transition temperature was observed, pointing towards an antiferromagnetic ordering scenario. This result shows that there is a competition between the magnetic exchange interaction and the Zeeman interaction. The latter favors the Co and Dy magnetic moments to be both aligned along the direction of the applied magnetic field, while the exchange interaction is minimized if the Dy and Co atoms are antiferromagnetically coupled, as in zero applied field.

  15. Determination of total Sb,Se Te, and Bi and evaluation of their inorganic species in garlic by hydride-generation-atomic-fluorescence spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Matos Reyes, M.N.; Cervera, M.L.; Guardia, M. de la [University of Valencia, Department of Analytical Chemistry, Burjassot, Valencia (Spain)

    2009-07-15

    A sensitive and simple analytical method has been developed for determination of Sb(III), Sb(V), Se(IV), Se(VI), Te(IV), Te(VI), and Bi(III) in garlic samples by using hydride-generation-atomic-fluorescence spectrometry (HG-AFS). The method is based on a single extraction of the inorganic species by sonication at room temperature with 1 mol L{sup -1} H{sub 2}SO{sub 4} and washing of the solid phase with 0.1% (w/v) EDTA, followed by measurement of the corresponding hydrides generated under two different experimental conditions directly and after a pre-reduction step. The limit of detection of the method was 0.7 ng g{sup -1} for Sb(III), 1.0 ng g{sup -1} for Sb(V), 1.3 ng g{sup -1} for Se(IV), 1.0 ng g{sup -1} for Se(VI), 1.1 ng g{sup -1} for Te(IV), 0.5 ng g{sup -1} for Te(VI), and 0.9 ng g{sup -1} for Bi(III), in all cases expressed in terms of sample dry weight. (orig.)

  16. Effect of current on the microstructure and performance of (Bi2Te3)0.2(Sb2Te3)0.8 thermoelectric material via field activated and pressure assisted sintering

    Institute of Scientific and Technical Information of China (English)

    Chen Ruixue; Meng Qingsen; Fan Wenhao; Wang Zhong

    2011-01-01

    (Bi2Te3)0.2(Sb2Te3)0.8 thermoelectric material was sintered via a field activated and pressure assisted sintering (FAPAS) process.By applying different current intensity (0,60,320 A/cm2) in the sintering process,the effects of electric current on the microstructure and thermoelectric performance were investigated.This demonstrated that the application of electric current in the sintering process could significantly improve the uniformity and density of(Bi2Te3)0.2(Sb2Te3)0.8 samples.When the current intensity was raised to 320 A/cm2,the preferred orientation of grains was observed.Moreover,positive effects on the thermoelectric performance of applying electric current in the sintering process were also confirmed.An increase of 0.02 and 0.11 in the maximum figure of merit ZT value could be acquired by applying current of 60 and 320 A/cm2,respectively.

  17. Epitope distance to the target cell membrane and antigen size determine the potency of T cell-mediated lysis by BiTE antibodies specific for a large melanoma surface antigen.

    Science.gov (United States)

    Bluemel, Claudia; Hausmann, Susanne; Fluhr, Petra; Sriskandarajah, Mirnalini; Stallcup, William B; Baeuerle, Patrick A; Kufer, Peter

    2010-08-01

    Melanoma chondroitin sulfate proteoglycan (MCSP; also called CSPG4, NG2, HMW-MAA, MSK16, MCSPG, MEL-CSPG, or gp240) is a surface antigen frequently expressed on human melanoma cells, which is involved in cell adhesion, invasion and spreading, angiogenesis, complement inhibition, and signaling. MCSP has therefore been frequently selected as target antigen for development of antibody- and vaccine-based therapeutic approaches. We have here used a large panel of monoclonal antibodies against human MCSP for generation of single-chain MCSP/CD3-bispecific antibodies of the BiTE (for bispecific T cell engager) class. Despite similar binding affinity to MCSP, respective BiTE antibodies greatly differed in their potency of redirected lysis of CHO cells stably transfected with full-length human MCSP, or with various MCSP deletion mutants and fusion proteins. BiTE antibodies binding to the membrane proximal domain D3 of MCSP were more potent than those binding to more distal domains. This epitope distance effect was corroborated with EpCAM/CD3-bispecific BiTE antibody MT110 by testing various fusion proteins between MCSP and EpCAM as surface antigens. CHO cells expressing small surface target antigens were generally better lysed than those expressing larger target antigens, indicating that antigen size was also an important determinant for the potency of BiTE antibody. The present study for the first time relates the positioning of binding domains and size of surface antigens to the potency of target cell lysis by BiTE-redirected cytotoxic T cells. In case of the MCSP antigen, this provides the basis for selection of a maximally potent BiTE antibody candidate for development of a novel melanoma therapy.

  18. Twin domain imaging in topological insulator Bi2Te3 and Bi2Se3 epitaxial thin films by scanning X-ray nanobeam microscopy and electron backscatter diffraction

    Science.gov (United States)

    Harcuba, Petr; Veselý, Jozef; Lesnik, Andreas; Bauer, Guenther; Springholz, Gunther; Holý, Václav

    2017-01-01

    The twin distribution in topological insulators Bi2Te3 and Bi2Se3 was imaged by electron backscatter diffraction (EBSD) and scanning X-ray diffraction microscopy (SXRM). The crystal orientation at the surface, determined by EBSD, is correlated with the surface topography, which shows triangular pyramidal features with edges oriented in two different orientations rotated in the surface plane by 60°. The bulk crystal orientation is mapped out using SXRM by measuring the diffracted X-ray intensity of an asymmetric Bragg peak using a nano-focused X-ray beam scanned over the sample. By comparing bulk- and surface-sensitive measurements of the same area, buried twin domains not visible on the surface are identified. The lateral twin domain size is found to increase with the film thickness.

  19. Point Defects in Pb-, Bi-, and In-Doped CdZnTe Detectors:Deep-Level Transient Spectroscopy (DLTS) Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Bolotnikov A.; GUL, R.; KEETER, K.; RODRIGUEZ, R.; BOLOTNIKOV, A.E.; HOSSAIN, A.; CAMARDA, G.S.; KIM, K.H.; YANG, Y.; CUI, Y.; CARCELEN, V.; FRANC, J.; LI, Z.; JAMES, R.B.

    2012-02-29

    We studied, by current deep-level transient spectroscopy (I-DLTS), point defects induced in CdZnTe detectors by three dopants: Pb, Bi, and In. Pb-doped CdZnTe detectors have a new acceptor trap at around 0.48 eV. The absence of a V{sub Cd} trap suggests that all Cd vacancies are compensated by Pb interstitials after they form a deep-acceptor complex [[Pb{sub Cd}]{sup +}-V{sub Cd}{sup 2-}]{sup -}. Bi-doped CdZnTe detectors had two distinct traps: a shallow trap at around 36 meV and a deep donor trap at around 0.82 eV. In detectors doped with In, we noted three well-known traps: two acceptor levels at around 0.18 eV (A-centers) and 0.31 eV (V{sub Cd}), and a deep trap at around 1.1 eV.

  20. How grain boundaries affect the efficiency of poly-CdTe solar-cells: A fundamental atomic-scale study of grain boundary dislocation cores using CdTe bi-crystal thin films.

    Energy Technology Data Exchange (ETDEWEB)

    Klie, Robert [Univ. of Illinois, Chicago, IL (United States)

    2016-10-25

    It is now widely accepted that grain boundaries in poly-crystalline CdTe thin film devices have a detrimental effect on the minority carrier lifetimes, the open circuit voltage and therefore the overall solar-cell performance. The goal of this project was to develop a fundamental understanding of the role of grain boundaries in CdTe on the carrier life-time, open-circuit voltage, Voc, and the diffusion of impurities. To achieve this goal, i) CdTe bi-crystals were fabricated with various misorientation angels, ii) the atomic- and electronic structures of the grain boundaries were characterized using scanning transmission electron microscopy (STEM), and iii) first-principles density functional theory modeling was performed on the structures determined by STEM to predict the grain boundary potential. The transport properties and minority carrier lifetimes of the bi-crystal grain boundaries were measured using a variety of approaches, including TRPL, and provided feedback to the characterization and modeling effort about the effectiveness of the proposed models.

  1. Effect of Substitutional Pb Doping on Bipolar and Lattice Thermal Conductivity in p-Type Bi0.48Sb1.52Te3

    Directory of Open Access Journals (Sweden)

    Hyun-sik Kim

    2017-07-01

    Full Text Available Cation substitutional doping is an effective approach to modifying the electronic and thermal transports in Bi2Te3-based thermoelectric alloys. Here we present a comprehensive analysis of the electrical and thermal conductivities of polycrystalline Pb-doped p-type bulk Bi0.48Sb1.52Te3. Pb doping significantly increased the electrical conductivity up to ~2700 S/cm at x = 0.02 in Bi0.48-xPbxSb1.52Te3 due to the increase in hole carrier concentration. Even though the total thermal conductivity increased as Pb was added, due to the increased hole carrier concentration, the thermal conductivity was reduced by 14–22% if the contribution of the increased hole carrier concentration was excluded. To further understand the origin of reduction in the thermal conductivity, we first estimated the contribution of bipolar conduction to thermal conductivity from a two-parabolic band model, which is an extension of the single parabolic band model. Thereafter, the contribution of additional point defect scattering caused by Pb substitution (Pb in the cation site was analyzed using the Debye–Callaway model. We found that Pb doping significantly suppressed both the bipolar thermal conduction and lattice thermal conductivity simultaneously, while the bipolar contribution to the total thermal conductivity reduction increased at high temperatures. At Pb doping of x = 0.02, the bipolar thermal conductivity decreased by ~30% from 0.47 W/mK to 0.33 W/mK at 480 K, which accounts for 70% of the total reduction.

  2. Infrared- and Raman-Spectroscopy Measurements of a Transition in the Crystal Structure and a Closing of the Energy Gap of BiTeI under Pressure

    OpenAIRE

    Tran, M. K.; Levallois, J.; Lerch, P.; Teyssier, J.; Kuzmenko, A. B.; Autès, G.; Yazyev, O. V.; Ubaldini, A.; Giannini, E.; D. van der Marel; Akrap, A.

    2014-01-01

    BiTeI is a giant Rashba spin splitting system, in which a non-centro symmetric topological phase has recently been suggested to appear under high pressure. We investigated the optical properties of this compound, reflectivity and transmission, under pressures up to $15$ GPa. The gap feature in the optical conductivity vanishes above $p \\sim 9$ GPa and does not reappear up to at least $15$ GPa. The plasma edge, associated with intrinsically doped charge carriers, is smeared out through a phase...

  3. Electrical and photoresponse properties of vacuum deposited Si/Al:ZnSe and Bi:ZnTe/Al:ZnSe photodiodes

    Science.gov (United States)

    Rao, Gowrish K.

    2017-04-01

    The paper reports fabrication and characterization of Bi:ZnTe/Al:ZnSe and Si/Al:ZnSe thin film photodiodes. The characteristics of the devices were studied under dark and illuminated conditions. The normalized spectral response, speed of photoresponse and variation of photocurrent with power density were studied in detail. Many vital parameters, such as diode ideality factor, barrier height, the thickness of the depletion region, trap depth, rise and decay times of photocurrent, were determined. Conduction mechanism in the photodiodes is discussed with the help of widely accepted theoretical models.

  4. Experimental evidence on the Altshuler-Aronov-Spivak interference of the topological surface states in the exfoliated Bi2Te3 nanoflakes

    Science.gov (United States)

    Li, Zhaoguo; Qin, Yuyuan; Song, Fengqi; Wang, Qiang-Hua; Wang, Xuefeng; Wang, Baigeng; Ding, Haifeng; Van Haesondonck, Chris; Wan, Jianguo; Zhang, Yuheng; Wang, Guanghou

    2012-02-01

    Here, we demonstrate the Altshuler-Aronov-Spivak (AAS) interference of the topological surface states on the exfoliated Bi2Te3 microflakes by a flux period of h/2e in their magnetoresistance oscillations and its weak field character. Both the oscillations with the period of h/e and h/2e are observed. The h/2e-period AAS oscillation gradually dominates with increasing the sample widths and the temperatures. This reveals the transition of the Dirac Fermions' transport to the diffusive regime.

  5. Two-step growth of high quality Bi{sub 2}Te{sub 3} thin films on Al{sub 2}O{sub 3} (0001) by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, S. E.; Huo, Y.; Harris, J. S. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Li, S. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Zhou, B.; Chen, Y. L. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Department of Physics, University of Oxford, Parks Road, OX1 3PU Oxford (United Kingdom); Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2013-04-29

    Large-area topological insulator Bi{sub 2}Te{sub 3} thin films were grown on Al{sub 2}O{sub 3} (0001) using a two-temperature step molecular beam epitaxy growth process. By depositing a low temperature nucleation layer to serve as a template for high temperature epitaxial film growth, a high quality terrace-step surface morphology with a significant reduction in three-dimensional defect structures was achieved. X-ray diffraction measurements indicate that high crystalline quality Bi{sub 2}Te{sub 3} layers were grown incoherently by van der Waals epitaxy using this technique. Angle resolved photoemission spectroscopy measurements verified the integrity of this growth method by confirming the presence of metallic surface states on cleaved two-step Bi{sub 2}Te{sub 3} samples.

  6. Influence of Doping and Nanostructuration on n-Type Bi2(Te0.8Se0.2)3 Alloys Synthesized by Arc Melting

    Science.gov (United States)

    Gharsallah, Mouna; Serrano-Sanchez, Federico; Nemes, Norbert M.; Martinez, Jose Luis; Alonso, Jose Antonio

    2017-01-01

    In competitive thermoelectric devices for energy conversion and generation, high-efficiency materials of both n-type and p-type are required. For this, Bi2Te3-based alloys have the best thermoelectric properties in room temperature applications. Partial replacement of tellurium by selenium is expected to introduce new donor states in the band gap, which would alter electrical conductivity and thermopower. We report on the preparation of n-type Bi2(Te1-xSex)3 solid solutions by a straightforward arc-melting technique, yielding nanostructured polycrystalline pellets. X-ray and neutron powder diffraction was used to assess Se inclusion, also indicating that the interactions between quintuple layers constituting this material are weakened upon Se doping, while the covalency of intralayer bonds is augmented. Moreover, scanning electron microscopy shows large surfaces perpendicular to the c crystallographic axis assembled as stacked sheets. Grain boundaries related to this 2D nanostructuration affect the thermal conductivity reducing it below 0.8 Wm-1K-1 at room temperature. Furthermore, Se doping increases the absolute Seebeck coefficient up to -140 μV K-1 at 400 K, which is also beneficial for improved thermoelectric efficiency.

  7. Surface origin of quasi-2D Shubnikov–de Haas oscillations in Bi{sub 2}Te{sub 2}Se

    Energy Technology Data Exchange (ETDEWEB)

    Kapustin, A. A., E-mail: kapustin@issp.ac.ru; Stolyarov, V. S.; Bozhko, S. I.; Borisenko, D. N.; Kolesnikov, N. N. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)

    2015-08-15

    Transport measurements at liquid helium temperatures were done on a number of Bi{sub 2}Te{sub 2}Se samples with thicknesses ranging from 30 to 200 μm in order to detect surface states. In each sample we observed Shubnikov–de Haas (SdH) oscillations and sublinear dependence of off-diagonal component of magnetoresistance tensor on magnetic field. The periods of SdH oscillations in inverse magnetic field were found to be the same within 15%. The positions of SdH oscillations are determined by the normal to surface component of magnetic field. We found that the measured conductivity can be well described by a model with two groups of electrons, 2D and 3D. The conductivity of 2D electrons was found to be relatively weakly varying from sample to sample and not depending on thickness in a systematic manner. This behavior can be explained only by their localization on the surface. Comparison of the results of magnetotransport measurements with our scanning tunneling spectroscopy results on atomically smooth Bi{sub 2}Te{sub 2}Se surface in ultrahigh vacuum led us to conclude that the surface electrons are separated from the bulk electrons by a depletion layer approximately 100 nm thick. This effect could provide the dominant contribution of surface electrons to conductivity in samples with thicknesses less than 200 nm.

  8. Temperature dependent electron-phonon coupling and heat capacity in thin slabs of topological insulator Bi2Te3 as pertinent to the thermal spike model

    Science.gov (United States)

    Patra, Paramita; Srivastava, S. K.

    2016-07-01

    Electron-phonon coupling strength and electronic heat capacity are essential ingredients of the widely accepted thermal spike model of swift heavy ion matter interaction. The concept, although applicable very well in metals, loses its validity in materials with a band gap, wherein it is customary to take the two quantities merely as adjustable parameters to fit the experimental results. Topological insulators, like Bi2Te3, are quite interesting in this regard because they are also metallic albeit near the surface. In this work, we compute by first-principles the electron density of states of ∼16 Å thick Bi2Te3 slabs of different orientations and demonstrate an unusually high metallicity for the [0 0 1] slab. The density of states is then used to calculate the electron-phonon coupling strength and electronic heat capacity as a function of electron temperature. Strongly electron temperature dependent but weak electron-phonon coupling has been observed, along with systematic deviations of the electronic heat capacity from the linear free-electron metal values.

  9. Raman scattering and electric conductivity in Bi{sub 2}(Te{sub 0.9}Se{sub 0.1}){sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kerimova, Afet; Abdullayev, Nadir A.; Abdullayev, Nadir M.; Aliguliyeva, Khayala; Mamedov, Nazim; Bayramov, Ayaz [Institute of Physics, Azerbaijan National Academy of Sciences, H. Javid ave, 33, 1143 Baku (Azerbaijan); Shim, Yong Gu [Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, 599-8531 Osaka (Japan); Wakita, Kazuki [Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, 275-0016 Chiba (Japan); Nemov, Sergey [St. Petersburg State Polytechnic University, 195251 St. Petersburg (Russian Federation)

    2013-08-15

    High-grade Bi{sub 2}(Te{sub 0.9}Se{sub 0.1}){sub 3} thin films have been obtained and studied by means of confocal Raman spectroscopy and electrical measurements. The annealed films demonstrate the Raman-active modes, A{sup 1}{sub 1g}(61 cm{sup -1}) and E{sup 2}{sub g}(101 cm{sup -1}), which were not observed on as-grown samples. At densities of incident laser irradiation above 50 W/mm{sup 2}, the infrared-active modes, (95 cm{sup -1}) and A{sup 2}{sub 1u}(120 cm{sup -1}), emerge in the Raman spectra. The last fact is ascribed to symmetry breaking that is resulting from the internal stress and structural deformations caused by local over-heating. The obtained Bi{sub 2}(Te{sub 0.9}Se{sub 0.1}){sub 3} films manifest dielectric rather than metallic conductivity that is usually observed for bulky crystals of this sort. The variable range hopping conduction has been found to be dominant at temperatures below 100 K. Localization radius and density of localized states at Fermi level have been estimated. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. In-plane topological p-n junction in the three-dimensional topological insulator Bi2-xSbxTe3-ySey

    Science.gov (United States)

    Tu, Ngoc Han; Tanabe, Yoichi; Satake, Yosuke; Huynh, Khuong Kim; Tanigaki, Katsumi

    2016-12-01

    A topological p-n junction (TPNJ) is an important concept to control spin and charge transport on a surface of three-dimensional topological insulators (3D-TIs). Here we report successful fabrication of such TPNJ on a surface of 3D-TI Bi2-xSbxTe3-ySey thin films and experimental observation of the electrical transport. By tuning the chemical potential of n-type topological Dirac surface of Bi2-xSbxTe3-ySey on its top half by using tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an organic acceptor molecule, a half surface can be converted to p-type with leaving the other half side as the opposite n-type, and consequently TPNJ can be created. By sweeping the back-gate voltage in the field effect transistor structure, the TPNJ was controlled both on the bottom and the top surfaces. A dramatic change in electrical transport observed at the TPNJ on 3D-TI thin films promises novel spin and charge transport of 3D-TIs for future spintronics.

  11. One-step electrochemical preparation of the ternary (Bi{sub x}Sb{sub 1-x}){sub 2}Te{sub 3} thin films on Au(1 1 1): Composition-dependent growth and characterization studies

    Energy Technology Data Exchange (ETDEWEB)

    Erdogan, Ibrahim Y. [Bingoel University, Sciences and Arts Faculty, Department of Chemistry, 12000, Bingoel (Turkey); Demir, Umit, E-mail: udemir@atauni.edu.t [Atatuerk University, Sciences Faculty, Department of Chemistry, 25240, Erzurum (Turkey)

    2010-09-01

    This study reports on the synthesis of ternary semiconductor (Bi{sub x}Sb{sub 1-x}){sub 2}Te{sub 3} thin films on Au(1 1 1) using a practical electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same solution containing Bi{sup 3+}, SbO{sup +}, and HTeO{sub 2}{sup +} at a constant potential. The thin films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structural, morphological, compositional and optic properties. The ternary thin films of (Bi{sub x}Sb{sub 1-x}){sub 2}Te{sub 3} with various compositions (0.0 {<=} x {<=} 1.0) are highly crystalline and have a kinetically preferred orientation at (0 1 5) for hexagonal crystal structure. AFM images show uniform morphology with hexagonal-shaped crystals deposited over the entire gold substrate. The structure and composition analyses reveal that the thin films are pure phase with corresponding atomic ratios. The optical studies show that the band gap of (Bi{sub x}Sb{sub 1-x}){sub 2}Te{sub 3} thin films could be tuned from 0.17 eV to 0.29 eV as a function of composition.

  12. Synthesis of fibrous reticulate nanocrystalline n-type MoBi{sub 2}(Se{sub 1−x}Te{sub x}){sub 5} thin films: Thermocooling applications

    Energy Technology Data Exchange (ETDEWEB)

    Salunkhe, Manauti M.; Kharade, Rohini R.; Kharade, Suvarta D. [Materials Research Laboratory, Department of Chemistry, Shivaji University, Kolhapur 416004 (India); Mali, Sawanta S.; Patil, P.S. [Thin Film Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416004 (India); Bhosale, P.N., E-mail: p_n_bhosale@rediffmail.com [Materials Research Laboratory, Department of Chemistry, Shivaji University, Kolhapur 416004 (India)

    2012-11-15

    Graphical abstract: Ostwald ripening: If small nucleus is close to a larger crystal, ions formed by particle dissolution of smaller crystal incorporated into larger crystal, and film formation takes place by ion by ion condensation. Display Omitted Highlights: ► Arrested Precipitation Technique is applied to deposit MoBi{sub 2}(Se{sub 1−x}Te{sub x}){sub 5}. ► X-ray diffraction confirms the proper phase formation of material. ► MoBi{sub 2}(Se{sub 1−x}Te{sub x}){sub 5} exhibits an n-type semiconducting behavior. ► Good thermoelectric performance suggests future fantasy. -- Abstract: In the present investigation n-type MoBi{sub 2}(Se{sub 1−x}Te{sub x}){sub 5} nanocrystalline thin films with various compositions of Se and Te were successfully deposited on ultrasonically cleaned glass substrates using recently developed Arrested Precipitation Technique (APT). The effect of composition on optical, morphological, structural, electrical and thermocooling properties of MoBi{sub 2}(Se{sub 1−x}Te{sub x}){sub 5} were investigated using UV–vis–NIR Spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometer, thermoelectric power and thermocooling measurements. Thermoelectric properties including electrical conductivity (σ), Seeback coefficient (S) and figure of merit (ZT) were measured at 300 K. Our aim is to investigate thermocooling behavior in respect of variation in composition of Se and Te in MoBi{sub 2}(Se{sub 1−x}Te{sub x}){sub 5} thin films along with optostructural and optoelectric properties.

  13. Optical parameters of ternary Te{sub 15}(Se{sub 100-x}Bi{sub x}){sub 85} thin films deposited by thermal evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Kameshwar; Thakur, Nagesh [Department of Physics, HP University, Shimla 171005 (India); Sharma, Pankaj [Department of Physics, Jaypee University of Information Technology, Waknaghat, Solan, HP 173215 (India); Katyal, S C, E-mail: kameshwarkumar01@gmail.com, E-mail: pankaj.sharma@juit.ac.in, E-mail: ntb668@yahoo.co.in [Department of Physics, Jaypee Institute of Information Technology, Noida, UP (India)

    2011-10-15

    Thin films of Te{sub 15}(Se{sub 100-x}Bi{sub x}){sub 85} (x=0, 1, 2, 3, 4 and 5 at.%) glassy alloys were deposited by thermal evaporation (at 10{sup -4} Pa) from bulk samples. Optical characterization of the films was done by analysing their transmission spectra taken in the spectral range 400-2300 nm. Swanepoel's method was used to calculate the refractive index (n) and extinction coefficient (k). It was found that the refractive index increases with an increase in Bi content. The Wemple-DiDomenico single-oscillator approach was used to calculate the average band gap energy (E{sub o}), dispersion energy (E{sub d}) and static refractive index (n{sub o}). The absorption coefficient ({alpha}) and film thickness were calculated from the transmission spectra of the films. The optical band gap (E{sub g}) was estimated using Tauc's extrapolation and was found to decrease from 1.37 to 1.21 eV with Bi addition from 0 to 5 at.% in glassy alloys. The decrease in optical band gap is explained on the basis of the decrease in cohesive energy of the samples and the difference of electronegativity of the atoms involved. The real ({epsilon}{sub r}) and imaginary parts ({epsilon}{sub i}) of the dielectric constant for the films were also calculated and reported.

  14. Intermetallic Reactions during the Solid-Liquid Interdiffusion Bonding of Bi2Te2.55Se0.45 Thermoelectric Material with Cu Electrodes Using a Sn Interlayer

    Directory of Open Access Journals (Sweden)

    Chien-Hsun Chuang

    2016-04-01

    Full Text Available The intermetallic compounds formed during the diffusion soldering of a Bi2Te2.55Se0.45 thermoelectric material with a Cu electrode are investigated. For this bonding process, Bi2Te2.55Se0.45 was pre-coated with a 1 μm Sn thin film on the thermoelectric element and pre-heated at 250 °C for 3 min before being electroplated with a Ni barrier layer and a Ag reaction layer. The pre-treated thermoelectric element was bonded with a Ag-coated Cu electrode using a 4 μm Sn interlayer at temperatures between 250 and 325 °C. The results indicated that a multi-layer of Bi–Te–Se/Sn–Te–Se–Bi/Ni3Sn4 phases formed at the Bi2Te2.55Se0.45/Ni interface, ensuring sound cohesion between the Bi2Te2.55Se0.45 thermoelectric material and Ni barrier. The molten Sn interlayer reacted rapidly with both Ag reaction layers to form an Ag3Sn intermetallic layer until it was completely exhausted and the Ag/Sn/Ag sandwich transformed into a Ag/Ag3Sn/Ag joint. Satisfactory shear strengths ranging from 19.3 and 21.8 MPa were achieved in Bi2Te2.55Se0.45/Cu joints bonded at 250 to 300 °C for 5 to 30 min, dropping to values of about 11 MPa for 60 min, bonding at 275 and 300 °C. In addition, poor strengths of about 7 MPa resulted from bonding at a higher temperature of 325 °C for 5 to 60 min.

  15. Microstructure and thermoelectric properties of Bi0.5Na0.02Sb1.48-xInxTe3 alloys fabricated by vacuum melting and hot pressing

    Institute of Scientific and Technical Information of China (English)

    Xing-Kai Duan; Kong-Gang Hu; Da-Hu Ma; Wang-Nian Zhang; Yue-Zhen Jiang; Shu-Chao Guo

    2015-01-01

    The Bi0.5Na0.02Sb1.48-xInxTe3 alloys (x =0.02-0.20) were synthesized by vacuum melting and hot pressing methods at 753 K,60 MPa for 30 min.Effects of Na and In dual partial substitutions for Sb on the thermoelectric properties were investigated from 300 to 500 K.Substituting Sb with Na and In can enhance the Seebeck coefficient effectively near room temperature.The electrical resistivity of the Na and In dual-doping samples is higher within the whole test temperature range.The Bi0.5Na0.02Sb1.48 xInxTe3 samples (x =0.02,0.06) play a great role in optimizing the thermal conductivity.As for the Bi0.5 Na0.02Sb1.46In0.02Te3 alloy,the minimum value of thermal conductivity reaches 0.53 W·m-1·K-1 at 320 K.The thermoelectric performance of the Na and In dualdoped samples is greatly improved,and a figure of merit ZT of 1.26 is achieved at 300 K for the Bi0.5Na0.02Sb1.42 In0.06Te3,representing 26 % enhancement with respect to ZT =1.0 of the undoped sample.

  16. Radiochemical neutron activation analysis for 36 elements in geological material: Au, Ag, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Sn, Te, Tl, U, and Zn as well as Sc, Y, and REE

    Energy Technology Data Exchange (ETDEWEB)

    Anders, E; Wolf, R; Morgan, J W; Ebihara, M; Woodrow, A B; Janssens, M J; Hertogen, J

    1988-01-01

    In lunar and terrestrial rocks and in meteorites, the radiochemical neutron activation method decribed here enables determination of the 21 trace and ultratrace elements Ag, Au, Bi, Br, Cd, Cs, Ga, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Te, Tl, U, Zn, as well as 13 rare earth elements (REE), Sc and Y. Materials, techniques and procedures are discussed. 81 refs.

  17. Two-dimensional universal conductance fluctuations and the electron-phonon interaction of surface states in Bi2Te2Se microflakes.

    Science.gov (United States)

    Li, Zhaoguo; Chen, Taishi; Pan, Haiyang; Song, Fengqi; Wang, Baigeng; Han, Junhao; Qin, Yuyuan; Wang, Xuefeng; Zhang, Rong; Wan, Jianguo; Xing, Dingyu; Wang, Guanghou

    2012-01-01

    The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se microflakes. The solely-B⊥-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such survived UCFs of the surface states result from the limited dephasing length of the bulk carriers in ternary crystals. The electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior.

  18. Nonlinear optical properties of quaternary amorphous Se80.5Bi1.5Te18-yAy (A = Sb, Ag) thin films

    Science.gov (United States)

    Kumar, Anup; Heera, Pawan; Sharma, Raman

    2014-04-01

    Effect of Sb and Ag addition on the optical constants of Se80.5Bi1.5Te18-yAy (A = Sb, Ag and y = 2.0 at. %) thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index increases with an increase in Sb or Ag content and the absorption coefficient is also found to increases with increase in optical energy. Whereas the optical band gap decreases with an increase in Sb content and increases with an increase in Ag content. Hence, the present results reveals that the addition of Sb and Ag produce remarkable change on the nonlinear optical properties of the thin film.

  19. Bismuth (III) Telluride (Bi2Te3) Based Topological Insulator Embedded in PVA as Passive Saturable Absorber in Erbium-Doped Fiber Laser

    Science.gov (United States)

    Apandi, N. H. M.; Ahmad, F.; Ambran, S.; Yamada, M.; Harun, S. W.

    2017-06-01

    We demonstrate a passive Q-switched by integrating a Bismuth (III) Telluride (Bi2Te3) dispersed in Polyvinyl Alcohol (PVA) as passive saturable absorber. The experimental works show that the proposed passive saturable absorber operated at input power ranging from 21.69 mW to 126.89 mW with central operating wavelength of 1531 nm. We observe the tunable repetition rate from 40 kHz to 166 kHz with the shortest pulse width of 1.32 μs. The laser produced maximum instantaneous output peak power and pulse energy of 1.62 mW and 11.2 nJ, respectively. The signal to noise ratio was measured at 49 dB which indicates the stability of the generated pulse.

  20. Holographic recording and characterization of photorefractive Bi{sub 2}TeO{sub 5} crystals at 633 nm wavelength light

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Ivan de, E-mail: ivan@ft.unicamp.br [Grupo de Óptica e Modelagem Numérica (GOMNI)-Faculdade de Tecnologia/UNICAMP, Limeira-SP (Brazil); Carvalho, Jesiel F., E-mail: carvalho@if.ufg.br; Fabris, Zanine V. [Instituto de Física/Universidade Federal de Goiás, Goiânia-GO (Brazil); Frejlich, Jaime, E-mail: frejlich@ifi.unicamp.br [Instituto de Física “Gleb Wataghin”/UNICAMP, Campinas-SP (Brazil)

    2014-04-28

    We report on the holographic recording on photorefractive Bi{sub 2}TeO{sub 5} crystals using λ=633 nm wavelength light. We studied the behavior of this material under the action of this low photonic energy light and found out the presence of a fast and a slow hologram, both of photorefractive nature and exhibiting rather high diffraction efficiencies. The faster and the slower holograms are based on the excitation and diffusion of oppositely charged carriers (likely electrons and holes). Relevant parameters for the photoactive centers responsible for both kind of holograms were characterized using purely holographic techniques. No evidences of non-photosensitive ionic charge carriers being involved in the recording process at room temperature nor self-fixing effects were found.

  1. Metallic conductivity and weak antilocalization in Bi{sub 2}Te{sub 2.7}Se{sub 0.3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Abdullayev, Nadir A.; Kerimova, Afet M.; Aliquliyeva, Khayala V.; Alekperov, Oktay Z.; Mamedov, Nazim T. [Institute of Physics, Azerbaijan National Academy of Sciences, H. Javid Ave. 131, Baku-1143 (Azerbaijan); Shim, Yong Gu; Mimura, Kojiro [Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531 (Japan); Wakita, Kazuki [Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016 (Japan); Zverev, Vladimir N. [Institute of Solid State Physics, 142432, Chernogolovka, Moscow district (Russian Federation)

    2015-06-15

    Submicron thin films of Bi{sub 2}Te{sub 2,7}Se{sub 0,3} solid solution is synthesized by thermal vacuum evaporation. The films are then subjected to after-growth vacuum annealing and characterized using X-ray diffraction and confocal laser microscopy techniques. Electron transport in the synthesized films is studied over the temperature range of 1.4-300 K at magnetic fields up to 8 T. Electron localization due to electron-electron interaction, along with weak anti-localization effect at weak magnetic fields and temperatures below 8 K is observed. The latter effect is commonly encountered in thin films of topological insulators grown by molecular beam epitaxy and has therefore been ascribed to the manifestation of the topological surface states. Finally, phase coherence length is estimated. (Copyright copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Growth of (Bi{sub 1-x}Sb{sub x}){sub 2}Te{sub 3} thin films by metal-organic chemical vapour deposition

    Energy Technology Data Exchange (ETDEWEB)

    Aboulfarah, B.; Mzerd, A. [Univ. MedV Agdal, Rabat (Morocco). Dept. de Physique; Giani, A.; Boulouz, A.; Pascal-Delannoy, F.; Foucaran, A.; Boyer, A. [Centre d' Electronique et de Micro-Optoelectronique de Montpellier (CEM 2), UM II UMR 5507 CNRS, Place E. Bataillon, 34095, Montpellier (France)

    2000-01-29

    The effects of VI/V ratio on electrical and thermoelectrical properties of p-type (Bi{sub 1-x}Sb{sub x}){sub 2}Te{sub 3} elaborated by metal-organic chemical vapour deposition (MOCVD) in horizontal quartz reactor are discussed. The deposited layers exhibit a polycrystalline structure and an improvement in the intensity is observed with increasing the VI/V ratio. The quality of the layers is measured by means of the Energy dispersive X-ray (EDX) microanalyser and scanning electron microscopy (SEM). It is observed that the layers are stoichiometric when the VI/V ratio exceeds 3 and the surface texture is improved with increasing this ratio. The electrical properties of the thin films dependent on the VI/V ratio. The measurements of the Seebeck coefficient suggest a significant potential of MOCVD growth for large-scale production of thermoelectric materials. (orig.)

  3. Origins of enhanced thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wei [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Chi, Hang; Walrath, J. C.; Chang, A. S.; Stoica, Vladimir A.; Endicott, Lynn; Uher, Ctirad, E-mail: cuher@umich.edu [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Tang, Xinfeng [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070 (China); Goldman, R. S. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2016-01-25

    In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materials with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m{sup −1} K{sup −2} is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films.

  4. Nd3+-doped TeO2-Bi2O3-ZnO transparent glass ceramics for laser application at 1.06 μm

    Science.gov (United States)

    Hu, Xiaolin; Luo, Zhiwei; Liu, Taoyong; Lu, Anxian

    2017-04-01

    The high crystallinity transparent glass ceramics based on Nd3+-doped 70TeO2-15Bi2O3-15ZnO (TBZ) compositions were successfully prepared by two-step heat treatment process. The effects of Nd2O3 content on the thermal, structural, mechanical, and optical properties of TBZ glass ceramics were studied. The incorporation of Nd2O3 enhanced the crystallization tendency in the matrix glass composition. The crystal phase and morphology of Bi2Te4O11 in the glass ceramics were confirmed by X-ray diffraction and field emission scanning electron microscopy. Due to precipitate more crystal phase, the hardness values increased from 3.21 to 3.66 GPa. Eight absorption peaks were observed from 400 to 900 nm and three emission bands appeared in the range of 850-1400 nm. With the increasing of Nd2O3 content from 0.5 to 2.5 wt%, the intensity of absorption peaks enhanced and the emission intensity increased up to 1.0 wt% and then fell down for further dopant concentration. The fluorescence decay lifetime decreased rapidly starting from 1.5 wt% Nd2O3 content due to the obvious energy migration among Nd3+. According to the extreme strong emission band around 1062 nm and the optimum Nd2O3 content (1.0 wt%), N10 glass ceramic was considered as a potential material for 1.06 μm laser applications.

  5. Effects of hydrogen reduction on the thermoelectric properties of spark-plasma-sintered Bi{sub 2}Te{sub 3}-based compounds

    Energy Technology Data Exchange (ETDEWEB)

    Lim, C. H.; Cho, D. C.; Lee, Y. S.; Lee, C. H. [Inha University, Incheon (Korea, Republic of); Kim, K. T.; Lee, D. M. [Korea Institute of Industrial Technology, Chonan (Korea, Republic of)

    2005-04-15

    The n-type Bi{sub 2}Te{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds were fabricated by using a spark plasma sintering technique after ball-milling a solidified ingot. Both the n-type and the p-type ingots exhibited low oxygen concentrations of 0.035 at.%. After pulverizing, the oxygen concentrations of both the n-type and the p-type powders considerably increased up to 1.836 at.% and 1.520 at.%, respectively. Due to hydrogen reduction, the oxygen concentrations of the n-type and the p-type powders decreased to 0.196 at.% and 0.234 at.%, respectively. The figure-of{sub m}erit Z of the sintered n-type compounds by using hydrogen-reduced powders was found to be remarkably improved up to 2.37 x 10{sup -3} K{sup -1}, compared with that of sintered n-type compounds by using non-reduced powders (1.32 x 10{sup -3} K{sup -1}) because of the removal of oxygen, which acted as a donor. However, the figure-of-merit Z of the sintered p-type compounds by using hydrogen-reduced powders somewhat increased from 2.72 x 10{sup -3} K{sup -1} to 3.09 x 10{sup -3} K{sup -1}. The p-type thermoelectric compounds are believed to be not significantly affected by hydrogen reduction.

  6. Synthesis, structure, and characterization of two new bismuth(III) selenite/tellurite nitrates: [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO{sub 3})](NO{sub 3})

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Chang-Yu; Wei, Ming-Fang [Department of Chemistry and Materials, Yulin Normal University,Yulin, Guangxi 537000 (China); Geng, Lei, E-mail: lgeng.cn@gmail.com [Department of Materials Science and Engineering, Huaibei Normal University, Huaibei, Anhui 235000 (China); Hu, Pei-Qing; Yu, Meng-Xia [Department of Chemistry and Materials, Yulin Normal University,Yulin, Guangxi 537000 (China); Cheng, Wen-Dan [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)

    2016-07-15

    Two new bismuth(III) selenite/tellurite nitrates, [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO{sub 3})](NO{sub 3}), have been synthesized by conventional facile hydrothermal method at middle temperature 200 °C and characterized by single-crystal X-ray diffraction, powder diffraction, UV–vis–NIR optical absorption spectrum, infrared spectrum and thermal analylsis. Both [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO3)](NO3) crystallize in the monoclinic centronsymmetric space group P2{sub 1}/c with a=9.9403(4) Å, b=9.6857(4) Å, c=10.6864(5) Å, β=93.1150(10)° for [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and a=8.1489(3) Å, b=9.0663(4) Å, c=7.4729(3) Å, β=114.899(2)° for Bi(TeO3)(NO3), respectively. The two compounds, whose structures are composed of three different asymmetric building units, exhibit two different types of structures. The structure of [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) features a three-dimensional (3D) bismuth(III) selenite cationic tunnel structure [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}] {sup 3}{sub ∞} with NO{sub 3}{sup −} anion group filling in the 1D tunnel along b axis. The structure of [Bi(TeO{sub 3})](NO{sub 3}) features 2D bismuth(III) tellurite [Bi(TeO{sub 3}){sub 2}]{sup 2}{sub ∞} layers separated by NO{sub 3}{sup −} anion groups. The results of optical diffuse-reflectance spectrum measurements and electronic structure calculations based on density functional theory methods show that the two compounds are wide band-gap semiconductors. - Graphical abstract: Two novel bismuth{sup III} selenite/tellurite nitrates [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) with 3D tunnel structure and [Bi(TeO{sub 3})](NO{sub 3}) with 2D layer structure have been firstly synthesized and characterized. Display Omitted - Highlights: • Two novel bismuth{sup III} nitrates [(Bi{sub 3}O{sub 2})(SeO{sub 3}){sub 2}](NO{sub 3}) and [Bi(TeO{sub 3})](NO{sub 3}) were firstly

  7. Effect of high pressure sintering and annealing on microstructure and thermoelectric properties of nanocrystalline Bi2Te2.7Se0.3 doped with Gd

    Institute of Scientific and Technical Information of China (English)

    Ping Zou; Guiying Xun; Song Wang; Penglei Chen; Fengzhu Huang

    2014-01-01

    Bi2Te2.7Se0.3 of high performance doped with Gd bulk materials was prepared by a high pressure (6.0 GPa) sintering (HPS) method at 593 K, 633 K, 673 K and 693 K. The sample was then annealed for 36 h in a vacuum at 633 K. The phase composition, crystal structure and morphology of the sample were analyzed by X-ray diffraction and scanning electron microscopy. The electric conductivity, Seebeck coefficient, and thermal conductivity aspects of the sample were measured from 298 K to 473 K. The results show that high pressure sintering and the doping with Gd has a great effect on the crystal structure and the thermoelectric properties of the samples. The samples are consisted of nanoparticles before and after annealing, and these nanostructures have good stability at high temperature. HPS together with annealing can improve the TE properties of the sample by decreasing the thermal conductivity of the sample with nanostructures. The maximum ZT value of 0.74 was obtained at 423 K for the sample, which was sintered at 673 K and then annealed at 633 K for 36 h. Compared with the zone melting sample, it was increased by 85%at 423 K. Hence the temperature of the maximum of figure of merit was increased. The results can be applied to the field of thermoelectric power generation materials.

  8. Studies on Microstructure and Thermoelectric Properties of p-Type Bi-Sb-Te Based Alloys by Gas Atomization and Hot Extrusion Processes

    Science.gov (United States)

    Park, Ki-Chan; Madavali, Babu; Kim, Eun-Bin; Koo, Kyung-Wan; Hong, Soon-Jik

    2016-10-01

    p-Type Bi2Te3 + 75% Sb2Te3 based thermoelectric materials were fabricated via gas atomization and the hot extrusion process. The gas atomized powder showed a clean surface with a spherical shape, and expanded in a wide particle size distribution (average particle size 50 μm). The phase of the fabricated extruded and R-extruded bars was identified using x-ray diffraction. The relative densities of both the extruded and R-extruded samples were measured by Archimedes principle with ˜98% relative density. The R-extruded bar exhibited finer grain microstructure than that of single extrusion process, which was attributed to a recrystallization mechanism during the fabrication. The R-extruded sample showed improved Vickers hardness compared to the extruded sample due to its fine grain microstructure. The electrical conductivity improved for the extruded sample whereas the Seebeck coefficient decreases due to its high carrier concentration. The peak power factor, ˜4.26 × 10-3 w/mK2 was obtained for the single extrusion sample, which is higher than the R-extrusion sample owing to its high electrical properties.

  9. Studies on Microstructure and Thermoelectric Properties of p-Type Bi-Sb-Te Based Alloys by Gas Atomization and Hot Extrusion Processes

    Science.gov (United States)

    Park, Ki-Chan; Madavali, Babu; Kim, Eun-Bin; Koo, Kyung-Wan; Hong, Soon-Jik

    2017-05-01

    p-Type Bi2Te3 + 75% Sb2Te3 based thermoelectric materials were fabricated via gas atomization and the hot extrusion process. The gas atomized powder showed a clean surface with a spherical shape, and expanded in a wide particle size distribution (average particle size 50 μm). The phase of the fabricated extruded and R-extruded bars was identified using x-ray diffraction. The relative densities of both the extruded and R-extruded samples were measured by Archimedes principle with ˜98% relative density. The R-extruded bar exhibited finer grain microstructure than that of single extrusion process, which was attributed to a recrystallization mechanism during the fabrication. The R-extruded sample showed improved Vickers hardness compared to the extruded sample due to its fine grain microstructure. The electrical conductivity improved for the extruded sample whereas the Seebeck coefficient decreases due to its high carrier concentration. The peak power factor, ˜4.26 × 10-3 w/mK2 was obtained for the single extrusion sample, which is higher than the R-extrusion sample owing to its high electrical properties.

  10. Epitaxial growth and improved electronic properties of (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} thin films grown on sapphire (0001) substrates: The influence of Sb content and the annealing

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wei; Stoica, Vladimir; Chi, Hang; Endicott, Lynn; Uher, Ctirad, E-mail: cuher@umich.edu

    2015-10-25

    In this research, we report on the epitaxial growth of basal plane-oriented (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} films (0 ≤ x ≤ 1) on sapphire (0001) substrates through Molecular Beam Epitaxy (MBE) and demonstrate the influence of composition, crystal orientation and post-annealing process on their electronic properties. The as-grown (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} films change gradually from a strong n-type to a strong p-type conduction when the Sb content increases from 0 to 1, which is attributed to the charge carrier compensation between the n-type Te{sub Bi} and p-type Sb{sub Te} antisite defects. The crossover between the n- and p-type conduction is found for x between 0.6 and 0.7. We also find that post-annealing (at 580 K) is beneficial for the electronic properties of the p-type (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} films: they attain improved carrier mobility and significantly increased hole density. However, annealing plays a negative role in the electronic properties of the n-type structures leading to an enhanced resistivity as well as a reduced Seebeck coefficient. The most plausible explanation for such annealing effects is an introduction of p-type defects in both the n-type and p-type (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} films. The as-grown Bi{sub 2}Te{sub 3} film possesses the largest thermoelectric power factor among all n-type films, reaching 4.1 and 2.5 mWm{sup −1} K{sup −2} at 122 and 300 K respectively, due to the high carrier mobility and proper carrier doping. In contrast, a remarkably improved power factor in p-type (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} films is achieved upon annealing at 580 K for 1 h. The highest power factor in p-type Bi{sub 0.6}Sb{sub 1.4}Te{sub 3} and Sb{sub 2}Te{sub 3} films is obtained at around 150 K and it increases from 0.2 mWm{sup −1} K{sup −2} (Bi{sub 0.6}Sb{sub 1.4}Te{sub 3}) and 1.8 mWm{sup −1} K{sup −2} (Sb{sub 2}Te{sub 3}) for the as-grown films to 3.5 mWm{sup −1} K

  11. Thermoelectric properties of n-type Bi{sub 2}Te{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} thin films deposited by direct current magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Bourgault, D. [Schneider-Electric France, 38TEC/T1, 37 quai Paul Louis Merlin, 38050 Grenoble Cedex 9 (France); Institut Neel/Centre National de la Recherche Scientifique, 25 Avenue des Martyrs, BP 166, 38042 Grenoble Cedex 9 (France)], E-mail: daniel.bourgault@grenoble.cnrs.fr; Garampon, C. Giroud; Caillault, N.; Carbone, L.; Aymami, J.A. [Schneider-Electric France, 38TEC/T1, 37 quai Paul Louis Merlin, 38050 Grenoble Cedex 9 (France)

    2008-10-01

    n-type and p-type thermoelectric thin films have been deposited by direct current magnetron sputtering from n-type Bi{sub 2}Te{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} targets on glass and Al{sub 2}O{sub 3} substrates. X-ray diffraction and energy dispersive spectrometry combined with electrical measurements such as Seebeck coefficient and electrical resistivity were used for the thermoelectric thin films characterization. It was found that the composition of the sputtered thin films was close to the sputtering target stoichiometry for the tested deposition conditions and that the thin film composition did not seem to be the determinant parameter for the thermoelectrical properties. Indeed, the chamber pressure and plasma power have a greater influence on the thermoelectrical performances of the films. Annealing in Ar atmosphere (250 deg. C for n-type and 300 deg. C for p-type films) enhanced the film crystallization and yield power factors higher than 1 mW/K{sup 2} m.

  12. Performance of a Composite Thermoelectric Generator with Different Arrangements of SiGe, BiTe and PbTe under Different Configurations

    Directory of Open Access Journals (Sweden)

    Alexander Vargas-Almeida

    2015-10-01

    Full Text Available In this study, we analyze the role of the thermoelectric (TE properties, namely Seebeck coefficient α, thermal conductivity κ and electrical resistivity ρ, of three different materials in a composite thermoelectric generator (CTEG under different configurations. The CTEG is composed of three thermoelectric modules (TEMs: (1 two TEMs thermally and electrically connected in series (SC; (2 two branches of TEMs thermally and electrically connected in parallel (PSC; and (3 three TEMs thermally and electrically connected in parallel (TEP. In general, each of the TEMs have different thermoelectric parameters, namely a Seebeck coefficient α, a thermal conductance K and an electrical resistance R. Following the framework proposed recently, we show the effect of: (1 the configuration; and (2 the arrangements of TE materials on the corresponding equivalent figure of merit Zeq and consequently on the maximum power Pmax and efficiency η of the CTEG. Firstly, we consider that the whole system is formed of the same thermoelectric material (α1,K1,R1 = α2,K2,R2 = α3,K3,R3 and, secondly, that the whole system is constituted by only two different thermoelectric materials Entropy 2015, 17 7388 (αi,Ki,Ri ≠ αj ,Kj ,Rj 6= αl,Kl,Rl, where i, j, l can be 1, 2 or 3. In this work, we propose arrangements of TEMs, which clearly have the advantage of a higher thermoelectric figure of merit value compared to a conventional thermoelectric module. A corollary about the Zeq-max for CTEG is obtained as a result of these considerations. We suggest an optimum configuration.

  13. Thermoelectric properties of porous (Bi0.15Sb0.85)2Te3 thermoelectric materials

    Institute of Scientific and Technical Information of China (English)

    Guiying Xu; Tingjie Chen; Jianqiang Liu; Zhangjian Zhou

    2003-01-01

    In order to obtain thermoelectric materials with high figure of merit, the concept of Hollow (Vacuum) Quantum Structure or Effect and related thermoelectric materials design were proposed. To demonstrate the theory, the materials of (Bio.15Sb0.85)2Te3 with porous structure have been fabricated. Their thermoelectric properties and the microstructure were investigated and compared with their density structure. It was found that the porous structure could improve their properties greatly.

  14. Heavily Cr-doped (Bi,Sb2Te3 as a ferromagnetic insulator with electrically tunable conductivity

    Directory of Open Access Journals (Sweden)

    Yunbo Ou

    2016-08-01

    Full Text Available With molecular beam epitaxy we have grown Cry(BixSb1-x2-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.

  15. Metal-insulator transition and tunable Dirac-cone surface state in the topological insulator TlBi1 -xSbxTe2 studied by angle-resolved photoemission

    Science.gov (United States)

    Trang, Chi Xuan; Wang, Zhiwei; Yamada, Keiko; Souma, Seigo; Sato, Takafumi; Takahashi, Takashi; Segawa, Kouji; Ando, Yoichi

    2016-04-01

    We report a systematic angle-resolved photoemission spectroscopy on topological insulator (TI) TlBi1 -xSbxTe2 which is bulk insulating at 0.5 ≲x ≲0.9 and undergoes a metal-insulator-metal transition with the Sb content x . We found that this transition is characterized by a systematic hole doping with increasing x , which results in the Fermi-level crossings of the bulk conduction and valence bands at x ˜0 and x ˜1 , respectively. The Dirac point of the topological surface state is gradually isolated from the valence-band edge, accompanied by a sign reversal of Dirac carriers. We also found that the Dirac velocity is the largest among known solid-solution TI systems. The TlBi1 -xSbxTe2 system thus provides an excellent platform for Dirac-cone engineering and device applications of TIs.

  16. Discovery of spin-textured single-Dirac-cone pi-Berry's phase Topological Insulator states in Bi2Se3, Bi2Te3 and Sb2Te3 and related new materials

    Science.gov (United States)

    Zahid Hasan, M.; Hsieh, David; Xia, Yuqi; Wray, L. Andrew; Qian, Dong; Dil, J. Hugo; Meier, Fabian; Patthey, Luc; Osterwalder, Jurg; Fedorov, Alexei; Lin, Hsin; Bansil, Arun; Grauer, David; Hor, Yewsan; Cava, Robert

    2010-03-01

    The topological insulator is a fundamentally new state of quantum matter that exhibits exotic quantum-Hall-like behavior even in the absence of an applied magnetic field. In this talk, I will present new results on the topological insulator in Bi1-xSbx beyond Ref-[1,2], and then report our discovery and findings of a new generation of topological insulators with a single spin-helical surface Dirac cone that can be gated by chemical tuning of the surface [3,4,5]. A method would be discussed how superconducting and magnetic interactions [6] can be realized within the topological matrix. [1] ``A topological Dirac insulator in a quantum spin Hall phase'', D. Hsieh et al., Nature 452, 970 (2008). [2] ``Observation of unconventional quantum spin textures in topological insulators'', D. Hsieh et al., Science 323, 919 (2009). [3] ``Observation of a large-gap topologicalinsulator class with a single Dirac cone on the surface'', Y. Xia et al., Nature Phys. 5, 398 (2009). [4] D. Hsieh et al., Phys. Rev. Lett., 103, 146401 (2009). [5] ``A tunable topological insulator in the spin helical Dirac transport regime'', D. Hsieh et al., Nature 460, 1101 (2009). [6] Preprint (2009).

  17. Effect of high pressure sintering and annealing on microstructure and thermoelectric properties of nanocrystalline Bi2Te2.7Se0.3 doped with Gd

    Directory of Open Access Journals (Sweden)

    Ping Zou

    2014-06-01

    Full Text Available Bi2Te2.7Se0.3 of high performance doped with Gd bulk materials was prepared by a high pressure (6.0 GPa sintering (HPS method at 593 K, 633 K, 673 K and 693 K. The sample was then annealed for 36 h in a vacuum at 633 K. The phase composition, crystal structure and morphology of the sample were analyzed by X-ray diffraction and scanning electron microscopy. The electric conductivity, Seebeck coefficient, and thermal conductivity aspects of the sample were measured from 298 K to 473 K. The results show that high pressure sintering and the doping with Gd has a great effect on the crystal structure and the thermoelectric properties of the samples. The samples are consisted of nanoparticles before and after annealing, and these nanostructures have good stability at high temperature. HPS together with annealing can improve the TE properties of the sample by decreasing the thermal conductivity of the sample with nanostructures. The maximum ZT value of 0.74 was obtained at 423 K for the sample, which was sintered at 673 K and then annealed at 633 K for 36 h. Compared with the zone melting sample, it was increased by 85% at 423 K. Hence the temperature of the maximum of figure of merit was increased. The results can be applied to the field of thermoelectric power generation materials.

  18. On the effect of carbon nanotubes on the thermoelectric properties of n-Bi{sub 2}Te{sub 2.4}Se{sub 0.6} made by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Lognoné, Quentin; Gascoin, Franck, E-mail: franck.gascoin@ensicaen.fr

    2015-06-25

    Highlights: • Mechanical alloying fabrication of MWCNTs/n-Bi{sub 2}Se{sub 0.6}Te{sub 2.4} composites. • Effect of the addition of MWCNTs on the carrier concentration. • Carrier concentration variation with MWCNTs’ content. - Abstract: Composite materials based on n-Bi{sub 2}Te{sub 2.4}Se{sub 0.6} with commercial multi walled carbon nanotubes (MWCNTs) have been synthesized via high energy ball milling and spark plasma sintering. The effect on the transport properties of the presence of MWCNTs during the ball billing step is studied. It is demonstrated that MWCNTs, even in small quantity, change dramatically the transport properties. Seebeck coefficient, electrical resistivity, thermal diffusivity and carrier concentration are measured and their variation discussed. The presence of MWCNTs during the ball milling step is discussed as it clearly induces three competing effects, the presence of tellurium vacancy, the decreased grain size of Bi{sub 2}Te{sub 2.4}Se{sub 0.6} either promoted during the ball milling or result of the a prevented grain growth during the sintering and a n-type doping. The large carrier concentration variation caused by the MWCNTs represents an alternative way of tuning the transport properties.

  19. Fabrication and Enhanced Thermoelectric Properties of Alumina Nanoparticle-Dispersed Bi0.5Sb1.5Te3 Matrix Composites

    Directory of Open Access Journals (Sweden)

    Kyung Tae Kim

    2013-01-01

    Full Text Available Alumina nanoparticle-dispersed bismuth-antimony-tellurium matrix (Al2O3/BST composite powders were fabricated by using ball milling process of alumina nanoparticle about 10 nm and p-type bismuth telluride nanopowders prepared from the mechanochemical process (MCP. The fabricated Al2O3/BST composite powders were a few hundreds of nanometer in size, with a clear Bi0.5Sb1.5Te3 phase. The composite powders were consolidated into p-type bulk composite by spark plasma sintering process. High-resolution TEM images reveal that alumina nanoparticles were dispersed among the grain boundary or in the matrix grain. The sintered 0.3 vol.% Al2O3/BST composite exhibited significantly improved power factor and reduced thermal conductivity in the temperature ranging from 293 to 473 K compared to those of pure BST. From these results, the highly increased ZT value of 1.5 was obtained from 0.3 vol.% Al2O3/BST composite at 323 K.

  20. The Broad Anti-AML Activity of the CD33/CD3 BiTE Antibody Construct, AMG 330, Is Impacted by Disease Stage and Risk.

    Science.gov (United States)

    Harrington, Kimberly H; Gudgeon, Chelsea J; Laszlo, George S; Newhall, Kathryn J; Sinclair, Angus M; Frankel, Stanley R; Kischel, Roman; Chen, Guang; Walter, Roland B

    2015-01-01

    The CD33/CD3-bispecific T-cell engaging (BiTE) antibody construct, AMG 330, potently lyses CD33+ leukemic cells in vitro. Using specimens from 41 patients with acute myeloid leukemia (AML), we studied the factors that might contribute to clinical response or resistance. For this purpose, thawed aliquots of primary AML samples were immunophenotypically characterized and subjected to various doses of AMG 330 in the presence or absence of healthy donor T-cells. After 48 hours, drug-specific cytotoxicity was quantified and correlated with CD33 expression levels, amounts of T-cells present, and other disease characteristics. AMG 330 caused modest cytotoxicity that was correlated with the amount of autologous T-cells (P = 0.0001) but not CD33 expression, as AMG 330 exerted marked cytotoxic effects in several specimens with minimal CD33 expression. With healthy donor T-cells added, AMG 330 cytotoxicity depended on the drug dose and effector:target (E:T) cell ratio. High cytotoxic activity was observed even with minimal CD33 expression, and AMG 330 cytotoxicity and CD33 expression correlated only at high E:T cell ratio and high AMG 330 doses (Pspectrum, while suggesting the presence of yet undefined, CD33-independent, relative resistance mechanisms in specific patient subsets.

  1. Effect of preparation procedure and nanostructuring on the thermoelectric properties of the lead telluride-based material system AgPbmBiTe2+m (BLST-m)

    Science.gov (United States)

    Falkenbach, Oliver; Schmitz, Andreas; Hartung, David; Dankwort, Torben; Koch, Guenter; Kienle, Lorenz; Klar, Peter J.; Mueller, Eckhard; Schlecht, Sabine

    2016-06-01

    We report on the preparation and thermoelectric properties of the quaternary system AgPbmBiTe2+m (Bismuth-Lead-Silver-Tellurium, BLST-m) that were nanostructured by mechanical alloying. Nanopowders of various compositions were compacted by three different methods: cold pressing/annealing, hot pressing, and short term sintering. The products are compared with respect to microstructure and sample density. The thermoelectric properties were measured: thermal conductivity in the temperature range from 300 K to 800 K and electrical conductivity and Seebeck coefficient between 100 K and 800 K. The compacting method and the composition had a substantial impact on carrier concentration and mobility as well as on the thermoelectric parameters. Room temperature Hall measurements yielded carrier concentrations in the order of 1019 cm-3, slightly increasing with increasing content of the additive silver bismuth telluride to the lead telluride base. ZT values close to the ones of bulk samples were achieved. X-ray diffraction and transmission electron microscopy (TEM) showed macroscopically homogeneous distributions of the constituting elements inside the nanopowders ensembles, indicating a solid solution. However, high resolution transmission electron microscopy (HRTEM) revealed disorder on the nanoscale inside individual nanopowders grains.

  2. Mid-infrared ultra-short mode-locked fiber laser utilizing topological insulator Bi2Te3 nano-sheets as the saturable absorber

    CERN Document Server

    Yin, Ke; Zheng, Xin; Yu, Hao; Cheng, Xiangai; Hou, Jing

    2015-01-01

    The newly-emergent two-dimensional topological insulators (TIs) have shown their unique electronic and optical properties, such as good thermal management, high nonlinear refraction index and ultrafast relaxation time. Their narrow energy band gaps predict their optical absorption ability further into the mid-infrared region and their possibility to be very broadband light modulators ranging from the visible to the mid-infrared region. In this paper, a mid-infrared mode-locked fluoride fiber laser with TI Bi2Te3 nano-sheets as the saturable absorber is presented. Continuous wave lasing, Q-switched and continuous-wave mode-locking (CW-ML) operations of the laser are observed sequentially by increasing the pump power. The observed CW-ML pulse train has a pulse repetition rate of 10.4 MHz, a pulse width of ~6 ps, and a center wavelength of 2830 nm. The maximum achievable pulse energy is 8.6 nJ with average power up to 90 mW. This work forcefully demonstrates the promising applications of two-dimensional TIs for ...

  3. Measurement of the topological surface state optical conductance in bulk-insulating Sn-doped Bi1.1Sb0.9Te2S single crystals

    Science.gov (United States)

    Cheng, Bing; Wu, Liang; Kushwaha, S. K.; Cava, R. J.; Armitage, N. P.

    2016-11-01

    Topological surface states have been extensively observed via optics in thin films of topological insulators. However, in typical thick single crystals of these materials, bulk states are dominant and it is difficult for optics to verify the existence of topological surface states definitively. In this Rapid Communication, we study the charge dynamics of the newly formulated bulk-insulating Sn-doped Bi1.1Sb0.9Te2S crystal by using time-domain terahertz spectroscopy. This compound shows much better insulating behavior than any other bulk-insulating topological insulators reported previously. The transmission can be enhanced an amount which is 5 % of the zero-field transmission by applying magnetic field to 7 T, an effect which we believe is due to the suppression of topological surface states. This suppression is essentially independent of the thicknesses of the samples, showing the two-dimensional nature of the transport. The suppression of surface states in field allows us to use the crystal slab itself as a reference sample to extract the surface conductance, mobility, charge density, and scattering rate. Our measurements set the stage for the investigation of phenomena out of the semiclassical regime, such as the topological magnetoelectric effect.

  4. Modification of the electronic band structure of the topological insulator Bi2Te3 by the adsorption of the organic molecule Manganese Phthalocyanine

    Science.gov (United States)

    Hewitt, Andrew; Boltersdorf, Jonathon; Maggard, Paul; Dougherty, Daniel

    Topological insulators (TIs) have a spin-textured surface state protected by time-reversal symmetry within a bulk insulating gap. Typical approaches to breaking time-reversal symmetry have been to introduce dilute magnetic impurities into a solid-solution synthesis. Organic molecules offer another route for magnetic-doping of TIs. It has been shown that a coupling may exist, along with a new hybrid-interface state, between the magnetic molecule Manganese Phthalocyanine (MnPc) and the TI Bi2Te3. We report the modification of the electronic band structure by the adsorption of MnPc molecules as measured by ultraviolet photoelectron spectroscopy. We show a new state emerging below the Fermi level at less than a monolayer coverage of MnPc molecules. We also observe an n-doping effect as charge is transferred from the molecule to the TI substrate in agreement with recent work. We suggest that this interface system may have important implications for understanding the role of local time reversal symmetry breaking in TI's and in controlling spin injection into these novel materials.

  5. High-quality and Large-size Topological Insulator Bi2Te3-Gold Saturable Absorber Mirror for Mode-Locking Fiber Laser

    Science.gov (United States)

    Chen, Hou-Ren; Tsai, Chih-Ya; Cheng, Hsin-Ming; Lin, Kuei-Huei; Yen, Po-Hsiu; Chen, Chyong-Hua; Hsieh, Wen-Feng

    2016-12-01

    A novel high-quality, large-size, reflection-type topological insulator Bi2Te3-Gold (BG) film-based nonlinear optical modulator has been successfully fabricated as a two-dimensional saturable absorber mirror (SAM) by pulsed laser deposition (PLD). This BG-SAM possesses saturation fluence of 108.3 μJ/cm2, modulation depth (ΔR) of 6.5%, non-saturable loss of 38.4%, high damage threshold above 1.354 mJ/cm2 and excellent uniformity providing for the generation of passive mode-locked (ML) pulses for erbium-doped fiber lasers (EDFLs) on a large sample area. Under 124 mW 976 nm pumping, We obtained 452-fs continuous-wave ML pulses with pulse energy of 91 pJ and full width at half-maximum (FWHM) of 6.72-nm from this EDFL. The results clearly evidence that the PLD is an efficient method for fabricating BG-SAM that is suitable for a compact ultrafast ML fiber laser system.

  6. The Broad Anti-AML Activity of the CD33/CD3 BiTE Antibody Construct, AMG 330, Is Impacted by Disease Stage and Risk.

    Directory of Open Access Journals (Sweden)

    Kimberly H Harrington

    Full Text Available The CD33/CD3-bispecific T-cell engaging (BiTE antibody construct, AMG 330, potently lyses CD33+ leukemic cells in vitro. Using specimens from 41 patients with acute myeloid leukemia (AML, we studied the factors that might contribute to clinical response or resistance. For this purpose, thawed aliquots of primary AML samples were immunophenotypically characterized and subjected to various doses of AMG 330 in the presence or absence of healthy donor T-cells. After 48 hours, drug-specific cytotoxicity was quantified and correlated with CD33 expression levels, amounts of T-cells present, and other disease characteristics. AMG 330 caused modest cytotoxicity that was correlated with the amount of autologous T-cells (P = 0.0001 but not CD33 expression, as AMG 330 exerted marked cytotoxic effects in several specimens with minimal CD33 expression. With healthy donor T-cells added, AMG 330 cytotoxicity depended on the drug dose and effector:target (E:T cell ratio. High cytotoxic activity was observed even with minimal CD33 expression, and AMG 330 cytotoxicity and CD33 expression correlated only at high E:T cell ratio and high AMG 330 doses (P<0.003. AMG 330 resulted in significantly higher cytotoxicity in specimens from patients with newly diagnosed AML than those with relapsed/refractory disease despite similar levels of CD33 on myeloblasts. AMG 330 cytotoxicity also appeared greater in specimens from patients with favorable-risk disease as compared to other specimens. Together, our data demonstrate that AMG 330 is highly active in primary AML specimens across the entire disease spectrum, while suggesting the presence of yet undefined, CD33-independent, relative resistance mechanisms in specific patient subsets.

  7. Study of Third-Order Optical Nonlinearities of Se-Sn (Bi,Te) Quaternary Chalcogenide Thin Films Using Ti: Sapphire Laser in Femtosecond Regime

    Science.gov (United States)

    Yadav, Preeti; Sharma, Ambika

    2017-01-01

    The objective of the present research work is to study the nonlinear optical properties of quaternary Se-Sn (Bi,Te) chalcogenide thin films. A Z-scan technique utilizing 800 nm femtosecond laser source has been used for the determination of the nonlinear refractive index ( n 2), two-photon absorption coefficient ( β 2) and third-order susceptibility ( χ (3)). In the measurement of n 2, an aperture is placed in the far field before the detector (closed aperture), while for the measurement of β 2, entire transmitted light is collected by the detector without an aperture (open aperture). Self-focusing has been observed in closed aperture transmission spectra. The appearance of the peak after the valley in this spectrum reflects the positive nonlinear refractive index. The calculated value of n 2 of the studied thin films varies from 1.06 × 10-12 cm2/W to 0.88 × 10-12 cm2/W. The compound-dependent behavior of n 2 is explained in this paper. We have also compared the experimental values of n 2 with the theoretically determined values, other compounds of chalcogenide glass and pure silica. The n 2 of the investigated thin films is found to be 3200 times higher than pure silica. The results of the open aperture Z-scan revealed that the value of β 2 of the studied compound is in the order of 10-8 cm/W. The behavior of two-photon absorption is described by means of the optical band gap ( E g) of the studied compound. The variation in the figure-of-merit from 0.32 to 1.4 with varying Sn content is also reported in this paper. The higher value of nonlinearity makes this material advantageous for optical fibers, waveguides and optical limiting devices.

  8. Study of Third-Order Optical Nonlinearities of Se-Sn (Bi,Te) Quaternary Chalcogenide Thin Films Using Ti: Sapphire Laser in Femtosecond Regime

    Science.gov (United States)

    Yadav, Preeti; Sharma, Ambika

    2016-09-01

    The objective of the present research work is to study the nonlinear optical properties of quaternary Se-Sn (Bi,Te) chalcogenide thin films. A Z-scan technique utilizing 800 nm femtosecond laser source has been used for the determination of the nonlinear refractive index (n 2), two-photon absorption coefficient (β 2) and third-order susceptibility (χ (3)). In the measurement of n 2, an aperture is placed in the far field before the detector (closed aperture), while for the measurement of β 2, entire transmitted light is collected by the detector without an aperture (open aperture). Self-focusing has been observed in closed aperture transmission spectra. The appearance of the peak after the valley in this spectrum reflects the positive nonlinear refractive index. The calculated value of n 2 of the studied thin films varies from 1.06 × 10-12 cm2/W to 0.88 × 10-12 cm2/W. The compound-dependent behavior of n 2 is explained in this paper. We have also compared the experimental values of n 2 with the theoretically determined values, other compounds of chalcogenide glass and pure silica. The n 2 of the investigated thin films is found to be 3200 times higher than pure silica. The results of the open aperture Z-scan revealed that the value of β 2 of the studied compound is in the order of 10-8 cm/W. The behavior of two-photon absorption is described by means of the optical band gap (E g) of the studied compound. The variation in the figure-of-merit from 0.32 to 1.4 with varying Sn content is also reported in this paper. The higher value of nonlinearity makes this material advantageous for optical fibers, waveguides and optical limiting devices.

  9. Possible flat band bending of the Bi1.5Sb0.5Te1.7Se1.3 crystal cleaved in an ambient air probed by terahertz emission spectroscopy

    OpenAIRE

    Soon Hee Park; Sun Young Hamh; Joonbum Park; Jun Sung Kim; Jong Seok Lee

    2016-01-01

    We investigate an evolution of the surface electronic state of the Bi1.5Sb0.5Te1.7Se1.3 single crystal, which is one of the most bulk insulating topological insulators, by examining terahertz light emitted from the sample surface upon the illumination of the near-infrared femtosecond laser pulses. We find that the surface state with a flat band bending can appear in the course of the natural maturation process of the surface state in an ambient air. Furthermore, we demonstrate that the evolut...

  10. Carrier dependent ferromagnetism in chromium doped topological insulator Cr{sub y}(Bi{sub x}Sb{sub 1−x}){sub 2−y}Te{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Li, Bin; Fan, Qingyan; Ji, Fuhao; Liu, Zhen; Pan, Hong; Qiao, S., E-mail: qiaoshan@fudan.edu.cn

    2013-10-30

    To understand the mechanism of ferromagnetism in topological insulator, we studied the structural, magnetic and transport characters of Cr{sub y}(Bi{sub x}Sb{sub 1−x}){sub 2−y}Te{sub 3} single crystals. The Curie temperature T{sub C}, which is determined from magnetization and anomalous Hall effect (AHE) measurements by Arrott plots, is found to be proportional to y{sub Cr}⁎p{sup 1/3}, where p is the hole density. This fact supports a scenario of Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction with mean-field approximation.

  11. Effect of spark plasma sintering conditions on the thermoelectric properties of (Bi{sub 0.25}Sb{sub 0.75}){sub 2}Te{sub 3} alloys

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Sang-Soon [Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Ju-Heon [High Temp. Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Kwon, Beomjin; Kim, Seong Keun [Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Park, Hyung-Ho [Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Lee, Ki-Suk; Baik, Jeong Min [School of Materials and Science Engineering, UNIST, Ulsan 689-798 (Korea, Republic of); KIST-UNIST Ulsan Center for Convergent Materials, UNIST, Ulsan 689-798 (Korea, Republic of); Choi, Won Jun [Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Kim, Dong-Ik [High Temp. Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Hyun, Dow-Bin; Kim, Jin-Sang [Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Baek, Seung-Hyub, E-mail: shbaek77@kist.re.kr [Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); KIST-UNIST Ulsan Center for Convergent Materials, UNIST, Ulsan 689-798 (Korea, Republic of); Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-333 (Korea, Republic of)

    2016-09-05

    As a field-assisted technique, spark plasma sintering (SPS) enables densification of specimens in a very short period of time compared to other sintering techniques. For high performance thermoelectric material synthesis, SPS is widely used to fabricate nanograin-structured thermoelectric materials by rapidly densifying the nanopowders suppressing grain growth. However, the microstructural evolution behavior of thermoelectric materials by SPS, another important process during sintering, has been rarely studied. Here, we explore SPS as a tool to control the microstructure by long-time SPS. Using p-type (Bi{sub 0.25}Sb{sub 0.75}){sub 2}Te{sub 3} thermoelectric materials as a model system, we systematically vary SPS temperature and time to understand the correlations between SPS conditions, microstructural evolution, and the thermoelectric properties. Our results show that the relatively low eutectic temperature (∼420 °C) and the existence of volatile tellurium (Te) are critical factors to determine both microstructure and thermoelectric property. In the liquid-phase sintering regime, rapid evaporation of Te leads to a strong dependence of thermoelectric property on SPS time. On the other hand, in the solid-phase sintering regime, there is a weak dependence on SPS time. The optimum thermoelectric figure-of-merit (Z) of 2.93 × 10{sup −3}/K is achieved by SPS at 500 °C for 30 min. Our results will provide an insight on the optimization of SPS conditions for materials containing volatile elements with low eutectic temperature. - Highlights: • Spark plasma sintering (SPS) is used to synthesize the thermoelectric (Bi{sub 0.25}Sb{sub 0.75}){sub 2}Te{sub 3}. • Liquid phase and volatile element are a key for the microstructure and thermoelectric property. • Thermoelectric figure-of-merit of 2.9 × 10{sup −3}/K is achieved at 500 °C for 30 min.

  12. New tellurite glasses and crystalline phases in the Bi{sub 2}O{sub 3}-CaO-TeO{sub 2} system: Synthesis and characterization

    Energy Technology Data Exchange (ETDEWEB)

    Chagraoui, Abdeslam; Tairi, Abdelmjid; Ajebli, Kaltoum; Bensaid, Hanane; Moussaoui, Abdenajib [Laboratoire de Chimie Analytique et Physico-chimie des Materiaux, Departement de Chimie, Faculte des Sciences Ben M' sik, Universite HassanII-Mohammedia Casablanca (Morocco)

    2010-04-09

    Tellurite glasses containing calcium and bismuth oxides have been prepared at 800 {sup o}C and investigated by X-ray diffraction, DSC, IR and Raman spectroscopy. The crystalline phases of glasses in TeO{sub 2}-CaO revealed {gamma}TeO{sub 2} phase which transforms into the stable {alpha}TeO{sub 2} phase up to 500 {sup o}C. IR and Raman studies show the transition of TeO{sub 4}, TeO{sub 3+1} and TeO{sub 3} units with increasing CaO content. The value of refractive index and density of glasses have been measured. The investigation in the system using XRD reveals new phases.

  13. Enhanced thermoelectric properties in p-type Bi{sub 0.4}Sb{sub 1.6}Te{sub 3} alloy by combining incorporation and doping using multi-scale CuAlO{sub 2} particles

    Energy Technology Data Exchange (ETDEWEB)

    Song, Zijun; Liu, Yuan; Zhou, Zhenxing; Lu, Xiaofang; Wang, Lianjun [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai (China); Institute of Functional Materials, Donghua University, Shanghai (China); Zhang, Qihao [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai (China); University of Chinese Academy of Sciences, Beijing (China); Jiang, Wan [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai (China); Institute of Functional Materials, Donghua University, Shanghai (China); School of Material Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen (China); Chen, Lidong [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai (China)

    2017-01-15

    Multi-scale CuAlO{sub 2} particles are introduced into the Bi{sub 0.4}Sb{sub 1.6}Te{sub 3} matrix to synergistically optimize the electrical conductivity, Seebeck coefficient, and the lattice thermal conductivity. Cu element originating from fine CuAlO{sub 2} grains diffuses into the Bi{sub 0.4}Sb{sub 1.6}Te{sub 3} matrix and tunes the carrier concentration while the coarse CuAlO{sub 2} particles survive as the second phase within the matrix. The power factor is improved at the whole temperatures range due to the low-energy electron filtering effect on Seebeck coefficient and enhanced electrical transport property by mild Cu doping. Meanwhile, the remaining CuAlO{sub 2} inclusions give rise to more boundaries and newly built interfaces scattering of heat-carrying phonons, resulting in the reduced lattice thermal conductivity. Consequently, the maximum ZT is found to be enhanced by 150% arising from the multi-scale microstructure regulation when the CuAlO{sub 2} content reaches 0.6 vol.%. Not only that, but the ZT curves get flat in the whole temperature range after introducing the multi-scale CuAlO{sub 2} particles, which leads to a remarkable increase in the average ZT. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Scanning thermal microscopy of Bi{sub 2}Te{sub 3} and Yb{sub 0.19}Co{sub 4}Sb{sub 12} thermoelectric films

    Energy Technology Data Exchange (ETDEWEB)

    Zeipl, Radek; Remsa, Jan; Kocourek, Tomas [Institute of Physics ASCR v.v.i., Prague (Czech Republic); Jelinek, Miroslav [Institute of Physics ASCR v.v.i., Prague (Czech Republic); Czech Technical University in Prague, Faculty of Biomedical Engineering, Kladno (Czech Republic); Vanis, Jan [Institute of Physics ASCR v.v.i., Prague (Czech Republic); Institute of Photonics and Electronics ASCR v.v.i., Prague (Czech Republic); Navratil, Jiri [Institute of Macromolecular Chemistry ASCR v.v.i., Prague (Czech Republic)

    2016-04-15

    Thermal conductivity of thermoelectric Bi{sub 2}Te{sub 3} and Yb{sub 0.19}Co{sub 4}Sb{sub 12} thin nanolayers of different thicknesses prepared by pulsed laser deposition on Si (100) substrates was studied by a scanning thermal microscope working in AC current pulse mode. A sensitivity of the approach is demonstrated on the steep Si substrate-layer boundary made by a Ga+ focused ion beam technique. Transport and thermoelectric properties such as in-plane electrical resistivity and the Seebeck coefficient were studied in temperature range from room temperature up to 200 C. The room temperature thermal conductivity of the layers was estimated from thermoelectric figure of merit that was measured by the Harman technique, in which parameters related to electrical conductivity, Seebeck coefficient and thermal conductivity are measured at the same place and at the same time with electrical current flowing through the layer. For Yb{sub 0.19}Co{sub 4}Sb{sub 12} and Bi{sub 2}Te{sub 3} layers, we observed room temperature electrical resistivity of about 7 and 1 mΩcm, the Seebeck coefficient of -112 and -61μVK{sup -1}, thermoelectric figure of merit about 0.04 and 0.13 and we estimated thermal conductivity of about 1.3 and 0.9 WK{sup -1}m{sup -1}, respectively. (orig.)

  15. Theory versus experiment for a family of single-layer compounds with a similar atomic arrangement: (Tl,X )/Si(111 )√{3 }×√{3 }(X =Pb,Sn,Bi,Sb,Te,Se)

    Science.gov (United States)

    Matetskiy, A. V.; Kibirev, I. A.; Mihalyuk, A. N.; Eremeev, S. V.; Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Zotov, A. V.; Saranin, A. A.

    2017-08-01

    Two-dimensional compounds made of one monolayer of Tl and one-third monolayer of Pb, Bi, Te, or Se (but not of Sn or Sb) on Si(111) have been found to have a similar atomic arrangement which can be visualized as a √{3 }×√{3 } -periodic honeycomb network of chained Tl trimers with atoms of the second adsorbate occupying the centers of the honeycomb units. Structural and electronic properties of the compounds have been examined in detail theoretically using density functional theory (DFT) calculations and experimentally using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) observations. It has been found that though structural parameters of the compounds are very similar for all species, the only common feature of their band structure is a considerable spin-splitting of the surface-state bands, while other basic electronic properties vary greatly with a change of species. The Tl-Pb compound is strongly metallic with two metallic surface-state bands; the Tl-Bi compound is also metallic but with a single metallic band; the Tl-Te and Tl-Se compounds appear to be insulators.

  16. Highly porous thermoelectric nanocomposites with low thermal conductivity and high figure of merit from large-scale solution-synthesized Bi{sub 2}Te{sub 2.5}Se{sub 0.5} hollow nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Biao; Wu, Yue [Department of Chemical and Biological Engineering, Iowa State University, Ames, IA (United States); Ames Laboratory, Department of Energy, Ames, IA (United States); Feng, Tianli; Ruan, Xiulin [Department of Mechanical Engineering, Purdue University, West Lafayette, IN (United States); Agne, Matthias T.; Snyder, G. Jeffery [Department of Materials Science and Engineering, Northwestern University, Evanston, IL (United States); Zhou, Lin [Ames Laboratory, Department of Energy, Ames, IA (United States)

    2017-03-20

    To enhance the performance of thermoelectric materials and enable access to their widespread applications, it is beneficial yet challenging to synthesize hollow nanostructures in large quantities, with high porosity, low thermal conductivity (κ) and excellent figure of merit (z T). Herein we report a scalable (ca. 11.0 g per batch) and low-temperature colloidal processing route for Bi{sub 2}Te{sub 2.5}Se{sub 0.5} hollow nanostructures. They are sintered into porous, bulk nanocomposites (phi 10 mm x h 10 mm) with low κ (0.48 W m{sup -1} K{sup -1}) and the highest z T (1.18) among state-of-the-art Bi{sub 2}Te{sub 3-x}Se{sub x} materials. Additional benefits of the unprecedented low relative density (68-77 %) are the large demand reduction of raw materials and the improved portability. This method can be adopted to fabricate other porous phase-transition and thermoelectric chalcogenide materials and will pave the way for the implementation of hollow nanostructures in other fields. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Exploiting nonlinear properties of pure and Sn-doped Bi2Te2Se for passive Q-switching of all-polarization maintaining ytterbium- and erbium-doped fiber lasers.

    Science.gov (United States)

    Bogusławski, Jakub; Kowalczyk, Maciej; Iwanowski, Przemysław; Hruban, Andrzej; Diduszko, Ryszard; Piotrowski, Kazimierz; Dybko, Krzysztof; Wojciechowski, Tomasz; Aleszkiewicz, Marta; Sotor, Jarosław

    2017-08-07

    Due to their broadband nonlinear optical properties, low-dimensional materials are widely used for pulse generation in fiber and solid-state lasers. Here we demonstrate novel materials, Bi2Te2Se (BTS) and Sn-doped Bi2Te2Se (BSTS), which can be used as a universal saturable absorbers for distinct spectral regimes. The material was mechanically exfoliated from a bulk single-crystal and deposited onto a side-polished fiber. We have performed characterization of the fabricated devices and employed them in polarization-maintaining ytterbium- and erbium-doped fiber lasers. This enabled us to obtain self-starting passively Q-switched regime at 1 µm and 1.56 µm. The oscillators emitted stable, linearly polarized radiation with the highest single pulse energy approaching 692 nJ. Both lasers are characterized by the best performance observed in all-polarization maintaining Q-switched fiber lasers with recently investigated new saturable absorbers, which was enabled by a very high damage threshold of the devices. This demonstrates the great potential of the investigated materials for the ultrafast photonics community.

  18. The orthorhombic to tetragonal phase transition in Bi{sub 1.75}Te{sub 0.25}SrNb{sub 1.75}Hf{sub 0.25}O{sub 9}

    Energy Technology Data Exchange (ETDEWEB)

    Alonso, R E [Departamento de Fisica, Universidad Nacional de La Plata, La Plata (Argentina); Ayala, A P [Departamento de Fisica, Universidade Federal do Ceara, Fortaleza (Brazil); Castro, A [Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid (Spain); Lima Silva, J J [Departamento de Fisica, Universidade Federal do Ceara, Fortaleza (Brazil); Lopez-GarcIa, A [Departamento de Fisica, Universidad Nacional de La Plata, La Plata (Argentina); Paschoal, A R [Departamento de Fisica, Universidade Federal do Ceara, Fortaleza (Brazil)

    2004-06-16

    The necessity to produce materials with better performances than those observed in ferroelectric perovskites has generated the creation of new oxides, especially those belonging to the Aurivillius family. In the last few years much attention has been paid to the study of these materials, and this has opened up new fields due to their basic and applied properties. In this contribution a Raman analysis and a hyperfine study by perturbed angular correlations spectroscopy of Bi{sub 1.75}Te{sub 0.25}SrNb{sub 1.75}Hf{sub 0.25}O{sub 9} were carried out to reveal information about the lattice and the electronic structure. By the use of these techniques, it was observed that the ferroelectric to paraelectric phase transition at about 570 K is driven by a soft mode, and the broadening of the dielectric constant as a function of temperature previously observed at T{sub C} is connected to disorder in the Bi/Te-O layer.

  19. Experimental and theoretical identification of a high-pressure polymorph of Ga{sub 2}S{sub 3} with α-Bi{sub 2}Te{sub 3}-type structure

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Xiaojing; Zhu, Feng; Qin, Shan; Wu, Xiang, E-mail: xiang.wu@pku.edu.cn [Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University and School of Earth and Space Sciences, Peking University, Beijing 100871 (China); Chen, Dongliang; Li, Yanchun [Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Science, Beijing 10049 (China); Yang, Ke [Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204 (China)

    2014-11-21

    Since the discovery of α-phase Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3}, and Bi{sub 2}Se{sub 3} as 3D topological insulators, many experimental and theoretical studies of A{sub 2}B{sub 3}-type chalcogenides have been performed to search for new materials with interesting elastic and electric properties at ambient and extreme conditions. In this study, high-pressure properties of Ga{sub 2}S{sub 3} have been characterized by in situ synchrotron X-ray diffraction (XRD), X-ray absorption near edge structure measurements, and Density-functional theory (DFT) calculations. At ∼16.0 GPa, a phase transition of α′-Ga{sub 2}S{sub 3} (Cc and Z = 4) is observed experimentally to a new polymorph, which is indentified to be the tetradymite-type or α-Bi{sub 2}Te{sub 3}-type crystal structure (R3{sup ¯}m and Z = 3) by laser-annealing XRD experiments and DFT calculations. The isothermal pressure-volume relationship of Ga{sub 2}S{sub 3} is well described by the second-order Birch-Murnaghan equation of state with K{sub 0} = 59(2) GPa and K{sub 0}{sup ′} = 4 (fixed) for the α′-Ga{sub 2}S{sub 3}, and K{sub 0} = 91(3) GPa, and K{sub 0}{sup ′} = 4 (fixed) for the tetradymite-type phase. In addition, band gap of α′-Ga{sub 2}S{sub 3} decreases on compression and the tetradymite-type Ga{sub 2}S{sub 3} exhibits metallization based on DFT calculations. The pressure-induced phase transition accompanying by changes of elastic and electrical properties may give some implications to other chalcogenides under high pressure.

  20. Experimental observation on a temperature-induced decoupling between the surface states in topological insulator nanoplates Bi{sub 2-0.15}(TeSe){sub 3+0.15}

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Haoran; Pan, Haiyang; Zeng, Junwen; Chen, Taishi; Song, Fengqi; Wang, Xuefeng; Miao, Feng [Nanjing University, National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and College of Physics, Nanjing (China); Zhang, Kang; Zhang, Rong [Nanjing University, National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and School of Electronic Science and Engineering, Nanjing (China)

    2016-04-15

    We report on the temperature-induced quantum decoupling between the surface states, demonstrated by weak antilocalization measurements, in the topological insulator Bi{sub 2-0.15}(TeSe){sub 3+0.15} nanoplates. The samples are prepared by a catalyst-free vapor-solid process with the dimension of 10 μm and the thickness of 20 nm. The channel indicator is extracted from the weak antilocalization, which presents a transition from 0.5 to 1 with the increasing temperature. This reveals the coherent decoupling between the two surface states, during which the dephasing length reaches the plate thickness. A bulk-mediated intersurface coupling model interprets the transition. (orig.)

  1. Laser angle-resolved photoemission as a probe of initial state kz dispersion, final-state band gaps, and spin texture of Dirac states in the Bi2Te3 topological insulator

    Science.gov (United States)

    Ä; rrälä, Minna; Hafiz, Hasnain; Mou, Daixiang; Wu, Yun; Jiang, Rui; Riedemann, Trevor; Lograsso, Thomas A.; Barbiellini, Bernardo; Kaminski, Adam; Bansil, Arun; Lindroos, Matti

    2016-10-01

    We have obtained angle-resolved photoemission spectroscopy (ARPES) spectra from single crystals of the topological insulator material Bi2Te3 using a tunable laser spectrometer. The spectra were collected for 11 different photon energies ranging from 5.57 to 6.70 eV for incident light polarized linearly along two different in-plane directions. Parallel first-principles, fully relativistic computations of photointensities were carried out using the experimental geometry within the framework of the one-step model of photoemission. A reasonable overall accord between theory and experiment is used to gain insight into how properties of the initial- and final-state band structures as well as those of the topological surface states and their spin textures are reflected in the laser-ARPES spectra. Our analysis reveals that laser-ARPES is sensitive to both the initial-state kz dispersion and the presence of delicate gaps in the final-state electronic spectrum.

  2. Tuning the Dirac point to the Fermi level in the ternary topological insulator (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Kellner, Jens, E-mail: kellner@physik.rwth-aachen.de; Liebmann, Marcus; Morgenstern, Markus [II Institute of Physics B, RWTH Aachen University, Aachen 52074 (Germany); Eschbach, Markus; Młyńczak, Ewa; Plucinski, Lukasz; Schneider, Claus M. [Peter Grünberg Institut (PGI-6), FZ Jülich GmbH, Jülich 52428 (Germany); Kampmeier, Jörn; Lanius, Martin; Mussler, Gregor; Holländer, Bernhard; Grützmacher, Detlev [Peter Grünberg Institut (PGI-9), FZ Jülich GmbH, Jülich 52428 (Germany)

    2015-12-21

    In order to stabilize Majorana excitations within vortices of proximity induced topological superconductors, it is mandatory that the Dirac point matches the Fermi level rather exactly, such that the conventionally confined states within the vortex are well separated from the Majorana-type excitation. Here, we show by angle resolved photoelectron spectroscopy that (Bi{sub 1−x}Sb{sub x}){sub 2}Te{sub 3} thin films with x = 0.94 prepared by molecular beam epitaxy and transferred in ultrahigh vacuum from the molecular beam epitaxy system to the photoemission setup match this condition. The Dirac point is within 10 meV around the Fermi level, and we do not observe any bulk bands intersecting the Fermi level.

  3. Imaging Dirac-Mass Disorder from Magnetic Dopant-Atoms in the Ferromagnetic Topological Insulator Crx(Bi0.1Sb0.9)2-xTe3 - Part II

    Science.gov (United States)

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon; Zhong, Ruidan; Schneeloch, John; Liu, Tiansheng; Tranquada, John; Gu, Genda; Davis, J. C.

    2015-03-01

    We present Part II of the spectroscopic imaging - scanning tunneling microscopy (SI-STM) study of ferromagnetic Crx(Bi0.1Sb0.9)2-xTe3 single crystals measured at 4.5 K. As Part II we show how both spectroscopic analysis in real and momentum space demonstrate the coincident Dirac mass gap identified. Distribution of gap width, gap center, and gap anisotropy will be discussed. The anticipated relationship Δ (r) ~ n (r) is confirmed throughout, and exhibits an electron-dopant interaction energy J* = 145 meV .nm2. These observations reveal how magnetic dopant atoms actually generate the TI mass gap and that, to achieve the novel physics expected of time-reversal-symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.

  4. Composition-dependent charge transport and temperature-dependent density of state effective mass interpreted by temperature-normalized Pisarenko plot in Bi2-xSbxTe3 compounds

    Science.gov (United States)

    An, Tae-Ho; Lim, Young Soo; Park, Mi Jin; Tak, Jang-Yeul; Lee, Soonil; Cho, Hyung Koun; Cho, Jun-Young; Park, Chan; Seo, Won-Seon

    2016-10-01

    Composition-dependent charge transport and temperature-dependent density of state effective mass-dependent Seebeck coefficient were investigated in Bi2-xSbxTe3 (x = 1.56-1.68) compounds. The compounds were prepared by the spark plasma sintering of high-energy ball-milled powder. High-temperature Hall measurements revealed that the charge transport in the compounds was governed dominantly by phonon scattering and influenced additionally by alloy scattering depending on the amount of Sb. Contrary effects of Sb content on the Seebeck coefficient were discussed in terms of carrier concentration and density of state effective mass, and it was elucidated by temperature-normalized Pisarenko plot for the first time.

  5. Nd{sup 3+}-doped TeO{sub 2}-Bi{sub 2}O{sub 3}-ZnO transparent glass ceramics for laser application at 1.06 μm

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Xiaolin; Luo, Zhiwei; Liu, Taoyong; Lu, Anxian [Central South of University, School of Materials Science and Engineering, Changsha (China)

    2017-04-15

    The high crystallinity transparent glass ceramics based on Nd{sup 3+}-doped 70TeO{sub 2}-15Bi{sub 2}O{sub 3}-15ZnO (TBZ) compositions were successfully prepared by two-step heat treatment process. The effects of Nd{sub 2}O{sub 3} content on the thermal, structural, mechanical, and optical properties of TBZ glass ceramics were studied. The incorporation of Nd{sub 2}O{sub 3} enhanced the crystallization tendency in the matrix glass composition. The crystal phase and morphology of Bi{sub 2}Te{sub 4}O{sub 11} in the glass ceramics were confirmed by X-ray diffraction and field emission scanning electron microscopy. Due to precipitate more crystal phase, the hardness values increased from 3.21 to 3.66 GPa. Eight absorption peaks were observed from 400 to 900 nm and three emission bands appeared in the range of 850-1400 nm. With the increasing of Nd{sub 2}O{sub 3} content from 0.5 to 2.5 wt%, the intensity of absorption peaks enhanced and the emission intensity increased up to 1.0 wt% and then fell down for further dopant concentration. The fluorescence decay lifetime decreased rapidly starting from 1.5 wt% Nd{sub 2}O{sub 3} content due to the obvious energy migration among Nd{sup 3+}. According to the extreme strong emission band around 1062 nm and the optimum Nd{sub 2}O{sub 3} content (1.0 wt%), N10 glass ceramic was considered as a potential material for 1.06 μm laser applications. (orig.)

  6. Characterization of Bi-Catalyzed Nanocrystalline CdTe Thin Films Prepared by Close Spaced Sublimation%近距离升华法制备Bi催化纳米晶CdTe薄膜的表征

    Institute of Scientific and Technical Information of China (English)

    李锦; 尚飞; 郑毓峰; 孙言飞; 简基康; 吴荣

    2009-01-01

    采用近距离升华法(Close-Spaced-Sublimation,CSS)引入Bi催化剂成功制备出了具有纳米线、近阵列排布的纳米棒等形貌的纳米晶CdTe薄膜.并利用X射线衍射(XRD)、扫描电子显微镜(SEM)、紫外可见分光光度计等研究了薄膜的结构、表面形貌和光学性能.讨论了CdTe纳米结构可能的生长机制.%Bi-catalyzed nanocrystalline CdTe films were prepared by close spaced sublimation (CSS) technique successfully.These nanocrystalline CdTe films had surface appearance of nanowires or a similar array arrangement nanorod.The structure,the surface topograph and the optical properties of these films were studied using X-ray diffraction(XRD),scanning electron microscopy(SEM) and ultroviolet-visible (UV-VIS) spectrophotometer.And the possible growth mechanisms of these nanostructures were discussed.

  7. Equilibrium Thermodynamics Analysis of Underpotential Deposition of Bi-Te Substrate System Thermoelectric Material%欠电势沉积Bi-Te基体系热电材料的平衡热力学分析

    Institute of Scientific and Technical Information of China (English)

    朱文; 杨君友; 周东祥; 鲍思前; 樊希安; 段兴凯

    2007-01-01

    基于普通的能斯特方程,建立了单原子层平衡电势的热力学模型.据此,分析了单原子层覆盖度以及电吸附价与欠电势之间的相互关系,获得了沉积物与衬底之间干涉特性.并且分析了Bi-Te基体系欠电势沉积热力学特性.通过对Bi欠电势沉积在几个不同的金属衬底体系的分析阐明了功函数随覆盖度的变化机制.研究了铋离子的浓度变化对铋的欠电势及覆盖度的影响关系,结果表明,铋在铂上欠电势沉积的体系在整个欠电势范围内具有恒定的电吸附价,而铋在覆盖了一层碲的铂衬底上欠电势沉积的体系其电吸附价随覆盖度的增加而降低,从热力学理论角度对铋在碲覆盖的衬底上导致欠电势负移的特性给予了解释.

  8. Imaging Dirac-Mass Disorder from Magnetic Dopant-Atoms in the Ferromagnetic Topological Insulator Crx(Bi0.1Sb0.9)2-x Te3 - Part I

    Science.gov (United States)

    Kim, Chung Koo; Lee, Inhee; Lee, Jinho; Billinge, Simon; Zhong, Ruidan; Schneeloch, John; Liu, Tiansheng; Tranquada, John; Gu, Genda; Davis, J. C. Seamus

    2015-03-01

    Topological insulators (TI) have a gapless surface state of Dirac fermions protected by the time reversal symmetry (TRS). However, TRS can be broken in the ferromagnetic state induced by magnetic doping. This leads to the opening of ``mass gap'' at the Dirac point. Such a gap is predicted to involve many exotic phenomena for which understanding the microscopic role of magnetic dopants is critical. But it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92 Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate directly is related to fluctuations in n(r), the areal Cr atom density at the surface. The relationship of the surface-state Fermi wavevectors to both the correlation length and anisotropic structure of Δ(r) are found consistent with predictions for ferromagnetism mediated by the surface states.

  9. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3.

    Science.gov (United States)

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J L; Zhong, Ruidan; Schneeloch, John A; Liu, Tiansheng; Valla, Tonica; Tranquada, John M; Gu, Genda; Davis, J C Séamus

    2015-02-03

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a "Dirac-mass gap" in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship [Formula: see text] is confirmed throughout and exhibits an electron-dopant interaction energy J* = 145 meV·nm(2). These observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.

  10. 125Te NMR in the single crystal of CeTe3: Spin polarized CDW

    Science.gov (United States)

    Chudo, H.; Michioka, C.; Itoh, Y.; Yoshimura, K.

    2007-03-01

    We report 125Te NMR studies for single crystals of CeTe3 between 22 and 307 K, under an applied field of H=7.4847 T along a- or b-axis. The 125Te NMR spectrum consists of superposition of broad and sharp peaks, which are assigned to the signals of 125Te(1) in Te(1) sheets and 125Te(2) in CeTe(2) bi-layers, respectively. The broad 125Te(1) NMR spectrum consists of three distinguishable lines, regarded as an evidence for the presence of the incommensurate charge-density wave (ICDW) modulation. The Knight shifts of 125Te(1) widely distribute from -0.16% to +0.58% at 110 K and the temperature dependence of each Knight shift is proportional to the bulk susceptibility, indicating that the conduction electron spin density is polarized by the Ce local moments in the CDW state.

  11. 125Te and 139La NMR Studies of Single Crystal LaTe3

    Science.gov (United States)

    Chudo, Hiroyuki; Michioka, Chishiro; Itoh, Yutaka; Yoshimura, Kazuyoshi

    2007-12-01

    We report 125Te and 139La NMR studies for single crystals of LaTe3 between 10 and 160 K under an applied field of H = 7.4841 T. We observed the broad 125Te(1) NMR signals of metallic Te(1) sheets with a superlattice modulation and the sharp 125Te(2) and 139La NMR signals of LaTe(2) bi-layers. Temperature dependence of 125Te(1) nuclear spin-lattice relaxation times of the modulated Te(1) sheets obeys a modified Korringa relation. The results indicate that the electronic state on the Te(1) sheets is a Landau-Fermi liquid on a misfit superlattice or a Tomonaga-Luttinger liquid in a two-dimensional charge-density wave ordering state.

  12. Facile synthesis and thermoelectric studies of n-type bismuth telluride nanorods with cathodic stripping Te electrode

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Guoqiu [School of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, Jiangsu (China); Li, Yusong [School of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, Jiangsu (China); Department of Chemistry and Chemical Engineering, Southeast University, 210092 Jiangsu (China); Bao, Ning [School of Public Health, Nantong University, Nantong 226019, Jiangsu (China); Miao, Jianwen [School of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, Jiangsu (China); Ge, Cunwang, E-mail: gecunwang@ntu.edu.cn [School of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, Jiangsu (China); Wang, Yihong [Department of Chemistry and Chemical Engineering, Southeast University, 210092 Jiangsu (China)

    2014-01-15

    Bismuth telluride (Bi{sub 2}Te{sub 3}) nanorods (NRs) of n-type thermoelectric materials were prepared using an electrogenerated precursor of tellurium electrode in the presence of Bi{sup 3+} and mercapto protecting agent in aqueous solution under atmosphere condition. The optimal preparation conditions were obtained with ratio of Bi{sup 3+} to mercapto group and Te coulomb by photoluminescence spectra. The mechanism for generation of Bi{sub 2}Te{sub 3} precursor was investigated via the cyclic voltammetry. The highly crystalline rhombohedral structure of as-prepared Bi{sub 2}Te{sub 3} NRs with the shell of Bi{sub 2}S{sub 3} was evaluated with high resolution transmission electron microscopy (HRTEM) and powder X-ray diffraction (XRD) spectroscopy. The near-infrared absorption of synthetic Bi{sub 2}Te{sub 3} NRs was characterized with spectrophotometer to obtain information of electron at interband transition. The thermoelectric performance of Bi{sub 2}Te{sub 3} NRs was assessed with the result of electrical resistivity, Seebeck coefficient, thermal conductivity, and the figure of merit ZT parameters, indicating that thermoelectric performance of as-prepared Bi{sub 2}Te{sub 3} nanocrystals was improved by reducing thermal conductivity while maintaining the power factor. - Graphical abstract: The nanorods of n-type chalcogenides semiconductors of Bi{sub 2}Te{sub 3} are prepared using electrochemical technique with Te electrode. The highly crystalline rhombohedral structure of Bi{sub 2}Te{sub 3} nanorods with the shell of Bi{sub 2}S{sub 3} is demonstrated. The thermoelectric measurement indicated that thermoelectric performance of Bi{sub 2}Te{sub 3} NRs was improved by a highly reduced thermal conductivity while maintaining the power factor. - Highlights: • The n-type Bi{sub 2}Te{sub 3} nanorods are prepared using an electrogenerated precursor. • The rhombohedral structure of Bi{sub 2}Te{sub 3} nanorods with the shell of Bi{sub 2}S{sub 3} is demonstrated. • Bi

  13. Agile BI – The Future of BI

    Directory of Open Access Journals (Sweden)

    Mihaela MUNTEAN

    2013-01-01

    Full Text Available In a rapidly changing economy, Business Intelligence solutions have to become more agile. This paper attempts to discuss some questions which help in creating an agile BI solution such as: What is Agile? Why agile is so well suited for BI? Which are the key elements that promote an agile BI solution? Also, this paper briefly looks at technologies that can be used for enabling an agile BI solution.

  14. Fabrication of Multilevel Switching High Density Phase Change Data Recording Using Stacked GeTe/GeSbTe Structure

    Science.gov (United States)

    Hong, Sung-Hoon; Lee, Heon; Kim, Kang-In; Choi, Yunjung; Lee, Young-Kook

    2011-08-01

    The multilevel switching characteristics of stacked phase change materials with the structures of Ge2Sb2Te5, AgInSbTe/Ge2Sb2Te5, and GeTe/Ge2Sb2Te5 were investigated at the nano scale using nanoimprint lithography and conductive atomic force microscopy. Stacked phase change materials devices consisting of nano pillars 200 nm in diameter were fabricated using nanoimprint lithography, and their electrical characteristics were evaluated using conductive atomic force microscopy, with a pulse generator and a voltage source. The stacked GeTe/Ge2Sb2Te5 phase change materials exhibited three levels of resistance with a difference of 2 orders in magnitude between them, while the single-layer and stacked phase change materials with similar electrical resistances, such as Ge2Sb2Te5/AgInSbTe exhibited only bi level switching characteristics.

  15. Bi-based Nanowire and Nanojunction Arrays: Fabrication and Physical Properties

    Institute of Scientific and Technical Information of China (English)

    Liang LI; Guanghai LI; Xiaosheng FANG

    2007-01-01

    This article reviews the recent developments in the fabrication and properties of one-dimensional (1D) Bi-based nanostructures, including Bi, Sb, BixSb1-x and Bi2Te3 nanowire arrays, and Bi-Bi and Bi-Sb nanojunction arrays. In this article, we present an efiective method to fabricate Bi nanowire arrays with difierent diameters in anodic alumina membrane (AAM) with a single pore size by the pulsed electrodeposition. The fabrication of the high-filling and ordered Bi1-xSbx and Bi2Te3 single crystalline nanowire arrays, the Bi nanowire metalsemiconductor homojunction and Bi-Sb nanowire metal-semiconductor heterojunction arrays by the pulsed electrodeposition are reported. The factors controlling the composition, diameter, growth rate and orientation of the nanowires are analyzed, and the growth mechanism of the nanowire and nanojunction arrays are discussed together with the study of the electrical and thermal properties of Bi-based nanowires and nanojunctions.Finally, this review is concluded with some perspectives on the research directions and focuses in the Bi-based nanomaterials fields.

  16. Bi-sulphotellurides associated with Pb - Bi - (Sb ± Ag, Cu, Fe) sulphosalts: an example from the Stan Terg deposit in Kosovo

    Science.gov (United States)

    Kołodziejczyk, Joanna; Pršek, Jaroslav; Voudouris, Panagiotis Ch.; Melfos, Vasilios

    2017-08-01

    New mineralogical and mineral-chemical data from the Stan Terg deposit, Kosovo, revealed the presence of abundant Bi-sulphotellurides associated with Bi- and Sb-sulphosalts and galena in pyrite-pyrrhotite-rich skarn-free ore bodies (ores without skarn minerals). The Bi-bearing association comprises Bi-sulphotellurides (joséite-A, joséite-B, unnamed phase A with a chemical formula close to (Bi,Pb)2(TeS)2, unnamed phase B with a chemical composition close to (Bi,Pb)2.5Te1.5S1.5), ikunolite, cosalite, Sb-lillianite, members of the kobellite series and Bi-jamesonite. Compositional trends of the Bi-sulphotellurides suggest lattice-scale incorporation of Bi-(Pb)-rich module and/or admixture with submicroscopic PbS layers in modulated structures, or complicated Bi-Te substitution. Cosalite is characterized by high Sb (max. 3.94 apfu), and low Cu and Ag (up to 0.72 apfu of Cu+Ag). Jamesonite from this mineralization has elevated Bi content, from 0.85 to 2.30 apfu. The negligible content of Au and Ag in the Bi-sulphotellurides, the low content of Ag in Bi-sulphosalts, together with the lack of Au-Ag bearing phases in the mineralization, indicate either ore deposition from fluid(s) depleted in precious metals, or physico-chemical conditions of ore formation preventing Au and Ag precipitation at the deposit site. The temperature of initial mineralization may have exceeded 400 °C as suggested by the lamellar exsolution textures observed in lillianite, which indicate breakdown textures from decomposition of high-temperature initial crystals. Non-stoichiometric phases among the Bi-sulphosalts and sulphotellurides studied at Stan Terg reflect modulated growth processes in a metasomatic environment.

  17. Reassessment of the carrier concentration in GeTe-based thermoelectric materials by ^125Te NMR

    Science.gov (United States)

    Levin, E. M.; Acton, J. D.; Schmidt-Rohr, K.

    2012-02-01

    Ge1-xAgx/2Sbx/2Te p-type thermoelectric materials (``TAGS-n'') were studied extensively in the 1970s and then again recently. They exhibit an unusual combination of large thermopower, S, and high hole concentration, p, reported based on the Hall effect data, which has not been explained. To solve this puzzle, we have synthesized GeTe, GeTe:Bi, and TAGS-n with n = 97, 94, 90, and 85 and studied XRD, thermopower, electrical resistivity, thermal conductivity, and ^125Te NMR. Most importantly, we have determined the carrier concentrations using ^125Te NMR spin-lattice relaxation and Knight shift. In GeTe and GeTe:Bi, we found that carrier concentrations generally agree with the values reported from Hall effect. In TAGS-n, they are much lower but agree better with the values expected from S vs. p for GeTe-based materials, solving the puzzle partially. The NMR vs. Hall effect discrepancy in TAGS-n can be due to the presence not only of holes but also electrons generated by Sb atoms, which results in artificially high hole concentration from Hall effect. Even though the true hole concentration is lower than reported, the thermopower of TAGS-n is still significantly larger than that of GeTe and GeTe:Bi at similar carrier concentration. This can be explained by energy filtering enhanced by potential barriers formed due to Ag-Sb pairs in the TAGS-n lattice.

  18. Thermoelectric properties of half-Heusler topological insulators MPtBi (M = Sc, Y, La) induced by strain

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Guangqian; Gao, G. Y., E-mail: guoying-gao@mail.hust.edu.cn; Yao, KaiLun [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Yu, Li [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Department of Basics, Air Force Early Warning Academy, Wuhan 430019 (China); Ni, Yun [Wenhua College, Wuhan 430074 (China)

    2016-01-14

    Thermoelectric (TE) materials and topological insulators (TIs) were recently known to exhibit close connection, which offers new prospects in improving the TE performance. However, currently known TE materials from TIs mostly belong to the early Bi{sub 2}Te{sub 3} family. In order to extend TE materials to other classes of TIs, we use the first-principles combined with Boltzmann transport theory to study the electronic and TE properties of experimental half-Heusler compounds MPtBi (M = Sc, Y, La). We find that all MPtBi are topological semimetals at equilibrium lattices while TIs under a stretched uniaxial strain, which is in agreement with previous works. We further predict that comparable TE performance with Bi{sub 2}Te{sub 3} can be realized in half-Heusler TI LaPtBi by an 8% stretched uniaxial strain. We also reveal that the lattice thermal conductivity of LaPtBi is unprecedented low compared with those of traditional half-Heusler compounds (not TIs). These findings indicate the potential of half-Heusler TIs as TE materials.

  19. Thermoelectric properties of half-Heusler topological insulators MPtBi (M = Sc, Y, La) induced by strain

    Science.gov (United States)

    Ding, Guangqian; Gao, G. Y.; Yu, Li; Ni, Yun; Yao, KaiLun

    2016-01-01

    Thermoelectric (TE) materials and topological insulators (TIs) were recently known to exhibit close connection, which offers new prospects in improving the TE performance. However, currently known TE materials from TIs mostly belong to the early Bi2Te3 family. In order to extend TE materials to other classes of TIs, we use the first-principles combined with Boltzmann transport theory to study the electronic and TE properties of experimental half-Heusler compounds MPtBi (M = Sc, Y, La). We find that all MPtBi are topological semimetals at equilibrium lattices while TIs under a stretched uniaxial strain, which is in agreement with previous works. We further predict that comparable TE performance with Bi2Te3 can be realized in half-Heusler TI LaPtBi by an 8% stretched uniaxial strain. We also reveal that the lattice thermal conductivity of LaPtBi is unprecedented low compared with those of traditional half-Heusler compounds (not TIs). These findings indicate the potential of half-Heusler TIs as TE materials.

  20. 不同碳源复合钨酸铋光催化剂的制备与性能%Preparation and properties of different biomass carbon composi te wi th Bi2 WO6

    Institute of Scientific and Technical Information of China (English)

    刘丁菡; 黄剑锋; 曹丽云; 陶兴旺; 张博烨

    2015-01-01

    The C‐Bi2 WO6 composite photo‐catalytic materials were synthesized by one‐step microwave hydrothermal using different biomass carbon source (starch ,cotton ,glucose ,oil , bamboo) .The samples of structure ,microstructure ,morphology and photo‐catalytic proper‐ties were characterized by XRD ,SEM ,FT‐IR and UV‐Vis spectrophotometer (UV‐2600) . Results show that when the cotton and glucose composite with Bi2 WO6 ,the photo‐catalytic activity of the sample is the best under visible light irradiation in 240 min ,the degradation ef‐ficiency of RhB reached 92% and 90 .8% ,respectively .T his may be attributed to the mor‐phology of the lamellar sheets stack on each other and form a hierarchical structure ,the con‐tact area of the photo‐catalyst and organic pollutants was increased .That is in favor of in‐crease of photo‐catalytic activity .Meanwhile ,FT‐IR analysis results indicate the interface synergistic effect between cotton and Bi2 WO6 is benefit for photo‐catalytic activity .%采用不同生物质碳源(淀粉、棉花、葡萄糖、油脂、竹炭)与硝酸铋、钨酸钠在一步微波水热条件下合成了C‐Bi2 WO6复合光催化材料.分别使用XRD、SEM 、FT‐IR和紫外可见分光光度计(U V‐2600)对产物的结构、微观形貌以及光催化性能进行了表征测试.结果表明:棉花、葡萄糖分别与钨酸铋复合所得产物的光催化活性较好,在可见光照射240 min后,对RhB的降解效率分别达到了92%和90.8%.这可能是由于此条件下所得产物的形貌为薄片状且相互堆叠形成了三维层状结构,这种结构增大了光催化剂与有机污染物的接触面积,有利于光催化活性的提高;同时,由红外分析结果可知,碳化棉花与钨酸铋界面之间的协同作用亦有利于光催化活性的提高.

  1. BoBI op weg. Tussentijdse evaluatie van het project Bodembiologische Indicator

    NARCIS (Netherlands)

    Schouten AJ; Rutgers M; Breure AM; ECO

    2002-01-01

    De ontwikkeling van de Bodembiologische Indicator (BoBI) is ingezet naar aanleiding van de volgende beleidsvraag: is er een instrument (te maken) waarmee milieubeleidsdoelstellingen kunnen worden geformuleerd voor behoud en duurzaam gebruik van biodiversiteit en bodemfuncties? BoBI is een

  2. Microstructure Evolution of Ag-Alloyed PbTe-Based Compounds and Implications for Thermoelectric Performance

    Directory of Open Access Journals (Sweden)

    Tom Grossfeld

    2017-09-01

    Full Text Available We investigate the microstructure evolution of Ag-alloyed PbTe compounds for thermoelectric (TE applications with or without additions of 0.04 at. % Bi. We control the nucleation and temporal evolution of Ag2Te-precipitates in the PbTe-matrix applying designated aging heat treatments, aiming to achieve homogeneous dispersion of precipitates with high number density values, hypothesizing that they act as phonon scattering centers, thereby reducing lattice thermal conductivity. We measure the temperature dependence of the Seebeck coefficient and electrical and thermal conductivities, and correlate them with the microstructure. It is found that lattice thermal conductivity of PbTe-based compounds is reduced by controlled nucleation of Ag2Te-precipitates, exhibiting a number density value as high as 2.7 × 1020 m−3 upon 6 h aging at 380 °C. This yields a TE figure of merit value of ca. 1.4 at 450 °C, which is one on the largest values reported for n-type PbTe compounds. Subsequent aging leads to precipitate coarsening and deterioration of TE performance. Interestingly, we find that Bi-alloying improves the alloys’ thermal stability by suppressing microstructure evolution, besides the role of Bi-atoms as electron donors, thereby maintaining high TE performance that is stable at elevated service temperatures. The latter has prime technological significance for TE energy conversion.

  3. Effet du nombre de recyclages de la biomasse de Saccharomyces uvarum sur quelques paramètres de la fermentation primaire au cours de la production de la bière en Côte d'Ivoire

    Directory of Open Access Journals (Sweden)

    Zebre, AC.

    2011-01-01

    Full Text Available Effect of the number of recycled biomass of the yeast Saccharomyces uvarum on some parameters of primary fermentation during beer production in Côte d'Ivoire. A study was conducted on the yeast Saccharomyces uvarum during the production of beer to determine the impact of the number of recycled yeast biomass on some primary fermentation parameters and to understand variations during primary fermentation time. The work was carried out with six cycles of beer production. The first cycle was done with the initial culture of S. uvarum and the five others with its recycled biomass. After each cycle of production, the yeast biomass obtained is re-used to inoculate another mash and the same operation was repeated until the sixth cycle of production of the beer. Thus during each of the six cycles, several parameters such as the rate of fermentation, the diacetyle reduction time, the rate of alcohol production, etc. were measured. The fifth and sixth cycles showed the longest primary fermentation time (10 days and the longest diacetyle reduction time (6.8 and 7.6 days respectively. The first and second cycles have the shortest primary fermentation time (8.33 and 8.25 days respectively and diacetyle reduction time (3.33 days for each cycle. The interval between the theoretical and the practical attenuation limit differs according to the cycle of production. The highest gap (0.51 was obtained with the last cycle (sixth while the shortest was obtained with the first cycle, 0.13. The fermentation rate varied from 1.71 to 1.97°P per day. The quantity of sugar consumed varied from 8.83 to 10.70°P and the rate of alcohol produced from 4.56 to 4.90°P. The yeast from the two last cycles flocculated quicker than the others. The number of cells in suspension for these cycles was 4.1.106 and 4.2.106 cells.ml-1 respectively versus 25.106 and 20.106 cells.ml-1 respectively for the two first cycles. The yeast biomass from the first four cycles should be used for the

  4. Bi-Force

    DEFF Research Database (Denmark)

    Sun, Peng; Speicher, Nora K; Röttger, Richard

    2014-01-01

    -clustering', has been successfully utilized to discover local patterns in gene expression data and similar biomedical data types. Here, we contribute a new heuristic: 'Bi-Force'. It is based on the weighted bicluster editing model, to perform biclustering on arbitrary sets of biological entities, given any kind...... of pairwise similarities. We first evaluated the power of Bi-Force to solve dedicated bicluster editing problems by comparing Bi-Force with two existing algorithms in the BiCluE software package. We then followed a biclustering evaluation protocol in a recent review paper from Eren et al. (2013) (A...... datasets from Gene Expression Omnibus were analyzed. All resulting biclusters were subsequently investigated by Gene Ontology enrichment analysis to evaluate their biological relevance. The distinct theoretical foundation of Bi-Force (bicluster editing) is more powerful than strict biclustering. We thus...

  5. Bi-based superconductor

    Directory of Open Access Journals (Sweden)

    S E Mousavi

    2009-08-01

    Full Text Available   In this paper, Bi-Sr-Ca-Cu-O (BCSCCO system superconductor is made by the solid state reaction method. The effect of doping Pb, Cd, Sb, Cu and annealing time on the critical temperature and critical current density have been investigated. The microstructure and morphology of the samples have been studied by X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The results show that the fraction of Bi-2223 phase in the Bi- based superconductor, critical temperature and critical current density depend on the annealing temperature, annealing time and the kind and amount of doping .

  6. Structural phase transitions in Bi2Se3 under high pressure

    Science.gov (United States)

    Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-Kwang

    2015-11-01

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.

  7. Experimental and Theoretical Study of the Feasibility of the Gunn Effect in BiSCl, BiSBr, BiSI, BiSeI, BiSeBr and BiSeCl.

    Science.gov (United States)

    1981-03-01

    BiSI has been measured with photon energy, from .2 ~e. to 3.6 eV. The band structures of BiSBr, BiSCI, BiSebr, BiSeCl and BiSel have 0.... been...ANDTIEORETICAL_,TUDY OF THE IASIBILITY OF TII-U EFFECT IN BI tlBiSBr, BISI, BiSel , WTSeBr ANWD BiSeCI* q ri1na Scientific Repot7- /t , .by J...measured with photon energy, lio, from 2.2 to 3.6 eV. The band structures of BiSBr, BiSCI, BiSI, BiSeBr, BiSeCI and BiSel have been calculated by using the

  8. HgTe-CdTe SUPERLATTICES

    OpenAIRE

    Smith, D; Mcgill, T.

    1984-01-01

    We report on a theoretical study of the electronic properties of HgTe-CdTe superlattices. The band gap as a function of layer thickness, effective masses normal to the layer plane and tunneling length are compared to the corresponding (Hg, Cd)Te alloys. We find that the superlattice possesses a number of properties that may make it superior to the corresponding alloy as an infrared material.

  9. 125Te NMR chemical-shift trends in PbTe-GeTe and PbTe-SnTe alloys.

    Science.gov (United States)

    Njegic, B; Levin, E M; Schmidt-Rohr, K

    2013-01-01

    Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in (125)Te NMR chemical shift due to bonding to dopant or "solute" atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the (125)Te NMR chemical shifts in PbTe-based alloys, Pb1-xGexTe and Pb1-xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS (125)Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the (125)Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

  10. High pressure monoclinic phases of Sb{sub 2}Te{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Souza, S.M.; Poffo, C.M.; Triches, D.M. [Departamento de Engenharia Mecanica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Lima, J.C. de, E-mail: fsc1jcd@fisica.ufsc.br [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Grandi, T.A. [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Polian, A.; Gauthier, M. [Physique des Milieux Denses, IMPMC, CNRS-UMR 7590, Universite Pierre et Marie Curie-Paris 6, 4 Place Jussieu, 75252 Paris Cedex 05 (France)

    2012-09-15

    The effect of pressure on nanostructured rhombohedral {alpha}-Sb{sub 2}Te{sub 3} (phase I) was investigated using X-ray diffraction (XRD) and Raman spectroscopy (RS) up to 19.2 and 25.5 GPa, respectively. XRD patterns showed two new high pressure phases (named phases II and III). From a Rietveld refinement of XRD patterns of {alpha}-Sb{sub 2}Te{sub 3}, the unit cell volume as a function of pressure was obtained and the values were fitted to a Birch-Murnaghan equation of state (BM-EOS). The best fit was obtained for bulk modulus B{sub 0}=36.1{+-}0.9 GPa and its derivative B{sub 0}{sup Prime }=6.2{+-}0.4 (not fixed). Using the refined structural data for {alpha}-Sb{sub 2}Te{sub 3}, for pressures up to 9.8 GPa, changes in the angle of succession [Te-Sb-Te-Sb-Te], in the interaromic distances of Sb and Te atoms belonging to this angle of succession and in the interatomic distances of atoms located on the c axis were examined. This analysis revealed an electronic topological transition (ETT) along the a and c axes at close to 3.7 GPa. From the RS spectra, the full widths at half maximum (FWHM) of the Raman active modes of {alpha}-Sb{sub 2}Te{sub 3} were plotted as functions of pressure and showed an ETT along the a and c axes at close to 3.2 GPa. The XRD patterns of phases II and III were well reproduced assuming {beta}-Bi{sub 2}Te{sub 3} and {gamma}-Bi{sub 2}Te{sub 3} structures similar to those reported in the literature for {alpha}-Bi{sub 2}Te{sub 3}.

  11. On the doping problem of CdTe films: The bismuth case

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Brown, M. [Department of Physics and Astronomy, The University of Toledo, 43606 Toledo, OH (United States); Ruiz, C.M. [Depto. Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Vidal-Borbolla, M.A. [Instituto de Investigacion en Comunicacion Optica, Av. Karakorum 1470, Lomas 4a. Secc., 78210 San Luis Potosi, SLP (Mexico); Ramirez-Bon, R. [CINVESTAV-IPN, U. Queretaro, Libramiento Norponiente No. 2000, Fracc. Real de Juriquilla, 76230 Santiago de Queretaro, Qro. (Mexico); Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico)], E-mail: mtufinovel@yahoo.com.mx; Calixto, M. Estela [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Compaan, A.D. [Department of Physics and Astronomy, The University of Toledo, 43606 Toledo, OH (United States); Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico)

    2008-08-30

    The controlled increase of hole concentration is an important issue and still an unsolved problem for polycrystalline CdTe-based solar cells. The typical hole concentration of as-grown CdTe thin-films goes up to 10{sup 13} cm{sup -3}, depending on the specific growth technique. The highest electron concentration obtained for CdS, the suitable window partner material of CdTe, is around 10{sup 15} cm{sup -3}. Thus, the PV-performance of a CdS/CdTe device can be optimized if the hole concentration in CdTe is increased. We have faced up this problem by studying the electrical properties of two types of CdTe films: CdTe films grown by Close Space Vapor Transport using a CdTe:Bi powder as the starting material and CdTe sputtered films doped by implantation with different Bi-doses. Temperature-dependent resistivity and Hall effect measurements and a discussion on the efficiency of both doping processes are presented.

  12. 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

    Science.gov (United States)

    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

  13. Reduction in thermal conductivity of Bi–Te alloys through grain refinement method

    Indian Academy of Sciences (India)

    Soma Dutta; V Shubha; T G Ramesh

    2013-10-01

    Ternary alloys of thermoelectric materials Bi–Sb–Te and Bi–Se–Te of molecular formula, Bi0.5Sb1.5Te3 ( type) and Bi0.36Se0.064Te0.576 ( type), were prepared by mechanical alloying method. The preparation of materials by mechanical alloying method has effectively reduced the thermal conductivity by generating a large number of induced grain boundaries with required degree of disorder. The process of frequent milling was adapted for grain refinement. Substantial reduction in thermal conductivity was achieved due to nano-structuring of these alloys. Thermal conductivity values were found to be very low at room temperature, 0.5W/mK and 0.8W/mK, respectively for p and n type materials.

  14. Spectroscopy of 193Bi

    Directory of Open Access Journals (Sweden)

    Herzáň A.

    2014-03-01

    Full Text Available An experiment aiming to study the shape coexistence in 193Bi has been performed at the Accelerator laboratory of the University of Jyväskylä, Finland (JYFL. Many new states have been found, hugely extending the previously known level scheme of 193Bi. The Iπ=292+${I^\\pi } = {{{29} \\over 2}^ + }$ member of the πi13/2 band de-excites also to the previously, only tentatively placed long-lived isomeric state. This link determines the energy of the isomeric state to be 2260(1 keV and suggests a spin and parity of (272+$\\left( {{{{{27} \\over 2}}^ + }} \\right$. The half-life of the isomeric state was measured to be 84.4(6 µs. A level structure on top of this isomeric state was constructed. However, transition directly depopulating this state could not be identified. A superdeformed band almost identical to that present in the neighboring isotope 191Bi has been identified.

  15. Numerical simulation of optical bi-stability in antiferromagnetic sandwich structure

    Energy Technology Data Exchange (ETDEWEB)

    Sun Dongmei [Provincial Key Laboratory of Low Dimensional and Mesoscopic Physics, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Fu Shufang, E-mail: shufangfu@yahoo.com [Provincial Key Laboratory of Low Dimensional and Mesoscopic Physics, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Zhou Sheng; Wang Xuanzhang [Provincial Key Laboratory of Low Dimensional and Mesoscopic Physics, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China)

    2012-01-15

    The magnetically optical bi-stability, a third-order nonlinear response, is investigated on an antiferromagnetic (AF) sandwich structure, where an AF film is sandwiched between two dielectric films. The configuration with the AF anisotropy axis and external static magnetic field both in the interfaces and normal to the incident plane is used. The incident wave is taken as a TE wave with its electric component transverse to the incident plane. We find that bistable switches can appear only in a finite frequency range and an incident angle range for a given regime of incident power, which means that there are the critical incident angle and frequency. The power threshold value for the bi-stability increases with the incident angle. In addition, the bi-stability also easily is modulated by the external magnetic field. - Highlights: > Antiferromagnetic sandwich NM/AF/NM. > Optical bi-stability near the resonant frequency. > Effect of magnetic field and incident angle.

  16. Surface Collective Modes in the Topological Insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex

    Energy Technology Data Exchange (ETDEWEB)

    Kogar, A.; Vig, S.; Thaler, A.; Wong, M. H.; Xiao, Y.; Reig-i-Plessis, D.; Cho, G. Y.; Valla, T.; Pan, Z.; Schneeloch, J.; Zhong, R.; Gu, G. D.; Hughes, T. L.; MacDougall, G. J.; Chiang, T. -C.; Abbamonte, P.

    2015-12-01

    We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex . Our goal was to identify the “spin plasmon” predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ '' ( q , ω ) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.

  17. Geometrical Effect in Magneto-Peltier Cooling of Bi and Bi0.88Sb0.12 Polycrystals

    Science.gov (United States)

    Yamashita, Osamu; Tomiyoshi, Shoichi

    2002-10-01

    The cooling temperatures of rectangular parallelepiped Bi and Bi0.88Sb0.12 polycrystals with various widths W and thickness t were measured at 293 K as a function of electric current in the magnetic field B up to 2.17 T, where the magnetic field is aligned along the thickness of a sample and the current flows along its length L through the copper leads soldered to both end whole surfaces of the cross section (W× t). Under such a configuration the temperatures were measured at both end surfaces. A thermoelement is not in contact with a heat sink. The cooling temperature at the cooled surface increased with increasing the magnetic field, and the rate of increase depended strongly on the cross-sectional area (W× t) of a sample, particularly in high magnetic fields. The highest cooling temperature was found to be achieved when a thermoelement has an optimum cross-sectional area (fitted to its length) so that Joule heating and the thermal conduction energies become equal under the operating conditions. The cooling temperature of Bi0.88Sb0.12 with optimum dimensions increased from 3.1 K in B=0 T to 6.4 K in B=± 2.17 T, so that it slightly exceeded a cooling temperature of 5.7 K which was obtained for a typical Bi2Te3 with a thermoelectric figure of merit of ZT=0.87 at 298 K.

  18. New Bi-Gravities

    CERN Document Server

    Akhavan, Amin; Nemati, Azadeh; Shirzad, Ahmad

    2016-01-01

    We show that the problem of ghosts in critical gravity and its higher dimensional extensions can be resolved by giving dynamics to the symmetric rank two auxiliary field existing in the action of these theories. These New Bi-Gravities, at linear level around the AdS vacuum, are free of Boulware-Deser ghost, kinetic ghost and tachyonic instability within the particular range of parameters. Moreover, we show that the energy and entropy of AdS-Schwarzschild black hole solutions of these new models are positive in the same range of parameters. This may be the sign that these new models are also free of ghost instabilities at the non-linear level.

  19. Bi-Cell Unit for Fuel Cell.

    Science.gov (United States)

    The patent concerns a bi-cell unit for a fuel cell . The bi-cell unit is comprised of two electrode packs. Each of the electrode packs includes an...invention relates in general to a bi-cell unit for a fuel cell and in particular, to a bi-cell unit for a hydrazine-air fuel cell .

  20. Spatial profile of thermoelectric effects during Peltier pulsing in Bi and Bi/MnBi eutectic

    Science.gov (United States)

    Silberstein, R. P.; Larson, D. J., Jr.

    1987-01-01

    The spatial profile of the thermal transients that occur during and following the current pulsing associated with Peltier Interface Demarcation during directional solidification is studied. Results for pure Bi are presented in detail and compared with corresponding results for the Bi/MnBi eutectic. Significant thermal transients occur throughout the sample that can be accounted for by the Peltier effect, the Thomson effect, and Joule heating. These effects are separated and their behavior is studied as a function of time, current density, and position with respect to the solid/liquid interface.

  1. A photoluminescence study of film structure in CdTe nanoparticle thin films.

    Science.gov (United States)

    Gardner, H C; Gallardo, D E; Dunn, S; Gaponik, N; Eychmüller, A

    2008-05-01

    The layer-by-layer deposition of thin films of CdTe nanoparticles and three different polyelectrolytes has been investigated. Photoluminescence spectra were used to monitor the energy transfer properties within the films. As the number of bilayers in a thin film was increased a decrease in the energy of the light emitted was observed. The wavelength change is a two-stage process. Deposition of the first one to two bi-layers of a thin film produced a sharp energy change (626 nm to 637 nm with the addition of a single bi-layer) whereas deposition of subsequent bi-layers produced a more gradual energy change (642 nm-646 nm with the addition of 5 bi-layers). A space-filling mechanism is suggested to account for these changes; smaller nanoparticles penetrate the earlier levels of a thin film and increase the inter-particle energy transfer opportunities within the layers.

  2. Professor WANG Fu-chun's Experience in Treating Bi Conditions

    Institute of Scientific and Technical Information of China (English)

    XU Shu-fen; XIAO Yuan-chun

    2004-01-01

    @@ Bi condition can be categorized into five types according to the depth of pathogenic factors, namely skin Bi condition, vessel Bi condition, tendon Bi condition,muscle Bi condition and bone Bi condition. In TCM categorization, Bi condition is usually categorized in the light of the nature of the pathogenic factors such as wind, cold, dampness and heat.

  3. Bilinguismes ou bi- appartenances

    Directory of Open Access Journals (Sweden)

    Jean-Charles Vegliante

    2012-10-01

    Full Text Available Dans cet essai, l’auteur évoque son sentiment de bi-appartenance lorsqu’il séjourne à Sienne, une de ses villes de prédilection. A l’occasion d’un congrès sur le thème : « Repenser la Méditerranée », ou de la projection d’un film évoquant les lendemains de massacres, il soulève des questions existentielles, en particulier la nécessité de « se parler ». Le bilinguisme se définit selon l’auteur comme une nécessité, une volonté de mieux entendre l’autre. Il évoque les exemples des poètes italiens Giuseppe Ungaretti (parfaitement francophone et Gabriele D’Annunzio, de l’allemand Franz Kafka et de l’anglais Milton. L’auteur passe du français à l’italien : « Lost in translation ?», comme il le dit plaisamment en conclusion.

  4. An EXAFS study of the luminescent Bi3+ center in LaPO4---Bi

    NARCIS (Netherlands)

    Zon, F.B.M. van; Koningsberger, D.C.; Oomen, E.W.J.L.; Blasse, G.

    1987-01-01

    In order to determine the oxygen coordination of the Bi3+ ion in LaPO4---Bi, extended X-ray absorption fine structure (EXAFS) spectra were measured of BiPO4 and LaPO4---Bi. Analysis of the EXAFS data shows that the Bi3+ ion in LaPO4---Bi occupies the La3+ site, but that the oxygen coordination of th

  5. Electrochemical behaviors of Bi (Ⅲ) in dimethylsulfoxide

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Cyclic voltammetry, chronoamperometry and chronopotentiometry were used to investigate the electrochemicalbehaviors of Bi(Ⅲ) in Bi(NO3)3-LiClO4-DMSO (dimethylsulfoxide) system on Pt and Cu electrodes. Experimental resultsindicated that the electroreducation of Bi(Ⅲ) to Bi(0) was irreversible on Pt and Cu electrodes. The diffusion coefficient andelectron transfer coefficient of Bi(Ⅲ) in 0.01 mol@ L-1 Bi(NO3)3-0.1 mol@L-1 LiClO4-DMSO system at 303 K were 1.75×10-6cm2@s-1 and 0.147 respectively.

  6. Topography and structure of ultrathin topological insulator Sb2Te3 films on Si(111) grown by means of molecular beam epitaxy

    Science.gov (United States)

    Lanius, M.; Kampmeier, J.; Kölling, S.; Mussler, G.; Koenraad, P. M.; Grützmacher, D.

    2016-11-01

    We have studied the growth process of the topological insulator (TI) Sb2 Te3 on Si(111) by scanning tunneling microscopy. High quality thin films from more than 22 nm down to 1 nm in thickness have been deposited by molecular beam epitaxy. To determine the thickness and domain formation of the films, x-ray reflectivity and x-ray diffraction were utilized. In comparison to previous studies of the TI Bi2 Te3 , the growth mechanism of Sb2 Te3 shows a similar transition from nucleation and growth in Sb-Te and Te-Te bilayers, respectively, to mound formation for thicker films. Atom probe tomography measurements reveal a intermixed interface between Sb2 Te3 and Si(111) substrate. These findings can explain the high density of defects and domains.

  7. Degradation and capacitance: voltage hysteresis in CdTe devices

    Science.gov (United States)

    Albin, D. S.; Dhere, R. G.; Glynn, S. C.; del Cueto, J. A.; Metzger, W. K.

    2009-08-01

    CdS/CdTe photovoltaic solar cells were made on two different transparent conducting oxide (TCO) structures in order to identify differences in fabrication, performance, and reliability. In one set of cells, chemical vapor deposition (CVD) was used to deposit a bi-layer TCO on Corning 7059 borosilicate glass consisting of a F-doped, conductive tin-oxide (cSnO2) layer capped by an insulating (undoped), buffer (iSnO2) layer. In the other set, a more advanced bi-layer structure consisting of sputtered cadmium stannate (Cd2SnO4; CTO) as the conducting layer and zinc stannate (Zn2SnO4; ZTO) as the buffer layer was used. CTO/ZTO substrates yielded higher performance devices however performance uniformity was worse due to possible strain effects associated with TCO layer fabrication. Cells using the SnO2-based structure were only slightly lower in performance, but exhibited considerably greater performance uniformity. When subjected to accelerated lifetime testing (ALT) at 85 - 100 °C under 1-sun illumination and open-circuit bias, more degradation was observed in CdTe cells deposited on the CTO/ZTO substrates. Considerable C-V hysteresis, defined as the depletion width difference between reverse and forward direction scans, was observed in all Cu-doped CdTe cells. These same effects can also be observed in thin-film modules. Hysteresis was observed to increase with increasing stress and degradation. The mechanism for hysteresis is discussed in terms of both an ionic-drift model and one involving majority carrier emission in the space-charge region (SCR). The increased generation of hysteresis observed in CdTe cells deposited on CTO/ZTO substrates suggests potential decomposition of these latter oxides when subjected to stress testing.

  8. Parents as Partners for Preparing Deaf Students for Bi-Bi Educational Programs.

    Science.gov (United States)

    LaSasso, Carol J.; Metzger, Melanie A.

    This paper describes Bilingual-Bicultural (BiBi) instructional programs for students with hearing impairments and proposes a model for BiBi instruction which uses parents as partners with instructors to develop the linguistic abilities of hearing-impaired students. In the model, traditionally spoken languages are conveyed via cued speech instead…

  9. Carrier dynamics and activation energy of CdTe/ZnTe nanostructures with different CdTe thicknesses

    Science.gov (United States)

    Han, Won Il; Lee, Ju Hyung; Choi, Jin Chul; Lee, Hong Seok

    2013-05-01

    We investigate the dimensional transition and optical properties of CdTe/ZnTe nanostructures with various CdTe thicknesses. The excitonic peak corresponding to the transitions from the ground electronic sub-band to the ground heavy-hole band in CdTe/ZnTe nanostructures shows different redshifts with increasing CdTe thickness due to variations in the dimensions of CdTe/ZnTe nanostructures. Time-resolved photoluminescence (PL) measurements used to study the carrier dynamics show that the decay time of 4.0 monolayer (ML) CdTe/ZnTe nanostructures is longer than that of CdTe/ZnTe nanostructures with different CdTe thicknesses. The activation energy of electrons confined in 4.0 ML CdTe/ZnTe nanostructures, as obtained from the temperature-dependent PL spectra, is higher than that of electrons confined in CdTe/ZnTe nanostructures with different CdTe thicknesses. These results indicate that the carrier dynamics and activation energy of CdTe/ZnTe nanostructures are affected by the thickness and dimensions of CdTe/ZnTe nanostructures.

  10. Towards Next Generation BI Systems

    DEFF Research Database (Denmark)

    Varga, Jovan; Romero, Oscar; Pedersen, Torben Bach

    2014-01-01

    Next generation Business Intelligence (BI) systems require integration of heterogeneous data sources and a strong user-centric orientation. Both needs entail machine-processable metadata to enable automation and allow end users to gain access to relevant data for their decision making processes...

  11. Bi-stable optical actuator

    Science.gov (United States)

    Holdener, Fred R.; Boyd, Robert D.

    2000-01-01

    The present invention is a bi-stable optical actuator device that is depowered in both stable positions. A bearing is used to transfer motion and smoothly transition from one state to another. The optical actuator device may be maintained in a stable position either by gravity or a restraining device.

  12. Geometrical effect in magneto-Peltier cooling of single crystal Bi

    Science.gov (United States)

    Yamashita, Osamu; Satou, Kouji; Tomiyoshi, Shoichi

    2004-06-01

    The cooling temperatures of rectangular parallelepiped Bi single crystals with various widths W and thickness t were measured at 293 K as a function of electric current in the magnetic field B up to 2.17 T. The magnetic field was aligned along the thickness of a sample and the current flows along its length L through the copper leads soldered to both end surfaces of cross section (W×t), where W, t, and L are parallel to the binary, bisector, and trigonal axes of Bi single crystal, respectively. The thermoelement was not in contact with a heat sink. The cooling temperature at the cooled surface increased with increasing the magnetic field, and it depended strongly on the thickness rather than the width of the crystal in high magnetic fields. The largest maximum cooling temperature was achieved when a thermoelement has optimum dimensions so that no heat energy is generated at the cold side. The cooling temperature of Bi single crystal with optimum dimensions of L=15 mm, W=4 mm, and t=2 mm increased from 4.1 K in B=0 T to 8.5 K in B=+2.17 T, so that it exceeded maximum cooling temperatures of 5.7 K obtained for a typical Bi2Te3 and 5.2 K measured previously for a polycrystalline Bi in B=+2.17 T.

  13. High-temperature thermoelectric properties of the β-As2-xBixTe3 solid solution

    Science.gov (United States)

    Vaney, J.-B.; Delaizir, G.; Piarristeguy, A.; Monnier, J.; Alleno, E.; Lopes, E. B.; Gonçalves, A. P.; Pradel, A.; Dauscher, A.; Candolfi, C.; Lenoir, B.

    2016-10-01

    Bi2Te3-based compounds are a well-known class of outstanding thermoelectric materials. β-As2Te3, another member of this family, exhibits promising thermoelectric properties around 400 K when appropriately doped. Herein, we investigate the high-temperature thermoelectric properties of the β-As2-xBixTe3 solid solution. Powder X-ray diffraction and scanning electron microscopy experiments showed that a solid solution only exists up to x = 0.035. We found that substituting Bi for As has a beneficial influence on the thermopower, which, combined with extremely low thermal conductivity values, results in a maximum ZT value of 0.7 at 423 K for x = 0.017 perpendicular to the pressing direction.

  14. (s, t, d)-bi-Koszul algebras

    Institute of Scientific and Technical Information of China (English)

    SI JunRu

    2009-01-01

    The paper focuses on the 1-generated positively graded algebras with non-pure resolutions and mainly discusses a new kind of algebras called (s, t, d)-bi-Koszul algebras as the generalization of bi-Koszul algebras. An (s, t, d)-bi-Koszul algebra can be obtained from two periodic algebras with pure resolutions. The generation of the Koszul dual of an (s, t, d)-bi-Koszul algebra is discussed. Based on it, the notion of strongly (s, t, d)-bi-Koszul algebras is raised and their homological properties are further discussed.

  15. (s,t,d)-bi-Koszul algebras

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The paper focuses on the 1-generated positively graded algebras with non-pure resolutions and mainly discusses a new kind of algebras called(s,t,d)-bi-Koszul algebras as the generalization of bi-Koszul algebras. An(s,t,d)-bi-Koszul algebra can be obtained from two periodic algebras with pure resolutions. The generation of the Koszul dual of an(s,t,d)-bi-Koszul algebra is discussed. Based on it,the notion of strongly(s,t,d)-bi-Koszul algebras is raised and their homological properties are further discussed.

  16. Facile synthesis of straight and branched CdTe nanowires using CdO as precursor.

    Science.gov (United States)

    Liu, Sheng; Yang, Chunyan; Zhang, Wen-Hua; Li, Can

    2011-12-01

    High-quality colloidal CdTe nanowires (NWs) containing both straight and branched ones were controllably prepared via a solution-based approach, using a low melting Bi nanoparticles as catalysts, CdO and tributylphosphine telluride (TBP-Te) as precursors, and a tri-n-octylphosphine oxide/tri-n-octylphosphine (TOPO/TOP) mixture as solvent. The resulting straight CdTe NWs have typical diameters below 20 nm accompanying with lengths exceeding 10 microm. In the case of branched CdTe NWs, tripod, V-shaped and y-shaped morphologies are obtained by decreasing the apparent Cd/Te molar ratio. It is found that, as the surface capping ligands, di-n-octylphosphinic acid (DOPA) is superior to decylphosphonic acid (DPA) in the reproducible growth of high-quality CdTe NWs. Since highly toxic dimethylcadmium, a cadmium precursor widely used in literatures, is replaced by CdO and the amount of the TOPO/TOP solvent mixture is significantly reduced, a relative safe and economical synthetic approach of high-quality colloidal CdTe NWs with controllable morphology is thus presented.

  17. Solution-processing of ultra-thin CdTe/ZnO nanocrystal solar cells

    Energy Technology Data Exchange (ETDEWEB)

    MacDonald, Brandon I. [CSIRO, Materials Science and Engineering, Bayview Ave, Clayton, Victoria, 3168 (Australia); School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Victoria, 3010 (Australia); Gengenbach, Thomas R.; Watkins, Scott E. [CSIRO, Materials Science and Engineering, Bayview Ave, Clayton, Victoria, 3168 (Australia); Mulvaney, Paul [School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Victoria, 3010 (Australia); Jasieniak, Jacek J., E-mail: Jacek.Jasieniak@csiro.au [CSIRO, Materials Science and Engineering, Bayview Ave, Clayton, Victoria, 3168 (Australia)

    2014-05-02

    We have carried out a detailed study into how modifications of the physical, chemical and optical properties of solution-processed, nanocrystalline CdTe layers influence the photovoltaic performance of sintered CdTe/ZnO nanocrystal solar cells. Such solar cells are fabricated through layer-by-layer assembly, which is enabled through an inter layer chemical and thermal treatment cycle. In this manner we are able to fabricate working solar cells with sintered CdTe layers as low as 90 nm, provided that grain size is precisely controlled. We show that the extent of grain growth achieved during the CdTe sintering process is strongly dependent on nanocrystal surface chemistry and chemical environment, with the removal of the organic capping ligands and the introduction of CdCl{sub 2} prior to annealing leading to greatly enhanced growth. Due to the air processing involved and the nanocrystalline nature of the CdTe, the overall performance of these solar cells is shown to be strongly dependent on both annealing temperature and time, with optimal results requiring a balance between crystal growth and degradation due to oxidation. Using this simple bi-layer device structure, optimized treatment conditions result in power conversion efficiencies of up to 7.7% and peak internal quantum efficiencies in excess of 95%. - Highlights: • We study the growth of nanocrystalline CdTe thin films from colloidal nanocrystals. • We examine the CdTe growth profiles as a function of surface chemistry. • We show that nanocrystalline CdTe is susceptible to oxidation under air annealing. • We show how this oxidation influences performance in CdTe/ZnO solar cells. • We demonstrate CdTe/ZnO solar cells with an efficiency of 7.7% fabricated in air.

  18. Heterojunction double dumb-bell Ag2Te-Te-Ag2Te nanowires

    Science.gov (United States)

    Som, Anirban; Pradeep, T.

    2012-07-01

    Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag2Te-Te-Ag2Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited.Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic

  19. Electronic structure of LaTe and CeTe

    Energy Technology Data Exchange (ETDEWEB)

    Chainani, A., E-mail: chainania@gmail.com [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan); Department of Physics, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan); Oura, M. [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan); Matsunami, M. [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Ochiai, A.; Takahashi, T. [Department of Physics, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan); Tanaka, Y. [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan); Graduate School of Material Science, University of Hyogo, 3-2-1 Kouto, Hyogo 678-1297 (Japan); Tamasaku, K.; Kohmura, Y.; Ishikawa, T. [RIKEN SPring-8 Centre, 1-1-1 Kouto, Hyogo 679-5148 (Japan)

    2016-04-15

    Highlights: • Hard X-ray and soft X-ray photoelectron spectroscopy of LaTe and CeTe. • Evidence for Kondo screening in antiferromagnetic(T{sub N} = 2.2 K) compound CeTe. • Suppressed Kondo resonance in CeTe compared to typical Kondo materials. - Abstract: We report a comparative study of the electronic structure of the compounds LaTe and CeTe, both of which crystallize in the rock salt structure. LaTe is a paramagnetic metal while CeTe is known to exhibit anomalous Kondo-like transport behaviour and undergoes a transition to a complex magnetically ordered state at low temperature (T{sub N} = 2.2 K). We carry out hard X-ray photoelectron spectroscopy (HAXPES) of the core-levels and valence band of LaTe and CeTe at T = 20 K, in order to characterize their intrinsic electronic structure, and to address the role of Kondo effect on the electronic structure of CeTe. The bulk sensitive core level HAXPES spectra show evidence of screened features in the La 3d and Ce 3d states mixed with plasmon features. From a careful analysis of the Te, La and Ce derived core levels, we separate out the respective origins of the satellites and show that CeTe indeed exhibits definitive but weak f{sup 0} and f{sup 2} satellites due to Kondo screening, in addition to the main f{sup 1} peak. The comparison of the valence band spectra of CeTe obtained using HAXPES and soft X-ray PES clearly identifies the Ce 4f derived features. Resonant photoelectron spectrosocopy across the Ce 3d − 4f threshold confirms the Ce 4f{sup 1} final state at the Fermi level, corresponding to the tail of the Kondo resonance feature which occurs above the Fermi level, while the Ce 4f{sup 0} final state feature is observed at a binding energy of 2.4 eV. The 4f{sup 0} and 4f{sup 1} final states show giant resonances compared to the off-resonant spectra. However, in contrast to typical Kondo systems, the tail of the Ce 4f{sup 1} Kondo resonance at the Fermi level is relatively suppressed compared to the Ce 4f

  20. Potentiality of photorefractive CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Moisan, J.Y.; Gravey, P.; Picoli, G.; Wolffer, N.; Vieux, V. (Dept. Technologies Appliquees a la Connectique, Centre National d' Etudes des Telecommunications, 22 - Lannion (France))

    1993-01-30

    For optical telecommunication networks, optical switching is now being studied. Different solutions have been proposed (integrated optics, free space switching, etc.), and reconfigurable optical interconnects, based on phase conjugation, should be one interesting method. For example, some results have been obtained with a double-phase conjugated mirror configuration, allowing reconfigurable connection between single-mode optical fibres. These phase-conjugated optics use photorefractive crystals and the first demonstration has been given using Bi[sub 12]TiO[sub 20] photorefractive crystals. In a telecommunication network, semiconductive crystals with a good efficiency in the near-IR wavelength are needed. Our first experiments were carried out with InP:Fe crystals at 1.3 [mu]m. However, it is well known, from published studies, that II-VI materials are, in principle, more interesting for the following reasons. The electro-optic coefficient is higher (and therefore the figure of merit is higher). The solubility of dopants is higher (and therefore the space charge electric field, which modulates the refractive index of the material, may be higher). Next we tested a CdTe:V crystal and, in a two-wave mixing experiment without an external electric field, an amplification gain was observed and a high photosensitivity demonstrated at 1.3 [mu]m. In this paper, we shall describe the photorefractive effect and explain our choice of the CdTe:V crystal, taking into account the parameters of this photorefractive effect and some other parameters required by the applications in the optical beam steering field. Next the results will be given, and finally an optical configuration using phase conjugation will be presented as an example of application. (orig.).

  1. Te/C nanocomposites for Li-Te Secondary Batteries

    National Research Council Canada - National Science Library

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    ... (ca. 550 mA h cm(-3) at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries...

  2. Te/C nanocomposites for Li-Te Secondary Batteries.

    Science.gov (United States)

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-22

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li(+)/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm(-3)), excellent cyclability (ca. 705 mA h cm(-3) over 100 cycles), and fast rate capability (ca. 550 mA h cm(-3) at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  3. In-situ synthesis of nanofibers with various ratios of BiOClx/BiOBry/BiOIz for effective trichloroethylene photocatalytic degradation

    Science.gov (United States)

    Zhang, Yifan; Park, Mira; Kim, Hak Yong; Ding, Bin; Park, Soo-Jin

    2016-10-01

    In this work, BiOClx/BiOBry/BiOIz (x + y + z = 1) composite nanofibers were prepared through electrospinning and the sol-gel methods. Photocatalytic degradation of trichloroethylene (TCE) by BiOClx/BiOBry/BiOIz/PAN nanofibers was systematically investigated via gas chromatography (GC). Optimum photocatalytic activity was achieved with BiOCl0.3/BiOBr0.3/BiOI0.4 fibers under solar light irradiation. X-ray photoelectron spectroscopy (XPS) peaks due to Csbnd O and Cdbnd O were observed at 286.0 and 288.3 eV, respectively, it indicated that the BiOClx/BiOBry/BiOIz mixture had been successfully doped on the polyacrylonitrile (PAN) fibers. Furthermore, X-ray diffraction (XRD) results also confirmed that we had synthesized the as-prepared composite nanofibers successfully. Photocatalytic activities of BiOCl0.3/BiOBr0.3/BiOI0.4 were up to 3 times higher than the pure BiOCl, BiOBr and BiOI samples, respectively.

  4. Magnetic interactions in BiFe₀.₅Mn₀.₅O₃ films and BiFeO₃/BiMnO₃ superlattices.

    Science.gov (United States)

    Xu, Qingyu; Sheng, Yan; Khalid, M; Cao, Yanqiang; Wang, Yutian; Qiu, Xiangbiao; Zhang, Wen; He, Maocheng; Wang, Shuangbao; Zhou, Shengqiang; Li, Qi; Wu, Di; Zhai, Ya; Liu, Wenqing; Wang, Peng; Xu, Y B; Du, Jun

    2015-03-13

    The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces.

  5. The properties of CdTe solar cells with ZnTe/ZnTe: Cu buffer layers

    Institute of Scientific and Technical Information of China (English)

    Song Huijin; Zheng Jiagui; Feng Lianghuan; Yan Qiang; Lei Zhi; Wu Lili; Zhang Jingquan; Li Wei; Li Bing

    2008-01-01

    CdS/CdTe solar cells with ZnTe/ZnTe:Cu buffer layers were fabricated and studied. The energy band structure of it was analyzed. The C-V, I-V characteristics and the spectral response show that the ZnTe/ZnTe:Cu buffer layers improve the back contact characteristic properties, the diode characteristics of the forward junction and the short-wave spectral response of the CdTe solar cells. The ZnTe/ZnTe:Cu buffer layers affect the solar cell conversion efficiency and its fill factor.

  6. Scavenger receptor BI boosts hepatocyte permissiveness to Plasmodium infection.

    NARCIS (Netherlands)

    Yalaoui, S.; Huby, T.; Franetich, J.F.; Gego, A.; Rametti, A.; Moreau, M.; Collet, X.; Siau, A.; Gemert, G.J.A. van; Sauerwein, R.W.; Luty, A.J.F.; Vaillant, J.C.; Hannoun, L.; Chapman, J.; Mazier, D.; Froissard, P.

    2008-01-01

    Infection of hepatocytes by Plasmodium falciparum sporozoites requires the host tetraspanin CD81. CD81 is also predicted to be a coreceptor, along with scavenger receptor BI (SR-BI), for hepatitis C virus. Using SR-BI-knockout, SR-BI-hypomorphic and SR-BI-transgenic primary hepatocytes, as well as s

  7. Development and Manufacture of Bi-2223 Wires

    Science.gov (United States)

    Kobayashi, Shin-Ichi

    This chapter reviews Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox (Bi-2223) wire made by the powder-in-tube technique (PIT). The currently leading high-temperature superconductors (HTS) wire technology for practical use is Bi-2223 wire, made by the controlled over-pressure (CT-OP) sintering process. The CT-OP process uses pressures up to 30MPa during heat treatment. The technique densifies the Bi-2223 filaments and enhances the uniformity of the electrical and mechanical performance in the Bi-2223 wire. Today, Bi-2223 wires are used in most HTS applications, such as power cables, many kinds of magnets, and motors for ship propulsion and electric vehicles.

  8. Bouwlogistieke innovaties weerbarstig te implementeren

    NARCIS (Netherlands)

    Ludema, M.W.; Vries, A.M.R.

    2015-01-01

    Toelevering van bouwmaterialen aan bouwprojecten is complex en verregaande gesegregeerd. De bouwsector staat voor een kans te innoveren op het vlak van de bouwlogistiek. In het verleden is ervaring opgedaan met ‘best-practices’ die voldoende kansen bieden de noodzakelijk innovatie door te voeren. Vi

  9. Efficient Charge Separation between Bi and Bi2 MoO6 for Photoelectrochemical Properties.

    Science.gov (United States)

    Ma, Ying; Jia, Yulong; Wang, Lina; Yang, Min; Bi, Yingpu; Qi, Yanxing

    2016-04-18

    Herein, porous Bi/Bi2 MoO6 nanoparticles have been prepared by a facile in-situ reduction approach. Moreover, the morphology and Bi content of product could be controlled by varying the reaction time. By controlled fabrication, the desired porous Bi2 MoO6 nanostructure with incorporation of Bi was obtained and exhibited high photoelectric and photocatalytic activity. In particular, the samples yield a photocurrent density of 320 μA cm(-2) , which is 3.2 times that of the pure Bi2 MoO6 nanosheet (100 μA cm(-2) ) under the same conditions. UV/Vis diffuse reflectance spectroscopy analysis confirmed the surface plasmon resonance in the as-prepared porous nanoparticles. The improved photoelectric properties could be the synergistic effect of the porous structure with large surface area and effective electron-hole separations between Bi and Bi2 MoO6 .

  10. Thermodynamic assessments of the Bi-U and Bi-Mn systems

    Energy Technology Data Exchange (ETDEWEB)

    Wang, C.P.; Yu, W.J.; Li, Z.S. [Department of Materials Science and Engineering, College of Materials, and Research Center of Materials Design and Applications, Xiamen University, Xiamen 361005 (China); Liu, X.J., E-mail: lxj@xmu.edu.cn [Department of Materials Science and Engineering, College of Materials, and Research Center of Materials Design and Applications, Xiamen University, Xiamen 361005 (China); Tang, A.T.; Pan, F.S. [College of Materials Science and Engineering, Chongqing University, Chongqing 400045 (China)

    2011-05-01

    The Bi-U and Bi-Mn binary systems have been critically assessed by using the CALPHAD (Calculation of Phase Diagrams) technique on the basis of the experimental data including thermodynamic properties and phase equilibria. The Gibbs free energies of the solution phases (liquid, bcc, fcc, {alpha}U, {beta}U, {alpha}Mn, (Bi), and {beta}Mn) were modeled by a sub-regular solution model with the Redlich-Kister equation, and those of the intermetallic compounds (UBi, U{sub 3}Bi{sub 4}, UBi{sub 2}, {alpha}BiMn and {beta}BiMn) in these two binary systems were described by a two-sublattice model. A proper set of thermodynamic parameters has been derived for describing the Gibbs free energies of each phase in the Bi-U and Bi-Mn systems. An agreement between the calculated results and experimental data is obtained.

  11. SOA, SoBI & EDA - Paradigms for Integration Capabilities of BI Platform

    National Research Council Canada - National Science Library

    STOICA, Marian; GHILIC-MICU, Bogdan; Marinela, MIRCEA

    2008-01-01

    A Business Intelligence (BI) provider may offer a basic solution, a packed application or a comprising BI platform which integrates components from individual technologies in a synergic system. The providersâ...

  12. Transitive bi-Lipschitz group actions and bi-Lipschitz parameterizations

    CERN Document Server

    Freeman, David M

    2012-01-01

    We prove that Ahlfors 2-regular quasisymmetric images of the Euclidean plane are bi-Lipschitz images of the plane if and only if they are uniformly bi-Lipschitz homogeneous with respect to a group. We also prove that certain geodesic spaces are bi-Lipschitz images of Carnot groups if they are inversion invariant bi-Lipschitz homogeneous with respect to a group.

  13. Magnetotransport study of (Sb1-xBix)2Te3 thin films on mica substrate for ideal topological insulator

    Science.gov (United States)

    Ni, Yan; Zhang, Zhen; Nlebedim, Cajetan I.; Jiles, David C.

    2016-05-01

    We deposited high quality (Sb1-xBix)2Te3 on mica substrate by molecular beam epitaxy and investigated their magnetotransport properties. It is found that the average surface roughness of thin films is lower than 2 nm. Moreover, a local maxima on the sheet resistance is obtained with x = 0.043, indicating a minimization of bulk conductivity at this composition. For (Sb0.957Bi0.043)2Te3, weak antilocalization with coefficient of -0.43 is observed, confirming the existence of 2D surface states. Moreover Shubnikov-de Hass oscillation behavior occurs under high magnetic field. The 2D carrier density is then determined as 0.81 × 1016 m-2, which is lower than that of most TIs reported previously, indicating that (Sb0.957Bi0.043)2Te3 is close to ideal TI composition of which the Dirac point and Fermi surface cross within the bulk bandgap. Our results thus demonstrate the best estimated composition for ideal TI is close to (Sb0.957Bi0.043)2Te3 and will be helpful for designing TI-based devices.

  14. Photocatalytic activity of Bi2WO6/Bi2S3 heterojunctions: the facilitation of exposed facets of Bi2WO6 substrate

    Science.gov (United States)

    Yan, Long; Wang, Yufei; Shen, Huidong; Zhang, Yu; Li, Jian; Wang, Danjun

    2017-01-01

    Bi2S3/Bi2WO6 hybrid architectures with exposed (020) Bi2WO6 facets have been synthesized via a controlled anion exchange approach. X-ray photoelectron spectroscopy (XPS) reveals that a small amount of Bi2S3 was formed on the surface of Bi2WO6 during the anion exchange process, thus leading to the transformation from the Bi2WO6 to Bi2S3/Bi2WO6. A rhodamine B (RhB) aqueous solution was chosen as model organic pollutants to evaluate the photocatalytic activities of the Bi2S3/Bi2WO6 catalysts. Under visible light irradiation, the Bi2S3/Bi2WO6-TAA displayed the excellent visible light photoactivities compared with pure Bi2S3, Bi2WO6 and other composite photocatalysts. The efficient photocatalytic activity of the Bi2S3/Bi2WO6-TAA composite microspheres was ascribed to the constructed heterojunctions and the inner electric field caused by the exposed (020) Bi2WO6 facets. Active species trapping experiments revealed that h+ and O2rad - are the main active species in the photocatalytic process. Furthermore, the as-obtained photocatalysts showed good photocatalytic activity after four recycles. The results presented in this study provide a new concept for the rational design and development of highly efficient photocatalysts.

  15. Influence of the initial Bi2223 phase content on microstructure development in Bi2223/Ag tapes

    DEFF Research Database (Denmark)

    Grivel, Jean-Claude; Yang, X P; Abrahamsen, Asger Bech;

    2010-01-01

    (Bi,Pb)2Sr2Ca2Cu3O10 (Bi2223) Ag-sheathed tapes were produced from precursors containing various amounts of pre-reacted Bi2223 phase obtained by means of controlled calcinations of the starting powder mixture. The evolution of the critical current density during the first 20h of the first heat...

  16. An optimized multilayer structure of CdS layer for CdTe solar cells application

    Energy Technology Data Exchange (ETDEWEB)

    Han Junfeng, E-mail: pkuhjf@gmail.com [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Liao Cheng, E-mail: Cliao@pku.edu.cn [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Jiang Tao [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Spanheimer, C.; Haindl, G.; Fu, Ganhua; Krishnakumar, V. [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Zhao Kui [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Klein, A.; Jaegermann, W. [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany)

    2011-04-28

    Research highlights: > Two different methods to prepare CdS films for CdTe solar cells. > A new multilayer structure of window layer for the CdTe solar cell. > Thinner CdS window layer for the solar cell than the standard CdS layer. > Higher performance of solar cells based on the new multilayer structure. - Abstract: CdS layers grown by 'dry' (close space sublimation) and 'wet' (chemical bath deposition) methods are deposited and analyzed. CdS prepared with close space sublimation (CSS) has better crystal quality, electrical and optical properties than that prepared with chemical bath deposition (CBD). The performance of CdTe solar cell based on the CSS CdS layer has higher efficiency than that based on CBD CdS layer. However, the CSS CdS suffers from the pinholes. And consequently it is necessary to prepare a 150 nm thin film for CdTe/CdS solar cell. To improve the performance of CdS/CdTe solar cells, a thin multilayer structure of CdS layer ({approx}80 nm) is applied, which is composed of a bottom layer (CSS CdS) and a top layer (CBD CdS). That bi-layer film can allow more photons to pass through it and significantly improve the short circuit current of the CdS/CdTe solar cells.

  17. Heterojunction double dumb-bell Ag₂Te-Te-Ag₂Te nanowires.

    Science.gov (United States)

    Som, Anirban; Pradeep, T

    2012-08-07

    Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag(2)Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag(2)Te-Te-Ag(2)Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited.

  18. Stripe structure CdTe-CdZnTe-CdTe in a bulk single crystal

    Science.gov (United States)

    Azoulay, M.; Sinvani, M.; Mizrachi, M.; Feldstein, H.

    1994-03-01

    In this paper we present a study that was aimed at performing a selective diffusion of Zn into CdTe. A single crystal CdTe wafer fabricated into a "tooth-like" structure which was further subjected to high temperature annealing in the presence of Zn vapour. The sample was then cut parallel to the diffusion direction and a Zn concentration analysis, using an electron microprobe, was performed. As expected, the stripe structure CdTe-CdZnTe-CdTe has been confirmed. The Zn decay profiles were fitted to a modified diffusion model, suggesting a bulk diffusion mechanism coupled with a surface reaction. Practical implementation of this stripe structure for an infrared light waveguide is being evaluated.

  19. Dual-bath electrodeposition of n-type Bi–Te/Bi–Se multilayer thin films

    Energy Technology Data Exchange (ETDEWEB)

    Matsuoka, Ken; Okuhata, Mitsuaki; Takashiri, Masayuki, E-mail: takashiri@tokai-u.jp

    2015-11-15

    N-type Bi–Te/Bi–Se multilayer thin films were prepared by dual-bath electrodeposition. We varied the number of layers from 2 to 10 while the total film thickness was maintained at approximately 1 μm. All the multilayer films displayed the X-ray diffraction peaks normally observed from individual Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} crystal structures, indicating that both phases coexist in the multilayer. The cross-section of the 10-layer Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains but the boundaries between the layers were not planar. The Seebeck coefficient was almost constant throughout the entire range of our experiment, but the electrical conductivity of the multilayer thin films increased significantly as the number of layers was increased. This may be because the electron mobility increases as the thickness of each layer is decreased. As a result of the increased electrical conductivity, the power factor also increased with the number of layers. The maximum power factor was 1.44 μW/(cm K{sup 2}) for the 10-layer Bi–Te/Bi–Se film, this was approximately 3 times higher than that of the 2-layer sample. - Highlights: • N-type Bi–Te/Bi–Se multilayer thin films were deposited by electrodeposition. • We employed a dual-bath electrodeposition process for preparing the multilayers. • The Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains. • The electrical conductivity increased as the number of layers was increased. • The power factor improved by 3 times as the number of layers was increased.

  20. Optimal Bi-Valued Auctions

    CERN Document Server

    Ben-Zwi, Oren

    2011-01-01

    We investigate \\emph{bi-valued} auctions in the digital good setting and construct an explicit polynomial time deterministic auction. We prove an unconditional tight lower bound which holds even for random superpolynomial auctions. The analysis of the construction uses the adoption of the finer lens of \\emph{general competitiveness} which considers additive losses on top of multiplicative ones. The result implies that general competitiveness is the right notion to use in this setting, as this optimal auction is uncompetitive with respect to competitive measures which do not consider additive losses.

  1. Ambipolar field effect in the ternary topological insulator (BixSb1–x)2Te3 by composition tuning

    KAUST Repository

    Kong, Desheng

    2011-10-02

    Topological insulators exhibit a bulk energy gap and spin-polarized surface states that lead to unique electronic properties 1-9, with potential applications in spintronics and quantum information processing. However, transport measurements have typically been dominated by residual bulk charge carriers originating from crystal defects or environmental doping 10-12, and these mask the contribution of surface carriers to charge transport in these materials. Controlling bulk carriers in current topological insulator materials, such as the binary sesquichalcogenides Bi 2Te 3, Sb 2Te 3 and Bi 2Se 3, has been explored extensively by means of material doping 8,9,11 and electrical gating 13-16, but limited progress has been made to achieve nanostructures with low bulk conductivity for electronic device applications. Here we demonstrate that the ternary sesquichalcogenide (Bi xSb 1-x) 2Te 3 is a tunable topological insulator system. By tuning the ratio of bismuth to antimony, we are able to reduce the bulk carrier density by over two orders of magnitude, while maintaining the topological insulator properties. As a result, we observe a clear ambipolar gating effect in (Bi xSb 1-x) 2Te 3 nanoplate field-effect transistor devices, similar to that observed in graphene field-effect transistor devices 17. The manipulation of carrier type and density in topological insulator nanostructures demonstrated here paves the way for the implementation of topological insulators in nanoelectronics and spintronics. © 2011 Macmillan Publishers Limited. All rights reserved.

  2. Electronic structure and band alignments of ZnTe/CrTe(0 0 1), CdSe/CrTe(0 0 1) and CdTe/CrTe(0 0 1) interfaces

    Indian Academy of Sciences (India)

    F Ahmadian; R Zare

    2011-08-01

    All-electron full potential calculations based on spin density functional theory were performed to study cubic zincblende (ZB) and hexagonal NiAs structures of bulk CrTe and ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces. The lattice mismatch effect in ZB CrTe and magnetic properties of CrTe in the ideal ZB CrTe structure were investigated. The band alignment properties of the ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces were computed and a rather large minority valence band offset of about 1.09 eV was observed in ZnTe/CrTe(0 0 1) heterojunction. Also in the CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces, the conduction band minimum of minority spin in CrTe was above the conduction band minimum of CdTe and CdSe and so the majority spin electrons could be directly injected to both semiconductors, indicating the possibility of highly efficient spin injection into the CdSe and CdTe semiconductors.

  3. ZnTe/CdTe thin-film heterojunctions

    Directory of Open Access Journals (Sweden)

    M.M. Kolesnyk

    2009-01-01

    Full Text Available In this work we have studied the structural and electrophysical properties of the ZnTe/CdTe heterojunctions, obtained by the method of thermal evaporation in quasi-closed volume. Investigations allowed to define the films structural parameters, such as texture, lattice constant, sizes of grains and coherent-scattering domains, micro-deformation level, and their dependence on the conditions of films production as well. Electrophysical investigations allowed to define the charge-transport mechanism in heterojunction.

  4. Facile synthesis of Bi/BiOCl composite with selective photocatalytic properties

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Dongling; Zhang, Min; Lu, Qiuju; Chen, Junfang [Research Institute for New Material Technology, Department of Research Center for Materials Interdisciplinary Science, Chongqing University of Arts and Science, Chongqing 402160 (China); Liu, Bitao, E-mail: liubitao007@163.com [Research Institute for New Material Technology, Department of Research Center for Materials Interdisciplinary Science, Chongqing University of Arts and Science, Chongqing 402160 (China); Wang, Zhaofeng, E-mail: zhaofeng.wang@uconn.edu [Department of Chemical & Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269 (United States)

    2015-10-15

    This paper presents a novel and facile method to fabricate Bi/BiOCl composites with dominant (001) facets in situ via a microwave reduction route. Different characterization techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), UV–vis diffuse reflectance spectrometry (DRS), X-ray photoelectron spectroscopy (XPS), electron spin resonance spectroscopy (ESR), cathodoluminescence spectrum (CL), and lifetime, have been employed to investigate the structure, optical and electrical properties of the Bi/BiOCl composites. The experimental results show that the introduction of Bi particles can efficiently enhance the photocatalytic performance of BiOCl for the degradation of several dyes under ultraviolet (UV) light irradiation, especially for negative charged methyl orange (MO). Unlike the UV photocatalytic performance, such Bi/BiOCl composite shows higher degradation efficiency towards rhodamine B (RhB) than MO and methylene blue (MB) under visible light irradiation. This special photocatalytic performance can be ascribed to the synergistic effect between oxygen vacancies and Bi particles. This work provides new insights about the photodegradation mechanisms of MO, MB and RhB under UV and visible light irradiation, which would be helpful to guide the selection of an appropriate catalyst for other pollutants. - Highlights: • Bi/BiOCl composites were synthesized via a microwave reduction. • Tunable selectivity photocatalytic activity can be achieved. • Photodegradation mechanism under UV and visible light were proposed.

  5. Nonlinear approximation with bi-framelets

    DEFF Research Database (Denmark)

    Borup, Lasse; Nielsen, Morten; Gribonval, Rémi

    2005-01-01

    We study the approximation in Lebesgue spaces of wavelet bi-frame systems given by translations and dilations of a finite set of generators. A complete characterization of the approximation spaces associated with best m-term approximation of wavelet bi-framelet systems is given...

  6. Barrier formation at graded HgTe/CdTe heterojunctions

    Science.gov (United States)

    Goren, D.; Asa, G.; Nemirovsky, Y.

    1996-11-01

    Numerical calculations of graded HgTe/CdTe heterojunction (HJ) band diagrams at equilibrium are presented and discussed. The calculations are performed in the entire compositional range (0HJs are examined as a function of the graded region width and the graded region doping profiles. The graded region width and doping profiles were found to be the two main factors that determine whether barriers are formed as well as their shape and magnitude. The calculated results indicate that epitaxial ohmic HgTe contacts to extrinsic CdTe are possible, provided that the graded region is wider than one micron, and that it has the same doping type as the doping of the substrate with equal or higher absolute value. Further numerical calculations take into consideration the possible existence of distributed interface charges in the graded region of the HJ. It is shown that by assuming a classical transport over the potential barrier, the effective graded interface charge can be determined from the zero bias differential resistance of the HJ. Experimental transport measurements of metalorganic chemical vapor deposition (MOCVD) grown HgTe/p-CdTe graded HJs show a varying degree of rectification, indicating variations in the graded interface charge distributions which result from different MOCVD growth conditions.

  7. Pathways toward higher performance CdS/CdTe devices: Te exposure of CdTe surface before ZnTe:Cu/Ti contacting

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T.A., E-mail: tim.gessert@nrel.gov; Burst, J.M.; Wei, S.-H.; Ma, J.; Kuciauskas, D.; Rance, W.L.; Barnes, T.M.; Duenow, J.N.; Reese, M.O.; Li, J.V.; Young, M.R.; Dippo, P.

    2013-05-01

    Many studies of thin-film CdS/CdTe photovoltaic devices have suggested that performance may be improved by reducing recombination due to Te-vacancy (V{sub Te}), Te antisite (Te{sub Cd}), or Te-interstitial (Te{sub i}) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it may be also coupled to the formation of beneficial cadmium vacancy (V{sub Cd}) defects. In this study, we expose the CdTe surface to Te vapor prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing V{sub Te} without significantly reducing V{sub Cd}. Initial results show that when this modified contact is used on a CdCl{sub 2}-treated CdS/CdTe device, poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or Cu{sub x}Te or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of V{sub Te} (e.g., oxygen and chlorine additions), adding even a small amount of Te may produce detrimental defects. - Highlights: ► Te exposure of CdS/CdTe back contact reduces device performance. ► Field strength and minority carrier lifetime reduced. ► Calculations suggest formation of Te on Cd antisite defect.

  8. 125Te NMR chemical-shift trends in PbTe–GeTe and PbTe–SnTe alloys

    Energy Technology Data Exchange (ETDEWEB)

    Njegic, Bosiljka [Ames Laboratory; Levin, Evgenii M. [Ames Laboratory; Schmidt-Rohr, Klaus [Ames Laboratory

    2013-10-08

    Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in 125Te NMR chemical shift due to bonding to dopant or “solute” atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the 125Te NMR chemical shifts in PbTe-based alloys, Pb1-xGexTe and Pb1-xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS 125Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the 125Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

  9. Thermal imaging of Bi2212 THz oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Akiyama, H.; Pyon, S. [Department of Applied Physics, The University of Tokyo, Tokyo 113-8656 (Japan); Tamegai, T., E-mail: tamegai@ap.t.u-tokyo.ac.jp [Department of Applied Physics, The University of Tokyo, Tokyo 113-8656 (Japan); Tsujimoto, M.; Kakeya, I. [Department of Electric Science & Engineering, Kyoto University, Kyoto 615-8510 (Japan)

    2015-11-15

    Highlights: • Temperature distributions of Bi2212 mesas at low temperatures are measured. • Fluorescent thermal imaging (FTI) method is applied in the thermal imaging. • Obtained thermal images reveal non-uniformity of the temperature distribution. - Abstract: Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} (Bi2212) mesas are promising candidates for THz oscillators, which can fill the frequency range around “THz gap”. However, it is known that Bi2212 mesas show self-heating effects (hot spots) when the current is passed along the c-axis due to the low thermal conductivity in this direction. Although several previous studies reported the relation of the hot spot and THz emission, consistent answer has not been obtained yet. In order to address this issue, imaging of temperature distributions on Bi2212 mesas is expected to be very effective. Here, we set up fluorescent thermal imaging (FTI) method for visualizing the surface temperature distribution on the Bi2212 mesa. We have succeeded in observing hot spots in the Bi2212 mesa with high spatial resolution.

  10. Composition dependence of electrical properties of ZnF2–MO–TeO2 glasses

    Indian Academy of Sciences (India)

    D K Durga; N Veeraiah

    2001-08-01

    Dielectric constant ('), loss (tan ), a.c. conductivity () of ZnF2–MO–TeO2 glasses with varying concentrations of MO (P2O5, As2O3 and Bi2O3) were measured as a function of frequency and temperature over moderately wide ranges. From the analysis of these studies along with IR spectra and DTA results of these glasses, the structural changes in the systems with the concentration of metal oxides are discussed.

  11. BiHermitian supersymmetric quantum mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Zucchini, Roberto [Dipartimento di Fisica, Universita degli Studi di Bologna, V Irnerio 46, I-40126 Bologna (Italy)

    2007-04-21

    BiHermitian geometry, discovered long ago by Gates, Hull and Rocek, is the most general sigma model target space geometry allowing for (2, 2) world sheet supersymmetry. In this paper, we work out supersymmetric quantum mechanics for a biHermitian target space. We display the full supersymmetry of the model and illustrate in detail its quantization procedure. Finally, we show that the quantized model reproduces the Hodge theory for compact twisted generalized Kaehler manifolds recently developed by Gualtieri. This allows us to recover and put in a broader context the results on the biHermitian topological sigma models obtained by Kapustin and Li.

  12. BiHermitian Supersymmetric Quantum Mechanics

    CERN Document Server

    Zucchini, R

    2006-01-01

    BiHermitian geometry, discovered long ago by Gates, Hull and Rocek, is the most general sigma model target space geometry allowing for (2,2) world sheet supersymmetry. In this paper, we work out supersymmetric quantum mechanics for a biHermitian target space. We display the full supersymmetry of the model and illustrate in detail its quantization procedure. Finally, we show that the quantized model reproduces the Hodge theory for compact twisted generalized Kaehler manifolds recently developed by Gualtieri. This allows us to recover and put in a broader context the results on the biHermitian topological sigma models obtained by Kapustin and Li.

  13. BiHermitian supersymmetric quantum mechanics

    Science.gov (United States)

    Zucchini, Roberto

    2007-04-01

    BiHermitian geometry, discovered long ago by Gates, Hull and Rocek, is the most general sigma model target space geometry allowing for (2, 2) world sheet supersymmetry. In this paper, we work out supersymmetric quantum mechanics for a biHermitian target space. We display the full supersymmetry of the model and illustrate in detail its quantization procedure. Finally, we show that the quantized model reproduces the Hodge theory for compact twisted generalized Kähler manifolds recently developed by Gualtieri in [33]. This allows us to recover and put in a broader context the results on the biHermitian topological sigma models obtained by Kapustin and Li in [9].

  14. Bi-log-concave Distribution Functions

    DEFF Research Database (Denmark)

    Dümbgen, Lutz; Kolesnyk, Petro; Wilke, Ralf

    2017-01-01

    Nonparametric statistics for distribution functions F or densities f=F′ under qualitative shape constraints constitutes an interesting alternative to classical parametric or entirely nonparametric approaches. We contribute to this area by considering a new shape constraint: F is said to be bi......-log-concave, if both logF and log(1−F) are concave. Many commonly considered distributions are compatible with this constraint. For instance, any c.d.f. F with log-concave density f=F′ is bi-log-concave. But in contrast to log-concavity of f, bi-log-concavity of F allows for multimodal densities. We provide various...

  15. Superconductivity in topological insulator Sb2Te3 induced by pressure.

    Science.gov (United States)

    Zhu, J; Zhang, J L; Kong, P P; Zhang, S J; Yu, X H; Zhu, J L; Liu, Q Q; Li, X; Yu, R C; Ahuja, R; Yang, W G; Shen, G Y; Mao, H K; Weng, H M; Dai, X; Fang, Z; Zhao, Y S; Jin, C Q

    2013-01-01

    Topological superconductivity is one of most fascinating properties of topological quantum matters that was theoretically proposed and can support Majorana Fermions at the edge state. Superconductivity was previously realized in a Cu-intercalated Bi2Se3 topological compound or a Bi2Te3 topological compound at high pressure. Here we report the discovery of superconductivity in the topological compound Sb2Te3 when pressure was applied. The crystal structure analysis results reveal that superconductivity at a low-pressure range occurs at the ambient phase. The Hall coefficient measurements indicate the change of p-type carriers at a low-pressure range within the ambient phase, into n-type at higher pressures, showing intimate relation to superconducting transition temperature. The first principle calculations based on experimental measurements of the crystal lattice show that Sb2Te3 retains its Dirac surface states within the low-pressure ambient phase where superconductivity was observed, which indicates a strong relationship between superconductivity and topology nature.

  16. Effect of geometrical shape on magneto-Peltier and Ettingshausen cooling in Bi and Bi0.88Sb0.12 polycrystals

    Science.gov (United States)

    Yamashita, Osamu; Tomiyoshi, Shoichi

    2002-10-01

    The cooling temperatures of rectangular parallelepiped Bi and Bi0.88Sb0.12 polycrystals of various dimensions were measured at 298 K as a function of electric current in magnetic fields up to 2.17 T, where the magnetic field was aligned along the thickness (t) direction of the sample and copper current leads were soldered to the centers of two ridges along the thickness direction on two diagonally opposite corners of a rectangle with length L and width W. With this configuration, the temperature measurements were carried out at both end surfaces with the cross section (W×t). The thermoelement was not in contact with a heat sink. The maximum cooling temperature at the cooled surface increases with increasing magnetic field, but it depends strongly on not only the aspect ratio of the sample but also its thickness. It was found that geometrically optimum shaping of a thermoelement is very important for achieving high-cooling efficiency. A thermoelement made of Bi0.88Sb0.12 with optimum dimensions of L=15 mm, W=2 mm, and t=3 mm effects the high-cooling temperature of 4.2 K in a magnetic field of 2.17 T. As a result, the cooling temperature reached 74% of the cooling temperature of 5.7 K obtained with p-type Bi2Te3 of L=12 mm and W=t=4.8 mm which has a thermoelectric figure of merit of ZT=0.87 at 298 K.

  17. Three-Dimensional BiOI/BiOX (X = Cl or Br Nanohybrids for Enhanced Visible-Light Photocatalytic Activity

    Directory of Open Access Journals (Sweden)

    Yazi Liu

    2017-03-01

    Full Text Available Three-dimensional flower-like BiOI/BiOX (X = Br or Cl hybrids were synthesized via a facile one-pot solvothermal approach. With systematic characterizations by X-ray diffraction (XRD, scanning electron microscopy (SEM, Transmission electron microscopy (TEM, the Brunauer-Emmett-Teller (BETspecific surface area, X-ray photoelectron spectroscopy (XPS, and the UV-Vis diffuse reflectance spectra (DRS, the BiOI/BiOCl composites showed a fluffy and porous 3-D architecture with a large specific surface area (SSA and high capability for light absorption. Among all the BiOX (X = Cl, Br, I and BiOI/BiOX (X = Cl or Br composites, BiOI/BiOCl stands out as the most efficient photocatalyst under both visible and UV light irradiations for methyl orange (MO oxidation. The reaction rate of MO degradation on BiOI/BiOCl was 2.1 times higher than that on pure BiOI under visible light. Moreover, BiOI/BiOCl exhibited enhanced water oxidation efficiency for O2 evolution which was 1.5 times higher than BiOI. The enhancement of photocatalytic activity could be attributed to the formation of a heterojunction between BiOI and BiOCl, with a nanoporous structure, a larger SSA, and a stronger light absorbance capacity especially in the visible-light region. The in situ electron paramagnetic resonance (EPR revealed that BiOI/BiOCl composites could effectively evolve superoxide radicals and hydroxyl radicals for photodegradation, and the superoxide radicals are the dominant reactive species. The superb photocatalytic activity of BiOI/BiOCl could be utilized for the degradation of various industrial dyes under natural sunlight irradiation which is of high significance for the remediation of industrial wastewater in the future.

  18. Three-Dimensional BiOI/BiOX (X = Cl or Br) Nanohybrids for Enhanced Visible-Light Photocatalytic Activity

    Science.gov (United States)

    Liu, Yazi; Xu, Jian; Wang, Liqiong; Zhang, Huayang; Xu, Ping; Duan, Xiaoguang; Sun, Hongqi; Wang, Shaobin

    2017-01-01

    Three-dimensional flower-like BiOI/BiOX (X = Br or Cl) hybrids were synthesized via a facile one-pot solvothermal approach. With systematic characterizations by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET)specific surface area, X-ray photoelectron spectroscopy (XPS), and the UV-Vis diffuse reflectance spectra (DRS), the BiOI/BiOCl composites showed a fluffy and porous 3-D architecture with a large specific surface area (SSA) and high capability for light absorption. Among all the BiOX (X = Cl, Br, I) and BiOI/BiOX (X = Cl or Br) composites, BiOI/BiOCl stands out as the most efficient photocatalyst under both visible and UV light irradiations for methyl orange (MO) oxidation. The reaction rate of MO degradation on BiOI/BiOCl was 2.1 times higher than that on pure BiOI under visible light. Moreover, BiOI/BiOCl exhibited enhanced water oxidation efficiency for O2 evolution which was 1.5 times higher than BiOI. The enhancement of photocatalytic activity could be attributed to the formation of a heterojunction between BiOI and BiOCl, with a nanoporous structure, a larger SSA, and a stronger light absorbance capacity especially in the visible-light region. The in situ electron paramagnetic resonance (EPR) revealed that BiOI/BiOCl composites could effectively evolve superoxide radicals and hydroxyl radicals for photodegradation, and the superoxide radicals are the dominant reactive species. The superb photocatalytic activity of BiOI/BiOCl could be utilized for the degradation of various industrial dyes under natural sunlight irradiation which is of high significance for the remediation of industrial wastewater in the future. PMID:28336897

  19. Photoreduction of non-noble metal Bi on the surface of Bi2WO6 for enhanced visible light photocatalysis

    Science.gov (United States)

    Zhang, Xiaojing; Yu, Shan; Liu, Yang; Zhang, Qian; Zhou, Ying

    2017-02-01

    In this report, Bi2WO6-Bi composite was prepared through an in situ photoreduction method and was characterized systematically by X-Ray diffraction, transmission electron microscopy, X-Ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The as-prepared Bi2WO6-Bi maintains the same crystal structure with the pristine Bi2WO6 regardless of some surface defects. Nevertheless, these surface defects result in the change of surface oxygen adsorption mode from hydroxyl to molecular oxygen on Bi2WO6. Photocatalytic activity over Bi2WO6-Bi is 2.4 times higher than that of Bi2WO6 towards the degradation of organic dye Rhodamine B (RhB) under visible light irradiation (λ > 420 nm). A deep study shows that cleavage of benzene ring is the main pathway for RhB degradation over Bi2WO6, but both the benzene cleavage and de-ethylation pathway coexist for RhB decomposition in the presence of Bi2WO6-Bi as the photocatalyst. Photoelectrochemical study including transient photocurrent tests and electrochemical impedance spectroscopy measurements shows that Bi2WO6-Bi could facilitate the charge transfer process compared to Bi2WO6. These data above has indicated a new insight into the promotion mechanism based on Bi related heterostructures.

  20. Bi-induced band gap reduction in epitaxial InSbBi alloys

    Energy Technology Data Exchange (ETDEWEB)

    Rajpalke, M. K.; Linhart, W. M.; Birkett, M.; Alaria, J.; Veal, T. D., E-mail: T.Veal@liverpool.ac.uk [Stephenson Institute for Renewable Energy and Department of Physics, School of Physical Sciences, University of Liverpool, Liverpool L69 7ZF (United Kingdom); Yu, K. M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Bomphrey, J. J.; Jones, T. S.; Ashwin, M. J., E-mail: M.J.Ashwin@warwick.ac.uk [Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom); Sallis, S.; Piper, L. F. J. [Materials Science and Engineering, Binghamton University, Binghamton, New York 13902 (United States)

    2014-11-24

    The properties of molecular beam epitaxy-grown InSb{sub 1−x}Bi{sub x} alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350 °C to 2.4% at 200 °C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626 Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172 meV (7.2 μm) for InSb to ∼88 meV (14.1 μm) for InSb{sub 0.976}Bi{sub 0.024}, a reduction of ∼35 meV/%Bi.

  1. Enhancement of magnetic circular dichroism in bi-layered ZnO-Bi:YIG thin films

    Directory of Open Access Journals (Sweden)

    Shinichiro Mito

    2017-05-01

    Full Text Available Bi-layered zinc oxide (ZnO and bismuth substituted yttrium iron garnet (Bi:YIG was fabricated and magneto-optically investigated. Enhancement of Faraday rotation and magnetic circular dichroism (MCD was observed. The wavelength of MCD enhancement was in good agreement with exciton wavelength of ZnO. This enhancement was only observed in the bi-layer, and implies that the exciton generated in ZnO interacted with Bi:YIG. Because the exciton wavelength of ZnO can be controlled by electro-optic effect, this result has the potential for realizing voltage control of magneto-optic effect.

  2. Disorder effects in Ga(AsBi)

    Energy Technology Data Exchange (ETDEWEB)

    Imhof, Sebastian; Thraenhardt, Angela [Technische Universitaet Chemnitz (Germany); Chernikov, Alexej; Chatterjee, Sangam; Koch, Stephan W. [Philipps-Universitaet Marburg (Germany); Lu, Xianfeng; Johnson, Shane [Arizona State University (United States); Beaton, Dan [University of British Columbia (Canada); Tiedje, Thomas [University of Victoria (Canada); Rubel, Oleg [Lakehead University and Thunder-Bay Regional Research Institute (Canada)

    2010-07-01

    The incorporation of Bi into GaAs reduces the band gap by as much as 60-80 meV per percent Bi. Thus a wide wavelength range in the near and middle infrared region can be reached and Ga(AsBi) is a serious candidate for many applications e.g. diode lasers. The photoluminesence of the present Ga(AsBi) samples show an S-shape and the PL linewidth has a maximum at intermediate temperatures. These are typical indications of disorder effects on a very large energy scale. We describe the disorder effects using a kinetic Monte-Carlo simulation. In order to characterize the disorder effects we use experimental time-integrated and time-resolved data and compare these to our theoretical results.

  3. Bi-weekly waterfowl survey data entry

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — Data sheet for the entry of bi-weekly waterfowl survey data from the state of Kansas. This Excel file contains the data entry sheet and a chart displaying waterfowl...

  4. The BiPo-3 detector.

    Science.gov (United States)

    Loaiza, P; Barabash, A S; Basharina-Freshville, A; Birdsall, E; Blondel, S; Blot, S; Bongrand, M; Boursette, D; Brudanin, V; Busto, J; Caffrey, A J; Calvez, S; Cascella, M; Cerna, C; Chauveau, E; Chopra, A; Capua, S De; Duchesneau, D; Durand, D; Egorov, V; Eurin, G; Evans, J J; Fajt, L; Filosofov, D; Flack, R; Garrido, X; Gómez, H; Guillon, B; Guzowski, P; Holý, K; Hodák, R; Huber, A; Hugon, C; Jeremie, A; Jullian, S; Kauer, M; Klimenko, A; Kochetov, O; Konovalov, S I; Kovalenko, V; Lang, K; Lemière, Y; Noblet, T Le; Liptak, Z; Liu, X R; Lutter, G; Macko, M; Mamedov, F; Marquet, C; Mauger, F; Morgan, B; Mott, J; Nemchenok, I; Nomachi, M; Nova, F; Ohsumi, H; Oliviéro, G; Pahlka, R B; Pater, J; Perrot, F; Piquemal, F; Povinec, P; Přidal, P; Ramachers, Y A; Remoto, A; Richards, B; Riddle, C L; Rukhadze, E; Saakyan, R; Sarazin, X; Shitov, Yu; Simard, L; Šimkovic, F; Smetana, A; Smolek, K; Smolnikov, A; Söldner-Rembold, S; Soulé, B; Štekl, I; Thomas, J; Timkin, V; Torre, S; Tretyak, Vl I; Tretyak, V I; Umatov, V I; Vilela, C; Vorobel, V; Waters, D; Žukauskas, A

    2017-05-01

    The BiPo-3 detector is a low radioactive detector dedicated to measuring ultra-low natural contaminations of (208)Tl and (214)Bi in thin materials, initially developed to measure the radiopurity of the double β decay source foils of the SuperNEMO experiment at the μBq/kg level. The BiPo-3 technique consists in installing the foil of interest between two thin ultra-radiopure scintillators coupled to low radioactive photomultipliers. The design and performances of the detector are presented. In this paper, the final results of the (208)Tl and (214)Bi activity measurements of the first enriched (82)Se foils are reported for the first time, showing the capability of the detector to reach sensitivities in the range of some μBq/kg. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Surface superconductivity in thin cylindrical Bi nanowire.

    Science.gov (United States)

    Tian, Mingliang; Wang, Jian; Ning, Wei; Mallouk, Thomas E; Chan, Moses H W

    2015-03-11

    The physical origin and the nature of superconductivity in nanostructured Bi remains puzzling. Here, we report transport measurements of individual cylindrical single-crystal Bi nanowires, 20 and 32 nm in diameter. In contrast to nonsuperconducting Bi nanoribbons with two flat surfaces, cylindrical Bi nanowires show superconductivity below 1.3 K. However, their superconducting critical magnetic fields decrease with their diameter, which is the opposite of the expected behavior for thin superconducting wires. Quasiperiodic oscillations of magnetoresistance were observed in perpendicular fields but were not seen in the parallel orientation. These results can be understood by a model of surface superconductivity with an enhanced surface-to-bulk volume in small diameter wires, where the superconductivity originates from the strained surface states of the nanowires due to the surface curvature-induced stress.

  6. Metaheuristics for bi-level optimization

    CERN Document Server

    2013-01-01

    This book provides a complete background on metaheuristics to solve complex bi-level optimization problems (continuous/discrete, mono-objective/multi-objective) in a diverse range of application domains. Readers learn to solve large scale bi-level optimization problems by efficiently combining metaheuristics with complementary metaheuristics and mathematical programming approaches. Numerous real-world examples of problems demonstrate how metaheuristics are applied in such fields as networks, logistics and transportation, engineering design, finance and security.

  7. Advances in Higher Purity Bi Sample Handling

    Institute of Scientific and Technical Information of China (English)

    ZHAO; Qing-zhang; HE; Ming; DONG; Ke-jun; SHEN; Hong-tao; YIN; Xin-yi; WU; Shao-yong; DOU; Liang; WANG; Xiao-ming; YANG; Xu-ran; XU; Yong-ning; LAN; Xiao-xi; PANG; Fang-fang; CAI; Li; JIANG; Shan

    2013-01-01

    Whether the decay rate of a radionuclide can be influenced by its external environment has always been a hot topic in nuclear science.Higher purity sample is very critical for the half-life measurements.Because using higher purity(6N)Bi metal instead of(4N)Bi target,in 210Po production to reduce the impact of radioactive impurity.The annealing process was performed to remove the damage in the lattice

  8. The bi Hermitian topological sigma model

    CERN Document Server

    Zucchini, R

    2006-01-01

    BiHermitian geometry, discovered long ago by Gates, Hull and Roceck, is the most general sigma model target space geometry allowing for (2,2) world sheet supersymmetry. By using the twisting procedure proposed by Kapustin and Li, we work out the type A and B topological sigma models for a general biHermtian target space, we write down the explicit expression of the sigma model's action and BRST transformations and present a computation of the topological gauge fermion.

  9. Forenzika elektronske pošte

    Directory of Open Access Journals (Sweden)

    Milorad S. Markagić

    2013-10-01

    ešće obavlja putem instant poruka. Radnici u okviru firme međusobno razgovaraju instant porukama, a veoma se često koriste i za lične međusobne razgovore. Osobe međusobno razmenjuju poruke koje putuju preko servera, a princip rada skoro je identičan kao princip rada elektronske pošte, sa osnovnom razlikom, da se odvija u realnom vremenu. Zaključak Današnja tehnologija omogućava promenu i manipulaciju digitalnim medijem na načine koji su pre nekoliko godina bili nemogući. Buduća tehnologija gotovo će sigurno omogućiti manipulacije digitalnih medija na način koji se danas čini nemogućim. Kako tehnologija nastavlja svoju evoluciju, biće sve važnije da  digitalna forenzika održi korak sa tim razvojem. Kako se razvijaju tehnike i metode za otkrivanje računarskih prevara, razvijaće se i nove sofisticiranije metode izrade falsifikata koje će biti teže otkriti. 

  10. CdTe and ZnTe metal interface formation and Fermi-level pinning

    Science.gov (United States)

    Wahi, A. K.; Carey, G. P.; Chiang, T. T.; Lindau, I.; Spicer, W. E.

    1989-01-01

    Interfacial morphology and Fermi-level pinning behavior at the interfaces of Al, Ag, and Pt with UHV-cleaved CdTe and ZnTe are studied using X-ray photoelectron and ultraviolet photoemission spectroscopies. Results are compared to metal/HgCdTe interface formation. For Al/CdTe, a case is found where significantly greater intermixing occurs in CdTe than seen on HgCdTe. The Al/ZnTe interface is also more abrupt than Al/CdTe. Band bending results for interfaces of all three metals with p-CdTe and p-ZnTe are presented and implications for metal/HgZnTe interface formation are considered.

  11. Dynamical scenarios for chromosome bi-orientation.

    Science.gov (United States)

    Zhang, Tongli; Oliveira, Raquel A; Schmierer, Bernhard; Novák, Béla

    2013-06-18

    Chromosome bi-orientation at the metaphase spindle is essential for precise segregation of the genetic material. The process is error-prone, and error-correction mechanisms exist to switch misaligned chromosomes to the correct, bi-oriented configuration. Here, we analyze several possible dynamical scenarios to explore how cells might achieve correct bi-orientation in an efficient and robust manner. We first illustrate that tension-mediated feedback between the sister kinetochores can give rise to a bistable switch, which allows robust distinction between a loose attachment with low tension and a strong attachment with high tension. However, this mechanism has difficulties in explaining how bi-orientation is initiated starting from unattached kinetochores. We propose four possible mechanisms to overcome this problem (exploiting molecular noise; allowing an efficient attachment of kinetochores already in the absence of tension; a trial-and-error oscillation; and a stochastic bistable switch), and assess their impact on the bi-orientation process. Based on our results and supported by experimental data, we put forward a trial-and-error oscillation and a stochastic bistable switch as two elegant mechanisms with the potential to promote bi-orientation both efficiently and robustly.

  12. Gd-substituted Bi-2223 superconductor

    Indian Academy of Sciences (India)

    D R Mishra

    2008-03-01

    The effects of gadolinium doping at calcium site on the normal and super-conducting properties of Bi-2223 system were studied. The Gd-doped (BiPb)-2223 series of specimens, namely Batch I, II and III were sintered at three different sintering temperatures 830, 850 and 895° C respectively. The properties investigated are (1) the normal state resistivity with a view to study metal-to-insulator transition, (2) the XRD patterns of the specimens with a view to study the relative composition of (BiPb)-2212 and (BiPb)-2223 phases and (3) the superconducting fluctuation behaviour (SFB) with a view to determine the effect of doping, if any, on the dimensionality of the fluctuation conductivity of the system. The normal state resistivity of Gd-substituted Bi-2223 specimens shows metallic, semiconducting and insulating behaviour. The c( = 0) values indicate that (BiPb)-2223 phase is responsible for the observed superconducting transitions in Batch I and Batch II specimens with Gd concentrations ≤ 0.7. This observation is further confirmed in the analysis of XRD patterns of these specimens. Gadolinium, being a magnetic impurity, has pair breaking effect near the Fermi level and decreases c( = 0). The analysis of the superconducting fluctuation behaviour (SFB) shows a 2D dimensionality without any cross-over.

  13. BiP Negatively Affects Ricin Transport

    Directory of Open Access Journals (Sweden)

    Kirsten Sandvig

    2013-05-01

    Full Text Available The AB plant toxin ricin binds both glycoproteins and glycolipids at the cell surface via its B subunit. After binding, ricin is endocytosed and then transported retrogradely through the Golgi to the endoplasmic reticulum (ER. In the ER, the A subunit is retrotranslocated to the cytosol in a chaperone-dependent process, which is not fully explored. Recently two separate siRNA screens have demonstrated that ER chaperones have implications for ricin toxicity. ER associated degradation (ERAD involves translocation of misfolded proteins from ER to cytosol and it is conceivable that protein toxins exploit this pathway. The ER chaperone BiP is an important ER regulator and has been implicated in toxicity mediated by cholera and Shiga toxin. In this study, we have investigated the role of BiP in ricin translocation to the cytosol. We first show that overexpression of BiP inhibited ricin translocation and protected cells against the toxin. Furthermore, shRNA-mediated depletion of BiP enhanced toxin translocation resulting in increased cytotoxicity. BiP-dependent inhibition of ricin toxicity was independent of ER stress. Our findings suggest that in contrast to what was shown with the Shiga toxin, the presence of BiP does not facilitate, but rather inhibits the entry of ricin into the cytosol.

  14. Ab initio Assessment of Bi1-xRExCuOS (RE=La, Gd, Y, Lu) Solid Solution as Semiconductor for Photochemical Water Splitting

    KAUST Repository

    Lardhi, Sheikha F.

    2017-04-12

    The investigation of BiCuOCh (Ch = S, Se and Te) semiconductors family for thermoelectric or photovoltaic materials is an increasing topic of research. These materials can also be considered for photochemical water splitting if one representative having a bandgap, Eg, around 2 eV can be developed. With this aim, we simulated the solid solution Bi1-xRExCuOS (RE = Y, La, Gd and Lu) from pure BiCuOS (Eg~1.1 eV) to pure RECuOS compositions (Eg~2.9 eV) by DFT calculations based on the HSE06 range-separated hybrid functional with inclusion of spin-orbit coupling. Starting from the thermodynamic stability of the solid solution, a large variety of properties were computed for each system including bandgap, dielectric constants, effective masses and exciton binding energies. We discussed the variation of these properties based on the relative organization of Bi and RE atoms in their common sublattice to offer a physical understanding of the influence of the RE doping of BiCuOS. Some compositions were found to give appropriate properties for water splitting application. Furthermore, we found that at low RE fractions the transport properties of BiCuOS are improved that can find applications beyond water splitting.

  15. Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

    Science.gov (United States)

    Yu, Chia-Chi; Wu, Hsin-Jay; Deng, Ping-Yuan; Agne, Matthias T.; Snyder, G. Jeffrey; Chu, Jinn P.

    2017-03-01

    The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8-360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10-20-10-23(m2/s), which is 106~107 and 1012~1013 times smaller than those of Ni [10-14-10-17(m2/s)] and Cu [10-8-10-11(m2/s)] in Bi2Te3, respectively.

  16. Thin-film metallic glass: an effective diffusion barrier for Se-doped AgSbTe2 thermoelectric modules

    Science.gov (United States)

    Yu, Chia-Chi; Wu, Hsin-jay; Deng, Ping-Yuan; Agne, Matthias T.; Snyder, G. Jeffrey; Chu, Jinn P.

    2017-01-01

    The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8–360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick’s second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10−20–10−23(m2/s), which is 106~107 and 1012~1013 times smaller than those of Ni [10−14–10−17(m2/s)] and Cu [10−8–10−11(m2/s)] in Bi2Te3, respectively.

  17. Growth and Characterization of Large Scale (Sb1-xBix)2 Te3 Thin Films on Mica

    Science.gov (United States)

    Ni, Yan; Zhang, Zhen; Jiles, David

    2015-03-01

    Topological insulators (TIs) attract attentions for both fundamental science and potential applications because of their bulk band inversion arising from the strong spin orbital coupling. However, it is necessary to tune the Fermi level and Dirac cone in 3D TI (Sb1-xBix)2 Te3 to make an ideal system for TI applications. In this work, we report high quality (Sb1-xBix)2 Te3 thin films grown on mica substrate by molecular beam epitaxy. The surface roughness of the thin film can reach as low as 0.7 nm in a large area by van der Waals epitaxy. (Sb1-xBix)2 Te3 thin film with x = 0.04 shows a local maxima in the room temperature sheet resistance, which indicates a minimization of the carrier density due to band structure engineering. Moreover, for higher Bi concentration, due to an increase of the surface roughness and corresponding reduction of electron mobility, the sheet resistance increases. Our results on the feasibility of depositing (Sb1-xBix)2 Te3 in wide Bi range on mica substrate will helpful for the application of TI at room temperature and flexible electronics. Authors would like to thank the financial support from the U.S. National Science Foundation under the Award No. 1201883.

  18. Magnetotransport study of (Sb1−xBix2Te3 thin films on mica substrate for ideal topological insulator

    Directory of Open Access Journals (Sweden)

    Yan Ni

    2016-05-01

    Full Text Available We deposited high quality (Sb1−xBix2Te3 on mica substrate by molecular beam epitaxy and investigated their magnetotransport properties. It is found that the average surface roughness of thin films is lower than 2 nm. Moreover, a local maxima on the sheet resistance is obtained with x = 0.043, indicating a minimization of bulk conductivity at this composition. For (Sb0.957Bi0.0432Te3, weak antilocalization with coefficient of -0.43 is observed, confirming the existence of 2D surface states. Moreover Shubnikov-de Hass oscillation behavior occurs under high magnetic field. The 2D carrier density is then determined as 0.81 × 1016 m−2, which is lower than that of most TIs reported previously, indicating that (Sb0.957Bi0.0432Te3 is close to ideal TI composition of which the Dirac point and Fermi surface cross within the bulk bandgap. Our results thus demonstrate the best estimated composition for ideal TI is close to (Sb0.957Bi0.0432Te3 and will be helpful for designing TI-based devices.

  19. Te hard van stapel gelopen.

    NARCIS (Netherlands)

    W-J. Verhoeven (Willem-Jan)

    2008-01-01

    textabstractHoe goed we ook trachten de samenleving te organiseren, fraude maakt er deel van uit. Dit blijkt uit spraakmakende grote schandalen zoals de Enron-zaak, de Bouwfraude-zaak en de Nigerian letter scams. Maar fraude komt ook op minder geruchtmakende schaal voor, zoals oplichting op veilings

  20. Te hard van stapel gelopen.

    NARCIS (Netherlands)

    W-J. Verhoeven (Willem-Jan)

    2008-01-01

    textabstractHoe goed we ook trachten de samenleving te organiseren, fraude maakt er deel van uit. Dit blijkt uit spraakmakende grote schandalen zoals de Enron-zaak, de Bouwfraude-zaak en de Nigerian letter scams. Maar fraude komt ook op minder geruchtmakende schaal voor, zoals oplichting op veilings